Jiuling Liu

Advances in SAW Gas Sensors Based on the Condensate-Adsorption Effect

A surface-acoustic-wave (SAW) gas sensor with a low detection limit and fast response for volatile organic compounds (VOCs) based on the condensate-adsorption effect detection is developed. In this sensor a gas chromatography (GC) column acts as the separator element and a dual-resonator oscillator acts as the detector element. Regarding the surface effective permittivity method, the response mechanism analysis, which relates the condensate-adsorption effect, is performed, leading to the sensor performance prediction prior to fabrication. New designs of SAW resonators, which act as feedback of the oscillator, are devised in order to decrease the insertion loss and to achieve single-mode control, resulting in superior frequency stability of the oscillator. Based on the new phase modulation approach, excellent short-term frequency stability (±3 Hz/s) is achieved with the SAW oscillator by using the 500 MHz dual-port resonator as feedback element. In a sensor experiment investigating formaldehyde detection, the implemented SAW gas sensor exhibits an excellent threshold detection limit as low as 0.38 pg.

Wireless and Passive Gyroscope based on Surface Acoustic Wave Gyroscopic Effect

The design and performance of a novel wireless and passive gyroscope based on the surface acoustic wave (SAW) gyroscopic effect on a 128° YX LiNbO3 substrate utilizing two parallel reflective delay lines with opposite directions is described. A theoretical model dealing with the gyroscopic effect using the surface effective permittivity method was established. A coupling of modes (COM) model was used to determine the optimal design parameters of the SAW devices prior to fabrication. The sensor performance towards external applied rotation was evaluated by the precise rate table referring to the network analyzer and antenna as the wireless reader unit. Good phase sensitivity and excellent linearity were observed in the measured results.

P6G-3 Switchable SAW Filter Bank with Both Narrow & Wide Channel Bandwidth and 10 Channels SAW Filter Bank

The design and testing of 8 channels and 10 channels low loss switchable SAW filter bank is described. There are both narrow & wide channel bandwidths in 8 channels filter bank. The 1 dB bandwidth of narrow channel is about 0.3% and that of wide channel more than 3.2 MHz. Cascade-connected two stages are constructed to achieve higher stop-band rejection. Every narrow bandwidth channel is constructed with two same SPUDT SAW filter on ST-X quartz with insertion loss less than 6 dB and stop-band rejection more than 40 dB. Each wide bandwidth channel includes of a fan-type SPUDT filter on X-112degY LiTaO3 with insertion loss less than 10 dB and a longitudinally-coupled DMS filter on 36degY-X LiTaO3 less than 2 dB. The experimental 8 channels SAW filter bank results in insertion loss less than 12.5 dB and stop-band rejection more than 70 dB. In 10 channels filter bank, the individual filter consists of fan-type SPUDT on X-112degY LiTaO3 with insertion loss of less than 12 dB, stop-band rejection more than 40 dB, magnitude ripples in pass-band less than 0.5 dB and nonlinear phase less than 2deg per 1 MHz. The experimental 10 channels filter bank results in insertion loss of 14.6 dB, deviation of insertion loss among different channels less than 0.5 dB, and stop-band rejection more than 40 dB.

Temperature-compensated Love wave based gas sensor on waveguide structure of SiO2/36° YX LiTaO3

A temperature-compensated Love wave device was proposed for gas sensing utilizing a waveguide structure of SiO2/36° YX LiTaO3. Significant improvement in the temperature stability of the hybrid Love wave device was implemented by varying the guiding layer thickness. The optimal values yielding low cross-sensitivity to temperature and high mass sensitivity in gas sorption were determined theoretically by solving the coupled electromechanical field equation in layered media. The theoretical analysis was confirmed experimentally in dimethylmethylphosphonate (DMMP) detection by using a fluoroalcoholpolysiloxane (SXFA) coated Love wave sensor. The experimental results indicate that better sensitivity and excellent temperature stability were obtained from the developed Love wave gas sensor over the Rayleigh surface acoustic wave (R-SAW) sensors.

Development of a New Surface Acoustic Wave Based Gyroscope on a X-112°Y LiTaO3 Substrate

A new micro gyroscope based on the surface acoustic wave (SAW) gyroscopic effect was developed. The SAW gyroscopic effect is investigated by applying the surface effective permittivity method in the regime of small ratios of the rotation velocity and the frequency of the SAW. The theoretical analysis indicates that the larger velocity shift was observed from the rotated X-112°Y LiTaO3 substrate. Then, two SAW delay lines with reverse direction and an operation frequency of 160 MHz are fabricated on a same X-112°Y LiTaO3 chip as the feedback of two SAW oscillators, which act as the sensor element. The single-phase unidirectional transducer (SPUDT) and combed transducers were used to structure the delay lines to improve the frequency stability of the oscillator. The rotation of a piezoelectric medium gives rise to a shift of the propagation velocity of SAW due to the Coriolis force, resulting in the frequency shift of the SAW device, and hence, the evaluation of the sensor performance. Meanwhile, the differential structure was performed to double the sensitivity and compensate for the temperature effects. Using a precise rate table, the performance of the fabricated SAW gyroscope was evaluated experimentally. A sensitivity of 1.332 Hz deg−1 s at angular rates of up to 1,000 deg s−1 and good linearity are observed.

Mass Sensitivity Optimization of a Surface Acoustic Wave Sensor Incorporating a Resonator Configuration.

The effect of the sensitive area of the two-port resonator configuration on the mass sensitivity of a Rayleigh surface acoustic wave (R-SAW) sensor was investigated theoretically, and verified in experiments. A theoretical model utilizing a 3-dimensional finite element method (FEM) approach was established to extract the coupling-of-modes (COM) parameters in the absence and presence of mass loading covering the electrode structures. The COM model was used to simulate the frequency response of an R-SAW resonator by a P-matrix cascading technique. Cascading the P-matrixes of unloaded areas with mass loaded areas, the sensitivity for different sensitive areas was obtained by analyzing the frequency shift. The performance of the sensitivity analysis was confirmed by the measured responses from the silicon dioxide (SiO2) deposited on different sensitive areas of R-SAW resonators. It is shown that the mass sensitivity varies strongly for different sensitive areas, and the optimal sensitive area lies towards the center of the device.

Enhanced Sensitivity of Surface Acoustic Wave-Based Rate Sensors Incorporating Metallic Dot Arrays

A new surface acoustic wave (SAW)-based rate sensor pattern incorporating metallic dot arrays was developed in this paper. Two parallel SAW delay lines with a reverse direction and an operation frequency of 80 MHz on a same X-112°Y LiTaO3 wafer are fabricated as the feedback of two SAW oscillators, and mixed oscillation frequency was used to characterize the external rotation. To enhance the Coriolis force effect acting on the SAW propagation, a copper (Cu) dot array was deposited along the SAW propagation path of the SAW devices. The approach of partial-wave analysis in layered media was referred to analyze the response mechanisms of the SAW based rate sensor, resulting in determination of the optimal design parameters. To improve the frequency stability of the oscillator, the single phase unidirectional transducers (SPUDTs) and combed transducer were used to form the SAW device to minimize the insertion loss and accomplish the single mode selection, respectively. Excellent long-term (measured in hours) frequency stability of 0.1 ppm/h was obtained. Using the rate table with high precision, the performance of the developed SAW rate sensor was evaluated experimentally; satisfactory detection sensitivity (16.7 Hz·deg·s−1) and good linearity were observed.

Theoretical analysis on gyroscopic effect in surface acoustic waves

The rotation of a piezoelectric medium gives rise to a shift of propagation velocity of surface acoustic wave (SAW) due to the Coriolis force, resulting in the frequency shift of the SAW device, and hence, the evaluation of the sensor performance. The phase velocity shift is investigated by applying surface effective permittivity method in the regime of small ratios of the rotation velocity and the frequency of the SAW. The gyroscopic effect for various SAWs propagating along several common piezoelectric substrates as ST-X quartz, YX 128°LiNbO3, and X-112°Y LiTaO3 were studied, and the calculated results indicates that the larger response to external rotation was observed in X-112°Y LiTaO3, which is consistent with the previous reported results. Also, the validity of the theoretical analysis was confirmed by the reported experimental results, it means the surface effective permittivity method is an effective way for gyroscopic effect analysis.

Switchable SAW filter bank with 78% bandwidth

The design and testing of 16 channel low loss switchable SAW filter bank with 78% bandwidth is described. To achieve low loss, the individual filter in each channel is made up of longitudinally coupled resonator filter. The switches are added to both input and output of filters. The single channel operation mode can make sure the required low loss for application. Three kinds of longitudinally coupled resonator filters are separately adopted in different channels, which are fabricated on 41° Y-X LiNbO3 using 1-3 mode, 41° Y-X LiNbO 3 using 1-2 mode and 64° Y-X LiNbO 3 using 1-3 mode, to get the same bandwidth as possible. The experimental filter bank results in insertion loss of less than 6.5dB (including the insertion loss of two-stage switch), channel bandwidth 17~23MHz and ultimate stopband rejection of more than 40 dB.

Advances in a developed surface acoustic wave based particulate matter 2.5 monitor

This paper presented a surface acoustic wave (SAW) based particulate matter (PM) 2.5 monitor, which consisted of a SAW dual-resonator oscillator, a thermophoresis unit and a virtual impactor. The structure optimization for improving the performance of the sensor by considering the particle distribution deposited by thermophoresis on the SAW detector was analyzed and verified in experiments. The size of thermophoresis micro-channel was obtained by Talbot formula and the movement of particles to the surface of the SAW detector was simulated by using the finite element method (FEM). Based on the theoretical results, the micro-channel was fabricated and the thermophoresis distribution was observed under an optical microscope. The optimal monsitoring structure of the SAW based PM2.5 monitor was established theoretically.