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

Abstract

Abstract-A compact sensing pixel for the determination of the localized complex permittivity at microwave frequencies is proposed. Implemented in 40-nm CMOS, the architecture comprises a square patch, interfaced to the material-under-test (MUT) 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-IF 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 0.15×0.3 mm 2 , allowing for future compact arrays of multiple sensors that facilitate 2-D dielectric imaging based on permittivity contrast.

Validation of a Broadband Tissue-Equivalent Liquid for SAR Measurement and Monitoring of Its Dielectric Properties for Use in a Sealed Phantom

“…The possibility of sensing through the polymer wall of the tank with a large-sized coaxial probe placed externally (i.e., a multilayer geometry [23]) was considered, but modelling showed that for the type of tank used for SAR measurement (wall thickness 2-mm), the measurement uncertainty would be unacceptably large. The possibility of using a resonance method [24][25][26], based on a device that has a split-ring or similar structure, was considered. While such devices are interesting, they were considered not to be well suited to the present application.…”

A 5×5 Microwave Permittivity Sensor Matrix in O.14-m CMOS

“…Miniaturized material permittivity measurements are gaining interest in various biomedical applications, including tissue and blood examination at bulk or single-cell level, in order to detect diseases and abnormalities such as cancer [1]. Although various standalone permittivity sensor implementations in CMOS technology have achieved accurate permittivity detection at GHz frequencies [2] [3], existing sensor matrixes have only been designed for frequencies below 100 MHz [4] [5]. Despite the difficulties inherent to a microwave matrix design, the incentive to move towards high-frequency broadband implementations derives from the flexibility to choose the frequency with the highest dielectric contrast, and the higher sensitivity achievable using redundant wideband data.…”