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 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 140m diameter and 5m thickness over a 2m cavity height, top-electrode of 10m width, sidewall of 10m 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 20m 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 4.22m to 19.05m of the reflector, the measurement accuracy of 4.6m. 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 24.8m to 162m. 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 33.5m, reflecting no difference time-domain signal, when the roughness is greater than 33.5m, then the signal attenuation significantly. This study compared Mitri [6] have obtained the transducer detects a wider measurement range, but roughness of 33.5m 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.