ID Integrated Batteryless Wireless Digital pH Sensor

Abstract

In this paper, an identification integrated pH sensor tag is presented for wireless pH sensing applications. Two electrodes based on silver/silver chloride and antimony/antimony oxide were fabricated using the standard lithography process. The electrode pair showed a linear response for different pH solutions ranging from 4.3 to 10.7 with a sensitivity of 46 mV/pH. The passive pH sensor tag was implemented using a transceiver antenna, an energy harvesting circuit and a low power digital modulation circuit. The digital modulation circuit generates an identification and converts the analog pH voltage into 8-bit digital bits. The pH sensor tag demonstrated wireless digital bit transfer at a data rate of 0.595 Kbps. No external battery power is required to activate and operate the sensor tag and hence the sensor tag is passive in nature. In a complete wireless measurement setup, a read range of 45 cm was achieved for the sensor tag at transmit power of 15 dBm. The prototype was fabricated by integrating sensor and discrete components on top of a low cost PCB.