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The near‐field directivity factor: A, simulation configuration; B simulated results as a function of frequency
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A miniaturized inset‐fed on‐body meandered bowtie antenna designed for brain microwave imaging systems is presented in this article. The proposed on‐body antenna can contribute to the realization of a wearable and portable brain microwave imaging system. The size of 18 × 18 mm2 is achieved at a frequency range of 0.75 to 4 GHz by the simultaneous u...
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Citations
... Despite different methods used to decrease its operating frequency, some studies have reported that the Vivaldi antenna still operates at a frequency higher than 1.3 GHz [100], [102] or even higher than 2 GHz [96], [97], [98], which limits its penetration inside biological tissues. Although bow-tie antennas [103], [104], substrate integrated waveguide antennas [105] and monopole antennas [106], [107] are reported in the literature for their small size, they are not suitable for high penetration since they do not provide unidirectional radiation. To address this issue, various techniques have been proposed such as reflectors [108], [109], cavity-backed [19], artificial magnetic conductors [110], and Yagi-Uda [111], which are integrated with the monopole antenna to direct waves in one direction, but this results in increased antenna complexity. ...
The increasing necessity for early detection of knee injuries to prevent extensive ligament damage and costly treatments has prompted the exploration of wearable and portable electromagnetic (EM) imaging systems. These systems offer the potential to revolutionize the diagnosis and monitoring of knee injuries and related conditions. However, the successful integration of EM knee imaging technology into clinical practice necessitates a comprehensive understanding of its specific application, the requisite system components, and the existing challenges. This article thoroughly reviews the current state of EM knee imaging technology, with a specific focus on the systems, frameworks, and challenges involved in its translation to practical clinical usage. The review serves as a valuable resource for researchers, clinicians, and engineers engaged in knee imaging research. Furthermore, the review explores potential solutions and ongoing research endeavours to address the outstanding challenges and facilitate the clinical implementation of EM knee imaging.
... Since the antenna and its array configuration play a major role in the success of imaging systems, several types of antennas and arrays for EM head imaging have been proposed in the literature alongside previously mentioned imaging systems [8,[13][14][15]. Realizing features such as compactness, low profile, body-matched, and directive patterns in such systems is challenging due to antenna size and frequency band limitations [4,16]. ...
... A method to effectively improve the reflection coefficient, as well as radiation characteristics of the antenna, is to immerse antennas in a coupling liquid which acts as an impedance-transformer medium between the radiator and the tissue. However, placing the antennas in the coupling liquid makes it impractical/hard to implement a transportable device [3,8,15]. ...
This paper presents an imaging system based on ultrawideband microwave radars for the detection of bleeding regions and strokes inside the human head. The proposed system is portable and focuses on revealing bleeding areas with unpredictable shapes using polarimetric data acquisition. A custom-designed dual-polarized bowtie patch antenna capable of pumping the UWB pulses inside the patient’s head is designed and presented as the biomedical sensor for the system. The antenna dimensions are 25×25 mm2. It mitigates the mismatch between the air and skin needles of any coupling liquid, resulting in safe SAR levels below 0.5 W/kg and wideband operating bandwidth that covers 1.2-4.5 GHz with unidirectional radiations. To collect the raw polarimetric data, an elliptical array of the proposed antenna is formed around the patient’s head model that includes 16 elements in direct contact with the phantom. The performance of the proposed method is validated through an imaging scenario with two nonuniform bleeding areas inside the patient head model. The whole structure is simulated with a Gaussian pulse as the excitation using CST Microwave Studio tools. To produce 2D images of the voxel model, the time-domain elliptical synthetic aperture radar (ESAR) imaging algorithm is applied. Accurately detecting the presence and shape of anomalies in reconstructed images using the proposed method demonstrates the efficiency of the proposed system and determines its advantages over single-polarization systems.
... Although using different approaches to reduce its operating frequency, it still operates at a frequency higher than 1.3 GHz in [135,139] and higher than 2 GHz in [131][132][133], resulting in low penetration inside the biological tissues due to high losses and high dielectric permittivity of those tissues. For miniaturized size, monopole [140,141], bow-tie antennas [142,143] are reported in the EMI related literature. Although the monopole antennas have a compact size and wide bandwidth, they provide a unidirectional pattern, making them unsuitable for achieving high penetration [128,144]. ...
The knee is prone to injuries more often than other joints in the body due to its complexity and weight-bearing role. These injuries are not only inherent to sports fields but also to everyday lifestyles. Connective tissue injuries are the most prevalent knee diagnoses, accounting for 50% of musculoskeletal injuries. They are the most critical knee injuries because they can require surgical intervention and prolonged rehabilitation. In the United States, roughly 17 million ligamentous injuries necessitate medical care each year, at an estimated cost of over $40 billion. Early detection of a partial tear for knee ligaments without obstructing natural activity reduces the severity of the injury and its transformation into a complete tear, which can only be treated using interventional surgery. Besides, the treatment period is shortened from nearly one year in complete tears to several weeks in the case of mild or moderate tears. Moreover, early detection decreases the risk of other injuries that are associated with complete ligament tears, such as meniscal and tendon tears, posttraumatic osteoarthritis, and dislocation. Therefore, onsite diagnostic tools are required because the current scanning modalities, such as MRI and CT, are not suitable for use outside the hospital.
Meanwhile, Electromagnetic imaging (EMI) has undergone rapid development and has become one of the promising biomedical imaging modalities because of its unique features, such as low cost, simple structure, portability, and non-ionization. EMI modality is based on the significant changes in dielectric characteristics of tissues due to abnormality or injuries. When the ligament tear happens for knee injuries, the synovial fluid increases inside the knee joint, which can be detected using EMI. Thus, EMI is an attractive solution to address the mentioned limitations.
Implementing a complete EMI system that includes antenna array designs, hardware platforms, and microwave imaging algorithms is of significant interest in this context. In order to test and validate new EMI systems for knee injuries, a realistic durable knee phantom is required. Therefore, the first contribution of this thesis is to introduce knee phantom with realistic dielectric and anatomical properties fabricated using proper molds and equivalent mixtures. The fabricated phantom is based on a composite material of polymer and additive materials such as aluminium-oxide and graphite.
In the second part of this thesis, a portable EMI system for knee injuries is designed, fabricated, tested, and validated for the first time in the literature. Specifically, design an eight-element wide band biconical antenna array at 0.7-2.2 GHz with a unidirectional radiation pattern to improve penetration into the knee. To reconstruct knee images, a modified multi-static confocal algorithm is used. Since humans' left and right knees are mirror-symmetrical, the modified algorithm uses a differential approach to remove signal clutters, muti-static coherence factor to improve the quality of channels, and applies dielectric mapping to reduce detection error. The images indicate the ability of the system to detect different types of ligament tears with an accurate localization. The third contribution in this thesis is presented as an essential step to verify the proposed system on the ex-vivo pig knee joint before clinical trials. Six healthy hind legs from three dead adult pigs were removed at the hip, suspended in the developed system, and scanned. Then, ligament tear was emulated by injecting distilled water into the middle of the left knee joint of each pig for early and mid-stage injuries. The injured knees were re-scanned. Furthermore, all knee’s connective tissues are extracted from a healthy hind leg along with collected synovial fluid. The extracted tissues and fluid were characterized and modelled, then imported to build an equivalent model for pig knee of 1 mm3 resolution in a realistic simulation environment to be used in the numerical studies by the researchers.
The last part of this thesis focuses on introducing textile brace systems to be more conformable with the knee and can be worn for knee imaging and daily monitoring. The two braces are designed to match the human knee for enhanced electromagnetic wave penetration. The antennas in two braces achieve wide bandwidth and unidirectional radiation. The first brace consists of a simple 12-element textile slot loop antenna array. In contrast, the second brace consists of 8-element dual-polarized octagonal aperture antenna array. The dual-polarized brace system demonstrates a high capability to detect accumulated fluid with an arbitrary shape, slant angle, small size or deeper than the center of the brace. The reconstructed knee images in this section are based on a modified double-stage delay multiply and sum algorithm.
The presented results in this context demonstrate the capability of detecting and monitoring knee injuries. The introduced systems break the hospital boundaries to real-time onsite scanning for knee injuries, can be used at home, sports fields, and clinics, making it easy to detect and manage early injuries and avoid serious consequences.
... In these systems, an ingestible capsule that is swallowed by the patient takes images of the gastrointestinal tract. These images can be sent out of the body by a wireless communication link, which typically consists of a capsule antenna and an on-body antenna [1][2]. ...
A transparent spherical spiral antenna for endoscopy capsule systems for gastrointestinal monitoring is presented in this article. The capsule antenna is designed for operating in the Medical Implant Communication Systems frequency band (i.e., 401-406 MHz) and has an impedance bandwidth of 397-409 MHz. The transparency of the antenna allows it to be implemented in front of the camera. This leads to more available space inside the capsule for embedding more subsystems. The proposed antenna also has a circularly polarized omnidirectional radiation pattern. These characteristics allow a stable wireless communication link during the monitoring operation.
... Table 6.3 shows the model parameters of a healthy human head phantom that consists of six layers: skin, fat, skull, dura, cerebrospinal fluid (CSF), and brain (mixture of grey and white matter). The relative dielectric constant and conductivity values are given for 1.6 GHz [24,25], which is the optimal imaging frequency for brain injury. In contrast, the dielectric properties of brain tumour and stroke are e r ¼ 59.7, s ¼ 1.91 S/m, and e r ¼ 55, s ¼ 7 S/m, respectively. ...
... An inset fed meandered bowtie antenna with dimensions 18Â18Â0.5 mm 3 is proposed in [24]. It is fabricated on an FR4 substrate (e r ¼ 4.3) and has an operating frequency range of 0.75À4 GHz. ...
Research into improving the functionality and capacities of wearable technology has surged as a result of its fast progress. The functioning of wearable technology is largely dependent on antenna design, which provides wireless connectivity and communication. This study of the literature searches many online sources for pertinent research on the various antenna designs for wearable technology. The findings verified that the materials vary based on the design being employed. An analysis was conducted on the gain, frequency, materials, and sizes. The review excels at synthesizing research and literature despite its restricted resources.
The rapid growth of wearable technologies within wireless body area networks (WBANs) has increased the demand for advanced wearable antennas. The human body's presence creates significant challenges for these antennas since it behaves differently as a wave propagation medium. It is necessary to prioritize specific requirements for antenna design, such as size, frequency, efficiency, wideband and multiband operation, because of body interaction and signal attenuation. The development of novel methodologies, the use of state-of-the-art fabrication methods, and the advancement of antenna designs have been the main areas of attention for researchers in this field in recent years. This research investigates contemporary advancements in wearable antennas, particularly emphasizing utilizing recent materials, fabrication processes, and new techniques. It also highlights the unique applicability of these antennas in advanced WBAN systems.
An on-body antenna, comprised of two closely-spaced antiphase patch elements, for microwave imaging may provide enhanced signal penetration into the tissue. By further integrating a 180-degree on-chip power splitter with the dual antiphase patch antenna element, a low-profile miniaturized antenna, integrated into a single 18.5 mm × 10 mm × 1.6 mm circuit board assembly, is designed and evaluated both numerically and experimentally. This is the smallest on-body antenna known to the authors for the given frequency band. This linearly polarized antenna may potentially serve as a building block of a dense antenna array for prospective high-resolution microwave imaging. A 2.4 GHz band was chosen as the design target. The final antenna size was a compromise between the miniaturization, the SNR (Signal-to-Noise Ratio), and the targeted antenna bandwidth (2.3–2.5 GHz). The effect of surface waves (the secondary radiating components) was also factored in the design consideration, while maximizing the detected signals’ SNR.
Microwave imaging has recently drawn increasing attention due to its potential for rapid stroke diagnosis using this low-cost, and non-ionizing modality. Besides, this modality can be built as a portable scanning device that can be utilized for both on-site and in-hospital settings. Over the past few years, there have been great efforts by many scientists and engineers to translate this life-saving technology to a clinical setting. Although recent progress indicates that microwave imaging has indeed evolved at a rapid pace, there are still several challenges to be addressed. This paper discusses the recent progress in addition to challenges and limitations that must be overcome to enable the development of clinical systems for stroke diagnosis with robust and reliable results. It provides a comprehensive review of recent systems, focusing on complete systems and processing algorithms.
