Title: Ultrasound Data Communications for Ultra-low-power Wake-up in Sensor Nodes
Description: In the power-starved wireless sensor node application, the main transceiver has to be duty-cycled to prolong the node battery lifetime. Wake-up is among the lowest power schemes to accomplish this; an always ON low-power receiver called the wake-up receiver is used to turn ON the main receiver when needed. In this thesis, we have demonstrated ultra-low-power wake-up by using through-air wireless ultrasound. We have achieved more than an order of magnitude reduction in wake-up receiver power consumption, compared to conventionally used radio frequencies. An ultra-low-power ultrasonic wake-up receiver IC was designed in a 65-nm CMOS process and has a power consumption of only 4.4 uW. For the proof-of-concept prototype demonstrated in this work, the digital back-end circuits were been implemented on a commercial FPGA. An ultrasound data network consisting of three receivers and one transmitter was set up in a lecture hall. For a transmit power of 27 uW, less than 10 % of the wake-up packets, at 1 pkt/s, were missed at each of the three receivers.

All the system blocks: receiver IC, ultrasound communication channel and TX-RX transducer pair, were individually characterized in different environments to understand the interaction between the electrical and mechanical domains. Also presented are techniques for increasing the distance ranges of wireless ultrasound and communication schemes for extending the use of ultrasound to environments where line-of-sight communication is not possible.