Split-Ring-Shaped Biodegradable pH Sensor for Wireless and Battery-Free Monitoring of Agricultural Fields

This paper describes a pH sensor for soil monitoring that is composed of fully biodegradable materials in the soil. Our biodegradable pH sensor is composed of only two key elements: One is a magnesium electromagnetic antenna that dissolves in water, and the other is a protection layer of hydroxyapatite that decomposes in response to pH. This sensor works as an electromagnetic split-ring resonator (metamaterial) that reflects electromagnetic waves with specific frequency in GHz band, enabling in wireless remote sensing without any electric circuits or batteries. We demonstrated wireless pH detection of soil for aiming to realize an environmentally friendly monitoring sensor that does not require collection after installation.