UC Berkeley

Temperature measurements find use in clinical settings for the monitoring of various disease states, and the monitoring of deep tissue temperature patterns in both space and time can provide valuable information about tissue health. Unfortunately, current clinical methods are not suitable for continuous monitoring of temperature measurements. Recently, acoustically-powered implants have been emerging as a method to enable small medical devices that can be implanted deep in the tissue. In this thesis, we demonstrated the development of two versions of implantable temperature sensors that we call thermal dust. Thermal dust motes are ultrasonically-powered, ultrasonically-communicating sensors, and were demonstrated as both a passive sensor mote and an active sensor mote. We designed passive thermal dust motes using only commercial off-the-shelf (COTS) components, and these sensors were fully sub-millimeter in all of their dimensions. We showed experimentally that passive thermal dust motes were able to encode temperature data using analog amplitudebackscatter modulation. Active thermal dust motes consist of a custom integrated circuit (IC) that we designed in a TSMC 0.18 μm biCMOS process. We experimentally demonstrated the operation of our thermal dust chip in the physiologically-relevant temperature range of 30 – 50°C as well as an elevated temperature range of 60 – 80°C to demonstrate the versatility of our device. Finally, we showed that the binary duty cycle modulation of the backscatter waveform envelope is a feasible method to encode temperature data, and we demonstrated fully wireless operation of an active thermal dust device.