Low profile ultra-wideband directional antenna operating in low microwave band for brain stroke diagnostic system

Worldwide, brain stroke is the leading cause of disability among adult. Present imaging systems do not offer a low cost and portable solution for the stroke diagnosis. Microwave imaging systems have the potential to provide that solution and substitute, or complement, existing systems. To achieve that target, a wideband antenna operating at the band used for that application with directional radiation for adequate penetration into the human head is needed. This paper introduces a novel ultra-wideband antenna design consisting of a folded dipole-like structure printed on two dielectric slabs of the same size. The antenna covers a 98% fractional bandwidth (0.77 to 2.25 GHz), which is used in head imaging. The antenna exhibits stable directional radiation patterns with an average gain of 4.5 dBi and front to back ratio of 8 dBi. The overall structure of the antenna is equivalent to 0.27 lambda(0) x 0.12 lambda(0) x 0.05 lambda(0), where lambda(0) is the corresponding wavelength at 0.77 GHz, which is a compact and low profile arrayable design suitable for microwave-based head imaging

Development of compact directional antenna utilising plane of symmetry for wideband brain stroke detection systems

Microwave-based brain stroke detection demands low profile, compact, directive and wideband antennas for efficient imaging using portable systems. Using image theory of electromagnetics, the magnetic symmetry plane of a folded antenna is utilised for its miniaturisation to half of its original volume without sacrificing its penetration capability or radiation directivity. The antenna achieves 63% fractional bandwidth (1.25-2.4 GHz) with 3.5 dBi average gain along the direction of radiation. Both the near-field and far-field radiations are characterised to ensure the antenna's applicability in the detection system. Moreover, the radiation safety is also analysed since the antenna has to operate in close proximity to the head. The overall dimensions of the proposed antenna are 0.29λ0 × 0. 12λ0 × 0.06λ0 (λ0 = lowest operating wavelength)

CPW-fed low-profile directional antenna operating in low microwave band for wideband medical diagnostic systems

Medical diagnostic systems demand wideband antennas with directive radiation patterns. In addition, portable systems require low profile and light weight antennas to be incorporated. These necessities of modern microwave-based diagnostic systems are addressed in this reported work. The antenna is built with two simple thoroughly printed structures connected to each other using two copper walls, forming a loop-like geometry. The top element is capacitively loaded with a pair of symmetrically placed slots and fed with a coplanar waveguide (CPW). The antenna works like a small loop in the lower resonating mode and as a folded-dipole in the higher modes. The antenna exhibits a 109% bandwidth with stable radiation patterns of an about 9 dB front-to-back ratio over most of the band with only a profile of 0.05λ (λ = wavelength at the lowest frequency). The measured and the simulated results show that the proposed antenna is suitable for wideband medical imaging systems

Wideband unidirectional antenna for head imaging system

Antennas with wideband performance, compact size and directional radiation are required in microwave imaging and monitoring systems for medical applications. An antenna with a low profile structure along the direction of radiation and 50ω port impedance are two other requirements in head imaging. To address these issues, a wideband low-profile compact antenna is proposed in this paper. The antenna mainly consists of two printed slabs of substrates that are separated by a properly designed cavity. The printed slabs are connected by two copper walls. The design flow of the antenna is described briefly with a description of various parameters. The antenna covers 48% fractional bandwidth with a stable gain, good radiation efficiency and well directional radiation characteristics

Detection and localization of brain strokes in realistic 3-D human head phantom

Stroke is the second leading cause of death worldwide. The treatment depends on the location and extent of stroke and it should be started within 4.5 hours of the attack. Thus rapid detection is a must. Existing imaging systems do not provide a solution to monitor the patient in real time and not portable, thus requires patient's movement. Addressing these limitations, a portable diagnostic system is proposed in this paper employing monostatic radar approach using only one antenna covering 73% fractional bandwidth centered at 1.85 GHz. A realistic three-dimensional (3-D) head phantom is generated to simulate different stroke conditions. The phantom anatomically holds the structure of a real human head with frequency dispersive electrical properties of respective biological tissues of head that are rigorously fitted with fourth-order Debye model for the simulation environment. A confocal imaging technique is used to map the abnormalities inside the head. The obtained images indicate the potential of the presented technique to detect and locate the position of both hemorrhagic and ischemic strokes

Compact 3-D slot-loaded folded dipole antenna with unidirectional radiation and low impulse distortion for head imaging applications

A compact 3-D antenna for microwave-based head imaging systems is presented. The antenna, which is fed by a coplanar waveguide, consists of a slot-loaded folded dipole structure with four furled sides. Because of the presence of stronger currents on the top layer and reflections from the slightly extended bottom layer, the antenna exhibits directional radiation in the frequency domain in both near and far fields. The transient response of the antenna is also analyzed. Despite the existence of multiple slot loading and folding in the proposed antenna, the investigation of the time domain responses reveals a directional low-distorted radiation (impulse fidelity factor of more than 80%) toward the boresight direction in both near and far fields. The antenna has the compact size and low profile, with respect to the lowest operating wavelength, of 0.29 × 0.08, and 0.04, respectively, and 67% fractional bandwidth over 1.1-2.2 GHz. Since the antenna is designed to operate within an array for head imaging, a 16-element array of the antenna is tested in a realistic simulation environment to confirm a safe radiation exposure level. Finally, the array is employed on a realistic human head model to successfully detect and locate a hemorrhagic brain injury

UWB antenna with notched band at 5.5 GHz

A slot antenna with a notched band at 5.5 GHz is proposed for UWB applications. The basic UWB antenna comprises of a rectangular radiating patch and a ground plane with a tapered shape slot and printed on 1.6 mm-thick FR4 dielectric substrate. To realise a notch band, two symmetrical slits are etched on the slot of the ground plane. Experimental results show that the proposed antenna exhibits wideband performance from 3.08 to more than 11 GHz with a notched frequency band centred at 5.5 GHz which can effectively mitigate the interference between the WLAN and UWB systems. It is also confirmed from the measurements that the insertion of slits does not affect the antenna performance, except at the notched frequency band

Developments of tomography and radar-based head imaging systems

Microwave-based diagnostic systems are increasingly attracting huge attention due to their low-cost, non-ionizing and non-invasive characteristics. This paper reviews the recent developments of head imaging systems reported for applications in medical emergencies. The reviewed systems include tomography and radar systems. It is shown that although microwave systems for head imaging have reached a mature stage, they still need a preclinical validation

Design of microstrip patch antenna using novel U-shaped feeding strip with unequal arm

A novel feeding technique is developed for the microstrip patch antenna. The U-shaped feeding strip with an unequal arm is proposed to feed a printed rectangular ring patch antenna to achieve high gain. Measured results of the prototype antenna agree very well with simulated results. According to the measured results, the antenna shows good impedance bandwidths satisfying ISM 2.45/5.8GHz with good impedance matching. Stable radiation patterns are achieved with maximum gains of 9.56 and 10.17dBi for both bands