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A Y type SAW mass sensor with metal array reflectors
Sensors and Actuators B 109 (2005) 244–248
A Y type SAW mass sensor with metal array reflectors Yang Ying∗ , Zhu Da-Zhong Department of Information Science and Electronics Engineering, Zhejiang University, #38 ZheDa RD., P.O. Box 1269, Hangzhou 310027, China Received 20 July 2004; received in revised form 17 December 2004; accepted 29 December 2004 Available online 1 February 2005
Abstract A new Y type dual path surface acoustic wave (SAW) mass sensor with apodized interdigital transducer (IDT) and metal array reflectors is reported. In order to suppress the spurious signal reflected from the chip edges and improve the sensitivity of the sensor, a metal array reflector is designed between the output IDT and the chip edge to change the original SAW propagation direction. The temperature effect on the measurement path is compensated by a reference path. The simulation result of the acoustic energy distribution of the reflectors has been reported. The characteristics of the sensor have been tested by the delay-line active oscillation circuit. The results show that passband ripple suppression is improved by more than 1 dB by reflectors. Also, a very low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C). The Q value of the sensor is up to 1.1 × 104 in oscillator mode. Mass loading effect sensitivity is about 5.24 GHz cm2 /g with a good linearity. © 2005 Elsevier B.V. All rights reserved. Keywords: SAW sensor; Mass loading effect; Metal array reflectors; Apodization; Q value
1. Introduction As the surface acoustic wave (SAW) propagates on the piezoelectric crystal surface, any changes in physical properties at the surface or near-surface region will affect the wave velocity (or frequency) and attenuation. Thus, some kinds of signals can be converted to electrical signals and then be detected. SAW sensors have many merits, so they have wide applications, such as gas sensor, biosensor, humidity sensor and so on [1]. These devices can be categorized into multiplefrequency device [2]; dual path device [3]; resonator device [4] and so on. However, the SAW and bulk wave propagate in the same direction in these devices. Becketr et al. [5,6] had reported two type of gas sensors based on multistrip couples (MSC) or reflectors. The sensitivity was improved by MSC and reflectors between the input and output IDT. On the other hand, in order to suppress the unwanted acoustic energy, which would distort the frequency response, it is uni∗
Corresponding author. Tel.: +86 13588842126; fax: +86 57187952404. E-mail address: [email protected] (Y. Ying).
0925-4005/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2004.12.056
versal practice to coat the end of a SAW device with absorber materials. However, disadvantage of the absorber materials lies in its incompatibility with the standard fabrication process of SAW devices. As we know, the temperature coefficient and Q value are two key factors to influence the sensitivity and accuracy of the sensor. Therefore, low temperature coefficient and high Q value still remain a challenge to designer. The objectives of this work were to develop a novel Y type dual path SAW mass sensor with apodized IDT and reflector array. The acoustic energy launched from one input IDT was equally distributed into measurement path and reference path by MSC. Not only can the dual delay line realize the temperature compensation but it can also avoid the bulk wave effect. Besides, the side-lobe suppression of frequency response is improved by apodized aperture. The SAW propagation direction is changed by 90◦ between the output IDT and chip edge by metallic reflector array, which aims at suppressing the unwanted energy reflected off the chip edges. The results show that passband ripple suppression is improved by about 1 dB by reflectors. Also, a very low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C). The
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Fig. 2. SAW oscillator. Fig. 1. Construction of Y type dual path SAW mass sensor.
high Q value (1.1 × 104 in oscillation mode) is seldom found in the literatures published. Mass loading effect sensitivity is about 5.24 GHz cm2 /g with a good linearity.
2. Sensor structure A Y type SAW sensor is comprised of one input apodized IDT (A), two MSC (B1, B2), two mass loading areas (C1, C2), two output IDTs (D1, D2), two metal array reflectors (E1, E2) as shown in Fig. 1. In the reflector the arrow represents the SAW propagation direction. Conventional λ/4 interdigital width design rule is used. Input and output IDTs have 93 and 39 finger pairs, respectively. The eigenfunction of apodization function of input IDT consists of the combination cosine squared weighting function. The output IDT has a uniform aperture of 2.2 mm. Both IDTs have a periodicity p of 32 m. The number of electrodes for optimal coupling in MSC is 108. Its metal strip width is 3λ/16. The track widths (Wa , Wb ) are 1.5 and 2.2 mm, respectively. The final energy transfer ratio FT = 96.4%. For a 90◦ reflection, the tilt-angle of reflectors is 45◦ with respect to the substrate and the wave front of the incident wave. The metal ratio of reflector is 0.5 and the periodicity is 32 m. The number of the slanting reflector strips is 100.
(2.6 × 10−4 g/ml) was used. If 1 l solution was dropped into the mass loading surface, the mass density would be 0.3 × 10−5 g/cm2 . The testing schematic is presented in Fig. 2. A variable attenuator and a two-stage broadband (1 GHz) RF amplifier having a maximum gain of 18 dB complete the oscillator loop. According to oscillator approach, the relationship between centre oscillation frequency shift and the loading mass is observed by Advantest R3765CG network analyzer.
4. Result and discussion 4.1. The simulation result and frequency domain analysis of the metal array reflectors Fig. 3a shows the structure of the reflector. The simulation result of the acoustic energy distribution along the propaga-
3. Experiments The SAW sensor was fabricated on the 128◦ YX-LiNbO3 . The centre frequency is 122 MHz. The mass loading area (3.6 mm × 2.4 mm) is patterned using photolithographic process, while other areas are protected by photoresist. To verify the absorbing effect of reflectors, an apodized Y type dual path mass sensor without reflectors was fabricated. They were of the same physical dimensions as those of the original sensor, except for the reflectors. To test the mass loading effect of this SAW delay line, some solution is dropped directly onto the mass loading area. A film is leaved after the evaporation of the solvent. As a result of the mass loading effect, the loading mass will cause a change of the SAW propagation velocity and a shift of the oscillator frequency correspondingly. NaCl solution
Fig. 3. Schematic and simulation result of the acoustic energy distribution of the metal array reflectors.
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tion direction in the reflector array is shown in Fig. 3b. In the simulation result the X-axis values = 2X/LX and the Z-axis values = 2Z/LZ . The Y-axis values represent the normalized intensity of the acoustic energy. This simulation result implies that the acoustic energy distribution is asymmetry in the reflector array. When the value of X/LX is small, the acoustic energy has a rapid attenuation, that is to say most SAW energy is reflected out of the reflectors after several reflections and few SAW energy can arrive at the chip edge. However, as the X/LX is increased, the acoustic energy gets attenuated more slowly. In other words, most of the SAW energy still passed the reflector, although all metal strips reflect it. This effect results from the multiple reflects [7]. Therefore, the unwanted energy reflected by the chip edges can be suppressed by the reflectors. The comparison of frequency spectrum of the device with and without reflectors is shown in Fig. 4.
Fig. 5. Oscillation spectrum under different temperatures of single path.
The insertion loss (IL) of the sensor with reflectors (Fig. 4a) is 15.763 dB, while the insertion loss of the sensor without reflectors (Fig. 4b) is 14.624 dB. In other words, the passband ripple suppression is improves by more than 1 dB because of reflectors. The IL of the sensor without reflectors is smaller than that of the device with reflectors. That is to say more unwanted reflected energy or the spurious signal is overlapped to the main signal. The experiment result is consistent with the simulation result. 4.2. Temperature compensation effect Since the temperature will affect the sensitivity and accuracy of the sensor, Y type dual path is used to realize the temperature compensation. A reference path is employed to correct the error on account of temperature fluctuation in measurement path. The oscillation spectrum of temperature property of single path is shown in Fig. 5. The temperature coefficient is 10.4 kHz/◦ C for single path. However, after compensating by dual path, the temperature coefficient becomes 6.2 Hz/◦ C, a decrease by three orders of magnitude. As we know, although SAW sensor is sensitive to temperature, the error caused by temperature drift can almost be neglected by means of temperature compensation of Y type dual path. 4.3. Mass loading sensitivity
Fig. 4. Comparison of frequency spectrum of the device: (a) with and (b) without reflectors.
The oscillation frequency response before and after mass loading is shown in Fig. 6. The oscillation frequency before mass loading is 121.17975 MHz. After 3 l solution (2.6 × 10−4 g/ml) is dropped in the measurement path, the oscillation frequency turns out to be 121.13475 MHz. That is to say an obvious frequency shift (45 kHz) is obtained as a result of the mass loading effect, when the NaCl mass density is 0.9 × 10−5 g/cm2 . According to Fig. 6, the Q value of the device is up to 1.1 × 104 , which implies this Y type sensor has a high sensitivity. Within the same frequency scope, the higher the Q value, the more accurate data can be obtained. To put it in another way, the device with higher Q value can be highly sensitive to the tiny frequency shift caused by tiny mass changing. Our research group has investigated a simple
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Fig. 8. Frequency shift vs. mass density for Y type dual channel SAW mass sensor with apodized IDT and metal array reflectors.
5. Conclusion Fig. 6. Oscillation frequency response before mass loading effect and after mass loading effect.
Y type sensor [8], which has no apodization and reflectors. The Q value of that sensor is only about 4000. However, owning to apodization and reflection technology, high Q value is obtained. The oscillation frequency spectrums for different mass densities of the sensor after temperature compensation are shown in Fig. 7. If environment temperature fluctuates 1 ◦ C, the oscillation frequency will shift about 10.4 kHz, which will affect the measurement accuracy seriously. But after temperature compensation, the frequency shift can be regarded as being determined only by the mass density. Fig. 8 represents the frequency shift is proportional to mass densities for mass sensor. The average sensitivity is 5.24 GHz cm2 /g. Compared with the result of the simple Y type sensor the sensitivity is improved due to high Q value.
A new Y type dual path SAW mass sensor with apodized IDT and metal array reflectors is investigated. Apodization and reflection technology is used to improve the sidelobe suppression, passband ripple, and Q value. According to the result of simulation and experiment, metal array reflectors have effect on the suppression of the spurious signal reflected by the chip edges. A low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C), so the frequency shift caused by environment temperature fluctuation can almost be neglected by means of temperature compensation of Y type dual path. The frequency shift (in oscillation mode) is proportional to mass densities for mass sensor. A high sensitivity is (5.24 GHz cm2 /g) obtained due to high Q value.
Acknowledgement This work was supported by the Chinese National Natural Science Foundation under Grant No. 60176027.
References
Fig. 7. Oscillation frequency spectrums for different mass densities of the sensor after temperature compensation. Numbers on the top of the peaks represent mass density (10−5 g/cm2 ).
[1] J.D. Sternhagen, C.E. Wold, W.A. Kempf, M. Karlgaard, K.D. Mitzner, R.D. Mileham, D.W. Galipeau, A novel integrated acoustic gas and temperature sensor, Sens. J. IEEE 2 (4) (2002) 301– 306. [2] A.J. Ricco, S.J. Martin, Multiple-frequency surface acoustic wave devices as sensors, Solid-State Sens. Actuator Workshop (1990) 5–8. [3] J. Hechner, T. Wrobel, The influence of PcCu layer crystalline structure on the parameters of SAW gas sensors, Eur. Frequency Time Forum (1996) 370–375. [4] T. Nomura, M. Takebayashi, A. Saitoh, Chemical sensor based on surface acoustic wave resonator using Langmuir–Blodett film, IEEE Trans. Ultrasonics, Ferroelectr. Frequency Contr. 45 (5) (1998) 1261–1265.
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[5] H. Becketr, M. von Schickfus, S. Hunklinger, A new sensor principle based on the reflection of surface acoustic waves, Sens. Actuators A 54 (1996) 618–621. [6] M. von Schickfus, H. Becketr, C. Rupp, S. Hunklinger, SAW gas sensing using reflectors and multistrip couplers, IEEE Ultrasonics Symp. (1995) 467–471. [7] B. Zhang, S.Y. Zhang, R.J. Wei, Reflective characteristics of SAW by reflection array with slanting metal strips, Acta Acoust. 14 (1) (1989) 58–67. [8] A.-L. Zhang, D.-Z. Zhu, A Y-type dual path surface acoustic wave mass sensor and its measurement system, Piezoelectr. Acoustoopt. 25 (6) (2003) 445–448.
Biographies Yang Ying received her BS and MS degrees in microelectronics from Xi’An University of Technology in 2000 and 2003, respectively. She is pursuing her PhD degree in microelectronics at Zhejiang University, China. She is interested in surface acoustic wave sensor designing and absorbing structure researching. Zhu Da-Zhong is Professor of the Department of Information and Electronic Engineering, Zhejiang University. His research included ASIC design, microwave sensor and MEMS technology. In recent years, he was charged with several projects of NSF in the field of RF device and IC designing.
A Y type SAW mass sensor with metal array reflectors Yang Ying∗ , Zhu Da-Zhong Department of Information Science and Electronics Engineering, Zhejiang University, #38 ZheDa RD., P.O. Box 1269, Hangzhou 310027, China Received 20 July 2004; received in revised form 17 December 2004; accepted 29 December 2004 Available online 1 February 2005
Abstract A new Y type dual path surface acoustic wave (SAW) mass sensor with apodized interdigital transducer (IDT) and metal array reflectors is reported. In order to suppress the spurious signal reflected from the chip edges and improve the sensitivity of the sensor, a metal array reflector is designed between the output IDT and the chip edge to change the original SAW propagation direction. The temperature effect on the measurement path is compensated by a reference path. The simulation result of the acoustic energy distribution of the reflectors has been reported. The characteristics of the sensor have been tested by the delay-line active oscillation circuit. The results show that passband ripple suppression is improved by more than 1 dB by reflectors. Also, a very low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C). The Q value of the sensor is up to 1.1 × 104 in oscillator mode. Mass loading effect sensitivity is about 5.24 GHz cm2 /g with a good linearity. © 2005 Elsevier B.V. All rights reserved. Keywords: SAW sensor; Mass loading effect; Metal array reflectors; Apodization; Q value
1. Introduction As the surface acoustic wave (SAW) propagates on the piezoelectric crystal surface, any changes in physical properties at the surface or near-surface region will affect the wave velocity (or frequency) and attenuation. Thus, some kinds of signals can be converted to electrical signals and then be detected. SAW sensors have many merits, so they have wide applications, such as gas sensor, biosensor, humidity sensor and so on [1]. These devices can be categorized into multiplefrequency device [2]; dual path device [3]; resonator device [4] and so on. However, the SAW and bulk wave propagate in the same direction in these devices. Becketr et al. [5,6] had reported two type of gas sensors based on multistrip couples (MSC) or reflectors. The sensitivity was improved by MSC and reflectors between the input and output IDT. On the other hand, in order to suppress the unwanted acoustic energy, which would distort the frequency response, it is uni∗
Corresponding author. Tel.: +86 13588842126; fax: +86 57187952404. E-mail address: [email protected] (Y. Ying).
0925-4005/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2004.12.056
versal practice to coat the end of a SAW device with absorber materials. However, disadvantage of the absorber materials lies in its incompatibility with the standard fabrication process of SAW devices. As we know, the temperature coefficient and Q value are two key factors to influence the sensitivity and accuracy of the sensor. Therefore, low temperature coefficient and high Q value still remain a challenge to designer. The objectives of this work were to develop a novel Y type dual path SAW mass sensor with apodized IDT and reflector array. The acoustic energy launched from one input IDT was equally distributed into measurement path and reference path by MSC. Not only can the dual delay line realize the temperature compensation but it can also avoid the bulk wave effect. Besides, the side-lobe suppression of frequency response is improved by apodized aperture. The SAW propagation direction is changed by 90◦ between the output IDT and chip edge by metallic reflector array, which aims at suppressing the unwanted energy reflected off the chip edges. The results show that passband ripple suppression is improved by about 1 dB by reflectors. Also, a very low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C). The
Y. Ying, Z. Da-Zhong / Sensors and Actuators B 109 (2005) 244–248
245
Fig. 2. SAW oscillator. Fig. 1. Construction of Y type dual path SAW mass sensor.
high Q value (1.1 × 104 in oscillation mode) is seldom found in the literatures published. Mass loading effect sensitivity is about 5.24 GHz cm2 /g with a good linearity.
2. Sensor structure A Y type SAW sensor is comprised of one input apodized IDT (A), two MSC (B1, B2), two mass loading areas (C1, C2), two output IDTs (D1, D2), two metal array reflectors (E1, E2) as shown in Fig. 1. In the reflector the arrow represents the SAW propagation direction. Conventional λ/4 interdigital width design rule is used. Input and output IDTs have 93 and 39 finger pairs, respectively. The eigenfunction of apodization function of input IDT consists of the combination cosine squared weighting function. The output IDT has a uniform aperture of 2.2 mm. Both IDTs have a periodicity p of 32 m. The number of electrodes for optimal coupling in MSC is 108. Its metal strip width is 3λ/16. The track widths (Wa , Wb ) are 1.5 and 2.2 mm, respectively. The final energy transfer ratio FT = 96.4%. For a 90◦ reflection, the tilt-angle of reflectors is 45◦ with respect to the substrate and the wave front of the incident wave. The metal ratio of reflector is 0.5 and the periodicity is 32 m. The number of the slanting reflector strips is 100.
(2.6 × 10−4 g/ml) was used. If 1 l solution was dropped into the mass loading surface, the mass density would be 0.3 × 10−5 g/cm2 . The testing schematic is presented in Fig. 2. A variable attenuator and a two-stage broadband (1 GHz) RF amplifier having a maximum gain of 18 dB complete the oscillator loop. According to oscillator approach, the relationship between centre oscillation frequency shift and the loading mass is observed by Advantest R3765CG network analyzer.
4. Result and discussion 4.1. The simulation result and frequency domain analysis of the metal array reflectors Fig. 3a shows the structure of the reflector. The simulation result of the acoustic energy distribution along the propaga-
3. Experiments The SAW sensor was fabricated on the 128◦ YX-LiNbO3 . The centre frequency is 122 MHz. The mass loading area (3.6 mm × 2.4 mm) is patterned using photolithographic process, while other areas are protected by photoresist. To verify the absorbing effect of reflectors, an apodized Y type dual path mass sensor without reflectors was fabricated. They were of the same physical dimensions as those of the original sensor, except for the reflectors. To test the mass loading effect of this SAW delay line, some solution is dropped directly onto the mass loading area. A film is leaved after the evaporation of the solvent. As a result of the mass loading effect, the loading mass will cause a change of the SAW propagation velocity and a shift of the oscillator frequency correspondingly. NaCl solution
Fig. 3. Schematic and simulation result of the acoustic energy distribution of the metal array reflectors.
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Y. Ying, Z. Da-Zhong / Sensors and Actuators B 109 (2005) 244–248
tion direction in the reflector array is shown in Fig. 3b. In the simulation result the X-axis values = 2X/LX and the Z-axis values = 2Z/LZ . The Y-axis values represent the normalized intensity of the acoustic energy. This simulation result implies that the acoustic energy distribution is asymmetry in the reflector array. When the value of X/LX is small, the acoustic energy has a rapid attenuation, that is to say most SAW energy is reflected out of the reflectors after several reflections and few SAW energy can arrive at the chip edge. However, as the X/LX is increased, the acoustic energy gets attenuated more slowly. In other words, most of the SAW energy still passed the reflector, although all metal strips reflect it. This effect results from the multiple reflects [7]. Therefore, the unwanted energy reflected by the chip edges can be suppressed by the reflectors. The comparison of frequency spectrum of the device with and without reflectors is shown in Fig. 4.
Fig. 5. Oscillation spectrum under different temperatures of single path.
The insertion loss (IL) of the sensor with reflectors (Fig. 4a) is 15.763 dB, while the insertion loss of the sensor without reflectors (Fig. 4b) is 14.624 dB. In other words, the passband ripple suppression is improves by more than 1 dB because of reflectors. The IL of the sensor without reflectors is smaller than that of the device with reflectors. That is to say more unwanted reflected energy or the spurious signal is overlapped to the main signal. The experiment result is consistent with the simulation result. 4.2. Temperature compensation effect Since the temperature will affect the sensitivity and accuracy of the sensor, Y type dual path is used to realize the temperature compensation. A reference path is employed to correct the error on account of temperature fluctuation in measurement path. The oscillation spectrum of temperature property of single path is shown in Fig. 5. The temperature coefficient is 10.4 kHz/◦ C for single path. However, after compensating by dual path, the temperature coefficient becomes 6.2 Hz/◦ C, a decrease by three orders of magnitude. As we know, although SAW sensor is sensitive to temperature, the error caused by temperature drift can almost be neglected by means of temperature compensation of Y type dual path. 4.3. Mass loading sensitivity
Fig. 4. Comparison of frequency spectrum of the device: (a) with and (b) without reflectors.
The oscillation frequency response before and after mass loading is shown in Fig. 6. The oscillation frequency before mass loading is 121.17975 MHz. After 3 l solution (2.6 × 10−4 g/ml) is dropped in the measurement path, the oscillation frequency turns out to be 121.13475 MHz. That is to say an obvious frequency shift (45 kHz) is obtained as a result of the mass loading effect, when the NaCl mass density is 0.9 × 10−5 g/cm2 . According to Fig. 6, the Q value of the device is up to 1.1 × 104 , which implies this Y type sensor has a high sensitivity. Within the same frequency scope, the higher the Q value, the more accurate data can be obtained. To put it in another way, the device with higher Q value can be highly sensitive to the tiny frequency shift caused by tiny mass changing. Our research group has investigated a simple
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Fig. 8. Frequency shift vs. mass density for Y type dual channel SAW mass sensor with apodized IDT and metal array reflectors.
5. Conclusion Fig. 6. Oscillation frequency response before mass loading effect and after mass loading effect.
Y type sensor [8], which has no apodization and reflectors. The Q value of that sensor is only about 4000. However, owning to apodization and reflection technology, high Q value is obtained. The oscillation frequency spectrums for different mass densities of the sensor after temperature compensation are shown in Fig. 7. If environment temperature fluctuates 1 ◦ C, the oscillation frequency will shift about 10.4 kHz, which will affect the measurement accuracy seriously. But after temperature compensation, the frequency shift can be regarded as being determined only by the mass density. Fig. 8 represents the frequency shift is proportional to mass densities for mass sensor. The average sensitivity is 5.24 GHz cm2 /g. Compared with the result of the simple Y type sensor the sensitivity is improved due to high Q value.
A new Y type dual path SAW mass sensor with apodized IDT and metal array reflectors is investigated. Apodization and reflection technology is used to improve the sidelobe suppression, passband ripple, and Q value. According to the result of simulation and experiment, metal array reflectors have effect on the suppression of the spurious signal reflected by the chip edges. A low relative temperature coefficient of the sensor is obtained (only about 6.2 Hz/◦ C), so the frequency shift caused by environment temperature fluctuation can almost be neglected by means of temperature compensation of Y type dual path. The frequency shift (in oscillation mode) is proportional to mass densities for mass sensor. A high sensitivity is (5.24 GHz cm2 /g) obtained due to high Q value.
Acknowledgement This work was supported by the Chinese National Natural Science Foundation under Grant No. 60176027.
References
Fig. 7. Oscillation frequency spectrums for different mass densities of the sensor after temperature compensation. Numbers on the top of the peaks represent mass density (10−5 g/cm2 ).
[1] J.D. Sternhagen, C.E. Wold, W.A. Kempf, M. Karlgaard, K.D. Mitzner, R.D. Mileham, D.W. Galipeau, A novel integrated acoustic gas and temperature sensor, Sens. J. IEEE 2 (4) (2002) 301– 306. [2] A.J. Ricco, S.J. Martin, Multiple-frequency surface acoustic wave devices as sensors, Solid-State Sens. Actuator Workshop (1990) 5–8. [3] J. Hechner, T. Wrobel, The influence of PcCu layer crystalline structure on the parameters of SAW gas sensors, Eur. Frequency Time Forum (1996) 370–375. [4] T. Nomura, M. Takebayashi, A. Saitoh, Chemical sensor based on surface acoustic wave resonator using Langmuir–Blodett film, IEEE Trans. Ultrasonics, Ferroelectr. Frequency Contr. 45 (5) (1998) 1261–1265.
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[5] H. Becketr, M. von Schickfus, S. Hunklinger, A new sensor principle based on the reflection of surface acoustic waves, Sens. Actuators A 54 (1996) 618–621. [6] M. von Schickfus, H. Becketr, C. Rupp, S. Hunklinger, SAW gas sensing using reflectors and multistrip couplers, IEEE Ultrasonics Symp. (1995) 467–471. [7] B. Zhang, S.Y. Zhang, R.J. Wei, Reflective characteristics of SAW by reflection array with slanting metal strips, Acta Acoust. 14 (1) (1989) 58–67. [8] A.-L. Zhang, D.-Z. Zhu, A Y-type dual path surface acoustic wave mass sensor and its measurement system, Piezoelectr. Acoustoopt. 25 (6) (2003) 445–448.
Biographies Yang Ying received her BS and MS degrees in microelectronics from Xi’An University of Technology in 2000 and 2003, respectively. She is pursuing her PhD degree in microelectronics at Zhejiang University, China. She is interested in surface acoustic wave sensor designing and absorbing structure researching. Zhu Da-Zhong is Professor of the Department of Information and Electronic Engineering, Zhejiang University. His research included ASIC design, microwave sensor and MEMS technology. In recent years, he was charged with several projects of NSF in the field of RF device and IC designing.