A free-space microwave nondestructive testing and evaluation module is developed for the low-power, non-ionizing, contactless, and real-time characterization of doped composite thin-film materials in an industrial context. The instrumentation proposed is built up with a handled vector network analyzer interfaced with corrugated horn antennas to measure the near-field complex reflection S₁₁ of planar prepreg composite materials in a roll-to-roll in-line production line. Dedicated modeling and calibrations routines are developed to extract the microwave conductivity from the measured microwave signal. Practical extraction of the radiofrequency (RF) conductivity of thin film prepreg composite materials doped with nano-powders is exemplary shown at the test frequency of 10 GHz.

This paper reports the development of a new composite material as a matching medium for medical microwave diagnostic systems, where maximizing the microwave energy that penetrates the interrogated tissue is critical for improving the quality of the diagnostic images. The proposed material has several advantages over what is commonly used in microwave diagnostic systems: it is semi-flexible and rigid, and it can maximize microwave energy coupling by matching the tissue’s dielectric constant without introducing high loss. The developed matching medium is a mirocomposite of barium titanate filler in polydimethylsiloxane (PDMS) in different weight-based mixing ratios. Dielectric properties of the material are measured using a Keysight open-ended coaxial slim probe from 0.5 to 10 GHz. To avoid systematic errors, a full dielectric properties calibration is performed before measurements of sample materials. Furthermore, the repeatability of the measurements and the homogeneity of the sample of interest are considered. Finally, to evaluate the proposed matching medium, its impact on a printed monopole antenna is studied. We demonstrate that the permittivity of the investigated mixtures can be increased in a controlled manner to reach values that have been previously shown to be optimal for medical microwave imaging (MWI) such as stroke and breast cancer diagnostic applications. As a result, the material is a good candidate for supporting antenna arrays designed for portable MWI scanners in applications such as stroke detection.

An electrochemical quartz crystal microbalance (EC-QCM) is a versatile gravimetric technique that allows for parallel characterization of mass deposition and electrochemical properties. Despite its broad applicability, simultaneous characterization of two electrodes remains challenging due to practical difficulties posed by the dampening from fixture parasitics and the dissipative medium. In this study, we present a dual electrochemical QCM (dual EC-QCM) that is employed in a three-electrode configuration to enable consequent monitoring of mass deposition and viscous loading on two crystals, the working electrode (WE) and the counter electrode (CE). A novel correction approach, along with a three standard complex impedance calibration, is employed to overcome the effect of dampening while keeping high spectral sensitivity. Separation of viscous loading and rigid mass deposition is achieved by robust characterization of the complex impedance at the resonance frequency. Validation of the presented system is done by cyclic voltammetry characterization of Ag underpotential deposition on gold. The results indicate mass deposition of 412.2 ng for the WE and 345.6 ng for the CE, reflecting a difference of the initially-present Ag adhered to the surface. We also performed higher harmonic measurements that further corroborate the sensitivity and reproducibility of the dual EC-QCM. The demonstrated approach is especially intriguing for electrochemical energy storage applications where mass detection with multiple electrodes is desired.

One-port reflection calibration is a widely used technique for RF and microwave VNA measurements in a broad range of applications including on-wafer chip testing, production testing, and microwave imaging. Recent developments in the field of antenna tuning components lead to advanced, highly stable MEMS-based variable capacitors. In this study we present the use of an antenna tuning integrated circuit (IC) for realizing a compact and fast transfer standard for one-port calibration. In contrast to traditional Short-Open-Load methods a new workflow that uses different capacitance states was developed. Together with least-squared-error solving this leads to improved calibration performance. Verification against metrology grade standards showed agreement of less than -45 dB vector difference. In addition, an estimation of the expected S-parameter error due to temperature deviations was performed. The new calibration workflow can be used in applications where multiple ports need to be calibrated fast and accurate.

Accurate knowledge of material dielectric properties is fundamental for numerous applications, varying from the characterization of manufactured electrical components to the development of numerical human models, and the design of novel electromagnetic medical devices. Material dielectric properties in the microwave frequency range are generally measured with an open-ended coaxial probe connected to a network analyzer (NA). Although the calibration of the dielectric measurement system has been standardized, there are numerous sources of errors that can compromise the quality of dielectric measurements, such as imprecise measurement calibration, NA drift, system perturbation, and NA internal trace noise. The internal trace noise of NA is generally estimated by repeated measurements on the same material under the same condition. Alternatively, in this work, the internal trace noise of the NA has been taken from the NA datasheet and directly translated into permittivity random error and compared with the measured permittivity random error. Comparison between the two methods suggests the use of low intermediate frequency bandwidth in order to reduce dielectric measurement errors due to trace noise of NA.