Contactless pH Measurement Based on High Resolution Enhanced Q Microwave Resonator
In this paper, it is shown that contactless pH sensing is enabled using high-resolution ultra-high Q microwave sensor. The platform is based on a passive planar resonator, which operates at 2.6 GHz and is reinforced by a positive active feedback circuitry. The positive feedback loop compensates the power loss of the sensor and, as a result, provides an extremely high quality-factor and selectivity enabling noncontact sensing of small complex permittivity variation. Solutions with various pH levels in the range of 1 to 10 have been detected distinctively. The sensor demonstrates a frequency shift of 275 kHz when the pH of the liquid changes from neutral pH (pH=7) to pH=1.