P3J-4 Binary Waveform Design for Coded Excitation in High Frequency Ultrasound

An approach to designing binary codes suitable for high-frequency applications of coded excitation is proposed. For a high-frequency ultrasound system, transmitting well-designed binary codes with a low sampling ratio (i.e., the bit rate divided by the transducer center frequency) is a practical way to improve the signal-to-noise ratio. While one conventional approach designs codes using a base sequence that modulates wideband sequences up to the transducer passband, the proposed approach searches all the codes that match the transducer passband using a genetic algorithm. The technique was tested using a bit rate of 5 MHz and a sampling ratio of 2; a low frequency was used due to limitations of the experimental equipment, but the results can be extended to higher frequencies. For a transducer with an ideal Gaussian frequency response with a center frequency of 2.5 MHz and a -6-dB bandwidth of 1.5 MHz, the signal-to-noise ratio for the same sidelobe extent was 1 to 6 dB higher for the codes designed using the proposed approach compared with those designed using the conventional approach. When a real transducer response with a center frequency of 2.40 MHz and a one-way -6-dB bandwidth of 1.48 MHz was considered, the codes designed using the proposed approach were superior by 1 to 5 dB. Therefore, our approach is better than the conventional approach for designing binary codes for high-frequency ultrasound, in which a low sampling ratio is practically desired