This paper introduces the design and fabrication of a microwave contactless sensor used to detect the presence of millimetric inclusions in a biological medium for biomedical applications. The hardware system comprises a self-resonant planar spiral coil (sensing element) inductively coupled to an external concentric single loop probe (reading probe), working at 648 MHz. The microwave sensor configuration relies on the Q-factor maximization of the spiral coil, i.e., the sensing element, through an optimization process, to obtain a stronger sensitivity and, thus, a millimeter resolution for the inclusions’ detection. The detection is achieved by recording both the amplitude variation and the frequency shift of the input impedance of the reading probe. In order to validate the proposed solution, full-wave simulations have been performed to design and preliminary evaluate the radiating system performance in detecting millimetric biological inclusions. As an applicative example, we focus on air bubbles detection in hemodialysis procedures; in particular, we carried out the experimental verification by employing an Agar phantom to replicate the dielectric characteristics of the blood tissue and PLA samples of various sizes to represent the air inclusions. We proved that the theoretical assumptions were in excellent agreement with both the numerical and experimental results, encouraging further analysis for the potential use of such sensor in biomedical applications. Indeed, the radiating device can be very helpful for all the operations where it is necessary to detect the presence of undesired and dangerous contaminants in a contactless way, making the procedure safer for patients.

Resonant inductive Wireless Power Transfer (WPT) offers a practical solution for supplying energy to consumer, industrial and medical devices. However, conventional WPT systems face severe limitations if one is interested to the dynamic and arbitrary control of the magnetic field distribution. Consequently, our paper explores the design and implementation of an electronically reconfigurable 5×5 magnetic metasurface for low-frequency WPT applications, operating at 3 MHz. The reconfigurable array is excited by a resonant transmitting coil operating in its near-field region. Through an analytical approach, the metasurface operation can be arbitrarily driven, obtaining the unit-cells current distribution which optimally reshapes the magnetic field for a desired application. In addition, the method also enables the precise determination of capacitive loads of each unit-cell for effectively synthetizing the metasurface response. Then, the reconfigurability process is accomplished by integrating varactor diodes within each unit-cell, providing real-time control of the currents pattern across the metasurface according to the analytical approach outputs. Finally, numerical simulations and experimental measurements on a fabricated prototype are presented, fully demonstrating the system's capability to efficiently switch between arbitrary configurations, either concentrating the magnetic field in specific areas or creating a uniform distribution. This dynamic adaptability addresses important challenges in WPT, such as reduction in alignment sensitivity and efficiency loss over distance, with enhanced flexibility, reliability, and safety.

This work presents an electromagnetic exposure intercomparison among representative human models with different body features (i.e., height, weight, and age) and genders when exposed to near-field, high-power, and broadband devices. Such devices are commonly used in the military field for communication and jamming purposes. With the aim of obtaining accurate and detailed whole-body-averaged (WBA) specific absorption rate (SAR) and 10-g SAR evaluations, a realistic scenario is numerically simulated. Three different antenna configurations are adopted, faithfully reproducing the radiative characteristics and operative frequency bands of similar devices (40–2,700 MHz). Then, we equally expose in the working band three different human body models (Hugo, Duke, and Ella). The obtained results show that the WBA-SAR is mainly related to the total body weight, as expected from its definition. Conversely, the 10-g SAR varies along with the frequency range, and different results are observed for each human model. Guidelines for exposure reduction and physical considerations are also presented. This study can be a useful reference for conducting complete and accurate radio-frequency (RF) dosimetry analysis for such particular and high-risk devices, differentiating the study for different genders and body shapes of human body models.

Structural composite materials have gained significant appeal because of their ability to be customized for specific mechanical qualities for various applications, including avionics, wind turbines, transportation, and medical equipment. Therefore, there is a growing demand for effective and non-invasive structural health monitoring (SHM) devices to supervise the integrity of materials. This work introduces a novel sensor design, consisting of three spiral resonators optimized to operate at distinct frequencies and excited by a feeding strip line, capable of performing non-destructive structural strain monitoring via frequency coding. The initial discussion focuses on the analytical modeling of the sensor, which is based on a circuital approach. A numerical test case is developed to operate across the frequency range of 100 to 400 MHz, selected to achieve a balance between penetration depth and the sensitivity of the system. The encouraging findings from electromagnetic full-wave simulations have been confirmed by experimental measurements conducted on printed circuit board (PCB) prototypes embedded in a fiberglass-based composite sample. The sensor shows exceptional sensitivity and cost-effectiveness, and may be easily integrated into composite layers due to its minimal cabling requirements and extremely small profile. The particular frequency-coded configuration enables the suggested sensor to accurately detect and distinguish various structural deformations based on their severity and location.

In this study, we present a wearable sensing system for monitoring the physiological status of damaged biological tissues based on a flexible, frequency-coded electromagnetic spiral resonator array. The physiological parameter evaluation is performed in a contactless way, avoiding the placing of electronically active elements directly upon the patient’s skin, thus ensuring safety and comfort. Firstly, we report in detail the physical principles behind the sensing strategy: a passive array is interrogated through an actively fed external single-loop probe that is inductively coupled with the double-layer spiral unit cells. The variation in the physiological parameters influences the array response, thus providing sensing information, due to the different complex dielectric permittivity values related to the tissue status. Moreover, the proposed frequency-coded approach allows for spatial information on the lesion to be retrieved, thus increasing the sensing ability. In order to prove the validity of this general methodology, we created a numerical test case, designing a practical implementation of the wearable sensing system working at a radiofrequency regime (10–100 MHz). In addition, we also fabricated prototypes, exploiting PCB technology, and realized stratified phantoms by incorporating opportune additives to control the dielectric properties. The numerical results and the experimental verification demonstrated the validity of the developed sensing strategy, showing satisfying agreement and, thus, proving the good sensibility and spatial resolution of the frequency-coded array. These results can open the path to a radically novel approach for self-care and monitoring of inflamed status and, more generally, for wearable sensing devices in biomedical applications.