Design of a Wireless Power and Data Transfer System for pH Sensing inside a Small Tube

This work presents a passive wireless measurement system for potentiometric chemical probes inside a small laboratory tube. An inductively coupled link is utilized with DC-to-frequency signal transduction via load modulation. The wireless power transfer part of the system features advantageous flexibility in coil separation distances and stability in the frequency providing maximum power transfer, as evidenced by the couple-mode theory analysis. We then demonstrate continuous pH sensing through a cap for a 50-ml centrifuge tube. Instrumentation and resultant data are presented, showcasing excellent linearity and tunable outputs. Our approach and system architecture can be used for numerous passive wireless potentiometric sensing applications in both laboratory and industry settings, as well as other wireless sensing systems, with minor circuit modification.