秌田 雅彦, 上田 光宏

Masahiko AKITA, Mitsuhiro UEDA

東京工業大学精密工学研究所

Research Laboratory of Precision Machinery and Electronics, Tokyo Institute of Technology

キーワード : noise, signal averaging, repetition rate, reverberation, damping resistance

The noise generated by an amplifier is contained in pulse echo signals, and it may hinder the detection of small echo signals. If this noise appears at random, the average of its amplitude is zero. Therefore, it is possible to extract from a wavetrain a signal which is lower in amplitude than the noise by means of signal averaging. But there is no reports that the method was applied to the pulse echo method at this time.
In this paper it is examined how much the noise amplitude decreases in proportion to the average number. But it became clear that the rate of improvement of S/N rate greatly depends upon the working condition of pulse echo method. That reason is that coherent noise by reverberation at inside of transducer or water bath is added to incoherent noise by thermal noise, etc. Therefore, there is the limit of average number in such a case. That was also proved in the experiment which used repetition rate of pulse and damping resistance of transducer as the parameter and examined the relation between average number and variance of noise. That became a good guide to apply signal averaging effectively. Its effect in B-mode pattern is also examined.