Haodong Wu

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.

Optimization of single-phase, unidirectional transducers using three fingers per period

Electrode width controlled (EWC) single-phase, unidirectional transducers (SPUDT) is widely used for low loss surface acoustic wave (SAW) filters. The insertion loss and fractional bandwidth of the filters are strongly related to the reflectivity of EWC cells. In order to achieve wide band and low loss simultaneously, it is necessary to obtain higher reflectivity. The relationship between geometrical configuration of EWC cells and reflection coefficient, (and transduction coefficient as well) is studied. Simulation results indicate that the reflectivity of the EWC SPUDT cell could exceed 5% on a 128/spl deg/ Y-X lithium niobate (LiNbO/sub 3/) substrate. Using such structure, low loss SPUDT test filters without weighting are fabricated. The measured 3 dB bandwidth is 3.9% and the insertion loss is 2.9 dB. The theoretical calculation is verified by the experiment.

Influence of material parameters on acoustic wave propagation modes in ZnO/Si bi-layered structures

The influences of material properties on acoustic wave propagation modes in ZnO/Si bi-layered structures are studied. The transfer matrix method is used to calculate dispersion relations, wave field distributions, and electromechanical coupling coefficients of acoustic wave propagation modes in ZnO/Si bi-layered systems, in which the thickness of the substrate is of the same order of magnitude as the wavelength of the propagating wave modes. The influences of the thin film parameters on the acoustic wave propagation modes and their electromechanical coupling coefficients of the wave modes also are obtained. In addition, some experimental results for characterizing the wave propagation modes and their frequencies have also been obtained, which agree well with the theoretical predictions.

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

The use of biomarkers in the antioxidant responses of Daphnia magna to the acute and chronic exposure to no. 20 diesel oil and 2,4-dichlorophenol

Abstract The effects of no. 20 diesel oil exposure, 2,4-dichlorophenol (2,4-DCP) exposure and combined exposure on the antioxidant defences of Daphnia magna have been studied systematically for the first time. Daphnia magna was exposed for 1 day or 10 days to several concentrations of 0, 0.005, 0.01, 0.05, 0.1, 0.5 or 1.0 mg L−1 solutions. Antioxidant defences consisting of the levels of reduced glutathione (GSH) and glutathione disulfide (GSSG) and activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), selenium dependent glutathione peroxidase (Se-GPx) and glutathione S-transferase (GST) of daphnids were determined to evaluate their protective roles and to analyse the occurrence of oxidative stress. The possible antioxidant defence mechanisms are discussed. Furthermore, GST can be a potential biomarker and an early-warning index for the pollutants in waters in that GST responded sensitively to 1 day and 10 days of exposure to diesel oil and 2,4-DCP and 10 days of combined exposure. Crossover comparisons showed an antagonistic action about the no-observed-effect concentration (NOEC) against Daphnia magna, which needs further studies.

Analysis of frequency-temperature behavior of surface acoustic wave (SAW) under periodic IDT

In this paper, we incorporate two thermal models with periodic FEM/BEM to analyze the temperature-frequency behavior of SAW under periodic IDT. One is the classical model based on Campbells theory, which has been widely used. We find that this model fails to predict temperature-frequency behavior of SAW for some cases, although we can get accurate results for many cases of some cuts and modes by using this model. The other is based on piezoelectric, Lagrangian equations. This one his proved to be a general model for the analysis of thermal effects on SAW, and is more accurate than the first one. But the application of this model is limited to quartz-based devices, because the temperature coefficients of material constants for other materials for piezoelectric, Lagrangian equations are not available at present. In practice, the two models are useful for the designing of SAW devices.

High selectivity SAW DMS filter with in-between shorted-gratings

A new structure is proposed to improve the selectivity of SAW DMS filter. Shorted-gratings are inserted between the input and output IDTs as additional reflectors which are designed to have a stopband at the frequencies just higher than the passband of the filter. The waves from input IDT to output IDT at the frequencies within the stopband of the in-between grating are strongly reflected, so the attenuation in the high frequency transition band of the filter can be drastically increased. Combining this novel structure with the concept of pitch-modulated IDT and reflector, and using effective global optimization algorithm, DMS filter with low insertion loss, wide band and high selectivity can be designed. The in-between reflector also makes it easier to realize DMS filter with 1–2% passband width on 42°LiTO3. The in-between reflector can be used to electrically connect busbars in layout design, thus inner bonding pads are not needed, which results in smaller chip size.1