Signal-to-noise ratio and bandwidth for pseudo-random codes in ultrasonic imaging system

Abstract

This study is concerned about the transducer excitation waveform in the ultrasonic imaging system to improve signal-to-noise ratio (SNR) and resolution under the constraint of a fixed system bandwidth and of detection of objects close to the transmitter/receiver. The waveforms considered are wideband unmodulated pseudo-random code (UPC), the modulated pseudo-random code(MPC), and deconvoluted pseudo-random code (DPC). From the computer simulation and experimental investigation, we see that the UPC system is inferier with respect to SNR but superier with respect to the bandwidth, to the MPC system. This systems from the fact that the UPC has a broader spectrum bandwidth than the bandwidth of the system itself and hence results in a wider bandwidth for the detected signal, while the SNR does not improve significantly due to the power transmission utilization. In contrast, the MPC has a power spectrum which matches to the system bandwidth and hence the bandwidth of the detected/signal is reduced while SNR is improved. It was also found that the DPC results in the best performance. In the DPC system the power spectrum of the correlator output is a function of only the window and the input UPC. The Hamming window holds widest bandwidth, and the Blackman window holds highest SNR.