Tài liệu Bộ phát sóng siêu âm vi cơ điện dung polime dùng cho xác định đối tượng: 57 TẠP CHÍ KHOA HỌC, Số 26, tháng 1/2018
BỘ PHÁT SÓNG SIÊU ÂM VI CƠ ĐIỆN DUNG POLIME
DÙNG CHO XÁC ĐỊNH ĐỐI TƯỢNG
Bùi Gia Thịnh
Khoa Điện - Cơ
Email: thinhbg@dhhp.edu.vn
Ngày nhận bài: 31/7/2017
Ngày PB đánh giá: 21/9/2017
Ngày duyệt đăng: 29/9/2017
TÓM TẮT
Mục đích của nghiên cứu là sử dụng bộ phát sóng siêu âm vi cơ điện dung polime
(CMUT) cho xác định đối tượng. Bộ phát sóng này siêu âm này có thể tự truyền và nhận tín
hiệu với độ định hướng cao. Bộ phát sóng siêu âm có thể đo khoảng cách của đối tượng theo
phương thẳng đứng lên tới 50mm với sai số 0.2mm. Nó cũng có thể đo độ nhám bề mặt từ
33µm đến 162µm. Bộ phát sóng siêu âm này có thể sử dụng như cảm biến không tiếp xúc sử
dụng trong kiểm tra công nghiệp.
Từ khóa: Bộ phát sóng siêu âm vi cơ điện dung, polime, xác định đối tượng, độ nhám
bề mặt.
Polymer-based capacitive micromachined ultrasonic
transducers used for object identification
ABSTRACT
The purpose of this research is to apply pol...
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57 TẠP CHÍ KHOA HỌC, Số 26, tháng 1/2018
BỘ PHÁT SÓNG SIÊU ÂM VI CƠ ĐIỆN DUNG POLIME
DÙNG CHO XÁC ĐỊNH ĐỐI TƯỢNG
Bùi Gia Thịnh
Khoa Điện - Cơ
Email: thinhbg@dhhp.edu.vn
Ngày nhận bài: 31/7/2017
Ngày PB đánh giá: 21/9/2017
Ngày duyệt đăng: 29/9/2017
TÓM TẮT
Mục đích của nghiên cứu là sử dụng bộ phát sóng siêu âm vi cơ điện dung polime
(CMUT) cho xác định đối tượng. Bộ phát sóng này siêu âm này có thể tự truyền và nhận tín
hiệu với độ định hướng cao. Bộ phát sóng siêu âm có thể đo khoảng cách của đối tượng theo
phương thẳng đứng lên tới 50mm với sai số 0.2mm. Nó cũng có thể đo độ nhám bề mặt từ
33µm đến 162µm. Bộ phát sóng siêu âm này có thể sử dụng như cảm biến không tiếp xúc sử
dụng trong kiểm tra công nghiệp.
Từ khóa: Bộ phát sóng siêu âm vi cơ điện dung, polime, xác định đối tượng, độ nhám
bề mặt.
Polymer-based capacitive micromachined ultrasonic
transducers used for object identification
ABSTRACT
The purpose of this research is to apply polymer-based capacitive micromachined
ultrasonic transducers (CMUT) for object identification. This CMUT can self-transmitting and
receiving signals with high directivity. The CMUT can measure vertical up to 50mm with
error of 0.2mm. It also can detect surface roughness from 33µm to 162µm. This CMUT can
be used as proximity sensor for industrial inspection.
Keywords: Capacitive Micromachined Ultrasonic Transducer, Polymer-based, Object
Identification, Surface Roughness.
1. INTRODUCTION
Capacitive Micromachined Ultrasonic
Transducers (CMUT) is a relatively new
concept in the field of ultrasonic transducers.
Most of the commercial ultrasonic transducers
today are based on piezoelectricity. CMUT is
a transducer based on the capacitor principle.
It is a transducer that consists of two parallel
electrodes, a vacuum cavity and vibration thin
film as shown in Figure 1. When applying a
DC voltage to the parallel plate capacitor of
CMUT, an electrostatic force will cause a
58 TRƢỜNG ĐẠI HỌC HẢI PHÒNG
deflection of the membrane. Driving the
membrane with an AC voltage superposed on
the bias generated ultrasound. If CMUT
receive ultrasonic wave signal, the bias
membrane will vibration. A current is
produced due to the capacitance change under
deformation of the film. The amplitude of the
current is a function of frequency, bias
voltage, and device capacitance. The
efficiency of CMUTs is determined by the
electromechanical transformer ratio, which
can be expressed as the product of the device
capacitance and the electric field strength
across the gap. The signal through appropriate
circuitry, analyses the ultrasonic signals as
showed in Figure 2.
Figure 1. CMUT ultrasonic
transmitter schematic.
Figure 2. CMUT reception sonic schematic.
This paper introduces the single and
2x1 array polymer-based CMUT design. The
single transducer has dimension of 3mm x
4mm, consist of 472 cells with membrane is
hexagonal shape of 140µm diameter. The
CMUT have been characterized by electrical
impedance analysis, showing resonance
frequency of 0.83MHz. The 2x1 array
CMUT size is 3mm x 3mm containing 416
single cells, which have the same size and
resonance frequency as shown in Figure 3
and Figure 4.
Figure 3. Single
CMUT.
Figure 4. Array
CMUT.
In this study, using an optical
microscope and scanning electron microscope
confirmed mechanical dimensions consistent
with the design, the measurement results
shown in Figure 4 and Figure 5. From the
image show the ultrasound transducer as
designed, with membrane of 140m diameter
and 5m thickness over a 2m cavity height,
top-electrode of 10m width, sidewall of
10m width.
Figure 4. Photo of CMUT
59 TẠP CHÍ KHOA HỌC, Số 26, tháng 1/2018
Figure 5. SEM photo of CMUT
Since 1996, Stanford University Khuri-
Yakub team [1] the use of MEMS (Micro
Electro Mechanical System) technology
developed silicon capacitive ultrasonic
transducer, its sensitivity, frequency response
and system integration advantages and prove
the resistance in water and air are similar, it
can be produced using thin-film ultrasonic
vibration signal, the signal emitted to the
reflector, and then receives the reflected signal
to be non-contact measurement [2], thus
gradually replaced piezoelectric transducer. In
2006, Sukmana et al [3] the use of air-coupled
capacitive ultrasonic transducer measuring the
reflected wave surface roughness can be
measured to 20m above the surface
roughness. In 2009, Chiu et al [4] use
ultrasonic echolocation principle to Newton's
method to calculate three-dimensional
coordinates of the fingertips, you can get
accurate information to prove the concept of
non-contact interaction. In 2010, Nakamura et
al [5] established a successful ultrasonic
positioning system moving objects in three-
dimensional space to get the position and
speed. In 2010, Mitri et al [6] to continuous
wave ultrasound reflection characteristics of
non-contact imaging and surface roughness
measurements, sensors overall size of 45mm,
a focal length of 70mm, the resonance
frequency of 3MHz to measure the roughness
ranging from 4.22m to 19.05m of the
reflector, the measurement accuracy of 4.6m.
In 2011, Park et al [7] using the local
oxidation and wafer direct bonding
manufacturing capacitive micromachined
ultrasonic sensors, the fabrication process
provides precise inter-system height control,
this process has easy processing chamber
elasticity, uniformity well, materials readily
available, low internal stress characteristics. In
2012, Lemmerhirt [8], who the first time
integrated the ultrasound array in the CMOS
feasibility of 4×4 cells in order to constitute an
ultrasonic transducer, and 32×32 an ultrasonic
transducer array, the authors placed on a
single chip thousands of stars ultrasonic
transducer and a CMOS integrated circuit
high-capacity design in the manufacturing
process to increase its complexity, and finally
the experiment proved this plane ultrasonic
array can capture 3-D images data.
An alternative technique to use thin-film
technology to produce lamination of flexible
polymer-based capacitive ultrasonic transducer,
with polymer materials can be produced at low
temperatures and lower-cost properties, to
replace the current need higher temperatures
and the higher cost of manufacturing silicon
capacitive ultrasonic transducer. The present
paper will discuss the simulation and
experiments of CMUT performance in air.
2. RESULT AND DISCUSSION
2.1. Characterization of CMUT
A DC bias is applied in this experiment
at VAC 100 V and 300 V, the reflection object
distance 10mm, the single pulse-echo
transducer signal is 600mV, the array
60 TRƢỜNG ĐẠI HỌC HẢI PHÒNG
transducer and the single transducer with the
same size, the same natural resonant frequency
of 0.83MHz, so the frequency domain response
and time domain response are also similar,
shown in Figure 6 and Figure 7.
Figure 6. CMUT time-domain response.
Figure 7. CMUT frequency response.
2.2. Optimal operating voltage of
CMUT
This test in order to get the best
transducer working conditions, applying
different DC bias and AC voltage, DC bias
voltage ranging from 0V to 200V, each
change of 50V, while the AC voltage from
100V to 300V, each change of 50V.
First, the fixed AC voltage at 300V, the
DC bias will increase from 0V to 200V,
respectively, relationship between measured
value and the echo signal bias is shown in
Figure 8. Secondly, the fixed DC bias at
100V, AC voltage increase from 100V to
300V, reflected frequency domain signals is
shown in Figure 9.
Figure 8. Fixed AC 300V, the frequency
response by changing the DC bias.
Figure 9. Fixed DC 100V, the frequency
response by changing the AC voltage.
The results from Figure 8 show that, if
the DC bias voltage is set at 200V, its signal
has decreased 5.4dB compared with 100V
amplitude cause of membrane too tight. If the
DC bias setting is 150 V, its amplitude
compared with a 100V larger 1.4 dB, but the
membrane displacement increased, the two
electrode plates could easily short circuit,
leading component to burn. Therefore, this
study chooses 100V DC bias and 300V AC
voltage for the operating voltage.
-4
-3
-2
-1
0
1
2
3
4
0 0.1 0.2 0.3 0.4 0.5
A
m
p
li
tu
d
e
(
V
)
Time (ms)
-80
-70
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5
A
m
p
li
tu
d
e
(
d
B
)
Frequency (MHz) -80
-70
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5
A
m
p
li
tu
d
e
(
d
B
)
Frequency (MHz)
AC 100 V
AC 150 V
AC 200V
AC 250 V
AC 300 V
-80
-70
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5
A
m
p
li
tu
d
e
(
d
B
)
Frequency (MHz)
DC 0 V
DC 50 V
DC 100 V
DC 150 V
DC 200 V
61 TẠP CHÍ KHOA HỌC, Số 26, tháng 1/2018
2.3. Determine vertical position
In this study, the transfer speed in the
air is defined accuracy vertical distance of the
ultrasound test position. The distance (d)
between transducer and reflector is
determined by one-half the speed of ultrasonic
in medium (v) and the time that sound travels
(Δt), the formula shown in Equation 1.
2
t
d
(1)
The transducer can measure the vertical
distance ranging from 0.5mm to 50mm. If the
vertical distance is too close, the pulse and
echo signal is mixing, resulting in
indistinguishable. If the vertical distance is too
far away, the reflected signal is very small, not
be resolved reflectivity signal and background
noise signal. Figure 10 is a graph distance and
travel time, get an ultrasound velocity in air of
342.8 m/s, the linearity error is 0.2mm, and
measurement temperature at 25℃ when the
acoustic velocity 340m/s.
Figure 10. Relative of the vertical distances
and travel times.
Figure 11 shows the amplitude of the
reflected signal from the diagram with
increasing distance from the reflected signal,
in terms of the time-domain signal
determines the vertical distance, linearity
error is 0.5 mm. This method is far less than
the travel time method used, so the vertical
distance measurement is not used this case.
Figure 11. Relative of amplitude and
vertical distance.
Finally, this study will use LabVIEW
Control panel features, showing the success of
the single element ultrasonic non-contact
measurement output panel, the results shown in
Figure 12, where the X-axis represents time
(second), Y axis represents the amplitude (V),
displays the calculated vertical distance 10.4
mm, the maximum amplitude of 88 mV.
Figure 12. Non-contact ultrasonic
measurement output panel.
2.4. Surface roughness testing
In this study, abrasive paper of 3M
Company is used as a roughness surface
reflected testing. P100, P120, P150, P180,
P240, P320, P400 and P600 are eight
different models, roughness ranging from
24.8m to 162m. Finally, the resulting
y = 171.64x - 0.4943
0
10
20
30
40
50
60
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
V
e
r
ti
c
a
l
d
is
ta
n
c
e
(
m
m
)
Time (ms)
y = -13.838x + 722.13
0
100
200
300
400
500
600
700
800
0 10 20 30 40 50 60
A
m
p
li
tu
d
e
(
m
V
)
Vertical distance (mm)
62 TRƢỜNG ĐẠI HỌC HẢI PHÒNG
surface roughness reflection of different time
domain and frequency domain signal as
shown in Figure 13 and Figure 14.
Figure 13. Roughness testing time domain
response.
In Figure 15, for example, when the
roughness of paper less than 33.5m,
reflecting no difference time-domain
signal, when the roughness is greater than
33.5m, then the signal attenuation
significantly. This study compared Mitri
[6] have obtained the transducer detects a
wider measurement range, but roughness
of 33.5m or less, the difference in height
between the peaks and troughs is small,
causing unresolved.
3. CONCLUSION
The micro capacitive ultrasonic
transducer shows the advantages of high
directivity, with the vertical detecting
distance of 50 mm, a vertical error of 0.2
mm. The study was completed vertical
position and the roughness tests to prove
an object can be used to identify the future
if combining LabVIEW development
program for industrial testing.
REFERENCES
1. M. Haller and B.T. Khuri-Yakub (1994), „A Surface Micromachined Electrostatic
Ultrasonic Air Transducer‟, Proc. IEEE Ultrasonics, Vol. 2, pp. 1241-1244, Oct. 1994.
2. M. Haller and B.T. Khuri-Yakub (1996), „A Surface Micromachined Electrostatic Ultrasonic
Air Transducer‟, IEEE Trans. Ultrason, Ferro., Freq. Contr, Vol. 43, Iss. 1, pp. 1-6, Jan. 1996.
3. D. D. Sukmana and I. Ihara (2006), „Quantitative Characterization of Two Kinds of
Surface Roughness Parameters from Air-Coupled Ultrasound Scattering‟, Ultrason-
Electron, pp.249-250, Nov. 2006.
4. T. Chiu, H. Deng, S. Chang, and S. Luo (2009), „Implementation of Ultrasonic Touchless
Interactive Panel Using the Polymer-based CMUT Array‟, IEEE Sensor, pp. 652-630, Oct. 2009.
5. S. Nakamura, T. Sato, M. Sugimoto, and H. Hashizume (2010), „An Accurate Technique
for Simultaneous Measurement of 3D Position and Velocity of a Moving Object Using a
Single Ultrasonic Receiver Unit‟, IEEE Indoor Positioning and Indoor Navigation, pp.1-
7, Sep. 2010.
0
100
200
300
400
500
600
0 20 40 60 80 100 120 140 160 180
A
m
p
li
tu
d
e
(
m
V
)
Roughness (m)
-25
-20
-15
-10
-5
0
0 20 40 60 80 100 120 140 160 180
A
m
p
li
tu
d
e
(
d
B
)
Roughness (m)
Figure 14. Roughness testing
frequency response.
63 TẠP CHÍ KHOA HỌC, Số 26, tháng 1/2018
6. F. G. Mitri, R. R. Kinnick, J. F. Greenleaf and M. Fatemi (2010), „Continuous-Wave
Ultrasound Reflectometry for Surface Roughness Imaging Applications‟, Ultrasonics,
Author manuscript, available in PMC January 2010.
7. K. K. Park, H. Lee, Khuri-Yakub (2011), „Fabrication of Capacitive Micromachined
Ultrasonic Transducers via Local Oxidation and Direct Wafer Bonding‟, Journal of
Microelectromechanical Systems, Vol. 20, no. 1, pp. 95-103, Feb. 2011.
8. D. F. Lemmerhirt, X. Cheng, R. D. White, C. A. Rich, M. Zhang, J. B. Fowlkes and O. D.
Kripfgans (2012), „A 32 × 32 Capacitive Micromachined Ultrasonic Transducer Array
Manufactured in Standard CMOS‟, IEEE Transactions on Ultrasonics, Ferroelectrics,
and Frequency Control, Vol. 59, No. 7, July 2012.
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