Low-Power Full-Duplex Transmit-Receive Circuits for Wearable Ultrasound Transducers

With faster computational ability and miniaturization of electronic hardware, research on wearable ultrasound technology is gaining momentum in both diagnostic and therapeutic applications. Low power operation is an important criterion for successful commercialization of these devices, which mandates the use of elongated waveforms suitable for pulse compression to optimize SNR and axial resolution. Such waveforms require a continuous transmit-receive operation, which is not possible using a diplexer circuit used in traditional pulse-echo ultrasound systems. In this paper, we have used a three-port circulator circuit designed using wideband operational amplifiers, for enabling the full-duplex mode of operation in wearable ultrasound transducers. With 50-Ohm load termination, we were able to achieve approximately 0 dB transmission characteristic over 10 MHz bandwidth and -44 to -24 dB isolation characteristic over 5-10 MHz bandwidth for different values of load termination. Finally, the full-duplex continuous transmit-receive feature of the circulator circuit was demonstrated by connecting it to a Philips D1914C Doppler transducer while imaging a cadaver human head specimen by transmitting a two-cycle sinusoidal signal and a chirp signal of 10-mu s duration with a frequency sweep of 1.3 - 2.5 MHz.