dynamic analysis of cmuts in different …users.metu.edu.tr/bbayram/baris...
TRANSCRIPT
Baris Bayram, Edward Hæggström,
A. Sanli Ergun, Goksen G. Yaralioglu, and
Butrus T. Khuri-Yakub
Ginzton Laboratory, Stanford University, CA
2003 IEEE Ultrasonics Symposium, Honolulu, Hawaii
‡This work is funded by Office of Naval Research
Khuri-Yakub Group, Ginzton Lab, Stanford University
DYNAMIC ANALYSIS OF
CMUTs IN DIFFERENT
REGIMES OF OPERATION
Khuri-Yakub Group, Ginzton Lab, Stanford University
Outline
Motivation
FEM model of a single CMUT cell
Dynamic FEM analysis
Results
Conclusion
Khuri-Yakub Group, Ginzton Lab, Stanford University
Motivation
Goal: Low voltage, high frequency CMUTs
with more output power & less nonlinearity
Method: Investigate different operation
regimes for CMUTs:
– Conventional (no contact)
– Collapsed (always in contact)
– Collapse-snapback (intermittent contact)
Khuri-Yakub Group, Ginzton Lab, Stanford University
Different Operation Regimes
Khuri-Yakub Group, Ginzton Lab, Stanford University
FEM model of a single CMUT cell
Axisymmetric 2-D model
Electrical Properties
Structural Properties
Fluid-structure Interface
Acoustic Wave Equation
Exact Absorbing Boundary
(Grote et al)
Basic Properties
Collapse: 80 V
Snapback: 50 V
Resonance: 5 MHz
Khuri-Yakub Group, Ginzton Lab, Stanford University
Dynamic FEM Analysis
Commercially available software (ANSYS 7.1)
Transient Analysis– Coupled electrical & structural analysis
– Fluid medium
– Contact capability
– Exact absorbing boundary (Grote et al)
Large Signal Characterization– Pulse and sinusoidal (AC) excitation
– Displacement and pressure output
– Nonlinear distortion: 2nd harmonic
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: Pulse Excitation
VBIAS=70V, VPULSE=+5V, tPULSE=20ns
Conventional Collapsed
Displacement (p-p) (Å) 39 70
Resonance freq. (MHz) 3.84 8.75
0 0.2 0.4 0.6 0.8 1-0.08
-0.078
-0.076
-0.074
0 1 2 3 4 5 6 7-0.024
-0.022
-0.02
Time (s)
Avera
ge D
isp
lacem
en
t (
m)
Conventional
Collapsed
0 1 2 3 4 5 6-0.05
0
0.05
Time (s)
Pre
ssu
re (
MP
a)
0 0.2 0.4 0.6 0.8 1-0.4
-0.2
0
0.2
0.4
Conventional
Collapsed
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: Pulse Excitation
Collapsed
operation
VBIAS=65 V
Pulse excitation:
VPULSE=15V
tPULSE=20ns
Displacement (p-p):
200 Å, 13 Å/V
Pressure (p-p):
2000 kPa, 133 kPa/V
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: Bias Voltage
VPULSE=+5V, tPULSE=20ns
Collapsed operation:
- Higher resonance frequency : contact radius effect
- Larger displacement & output pressure
55 60 65 70 75 8020
30
40
50
60
70
Bias Voltage(V)
Dis
pla
cem
en
t (p
-p)
(A)
CollapsedConventional
55 60 65 70 75 800
2
4
6
8
10
Bias Voltage(V)
Reso
nan
ce F
req
uen
cy (
MH
z)
CollapsedConventional
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: AC Excitation
Collapsed
operation
VBIAS=70 V
AC excitation:
fEXC=1 MHz
VP-P=30V
2nd harmonic:
-23 dB
Displacement (p-p):
200 Å, 7 Å/V
Pressure (p-p):
36 kPa, 1.2 kPa/V
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: AC Amplitude
VBIAS=65 V, fEXC=1 MHz
Collapsed operation: MORE LINEAR RESPONSE
10 15 20 25 30-28
-26
-24
-22
-20
-18
-16
-14
AC Amplitude (p-p) (V)
2n
d o
rder
harm
on
ic level (d
B)
ConventionalCollapsed
10 15 20 25 3080
100
120
140
160
180
200
220
240
AC Amplitude (p-p) (V)
Avera
ge D
isp
lacem
en
t (p
-p)
(A)
ConventionalCollapsed
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: Collapse-snapback
Collapse-snapback
operation
VBIAS=70 V
AC excitation:
fEXC=1 MHz
VP-P=40 V
2nd harmonic:
-18 dB
3rd harmonic:
-10 dB
Displacement (p-p):
1200 Å, 30 Å/V
Pressure (p-p):
3600 kPa, 90 kPa/V
Khuri-Yakub Group, Ginzton Lab, Stanford University
Results: Collapse-snapback
Collapse-snapback
operation
VBIAS=65 V
AC excitation:
fEXC=5 MHz
VP-P=60 V
Displacement (p-p):
1600 Å, 26 Å/V
Pressure (p-p):
9500 kPa, 158 kPa/V
Khuri-Yakub Group, Ginzton Lab, Stanford University
Comparison of Operation Regimes
Performance Conventional Collapsed Collapse-
Snapback
VBIAS High Low Low
VTOTAL <VCOLLAPSE >VSNAPBACK >VCOLLAPSE
<VSNAPBACK
Output
Power
Low Medium High
Linearity Good Better Worse
Khuri-Yakub Group, Ginzton Lab, Stanford University
Investigated different regimes of operation using transient analysis in FEM
• Collapsed operation:
– More linear
– Low voltage bias
– Higher frequency
• Collapse-snapback operation:
–Higher output pressure
Future work: 3D analysis of CMUT arrays
Conclusion