Electrolyte-based Wireless Humidity Sensor

Abstract: This master thesis was initiated in the Organic Electronics group at Linköping University within a project called ‘Brains & Bricks’. The purpose was to develop a prototype of a wireless humidity sensor with a solid polyelectrolyte as the humidity sensing material. The humidity levels can be estimated from the resonant frequency of a testing circuit. The readings were performed by a wireless method between two coils. Both the testing circuit and the simulation programs were designed in this thesis work. The operating frequency of the sensor was chosen to be in the range of 100 kHz to 200 kHz at which the solid polyelectrolyte, Polystyrene Sulfonic Acid (PSSH), was sensitive to humidity variations. Three different types of humidity sensors were fabricated and tested. These sensor heads promised for printability and low-cost manufacturing. A shift, responding to a humidity variation, in the resonant frequency of the testing circuit was detected by a reader coil which was 1 cm away from a sensor coil. These measurements matched the results simulated by a Matlab program. The feasibility of fabricating a low-cost wireless humidity sensor with a solid polyelectrolyte as humidity sensing material by printing technique was proved in the thesis work. Subsequent research will be continued to develop humidity sensors having a lateral structure and an improved performance.