Ultra-wideband Microwave Imaging Research Articles

An Ultra-Wide Band MIMO Antenna System with Enhanced Isolation for Microwave Imaging Applications.

This paper introduces a novel two-port ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna system with enhanced isolation characteristics. The antenna, designed on a thin 0.787 mm RO5880 substrate, achieves a compact form factor of 52 × 26 mm2 and offers a wide bandwidth of 9.2 GHz (2.3 GHz to 11.5 GHz) while meeting the VSWR 2:1 criterion. Notably, the proposed antenna demonstrates an impressive increase in isolation, up to 16 dB, through the integration of a shared radiator with small rectangular slots, effectively reducing interference and improving overall performance. Furthermore, a comprehensive analysis of additional MIMO performance parameters, including the envelope correlation coefficient (ECC) and diversity gain, confirms their satisfactory limits, validating the potential of the proposed UWB-MIMO antenna for various UWB applications. The time domain analysis of the UWB antenna is also analyzed, and results are found to be within satisfactory limits. Simulation and measurement results further support the practicality and effectiveness of the antenna design, highlighting its compact size, wide bandwidth, and enhanced isolation characteristics, positioning it as a promising solution for advanced UWB microwave imaging systems.

A Novel Corner Etched Rectangular Shaped Ultrawideband Antenna Loaded with Truncated Ground Plane for Microwave Imaging

Microwave imaging has become a popular research issue in recent decades as a result of its several benefits over traditional imaging technologies. To analyze biological tissues in depth, a microwave imaging instrument is employed. The test determines the presence and location of morphological alterations in specific biological tissues. Ultrawideband (UWB) microwave imaging is a new technique that produces improved results while avoiding the use of ionizing radiation. Antennas play a critical part in these systems, and as a result, antenna optimization has become a hot topic due to the device's proximity to the human body. Recent research has revealed a number of initiatives to improve the electromagnetic sensors employed in these systems, whether as single or array components. In this article, the development of a compact ultrawideband (UWB) antenna functioning in the frequency range of 3.25–14.63 GHz is proposed. The reported antenna comprises of a rectangular patch and a modified ground plane "etched on an FR4" substrate excited by a 50 Ω feed line. The overall dimension of the antenna is 0.44 {lambda }_{0}times 0.38 {lambda }_{0}times 0.02{lambda }_{0}. The proposed antenna has been fabricated on FR-4 substrate. Measured and simulated results are in good agreement. The proposed antenna is compact and displays good radiation characteristics along with good gain.

Microwave Imaging Approach for Breast Cancer Detection Using a Tapered Slot Antenna Loaded with Parasitic Components

In this paper, a wideband antenna is proposed for ultra-wideband microwave imaging applications. The antenna is comprised of a tapered slot ground, a rectangular slotted patch and four star-shaped parasitic components. The added slotted patch is shown to be effective in improving the bandwidth and gain. The proposed antenna system provides a realized gain of 6 dBi, an efficiency of around 80% on the radiation bandwidth, and a wide impedance bandwidth (S11 < -10 dB) of 6.3 GHz (from 3.8 to 10.1 GHz). This supports a true wideband operation. Furthermore, the fidelity factor for face-to-face (FtF) direction is 91.6%, and for side by side (SbS) is 91.2%. This proves the excellent directionality and less signal distortion of the designed antenna. These high figures establish the potential use of the proposed antenna for imaging. A heterogeneous breast phantom with dielectric characteristics identical to actual breast tissue with the presence of tumors was constructed for experimental validation. An antenna array of the proposed antenna element was situated over an artificial breast to collect reflected and transmitted waves for tumor characterization. Finally, an imaging algorithm was used to process the retrieved data to recreate the image in order to detect the undesirable tumor object inside the breast phantom.

Investigation and Analysis of EM Pulse Propagation Inside Human Head for High-Resolution UWB Elliptical SAR Imaging

In this paper, an ultra-wideband (UWB) microwave imaging system based on an elliptical synthetic aperture radar (ESAR) is proposed as a possible solution for human head imaging. The system along with the image reconstruction method operates in the time domain. We have adopted the global back-projection technique to an elliptical trajectory of data acquisition, to shape around the head. A miniaturized, low profile custom-designed, UWB patch antenna capable of operating in the proximity of the head tissues is used as a sensor. The antenna aperture impedance is matched to the head tissues to enable pumping radiating electromagnetic waves into the human head needles of any coupling liquid. The impact of operational bandwidth and radiated power on system key performance factors i.e., penetration depth, range-resolution, and safety aspects are fully investigated based on calculations as well as full-wave simulations. It is observed that by increasing the bandwidth of radiated pulse from 0.8∼2.8 GHz (which was used in most of the previous works) to 1.0∼5.2 GHz, the range resolution can be improved remarkably from 23.0 mm to 16.0 mm deep inside the head. However, further increase in operational bandwidth will not improve the resolution of the system and a significant fraction of the radiated power will be dissipated in the brain tissues. To demonstrate the system performance, a constellation of 12 antenna elements is placed in an elliptical shape directly attached to the 3D phantom to acquire the raw data using full-wave simulations. Finally, an image from a 3D MRI-derived phantom is reconstructed to validate the imaging capability of the designed system. The proposed system can be used as a tool for early diagnosis as well as for treatment monitoring while getting therapy like chemo or radiotherapies.

Concealed Object Detection With Microwave Imaging Using Vivaldi Antennas Utilizing Novel Time-Domain Beamforming Algorithm

A time-domain novel beamforming algorithm for ultra-wideband (UWB) microwave imaging is furnished in this paper. A monostatic and bistatic antenna setup is utilized to transmit and receive custom UWB pulses. This setup is employed to image various metallic and non–metallic threats attached to a human body. The imaging results demonstrate that the proposed beamforming algorithm allows effective reconstruction of different targets for both monostatic and bistatic cases. An ultra-wideband high gain Antipodal Vivaldi Antenna (AVA) is used as the transducer for the proposed imaging setup. The designed transducer demonstrates measured impedance bandwidth from 660 MHz to 15 GHz (182%) with a peak gain of 15 dBi at 8 GHz. The quality and accuracy of the proposed beamforming algorithm is tested outside the anechoic chamber just to make it more convincing in a real-world dynamic scenario. The result shows that different concealed materials can be detected accurately with the beamforming algorithm. To the best of the authors’ knowledge, the proposed algorithm can effectively add up the target responses to obtain a clear and distinct image of the metallic and non-metallic targets.

Developing Artefact Removal Algorithms to Process Data from a Microwave Imaging Device for Haemorrhagic Stroke Detection.

In this paper, we present an investigation of different artefact removal methods for ultra-wideband Microwave Imaging (MWI) to evaluate and quantify current methods in a real environment through measurements using an MWI device. The MWI device measures the scattered signals in a multi-bistatic fashion and employs an imaging procedure based on Huygens principle. A simple two-layered phantom mimicking human head tissue is realised, applying a cylindrically shaped inclusion to emulate brain haemorrhage. Detection has been successfully achieved using the superimposition of five transmitter triplet positions, after applying different artefact removal methods, with the inclusion positioned at 0, 90, 180, and 270. The different artifact removal methods have been proposed for comparison to improve the stroke detection process. To provide a valid comparison between these methods, image quantification metrics are presented. An “ideal/reference” image is used to compare the artefact removal methods. Moreover, the quantification of artefact removal procedures through measurements using MWI device is performed.

Classification of breast tumor models with a prototype microwave imaging system.

The assessment of the size and shape of breast tumors is of utter importance to the correct diagnosis and staging of breast cancer. In this paper, we classify breast tumor models of varying sizes and shapes using signals collected with a monostatic ultra-wideband radar microwave imaging prototype system with machine learning algorithms specifically tailored to the collected data. A database comprising 13 benign and 13 malignant tumor models with sizes between 13 and 40mm was created using dielectrically representative tissue mimicking materials. These tumor models were placed inside two breast phantoms: a homogeneous breast phantom and a breast phantom with clusters of fibroglandular mimicking tissue, accounting for breast heterogeneity. The breast phantoms with tumors were imaged with a monostatic microwave imaging prototype system, over a 1-6GHz frequency range. The classification of benign and malignant tumors embedded in the two breast phantoms was completed, and tumor classification was evaluated with Principal Component Analysis as a feature extraction method, and tuned Naïve Bayes (NB), decision trees (DT), and k-nearest neighbours (kNN) as classifiers. We further study which antenna positions are better placed to classify tumors, discuss the feature extraction method and optimize classification algorithms, by tuning their hyperparameters, to improve sensitivity, specificity and the receiver operating characteristic curve, while ensuring maximum generalization and avoiding overfitting and data contamination. We also added a realistic synthetic skin response to the collected signals and examined its global effect on classification of benign vs malignant tumors. In terms of global classification performance, kNN outperformed DT and NB machine learning classifiers, achieving a classification accuracy of 96.2% when classifying between benign and malignant tumor phantoms in a homogeneous breast phantom (both when the skin artifact is and is not considered). We experimentally classified tumor models as benign or malignant with a microwave imaging system, and we showed a methodology that can potentially assess the shape of breast tumors, which will give further insight into the correct diagnosis and staging of breast cancer.

3-D experimental UWB microwave imaging in dispersive media

ABSTRACTThree-dimensional (3D) microwave imaging in very dispersive media using a phase shift and sum (PSAS) algorithm is presented. The phase shift and amplitude attenuation within the dispersive media are compensated individually for each frequency component and then integrated to calculate the pixel values in the region of interest (ROI). Therefore, the multi-speed and multipath issue when an ultra-wide band (UWB) signal propagates in the dispersive media is overcome. The current approach is validated by lab-collected data using our self-developed 3-D UWB microwave measurement system. Image results are compared with prior arts at the end of this paper.

EARLY DETECTION OF BREAST CANCER USING ULTRA WIDE BAND SLOT ANTENNA

Breast cancer is the transformation of normal cells in the breast area into a malignant tumor, which is the second largest disease as a cause of death for women. Early detection is one way to avoid significant risks in breast cancer. X-ray mammography and magnetic resonance imaging (MRI) techniques are used to detect breast cancer. However, those techniques have several limitations. Ultra-wideband (UWB) microwave imaging, approved by The Federal Communications Commission (FCC) in the United States, has promising capabilities in detecting breast cancer. Microwave imaging uses a microstrip antenna that has the advantage of convenience, potentially low cost, and is a non-ionized and safe alternative. In this paper, the ultra-wideband microstrip antenna for breast cancer detection is proposed. The antenna was designed by adding some rectangular slots on a rectangular patch to meet the UWB specifications. The antenna works well at 8.41 GHz to 10.29 GHz with directivity of 6.451 dBi and SAR value of 1.6 W / kg. The antenna was simulated with breast phantom. The tumor sizes of 6 mm and 10 mm are added to evaluate the E/H fields and current density with and without tumor. The highest E-Field value of 928.8 V / m was obtained at 10 GHz with a 10 mm tumor size. The highest H-Field value of 4.06 V / m was achieved at 10 GHz with a 6 mm tumor size. From the simulation, the E/H-field and current density are higher if there is a tumor in the breast compared to the breast without the tumor.

A Parasitic Resonator-Based Diamond-Shaped Microstrip Antenna for Microwave Imaging Applications

This study proposes a new parasitic resonator-based diamond-shaped microstrip patch antenna for ultra-wideband microwave imaging applications. The antenna consists of a diamond-shaped radiating patch, partial ground plane, and four-star shape parasitic elements. The use of parasitic elements improves the antenna performance in terms of the bandwidth and gain. The proposed prototype has a compact dimension of 30 × 25 × 1.6 mm3. The antenna achieves an overall bandwidth (S11&lt;-10dB) of 7.6 GHz (2.7–10.3 GHz) with more than 4 dBi realized gain and 80% efficiency across the radiating bandwidth. The modified structures of the design extended the usable upper frequency from 9.7 GHz to 10.3 GHz, and the lower frequency is decreased from 3.4 GHz to 2.7 GHz with maintaining the omnidirectional radiation pattern. The design and simulation of the antenna are performed in the 3D electromagnetic simulator CST Microwave Studio. The proposed antenna is used for breast phantom measurement system to analyze the variation of backscattering signal and transmit-received pulses. The observation during the analysis of the numerical and measured data reveals that the designed antenna is a suitable candidate for ultra-wideband (UWB)-based microwave imaging applications.

A Time-Domain Measurement System for UWB Microwave Imaging

A fully automatic time-domain measurement system for ultra-wideband (UWB) microwave imaging is presented. The system uses a pair of movable antennas to transmit and receive custom UWB pulse designs with each antenna able to be independently controlled to rotate about a region of interest. A full measurement, consisting of both incident and total field collections, is completed within 20 min using custom software. The collected data is processed to reconstruct images of three test objects. Imaging results demonstrate the system can localize and recognize different shaped objects, and differentiate multiple objects. The precision of antenna positioning and the impact of random noise on the microwave signal are investigated. The maximal positioning error for the antennas allows for accurate use of the system up to 7 GHz. A comparison between the time-domain system and a frequency-sweep method shows both methods allow for accurate imaging results. The signal-to-noise ratio and image quality may be improved with time-domain results when properly selecting a time window for the received signal.

LUNG TUMOUR DETECTION USING ULTRA-WIDEBAND MICROWAVE IMAGING APPROACH

The use of Ultra-Wideband (UWB) microwave imaging for tumour detection has gained increasing popularity within the bio-medical field. Microwave imaging turned out more efficiently accurate to some body parts such as breast and brain imaging. This work presents on the possibility and the effectiveness of UWB microwave imaging technique on lung tumour detection. Simple technique of using reflection method was studied and then applied for lung tumour detection by using UWB antenna. The simulated results show that the proposed method is capable to detect a lung tumour with minimum radius size of 4 mm for different positions inside the lungs at the frequency of 3.67 GHz. It is a promising technique to be further developed in modern UWB imaging systems which demand perfect results at very low cost.Keywords: ultra-wideband; microwave imaging; lung tumour; Antenna.

Development of an ultra-wideband, stable and high-directive monopole disc antenna for radar-based microwave imaging of breast cancer

ABSTRACTRadar-based ultra-wideband (UWB) microwave imaging (MI) system has recently attracted considerable attention for detection of breast cancer at early stage. A key component of the system is the sensor (antenna) that is used to radiate and receive the UWB pulses. In this study, a compact-size, UWB, directive, and microstrip-fed planar circular disc monopole antenna (PCDMA) with modified L-shaped ground plane for the radar-based UWB MI system is developed. Analysis and the performance optimization of the proposed antenna are performed by HFSS software. In the development process of the antenna design, some modifications such as adjusting feed point, adding parasitic element, slot, notches are made on the conventional PCDMA to improve the bandwidth, directivity and half-power beamwidth (HPBW) of the antenna. After obtaining the optimum parameters, the proposed antenna is fabricated and then tested by using Vector Network Analyser. Impedance bandwidth of the designed antenna covers the broad frequency range of 3–10 GHz (108%) for Return Loss < –10 dB. The good stability of the directional radiation patterns is obtained in the 3–10 GHz. The direction of the maximum radiation moves from 32° to 54° and HPBW decreases from 56° to 30° through the frequency band. The directivity changes between 6.2 and 9.4 dB in the 3–10 GHz. Results confirm that the proposed antenna is suitable for using in radar-based UWB MI of the breast cancer.

Compressive sensing for microwave breast cancer imaging

The long time for collecting the data and a considerable amount of data are important technical challenges in microwave imaging for the detection of breast cancer. From the other point of view, compressive sensing (CS) is an interesting representation and analysis of sparse signals. In this study, a new imaging method for monostatic ultra-wideband microwave imaging of breast cancer using CS is presented. Instead of using all of the conventional radar returned signals, a few received signals, by random choosing the antenna, are sufficient for obtaining reliable images even at high noise levels. Using simulations done, it is shown that sparser images are obtained comparing to the delay-and-sum beamforming technique using only a few received signals.

A Time-Reversal Imaging System for Breast Screening: Theory and Initial Phantom Results.

In this paper, a working ultrawideband (UWB) microwave imaging (MI) system using basic techniques is proposed to detect and localize a tumor model. The system harnesses the time reversal-decomposition of time reversal operator (DORT) signal processing method. We suggest a modified background Green's function and suitable spiral antennas for time reversal imaging of a breast cancer tumor. In this method, scatterings from a breast phantom are measured. Then, reflected signals are processed using the decomposition of time reversal (TR), known under French acronym DORT, algorithm. In a conventional TR imaging method, free-space Green's function is used for detection. However, in the present method, we employ cylindrical Green's functions of a two-layer medium. This makes a better model of the background medium for TR-DORT imaging. Also, the performance of TR-DORT detector against signal to clutter ratio, and its ability to detect and localize different shapes, sizes, and permittivity values of breast tumor are discussed. Furthermore, a fatty tissue phantom model is used to verify the results experimentally. The MI system is tested to localize a tumor within the breast Debye phantom at the frequency range of 3.1-10.6GHz. The experimental results show the validity of our proposed system.

A Compact Modified Square Printed Planar Antenna for UWB Microwave Imaging Applications

In this paper, both frequency and time domain performances of a new compact planar antenna for the ultra-wideband (UWB) applications are fully investigated. The proposed antenna has the size of 12x18 mm² providing a fractional bandwidth more than 128123% (3.057 GHz to 13.98 GHz, S11<-10 dB). The results show that the proposed antenna performances in term of wide bandwidth, small size, gain and radiation pattern, transmission coefficient and system fidelity factor are very satisfactory. Moreover, by fabricating and testing the proposed antenna, the simulation results are fairly verified.

Automated modification and fusion of voxel models to construct body phantoms with heterogeneous breast tissue: Application to MRI simulations.

Human voxel models incorporating detailed anatomical features are vital tools for the computational evaluation of electromagnetic (EM) fields within the body. Besides whole-body human voxel models, phantoms representing smaller heterogeneous anatomical features are often employed; for example, localized breast voxel models incorporating fatty and fibroglandular tissues have been developed for a variety of EM applications including mammography simulation and dosimetry, magnetic resonance imaging (MRI), and ultra-wideband microwave imaging. However, considering wavelength effects, electromagnetic modeling of the breast at sub-microwave frequencies necessitates detailed breast phantoms in conjunction with whole-body voxel models. Heterogeneous breast phantoms are sized to fit within radiofrequency coil hardware, modified by voxel-wise extrusion, and fused to whole-body models using voxel-wise, tissue-dependent logical operators. To illustrate the utility of this method, finite-difference time-domain simulations are performed using a whole-body model integrated with a variety of available breast phantoms spanning the standard four tissue density classifications representing the majority of the population. The software library uses a combination of voxel operations to seamlessly size, modify, and fuse eleven breast phantoms to whole-body voxel models. The software is publicly available on GitHub and is linked to the file exchange at MATLAB® Central. Simulations confirm the proportions of fatty and fibroglandular tissues in breast phantoms have significant yet predictable implications on projected power deposition in tissue. Breast phantoms may be modified and fused to whole-body voxel models using the software presented in this work; user considerations for the open-source software and resultant phantoms are discussed. Furthermore, results indicate simulating breast models as predominantly fatty tissue can considerably underestimate the potential for tissue heating in women with substantial fibroglandular tissue.

MRI-aided tissues interface characterization: An accurate signal propagation time calculation method for UWB breast tumor imaging

Radar-based ultrawideband (UWB) microwave imaging is expected to be a safe, low-cost tool for breast cancer detection. However, since radar wave travels at different speeds in different tissues, propagation time is hard to be estimated in heterogeneous breast. Wrongly estimated propagation time leads to error of tumor location in resulting image, aka imaging error. In this paper, we develop a magnetic resonance imaging-aided (MRI-aided) propagation time calculation technique which is independent from radar imaging system but can help decrease the imaging error. The technique can eliminate the influence of the rough interface between fat layer and gland layer in breast and get relative accurate thicknesses of two layers. The propagation time in each layer is calculated and summed. The summed propagation time is used in Confocal imaging algorithm to increase the accuracy of resulting image. 25 patients’ breast models with glands of varying size are classified into four categories for imaging simulation tests. Imaging accuracy in terms of tumor location along x-direction has been improved for 21 among 25 cases, as a result, overall around 50% improvement compared to conventional UWB imaging.

A high performance UWB antenna design for microwave imaging system

ABSTRACTIn this paper, a new design of ultra‐wideband (UWB) antenna is reported for a microwave imaging system aimed to cover the UWB bandwidth from 3.1 to 10.6 GHz. The structure has a very simple Hibiscus petal pattern patch with tapered microstrip fed a line and partial trapezoid ground plane. The gap between the Hibiscus petal pattern patch and partial ground of the antenna are optimized to achieve wide impedance bandwidth. Results show that the antenna has a fractional bandwidth of about 120% from 3.04 to 11 GHz with S11 &lt; −10 dB with stable omnidirectional radiation pattern. The average gain of proposed prototype is 5.1 dBi and the radiation efficiency is about 85% on an average over the bandwidth. The fidelity factor for face to face is 0.8469 and for side by side is 0.9232 which represent the lower distortion of signal. The characteristics of proposed antenna are successfully simulated, prototyped and measured. Fairly good agreements between the simulations and measurements have been achieved. The reported antenna has a better impedance match and mutual coupling that provides a practical approach to realize the antenna for the UWB microwave imaging system. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1824–1831, 2016

An Efficient Image Reconstruction Method for Breast Cancer Detection Using an Ultra-Wideband Microwave Imaging System

ABSTRACTMicrowave breast imaging uses backscattered radar signals to identify cancerous tissue within the breast. It is a non-invasive technique and uses non-ionizing radiation; it is currently a potential alternative for classical techniques. This article presents an efficient image reconstruction method for breast cancer detection using an ultra-wideband microwave imaging system. This method consists of applying the improved version of the delay-and-sum algorithm and post-processing the resultant images. For that, we have used a numerical 3D breast phantom in CST software simulation tool (CST Inc., 2014). The breast was illuminated with ultra-wideband (UWB) pulse from a number of antenna locations, and then collected reflections were synthetically focused to create an energy map of the breast. A new algorithm is also introduced that post-processes the resulting images obtained through different configurations of acquisition point positions. This post-process allows a much clearer image to be obtained with less interference. In the constructed and post-processed image, the presence and location of single and double breast cancer tumors of 2 mm in diameter can clearly be identified.