Concept proof of low-energy consumption and compact ingestible thermometer based on gastric acid power generation

This paper presents system design and construction of an ingestible core body thermometer based on the generation of gastric acid power for daily monitoring of basal body temperature during sleep. A custom integrated circuit (IC) with voltage boosting, coding, modulating, and transmitting functions was prototyped. A chip-shaped gastric acid battery based on a pair of Mg and Pt thin-film electrodes was fabricated using microfabrication technology. Charge storage in a multilayer ceramic capacitor at a boosted voltage was demonstrated with the battery and boost circuit in the IC. An evaluation board of the system was also prepared. The essential electrical components were mounted on 3-pieces print circuit board with the diameter of approximately 10 mm, which suggested the possibility of miniaturizing this system to the size of a tablet. The magnetic-field coupling telecommunication of data between a small transmission coil and a loop antenna, as a receiver, was successfully demonstrated. The energy consumption for temperature measurement and transmission was low enough for multiple measurements during sleep. These results proved the feasibility of an ingestible thermometer system.