Abstract
This paper presents a study of a planar antenna-array inspired by the metamaterial concept where the resonant elements have sub-wavelength dimensions for application in microwave medical imaging systems for detecting tumors in biological tissues. The proposed antenna consists of square-shaped concentric-rings which are connected to a central patch through a common feedline. The array structure comprises several antennas that are arranged to surround the sample breast model. One antenna at a time in the array is used in transmission-mode while others are in receive-mode. The antenna array operates over 2–12 GHz amply covering the frequency range of existing microwave imaging systems. Measured results show that compared to a standard patch antenna array the proposed array with identical dimensions exhibits an average radiation gain and efficiency improvement of 4.8 dBi and 18%, respectively. The average reflection-coefficient of the array over its operating range is better than S11 ≤ −20 dB making it highly receptive to weak signals and minimizing the distortion encountered with the transmission of short duration pulse-trains. Moreover, the proposed antenna-array exhibits high-isolation on average of 30dB between radiators. This means that antennas in the array (i) can be closely spaced to accommodate more radiators to achieve higher-resolution imaging scans, and (ii) the imagining scans can be done over a wider frequency range to ascertain better contrast in electrical parameters between malignant tumor-tissue and the surrounding normal breast-tissue to facilitate the detection of breast-tumor. It is found that short wavelength gives better resolution. In this experimental study a standard biomedical breast model that mimics a real-human breast in terms of dielectric and optical properties was used to demonstrate the viability of the proposed antenna over a standard patch antenna in the detection and the localization of tumor. These results are encouraging for clinical trials and further refinement of the antenna-array.
Highlights
Medical imaging is an effective technique in diagnosing and treating a variety of diseases by providing a visual representation of inner organs of the human body [1], [2]
Various medical imaging technologies have been developed over the past few decades including ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine imaging
The proposed antenna is shown to exhibit significantly improved isolation, which is necessary to mitigate unwanted mutual coupling between adjacent radiators that can adversely affect the radiation characteristics of array. This means that an antenna array implemented with the proposed antenna avoids the use of decoupling structures which are normally inserted between radiators
Summary
Medical imaging is an effective technique in diagnosing and treating a variety of diseases by providing a visual representation of inner organs of the human body [1], [2]. Investigations show that microwaves allow dielectric properties of healthy and malignant tissues to be contrasted which enables medical images to be created relatively due to the interaction of EM waves with matter [12]. This is because interaction of EM waves and matter is a function of dielectric properties which can be directly related to various types of biological constituents due to their varying degree of water content: bone, fat, muscle, etc. Detection of cancer can be achieved by electrically characterizing the biological tissue under investigation This is usually done using highly directive microwave antennas in the microwave imaging system.
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