Weaver R L, Lobkis O I
Theoretical & Applied Mechanics, University of Illinois, Urbana, Illinois 61801, USA.
Phys Rev Lett. 2001 Sep 24;87(13):134301. doi: 10.1103/PhysRevLett.87.134301. Epub 2001 Sep 7.
Noise generated in an ultrasonic receiver circuit consisting of transducer and amplifier is usually ignored, or treated as a nuisance. Here it is argued that acoustic thermal fluctuations, with displacement amplitudes of 3 fm, contain substantial ultrasonic information. It is shown that the noise autocorrelation function is the waveform that would be obtained in a direct pulse/echo measurement. That thesis is demonstrated in experiments in which direct measurements are compared to correlation functions. The thermal nature of the elastodynamic noise that generates these correlations is confirmed by an absolute measurement of their strength, essentially a measurement of the sample temperature.
由换能器和放大器组成的超声接收器电路中产生的噪声通常被忽略，或被视为一种干扰。本文认为，位移幅度为3飞米的声学热涨落包含大量超声信息。结果表明，噪声自相关函数就是在直接脉冲/回波测量中所获得的波形。通过将直接测量结果与相关函数进行比较的实验来证明这一论点。通过对其强度进行绝对测量，本质上是对样品温度的测量，证实了产生这些相关性的弹性动力学噪声的热性质。
