toshiharu mizukaki*, takeshi seto**, kazuyoshi takayama* * tohoku university, sendai, japan
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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
3
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
4
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
5
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
6
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
7
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
9
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
10
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
11
Measurement system
ICOSN2001 Yokohama, Japan
12
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
13
Experimental results
Min.
Max.
Wall-pressure profile Phase map Density change along A-B
ICOSN2001 Yokohama, Japan
14
Conclusions
Digital phase shift holographic interferometry
can non-intrusively measure small density changes– at high frequency– in liquid– in confined test sections
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