Microwave temperature measurement in microfluidic devices.

In spite of various existing thermometry methods for microfluidic applications, it remains challenging to measure the temperature of individual droplets in segmented flow since fast moving droplets do not allow sufficient exposure time demanded by both fluorescence based techniques and resistance temperature detectors. In this contribution, we present a microwave thermometry method that is non-intrusive and requires minimal external equipment. This technique relies on the correlation of fluid temperature with the resonance frequency of a microwave sensor that operates at a GHz frequency range. It is a remote yet direct sensing technique, eliminating the need for mixing fluorescent dyes with the working fluid. We demonstrated that the sensor operates reliably over multiple tests and is capable of both heating and sensing. It measures temperature to within ±1.2 °C accuracy and can detect the temperature of individual droplets.