Binary Phase Coded Excitation Ultrasound Improve The Signal To Noise Ratio Is Detected Based On Pulse Compression

Ultrasonic imaging is considered to be an convenient,effective,cheap diagnosing means,and it has been widely used in the domain of medical diagnosing.Due to the limitation of the tissue's bioeffets,the amplitude of the single pulse used in traditional single pulse excitation mode is limited, the penetration depth and resolution can not be obtained in the same time.Through using the large time-bandwidth product signal which is usually applied in radar system,the paradox of the penetration depth and resolution can be well resolved in ultrasonic detection and ultrasonic imaging,the SNR(signal to noise ratio)of the echo can be enhanced significantly after pulse compression with the same resolution compared with the single pulse excitation,and the penetration depth is been increased, the quality of the traditional ultrasonic imaging is been elevated,and coded excitation has become a hot spot in the medical ultrasonic diagnosing research.In this study, considering the equivalent bandpass filterting property of the transducer, a series of bi-phase coding signals have been used to excite the transducer in simulation and experiment research, the matched filter and mismatched filter have been designed. The transducer effect on the exciting signals in time and frequency domain is analyzed,and curve fitting is used to analyze the SNR gain loss and the resolution loss caused by the trandcucer effect on the pulse compression result.The optimum exciting signal is chosen to experiment in the multi-target environment after the modulation parameter is optimized.This study covers the following aspects:(1) Different from the bi-phase coding signal modulated by base code in the traditional coded excitation imaging, this study uses the bi-phase coding signal modulated by the sine carrier to excite the transdcucer, and the matched filter and mismatched filter used for pulse compression is designed. Considering the bi-phase coding signal's property, also the echo signal is processed by matched filter and mismatched filter.(2) The bi-phase coding signal used in experiment is produced by the arbitrary waveform editing software which can control the arbitrary waveform generator through personal computer to transmit the designed signal to excite the transducer. Then the received echo signal is processed through matched filter and mismatched filter,the SNR gain after pulse compression is analyzed. (3) Considering the equivalent bandpass filterting property of the transducer, the barker code signals with each chip modulated by different period number of sine carrier are used to excite the transducer, for simulation and experiment the echo is processed in time and frequency domain. Considering the SNR gain and resolution loss,the transducer effect on the pulse compression result is analyzed.The optimum exciting signal is chosen for the following research.(4) Considering the complex echo during the multi-target environment, the transducer is excited by the optimum signal, and the echo signal reflected by four target wires is processed through pulse compression technique. After pulse compression, four narrow pulse which has large amplitude is obtained, and the result of the SNR and resolution after pulse compression compared with the single pulse mode is analyzed.The results of this study shows that:(1) From the analysis result of the transducer effect on both the exciting signal itself and the pulse compression result,we can infer that the frequency spectrum and energy of the exciting signal decreases after passing the transducer.Compared with the ideal pulse compression result without considering the transducer effect,the property of the actual pulse compression result is degraded, its SNR gain and resolution both decrease.After the modulation parameter is optimized considering the transducer frequency spectrum property,the 13 bit barker code signal with each chip modulated by 3 period sine carrier is chosen to be the optimum signal to excite the transducer.(2) The optimum signal is chosen to excite the transducer during the multi-target environment, after using the matched filter and mismatched filter to compress the echo reflected by four target wires, we can obtain the compressed signal which has nearly-40dB PSL.The SNR of the echo can be enhanced significantly with the same resolution using bi-phase coded excitation and pulse compression technique compared with the traditional single pulse excitation mode,it can detect the weak signal submerged in the background noise,it proves that coded excitation and pulse compression technique can be well applied in the domain of ultrasonic imaging system.