Xiaojun Ji

A wireless demodulation system for passive surface acoustic wave torque sensor

Surface acoustic wave (SAW) resonators are utilized as torque sensors for their passive and wireless features. However, the response of a SAW torque sensor is difficult to detect because of the transient response duration and interruption of channel noise, which limit the application of SAW torque sensors. The sensitive mechanism and response function of a passive wireless SAW torque sensor are analyzed in this study. A novel demodulation system involving both hardware and software is developed for the SAW torque sensor. A clipping amplifier is utilized in the hardware to widen the dynamic response range and increase the length of the valid signal. Correlation extension and centroid algorithms are designed to lengthen the received signal and improve the estimation accuracy of the center frequency of the response signal, respectively. Meanwhile, a fast binary search algorithm is proposed to accelerate the scanning cycle according to the developed response function. Finally, the SAW torque sensor demodulation system is set up and SAW resonators with high sensitivity are fabricated on a quartz substrate. The presented demodulation system is tested, and a standard deviation of 0.28 kHz is achieved. This value is much smaller than that of classic and modern spectrum estimation methods. The sensitivity of resonance frequency shift versus torque on the shaft of the assembled senor is 2.03 kHz/Nm; the coefficient of determination is 0.999, and the linearity is 0.87%. Experimental results verify the validity and feasibility of the proposed SAW torque sensor demodulation system.

Theoretical analysis of surface acoustic wave propagating properties of Y-cut nano lithium niobate film on silicon dioxide

The surface acoustic wave (SAW) propagating characteristics of Y-cut nano LiNbO3 (LN) film on SiO2/LN substrate have been theoretically calculated. The simulated results showed a shear horizontal (SH) SAW with enhanced electromechanical coupling factor K2 owing to a dimensional effect of the nanoscale LN film. However, a Rayleigh SAW and two other resonances related to thickness vibrations caused spurious responses for wideband SAW devices. These spurious waves could be fully suppressed by properly controlling structural parameters including the electrode layer height, thickness, and the Euler angle (θ) of the LN thin film. Finally, a pure SH SAW was obtained with a wide θ range, from 0° to 5° and 165° to 180°. The largest K2 achieved for the pure SH SAW was about 35.1%. The calculated results demonstrate the promising application of nano LN film to the realization of ultra-wideband SAW devices.

A surface acoustic wave response detection method for passive wireless torque sensor

This paper presents an effective surface acoustic wave (SAW) response detection method for the passive wireless SAW torque sensor to improve the measurement accuracy. An analysis was conducted on the relationship between the response energy-entropy and the bandwidth of SAW resonator (SAWR). A self-correlation method was modified to suppress the blurred white noise and highlight the attenuation characteristic of wireless SAW response. The SAW response was detected according to both the variation and the duration of energy-entropy ascension of an acquired RF signal. Numerical simulation results showed that the SAW response can be detected even when the signal-to-noise ratio (SNR) is 6dB. The proposed SAW response detection method was evaluated with several experiments at different conditions. The SAW response can be well distinguished from the sinusoidal signal and the noise. The performance of the SAW torque measurement system incorporating the detection method was tested. The obtained repeatability error ...

Fast surface acoustic wave solution method based on the generalized Green’s function

The characteristics of generalized Green’s function elements with different materials and cuts are analyzed. The real part has only one zero crossing point that corresponds to a free surface acoustic wave (SAW) when the imaginary part of elements H33 is zero. Moreover, the signs of the real part on two sides of the zero crossing point are opposite. A fast SAW solution algorithm is developed on the basis of the characteristics of H33. Free surface SAW velocity vf is obtained by searching the zero crossing point of H33, and metal surface SAW velocity vm is obtained by searching the zero crossing point of an effective permittivity that is smaller than vf. A numerical simulation is performed. Results show that the obtained SAW velocity and electromechanical coupling coefficients are consistent with the reported results. Moreover, the calculation time of the proposed SAW solution method is approximately 10% of the existing methods, which verify its feasibility.

Full-Wave Analysis of Ultrahigh Electromechanical Coupling Surface Acoustic Wave Propagating Properties in a Relaxor Based Ferroelectric Single Crystal/Cubic Silicon Carbide Layered Structure

This paper describes a full-wave analysis of ultrahigh electromechanical coupling surface acoustic wave (SAW) of Y-cut X propagating Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (YX-PIMNT) single crystals on a cubic silicon carbide (3C-SiC) substrate. There are several eigenmodes including shear horizontal (SH) and Rayleigh SAWs. Based on the finite-element method (FEM), the phase velocity () and coupling factor () of SAWs varying with the top electrode thickness, thickness, and Euler angle () of the YX-PIMNT substrate have been investigated. of SH SAW can reach an extremely high value of 75.9%. The proper control of structural parameters can suppress unwanted responses caused by other modes without deteriorating the coupling factor. The large value of SH SAW and suppression of unwanted responses have highly promising applications in developing ultrawideband and tunable SAW filters. Finally, the performance of 3C-SiC and 6H-SiC as substrates was investigated, and 3C-SiC was identified as a more attractive substrate candidate than 6H-SiC.

Suppression of Rayleigh wave spurious signal in ultra-wideband surface acoustic wave devices employing 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

The propagation characteristics of surface acoustic waves (SAWs) on rotated Y-cut X-propagating 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMN-33%PT) substrate are theoretically analyzed. It is shown that besides the existence of a shear horizontal (SH) SAW with ultrahigh electromechanical coupling factor K2, a Rayleigh SAW also exists causing strong spurious response. The calculated results showed that the spurious Rayleigh SAW can be sufficiently suppressed by properly selecting electrode and its thickness with optimized rotating angle while maintaining large K2 of SH SAW. The fractional -3 dB bandwidth of 47% is achievable for the ladder type filter constructed by Au IDT/48oYX-PMN-33%PT resonators.

Design of ultra-wideband surface acoustic wave filters

This paper describes working principles of traditional ladder-type surface acoustic wave (SAW) filter composed by resonators. The simulation model was founded by utilizing Quite Universal Circuit Simulator (QUCS) for a seven stepped SAW filters on substrate of relaxor based ferroelectric single crystals. An extremely large wideband SAW filter of 620 MHz at 1 GHz could be obtained due to large electromechanical coupling factor (K2~60%) when the substrate is poled along (111) plane, which is presently three times larger than that achieved by conventional piezoelectric material. The band rejection could be improved by adjusting static capacitance ratio of series and parallel arm resonators. In order to optimize overall properties of the ultra-wideband SAW filter, we have modified the structure of a conventional ladder-type filter by adding a resonator to series or parallel arm to form two new notches, which sacrifices some bandwidth, but could achieve large transition band, steep transition zone and also band rejection. Finally, we discussed the influence of quality factor on the insertion loss of the SAW filters.

Comprehensive characterization of surface acoustic wave resonators using relaxor based ferroelectric single crystals

One-port surface acoustic wave resonators (SAW) were fabricated and characterized using Y-cut X propagating relaxor based ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3-33%PbTiO3 and Pb(In1/3Nb2/3)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT). The experimental results demonstrated ultrahigh electromechanical coupling factor K2 of ∼60% for shear horizontal SAW and a relatively strong spurious resonance due to the Rayleigh-type SAW which can be sufficiently suppressed with Au electrode of large thickness. Characteristics of temperature stability, sensitivity to DC bias voltage, and homogeneity for the two resonators were evaluated and compared. The results showed similar instability of domain structure, and PIN-PMN-PT resonators have better temperature stability, but inferior homogeneity compared to that of PMN-33%PT resonators.