Transcript SCHLIEREN IMAGING METHOD AND ITS APPLICATION FOR

SCHLIEREN IMAGING METHOD
AND ITS APPLICATION FOR VISUALIZING
OF SOME PHYSICAL PROCESSES
V. Ohanesjan, R. Popeski-Dimovski, and S. Topuzoski
Introduction
• Schlieren imaging as technique for visualization of nonhomogeneous regions.
• Word “Schlieren” origins from old German, meaning bits or pieces.
• Shimmering mirages on a hot road or optical distortions caused by the hot air
from jet engine are everyday life examples of schlieren effect.
• We present here a theoretical explanation of the schlieren imaging, and a
simple experimental procedure.
Fig. 2
Fig. 3
• During the time, many different apparatus for Schlieren imaging have been
developed (two mirrors, one mirror, two lenses (Toepler), one mirror). Our
schlieren system is with two lenses. “convergent”
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Fig. 1
IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Historical facts
• First observations on schlieren effect were reported by Hooke and Huygens in
XVII century.
•
August Toеpler (1836-1912)
 Gave a name to this technique (Schlieren);
 First basic apparatus for flow visualization by using a knife – edge;
 “Classics of Exact Science” ;
• Hubert Schardin was recognized as a modern pioneer of the color schlieren
technique.
Fig. 4
• In present time, the most significant names in this field of physics are Leonard
M. Weinstein and Gary S. Settles.
Fig. 5
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Schlieren method and application
• Human eyes and CCD detectors are only color and intensity sensitive.
• The light wave changes its phase during propagation in a transparent medium
with refractiv index gradient. Using the schlieren optical method the phase
variation is transformed into intensity variation, allowing us to detect refractive
index gradient.
• Gary S. Settles has made a lot of outdoor observations on different phenomena.
• Application of the method to liquid membranes, sonar pulses, optically
transparent polymers and polymericFigfoils.
.6
• M. Weinstein had transformed an telescope into schlieren apparatus.
Fig. 7
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Experimental setup
• Optical fiber from Oceans Optics Spectrometer as a point light source.
• Two convergent plano – convex lenses with 9 cm diameter and 50 cm focal length.
• Micrometer diaphragm as a knife – edge.
• Nikon d 5000 with AF-S Nikkor lens 55-200mm.
Fig. 8
• Computer software: Camera Control Pro 2 and Capture NX 2
Fig. 9
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Theoretical explanation
• Gladstone – Dale equation gives a relation between air density 𝜌 and refractive
index 𝑛
n 1

 G ( )
G ( )  Gladstone-Dale number
  wavelength
𝑀𝑝
• From the ideal gas law 𝜌 = 𝑅 𝑇 it follows that the air density can be
modified by varying its pressure and temperature.
• The light rays propagating in medium with refractive index gradient bend
fractionally to the regions of greater index due to the change of the speed of
the light.
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
• Light wave deviation angle ∆𝜀, figure 10 ,may be found by solving the Fresnel
diffraction integral or simpler, by using geometrical optics.
y
tv
2
y


x
1
Fig. 10
• One can easily see from Figure 2 that: ∆𝜀 ≈ sin ∆𝜀 =
∆𝑣∆𝑡
∆𝑦
• For infinitesimally small ∆𝜀 ≈ 𝑑𝜀 and introducing ∆𝑣 ≈
beam deviation one gets:
d 
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𝑐∆𝑛
𝑛2
for the angular
1 dn
dx
n dy
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20-23 September 2012, Ohrid, R Macedonia
L1
L2
dn
dy
Point
source
detector
y
phase
object
knifeedge
f2
p
l
s
y
’

y 
Fig. 11
• From Fig.11, using small angle approximation and thin-lens equation
1
𝑝
1
1
+𝑙 =𝑓
for second lens, the offset distance of the deviated light rays on the knife-edge
∆𝑦 is obtained:
y  f 2 tan  y  f 2  y
L
where
y  
0
•
1 n
dx
n y
The contrast of the final image is proportional to ∆𝑦.
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C ~ f 2 y
IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Experimental results
• Knife - edge orientation
Fig. 14: Turbulent air flow. Here
case temperature
Fig. 12 : Horizontal temperature
Fig. 13in: this
Horizontal
is no
preferred axis, because
of that and
knifevertically orientated
gradient due to the lighted
match,
gradient,
edgeknife
orientation does not knife
influence
and horizontally orientated
edge.
significantly.
edge.
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IX Conference of the Society of Physicists of Macedonia
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• Image digital processing
Fig. 15: Just captured image.
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Fig. 16: Post processed image with
Capture NX2
IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
• Other examples
Electrostatic discharge
Fig. 17: Human breathing.
Fig. 18: Electrostatic discharge between
the electrodes of the high voltage
supply.
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Conclusion
• We succeeded to set up a schlieren system with the optical elements we have in
our laboratory and tested its sensitivity.
• We have observed and recorded by camera: laminar and turbulent gas flow, an
electric discharge in air, temperature gradient, breathing and heat flow from palm.
• These experiments are also valuable from the educational point of view, because
they serve as an introduction in optical design and alignment for undergraduate
students.
• Some of the experimental processes visualized by this method can help in studying
the corresponding physical phenomena.
• Part of this paper was presented on the student competition Primatijada 2012, and
was awarded as a best student project in physics.
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IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia
Thank you for your attention !
21.09.2012
IX Conference of the Society of Physicists of Macedonia
20-23 September 2012, Ohrid, R Macedonia