A 40-nm CMOS Complex Permittivity Sensing Pixel for Material Characterization at Microwave Frequencies

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A compact sensing pixel for the determination of the localized complex permittivity at microwave frequencies is proposed. Implemented in the 40-nm CMOS, the architecture comprises a square patch, interfaced to the material-under-test sample, that provides permittivity-dependent admittance. The patch admittance is read out by embedding the patch in a double-balanced, RF-driven Wheatstone bridge. The bridge is cascaded by a linear, low-intermediate frequency switching downconversion mixer, and is driven by a square wave that allows simultaneous characterization of multiple harmonics, thus increasing measurement speed and extending the frequency range of operation. In order to allow complex permittivity measurement, a calibration procedure has been developed for the sensor. Measurement results of liquids show good agreement with theoretical values, and the measured relative permittivity resolution is better than 0.3 over a 0.1-10-GHz range. The proposed implementation features a measurement speed of 1 ms and occupies an active area of 0.15x0.3 mm², allowing for future compact arrays of multiple sensors that facilitate 2-D dielectric imaging based on permittivity contrast.
Original languageEnglish
Pages (from-to)1619-1634
Number of pages16
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number3
Publication statusPublished - 2018

Bibliographical note

Accepted Author Manuscript


  • Biomedical sensors
  • bridge circuits
  • complex permittivity measurement
  • integrated microwave circuits
  • micro-wave sensors

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