ICOSN2001 Yokohama, Japan

1

Measurement of density distribution in a small cell by digital phase-shift

holographic interferometry

Toshiharu Mizukaki*, Takeshi Seto**,

Kazuyoshi Takayama*

* Tohoku University, Sendai, Japan

** Seiko-Epson Corporation, Japan

(presented by Harald Kleine *)

ICOSN2001 Yokohama, Japan

2

Objectives

Ordinary sensors require finite volume in the area of interest.

optical diagnostics

no seeding !

appropriate density-sensitive

visualization technique

Development of a non-intrusive measurementsystem for the evaluation of fluid flow in

micro-machines

ICOSN2001 Yokohama, Japan

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Objectives

• determine density changes in liquid

– in a small cylinder (dimensions: order of millimeters)

– under high-frequency oscillation– with high precision (within a few percent)

interferometry

ICOSN2001 Yokohama, Japan

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Experimental Approach

Cylindrical test section:

Light rays are distorted.

Compensation of distortion adequately shaped outer surface of the cylinder cylinder material: plexiglass optical method: holographic interferometry

ICOSN2001 Yokohama, Japan

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Experimental Approach

Reference beam interferometry:

Sensitivity of the apparatus is limited and fixed.

In plane flows:

KL

: wavelengthK: Gladstone-Dale constantL: depth of test section

Increased accuracy of interpolation between fringes multiple reference beams

ICOSN2001 Yokohama, Japan

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Experimental Approach

• Measurement method

Digital phase-shift holographic interferometry (DPSHI)

- two reference beam interferometry

- digital data acquisition and image processing

- accuracy/resolution of the order of 1/100 fringe

• Test section design

- cylinder with aspheric-lens-type outer surface

ICOSN2001 Yokohama, Japan

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Design of the test section

• rays have to be parallel after passing the test section

ntube

ncel

nenv

2

2

2

0

sinsin

)sin(

)cos(

),(),(),(

n

m

l

mlrSyxXyxX i

ICOSN2001 Yokohama, Japan

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DPSHI – recording system

Laser: Ruby laser (694.3 nm, 2J/pulse, 30 ns pulse width)

Recording material: Holographic film (ILFORD HOTEC-R, 7000 lines/mm)

Method: Double exposure Fresnel hologram (with diffuse object beam, two reference beams)

ICOSN2001 Yokohama, Japan

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DPSHI – reconstruction system

Optics: Michelson interferometer (with PZT mounted mirror, tilted mirror and two reconstruction beams)

Laser: He-Ne laser (632.8 nm, 35 mW, cw)

Image capturing device: CCD camera (480 pixels by 640 pixels)

ICOSN2001 Yokohama, Japan

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Phase demodulation

+α

+α

+α

I0 I1

I2

I3

I4

φ -3/2α

φ -1/2α

φ +1/2α

φ+3 /2α

φ i,j (unknown)

φ i,j (calculated)

recorded intensity (I1 , I2 , I3 , I4)

By shifting amirror with PZT

i

j

φ (x,y)

φ : target phaseα : added phase by PZTψ : fringe phase Ｉ : image intensityγ : contrast function

ICOSN2001 Yokohama, Japan

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Measurement system

ICOSN2001 Yokohama, Japan

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Conditions

• Cylinder dimensions:

7.8 mm x 37 mm

• Liquid:

distilled water

• Oscillation frequency:

20 kHz with 17 m amplitude

• Observation trigger:

Maximum wall pressure, minimum wall pressure

ICOSN2001 Yokohama, Japan

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Experimental results

Min.

Max.

Wall-pressure profile Phase map Density change along A-B

ICOSN2001 Yokohama, Japan

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Conclusions

Digital phase shift holographic interferometry

can non-intrusively measure small density changes– at high frequency– in liquid– in confined test sections