Passively powered pH sensor for study of gastric disorders

Abstract

A fully passive wireless implantable pH sensor that is implantable in an animate silicone stomach environment has been developed for the study of gastric disorders. The system has applications in medical training and testing. It can be used for pH monitoring as well as testing the efficiency of antacid medication. To achieve this, wireless power is sent from a reading circuit, via a class E amplifier connected to an inductive coil. The implanted circuit harvests the energy sent with a charge pump, and returns the measured pH via Frequency Shift Keying (FSK) modulation. The electronic components were simulated using Keysight Advanced Design System (ADS), prototyped on breadboards, amended, and finally manufactured onto Printed Circuit Boards (PCBs). To make the stomach, an injection molding process was employed using a sacrificial wax inner core and a 3D printed mold. The completed stomach model features 5mm thick walls at life-size scale, and demonstrates realistic digestive motion. The current implant design uses a traditional pH probe for proof of concept, fits within the stomach at 2.5cm by 5cm, and is capable of returning readings at a distance of up to 4 inches with an accuracy within 0.2pH. The reader coil can read pH once every ten minutes for 43 hours on a single charge.