Utilizing vector hydrophones to achieve an active anechoic terminal in an acoustic tube

A new vector hydrophones based active absorbing terminal used for the anechoic terminal of impedance tube is presented in this paper. Based on this, the reflected and the incident waves can be separated, and hence the absorbing spectrum can be achieved in a wider low-frequency band. The method overcomes the limit of frequency and size by using the traditional two-hydrophone method. The effect of hydrophone sensitivity on the terminal's absorbing performance is evaluated, and a correction method of reflection and transmission coefficients is also provided. Experimental results show that the absorbing coefficient in the frequency band of 100~2000 Hz is over 0.98, which is agree well with the theoretical results.