1

Author: Lohoff, Andrew, D

Title: Design and Development of Microwave Package for Company XYZ

The accompanying research report is submitted to the University of Wisconsin-Stout, Graduate School in partial

completion of the requirements for the

Graduate Degree/ Major: MS Technology Management

Research Adviser: Jim Keyes, Ph.D.

Submission Term/Year: Spring, 2011

Number of Pages: 53

Style Manual Used: American Psychological Association, 6th

edition

I understand that this research report must be officially approved by the Graduate School and

that an electronic copy of the approved version will be made available through the University

Library website

I attest that the research report is my original work (that any copyrightable materials have been

used with the permission of the original authors), and as such, it is automatically protected by the

laws, rules, and regulations of the U.S. Copyright Office.

STUDENT’S NAME: Andrew Lohoff

STUDENT’S SIGNATURE: ________________________________________________ DATE:

ADVISER’S NAME : Dr. Jim Keyes

ADVISER’S SIGNATURE: __________________________________________________DATE:

---------------------------------------------------------------------------------------------------------------------------------

This section for MS Plan A Thesis or EdS Thesis/Field Project papers only

Committee members (other than your adviser who is listed in the section above)

1. CMTE MEMBER’S NAME:

SIGNATURE: ____________________________________________ DATE:

2. CMTE MEMBER’S NAME:

SIGNATURE: ____________________________________________ DATE:

3. CMTE MEMBER’S NAME:

SIGNATURE: ____________________________________________ DATE:

----------------------------------------------------------------------------------------------------------------------------- ---- This section to be completed by the Graduate School This final research report has been approved by the Graduate School.

___________________________________________________ ___________________________

(Director, Office of Graduate Studies) (Date)

2

Lohoff, Andrew D. Design and Development of a Microwave Package for Company XYZ

Abstract

Microwave cooking has long been employed to conveniently cook food items

whether they are leftovers or a store bought microwave ready meal. Such microwave

meals may be stored at ambient, refrigerated, or even frozen temperatures. A known

disadvantage of microwaving food items is the lack of control over temperatures which

often results in over/under heating of food areas. For instance, the outer edges of a food

item may be burnt meanwhile the center of the food item would remain undercooked. It

would be desirable to create a vehicle that would yield even food temperatures

throughout a container. By preventing or reducing the amount of microwaves that could

penetrate the food item(s), the amount of energy can be controlled resulting in a more

uniform temperature distribution resulting in a higher quality meal. Using specially

developed materials Company XYZ has solved the problem by strategically placing

specially designed shielding materials in locations where sparking and safety concerns

are no longer a problem. Through extensive literature research and testing Company

XYZ has delivered a client request and produced a quality safe product.

3

Table of Contents Abstract 2

Chapter I: Introduction 6

Statement of the Problem .................................................................................................... 7

Purpose of the Study ........................................................................................................... 7

Assumptions of the Study ................................................................................................... 7

Definition of Terms............................................................................................................. 8

Limitations of the Study...................................................................................................... 9

Methodology ....................................................................................................................... 9

Chapter II: Literature Review 11

Penetration Depth.............................................................................................................. 11

Dielectric Properties.......................................................................................................... 13

Package Geometry ............................................................................................................ 16

Chapter III: Packaging Materials 18

Food Geometry ................................................................................................................. 19

Other Factors Affecting Microwave Heating ................................................................... 20

Package Design ................................................................................................................. 23

Instrumentation ................................................................................................................. 23

Chapter IV: Results 32

Package Design Tested ..................................................................................................... 32

Experimental Results ........................................................................................................ 34

Design Problem: Arcing ................................................................................................... 38

4

Summary ........................................................................................................................... 41

Chapter V: Discussion 42

Limitations ........................................................................................................................ 42

Conclusions ....................................................................................................................... 42

Packaging Material ........................................................................................................... 43

Further Development ........................................................................................................ 44

Recommendations ............................................................................................................. 45

References 46

Appendix A: Microwave meal with center compartment shielded by surrounded compartments

……………………………………………………………………………………………………48

Appendix B: IEC Microwave Testing Data Table……………………………………………….49

Appendix C: Microwave Package Design: Top View…………………………………………... 50

Appendix D: Microwave Package Design: Bottom Profile……………………………………... 51

Appendix E: Microwave Meal: Side Profile……………………………………………………..52

Appendix F: Microwave Meal: Top Profile……………………………………………………...53

5

List of Figures

Figure 1: Penetration depth of standard rectangular container ..................................................... 12

Figure 2: Dielectric Properties Equation. ..................................................................................... 13

Figure 3.Temperature Dependence of ε’ (a) and ε” (b) for various food substances at 2.8 GHz. 14

Figure 4. Dielectric properties food map at 20-25°C.. .................................................................. 15

Figure 5. Rectangular Hot Spots. .................................................................................................. 16

Figure 6. Cylindrical / Oval Uniformity. ...................................................................................... 17

Figure 7. Distribution of microwaves in a vertically oriented cylindrical .................................... 17

Figure 8. The effect of foodstuff diameter on microwave foodstuff near center and surface of a)

spheres and b) cylinders. ............................................................................................................... 19

Figure 9. Microwave Wattage Variance. ...................................................................................... 21

Figure 10: Top shielding variables. .............................................................................................. 25

Figure 11. Microwave Temperature Locations ............................................................................. 27

Figure 12: Sample Data Table ...................................................................................................... 28

Figure 13: Disaster Testing Data Sheet ........................................................................................ 30

Figure 14: Histogram of Unshielded Tray Compartment ............................................................. 35

Figure 15: Histogram of Shielded Tray Compartmet ................................................................... 36

Figure 16: Experimental Values of Microwave Shielding Designs.............................................. 37

Figure 17: Disaster Testing Results. ............................................................................................. 40

6

Chapter I: Introduction

Use of microwaves to heat a specific product quickly is now the norm in today’s quick on

the go society, however the microwave was not always a common household item. It wasn’t until

the technology of using electromagnetic waves was accidently discovered by Percy Spencer in

1945 (Buffler, 1993). Microwave oven sales did not take off until the early eighties due to large

amounts of skepticism on safety and food quality, however, when doubts were largely erased

sales rose from 4 million units shipped in 1982 to 11 million in 1985 and are continuing to rise

(Schiffman, 2008,). The microwave meal is no longer seen as two parts; package and food

Packaging material choices are viewed now as importantly as food ingredients.

Microwaves react in many similar ways to light, as the International Microwave Power

Institute (1975) reports “microwaves have similar properties to light, they reflect, transmit, and

absorb” (p. 24) utilizing these three core tendencies of light an engineer can design a package

that can accentuate one of these particular properties. For example, some materials such as

aluminum reflect waves such as foil or metal; this is why the walls of the oven cavity are made

out of metal so they can reflect waves back into the food providing a more uniform cook, while

other waves are absorbed by paper or plastic materials (p. 24).

Two types of microwave packages currently exist, passive and active. Passive packaging

exists to just hold the foodstuff and do not contribute to heating the food. Active packaging

contributes to cooking. Such active packages include steam packs, susceptors which help crisp

food, shields, and field modifiers. Both packages have markets and specific uses.

A variety of trays may be used to fulfill the needs of the consumer whether it is a multi-

compartment or single serve tray. Trays come essentially in two different materials, either

plastic or paperboard. Plastic trays comprise of either crystallized polyethylene (CPET) or

7

polypropylene (PP). It is best to use CPET (crystallized polyethylene terephthalate) as the main

thermoformed tray material because of its ability to withstand multiple environments such as

conventional oven to microwave. Studies show that 3% of end users still use the conventional

oven to heat their microwave meals due to safety concerns (Shiffman 2008). Polypropylene is

still a viable and usually a more cost effective solution but does not offer the capability of being

used in convection ovens it is more safe to use CPET.

Statement of the Problem

Company XYZ had a need to design and manufacture a microwave food package that

will be able to control temperatures between different food compartments within the package.

Failure to complete the project could result in Company XYZ losing an important customer

which would negatively impact the bottom line.

Purpose of the Study

The purpose of the study was to develop a microwave package that will create a new

market in microwavable meals. A gap in microwave packaging has been identified by a

customer who wants to offer a higher quality meal to its consumers. The customer has identified

a want by the consumer to produce a quick yet high quality meal that offers different

temperatures of food within the same tray. An example could possibly be the pairing of ice

cream and lasagna in different compartments within the same tray. A goal has been established

between Company XYZ and its customer; Company ABC is to deliver a package that will be

able to control compartment temperatures independently of a one or more compartment tray.

Assumptions of the Study

Packaging materials to construct the microwave package are of polymer nature and were

produced under the manufacturing practices of Company XYZ.

8

Definition of Terms

Conductivity. Describes a materials ability to conduct electric currents by the

displacement of electrons and ions (Schiffman 1990).

Conductors. Materials with free electrons, that have the ability to carry an

electromagnetic current (Schiffman 2009).

Dielectric property. These describe how a material is affected by the microwaves. They

control how a material heats and reacts to the microwaves (Schiffman 2009).

Dipolar rotation. The most common heating mechanism, based largely on the presence

of water.

Dielectric Constant. See permittivity.

Insulators. Electrically non-conductive materials, such as glass, ceramics and air, which

reflect and absorb electromagnetic waves to a negligible extent.

Ionic Conduction. A form of heating based largely on the presence of salt, and has a

serious effect on foods.

Loss Tangent Factor. Is a parameter of a dielectric material that quantifies its inherent

dissipation of electromagnetic energy. The term refers to the tangent of the angle in

a complex plane between the resistive component of an electromagnetic field and its reactive

component.

Penetration Depth. The distance that waves dissipate, the longer the penetration depth

the more uniform the heating becomes (Schiffman 2009).

Permittivity. The ability of a substance to hold an electrical charge.

9

Retort. The process of using pressure to pre-cook a meal making it shelf stable and ready

to eat upon opening.

Specific heat capacity. The amount of heat required to raise the temperature of 1 gram

of material, 1 degree Celsius.

Limitations of the Study

Company XYZ is limited in selection of materials in order to meet compliance by the

Federal Drug Administration. Company XYZ has only at its deposal polymer thermoplastics

including thermoformed crystallized polyethylene and polyethylene for the container. Company

XYZ has countless polymer laminations at is disposable for container lidding film. Such

materials include a wide array of processing from blown film extrusion to cast film extrusion.

Methodology

Discussed in the remainder of the paper are numerous decisions made by Company XYZ

that explain the development process of the dual temperature microwave tray. Decisions are

based on material composition, package design, and testing protocol. Once the package had

been designed with all considerations taken into account, testing was conducted to ensure public

safety when using the meal for enjoyment.

Throughout the research, the researcher used various different sources of information to

yield a tangible product to present to his customer. The design of the dual temperature

microwave meal was aided by extensive research on microwave properties, food chemistry, and

package design. During the research and development of the project the researcher had

conducted extensive and strenuous testing on multiple levels, continually isolated the

components of the package by food composition, packaging materials, microwave, and lastly the

end consumer’s behavior in handling of the product. A large part of the development of the

10

microwave package was performed in a controlled research laboratory. Items that remained

constantly controlled were: meal temperature, microwave power output, temperature reading

locations, and calibration of the thermometers.

Embodiments with the location of the microwave shield were performed to investigate if

food distribution throughout the microwave container could further act as a significant factor in

the quality and safety of the meal. Furthermore, numerous package designs were tested in

attempt to gain further understanding of how different components affected the overall meal

quality. Components ranged from food type, food temperature, packaging tray material, tray

geometry, and cook time, along with numerous different shielding materials.

Summary

The microwave meal market was stagnant and had little innovation within the last five

years. Through the discovery of unused physical and chemical properties of flexible and rigid

polymers a new niche in the microwave meal had been uncovered. Through this discovery

Company XYZ was to utilize these new discoveries to create a tangible product for its client.

With the project clearly defined from its client Company XYZ used extensive literature review to

create a microwave meal that had the ability to control temperatures between different food

compartments within the package.

11

Chapter II: Literature Review

Basic understanding of how microwaves work is essential for a product packaging

developer designing an effective microwave package. First, microwaves do not produce any

heat inside the cavity of the oven; microwaves produce electromagnetic waves which use the

dielectric properties of the food to excite the water molecules which produce heat (Schiffman,

2008). According to the International Microwave Power Institute (1975) the real cooking is in

the dipolar reaction (p. 21). Symmetrically aligned positive and negative charges provide the

food in the meal with potential kinetic energy. It is this dipolar nature of water that makes it

possible to cook so effectively in the microwave, and since most foods contain high amounts of

water the marriage between foods and microwaves is perfect. For example, if one were to want

to cook noodles in the microwave without water nothing would happen to the noodles because of

the absence of water. With the presence of water, noodles would be able to use the dipolar

charge to cook (Schiffman 2009.p 22).

Penetration Depth

Penetration depth is an important topic and must be taken in to account when designing

the physical package. Schiffman (2008) defines penetration depth as the distance that waves

dissipate into a material of a specific item. The longer the penetration depth the more uniform

heating will become (note see figure 1).

12

Figure 1: Penetration depth of standard rectangular container (Shiffman 2009, P. 7) From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA. As incident waves travels into the package at one specific point (numerous incident waves are

occurring at any specific moment) some of the rays are transmitted through the packaging

material into the food. The equation in Figure 2 below can mathematically calculate the optimal

point where the incident ray can reach. The optimal point calculated results in an attenuation

point where maximum cooking occurs. The importance of this is to design a package where the

maximum penetration depth equals the overall height of the container, thus optimizing the

package for cooking. Building a package where the penetration depth is equal with the package

height one can optimize the cooking of the food. Table 1 provides information on various

starting states of the microwave meal ranging from frozen to hot water. The shorter the distance

in penetration depth the more quickly the microwaves can reach and cook the foodstuff.

12

Figure 1: Penetration depth of standard rectangular container (Shiffman 2009, P. 7) From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA. As incident waves travels into the package at one specific point (numerous incident waves are

occurring at any specific moment) some of the rays are transmitted through the packaging

material into the food. The equation in Figure 2 below can mathematically calculate the optimal

point where the incident ray can reach. The optimal point calculated results in an attenuation

point where maximum cooking occurs. The importance of this is to design a package where the

maximum penetration depth equals the overall height of the container, thus optimizing the

package for cooking. Building a package where the penetration depth is equal with the package

height one can optimize the cooking of the food. Table 1 provides information on various

starting states of the microwave meal ranging from frozen to hot water. The shorter the distance

in penetration depth the more quickly the microwaves can reach and cook the foodstuff.

13

ε’= Relative dielectic strength, in volts per unit distance ε’’= Dilectic loss factor, unitless λ= Wavelength of Microwave Oven Figure 2: Dielectric Properties Equation. From Schiffman, R. F. (1990, March). Mirowave foods: Basic Design Considerations [Electronic version]. TAPPI Journal, 209-212. In the subsequent paragraph Ryynänen (2002) summarizes the theory of penetration depth.

“ Theoretically, the penetration depth dp (or power penetration depth) is defined as

the depth below a large plane surface of a substance at which the power density of

a perpendicularly impinging, forward propagating plane electromagnetic wave

has decayed by 1/e from the surface value(1/e is about 37 %) (p.17)”

Table 1: Penetration Depth of Starting Package Temperatures

Temperature Dp (cm/in)

Water (ICE) Frozen (32 F) 1160/460

Water Room (72 F) 1.4/0.6

Water Hot (100 F) 2.8 / 1.1

Salt Water Room (72 F) 0.2/0.08

Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

Dielectric Properties

Active packages interact with the food contents of the package, more specifically

changing the electric or magnetic field configuration therefore modifying the heating pattern of

the food product. The primary components in active packaging that change are the dielectric

properties. Dielectric food properties are determined by chemical structure. The amount of

water or salt content impacts the ability for the foodstuff to conduct an electrical current. It is

14

this ability to hold an electrical current that influences how fast and how uniform a food product

will cook in a microwave oven. Many microwave meal products are of the homogenous nature,

mostly ice, water, and solids (Ryynänen 2002). Food products with a high water content show a

drastic increase in ε’ and ε” when in a semi-aqueous state and decreases with an increase in

temperature, whereas only salty foods show an increase in ε” with temperature (Ryynänen 2002).

See Figure 3 for graphical representation of the effects of temperature related to dielectric

constants. Fattier foods such as meats and cheeses appear to conduct less electrical current due

to the dilution of water (Bengtsson and Risman, 1971; Ohlsson et al., 1974a). The large

differences in properties between thawed and frozen food products does not aid in cook

uniformity. These large differences result in a term know as thermal runaway. Thermal

runaway is where a thawed part is heating rapidly meanwhile there are still some parts of the

meal frozen leaving the rest of the meal cold and undercooked (Ryynänen 2002).

Figure 3.Temperature Dependence of ε’ (a) and ε” (b) for various food substances at 2.8 GHz. From Ryynänen, S. (2002). MICROWAVE HEATING UNIFORMITY OF MULTICOMPONENT

PREPARED FOODS (Doctoral dissertation, University of Helsinki Department of Food Technolo, Helsinki). Retrieved February 29, 2012, from EBSCOHOST.

15

Figure 4. Dielectric properties food map at 20-25°C. From Ryynänen, S. (2002). MICROWAVE

HEATING UNIFORMITY OF MULTICOMPONENT PREPARED FOODS (Doctoral dissertation, University of Helsinki Department of Food Technolo, Helsinki). Retrieved February 29, 2012, from EBSCOHOST. Dielectric properties of common foods such as ham, potatoes and carrots, can be found in

numerous databases (Tinga and Nelson, 1973; Stuchly and Stuchly, 1980; Kent, 1987; Thuery,

1992; Datta et al., 1995). For more complex foods like chicken pot pie dielectric properties must

be measured and will depend on specific ingredient amounts.

16

Package Geometry

Shape has a drastic impact on the outcome of microwave food products (Ryynänen

2002). The shape can help influence uniform cooking. Rectangular packages especially have a

lot of disadvantages. With rectangular shapes the issue comes into play in the corners, where

there are too many points of access to the food product. The red arrows represent the incident

waves. As one can view there are four points of occurrence from the top, bottom, and two sides.

With the four incident waves transmitting on such a small location two events can happen.

Testing shows (Hodson, Douglas, Klittich, Cvancara, Lohoff, 2010) that either burning of the

food product or a major concern in sparking can happen and will eventually start the package on

fire.

Figure 5. Rectangular hot spots. Incident waves are represented by red arrows. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

This phenomenon can be avoided introducing an alternative shape, an oval or circular

package. In the diagram below one can view that the waves may only penetrate at three different

points, along the side, top, and bottom. There is little possibility that the rays can meet, resulting

in a more uniform food product.

17

Figure 6. Cylindrical / Oval Uniformity. Red arrows represent incident waves. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

Tall packaging containers such as tubs, jars, and glasses are not ideal for meals due to

safety issues. The lens affect is a serious issue in microwave packaging. The lens affect is

illustrated in Figure 7 below.

Figure 7. Vertically oriented cylindrical jar where incident waves enter a package and become entrapped thus resulting in hidden hot spots within the package. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

INCIDENT WAVE

REFLECTED WAVES

TRA

NSM

ITTI

NG

WA

VES

18

When package depth exceeds two inches microwaves become entrapped. Reflecting within the

package waves cannot dissipate into the microwave atmosphere, and this entrapment results in

random hot spots and non-uniform heating.

Packaging Materials

Numerous packaging materials can be used to contain the food, aid in cooking, and

provide an extended shelf life for the meal. Microwave meal packaging should be transparent to

microwaves to allow for optimal heating. However, certain materials such as aluminum can be

used to shield microwaves for a more controlled cook. The packaging container should be able

to withstand high localized temperatures cause by fatty or sugary food items. The most common

packaging materials for microwaves meals are of multi-layer polymers, fiber trays, and plastic-

coated cardboard (Ahvenainen et al. 1989; Buffler 1993; Thorsell 1994; Ohlsson and Bengtsson,

2001; Ryynänen 2002).

Fiberboard trays are commonly used because of price but cannot offer the inertness of

multi-layer polymer trays. Migration of odors and off-flavors can transfer from the fibreboard

container. Multi-layer polymer trays are not without concern as they can spark due to the

various food contents paired with the geometric shape of the container (Ryynänen 2002).

Aluminum containers are a viable solution to controlling the amounts of energy a meal is

receiving. Aluminum has not been used because of consumer safety risks. Aluminum is now a

safe solution because the magnetron within the oven cavity is now more rugged and is encased,

which doesn’t allow for an aluminum container to spark (Ryynänen 2002, Schiffman 2008).

Aluminum can prevent corners from overheating because the overall heating time is longer than

a transparent package (Ryynänen 2002). Ahvenainen and Heiniö (1992) concluded through

studies that aluminum containers were most suitable for casserole-type foods.

19

Food Geometry

Food product geometry is often an afterthought and needs more attention when

developing microwave meals. Foodstuff that is whole or in slab orientation has a higher

tendency to burn or become tough in nature. Lack of ideal cook preparedness results from how

microwaves cook, from the outside in. Cooking foodstuff from outside in focuses the majority

of the microwave energy on the corner/edges of the foodstuff, thus resulting in charred and

burned edges. To combat this problem and aid in uniformity smaller chunked foodstuff is used.

The penetration depth of the microwaves can reach the centre of the foodstuffs and begin to cook

inside more uniformly ((Risman et al., 1987; Ohlsson, 1990; Buffler, 1993). If penetration depth

is intermediate, normal amounts of microwave energy can reach the center and attenuation

occurs. Ohlosson and Risman (1978) have proved this circumstance with imaging and model

foods in Figure 8.

Figure 8. The effect of foodstuff diameter on microwave foodstuff near center and surface of a) spheres and b) cylinders. From Ohlsson, T. & Risman, P.O. 1978. Temperature distribution of microwave heating – spheres and cylinders. J. Microwave Power 13: 303-310. Doubling the amount of food within the oven cavity commonly doubles the amount of

cook time. Increase in cook time depends on the amount of food and food ingredients, most

20

notably salt. Greater loads up to a certain point are heated more efficiently and uniformly

(Ryynänen 2002).

Other Factors Affecting Microwave Heating

A plethora of food properties and other factors influence how microwave meals are

heated in microwave ovens. The initial temperature of food greatly influences the quality and

heating time. If a frozen meal is taken directly from the freezer to oven it will take considerably

more time to cook than a thawed or retorted meal. The difference between thawed or retorted is

not easily visible. Heating rates of food products within a multi-compartment meal can be

modified by product arrangement. Various components can shield each other. Studies from US

patent application 20100230402 A1 demonstrate the ability to shield food products within multi-

compartment trays. In Appendix 1an inner dish comprised of applesauce was kept to a

significant lower temperature than those of the surrounding compartments (Hodson et al.,2010)

Testing Overview

When developing a microwave package it is critical to make sure the product is

dependable, reliable, and safe. To certify that the package can meet all criteria to the consumer

and ensure safety, numerous tests must be completed before it hits the market. Numerous items

such as meal temperature, microwave power, and thermometer calibration must be done to set up

a repeatable controlled test. Charles Buffler (1993) states that line voltage determines of how

much wattage each oven can output. To ensure repeatability each line must be monitored and

isolated from all other electronics. Classifications of microwaves are grouped into high or low.

Low ovens are classified as less than 500 Watts, low power ovens range from 500 to 600 Watts

and High power is anything 600 W and above (Schiffman 2009). It is critical according to

Schiffman (2008) that each microwave is logged and that the power rating is monitored daily and

21

before each test trial. This is best done by using the IEC 705 test (Appendix II). Schiffman

(2008) and Buffler (1993) have both put together guidelines for microwave package testing.

The manufacture rated power is an average of many tests therefore is not accurate to the

current microwave output. Under the best circumstances the ovens power may vary plus or

minus 15 percent. Figure 9 below graphically depicts the variation over a three week testing

period. Microwave oven power changes after use and power will stabilize after 10 minutes of

continuous heating. To preheat an oven one must heat a liter of water in a microwave safe

package for 10 minutes of consecutive heating. This will warm up all the components and allow

them to reproduce consist wattage outputs. Oven power changes daily and it is necessary to run

the IEC 705 test every day and before every test. (p. 20 p. 107)

Figure 9. Microwave Wattage Variance. From From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

22

Summary

Many aspects of microwave meal creation were not understood from a standpoint of the role the

food played in the quality output of the meal. Additionally, in many ways the selection of a

proper packaging system is more important with microwaveable foods than with most other

products. Too often developer’s think of packaging as an afterthought, however it is crucial that

as much thought be put into both the choice of food items and packaging material choices.

23

Chapter III: Methodology

Company XYZ is required to design and manufacture a microwave food package that

will be able to control temperatures between different food compartments within the package.

Failure to complete the project could result in Company XYZ losing an important customer

which would negatively impact the bottom line. Testing is part of the development process in

this specific project and is the most important in order to determine the proper combination of

materials to achieve the customer’s goal.

Products are generally tested to decipher if the product will be accepted by the consumer

in terms of aesthetics. Seldom is the product tested in regards to how it will perform out in the

field or how the consumer will handle the product. Microwave food testing is very different

compared to regular product tests due to greater variables influenced by the consumer. Such

variables include: temperature of the meal, interpretation of instructions, and type of microwave

amongst others.

Package Design

Different package designs will be tested. The thermoformed packaging container will

remain constant throughout the testing and design stages. Metallized aluminum shielding labels

will be placed on strategic points on the tray to control microwave heating. Metallized

aluminum shielding labels will cover the container’s sides, bottom surface, and portions of the

top surface. Variables are as follows: height of label on side of container, label size covering top

surface, surface label coverage of bottom surface.

Instrumentation

Meals are to be frozen at minimum for 48 consecutive hours to ensure the food

components are frozen thoroughly; meal temperature shall begin at 0°F to 10°F. To ensure

24

repeatability, a calibrated programmable thermometer probe shall be used for every testing

procedure.

Subject Selection

Control Selection

In determining the correct amount of shielding for specific meals a baseline must

be achieved for common foods found in meals such as spaghetti, macaroni and cheese, and other

sauce/pasta combinations. The researchers used as a control group with the study a meal with a

two compartment CPET tray with standard low density polyethylene (LDPE) lidding film. A

standard food weight found common in microwave meals is 12 ounces, so the 12 ounces were

divided unequally into two compartments; 4.5 ounces in the smaller compartment and 7.5 ounces

in the larger compartment. For this experiment applesauce and macaroni and cheese were the

experimental food choices because of the high potential for thermal runaway due to the amount

of sugars within the foods.

Each control sample was frozen for 24 consecutive hours at a temperature of zero degrees

Fahrenheit. The control tray design had no shielding on either the small or large compartment.

Variable Selection

Variables were created varying the size of the shielding placed on the top, bottom,

and side portions of the tray. The drawing in Figure 10 shows that by reducing the area of

shielding covering the specific area whether it is top/bottom/side, a new variable had been

achieved. The end combination is determined by the food contents and desired temperature by

the customer.

25

Figure 10: Top shielding variable. The figure shows that by reducing the area of the label adhered to the lidding film different variables are created to achieve various temperatures.

Data Collection Procedures

An ideal testing procedure accounts for all variables and has the ability to control

variables. Some variables can cause larger influences in testing results; in this case the

microwave oven is the most inconsistent variable. To control the microwave variable these steps

were followed:

26

1) Stabilize the microwave wattage output. To do so isolate the microwave from all

electronics.

2) Preheat microwave oven: heat one liter of distilled water in a microwave safe

container for 10 minutes of consecutive heating, this will warm up all the components

and allow them to reproduce consist wattage outputs. Let microwave oven door stand

open for 15 minutes to bring oven cavity atmosphere back to neutral state.

3) Refer to IEC 705 Test in Appendix II, repeat test three times, and calculate average

wattage outputs.

4) Note: Microwave wattage output changes daily, repeat testing procedure before every

testing sequence to ensure traceability of results.

5) Once microwaves have been preheated following IEC 705 standard, testing of

samples may begin.

Sample measurements are extremely important; each procedure step must be followed to

ensure repeatability. Sample testing procedure should only begin after microwave stability has

been reached. Sample measurement procedure and data recording are as follows:

1) Cut one 2” slit in film covering the hot food compartment

2) Place microwave meal in center of microwave oven

3) Set time to 3 minutes 30 seconds

4) Take meal out of microwave immediately after cook cycle is complete. Let cool for 2

minutes. Letting item cool for 2 minutes lets the meal finish the cooking process.

5) Take measurements using calibrated thermometer. Temperatures shall be taken

according to Figure 10.

27

Figure 11. Microwave Temperature Locations

6) Record temperatures in data sheet.

7) Let microwave cool with microwave door open for 10 minutes to allow cavity to

return to room temperature. Wipe off excess moisture inside cavity.

8) Repeat Test

6

28

Figure 12: Sample data table

Destructive Testing

An important part of product development is making certain that your product is safe for

the consumer no matter how the consumer may use or misinterpret the intended use of the

product. There is no set standard for destructive microwave meal testing so the development

team assumed and attempted to replicate worst case scenarios the product could encounter.

Worst case scenarios included microwaving the tray for an extended period of time such as a

meal intended to cook for 3 minutes would cook for a half hour or longer. Additional scenarios

included mishandling of the directions, and putting more than one tray in a microwave cycle. It

is nearly impossible to come up with all possible scenarios a consumer can use a product. The

development team used the most logical scenarios for meal testing procedures.

Destruction Test Set-Up

The following consumer misuse scenarios were created:

1. Production facility under fills food tray weights

a. Half fill and quarter fill of intended weights

2. Consumer increases cook time

b. ½ hour, 15 minutes

3. Consumer re-uses tray

29

4. Consumer puts more than one tray in microwave cycle

5. Distribution cycle damages tray causing labels to detach

6. Consumer fails to remove tray from shipping carton and

microwaves tray

Each scenario had three replicate tests and was tested in a different microwave. At this

point in the development process it is understood that this is only a start in consumer disaster

testing; if the client decides to fully commit to the product being designed a full case study must

be conducted on the safety of the product.

Disaster Testing Procedure

1) Stabilize the microwave wattage output. To do so isolate the microwave from all

electronics.

2) Preheat microwave oven: heat one liter of distilled water in a microwave safe

container for 10 minutes of consecutive heating, this will warm up all the components

and allow them to reproduce consist wattage outputs. Let microwave oven door stand

open for 15 minutes to bring oven cavity atmosphere back to neutral state.

3) Refer to IEC 705 Test in Appendix II, repeat test three times, and calculate average

wattage outputs.

4) Note: Microwave wattage output changes daily; repeat testing procedure before every

testing sequence to ensure traceability of results.

5) Once microwaves have been preheated following IEC 705 standard, testing of

samples may begin.

6) After sample had been tested leave microwave oven door open for 15 minutes to let

microwave cavity return to ambient temperature and humidity.

30

7) After 15 minutes and microwave is back to ambient temperature and humidity, test

next sample. Repeat step 6 after every sample until data collection process is

complete.

Limitations

A limitation of the study is the ability to record multiple temperatures simultaneously.

To get the most accurate readings during temperature recording all temperatures should be taken

simultaneously. This would allow for the developer to see a more accurate temperature profile.

The longer it takes to take temperatures the more inaccurate they will become due to cooling.

Another limitation is being able to look at temperature profiles at different depths of the food.

Uniformity throughout the meal is the goal and without advanced equipment it is difficult to take

accurate temperatures at different depths of the food.

Summary

Figure 13: Disaster testing data sheet

31

Company XYZ used a stringent testing method to analyze the effectiveness of its

prototype designs in an attempt to fulfill its customers’ needs. Strategic measurements were

taken following the previously outlined testing protocol. In this chapter, the researcher supplied

simple statistical methods for collecting data later to be analyzed.

32

Chapter IV: Results

Microwave cooking has long been engaged with the task of conveniently heating and

providing quick meals for consumers. It is the current market trend to offer a more quality meal

for the consumer. A gap in microwave packaging has been identified through market analysis

identifying customers now want higher quality meals. The customer has identified a want by the

consumer to produce a quick yet high quality meal that offers different temperatures of food

within the same tray. An example could possibly be the pairing of ice cream and lasagna in

different compartments within the same tray. Developing a microwave package that will create a

new market in microwavable meals is inevitably the goal for Company XYZ, providing their

customer with a game changing new product line.

Reiterating the given specifications provided by the consumer product goods company

which enlisted Company XYZ to design the new microwavable package as follows.

1) Must be at a minimum one compartment offering controlled heating with noticeable

improvements over current products

2) The container must be able to withstand microwave conditions as well as household oven

and convection ovens.

3) Microwave container must possess a sealed lidding film to the container

4) Have the ability to be manufactured on current manufacturing equipment at the

customer’s facilities

5) Be cost effective to produce

Package Design Tested

The experiments of example 1 were performed on a microwave container comprising of

crystallized polyethylene terephthalate (CPET) as the microwave transparent container.

33

Aluminum foil was identified from research to posses the ability to block/redirect microwave

energy away from selected areas where aluminum foil was applied. The microwave container

comprised of two compartments, design of the tray can be viewed in Appendix 5. The test food

was macaroni and cheese in the large compartment (7.5 ounces) and applesauce in the smaller

compartment (4.5 ounces). Aluminum foil was applied with adhesive tape to the lidding film as

pictured in Appendix 5.

As discussed above, a microwave shield is configured to reflect, block, and /or absorb at

least a portion of the microwave energy directed at a container in a microwave oven. In certain

embodiments, a first microwave shield is provided in a shape that substantially conforms to the

outer structure of at least a portion of the container. Referring to Appendix 3, the figure shows an

upside down microwave tray covered by a material that is substantially transparent to microwave

energy comprising a first compartment, see Appendix 5, where surrounded by a material opaque

to microwave energy: a piece of metal foil shield defining that is located approximately in the

center of the base of the metal foil. Referring to the figure in Appendix 3, the aperture comprises

of the same general shape as the base, and at least one of the height or width of the aperture is at

least half of one inch. In this embodiment the aperture semi-circle comprises a radius (i.e., the

height at the tallest portion of the semi-circle aperture) of three-quarters of an inch, and width of

one and three-quarters inches. The height and width of the shield aperture are each a minimum of

about one-quarter of an inch, and may be selected depending on the amount of microwave

energy desired to be allowed into the container or container compartment through the base of the

container. Foods having a higher specific heat capacity typically require more microwave energy

to increase their temperatures than foods having a lower specific heat capacity, and thus an

aperture having a larger area would be selected to allow more microwave energy to enter the

34

container that with an aperture having a smaller area.

Referring to Appendix 3, the polymetric film lidding of the microwave tray further

embodies a second microwave shield adhered to the lidding. The second microwave comprises

of aluminum foil and additional adhesives to adhere to the lidding that substantially become

opaque to microwave energy and are centered on the lidding separated from the perimeter or

upper edges of the sidewalls by a predetermined distance. In certain embodiments, the second

microwave shield is spaced from the sidewalls by an approximately even distance of at least one

quarter of an inch, or of at least half of an inch.

Experimental Results

Testing of the previously mentioned design follows the outlined methodology in Chapter

3, and no deviations were made from the outlined methodology.

The desired temperatures for the unshielded compartment are desired to be between 170-

180 degrees Fahrenheit. The microwave testing cycle was for three minutes and thirty seconds,

upon completion it was discovered that the desired time to heat the meal was not enough. The

customer will need to adjust their settings and increase the amount of time to heat the meal. It is

a fact that increasing the cook time will provide not only higher temperatures but also more even

temperatures. The testing confirms the concerns over test repeatability due to the inconsistencies

in the microwave ovens. Sample two and four reached much lower temperatures than previously

tested samples one and three.

35

The second compartment is fixated with microwave shields as previously discussed, which

can be viewed in the Apendices 3-5. Figure 12 displays data from five samples with average

temperatures displayed taken from Figure 10. The microwave shields have shown the ability to

redirect microwaves in a positive manner in being able to control the amount of heating at

specific locations depending on the specific heat capacity and nature of the food at hand. Further,

the data shows that the shielding results in even heating, with a maximum temperature difference

between the locations of less than 20 degrees Fahrenheit. The greatest difference in temperature

was from the material at the corner location 1 to the material in the middle of the tray. The

Figure 14: Graphically depicts the food temperatures of the unshielded tray compartment. Temperatures were taken in accordance to figure 10. Refer to Appendix 5 for pictorial description of tray.

36

In figure 13, the numerous tray designs were tested varying the amount of shielding placed

upon the microwavable trays. The variables were: the amount of exposed area on the lidding film

exposed to microwaves (Appendix 3), the height of the side walls of the fixed aperture

(Appendix 5), and the size of the cutout in the bottom aperture (Appendix 4). The graph dipicts

that through changing the amount of shielding applied to the tray a wide variety of temperatures

can be obtained to suit a specific food product. From the expereiment a better understanding of

how specific shielding areas hindered or helped aid in uniformity and temperture control.

Figure 15: Graphically depicts the food temperatures of the shielded tray compartment. Temperatures were taken in accordance to figure 10. Refer to Appendix 5 for pictorial description of tray.

37

Figure 16: Various microwave shielding designs: Different shielding designs were tested and measured. The green zone represents the target temperature for the cold compartment whereas the red horizontal bar represents the goal for the desired hot food compartment.

38

Design Problem: Arcing

The complementary arrangement of the microwave energy shields poses little to no risk

of causing sparking or arcing within the microwave oven during cooking. However, the

potential does exist and occurrences of sparking/arcing have occurred during the experimental

tests. In particular, it was discovered that keeping the first and second shields independent of

each other and at sufficient distance minimizes the potential for arcing between the shields and

possibly resulting in fire within the microwave oven. During cooking, energy on the shields

may build up to an amount of over 3000 volts. Not to be bound without theory, it is believed

that when similar pieces of metallic shielding come into close contact, the air molecules may be

disrupted and break down, which in turn allows the water molecules to achieve a plasma state.

The plasma produces a conductor between two separate shields, thus resulting in an arc or spark

bridging the gap between the two shields. Close proximity of the edges of microwave energy

shields therefore provides a greater likelihood of sparks leaping between the shields. Critical

findings during testing were:

Experiments with the location of first and second microwave shields were performed to

investigate if food weight and food distribution throughout the microwave container could

further act as a significant factor in sparking. It was discovered that sparking is more prone to

happen when there is little to no food within the container. This increase in risk is attributed to

the lack of mass to absorb the remaining microwave energy. A balance between reflection and

absorption of microwave energy must be found, otherwise too much reflection results in too

much energy within the microwave cavity resulting in sparking.

39

The location of the top microwave energy shield is critical; if it is placed off center closer

to the sidewalls or in contact with the second larger compartment sparking/arcing is more prone

to occur. During testing it was discovered that if the second shield is directly lined up with a

sidewall of the first shield, there is significantly greater potential for arcing through the

microwave container. Furthermore, if the second shield were to be placed off-center or to

extend to the sidewall edges of the container or the first shield there would be a higher risk of

sparking if more than one of the same type of microwave container were placed together within

a microwave. Placing two containers adjacent and each having such second shields, the two

second shields may come into contact with each other if located side by side, and potentially

provide sparking between the second shields. Experiments showed that sparks were created

when two containers comprising second shields extending to the sidewall edges of the container

were placed touching or up to a half of an inch, but not when placed farther than half an inch

apart.

Results from testing different tray weights were successful in finding limitations in tray

weight. It was found that sparking occurred when the tray weight was less than once ounce in

each compartment. It is critical when manufacturing the trays that a proper weight check is in

place so that no meals leave the production facility under weight. Figure 17 shows holes that

had developed in the tray because the tray did not have a substantial food load to absorb the

microwave energy penetrating through the tray, thus resulting in holes at the weaker points of

the tray.

40

If a consumer makes the mistake of adding an extra zero to the time limit, (for example,

the desired time is 3:00 minutes, however, if the consumer presses an extra zero and walks away

the time limit will be 30:00), this could pose a large safety problem for any microwave meal

product. In this case, adding additional foreign materials into the arena could exponentially

heighten the potential for problems. Through testing the developers have found the proposed

meal to be microwave safe for extended periods of time. Results from the testing showed the

films and labels were able to withstand the lengthened cook times if a consumer fails to follow

directions. The tray will not deteriorate so the only consequence to the customer would be the

smell of burnt food if they make the mistake of adding too much time to the microwave cycle.

Figure 17: Holes developed in the microwave tray compartment because of

the lack of food load to absorb the microwave energy.

41

Summary

Vital information was found during the analysis of the testing phase. From the data the

microwave meal can be optimized per its food contents. The developers have discovered the

relationship between the amounts of shielding to temperature of the compartments. The top

shield affects the surface temperature of the meal, while the amount of shielding on the bottom

controls the temperature of the inner parts of the trays, zone 5 from Figure 11. Furthermore, the

side shielding labels control the temperature zones 1,2,3,4 in Figure 11. When these variables

are all put together the possibilities for food combinations are endless.

42

Chapter V: Discussion

Microwave heating is a quick and easy way to enjoy a meal in a hurry. Microwave

heating is more complicated than other methods such as conventional oven or stove top cooking.

There are more variables in microwave heating such as package geometry, package material,

food ingredients, and most importantly the microwave itself. Throughout this study the

researcher attempted to utilize product uniformity, optimal temperature, and package geometry.

In the literature review much detail was given on how to accomplish the task of creating a dual

temperature multi-compartment microwave meal. Using the literature review as a baseline the

development team set out to accomplish the project goal of developing a new microwave food

package that has the ability to control temperatures between different food compartments.

Limitations

Company XYZ is limited in selection of materials in order to meet compliance by the

Federal Drug Administration. Company XYZ has only at its deposal polymer thermoplastics

including thermoformed crystallized polyethylene and polyethylene for the container. Company

XYZ has countless polymer laminations at is disposable for container lidding film. Such

materials include a wide array of processing from blown film extrusion to cast film extrusion.

Conclusions

Numerous findings have been made in correlation to the literature review found in

Chapter III. An affirmation was found that the food selection within the microwave package

made the meal either easier or more difficult to control depending on sugar levels, starch, and

proteins within the makeup of the food product. Sugars and starches often resulted in intense

thermal hotspots causing the food product to be very difficult to control due inability to harness

the intense electrical charge presented in microwaves. Furthermore, the importance of salt was

43

the greatest influence on uniformity because of its conductivity within a microwave cavity. The

large presence of salt in foods largely impacted the uniformity of heating; it was evident that the

presence of salt caused intense localized heating in specific areas of the package, especially in

the corners and edges. Modification attempts may be made to the food stuff within the tray,

however, Company XYZ does not have the ability to modify the food that will occupy the

microwave meal compartment, and will rely on packaging materials and package geometry to

negate the common problems associated with current microwave technologies.

Relating back to the literature review in Chapter III, fellow research on the topic of

microwave meals has provided instrumental help in developing the package. Such studies of

importance were Schiffman’s studies on the affects of microwaves on packaging geometry

(Schiffman 2008). During the development phase numerous package designs were tested many

succeeded in a (controlled environment, yet failed miserably when put in the hands of the

consumer in an uncontrolled environment. An example is a cylindrical tray with a vertical height

of four inches which succeeded in maintaining a temperature between 60-80 degrees Fahrenheit.

However, the consumer found abnormal hot spots within the container on a consistent basis,

rendering the package unsafe. Schiffman, pointed out this common occurrence in Figure 7

noting the microwaves begin to amplify based on the reflections off of the container’s walls, thus

making temperatures difficult to control.

Packaging Material

Developers have put together a group of materials that is not only safe for microwave

heating but effective as well. The one or more compartment tray will be constructed out of

crystallized polyethylene (CPET), which allows consumers to either microwave or use a

conventional oven to cook their meals. CPET was chosen as the tray material because a fair

44

amount of consumers still use ovens to heat meals, and because other materials such as

polypropylene would not stand up to the heat in a conventional oven, resulting in safety issues.

Lidding material will be LDPE that has adequate barrier properties for the frozen meal. LDPE

has a good moisture barrier and makes an excellent sealant allowing for a high rate of

production. Shielding labels will be an aluminum foil label of some weight that will negate curl

allowing for faster production speeds. Further testing and examination will determine the exact

weight of the material in order to compromise between cost and curl.

Further Development

Further examination of the market for frozen meals needs to be explored on how

marketing will attack the potential market with shelf positioning, pricing, and graphics.

However, before any meals get deployed into the actual market consumer testing is necessary to

decipher what food combinations to pair together to match specific markets. Included in the

consumer testing are a series of testing involving focus groups. Focus groups are used to get

unbiased results on how the consumer actually views the product and uses the product.

Developing a new product line may require new equipment or changes to the existing

production facilities. This part of the project is going to need to employ new team members

focused on production of the meal. The current team is of the material and design nature and

will need to gain the expertise of manufacturing/equipment personnel for the project to continue.

At this point in the project it is the customer that will need to open up their production facilities

to Company XYZ so its engineering team can examine the customers existing production lines

and equipment to enable the team to put together a plan for production and shipment.

Lastly, a distribution test may be necessary of the package to ensure that all components

within the package arrive at the grocer able to perform. Such testing would include a full

45

ASTM-4169 distribution test encompassing a series of drop tests and vibration tests. Another

test protocol that would be beneficial is ISTA-1A. During the distribution test the experimenter

should concentrate on damage of the integral component thus being the aluminum foil shield.

The aluminum foil shield may pose safety concerns if severely damaged; damage would

constitute as severe if the foil label becomes ripped, misaligned, or dislodged from the lidding

film.

Recommendations

It is the recommendation of the experimenters that the development of this project

continue past the described responsibilities of the material and design team. Reiterating the goal,

the goal was that the development team brings a working solution to the customer in this case a

dual temperature microwave meal. To ensure the best results more consumer research should

be conducted to determine the correct foods to be paired together so that the development team

can fully optimize the amounts of shielding to render the best meal for the consumer.

Additionally, the customer must think about educating the consumer by means of graphics or

external packaging to ensure the consumer does not misuse the product and harm them self in the

event of an accident. Such education of the consumer can be through enlarging the directions on

the packaging, duplicating directions on the primary package and secondary package, or through

other media such as television commercials. The developers have brought a working solution

that achieves the goal while keeping the consumer safe and believes that the proposed solution

will change the way microwave meals are manufactured and will change the perception of

microwave meals as low quality fast food into a more gourmet experience.

46

References

Ahvenainen, R. and Heiniö, R.-. L. (1992), Factors affecting the suitability of aluminium-foil

trays for microwave oven heating: Comparison with plastic trays. Packaging Technology

and Science, 5: 255–264. doi: 10.1002/pts.2770050506 Ahvenainen, R., Liukkonen-Lilja,

H. & Kivikataja, R.-L. 1989. Food packages in microwave oven heating. PTR Report 21

A. Association of Packaging Technology & Research, Finland. ISBN 951-8988-00-5.

Bengtsson, N.E. & Risman, P.O. 1971. Dielectric properties of food at 3 GHz as determined

by a cavity perturbation technique. II. Measurements on food materials. J. Microwave

Power 6: 107-123.

Buffler, C.R. 1993. Microwave Cooking and Processing. Van Nostrand Reinhold. New York.

Buffler, C.R. & Stanford, M.A. 1991. Effects of dielectric and thermal properties on the

microwave heating of foods. Microwave World 12(4): 15-23.

Hodson, Jay; Douglas, Brian; Klittich, Mena; Cvancara, Lance; Lohoff, Andrew. BANNER &

WITCOFF, LTD. Microwave Cooking Containers With Shielding. United States Patent

20100230403

Ohlsson, T., Bengtsson, N.E. & Risman, P.O. 1974a. The frequency and temperature

dependence of dielectric food data as determined by a cavity perturbation technique. J.

Microwave Power: 129-145.

Ohlsson, T. & Risman, P.O. 1978. Temperature distribution of microwave heating – spheres

and cylinders. J. Microwave Power 13: 303-310.

Roussy, G., Chaabane, H., & Esteban, H. (2004). Permittivity and Permeability Measurement of

Microwave Packaging Materials. IEEE Transactions on Microwave Theory &

Techniques, 52(3), 903-907. doi:10.1109/TMTT.2004.823571

47

Ryynänen, S. (2002). MICROWAVE HEATING UNIFORMITY OF MULTICOMPONENT

PREPARED FOODS (Doctoral dissertation, University of Helsinki Department of Food

Technolo, Helsinki). Retrieved February 29, 2012, from EBSCOHOST.

Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA.

Schiffman, R. F. (1990, March). Mirowave foods: Basic Design Considerations [Electronic

version]. TAPPI Journal, 209-212.

Thorsell, U. 1994. Guide to the development of food products and packages for microwave

oven. Packages and products for heating in microwave ovens. SIK Report 608. The

Swedish Institute for Biotechnology, Göteborg, Sweden.

48

Appendix A: Microwave meal with center compartment shielded by surrounded

compartments

49

Appendix B: IEC Microwave Testing Data Table

Date

IEC OVEN POWER TESTS

Oven:

Manufacturer

Mode l II

Rated Power Output

Test 11 AMBIENT INITIAL FINAL CONTAINER WATER OVEN VOLTS IEC

TEMP {F) WATER WATER MASS {GM) MASS {GM) TIME {SEC) WATTS

TEMP {F) TEMP {F) {F) {F) Mw

To T1 T2 Me Mw t

1 22.2 10.6 34.5 429.9 1000.2 120 873.00

2 IIDIV/0!

3 IIDIV/0!

Average • IIDIV/0!

NEW IEC METHOD

p=4.187 Mw{t2-tl) +0.88 Mc{T2-TO)/t

P= Power in watts

Mw=mass of water { GM)

Me = Mass of Glass Container

TO= amb ient & glass temperature

T1 =In itial water temperature

T2 = Final water temperature

t = heating time in seconds

50

Appendix C: Microwave Package Design: Top View

150

51

Appendix D: Microwave Package Design: Bottom Profile

52

Appendix E: Microwave Meal: Side Profile

53

Appendix F: Microwave Meal: Top Profile

13

ε’= Relative dielectic strength, in volts per unit distance ε’’= Dilectic loss factor, unitless λ= Wavelength of Microwave Oven Figure 2: Dielectric Properties Equation. From Schiffman, R. F. (1990, March). Mirowave foods: Basic Design Considerations [Electronic version]. TAPPI Journal, 209-212. In the subsequent paragraph Ryynänen (2002) summarizes the theory of penetration depth.

“ Theoretically, the penetration depth dp (or power penetration depth) is defined as

the depth below a large plane surface of a substance at which the power density of

a perpendicularly impinging, forward propagating plane electromagnetic wave

has decayed by 1/e from the surface value(1/e is about 37 %) (p.17)”

Table 1: Penetration Depth of Starting Package Temperatures

Temperature Dp (cm/in)

Water (ICE) Frozen (32 F) 1160/460

Water Room (72 F) 1.4/0.6

Water Hot (100 F) 2.8 / 1.1

Salt Water Room (72 F) 0.2/0.08

Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

Dielectric Properties

Active packages interact with the food contents of the package, more specifically

changing the electric or magnetic field configuration therefore modifying the heating pattern of

the food product. The primary components in active packaging that change are the dielectric

properties. Dielectric food properties are determined by chemical structure. The amount of

water or salt content impacts the ability for the foodstuff to conduct an electrical current. It is

16

Package Geometry

Shape has a drastic impact on the outcome of microwave food products (Ryynänen

2002). The shape can help influence uniform cooking. Rectangular packages especially have a

lot of disadvantages. With rectangular shapes the issue comes into play in the corners, where

there are too many points of access to the food product. The red arrows represent the incident

waves. As one can view there are four points of occurrence from the top, bottom, and two sides.

With the four incident waves transmitting on such a small location two events can happen.

Testing shows (Hodson, Douglas, Klittich, Cvancara, Lohoff, 2010) that either burning of the

food product or a major concern in sparking can happen and will eventually start the package on

fire.

Figure 5. Rectangular hot spots. Incident waves are represented by red arrows. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

This phenomenon can be avoided introducing an alternative shape, an oval or circular

package. In the diagram below one can view that the waves may only penetrate at three different

points, along the side, top, and bottom. There is little possibility that the rays can meet, resulting

in a more uniform food product.

17

Figure 6. Cylindrical / Oval Uniformity. Red arrows represent incident waves. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

Tall packaging containers such as tubs, jars, and glasses are not ideal for meals due to

safety issues. The lens affect is a serious issue in microwave packaging. The lens affect is

illustrated in Figure 7 below.

Figure 7. Vertically oriented cylindrical jar where incident waves enter a package and become entrapped thus resulting in hidden hot spots within the package. From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

INCIDENT WAVE

REFLECTED WAVES

TRA

NSM

ITTI

NG

WA

VES

21

before each test trial. This is best done by using the IEC 705 test (Appendix II). Schiffman

(2008) and Buffler (1993) have both put together guidelines for microwave package testing.

The manufacture rated power is an average of many tests therefore is not accurate to the

current microwave output. Under the best circumstances the ovens power may vary plus or

minus 15 percent. Figure 9 below graphically depicts the variation over a three week testing

period. Microwave oven power changes after use and power will stabilize after 10 minutes of

continuous heating. To preheat an oven one must heat a liter of water in a microwave safe

package for 10 minutes of consecutive heating. This will warm up all the components and allow

them to reproduce consist wattage outputs. Oven power changes daily and it is necessary to run

the IEC 705 test every day and before every test. (p. 20 p. 107)

Figure 9. Microwave Wattage Variance. From From Schiffman, R. F., & Sacharow, S. (2008). Microwave Active Packaging. New York City: PIRA

35

The second compartment is fixated with microwave shields as previously discussed, which

can be viewed in the Apendices 3-5. Figure 12 displays data from five samples with average

temperatures displayed taken from Figure 10. The microwave shields have shown the ability to

redirect microwaves in a positive manner in being able to control the amount of heating at

specific locations depending on the specific heat capacity and nature of the food at hand. Further,

the data shows that the shielding results in even heating, with a maximum temperature difference

between the locations of less than 20 degrees Fahrenheit. The greatest difference in temperature

was from the material at the corner location 1 to the material in the middle of the tray. The

Figure 14: Graphically depicts the food temperatures of the unshielded tray compartment. Temperatures were taken in accordance to figure 10. Refer to Appendix 5 for pictorial description of tray.

36

In figure 13, the numerous tray designs were tested varying the amount of shielding placed

upon the microwavable trays. The variables were: the amount of exposed area on the lidding film

exposed to microwaves (Appendix 3), the height of the side walls of the fixed aperture

(Appendix 5), and the size of the cutout in the bottom aperture (Appendix 4). The graph dipicts

that through changing the amount of shielding applied to the tray a wide variety of temperatures

can be obtained to suit a specific food product. From the expereiment a better understanding of

how specific shielding areas hindered or helped aid in uniformity and temperture control.

Figure 15: Graphically depicts the food temperatures of the shielded tray compartment. Temperatures were taken in accordance to figure 10. Refer to Appendix 5 for pictorial description of tray.