Spectrum Compensation for Time-Reversal Method on Ultrasonic Target Detection Using Pulse Compression

This paper discusses a method of time reversal (TR) for target detection using a signal with a higher signal-to-noise ratio (SNR) and higher resolution. To acquire a signal with a higher SNR and broader spectrum, we have proposed a sensitivity-compensated (SC) signal. In this paper, we propose three types of SC-for-TR signals. An SC-amplitude-modulated (AM)-for-TR signal and an SC-frequency-modulated (FM)-for-TR signal are calculated using squared spectrum compensation. Moreover, to enhance the transmitting energy of a time-reversed wave for a higher SNR, we propose an SC-amplitude-and-frequency-modulated-for-TR (SCAFM-for-TR) signal. The SCAFM-for-TR signal is calculated by AM and FM for deriving a TR wave with a constant envelope waveform and compensated spectrum. In this paper, the efficiency of the SC-for-TR signals is investigated on target ranging in water using pulse compression. Accordingly, the SC-for-TR signals derive a pulse compressed signal with a higher resolution. In addition, the precision of target ranging using the SCAFM-for-TR signal is greater than that using the other SC-for-TR signals at an arrangement when a target was fixed at a position where a signal with a lower SNR is received. These results show that the measurements using the SC-for-TR signals improve time resolution and the SNR.