A Compact Double-Folded Substrate Integrated Waveguide Re-Entrant Cavity for Highly Sensitive Humidity Sensing

In this study, an ultra-compact humidity sensor based on a double-folded substrate integrated waveguide (SIW) re-entrant cavity was proposed and analyzed. By folding a circular re-entrant cavity twice along its two orthogonally symmetric planes, the designed structure achieved a remarkable size redu...

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Bibliographic Details
Published in:Sensors (Basel, Switzerland) Switzerland), 2019-07, Vol.19 (15), p.3308
Main Authors: Wei, Zhihua, Huang, Jie, Li, Jing, Li, Junshan, Liu, Xuyang, Ni, Xingsheng
Format: Article
Language:English
Subjects:
Design
Electric fields
folded SIW
Humidity
humidity sensor
microwave
Permeability
Perturbation theory
re-entrant cavity resonator
Relative humidity
Resonant frequencies
Sensitivity
Sensors
Size reduction
Substrate integrated waveguides
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Summary:In this study, an ultra-compact humidity sensor based on a double-folded substrate integrated waveguide (SIW) re-entrant cavity was proposed and analyzed. By folding a circular re-entrant cavity twice along its two orthogonally symmetric planes, the designed structure achieved a remarkable size reduction (up to 85.9%) in comparison with a conventional TM -mode circular SIW cavity. The operating principle of the humidity sensor is based on the resonant method, in other words, it utilizes the resonant properties of the sensor as signatures to detect the humidity condition of the ambient environment. To this end, a mathematical model quantitatively relating the resonant frequency of the sensor and the relative humidity (RH) level was established according to the cavity perturbation theory. The sensing performance of the sensor was experimentally validated in a RH range of 30%-80% by using a humidity chamber. The measured absolute sensitivity of the sensor was calculated to be 135.6 kHz/%RH, and the corresponding normalized sensitivity was 0.00627%/%RH. It was demonstrated that our proposed sensor not only has the merits of compact size and high sensitivity, but also benefits from a high Q-factor and ease of fabrication and integration. These advantages make it an excellent candidate for humidity sensing applications in various fields such as the agricultural, pharmaceutical, and food industries.
ISSN:1424-8220
1424-8220
DOI:10.3390/s19153308