Asymptotic semi-soft function has been proposed to overcome the discontinuous shortcoming of the hard-threshold function and the dispersion between the estimated wavelet coefficients and the decomposed wavelet coefficients of the soft-threshold function,as well as the problem how to select the parameter in the threshold function.It was testified that the estimated wavelet coefficients gradually approached the authentic wavelet coefficients as the threshold function using the asymptotic adjustment factor.Simulation results showed that the asymptotic semi-soft function could obtain higher signal-to-noise ratio(SNR) and smaller mean squared error (MSE) in ultrasonic signal denosing.A better denoising effect had been obtained in comparison with the hard-threshold function.%针对硬阈值函数的不连续性和软阈值函数存在恒定偏差,以及阈值函数中参数选择的问题,提出了渐近半软阈值函数.超声探伤信号处理中,该阈值函数通过使用渐近的调节系数,使得估计的小波系数逐渐逼近真实的小波系数.仿真结果表明:渐近半软阈值函数与硬阈值函数和软阈值函数相比,在超声信号去噪中能够获得更高的信噪比以及更小的均方误差,具有更好的去噪效果.
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