An oscillator based active bridge circuit for converting capacitance change into frequency for capacitive humidity sensor

Abstract

A simple signal conditioning circuit for converting capacitance change into frequency for capacitive humidity sensors is presented. It is based on a relaxation oscillator in which output frequency is linearly related to the capacitive unbalance of an active bridge. The design, analysis, and experimental results of the circuit and its application to a sol gel thin film porous -Al 2 O 3 based humidity sensor are reported. Experimental results confirm the theoretical value predicted. The circuit covering wide capacitance measurement range has the potential for remotely monitoring measurement parameters accurately.

Substrate integrated circular cavity resonator filled with nano-fibrillated cellulose for humidity detection

“…To comply with the requirements of the current in demand humidity sensing performance requirements, most of the humidity sensors on the market are active [1,2] and integrate within their structures materials which are sensitive to humidity such as dielectric [3,4], inorganic polymers [5,6], alumina thin films [7], etc. However, due to the complex challenge of integrating power supply, analog to digital converters (ADC) and amplifiers, a great deal of effort has been made to develop passive sensors.…”