Sample Tube pH Monitoring via Passive Powering and Communication

This paper presents the application of a simple, inductively-coupled potentiometric pH measurement system into the cap of standard laboratory sample tubes, thus enabling continuous, wireless monitoring of a bevy of samples. The system is powered by a compact Class E amplifier using inductive coupling via a designed resonance frequency of 1 MHz. Signals are transmitted back via load modulation at frequencies a fraction of the power carrier frequency, thus allowing for extraction of the signal frequency. Results are demonstrated which clearly show that modulation frequency tracks closely with open circuit potential, and the system as a whole features good sensitivity and linearity. This system holds promise for a host of applications.