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Microwave Technologies for Biomedical Applications: from Sensing to Therapy

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Biomedical Sensors".

Deadline for manuscript submissions: closed (30 November 2022) | Viewed by 31588

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Prof. Dr. Marta Cavagnaro

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Guest Editor

Department of Information Engineering, Electronics and Telecommunications Sapienza University, Via Eudossiana, 18-00184 Rome, Italy
Interests: microwave thermal ablation; antennas; dielectric properties of tissues; hyperthermia
Special Issues, Collections and Topics in MDPI journals

Dr. Lorenzo Crocco

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Guest Editor

IREA – Institute for Electromagnetic Sensing of the Environment, Via Diocleziano 328, 8014 Napoli, Italy
Interests: microwave imaging; noninvasive electromagnetic diagnostics; therapeutic applications of EM fields; forward and inverse electromagnetic scattering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent years, microwave technologies have played an ever-growing role in the field of biomedical applications, both for diagnostic and therapeutic purposes. Microwave technologies are used to noninvasively detect and image tumors or brain stroke, to monitor vital parameters such as respiratory and heart activities, to set radio link for RF-ID applications and implement point-of-care sensors. Moreover, they can are clinically exploited for anti-cancer hyperthermia or thermal ablation treatments, wherein microwave sensing can also be used to detect the temperature. The above are only a few examples of the many different uses of electromagnetic fields at microwave frequencies in the medical field. Many other emerging techniques are being developed in recent years. The design and analysis of such systems require knowledge of the dielectric behavior of biological tissues, as well as the proper modeling of the interaction between the electromagnetic fields and the biological scenario.

This Special Issue will gather a showcase of the most recent developments in Microwave Technologies for Biomedical Applications, with particular reference, but not limited, to the following topics:

- Microwave sensors;

- Numerical modelling;

- Theranostic applications;

- Bioradar;

- Point-of-care sensors;

- Hyperthermia and ablation treatments;

- Treatment monitoring;

- In vivo measurements;

- Electromagnetic diagnostics;

- Noninvasive sensors;

- Dielectric characterization of biological media;

- Electromagnetic interactions with biological media;

- Experimental validation

Prof. Dr. Marta Cavagnaro
Dr. Lorenzo Crocco
Guest Editors

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Published Papers (14 papers)

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14 pages, 3169 KiB

Open AccessArticle

Design and Validation of Experimental Setup for Cell Spheroid Radiofrequency-Induced Heating

by Ioannis Androulakis, Riccardo Ferrero, Rogier van Oossanen, Alessandra Manzin, Antonia G. Denkova, Kristina Djanashvili, Robin Nadar and Gerard C. van Rhoon

Sensors 2023, 23(9), 4514; https://doi.org/10.3390/s23094514 - 05 May 2023

Viewed by 1800

Abstract

While hyperthermia has been shown to induce a variety of cytotoxic and sensitizing effects on cancer tissues, the thermal dose–effect relationship is still not well quantified, and it is still unclear how it can be optimally combined with other treatment modalities. Additionally, it is speculated that different methods of applying hyperthermia, such as water bath heating or electromagnetic energy, may have an effect on the resulting biological mechanisms involved in cell death or in sensitizing tumor cells to other oncological treatments. In order to further quantify and characterize hyperthermia treatments on a cellular level, in vitro experiments shifted towards the use of 3D cell spheroids. These are in fact considered a more representative model of the cell environment when compared to 2D cell cultures. In order to perform radiofrequency (RF)-induced heating in vitro, we have recently developed a dedicated electromagnetic field applicator. In this study, using this applicator, we designed and validated an experimental setup which can heat 3D cell spheroids in a conical polypropylene vial, thus providing a reliable instrument for investigating hyperthermia effects at the cellular scale. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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21 pages, 9953 KiB

Open AccessArticle

Broadband Dielectric Spectroscopy with a Microwave Ablation Antenna

by Klementina Vidjak, Carolin Hessinger and Marta Cavagnaro

Sensors 2023, 23(5), 2579; https://doi.org/10.3390/s23052579 - 26 Feb 2023

Cited by 2 | Viewed by 1316

Abstract

Microwave ablation is a technique used to treat tumorous tissue. Its clinical use has been greatly expanding in the last few years. Because the design of the ablation antenna and the success of the treatment greatly depend on the accurate knowledge of the dielectric properties of the tissue being treated, it is highly valuable to have a microwave ablation antenna that is also able to perform in-situ dielectric spectroscopy. In this work, an open-ended coaxial slot ablation antenna design operating at 5.8 GHz is adopted from previous work, and its sensing abilities and limitations are investigated in respect of the dimensions of the material under test. Numerical simulations were performed to investigate the functionality of the floating sleeve of the antenna and to find the optimal de-embedding model and calibration option for obtaining accurate dielectric properties of the area of interest. Results show that, as in the case of the open-ended coaxial probe, the accuracy of the measurement greatly depends on the likeness between the calibration standards’ dielectric properties and the material under test. Finally, the results of this paper clarify to which extent the antenna can be used to measure dielectric properties and paves the way to future improvements and the introduction of this functionality into microwave thermal ablation treatments. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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16 pages, 2492 KiB

Open AccessArticle

An Effective Framework for Deep-Learning-Enhanced Quantitative Microwave Imaging and Its Potential for Medical Applications

by Álvaro Yago Ruiz, Marta Cavagnaro and Lorenzo Crocco

Sensors 2023, 23(2), 643; https://doi.org/10.3390/s23020643 - 06 Jan 2023

Cited by 10 | Viewed by 1804

Abstract

Microwave imaging is emerging as an alternative modality to conventional medical diagnostics technologies. However, its adoption is hindered by the intrinsic difficulties faced in the solution of the underlying inverse scattering problem, namely non-linearity and ill-posedness. In this paper, an innovative approach for a reliable and automated solution of the inverse scattering problem is presented, which combines a qualitative imaging technique and deep learning in a two-step framework. In the first step, the orthogonality sampling method is employed to process measurements of the scattered field into an image, which explicitly provides an estimate of the targets shapes and implicitly encodes information in their contrast values. In the second step, the images obtained in the previous step are fed into a neural network (U-Net), whose duty is retrieving the exact shape of the target and its contrast value. This task is cast as an image segmentation one, where each pixel is classified into a discrete set of permittivity values within a given range. The use of a reduced number of possible permittivities facilitates the training stage by limiting its scope. The approach was tested with synthetic data and validated with experimental data taken from the Fresnel database to allow a fair comparison with the literature. Finally, its potential for biomedical imaging is demonstrated with a numerical example related to microwave brain stroke diagnosis. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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11 pages, 3582 KiB

Open AccessArticle

Assessment of Finger Fat Pad Effect on CSRR-Based Sensor Scattering Parameters for Non-Invasive Blood Glucose Level Detection

by Chaouki Hannachi, Frédérique Deshours, George Alquie and Hamid Kokabi

Sensors 2023, 23(1), 473; https://doi.org/10.3390/s23010473 - 02 Jan 2023

Cited by 2 | Viewed by 2057

Abstract

This paper examines the effect of finger fat pad thickness on the accuracy performance of complementary split-ring resonator (CSRR)-based microwave sensors for non-invasive blood glucose level detection. For this purpose, a simplified four-layer Cole–Cole model along with a CSRR-based microwave sensor have been comprehensively analyzed and validated through experimentation. Computed scattering parameter (S-parameter) responses to different fat layer thicknesses are employed to verify the concordance of the studied model with the measurement results. In this respect, a figure of merit (FM) based on the normalized squared difference is introduced to assess the accuracy of the considered Cole–Cole model. We have demonstrated that the analyzed model agrees closely with the experimental validation. In fact, the maximum error difference for all five fingertips does not exceed 1.73 dB over the entire frequency range of interest, from 1 GHz to 4 GHz. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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13 pages, 3459 KiB

Open AccessArticle

MWA Performed at 5.8 GHz through ‘Side Firing’ Approach: An Exploratory Study

by Anna Bottiglieri, Christopher Brace, Martin O’Halloran and Laura Farina

Sensors 2022, 22(23), 9320; https://doi.org/10.3390/s22239320 - 30 Nov 2022

Viewed by 1094

Abstract

Recent studies have shown that ablation techniques have the potential to eradicate adrenal adenomas while preserving the functionalities of the adrenal gland and the surrounding anatomical structures. This study explores a new microwave ablation (MWA) approach operating at 5.8 GHz and using anatomical and dielectric characteristics of the target tissue to create directional heating patterns. Numerical simulations are executed in planar and 3D adrenal models, considering two energy doses. The numerical study is refined accounting for the vaporization of the tissue water content. Ex vivo experimental evaluations on porcine adrenal models complete the study. The numerical and experimental results show that spherical ablation zones are able to cover the target for both energy doses considered. Nonetheless, most of the non-targeted tissues can be preserved from excessive heating when low energy level is used. Numerical models accounting for water vaporization are capable to foresee the experimental temperature values. This study shows that the proposed MWA directional approach operating at 5.8 GHz can be considered for creating effective and selective ablation zones. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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15 pages, 6909 KiB

Open AccessArticle

A Highly Sensitive Molecularly Imprinted Polymer (MIP)-Coated Microwave Glucose Sensor

by Amir Hossein Omidvar, Atena Amanati Shahri, Ariana Lacorte Caniato Serrano, Jonas Gruber and Gustavo Pamplona Rehder

Sensors 2022, 22(22), 8648; https://doi.org/10.3390/s22228648 - 09 Nov 2022

Cited by 4 | Viewed by 1779

Abstract

A novel, low-cost, sensitive microwave microfluidic glucose detecting biosensor incorporating molecularly imprinted polymer (MIP) is presented. The sensing device is based on a stub resonator to characterize water glucose solutions. The tip of one of the stubs is coated with MIP to increase the selectivity of the sensor and hence the sensitivity compared to the uncoated or to the coated with non-imprinted polymer (NIP) sensor. The sensor was fabricated on a FR4 substrate for low-cost purposes. In the presence of the MIP, the sensor loaded with a glucose solution ranging from 50 mg/dL to 400 mg/dL is observed to experience an absorption frequency shift of 73 MHz when the solutions flow in a microfluidic channel passing sensing area, while the lower limit of detection (LLD) of the sensor is discovered to be 2.4 ng/dL. The experimental results show a high sensitivity of 1.3 MHz/(mg/dL) in terms of absorption frequency. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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15 pages, 5218 KiB

Open AccessArticle

Non-Contact VITAL Signs Monitoring of a Patient Lying on Surgical Bed Using Beamforming FMCW Radar

by Sungmook Lim, Gwang Soo Jang, Wonyoung Song, Baek-hyun Kim and Dong Hyun Kim

Sensors 2022, 22(21), 8167; https://doi.org/10.3390/s22218167 - 25 Oct 2022

Cited by 3 | Viewed by 2851

Abstract

Respiration and heartrates are important information for surgery. When the vital signs of the patient lying prone are monitored using radar installed on the back of the surgical bed, the surgeon’s movements reduce the accuracy of these monitored vital signs. This study proposes a method for enhancing the monitored vital sign accuracies of a patient lying on a surgical bed using a 60 GHz frequency modulated continuous wave (FMCW) radar system with beamforming. The vital sign accuracies were enhanced by applying a fast Fourier transform (FFT) for range and beamforming which suppress the noise generated at different ranges and angles from the patient’s position. The experiment was performed for a patient lying on a surgical bed with or without surgeon. Comparing a continuous-wave (CW) Doppler radar, the FMCW radar with beamforming improved almost 22 dB of signal-to-interference and noise ratio (SINR) for vital signals. More than 90% accuracy of monitoring respiration and heartrates was achieved even though the surgeon was located next to the patient as an interferer. It was analyzed using a proposed vital signal model included in the radar IF equation. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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14 pages, 4022 KiB

Open AccessArticle

Contactless Fall Detection by Means of Multiple Bioradars and Transfer Learning

by Vera Lobanova, Valeriy Slizov and Lesya Anishchenko

Sensors 2022, 22(16), 6285; https://doi.org/10.3390/s22166285 - 21 Aug 2022

Cited by 4 | Viewed by 1567

Abstract

Fall detection in humans is critical in the prevention of life-threatening conditions. This is especially important for elderly people who are living alone. Therefore, automatic fall detection is one of the most relevant problems in geriatrics. Bioradiolocation-based methods have already shown their efficiency in contactless fall detection. However, there is still a wide range of areas to improve the precision of fall recognition based on view-independent concepts. In particular, in this paper, we propose an approach based on a more complex multi-channel system (three or four bioradars) in combination with the wavelet transform and transfer learning. In the experiments, we have used several radar configurations for recording different movement types. Then, for the binary classification task, a pre-trained convolutional neural network AlexNet has been fine-tuned using scalograms. The proposed systems have shown a noticeable improvement in the fall recognition performance in comparison with the previously used two-bioradar system. The accuracy and Cohen’s kappa of the two-bioradar system are 0.92 and 0.86 respectively, whereas the accuracy and Cohen’s kappa of the four-bioradar system are 0.99 and 0.99 respectively. The three-bioradar system’s performance turned out to be in between two of the aforementioned systems and its calculated accuracy and Cohen’s kappa are 0.98 and 0.97 respectively. These results may be potentially used in the design of a contactless multi-bioradar fall detection system. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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16 pages, 3726 KiB

Open AccessArticle

Design and Characterization of an RF Applicator for In Vitro Tests of Electromagnetic Hyperthermia

by Riccardo Ferrero, Ioannis Androulakis, Luca Martino, Robin Nadar, Gerard C. van Rhoon and Alessandra Manzin

Sensors 2022, 22(10), 3610; https://doi.org/10.3390/s22103610 - 10 May 2022

Cited by 4 | Viewed by 2581

Abstract

The evaluation of the biological effects of therapeutic hyperthermia in oncology and the precise quantification of thermal dose, when heating is coupled with radiotherapy or chemotherapy, are active fields of research. The reliable measurement of hyperthermia effects on cells and tissues requires a strong control of the delivered power and of the induced temperature rise. To this aim, we have developed a radiofrequency (RF) electromagnetic applicator operating at 434 MHz, specifically engineered for in vitro tests on 3D cell cultures. The applicator has been designed with the aid of an extensive modelling analysis, which combines electromagnetic and thermal simulations. The heating performance of the built prototype has been validated by means of temperature measurements carried out on tissue-mimicking phantoms and aimed at monitoring both spatial and temporal temperature variations. The experimental results demonstrate the capability of the RF applicator to produce a well-focused heating, with the possibility of modulating the duration of the heating transient and controlling the temperature rise in a specific target region, by simply tuning the effectively supplied power. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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13 pages, 5113 KiB

Open AccessArticle

A Microwave-Based Microfluidic Cell Detecting Biosensor for Biological Quantification Using the Metallic Nanowire-Filled Membrane Technology

by Atena Amanati Shahri, Amir Hossein Omidvar, Gustavo Pamplona Rehder and Ariana Lacorte Caniato Serrano

Sensors 2022, 22(9), 3265; https://doi.org/10.3390/s22093265 - 24 Apr 2022

Viewed by 2199

Abstract

A label-free, sensitive, miniaturized sensing device was developed for detecting living cells in their flow stream. The outstanding performance of this biosensor in distinguishing living cells in cell suspension was achieved by integrating microstrip stub resonator above a microfluidic structure using the metallic nanowire-filled membrane technology. The cell suspension flows in a microfluidic channel placed between the tip of the stub resonator and its ground plane as the substrate to take advantage of the uniform and concentrated field distribution. We studied the changes in relative permittivity due to the presence of a single living cell in the phase of the transmitted signal (S₂₁). An average variation of as much as 22.85 ± 1.65° at ~11.1 GHz is observed for the living cell sensing using this optimized device. This biosensor could detect rapid flowing cells in their biological medium in real-time and hence, can be used as an early diagnosis and monitoring tool for diseases. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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25 pages, 5228 KiB

Open AccessArticle

Three-Dimensional Microwave Head Imaging with GPU-Based FDTD and the DBIM Method

by Pan Lu and Panagiotis Kosmas

Sensors 2022, 22(7), 2691; https://doi.org/10.3390/s22072691 - 31 Mar 2022

Cited by 9 | Viewed by 2245

Abstract

We present a preliminary study of microwave head imaging using a three-dimensional (3-D) implementation of the distorted Born iterative method (DBIM). Our aim is to examine the benefits of using the more computationally intensive 3-D implementation in scenarios where limited prior information is available, or when the target occupies an area that is not covered by the imaging array’s transverse planes. We show that, in some cases, the 3-D implementation outperforms its two-dimensional (2-D) counterpart despite the increased number of unknowns for the linear problem at each DBIM iteration. We also discuss how the 3-D algorithm can be implemented efficiently using graphic processing units (GPUs) and validate this implementation with experimental data from a simplified brain phantom. In this work, we have implemented a non-linear microwave imaging approach using DBIM with GPU-accelerated FDTD. Moreover, the paper offers a direct comparison of 2-D and 3-D microwave tomography implementations for head imaging and stroke detection in inhomogenous anatomically complex numerical head phantoms. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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18 pages, 3002 KiB

Open AccessArticle

A Non-Invasive Hydration Monitoring Technique Using Microwave Transmission and Data-Driven Approaches

by Deepesh Agarwal, Philip Randall, Zachary White, Bayleigh Bisnette, Jenalee Dickson, Cross Allen, Faraz Chamani, Punit Prakash, Carl Ade and Balasubramaniam Natarajan

Sensors 2022, 22(7), 2536; https://doi.org/10.3390/s22072536 - 25 Mar 2022

Viewed by 2310

Abstract

Dehydration in the human body arises due to inadequate replenishment of fluids. An appropriate level of hydration is essential for optimal functioning of the human body, and complications ranging from mild discomfort to, in severe cases, death, could result from a neglected imbalance in fluid levels. Regular and accurate monitoring of hydration status can provide meaningful information for people operating in stressful environmental conditions, such as athletes, military professionals and the elderly. In this study, we propose a non-invasive hydration monitoring technique employing non-ionizing electromagnetic power in the microwave band to estimate the changes in the water content of the whole body. Specifically, we investigate changes in the attenuation coefficient in the frequency range 2–3.5 GHz between a pair of planar antennas positioned across a participant’s arm during various states of hydration. Twenty healthy young adults (10M, 10F) underwent controlled hypohydration and euhydration control bouts. The attenuation coefficient was compared among trials and used to predict changes in body mass. Volunteers lost

1.50 \pm 0.44 %

and

0.49 \pm 0.54 %

body mass during hypohydration and euhydration, respectively. The microwave transmission-based attenuation coefficient (2–3.5 GHz) was accurate in predicting changes in hydration status. The corresponding regression analysis demonstrates that building separate estimation models for dehydration and rehydration phases offer better predictive performance (88%) relative to a common model for both the phases (76%). Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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23 pages, 9960 KiB

Open AccessArticle

MNP-Enhanced Microwave Medical Imaging by Means of Pseudo-Noise Sensing

by Sebastian Ley, Jürgen Sachs, Bernd Faenger, Ingrid Hilger and Marko Helbig

Sensors 2021, 21(19), 6613; https://doi.org/10.3390/s21196613 - 04 Oct 2021

Cited by 7 | Viewed by 2154

Abstract

Magnetic nanoparticles have been investigated for microwave imaging over the last decade. The use of functionalized magnetic nanoparticles, which are able to accumulate selectively within tumorous tissue, can increase the diagnostic reliability. This paper deals with the detecting and imaging of magnetic nanoparticles by means of ultra-wideband microwave sensing via pseudo-noise technology. The investigations were based on phantom measurements. In the first experiment, we analyzed the detectability of magnetic nanoparticles depending on the magnetic field intensity of the polarizing magnetic field, as well as the viscosity of the target and the surrounding medium in which the particles were embedded, respectively. The results show a nonlinear behavior of the magnetic nanoparticle response depending on the magnetic field intensity for magnetic nanoparticles diluted in distilled water and for magnetic nanoparticles embedded in a solid medium. Furthermore, the maximum amplitude of the magnetic nanoparticles responses varies for the different surrounding materials of the magnetic nanoparticles. In the second experiment, we investigated the influence of the target position on the three-dimensional imaging of the magnetic nanoparticles in a realistic measurement setup for breast cancer imaging. The results show that the magnetic nanoparticles can be detected successfully. However, the intensity of the particles in the image depends on its position due to the path-dependent attenuation, the inhomogeneous microwave illumination of the breast, and the inhomogeneity of the magnetic field. Regarding the last point, we present an approach to compensate for the inhomogeneity of the magnetic field by computing a position-dependent correction factor based on the measured magnetic field intensity and the magnetic susceptibility of the magnetic particles. Moreover, the results indicate an influence of the polarizing magnetic field on the measured ultra-wideband signals even without magnetic nanoparticles. Such a disturbing influence of the polarizing magnetic field on the measurements should be reduced for a robust magnetic nanoparticles detection. Therefore, we analyzed the two-state (ON/OFF) and the sinusoidal modulation of the external magnetic field concerning the detectability of the magnetic nanoparticles with respect to these spurious effects, as well as their practical application. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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Review

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38 pages, 1564 KiB

Open AccessReview

Ultra-Wideband Antennas for Biomedical Imaging Applications: A Survey

by Umair Rafique, Stefano Pisa, Renato Cicchetti, Orlandino Testa and Marta Cavagnaro

Sensors 2022, 22(9), 3230; https://doi.org/10.3390/s22093230 - 22 Apr 2022

Cited by 16 | Viewed by 3481

Abstract

Microwave imaging is an active area of research that has garnered interest over the past few years. The main desired improvements to microwave imaging are related to the performances of radiating systems and identification algorithms. To achieve these improvements, antennas suitable to guarantee demanding requirements are needed. In particular, they must operate in close proximity to the objects under examination, ensure an adequate bandwidth, as well as reduced dimensions and low production costs. In addition, in near-field microwave imaging systems, the antenna should provide an ultra-wideband (UWB) response. Given the relevance of the foreseen applications, many UWB antenna designs for microwave imaging applications have been proposed in the literature. In this paper, a comprehensive review of different UWB antenna designs for near-field microwave imaging is presented. The antennas are classified according to the manufacturing technology and radiative performances. Particular attention is also paid to the radiation mechanisms as well as the techniques used to reduce the size and improve the bandwidth. Full article

(This article belongs to the Special Issue Microwave Technologies for Biomedical Applications: from Sensing to Therapy)

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