In this paper, a low-cost contactless passive sensor is designed and manufactured. The structure consists of a short-circuited printed monopole antenna coupled to two split-ring resonators. The permittivity of the materials under test is characterized within a near-field link between the sensor and a contactless reader. Concretely, the reader has been implemented by using a broadband patch antenna. The sensing principle relies on the reader detection of the notch introduced by the resonators in the power reflected by the sensor. Specifically, when a sample is placed over the sensor, the change in its effective permittivity produces a frequency shift of the notch detected in the reflection coefficient of the reader. A complete equivalent circuit model of the whole system is proposed. Moreover, the results are corroborated through full-wave simulations. Finally, the whole system is manufactured and measured. It is shown that the system can reliably detect the permittivity of the materials placed over the sensor at a distance between the reader and the sensor equal to 9.52 mm.
Keywords: Contactless system, near-field link, passive electromagnetic sensor, permittivity characterization, printed monopole antenna, split-ring resonator (SRR).
IEEE Sensors Journal. Volumen: 18 Numero: 11 Páginas: 4491-4502
Journal Impact Factor: JCR impact factor 2.617 (2017)
DOI reference: 10.1109/JSEN.2018.2826982
Publicado en papel: Junio 2018. Publicado on-line: Abril 2018.