Development of Tablet-Shaped Ingestible Core-Body Thermometer Powered by Gastric Acid Battery

In this paper, we have developed a tablet-shaped ingestible core-body temperature sensor based on gastric acid power generation for daily health care. A custom integrated circuit (IC), which had voltage boosting, bit-rate conversion, coding, modulating, and transmitting functions, was prototyped for the feasibility study of this system. A pair of Mg and Au electrodes was chosen as the negative and positive electrodes for the gastric acid battery, respectively. The battery with a diameter of 2 mm in an artificial gastric juice generated approximately 1.2 V of output voltage. Subsequently, it successfully boosted the generated voltages to more than 3.5 V by the custom IC and demonstrated the charging of a multilayer ceramic capacitor at the boosted voltage within a reasonably short time. The feasibility of mass production of the Mg thin-film-based battery on a print circuit board (PCB) was also verified through sputter deposition of a Mg thin film on a Au pad of a PCB. Next, electrical components of diameter approximately 7 mm were mounted on the PCBs and compactly packaged with a resin. Consequently, a tablet-shaped device of diameter 10 mm and height 8 mm was prototyped as a specimen for a telemetry experiment. Finally, we successfully demonstrated that the temperature data measured by the device in pork were transferred to a commercially available loop antenna as a receiver at a distance of more than 20 cm via magnetic-field coupling telecommunication. This achievement paves the way to realizing a safe and ingestible core-body thermometer for daily use.