Ultrasound Transmission Spectral Compensation Using Arbitrary Position and Width Pulse Sets

Ultrasonic testing systems are widely used for the analysis and characterization of materials. In many applications, such as ultrasonic imaging and spectroscopy, wide bandwidth, spectral flatness, and signal-to-noise ratio (SNR) are essential. The transfer function of the ultrasonic transducer is the bandwidth limiting factor. Pulse excitation has limitations in spectral coverage and achievable SNR. Spread spectrum (SS) signals combined with amplitude modulation are used to compensate the spectral losses and widen the bandwidth. Yet, SS signals require arbitrary waveform generation using digital-to-analog converters and linear power amplifiers, resulting in costly, large, and inefficient equipment. To overcome the aforementioned problems, we propose the use of bipolar arbitrary position and width pulses (APWP) sequences derived from nonlinear frequency modulated SS signals. APWP are obtained by an iterative optimization for the spectral flatness and bandwidth of the received signal. Comparisons of the proposed signals with known linear and nonlinear modulation signals are shown in terms of bandwidth and spectral flatness.