A sub-sampling pulse-resonance OOK modulated digital ultrasound communication system for biomedical IoT

Abstract

A pulse-resonance On-Off keying ultrasound communication microsystem is presented. It is a viable alternative to today's widely used RF technologies in order to avoid the associated health risks for a specific group of interest, namely babies. Special signal processing and circuit techniques are proposed to overcome drawbacks of classical ultrasound communications; such as echoes and excess ringing, achieving a measured communication range of 28m with a 50bit/is data rate and bit error rate (BER) of 0.01. Targeting a biomedical sensory pacifier, the proposed design needs to be insulated, small size, and low power. Utilizing a 40 kHz ultrasound transducer and a 5-pin low-power controller, a wirelessly-charged high-accuracy remote temperature sensor system with nominal average current consumption of 0.416 mu A is designed and tested. Multiple subsystems were merged in total volume of 12mm diameter and 15mm height, excluding the charging coil, which is designed as the pacifier's handler. Thanks to echo avoidance, ringing suppression, dynamic detection threshold adjustment techniques along with 3-bit preamble synchronization; the proposed low-power sub-sampling IQ demodulation of OOK bits results in high-sensitivity robust ultrasound communication system without any alignment requirement for the transducers. The lifetime of the sensor prototype with 8mAh LiR battery is about 27 months.