8/17/2019 Lecture 8-7 acoustic.pdf
1/52
Acoustic Wave Devices
Lecture 8-7ME2082
8/17/2019 Lecture 8-7 acoustic.pdf
2/52
Acoustic wave devices
Surface acoustic wave sensors
– biological and chemical sensor
– viscosity sensor
– force sensors
– stress/strain sensors Bulk Sensors
– acoustic pressure sensor
– pressure sensors
– accelerometers
Plate wave ((lamb wave) – Piezo-motors
Monolithic SAW device
– SAW on piezoelectric substrate
– SAW on non-piezoelectric
substrate (e.g.)
» Bi-layer or multi-layer
» Polycrystalline structure
» roughness larger
– Common configuration to excite
SAW wave
» IDT--interdigital transducer
» frequency determined by thephotolithographic process
8/17/2019 Lecture 8-7 acoustic.pdf
3/52
Acoustic wave devices Acoustic waves can be excited by various means such
as mechanical impact, pulsed thermal energy, or the
inverse piezoelectric effect. The last is by far the most
important for acoustic devices.
There are two groups of acoustic devices which make
use of two distinctive transducer types: surface acousticwave (SAW) and bulk acoustic wave (BAW) devices.
– The SAW employs interdigital transducers (IDTs), i.e.,
thin-film metal comb (‘finger’) structures as depicted in
the Figure. The principle of IDTs: if an alternating
electric field is applied at the comb structure, a time-
harmonic periodic deformation is induced in the
piezoelectric substrate underneath. Thus, an acoustic
wave perpendicular to the finger direction is excited by
each finger pair.
– The BAW is generally excited by means of thin-film
transducers covering the excited volume of a
piezoelectric material.
Interdigital transducer (IDT)
for the excitation of surface
acoustic waves (SAW)
8/17/2019 Lecture 8-7 acoustic.pdf
4/52
Acoustic wave devices
Top view of a SAW delay line consisting of
a quartz plate and interdigital metal
transducers. The lower figure indicates the
wave motion and direction of surface
particle displacement.
Top view of a TSM consisting of a
quartz disc, metal electrodes and
electric contacts. The smaller figure
illustrates the wave motion and the
direction of particle displacement.
BAW SAW
8/17/2019 Lecture 8-7 acoustic.pdf
5/52
Acoustic wave devices
Example: BAW-- Quartz thickness shear mode (TSM) resonators
A
m f f
∆×−=∆
2/1
2
0
)(
2
µ ρ
For the case of thin, rigid and
uniform mass layer on the surface of
the device, there is a relationship between the mass increase (∆m) at
the quartz surface and the resonant
frequency shift (∆ f )
where f 0 is the resonant frequency ofthe quartz crystal, A is the active area
of the coated crystal, µ Q is the shear
modulus of the quartz crystal and ρ Q is
the density.
8/17/2019 Lecture 8-7 acoustic.pdf
6/52
Acoustic wave devices
C0 C
1
R1
L1
liquid loading
C0
L2
C1
R1
L1
R2
unperturbed
TSM resonator
L3
mass loading
liquid loading
C0
L2
C1
R1
L1
R2
unperturbed
TSM resonator
L3
mass loading
Example: BAW-- Quartz thickness shear mode (TSM) resonators
For the liquid loading, Kanazawa and Gordon found that
for the Newtonian liquid contacting with one side of
resonator sensor, the resonant frequency shift depends upon
the viscosity (µ L) and density ( ρ L) of the liquid
2/1
2/12/3
0
)(
)(
L L f f µ πρ
η ρ −=∆
8/17/2019 Lecture 8-7 acoustic.pdf
7/52
Acoustic wave devices
Example: BAW-- Quartz thickness shear mode (TSM) resonators
The electrical admittance spectra Y(w) generated
from BVD model is given by:
( )
0
111 1
1 C j
C j L j R
jBGY
ω ω ω
ω
+
++
=
+=
2/1
11 )(
1
2
1
C L f s
π =
For unperturbed TSM resonator, the series resonance
frequency f s at which G is maximum (Gmax), is given by:
8/17/2019 Lecture 8-7 acoustic.pdf
8/52
Acoustic wave devicesQuartz TSM resonator impedance
8/17/2019 Lecture 8-7 acoustic.pdf
9/52
Acoustic wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
10/52
Acoustic wave devices
Quartz thickness shear mode BAWFrequency
phase
8/17/2019 Lecture 8-7 acoustic.pdf
11/52
Acoustic wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
12/52
Acoustic wave devicesExample: BAW-- Quartz crystal microbalance (QCM) gas sensor
Typical response to 50 ppm of NO2 of the device coated with
NO2-absorbing polymer
8/17/2019 Lecture 8-7 acoustic.pdf
13/52
Acoustic wave devicesExample: BAW-- Quartz crystal microbalance (QCM) gas sensor forammonia detection at ppb level
QCM is coated with fibrous
polyacrylic acid (PAA)
membrane
8/17/2019 Lecture 8-7 acoustic.pdf
14/52
Acoustic wave devices
For SAW device – If multiple finger pairs exist, interference occurs
yielding to a maximum SAW magnitude if
,.....3,2,1,0,
12=⋅
+=
nv
n
f n λ
with the excitation frequency f , the acoustic wavevelocity v of the particular mode, and the transducer
period λ=2(a+b).
– Hence an IDT is a frequency-selective element.The frequency of the lowest order mode f o iscalled the characteristic frequency.
8/17/2019 Lecture 8-7 acoustic.pdf
15/52
Acoustic wave devices
SAW: Basic Acoustic Structures
– One of the simplest and best known acoustic structures is the delay line
shown in Figure. The transducer IDT1 serves as the input for an electric
radio-frequency (RF) signal which is transformed by means of the inverse
piezoelectric effect into an acoustic wave traveling to the outputtransducer IDT2. Here, a re-transformation takes place back into the
electrical domain. Hence the electrical signal experiences a delay τ
because the acoustic wave is five orders of magnitude slower than the
velocity of light:
⋅=
ν τ CC
8/17/2019 Lecture 8-7 acoustic.pdf
16/52
Acoustic wave devices
If no transmission loss occurs, the delay linetransfer function H DL(f ) can be written as
with the transfer functions H 1(f) and H 2(f) of IDT1
and IDT2, respectively.
( ) ( ) ( ) ( )⋅⋅−⋅= τ π f j f H f H f H DL 2exp21
The magnitude of the transfer function depends on the IDTcharacteristics, whereas CC determines the phase ϕ
( ) ( )o f f vCC f −⋅⋅−= π ϕ 2
Hence, amplitude and phase characteristics can be chosenindependently of each other. Changes of both quantities due toexternal influences may serve as measuring effects.
8/17/2019 Lecture 8-7 acoustic.pdf
17/52
Acoustic wave devices
By Materials
– Bulk wave
– Surface wave
– Flexural plate wave
By wave forms
– Longitudinal wave
– Transverse wave
– Raleigh wave (mixed long. and trans. wave)
Bulk Materials – Quartz
– Piezo-ceramic materials
Thin films materials
– ZnO
– PZT
– organic polymer
– GaAs
Surface acoustic wave transducers
Electrical -Mechanical
Transducer
Mechanical - Electrical
Transducer Electrical
input
Electrical
output
Mechanical
output
Frequency
Amp.
Phase
Delay line
(temperature, mass,
stress, morphology)Oscillator
8/17/2019 Lecture 8-7 acoustic.pdf
18/52
Acoustic wave devices
Frequency: f
Pitch
Phase velocity: v p
Important parameters:
8/17/2019 Lecture 8-7 acoustic.pdf
19/52
Acoustic wave devices
λ=4d
8/17/2019 Lecture 8-7 acoustic.pdf
20/52
Acoustic wave devices
SAW chemical sensors
8/17/2019 Lecture 8-7 acoustic.pdf
21/52
Acoustic wave sensors
Dual delay line configuration.
8/17/2019 Lecture 8-7 acoustic.pdf
22/52
Acoustic wave devices
SAW Devices Measurement Methods: Oscillator vs. delay line approach
– Oscillator: frequency f/f = Sm m
Sm: mass sensitivity, ∆m: mass/unit area
Delay line: phase shift (time delay)
amplitude(dispersion)quality factor (Q)
Love Mode SAW
– High sensitivity
Flexural Wave (Lamb) Plate
High sensitivity than SAW
Using a low velocity lamb wave allows the device to operate at low frequency
The velocity can be made lower than the velocity of compression wave in
common liquid, permitting low loss operation
Heat capacity is low due to the reduced thickness
8/17/2019 Lecture 8-7 acoustic.pdf
23/52
Acoustic Wave Devices
Love Mode SAW Devices as gas sensormolecularly imprinted materials (MIM).
8/17/2019 Lecture 8-7 acoustic.pdf
24/52
Acoustic wave devices
SEM of liquid traps at the border between an IDT
and the propagation path of a Love mode sensor
8/17/2019 Lecture 8-7 acoustic.pdf
25/52
Acoustic Wave Devices
Love Mode SAW Devices
8/17/2019 Lecture 8-7 acoustic.pdf
26/52
Acoustic Wave Devices
Love Mode SAW Device as gas sensor
Relative frequency change
∆ f/ ∆ f c due to MMP exposure
for imprinted and non-imprinted (control)device.
2-methoxy 3-methyl pyrazine,
MMP, is a substance used in
perfume industry.,
8/17/2019 Lecture 8-7 acoustic.pdf
27/52
Acoustic Wave Devices
Love Mode SAW Devices as gas sensor
8/17/2019 Lecture 8-7 acoustic.pdf
28/52
Acoustic wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
29/52
Acoustic wave devices
Lamb Wave sensor
Effective mass
8/17/2019 Lecture 8-7 acoustic.pdf
30/52
Acoustic wave devices
Consideration when designing anacoustic wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
31/52
Acoustic wave devices
Measurement Methods: Oscilaltor vs. delay line approach – Oscillator: frequency f/f = Sm m
Sm: mass sensitivity, ∆m: mass/unit area
Delay line: phase shift (timr delay)
amplitude(dispersion)
quality factor (Q)
8/17/2019 Lecture 8-7 acoustic.pdf
32/52
Acoustic Wave
Devices
Love mode
8/17/2019 Lecture 8-7 acoustic.pdf
33/52
Acoustic wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
34/52
8/17/2019 Lecture 8-7 acoustic.pdf
35/52
Acoustic wave devices
Influence of Newtonian
liquid viscosity on Love
wave phase velocity
Acoustic Love wave devices
8/17/2019 Lecture 8-7 acoustic.pdf
36/52
8/17/2019 Lecture 8-7 acoustic.pdf
37/52
Acoustic wave devices
Cantilever beam accelerometer
8/17/2019 Lecture 8-7 acoustic.pdf
38/52
Acoustic wave devices
Accelerometer
8/17/2019 Lecture 8-7 acoustic.pdf
39/52
Vibration and acceleration sensors
8/17/2019 Lecture 8-7 acoustic.pdf
40/52
Vibration and acceleration sensors
8/17/2019 Lecture 8-7 acoustic.pdf
41/52
Torque Sensors
8/17/2019 Lecture 8-7 acoustic.pdf
42/52
Gyro Sensor
8/17/2019 Lecture 8-7 acoustic.pdf
43/52
Humidity Sensors
8/17/2019 Lecture 8-7 acoustic.pdf
44/52
Dew point sensor
8/17/2019 Lecture 8-7 acoustic.pdf
45/52
Voltage sensor
8/17/2019 Lecture 8-7 acoustic.pdf
46/52
Flow Sensor
8/17/2019 Lecture 8-7 acoustic.pdf
47/52
Others
8/17/2019 Lecture 8-7 acoustic.pdf
48/52
Acoustic Wave Devices
8/17/2019 Lecture 8-7 acoustic.pdf
49/52
8/17/2019 Lecture 8-7 acoustic.pdf
50/52
Electrostatic ink jet printer
8/17/2019 Lecture 8-7 acoustic.pdf
51/52
Electrostatic ink jet printer
8/17/2019 Lecture 8-7 acoustic.pdf
52/52
Electrostatic ink jet printer