Development Of An Accurate Benchmarking System For Microwave Breast Imaging

This thesis is a discussion of the design and implementation of benchmarking system for microwave imaging systems. The current benchmarking tools for microwave imaging setups are not adaptable. A novel method for of the development of a dielectric phantom using regression analysis is presented. This is followed by a discussion of the design of a novel sensor for the purpose of in vivo dielectric properties measurements. The goal is to provide information for microwave tomography algorithms and phantom development based on in vivo dielectric properties of breast tissues Through the progress of this research two major novel advances have been made toward producing a better microwave imaging benchmark. First, a technique for systematically developing a breast phantom using regression analysis has been developed. This defines a process for researchers to produce a phantom quickly and easily, avoiding the simple trial and error development techniques of the past. Secondly, a method for measuring dielectric constant of a material through an embedded sensor was developed. Both advances are very important in producing accurate phantoms, providing in vivo tissue properties for tomography algorithms and designing matching materials for microwave imaging

Conformal antenna-based wireless telemetry system for capsule endoscopy

Capsule endoscopy for imaging the gastrointestinal tract is an innovative tool for carrying out medical diagnosis and therapy. Additional modalities beyond optical imaging would enhance current capabilities at the expense of denser integration, due to the limited space available within the capsule. We therefore need new designs and technologies to increase the smartness of the capsules for a given volume. This thesis presents the design, manufacture and performance characterisation of a helical antenna placed conformally outside an endoscopic capsule, and the characterisation in-silico, in-vitro and in-vivo of the telemetry system in alive and euthanised pigs. This method does not use the internal volume of the capsule, but does use an extra coating to protect the antenna from the surrounding tissue and maintain biocompatibility for safe use inside the human body. The helical antenna, radiating at 433 MHz with a bandwidth of 20 MHz within a muscle-type tissue, presents a low gain and efficiency, which is typical for implantable and ingestible medical devices. Telemetry capsule prototypes were simulated, manufactured and assembled with the necessary internal electronics, including a commercially available transceiver unit. Thermistors were embedded into each capsule shell, to record any temperature increase in the tissue surrounding the antenna during the experiments. A temperature increase of less than 1°C was detected for the tissue surrounding the antenna. The process of coating the biocompatible insulation layer over the full length of the capsule is described in detail. Data transmission programmes were established to send programmed data packets to an external receiver. The prototypes radiated at different power levels ranging from -10 to 10 dBm, and all capsules demonstrated a satisfactory performance at a data rate of 16 kbps during phantom and in-vivo experiments. Data transmission was achieved with low bit-error rates below 10-5. A low signal strength of only -54 dBm still provided effective data transfer, irrespective of the orientation and location of the capsule, and this successfully demonstrated the feasibility of the system

Antennas And Wave Propagation In Wireless Body Area Networks: Design And Evaluation Techniques

Recently, fabrication of miniature electronic devices that can be used for wireless connectivity becomes of great interest in many applications. This has resulted in many small and compact wireless devices that are either implantable or wearable. As these devices are small, the space for the antenna is limited. An antenna is the part of the wireless device that receives and transmits a wireless signal. Implantable and wearable antennas are very susceptible to harmful performance degradation caused by the human body and very difficult to integrate, if not designed properly. A designer need to minimize unwanted radiation absorption by the human body to avoid potential health issues. Moreover, a wearable antenna will be inevitably exposed to user movements and has to deal with influences such as crumpling and bending. These deformations can cause degraded performance or a shifted frequency response, which might render the antenna less effective. The existing wearable and implantable antennas’ topologies and designs under discussion still suffer from many challenges such as unstable antenna behavior, low bandwidth, considerable power generation, less biocompatibility, and comparatively bigger size. The work presented in this thesis focused on two main aspects. Part one of the work presents the design, realization, and performance evaluation of two wearable antennas based on flexible and textile materials. In order to achieve high body-antenna isolation, hence, minimal coupling between human body and antenna and to achieve performance enhancement artificial magnetic conductor is integrated with the antenna. The proposed wearable antennas feature a small footprint and low profile characteristics and achieved a wider -10 dB input impedance bandwidth compared to wearable antennas reported in literature. In addition, using new materials in wearable antenna design such as flexible magneto-dielectric and dielectric/magnetic layered substrates is investigated. Effectiveness of using such materials revealed to achieve further improvements in antenna radiation characteristics and bandwidth and to stabilize antenna performance under bending and on body conditions compared to artificial magnetic conductor based antenna. The design of a wideband biocompatible implantable antenna is presented. The antenna features small size (i.e., the antenna size in planar form is 2.52 mm3), wide -10 dB input impedance bandwidth of 7.31 GHz, and low coupling to human tissues. In part two, an overview of investigations done for two wireless body area network applications is presented. The applications are: (a) respiratory rate measurement using ultra-wide band radar system and (b) an accurate phase-based localization method of radio frequency identification tag. The ultimate goal is to study how the antenna design can affect the overall system performance and define its limitations and capabilities. In the first studied application, results indicate that the proposed sensing system is less affected and shows less error when an antenna with directive radiation pattern, low cross-polarization, and stable phase center is used. In the second studied application, results indicate that effects of mutual coupling between the array elements on the phase values are negligible. Thus, the phase of the reflected waves from the tag is mainly determined by the distance between the tag and each antenna element, and is not affected by the induced currents on the other elements

Evaluating a breast tumor monitoring vest with flexible UWB antennas and realistic phantoms:a proof-of-concept study

Abstract. The introduction provides an overview of the global significance of breast cancer as a health concern and the limitations of existing breast cancer screening methods. It introduces the concept of microwave-based breast cancer monitoring and highlights the promising findings from a previous research paper. The objective of the master thesis is presented, which is to develop and evaluate a self-monitoring vest equipped with UWB antennas and channel analysis to overcome the limitations of current screening methods and enable regular breast cancer monitoring from home. The "Background and Literature Review," provides a comprehensive overview of the relevant topics related to microwave techniques for breast cancer detection. It starts by discussing the anatomy of the female breast, highlighting the importance of understanding its structure for effective tumor detection. The section then delves into the microwave properties of the human breast, elucidating the interactions between microwaves and breast tissue. The basic principle of microwave channel analysis is explained, emphasizing its significance in detecting breast tumors. Furthermore, the advantages of microwave-based tumor detection methods are explored, showcasing their potential for improved breast cancer screening. Various microwave techniques used in breast cancer detection, including microwave tomography and radar-based UWB microwave imaging, are discussed, along with different self-monitoring vests integrated with UWB antennas. This section serves as a foundation for the subsequent chapters of the thesis, providing a comprehensive background and literature review to support the research and development of the practical self-monitoring vest for early detection of small-sized breast tumors. The "Preparation of Tissue Phantoms" section in the master’s thesis explores the comprehensive methodology for creating tissue phantoms that replicate the dielectric properties of various human tissues. While the section primarily focuses on fat tissue, it also acknowledges the existence of other phantom types. The outlined approach involves careful ingredient selection, formulation development, fabrication techniques, and stability evaluation for the creation of skin, muscle, fat, tumor, and gland tissue phantoms. By following these procedures, researchers can successfully produce tissue phantoms that closely mimic the properties of real human tissues. These phantoms serve as essential tools for investigating microwave-based applications in medical diagnostics and provide a reliable and versatile platform for further research in the field. The third section discusses the assembly of heterogeneous breast phantoms used for evaluating the performance of the tumor detection vest. The phantoms consisted of outer and inner molds, with the outer molds resembling the shape of a prone human breast. Two breast density types, representing very dense and less dense breasts, were used. For the dense breast phantoms, liquid fat material was solidified in the outer molds, and a glandular liquid was poured into the inner mold, with tumors inserted and covered with additional glandular liquid. For the less dense breast phantoms, fat liquid was solidified in the outer molds, and cylindrical glandular molds were inserted. A skin layer and muscle layer were added to complete the assembly, accurately simulating the composition and structure of a breast. This realistic breast phantom assembly allowed for accurate measurements and evaluation of the vest’s performance under different breast density conditions, contributing to breast imaging research and development. The "Monitoring Vest" section discusses the antennas used in the tumor detection vest and the design of two different vest versions. Antenna1 is a UWB monopole antenna with a flexible laminate substrate, while Antenna2 is a textile-based version of Antenna1. Antenna3 has a Kapton-based substrate and larger dimensions. The combination of these antennas ensures accurate tumor detection in various breast conditions. The section also highlights the measurement and comparison of the S11 parameter for the PCB antenna in free space and when placed on the skin, emphasizing the impact of the skin on antenna performance. The section concludes by describing the design of the vests, including the arrangement of pockets and the use of RF cables for connection. The careful design and implementation of the vests and antenna placement ensure accurate measurements and reliable performance evaluation. The results section of the study shows that the presence of tumors in breast tissue leads to a noticeable decrease in channel attenuation. The higher dielectric properties of tumors cause additional reflections and diffraction, affecting signal propagation within the breast. These changes in channel characteristics are influenced by factors such as tumor size, breast density, and antenna configuration. The study demonstrates the detectability of tumors and provides valuable insights for developing effective tumor detection systems in different breast tissue scenarios. In this master thesis, a prototype of a breast tumor monitoring vest utilizing UWB flexible antennas was developed and evaluated. The research demonstrated the effectiveness of the vest in detecting breast tumors, even as small as 1cm, by leveraging the distinct characteristics of radio channels among multiple on-body antennas embedded in the vest. Higher frequencies in the 7–8 GHz range showed improved resolution and contrast in relative permittivity, enhancing the accuracy of tumor detection. The development of tissue phantoms played a crucial role, enabling reliable experiments to mimic human tissues. Integration of advanced AI algorithms and 6G technology holds promise for enhancing diagnostic capabilities and revolutionizing healthcare. Overall, the breast tumor monitoring vest shows potential for widespread implementation in breast health checks, home monitoring, and wireless healthcare systems

EMPLOYING DIELECTRIC-BASED MEDIA FOR CONTROLLING FIELD PATTERNS AND WAVE PROPAGATION IN ADVANCED ELECTROMAGNETIC DEVICES

Rapid progress in developing electromagnetic devices and in governing the wave propagation during last years caused renewed interest to dielectric materials. First, engineered dielectric structures with spatial dispersion of their parameters came to replace uniform substrates in antennas and other resonance devices. Then additional boom of dielectric applications was caused by the possibility to employ dielectrics as materials of artificial media. Later, attention of researchers was attracted to properties of the media composed of dielectric resonators (DRs). Currently DRs are used to create metamaterials – the media with unprecedented properties, which cannot be found in nature. Dielectric photonic crystals and metamaterials are considered as the most perspective materials for photonics, since they can be integrated in devices without loss problems, which characterize, for example, plasmonic techniques. Recently, a booming interest emerged to employing in photonics directional light scattering from dielectric particles, since the wavelengths of this light could be controlled by dimensions of particles and their dielectric permittivity. Our work followed basic innovations, which defined contemporary employment of dielectrics in electromagnetics and photonics. In particular, we started from working out new engineering approaches to developing dielectric substrates in patch structures inspired by microstrip patch antennas, which are proposed to serve as MRI RF probes (Chapter 2). Then we redirected our attention to the problems, which restricted employment of dielectrics in left-handed media. In particular, we have shown that negative refraction in all-dielectric metamaterials is irrelevant to Mie resonances in dielectric elements (Chapter 3). Next, we turned to analysis of problems defining directional scattering from dielectric metasurfaces and have demonstrated that the nature of observed phenomena cannot be correctly understood without accounting for strong interaction between “atoms” of metasurafces (Chapter 4). Finally we discussed selected problems met at implementation of photonic crystals in the media of transformation optics based devices and have shown that some of the problems can be solved at employing the phenomenon of self-collimation, characteristic for periodic photonic structures (Chapter 5)

Microwave sensing for neurodegenerative diseases

The rapidly increasing rate of the ageing population has led to a higher rate in people suffering from neurodegenerative diseases. Neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, are characterised by the progressive loss of brain cells, which leads to a decline in a person’s cognitive abilities, and eventually leads to death. The alarming increase in people suffering from these diseases has created a global socioeconomic burden that affects caregivers, nurses, and family members, just as much as the patient themselves. Due to the critical nature of these diseases, it is paramount that systems and devices can detect and monitor neurodegenerative diseases as early as possible, so that the right treatment can be provided to hinder its progression. Existing technologies have provided key results in the detection and monitoring of neurodegenerative diseases. However, they are limited by their bulky size, high costs, and inconvenient or invasive approach. Meanwhile, microwave sensing technology has generated promising results in several medical applications, such as cancer and stroke detection. The ability to fabricate components easily and integrate them into a wearable prototype makes microwave sensing a promising non-invasive, cost-effective, and portable or wearable solution for medical diagnostics. This work proposes the use of microwave sensing as an inexpensive, non-invasive, reliable, accurate, efficient, and wearable tool for monitoring the progression of neurodegenerative diseases. For evaluation, models were created to emulate symptoms of Alzheimer’s disease to demonstrate the technology. It is observed that microwave sensing was able to detect brain atrophy and lateral ventricle enlargement with a minimum change of 5%. In addition, microwave sensing could non-invasively detect and image regions of the brain affected by Alzheimer’s disease pathology, providing a transformational and major improvement compared to PET scans that rely on biomarkers. Moreover, microwave sensing could detect Alzheimer’s disease at one of its earliest stages: mild cognitive impairment. This work provides a promising and transformative approach for wearable and non-invasive neurodegenerative disease monitoring

Intelligent Microwaves-Based Modalities for Breast Cancer Detection

Breast cancer is considered to be one of the major causes of mortality in women worldwide. Detection of breast tumors in their early stage is the key factor for possible successful treatment and can significantly reduce mortality rates. In recent years, microwaves have emerged as a potential technique for breast cancer detection one that avoids the discomfort, risks and costs associated with x-rays and excessive cost and availability of MRI. Microwave technique is simpler to use, much less expensive to generate, and is non-ionizing. The microwave detection used in earlier works relied on the sharp contrast in the electrical properties between tumors and healthy tissue. In such methods, the breast was scanned by microwaves of various frequencies and the reflection recorded. An image depicting the electrical properties of the breast was then developed. The challenge, however, is that female breasts contain a complex network of fat and fibrous tissues, the electrical properties of which can very well resemble those of cancerous or benign tumors. Also, the electrical properties of the breast vary with frequency, requiring the earlier techniques to employ complex receptors. Motivated by these drawbacks, this thesis addresses the development of an inexpensive, non-ionizing and highly sensitive microwave technique for detecting early-stage breast tumors. In the first part of this dissertation, anatomically-realistic numerical breast phantom models are constructed using computer simulation technology (CST). The phantoms are anatomically realistic three dimensional (3D) numerical models that are realistic in both structural and dielectric properties. In the second part of the thesis, first a single electric probe and then a magnetic probe are individually combined with classification algorithms to help in detecting the presence of breast tumors. A key feature of our proposed detection concept is the almost simultaneous sensing of both a woman breasts, since right and left healthy breasts are morphologically and materially identical except amongst very small percentage of women. The two tests then can be compared to reveal any tissues property discrepancies. The concept employs a near-field resonant probe with an ultra-narrow frequency response. The resonant probe is highly sensitive to any changes in the electromagnetic properties of breast tissues, such that the presence of a tumor can be gauged by determining the changes in the magnitude and phase response of the sensor's reflection coefficient. Once the probe response is recorded for both breasts, Principle Component Analysis (PCA) method is employed to emphasize any difference in probe responses. For validation of the concept, tumors embedded in realistic breast phantoms were simulated. To provide additional confidence in the detection modality introduced here, experimental results of three different sizes of metallic spheres, mimicking tumors, inserted inside chicken and beef meat were detected, first by using an electric probe and then using a magnetic probe, operating at 200 and 528 MHz respectively. The results obtained from the numerical tests and experiments strongly suggest that the detection modality presented here might lead to inexpensive and portable modality for early and regular breast tumor detection. A novel modality proposed in the third part of the thesis significantly enlarges the sensitivity area beyond that of a single probe. This modality, based on a sensor we developed, relies on a 4-element identical antenna array fed with a single port. The use of this senor array improves the sensitivity area as compared to a single sensor, resulting in better detection of tumors located deeply inside breast tissues. Two different sensors are developed in this part,a dipole sensor and a loop sensor. The dipole sensor comprises a 4-element identical dipole antenna array fed with a single port. Numerical simulations have been conducted using a numerical breast model with and without tumor cells placed in the near-field of the sensor. The sensor is capable of detecting a breast tumor inserted at four different locations and of various sizes. Experimental validation was conducted using chicken meat and metallic and dielectric spheres that resemble healthy and tumourous breast tissues. The simulation and experimental results show that the array sensor has a high sensitivity for detecting various sizes of breast tumor inserted at different locations. The developed loop sensor comprises a 4-element identical loop antenna array fed with a single port. Numerical simulations have been conducted using a numerical breast model with and without tumor cells placed in the near-field of the sensor. The sensor is capable of detecting various sizes of tumor inserted at five different locations. Experimental validation was conducted using a glass box filled with vegetable oil and metallic spheres that resemble healthy and tumourous breast tissues, respectively. The simulation and experimental results show that the array sensor has a high sensitivity for detecting a metallic sphere placed at five different locations inside a dielectric medium as well as for detecting variable sizes of metallic sphere. In the fourth part of this thesis, a near-field metasurface sensor is introduced whereby a near-field array sensor operating in the microwave regime is used statically to identify the presence of a breast tumor. In a departure from conventional near-field sensors, the sensor is a metasurface comprising an array of 8$\times$8 electrically-small resonating elements. The elements of the metasurface are designed to respond to both electric and magnetic fields. This capability enables the metasurface to emphasize seemingly small changes in the composition of the electric and magnetic fields in its environment, thus leading to higher overall sensor sensitivity. Furthermore, unlike previous near-field probes, the overall metasurface sensor is not electrically small, which means that it provides a larger sensing surface while maintaining the effectiveness of near-field probes in the sense of detecting material changes in the near proximity of the sensor. Numerical and experimental tests were used to validate the proposed detection methodology. This was achieved by testing the metasurface with a breast phantom having tumor placed at single location at three different stand off distances and with a breast phantom having tumors placed at different locations. Measurements were carried out on a realistic phantom that mimic a real female breast in terms of electric properties. The results showed high sensitivity of the metasurface which can indicate the existence of an anomaly that resembles a tumor inside a breast phantom having inhomogeneous material composition. The advantage of the proposed metasurface sensor array as compared to previously introduced sensors is that the proposed array sensor is fed by a single-feed point. Unlike multiple-feed points sensors, this single feeding port sensor array significantly reduces the computational cost and complexity caused by processing the data from multiple feeds. The thesis then discusses the idea of using machine learning approaches to improve the performance of the proposed microwave detection system. The machine learning methods proposed discriminated between normal and abnormal breast phantoms in different sizes and classes of breasts, then also significantly improved the accuracy, sensitivity and specificity of the proposed detection system. As future work, the last part introduces several ideas for solving challenges in various aspects of the proposed sensors and the classification logarithms introduced in the developed system. The first idea is introduced to improve the sensitivity of the metasurface sensor by using multiple polarization sensors. The metasurface sensor, presented in chapter seven has one diploe in the middle of the loop, which will be extended to have two cross dipoles for vertical and horizontal polarization excitations. The second idea is to improve the sensitivity area of the proposed system by using multiple metasurface sensors that cover the whole breast and therefore eliminate the use of mechanical motors to move the sensor all over a breast. The third idea is to develop a portable detection system and integrate of the standalone VNA and the sensor into one miniaturized unit. The VNA circuitry will be positioned at the back of the sensor and will be connected with a laptop

Electromagnetic Absorption by the Human Body from 1 - 15 GHz

Microwave radiation is emitted by a wide variety of computing, communications and other technologies. In many transport, industrial and medical contexts, humans are placed in close proximity to several of these sources of emission in reflective, enclosed cavities. Pseudo-reverberant conditions are created, in which absorption by human bodies can form a significant, even the dominant loss mechanism. The amount of energy stored, and hence the field intensities in these environments depend on the nature of electromagnetic absorption by the human body, so quantifying human absorption at these frequencies is necessary for accurate modelling of both electromagnetic interference and communications path loss in such situations. The research presented here aims to quantify absorption by the body, for the purpose of simulating its effect on the environments listed above. For this purpose, nine volunteer participants are enlisted in a preliminary study in which their height and mass are taken and their electromagnetic absorption cross section is measured in a reverberation chamber. The preliminary study is unable to gather enough data to provide precise measurements during the time that a participant is willing to sit motionless in the chamber. Issues also exist due to power loss in some parts of the equipment. A number improvements are made to both the experimental equipment and methodology, and the study is repeated with a sample of 60 adult volunteer participants. The results are compared to the preliminary data and found to match, once unwanted absorption in the latter has been subtracted. The results are also validated using data from absorption by a spherical phantom of known absorptive properties. The absorption cross section of the body is plotted and its behaviour is compared to several biometric parameters, of which the body’s surface area is found to have a dominant effect on absorption. This is then normalised out to give an absorption efficiency of the skin, which is again compared to several biometric parameters; the strongest correlation is found to be with an estimate for average thickness of the subcutaneous fat layer. These data are used to model the effect of 400 passengers on the Q-factor of an airliner’s cabin. Absorption by the passengers is shown to be the dominant loss mechanism in the cabin, showing the importance of accounting for human absorption when modelling electromagnetic propagation and interference in situations that include human occupants. The relationship between subcutaneous fat and absorption efficiency is suggested for further research, as it promises development of new tools to study body composition, with possible medical applications