用时域自易法测量超声换能器灵敏度

超声换能器的灵敏度是实际应用中很重要的物理参量，传统测试方法是在消声水槽中用连续正弦波进行逐点频率测量，过程较繁复，测量频率范围也受到限制，并且不能获得重要的相位信息．本文所采用的时域自易法是一种新颖的换能器核准方法．通过对超声换能器的激励电流和回波电压脉冲进行傅氏变换，可得到灵敏度的幅频相频特性，且具有测量速度快、频带宽和易于操作等优点．把时域自易法所测得结果与频域法测量所得结果进行比较，证实相符．     

A SURFACE LEAKY WAVE RESONATOR WITH LOW INSERTION LOSS AND SMALL DIMENSIONS

Surface leaky wave(SLW)resonator is designed and fabricated by using high electromechanicalcoupling and large impedance changes under the shorted metallized strips of the surface leaky wave,excited on the surface of the 49°rotated Y-cut LiNbO_3.The prominent advantage over the con-ventional surface acoustic wave resonator(SAWR)is that the required area of the piezo-electric sub-strate could be reduced to 1/4—1/5 of SAWR at the same frequency and its insertion loss is only2—5 dB in 50Ω system. The electromechanical coupling constant k_s~2 and acoustic impedance mismatching ratio|ε| aremeasured and thus the reflective frequency responses of the shorted metaliized array are calculated.The factors relating with the insertion loss are analyzed by utilizing an equivalent circuit model.Some typical experimental results are shown in this paper as well.     

WITHDRAWAL WEIGHTING OF INTERDIGITAL TRANSDUCER

Previous design method for withdrawal weighing is only used in the design of narrow bandwidthtransducers and is directly given without detailed mathematical argumentations.In this paper themathematical expressions for withdrawal weighting are given.An improved method of withdrawalis presented,in which the corrections of end and neighbour effect are not necessary.It is noticedthat the initial weighting functions must satisfy certain conditions.Because of having consideredthese conditions and used computer-aided-design procedure,the performances of withdrawal weightedSAW filters can be improved greatly.The 3 dB relative bandwidth is increased up to 8% andthe initial weighting can have phase-reverse sidelobes.Some experimental withdrawal weighted SAWfilters have been developed.Experimental results agree well with the theory.