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抽指加权避免了切趾加权的末端效应和衍射效应,所以可以从理论上预计出准确的结果,并能进行双加权,但它只能适用于带宽较窄的器件。本文为抽指加权给出了数学表达式,提出了用不着近邻效应修正和相位修正的设计方法,使设计和工艺都大为简化,并且实验上容易保证预期的结果。由于注意到了抽指加权应满足的条件,并用计算机选出最佳的设计方案,本文所设计的滤波器可以超过前人用抽指方法所达到的带宽。本文编制出抽指加权的计算机程序,对辛克函数凯塞窗口加权换能器和海明加权换能器设计出3dB带宽达2—8％的带通滤波器,实验与理论结果基本一致。
Suffix weighting avoids apodization-weighted end-effects and diffraction effects, so accurate results can be predicted theoretically and double-weighting is possible, but it can only be applied to devices with narrow bandwidths. In this paper, a mathematical expression is given for fingering weighting, and a design method that does not require neighbor effect correction and phase correction is proposed. The design and the process are greatly simplified, and the expected results are easily guaranteed experimentally. Because of noting the conditions that the weighting should meet and using the computer to select the best design scheme, the filter designed in this paper can surpass the bandwidth which the predecessors used the fingering method. In this paper, a computer program is developed to extract the weight of fingers. The bandpass filter with 3dB bandwidth of 2-8% is designed for Kaeser window weighting transducer and Hamming weighting transducer. The experimental and theoretical results are basically the same.