Implementation of GHz SAW filters using quasi-harmonic interdigital transducers

本文利用准谐频设计方法,在常规光刻工艺水平上,成功地实现了GHz级声表面波(SAW)器件。准谐频叉指换能器(QHIDT)的优点为其指条宽与指间隙可以比一般的单指换能器宽,克服了单指换能器内指间的多次反射,并且又较好地解决了普通谐频叉指换能器基频抑制不好的缺点。本文给出了制作在ST石英基片上,工作频率1128MHz的声表面波滤波器的实验结果。     

抽指加权宽带扇形叉指声表面波滤波器的等效电路分析

扇形换能器可以看成若干个沿孔径方向划分的均匀孔径换能器电端并联而成，根据梅森(Mason)等效电路模型以及由其延伸的混合场等效电路模型，推导出整个扇形换能器的导纳矩阵和频率响应，其中采用复阻抗模型考虑了叉指电极与自由表面的阻抗不连续的因素。本方法能够模拟指间反射、三次行程、指条寄生阻抗以及外围电路等对器件性能的影响；理论模拟与实验结果吻合。     

Full-wave modeling of piezoelectric transducers for SAW acousto-optical interactions

In this paper we present an accurate and efficient numerical method for a rigorous full-wave analysis of interdigital transducers (IDT) for the excitation of surface acoustic waves on the piezoelectric substrate of acousto-optical devices. The problem is formulated in terms of an integral equation that is solved by the method of moments. The transducer input admittance and the power coupling factors to both surface and bulk waves are computed. Numerical results for some configurations of X-Y LiNbO₃ IDT for acousto-optic applications are in very good agreement with measured data. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band transducers for acousto-optical devices.     

移动通讯用声表面波器件发展近况

本文首先回顾了民用声表面波器件的最新发展概况．随着移动通讯的发展，声表面波器件的最大应用市场将是通讯，而低插损声表面波滤波器成为新的研究高潮．本文因此随后简要介绍了几种主要的低插损结构的研究情况及其在移动通讯中的应用．最后，展望了声表面波器件的发展趋势．     

Development of human IgE biosensor using Sezawa-mode SAW devices

This paper reports Sezawa-mode surface acoustic wave (SAW) devices with via-isolated cavity to construct the allergy biosensor. To fabricate Sezawa-mode SAW devices, the RF magnetron sputtering method for the growth of piezoelectric ZnO thin films are adopted and influences of the sputtering parameters are investigated. The optimal substrate temperature of 300 °C, RF power of 120 W and sputtering pressure of 2 Pa were used to deposit piezoelectric ZnO films with a smooth surface, uniform grain size and strongly c-axis-orientated crystallization. A back-etched SAW resonator is used in this study. The wet etching of (100)-oriented silicon wafers is used to form a back-side cavity which is critical to the formation of a hopper cavity for holding bio-analytes. The remaining membrane structure silicon thickness was 25 μm. In this report, the chrome (Cr, 12 nm)/gold (Au, 66 nm) layer was initially deposited onto the sensing area of SAW devices as the binding layer for biochemical sensor. The resonance frequency of the Sezawa-mode SAW device is 1.497 GHz. The maximum sensitivity of the Sezawa-mode is calculated to be 4.44 × 10⁶ cm²/g for human immunoglobulin-E (IgE) detection. The stability for human IgE detection is calculated to be 80% and the variation of the stability ±3% was obtained after several tests.     

利用锥型换能器的宽带低损耗声表面波滤波器设计

分析锥型换能器的基本原则是把换能器沿孔径方向划分成足够多的通道来进行近似,设计制作的关键是加权技术和数据处理技巧。由于SPUDT的特性,把EWC型的SPUDT引入到锥型换能器对制作宽带、低损耗器件是十分有用的;我们在Y128°LN基片上采用一般型和SPUDT型锥型换能器制作了相对带宽约15%的声表面波滤波器,一个换能器采用“块加权”,另一个换能器采用抽指加权。文中给出了两种器件的实验结果,SPUDT型声表面波滤波器的插损仅7.5dB。     

应用LiNbO_3声表面波驱动的全光纤声光频移器

介绍一种工作在10.7MHz的全光纤声光频移器.它由在LiNbO_3基片上制作的叉指电极换能器产生的声表面波驱动.当驱动电功率1.5W时,频移光转换效率达35％.     

Sniffing lung cancer related biomarkers using an oxidized graphene SAW sensor

Decane is one of the volatile organic compounds (VOCs) in human breath. Successful detection of decane in human breath has vast prospects for early lung cancer diagnosis. In this paper, a novel detecting device based on a filter surface acoustic wave (SAW) gas sensor is presented. SAW sensors coated with a thin oxidized graphene film were used to detect decane in parts per million (ppm) concentrations. Control and signal detection circuits were designed using a vector network analyzer with a detection resolution of insertion loss down to 0.0001 dB. The results showed that the SAW sensor could respond quickly with great sensitivity when exposed to 0.2 ppm decane. This device shows tremendous potential in medical diagnosis and environmental assessment.     

Estimating the absolute flux distribution for a synchrotron X‐ray beam using ionization‐chamber measurements with various filters

It is shown that an extensive set of accurate ionization‐chamber measurements with a primary polychromatic synchrotron X‐ray beam transmitted through various filter combinations/thicknesses can be used to quite effectively estimate the absolute flux distribution. The basic technique is simple but the `inversion' of the raw data to extract the flux distribution is a fundamentally ill‐posed problem. It is demonstrated, using data collected at the Imaging and Medical Beamline (IMBL) of the Australian Synchrotron, that the absolute flux can be quickly and reliably estimated if a suitable choice of filters is made. Results are presented as a function of the magnetic field (from 1.40 to 4.00 T) of the superconducting multi‐pole wiggler insertion device installed at IMBL. A non‐linear least‐squares refinement of the data is used to estimate the incident flux distribution and then comparison is made with calculations from the programs SPECTRA, XOP and spec.exe. The technique described is important not only in estimating flux itself but also for a variety of other, derived, X‐ray properties such as beam quality, power density and absorbed‐dose rate. The applicability of the technique with a monochromatic X‐ray beam for which there is significant harmonic contamination is also demonstrated. Whilst absolute results can also be derived in this monochromatic beam case, relative (integrated) flux values are sufficient for our primary aim of establishing reliable determinations of the percentages of the various harmonic components.     

Broad omnidirectional high-precision filters design using genetic algorithm

An application of the genetic algorithm in designing omnidirectional optical filters is reported in this paper. Concerning different periodic numbers and thickness ratios in the heterostructure, we gave some optimization examples and finally achieved a photonic heterostructure with very broad omnidirectional filter bandwidth as well as a very narrow transmission window. And it is found that when the normal incident beam is tilted at a negligibly small angle, the perfect transmittance peak will vanish. Hence, this heterostructure can be regarded as omnidirectional high-precision filters with potential application in optical filters, optical switches, and many other optical telecommunication areas.     

Design of interdigital transducers for crack detection in plates

Interdigital transducers (IDT) for non-destructive evaluation (NDE) of cracks in plates are designed based on an analytical model established previously. Key considerations include mode selectivity, excitation strength, collimation of wave and cost. The advantage of mode selectivity of IDT over PZT patch is presented both analytically and experimentally. Effects of parameters, namely finger spacing, width, length, number of fingers, and the size of IDT, on the excitation strength and mode selectivity are considered. This led to the design of a mobile double-sided IDT as an efficient device where excitation strength is strong and focused. The device was fabricated in-house using commercially available piezoelectric ceramics and used to develop a procedure for accurate identification of the direction and extent of cracks in plates. Three aluminum plates, one with a linear deep crack, another with a piecewise linear shallower crack and the third with a curved crack, were used to illustrate the accuracy and efficiency of both the proposed device and procedure for effective NDE.