A novel compact microstrip resonant dielectric permittivity sensor with dual-band operation is presented in this paper. The circuit makes use of a single stepped-impedance-resonator as the sensing element, working at the 2.45-GHz and 5.8-GHz ISM bands, under differential and common modes, respectively. Sensitivity of the circuit and resonator coupling at each band can be configured independently. Moreover, testing of the sample is done by using a single sensing region without the need of duplicating the sample location. Experimental measurements are carried out using a very small amount of liquids and the results are presented validating the theory. This work delivers a compact, reusable, label-free and non-destructive microwave device and paves a way for sensing dielectric properties of chemicals with accuracy due to the dual-band performance.

A novel microstrip directional filter for multiplexing applications is presented. This device uses composite right-left-handed transmission lines and resonators to achieve dual-band frequency response. In addition, by cascading two or more stages using dual frequency immitance inverters, multi-pole configurations can be obtained. Simulation and experimental results are presented with good agreement.

An analysis of the complex dielectric permittivity of rum ʻHavana Club Añejo 3 Añosʼ and its mixtures with methanol, ethanol, and deionized water is presented in this work. Measurements are carried out using the open-ended coaxial probe technique within a frequency range from 500 MHz to 15 GHz. Curves of the real and imaginary parts as well as the permittivity spectra (Cole–Cole diagram) and relaxation parameters of the liquids-under-test are presented. Distribution of the relaxation parameters for the different inclusion levels is analyzed and modelled. Comparison between the measured data and permittivity mixture theory is carried out; comments on the accuracy of each are discussed. A validation of the measurement process is realized by means of an evaluation of the experimental and literature dielectric permittivity values.

The λ/2 strip-resonator directional filter has good balance between compactness and robustness against manufacturing error. However, there have been difficulties in generalizing the strip-resonator directional filter to realize multipole filtering responses. This paper presents the theory, experiments, and improvement of a new structure of strip-resonator directional filter based on a band-reject filter. This new structure allows the realization of multipole responses and theoretically does not limit the types of filter responses. A three-pole elliptic directional filter prototype is studied thoroughly to show that its performance can be predicted accurately by a conventional filter structure. We also propose a modification of the delay-line part using composite right-/left-handed transmission line to improve the isolation. An isolation level of 30 dB is shown to be achieved consistently.

Human body communication (HBC) technologies have vast potential in the healthcare landscape. This work focuses on Magnetic Human Body Communication (MHBC), supporting for the first time that this technique is more efficient when planar inductors are used as transceivers. A systematic study was performed to establish the most appropriate way to excite the signal into the human body to improve the channel usability and provide a design criterium for transceiver designers. Furthermore, a physical-based model is proposed and tested against channel measurements, obtaining excellent experiment-model correlation at frequencies up to 20 MHz.

The identification of different plastic materials in pellet form using a microwave negative-order-resonance sensor along with the evaluation of classification algorithms from machine learning is presented in this paper. Operation of the sensor is within the unlicensed ISM 2.5 GHz band, and identification of the materials is based on the measured resonant parameters from the sensor. Several classifiers are used to process the resonant parameters having uncertainty factors involved in pellet measurements (air gaps, pellet positions, dimensions and shapes), and performance comparison between the algorithms is carried out in terms of accuracy in the classification. Moreover, the presented measurement method is proposed as a fast, non-destructive, and low-power consumption way to identify plastic raw materials using a low-profile circuit having a high potential of being used in industrial processes.