Microwave sensors: a new sensing principle. Application to humidity detection

We are presenting here a new approach to gas sensor, using the electromagne tic (e.m) properties variation of some sensitive materials in the presence of gas at ultrahigh frequencies (ca. 1 GHz). The chemical sensor basically consists of a microwave resonator to which a sensitive coating is added. Th e e.m perturbation can be seen through a frequency variation measurement wh en the sensor serves as feedback element in an oscillator chain. After the development of a narrow-band-pass filter, a permittivity variation study is done, thanks to an e.m simulator HP-MDS. Then a humidity sensor is designe d and rested. A good sensitivity as well as a great reversibility are obtai ned. (C) 2000 Elsevier Science S.A. All rights reserved.