When time reversal technique is used in phased array high intensity focused ultrasound system to obtain self-adaptive focusing, it is needed to calculate the initial phase of the sources. Because of the frequency shifting when the phase lock loop is initiated, different results are gotten in different segments using conventional methods.

In order to solve the problem, WANG Junlin, Wang Xiaodong and XIAO Ling of Institute of Acoustics, Chinese Academy of Sciences carried out a series of studies and put forward a new method of calculating the phase difference.

The researchers first conducted the frequency measurement of the collected signals. Through computation, they got the sine and cosine functions of the emission and the received signals, respectively. Then they conducted trigonometrically transform of these four functions to get the phase difference of the emission and received signals. The new method can display the changes of phase difference in real-time, the steady phase differences can be regarded as the initial phase of the sources. The experimental results show that using the phase difference obtained by this method can get a better distribution of sound field in some spatial extent.