To find out Polerizability of a Dielectric substance

WHAT IS A DIELECTRIC SUBSTANCE.

A dielectric is an electrical insulator that can be polarized by an applied electric field.

Dielectric polarizationWhen a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Permittivity ( ) is a measure of the ability of a material to be polarized by an electric field.

CAPACITANCEIt is, however, easier to grasp the concept of permittivity by first discussing a closely related property, capacitance (C). Capacitance is a measure of the ability of a material to hold charge if a voltage is applied across it, and is best modeled by a dielectric layer that's sandwiched between two parallel conductive plates.

The capacitance of a capacitor depends on the permittivity of the dielectric layer, as well as the area A of the capacitor and the separation distance d between the two conductive plates. Permittivity and capacitance are mathematically related as follows: C = (A/d). where is the permittivity of vacuum (8.85 x 10-12 F/m).

The dielectric constant

The dielectric constant (k) of a material is the ratio of its permittivity to the permittivity of vacuum 0, so k = / 0. The dielectric constant is therefore also known as the relative permittivity of the material.

TYPES OF DIELECTRICS

Low-k dielectrics are very good insulators for isolating signalcarrying conductors from each other. Thus, low-k dielectrics are a necessity in very dense multi-layered IC's, wherein coupling between very close metal lines need to be suppressed to prevent a degradation in device performance High-k dielectrics are good at holding charge, they are the preferred dielectric for capacitors. High-k dielectrics are also used in memory cells that store digital data in the form of charge.

ExamplesSolids. Porcelain (ceramic), mica, glass, plastics, and the oxides of various metals. Liquids Distilled water is a fair dielectric. Gasses Dry air is an excellent dielectric, and is used in variable capacitors and some types of transmission lines. Vacuum is an exceptionally efficient dielectric

SOLID DIELECTRICSSolid dielectrics: Some examples include porcelain, glass, and most plastics. Gaseous dielectrics: Air, nitrogen and sulfur hexafluoride are the three most commonly used gaseous dielectrics. Industrial coatings such as parylen provide a dielectric barrier between the substrate and its environment.

Property of a dielectric 1.Dielectric loss 2.Dielectric constant 3.Dielectric breakdown

DIELECTRIC POLARIZATIONAny dielectric substance placed in an electric field undergoes polarization, which involves the appearance of bound charges on the surface of the dielectric. Polarization is defined as the dipole moment per unit volume and it may be divided into two categories: induced and orientation polarization

POLARIZABILITY EWhen a body is placed in a uniform electric field Eo in vacuum caused by a vacuum, fixed charge distribution, its dipole moment will in general changed.The difference between the dipole moments before and after the application of the field Eo is called the induced dipole moment m. If a body shows an induced dipole moment differing from zero upon application of a uniform field Eo, it is said to be polarizable. polarizable. In most cases polarizable bodies are polarized linearly, that is, the induced moment m is proportional to Eo. In this case one have:

m ! EEwhere E is called the (scalar) polarizability of the body.

(2.19)

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From the dimensions of the dipole moment, [e][l], and the field intensity, [e][l]-2, it follows that the polarizability has the dimension of a volume. Using the above definition of the polarizability, we conclude from equation (2.12) that a dielectric sphere of dielectric constant I and with radius a has a polarizability:

E!

I 1 3 a I 2(2.12)

(2.20)

m!

I 2 I1 3 a I 2 2 I1

0

For a conducting sphere in the case Ipg from the relation (2.20) one can obtain that a conducting sphere with radius a has a polarizability:

E ! a3

(2.21)

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USES1.Dielectric wireless receiver 2.Capacitors 3.Dielectric resonator 4 Glucose Testing 5.Cellular phone 6.Van de Graff generator

1. DIELECTRIC WIRELESS RECEIVER

Dielectric wireless receiver is a type of radiofrequency receiver front-end featuring a complete absence of electronic circuitry and metal interconnects. It offers immunity against damage from intense electromagnetic radiation

The Dielectric Resonator Antenna (DRA) in the front-end, functions as a concentrator of incoming electromagnetic field. When the electromagnetic (EM) field excites the resonance of DRA, a mode field pattern is built up inside the structure. The electro-optic (EO) resonator is placed at the location of the peak field magnitude The EO resonator converts the received EM signal to an intensity modulated optical signal which is then carried away from the antenna front-end via an optical fiber. At the remote location, the signal is converted back to an RF signal which is then amplified and processed using conventional techniques. This front-end design significantly increases the threshold for damage associated with high power microwave signals.

2. CAPACITORS

Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric reduces the field and increases the capacitance. Commercially manufactured capacitors typically use a solid dielectric material with high permittivity as the intervening medium between the stored positive and negative charges. This material is often referred to in technical contexts as the "capacitor dielectric" .

Capacitors, like all electrical components, have limitations which must be respected for the sake of reliability and proper circuit operation. Working voltage: Since capacitors are nothing more than two conductors separated by an insulator (the dielectric), If too much voltage is applied, the "breakdown" rating of the dielectric material.

DRAM SEM MICROGRAPHThe two deep "trenches" (they are really holes) contain the capacitors on their walls. The dielectric (with ~ 7 nm far too thin to be visible) is "ONO", a triple layer of Oxide (SiO2) Nitride (Si3N4) Oxide (SiO2). This is an early 64 MBit DRAM (1996).

Hynix Announces 512Mbit Mobile DRAMHynix Semiconductor, a noted memory maker has said it has developed the world's fastest and smallest 512 MBit mobile DRAM. The new DRAM operates at 200 MHz and processes 1.6 GB of data per second. "The product will deliver the memory capacity and speed required for third generation mobile phones that provide new services, such as digital media broadcast (DMB), to subscribers," the chip maker has said. It is expected that Hynix will combine this 512Mb mobile DRAM and Nand Flash in a multi-chip package which will allow mobile manufacturers to make slimmer mobile phones.

3. Dielectric resonator A dielectric resonator oscillator (DRO) is an electronic component that exhibits resonance for a narrow range of frequencies, generally in the microwave band. It consists of a "puck" of ceramic that has a large dielectric constant and a low dissipation factor. Such resonators are often used to provide a frequency reference in an oscillator circuit. An unshielded dielectric resonator can be used as a Dielectric Resonator Antenna (DRA).

If the dielectric resonator is placed in an open environment, power is lost in the radiated fields. This fact makes dielectric resonators useful as antenna elements. Dielectric resonator antennas (DRA) offer following attractive features: The dimension of a DRA is of the order of , where 0; is the free-space wavelength and r is the dielectric constant of the resonator material. Thus, by choosing a high value of r , the size of the DRA can be significantly reduced.

There is no inherent conductor loss in dielectric resonators. This leads to high radiation efficiency of the antenna. This feature is especially attractive for millimeter (mm)-wave antennas, where the loss in metal fabricated antennas can be high. The dimension of a DRA is of the order of

4Pendragon Medical is a company in the field of life sciences co-founded in March 2000 by coa man suffering from diabetes, who himself is a medical doctor The company has developed a unique, non-invasive sensor technology based on nonimpedance spectroscopy to monitor blood glucose levels continuously

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NonNon-invasive Blood Glucose Monitoring Based on New Techniques

likeOptical rotation of polarized light Infrared (Mid(Mid-and Near-IR) Nearspectroscopy Impedance or dielectric spectroscopy

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Dielectric (Impedance) SpectroscopyBroadband Dielectric Spectroscopy Time Domain Dielectric Spectroscopy10-1 100 101 102 103 104 105

106

107

108

109

1010

1011

f (Hz)

Bound Water

Proteins Tissue DNA Ice Lymphocyte Erythrocyte

Water

Lipids

E-Dispersion e.g. Tissue

F -Dispersion e.g. Cells, Proteins

H-Dispersion e.g. Lipids, AA

K-Dispersion e.g. Water

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Dielectric (Impedance) SpectroscopyWhat is measured? Why can it be measured?Varying blood glucose concentration Effect of changes in electrolytes due to variations in blood glucose concentrations Impact on the electrolyte concentrations in plasma Conductivity & permittivity of the cell membrane (e.g.erythrocytes)

ResultImpact of glucose on the impedance pattern at radio wave frequencies that can be detected

as an adjunctive device to supplement blood glucose measuring to help to detect trends and patterns in glucose levels in adults with diabetes for use in health care facilities as well as at home The device will help physicians to simplify the control of patients therapy... ... and the patients will benefit from easier self-control, which results in an improvement selfof their quality of life

Device

PENDRA - Sensor

Arm

Sensor plate

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5. Dielectric as a piezoelectric MaterialSome dielectrics can generate a potential difference When subjected to mechanical stress, or change physical shape if an external voltage is applied across the material. This property is called piezoelectricity. Piezoelectric materials are another class of very useful dielectrics.

6. DIELECTRIC AS A FERROELECTRIC MATERIALSome ionic crystals and polymer dielectrics exhibit a spontaneous dipole moment which can be reversed by an externally applied electric field. This behavior is called the ferroelectric effect. These materials are analogous to the way ferromagnetic materials behave within an externally applied magnetic field. Ferroelectric materials often have very high Dielectric constants, making them quite useful for capacitors.

FERROELECTRIC CERAMICS: PZT

(PBZRTIO3) STRUCTURE

Ferroelectric ceramics are widely used in modern technology with various applications (sensors, actuators, generators, transducers to very recent IC for RAM). They can be used for DRAM (dynamic random access memory), and high remanent

polarisation and low coercive field for being used as NVRAM (non-volatile random accessmemory).

Examples of piezoelectric microsensors on silicon: (a) microphone and (b) accelerometer. (OPA N.V., Taylor and Francis Ltd.)

VOLTAGE-DEPENDENT RESISTORS (VARISTORS)

There are a number of situations in which it is valuable to have a resistor which offers a high resistance at low voltages and a low resistance at high voltages. Such a devices can be used to protect a circuit from high-voltage transients by providing a path across the power suply that takes only a small current under normal conditions but takes large current if the voltage rises abnormally, thus preventing high-voltage pulses from reaching the circuit. Schematic use of a VDR to protect a circuit against transients,

Source

VDR

Circuit to be protected

Schematic representation of varistor-capacitor device construction and its equivalent circuit.

7.INDUSTRIAL COATINGS

Industrial coatings such as parylen provide a dielectric barrier between the substrate and its environment. Mineral oil is used extensively inside electrical transformers as a fluid dielectric and to assist in cooling. Dielectric fluids with higher dielectric constants, such as electrical grade castor oil, are often used in high voltage capacitors to help prevent corona discharge and increase capacitance.

8. Dielectric as Electrets

Specially processed dielectrics, called electrets (also known as ferroelectrics), may retain excess internal charge or "frozen in" polarization. Electrets have a semi permanent external electric field, and are the electrostatic equivalent to magnets. Electrets have numerous practical applications in the home and industry.

Electret is a dielectric material that has a quasipermanent electric charge or dipole polarization. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet..

9.VAN DE GRAFF GENERATOR

Because dielectrics resist the flow of electricity, the surface of a dielectric may retain stranded excess electrical charges. This may occur accidentally when the dielectric is rubbed (the triboelectric effect). This can be useful, as in a Van de Graff generator

10. CELLULAR TELEPHONE

Portable communication devices such as cordless, portable, and car telephone have become popular worldwide. Do you know what kind of dielectric and ferroelectric components are used in a cellular phone?

CELLULAR TELEPHONE

Chip Monolithic ceramic capacitors Microwave Oscillators Microwave Filters Ceramic Resonators

High Frequency SAW Filter Ceramic Filters Piezoelectric Receivers Piezoelectric Speakers

Johanson Dielectrics Capacitor Products: Ceramic SMT and Leaded High Voltage and High Temperature, Dual and Multi Capacitor Arrays, Low Inductance, X2Y, Switchmode.

CAPACITORS

DIELECTRIC MATERIALS AND DEVICES

CAPACITORS

MULTILAYER CERAMIC CAPACITOR

Cut-away view of multilayer ceramic capacitor.

Dielectric substrate is Grain Boundary Barrier Layer (GBBL) material, which has the highest dielectric constant in ceramic capacitor industry. Dielectric ceramic powder is Ultra Low fired material that can be fired at lower than 920 C. This low fired temperature allows manufacture to use low cost electrode system such as 95Ag/5Pd or 100% Silver to make Multilayer Ceramic Capacitor MLCC).

MULTILAYER CERAMIC CAPACITOR

The demands for miniaturization largely preclude an increase in the face area A. One exception is the multilayer ceramic capacitor (MLCC), in which case:C ! I rI o A( N ) d

where N is the number of stacked plates. Ideally, the dielectric should have a low electrical conductivity so that the leakage current is not too large.