Yongan Shui

Reflection and scattering characteristics of reflectors in SAW tags

As a foundation of an optimal design for SAW tags,the reflection, scattering, and transmission of the reflector composed of a few electrodes are discussed. A source regeneration method based on Greens function and the finite element method/boundary element method is used to obtain the reflection coefficient and the scattering coefficient for the short-circuited and open circuit reflectors. Examples are presented to show how one can use structure variance to satisfy the requirements for SAW tag design according to the reflection and scattering characteristics.

Rayleigh Wave Reflection and Scattering Calculation by Source Regeneration Method

The analysis and precise calculation of reflection and scattering of Rayleigh wave by electrodes is important for surface acoustic wave (SAW) device models, especially for SAW identification (ID) tag design. We present a source regeneration method, which utilizes Greens function combined with finite-element method (FEM)/boundary-element method (BEM) to obtain accurate values of reflection, transmission, and scattering coefficients in a direct way. We take one electrode as the reflector on 128deg YX-LiNbO3 substrate to show the result as an example. The results are very accurate and are obtained with short computing time. The new analysis way shows its powerful ability for other advanced discussion of SAW devices.

Fast, precise, and full extraction of the COM parameters for multielectrode-type gratings by periodic Green's function method

It is very important to extract all four coupling-of-modes (COM) parameters of the electrode cells for the simulation and optimal design of a low loss surface acoustic wave (SAW) filter. A new approach for fast and full extraction of the COM parameters for multielectrode-type grating is proposed. The field distribution of the wave under the periodic shorted grating is calculated by periodic Greens function method. The phase of the reflection is determined from the positions of the standing wave node. The transduction coefficient and its phase are determined by the charge distribution at low frequency. The COM parameters of the commonly used electrode width controlled (EWC) single phase unidirectional transducer (SPUDT) is computed. It shows that this is a simple and direct way to extract all the COM parameters for SPUDT and, accordingly, is a powerful tool for the optimization of the filter structure.

The second harmonic generation in piezoelectric resonators

The effect of frequency-amplitude, nonlinear dependence of vibration amplitude on applied voltage and second-order harmonic (SH) generation are the main manifestations of nonlinear behaviors in piezoelectric resonators. These nonlinear effects will degrade the resonator as a frequency-control device. On the other hand, they do suggest some directions to determine high-order elastic and piezoelectric constants of piezoelectric materials. In the present paper the theoretical and experimental studies are reported, addressing the SH generation of resonators due to medium nonlinearity. Experiment was carried out for Z-cut LiNbO3 to observe the SH vibration at the free surface of an electrically excited thin plate. Its amplitude is measured by a capacitive detector which is able to be calibrated absolutely, showing that the strongest efficiency of SH generation appears near the frequency of anti-resonance, as predicted by the corresponding theory using successive approximation. Mathematical solution to the problem relates the SH amplitude to high-order constants of piezoelectric crystals. Further development is expected to apply this technique to measurement of material parameters by means of the aforementioned nonlinear coefficients

The piezoelectric coupling of 2-2 composite transducers

A field solution is developed to predict dynamic behavior of piezoceramic polymer composite with 2-2 connectivity. The solution is derived based on a concept of Lamb wave propagation along the thickness direction of the 2-2 composite. Dynamic characteristics of various resonant modes are investigated theoretically and experimentally over a broad frequency range. Dispersion curves of the resonant modes are calculated and measured for composites with different ceramic volume fractions. Strong interactions between thickness and lateral resonant modes are observed in transition zones where two resonant modes approach each other. Electromechanical thickness coupling coefficient k/sub t/ is evaluated for the first time from a dynamic analysis point of view as a function of ceramic volume fraction as well as the aspect ratio. Results show that the coupling coefficient k/sub t/ reaches its maximum value when thickness oscillation is decoupled from lateral modes.

Second‐harmonic generation of interface waves

The second‐harmonic generation of leaky waves at the interface between glass and iron has been investigated. Fundamental frequency interface waves are excited by bulk shear waves, incident at the critical angle, and the generated second‐harmonic surface waves are detected by reradiated bulk shear waves. The amplitudes of the generated second harmonic obey the square law. The second‐harmonic generation decreases sharply as the incident and detection drive deviate from the critical angle.

Errors of phases and group delays in SAW RFID tags with phase modulation

To achieve high-volume code capacity for SAW-based radio frequency identification(RFID) tags, it is very important to improve the delay time resolution. An efficient encoding method is to use the phase delay of the carrier wave in the pulses, but one has to solve the issues of the phase ambiguity at unknown temperatures and the location of reflectors to exact positions. In this paper, a method is proposed to obtain a high-phase delay resolution by measuring group delays and constructing a certain restriction on the exact positions of reflectors. To define the restriction parameter for a SAW RFID system with large code capacity, it is imperative to have a priori knowledge of the errors of the phases and group delays. The experimental and simulation errors for both the phases and the group delays, originated from the design procedure, the temperature effect, the fabrication process and the measurement, are presented. The error probability distribution curves in simulation and experiments are plotted. The maximum error of phase delay is about plusmn 14deg, and the maximum error of group delay is about plusmn 4 periods. The temperature range in investigation is from -5 to 45degC.

Rayleigh wave reflection and scattering calculation for short reflector by sources regeneration method

The analysis and precise calculation of reflection and scattering of Rayleigh wave by electrodes is important for surface acoustic wave (SAW) devices modeling, especially for SAW identification (ID) tags design. We present a source regeneration method, which takes the stress and electric charge under electrodes as the sources, and the reflection and scattering could be considered as two processes: the incident Rayleigh wave produces a source under the reflector; and the source regenerates the reflection wave, scattering bulk wave, etc. The method utilizes Greens function combined with Finite Element Method (FEM)/Boundary Element Method (BEM) to obtain accurate values of sources, and then, reflection, transmission and scattering coefficients. We take 128o YX-LiNbO3 as substrate to show the results as examples. In the results, we show the best way to combine a few electrodes as a reflector for a lowest bulk wave loss and largest reflection. The results are very accurate and are obtained in a short computing time.

P2H-2 Phases of Carrier Wave in a SAW Identification Tags

The implementation of SAW tags with phase modulation is more difficult than the amplitude and the time position modulation. Using the source regeneration theory, the optimization design of the pulse position with simultaneous phase modulation tags is discussed in this paper. Several SAW tags at 915 MHz are simulated using FEM/BEM simulators. The phase, peak value and delay time of each reflective echo are well agreed with the designing. The phase deviation is less than 10deg, in general is less than 2-3deg, the peak value fluctuation is less than +0.8 dB

Switchable single mode Lamb wave transduction by means of both side excitation

Two identical interdigital transducers, deposited on both sides of the 127.86/spl deg/ Y-X LiNbO/sub 3/ plate symmetrically, were used to generate Lamb waves. For the case of electrically symmetrical connection of transducers, the S/sub 0/ mode was generated four or five times more strongly than that for the same transducer on one side, while the A/sub 0/ mode was reduced by about 10 dB. For antisymmetrical electric connection, the A/sub 0/ mode is strong and the S/sub 0/ mode is suppressed. Experiments on nonpiezoelectric medium glass with 121/spl deg/ Y-X LiNbO/sub 3/ on both sides showed a similar result. A delay line composed of such a structure has an insertion loss of only 3 dB.