2. Micro-Optical Shear
Stress Sensor
First ever shear stress sensor to measure the direct wall
shear stress of a reattaching flow.
Capable of measuring both the mean and fluctuating
component of turbulent flow
Flexible design: By changing the sensing element’s
material type and size, the resolution and the sensor
bandwidth can be adjusted to accommodate varying
flows.
Because of its superiority to the competition, the sensor
is used to test a vortex generator developed in Vanderbilt
University.
It is immune to electromagnetic interference
Experimentally measured dynamic range > 105dB
3. Design Inputs
Market Needs Obtained from Objective value
Direct
Measurement
Funded research grants
Sensor should measure stress or something that
has similar units to stress
“Small”
Literature survey and
competition
Largest dimension of the sensing surface should
be less than 0.8mm
“Fast”
Literature survey and
competition
Frequency response should be better than the
largest time scale of the turbulent structures
“High sensitivity”
Funded research grants,
literature and market
survey, competition
Sensor should be able to measure both the mean
and the fluctuating component (Less than 1% of
the mean component in magnitude) of the shear
stress
“High Dynamic
Range”
Competition
MEMs based indirect sensors had 60-100 dB
dynamic range.
4. Sensor Design Characteristics
Membrane to
stop the backflow
Sensing plate: Converts the skin
friction to applied force
Pivoting axle
D-Shaped silica fiber lever:
Translates the applied force at
the sensing plate to the
microsphere
Additional Perks:
• Optical Sensor: Immune to Electromagnetic
Interference
• Flexible design: Changing the sphere material
and size, the sensitivity-bandwidth range can be
made to accommodate a wide range of
applications
5. Sensitivity and
Bandwidth Analysis
Sensitivity dependence plot on sphere
material’s elastic modulus and size
Experimental validation of
sensitivity analysis
Sensitivity is a function of sphere material (E)
and size (D).
Using Hertz’ Contact Theory for spherical
surfaces, the force sensitivity of the sensing
element is solved based on its elastic modulus
and size (graph on top right)
The analysis have been verified experimentally
for PMMA spheres (graph on right bottom
corner)
The bandwidth of the sensing element is also
analytically solved
For this analysis, the first natural frequency of
the sensing element is assumed to be the
sensor bandwidth
The graph on the left shows the estimated
sensor bandwidths based on the elastic
modulus and the size of the sensing element
Bandwidth of the sensing
element
6. Sensor Calibration
Designed shear stress sensor has a lever and a membrane.
The friction at the pivot and membrane elasticity will also
contribute to the sensitivity.
The sensor is experimentally calibrated for 2 different
sphere materials, both for the sensitivity and bandwidth
Pivot location:
The clearance is
filled with PDMS
Lever Contact
Calibration Setup
8. Design Verification Tests
Sensor is tested for both steady and
unsteady flows
For steady flows, a pump in suction mode
provided a 2-D flow. I have changed the
pump input over time to test the sensor
at varying flow speeds
For the unsteady flow tests, a planewave
tube is designed and built. A speaker
delivered the unsteady flow and a
microphone recorded the pressure
gradient, from which the shear stress is
calculated
The sensor performed well in both
unsteady and steady flows, with 99%
linear response up to 3.5 kHz.
Unsteady Flow Tests at
1.4kHz and 3.2 kHz
Experimental Setup for
Unsteady Flow Tests
/
/
0
1
iRJ
iRJ
dx
dP
c
i
9. Challenge: Shear Stress
of Reattaching Flow
-0.004
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
0.004
0.005
0.006
0 5 10 15 20
Cf
x/H
Re=2500
Re=3600
Re=4600
Spazzini et al (Re=5100) [50]
Jovic et al (Re=5000) [49]
Skin friction coefficient distribution along the step wall
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20
FFP
X/H
Current measurement
Spazzini et al (Re=3500) [50]
Forward flow probability for Re = 3600
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 5 10 15 20
x/H
Spazzini et al (Re=3500) [50]
Present work
Tihon et al (Re=3800) [51]
RMS of fluctuating wall shear stress (Re = 3600)
After the lab tests, an experimental
setup is designed to test the sensor in
a real flow challenge: The reattaching
flow
There is no direct shear stress
measurement of this flow, only
analytical work or measuring other
parameters and relying on models
Since there is no other sensor that
can perform this measurement, the
sensor output is compared to
analytical studies in the literature
The results show good agreement
Thus, the shear stress of reattaching
flow has been measured directly for
the first time
10. Whispering Gallery Mode
Seismometer:
WhiGS
Directly measures acceleration, without
relying on velocity measurements
Immune to Electromagnetic Interference
Measurement resolution of 1 micro-g
Constant sensitivity up to 20 Hz.
1000 S/s data acquisition rate
Small size: 10cm3 for single axis
measurement.
11. Design Inputs
Market Needs Obtained from Objective value
“High sensitivity” Requirement
Sensor should be able to pick up vibration at 1
micro-g
“Fast”
Requirement and
competition
Sensor should be able to measure vibration up to
20 Hz.
High Dynamic
Range
Competition
MEMs based indirect sensors had 60-100 dB
dynamic range.
Small size Requirement Sensor dimensions should not exceed 10-cm
Immune to EMI Requirement Sensing principle must be optical
Flexible Design Intended use
Sensor bandwidth and resolution should
accommodate for variety of measurement ranges
13. Sensor Design
Characteristics
Cross Sectional View of the Sensor
Proof Mass
Spring
Carrier: Houses the sphere
and is independent from
the spring-mass assembly
(3x)M1.6 adjustment screw:
provides vertical translation
to bring the sphere in
contact with proof mass
Together,the
spring-mass
assembly
converts the
vibration into
force
Dielectric
microsphere:
Sensing element
14. Sensor Design Characteristics
Optical Fiber:
Input/Output
port of the
sensor
Fiber support:
provides a stable
coupling
Sphere Housing
Rubber Washer to
provide cushioning
between carrier
and housing
UV curable
bonding agent (nm
precision)
15. Manufactured Sensor
Machined with CNC milling and lathe machines
Fiber support and the spring-mass assembly and
housing parts require miniature tools (<1mm)
Electronics packaging for sensor’s
signal process
16. Design Verification Tests
The laboratory tests are carried out by mounting the
sensor assembly on a shaker table and comparing the
sensor output to the input to the shaker table
The input to the shaker table were sinusoidal waves at
varying frequencies and magnitudes
A typical measurement at 1 Hz is provided
3.84 mg_8 Hz Filtered
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.35 0.36 0.37 0.38 0.39 0.4 0.41
Time (s)
Vibration(V)
-8
-6
-4
-2
0
2
4
6
8
10
12
14
WGMShift(pm)
Voltage Input
WGM Shift
180ug_1Hz
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 1 2 3 4 5
Time (s)
Vibration(V)
-4
-3
-2
-1
0
1
2
3
4
WGMShift(pm)
Voltage Input
WGM Shift Filtered
Parameters
Mass (kg) 0.015
Stiffness (N/m) 631
Resistance Constant (kg/s) 0.5
Sphere: PDMS 181 pm/mN
Q Factor (Mechanical) 5
Decay Modulus (s) 0.04
WhiGs
Sensor
Experimental setup
Typical Measurement at 1 Hz at 180 micro g Sensor Characteristics
17. Design Validation
Test
After the lab tests, the sensor is tested
against CMG3T seismometer
The data shown compares the seismic
activity measurement between WhiGS
sensor and the commercial CMG3T
outputs on March 22nd 2012 01.18 hrs
GMT.
As illustrated in the graph, there is good
agreement between the data sets.
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 10 20 30 40 50
WhiGs,pm
-150
-100
-50
0
50
100
150
0 10 20 30 40 50
Verticalacceleration,ug
Time, s
Time, s
18. Micro-Optical Pressure Sensor
Immune to electromagnetic interference
Machinable by micro milling and lathe tools
Received attention of Ford Motor Company to
be used in future car designs
Flexible design: by changing the sphere
material and size sensor performance
characteristics can be modified to
accommodate a wide range of applications
19. Design Inputs
Market Needs Obtained from Objective value
“Small”
Literature survey and
competition
Largest dimension of the sensing surface should
be less than 0.8mm
“Fast”
Literature survey and
competition
Frequency response should be higher than the
frequency scale of the turbulent structures
“High sensitivity”
Funded research grants,
literature and market
survey, competition
Sensor should be able to measure the fluctuating
component of the pressure
High Dynamic
Range
Competition
MEMs based indirect sensors had 60-100 dB
dynamic range.
Low Power
consumption
Competition, intended
use
Power consumption should be ≤ 1mW
20. Design Characteristics Elastic Membrane, delivers
the pressure applied to its
surface to the sensing
element
Ring: Clamps the
membrane
Dielectric microsphere:
Sensing Element
M06 set screw: Used to
bring sphere in contact
with the membrane
D-shaped fiber: facilitates
light coupling to the
sensing element
Fiber guide:
ruggedizes the fiber
Clearance: The gap between the
fiber guide and the housing can
accommodate changes in sphere
sizes up to 20%
Section view
23. Analysis of the Sensor
Sensor is modeled as a linear system
The membrane and the dielectric sphere are linear springs
connected in parallel.
The spring constants depend on the geometry and the
material properties of the membrane and the
microsphere
The membrane thickness was not constant. It varied
between 50 micron to 75 micron. The analysis took into
account both extremes
Analytical work is compared with the experimental
measurements
Experimental validation of analysis
Mechanical Model of the
Sensor
24. Design Verification Tests
Steady flow tests have been carried out in a 2-D wind
channel.
The flow speed is varied and the sensor measurement is
compared to that of a commercial pressure sensor
The results show strong agreement between the two
measurements
Steady Flow Tests
Steady Flow Test Setup
25. Design Verification Tests
Unsteady flow tests have been carried out in a plane wave
tube.
A speaker is driven at sinusoidal inputs and the resulting
pressure is recorded
The measurements of the sensor are compared to that of a
microphone.
1.8kHz
400Hz
2 measurements at 400Hz and 1.8kHz are
shown here as sample
26. WGM Electric Field Sensor
Measured sensitivity of 30V/m
By adding coating layers on the
sphere, the sensitivity is further
improved
Led to the foundation of Neuro-
Photonic Research Center to
initiate the development of
electro-mechanical prosthetic
with the ability to “feel”. The
project received $5M in funding
from DARPA
27. Design Inputs
Market Needs Obtained from Objective value
Non-toxic Intended use, FDA
Sensor should have no adverse effect on live
tissue
“Fast” Intended use
Frequency response should be higher than 300
Hz, the frequency of signal from a neuron
“High sensitivity” Requirement
Sensor should be able to measure 3V/m Electric
field
Soft material Market survey
Sensor parts in direct contact with organic tissue
should have similar Youngs moduli as the tissue
Low Power
consumption
Competition, intended
use
Power consumption should be ≤ 1mW
28. WGM Electric Field
Sensor
PDMS sphere, polarized by 1MV/m
Without coating, the sensor resolution is 30V/m
Sensitivity: 0.0055 pm/Vm-1
29. Sensitivity
Improvement
The sphere is changed to a silica core and an uncured PDMS
coat over
The resulted sensitivity increased to 0.2 pm/Vm-1
Measurement resolution with this sphere is 2.5 V/m
This increased sensitivity is high enough to use the sensor in
detecting the brain signals
The sensor is also bio-compatible
30. Neuro-Photonic Sensor
By detecting the brain-signals, the commands of the
brain can be transmitted to a prosthetic
Prosthetic can be equipped with embedded pressure
and temperature sensors that can give feedback that
will let the brain “feel” with the prosthetic.
31. List of Publications Related to the
Design Work Presented Here
PATENT
M.V. Ötügen, T. Ioppolo and U.K. Ayaz “Micro-optical sensor for electric field detection, “US 20110277540 A1, issued
November 2011.
BOOK CHAPTER
A. Serpengüzel, Y.O. Yılmaz, U.K. Ayaz, and A. Kurt, “Silicon Microspheres for VLSI Photonics,” in “VLSI Micro- and
Nanophotonics: Science, Technology, and Applications,” El-Hang Lee, Louay Eldada, M. Razeghi, and C. Jagadish, CRC
Press, Taylor and Francis Group, Boca Raton, Florida pp. 3.1-3.12 (2010). ISBN: 1574447297.
PUBLICATION LIST
U. K. Ayaz, T. Ioppolo, M.V. Ötügen, “Direct measurement of wall shear stress in a reattaching flow using an optical
wall shear stress sensor.” Journal of Measurement Science & Technology, vol. 24, 124001, (2013) doi:10.1088/0957-
0233/24/12/124001.
T. Ioppolo, V. Ötügen, U. Ayaz, “Development of Whispering Gallery Mode Polymeric Micro-optical Electric Field
Sensors,” Journal of Visualized Experiments, vol. 71, e50199, (2012).
M. Manzo, T. Ioppolo, U.K. Ayaz, V. Lapenna, M. V. Ötügen, “A Photonic Wall Pressure Sensor for Fluid Mechanics
Applications,” Review of Scientific Instruments, vol. 83, 105003 (2012).
U.K. Ayaz, T. Ioppolo, M.V. Ötügen, “Wall Shear Stress Sensor Based on the Optical Resonances of Dielectric
Microspheres,” Journal of Measurement Science & Technology, vol. 22, (2011).
T. Ioppolo, U.K. Ayaz, M.V. Ötügen, “Tuning of Whispering Gallery Modes of Spherical Resonators Using an External
Electric Field,” Optics Express, vol. 17, 19, pp. 16465-16479 (2009).
32. List of Publications (Continued..)
T. Ioppolo, U.K. Ayaz, M.V. Ötügen, “High Resolution Force Sensor Based on Morphology Dependent Optical
Resonators Polymeric Spheres,” Journal of Applied Physics, vol. 105, 013535, (2009).
U.K. Ayaz, A. Kurt, A. Serpengüzel, “Silicon Microspheres for Electronic and Photonic Integration,” Photonics and
Nanostructures- Fundamentals and Applications, vol. 6, pp. 179-182, (2008)
U.K. Ayaz, T. Ioppolo, M.V. Ötügen, “Micro-optical Wall Shear Stress Sensor for Fluid Mechanics Applications,”
Progress in Electromagnetics Research Symposium, Prague, July 2015.
T. Ioppolo, U.K. Ayaz, V. Ötügen, “Force Sensors Based on the Whispering Gallery Modes of Dielectric
Microspheres,” SPIE Photonics West conference, 24-29 January 2009, San Jose, California.
U.K. Ayaz, A. Kurt and A. Serpengüzel, “Silicon microspheres for integrated photonics” in “Proc. of the SPIE
Symposia: Optoelectronic Integrated Circuits IX,” San Jose, California, USA, L. A. Eldada, E.-H. Lee, Eds, published by
the SPIE, Bellingham, Washington, USA, 6476,6476061-6476062(2007).
A. Serpengüzel, A. Kurt and U.K. Ayaz, “Silicon microspheres photonics” in “Proc. of the SPIE Symposia: Photonic
Materials, Devices, and Applications II,” San Jose, Gran Canaria, Spain, A. Serpengüzel, G. Badenes, and G. Righini,
Eds, published by the SPIE, Bellingham, Washington, USA, 6593, 659301-659307(2007).
U.K. Ayaz, T. Ioppolo and M.V. Ötügen, “Direct measurement of wall shear stress in a backward facing step flow using
a photonic wall shear stress sensor,” presented at the 65th Annual meeting of APS Division of Fluid Dynamics, 19-21
November 2012, San Diego, California.
D. Fourguette, M. Ötügen, L. Larocque, U. Ayaz, G. Ritter, “Optical MEMS-Based Seismometer,” Proceedings of the 2012
Monitoring Research Review, Sept. 18-20, 2012, Albuquerque, New Mexico.
33. List of Publications (Continued..)
J. Stubblefield, D. Womack, T. Ioppolo, U. Ayaz, M.V. Ötügen, “Composite micro-sphere optical resonators for electric
field measurement,” Proceedings of SPIE 8236, Feb. 2012.
U.K. Ayaz, T. Ioppolo and M.V. Ötügen, “High Resolution Micro-Optical Wall Shear Stress Sensor,” 49th AIAA
Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 5-8 January 2011,
Orlando, Florida.
T. Ioppolo, U.K. Ayaz, V. Ötügen: “Tuning of whispering gallery modes of polymeric micro-spheres and shells using
external electric field.” SPIE Photonics West conference, 23-28 January 2010, San Francisco, California.
T. Ioppolo, U.K. Ayaz, M.V. Ötügen, “Performance of a Micro-Optical Wall Shear Stress Sensor Based on Whispering
Gallery Mode Resonators,” 47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and
Aerospace Exposition, 5-8 January 2009, Orlando, Florida.
T. Ioppolo, U.K. Ayaz, V. Ötügen: “Whispering Gallery Mode Based Micro-Optical Sensor for Electromagnetic Field
Detection,” AIAA InfoTech Aerospace Conference and Exhibit, April 2009, Seattle, Washington (oral presentation).
T. Ioppolo, U.K. Ayaz, V. Ötügen: “Performance of a Micro-Optical Wall Shear Stress Sensor Based on Whispering
Gallery Mode Resonators,” 47th AIAA Aerospace Sciences Meeting and Exhibit, Orlando, Florida AIAA-2009-0314.
T. Ioppolo, U.K. Ayaz, V. Ötügen: “High-Resolution Whispering Gallery Mode Force Micro-Sensor Based on Polymeric Spheres,” 47th
AIAA Aerospace Sciences Meeting and Exhibit, Orlando, Florida AIAA-2009-0314.
T. Ioppolo, U.K. Ayaz, V. Ötügen and V.A. Sheverev: “A Micro-Optical Wall Shear Stress Sensor Concept Based on Whispering Gallery
Mode Resonators,” 46th AIAA Aerospace Sciences Meeting and Exhibit, January 2008, Reno, Nevada.
U.K. Ayaz and A. Serpengüzel, “Resonance Shifts in an Electrically Driven Silicon Microsphere,” Balkan Physics Union, 2006 August,
Istanbul, Turkey (oral presentation).
