| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 104 === Quadrature phase shift is required in the ultrasound transmit end for harmonic Golay encoding. Nonetheless, typical 3-level square transmit waveform fails to reproduce the 90° phase shift and thus the resultant harmonic code is not exactly encoded as the phased-inverted symbols of +1 and -1. This introduces coding error and subsequent range side lobe artifacts after complementary decoding. In this work, pulse-width-modulation (PWM) of phased arbitrary transmit waveforms is applied for complementary Golay encoding to suppress peak range side lobe level (PRSL). Results show that, among 3-level waveforms, PWM transmit with high sampling rate (fs = 100f0) provides the lowest PRSL but the PRSL increases rapidly when the sampling rate decreases. Compared to the typical square wave, the PRSL of PWM transmit could be even higher if the sampling rate is lower than 20 times f0. A novel orthogonal Golay decoding technique is also developed by using two mutually orthogonal Golay transmit pairs to eliminate the coding error from incomplete phase inversion in Golay encoding. Results indicate that the orthogonal decoding can improve the B-mode image contrast by 9.5 dB by removing side lobe artifacts in the anechoic cyst region, compared to the conventional matched decoding.
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