Application of Golay codes and piezoelectric ultrasound transducer to biomedical noninvasive measurement

Golay codes posses the property that combining the products of the two individual codes of the pair causes the self-induced noise to cancel out. This gives significant improvements in the signal to noise ratio obtained with short codes in signal to noise ratio enhancement systems, making the codes useful in biomedical Doppler applications. The present work combines these codes with an experimental piezoelectric ultrasound transducer in a water bath. It is shown that the resulting signal-to-noise-ratio improvements are greatest when the input-signal-to-noise ratio is greater than unity and the target is obscured by clutter. This system can be used to send multiple codes, with code identification after detection, to extend the range-velocity limit in medical Doppler systems. It is also shown that pulse shape integrity is important in these systems, and that the required bandwidth is large. Transducers using polyvinylidene fluoride (PVDF) sensor material are shown to give increased pulse integrity and bandwidth in comparison with PZT