S. Ahdi Rezaeieh

Equivalent circuit model for finding the optimum frequency range for the detection of heart failure using microwave systems

A circuit model is used to estimate the useful frequency bands that can be used in a microwave system designed for heart failure detection. That detection is realized by monitoring the accumulation of fluids in lungs (pulmonary edema) that is associated with heart failure. The circuit model is derived from the electrical properties of human tissues in the torso area. To include the effect of the variation in the electrical properties of human lungs due to respiration, the model considers the two normal situations of human lungs (inflated and deflated). It is shown that the attenuation of the signal increases significantly with frequency as expected in any lossy medium. However, using a suitable coupling medium reduces the attenuation and makes it almost constant across the frequency band from 0.5 GHz to around 1 GHz. The attenuation increases rapidly beyond that band. The results presented in this initial work suggest that the band from 0.5 GHz to 1 GHz is suitable for the detection of heart failure, especially when using a proper coupling medium.

Compact CPW-Fed Planar Monopole Antenna With Wide Circular Polarization Bandwidth

The design and implementation of a coplanar waveguide-fed planar monopole antenna with circular polarization and broadband operation is presented. The antenna operates in the Industrial, Scientific, and Medical (ISM) and wireless local area network (WLAN) (5 GHz) bands with circular polarization (CP) in both bands. It is demonstrated that a fractional bandwidth for CP larger than 33% can be attained simply by introducing an inverted L-shaped slot in the ground plane and parallel-aligning an inverted-L-shaped strip. The advantages of the proposed antenna are the simple yet efficient design of the radiator, a wide 3-dB axial-ratio operating band, and a compact size.

Wideband and Unidirectional Folded Antenna for Heart Failure Detection System

A wideband folded antenna, which is specifically designed for an early heart failure detection system operating at the ultra-high frequency (UHF) band, is presented. The design procedure starts with a planar structure that includes a loop antenna, a dual monopole, and a loaded parasitic patch. To significantly reduce the size of the antenna and achieve directional radiation as needed for the intended application, the planar structure is folded to form a three-dimensional antenna with the dimensions 0.1λ×0.29λ×0.09λ, where λ is the wavelength at the lowest operating frequency. The final tested antenna achieves a peak gain of 4.2 dBi, front-to-back ratio of 7-13 dB and efficiency of more than 87% over 62% fractional bandwidth (560-1060 MHz) at 10-dB return-loss reference. The antenna in addition to a compact microwave transceiver and an adjustable platform are then used to build a monostatic-radar-based heart failure detection system. The system is tested on an artificial torso phantom to verify the potential of such a system in the early detection of heart failure. The used imaging algorithm and obtained promising results are reported in the letter.

3-D Wideband Antenna for Head-Imaging System with Performance Verification in Brain Tumor Detection

A 3-D slot-rotated antenna for a microwave head- imaging system is presented. The antenna is designed to have a wideband and unidirectional performance at the low microwave frequency band that are the requirements of the specified imaging system. Starting from a traditional wide-slot antenna, several conventional techniques are applied to enhance its bandwidth and directivity while miniaturizing its size. In that regard, four series of staircase-shaped slots are applied to lower the operating frequency, whereas a folding process is used to enhance the directivity and reduce the overall size. In addition, two parasitic patches are connected to the slot area to increase the operating bandwidth. The final design has the dimensions of 0.11 λ×0.23 λ×0.05 λ. ( λ is the wavelength of the lowest measured operating frequency.) It has a measured VSWR fractional bandwidth of 87% (1.41-3.57 GHz) and a peak front-to-back ratio of 9 dB. To verify the suitability of the antenna in head imaging, it is connected to a wideband microwave transceiver and used to circularly scan an artificial head phantom in 20° angle steps in a monostatic mode. The collected backscattered data are then processed and used to generate an image that successfully shows brain tumors. The compact size, wide operating bandwidth, unidirectional radiation, and detection viability are merits of the presented antenna and the subsequent system.

Wideband Unidirectional Antenna of Folded Structure in Microwave System for Early Detection of Congestive Heart Failure

A three-dimensional antenna based on a combination of loop and dual monopole structures with parasitic elements is presented. The antenna is specifically designed for a microwave system aimed at the early detection of congestive heart failure. The antenna is first designed as a planar structure and then folded over optimally defined folding lines to properly alter the path and phase of the surface currents for a unidirectional radiation and compact size as needed for the detection system. A prototype antenna of size 0.29λ × 0.08λ × 0.08λ (where, λ is the wavelength of the lowest resonant frequency) is developed to cover the band required in the targeted application. The measured results indicate 53% fractional bandwidth (580 - 1000 MHz), 6-8 dB front to back ratio, and 3-5 dBi gain. The antenna is then used to build a heart failure detection system, which also includes a compact microwave transceiver, a processing and image reconstruction algorithm based on the synthetic aperture focusing technique, and a display unit. The system is used to successfully detect an early case of congestive heart failure in an artificial torso phantom that includes the main torso organs (lungs, heart, ribs, and fat).

Feasibility of Using Wideband Microwave System for Non-Invasive Detection and Monitoring of Pulmonary Oedema.

Pulmonary oedema is a common manifestation of various fatal diseases that can be caused by cardiac or non-cardiac syndromes. The accumulated fluid has a considerably higher dielectric constant compared to lungs’ tissues, and can thus be detected using microwave techniques. Therefore, a non-invasive microwave system for the early detection of pulmonary oedema is presented. It employs a platform in the form of foam-based bed that contains two linear arrays of wideband antennas covering the band 0.7–1 GHz. The platform is designed such that during the tests, the subject lays on the bed with the back of the torso facing the antenna arrays. The antennas are controlled using a switching network that is connected to a compact network analyzer. A novel frequency-based imaging algorithm is used to process the recorded signals and generate an image of the torso showing any accumulated fluids in the lungs. The system is verified on an artificial torso phantom, and animal organs. As a feasibility study, preclinical tests are conducted on healthy subjects to determinate the type of obtained images, the statistics and threshold levels of their intensity to differentiate between healthy and unhealthy subjects.

Defining optimum frequency range for heart failure detection system considering thickness variations in human body tissues

One of the most apparent symptoms of heart failure that can be used for its primary detection is the accumulation of fluids in lungs (pulmonary edema). However, the competency of the non-invasive microwave detection system on varying tissues thickness (mainly fat and muscle) between the skin and lungs is one of the major challenges in the design of a successful microwave detection system. The penetration of microwave signals in human body tissue depends on the utilized frequency as well as the properties and thickness of the tissues. Hence, this study investigates optimum frequencies that can be used in monitoring the accumulation of fluids in the lungs for different thicknesses of tissues layers in the torso area. The investigation uses an equivalent circuit model of the tissues in the torso area with properties that are emulated using the fourth-order Cole-Cole model. To achieve reasonable resolution, the current study focuses on the frequency band from 0.5 GHz to 1.5 GHz. A conclusion is made from all the utilized combinations in the study that the optimum band for the investigated cases extends from 0.5 GHz to 0.9 GHz.

Three-Dimensional Open-Ended Slot Antenna for Heart Failure Detection System Employing Differential Technique

The design of a folded open-ended slot antenna for an early-stage congestive heart failure (CHF) detection system operating at ultra-high frequency (UHF) is presented. The antenna is formed using a three-dimensional open-ended slot with a compact size of 0.24 λ0 × 0.09λ0 × 0.04 λ0 (λ0 is the lowest operating frequency of the antenna), and a slotted microstrip feeder used to achieve wide operating bandwidth of 58% (550-1000 MHz). A CHF detection system is then built using the proposed antenna, a compact microwave sensor, and a differential detection technique. The main objective of such a system is to map the torso area searching for any fluid accumulation in the lungs as the main symptom of CHF. To that end, a pair of the proposed antenna is attached to an adjustable platform to vertically scan the torso. A differential detection technique is applied on the backscattered signals to map the scattering profile of the torso and detect any changes in the electrical properties of the lungs caused by fluid accumulation. A detection threshold is applied to differentiate between healthy and unhealthy cases. The obtained images have a pixel resolution of 0.1 cm in depth and 1 cm in height. The experimental results on an artificial torso indicate that the system can detect fluid differences as small as 4 mL, with a measurement error of less than 3%.

Broadband UHF antenna for heart failure detection system

A three-dimensional cavity backed coplanar waveguide fed ultra-high frequency (UHF) antenna is presented. The antenna is designed to operate in microwave system for heart failure detection. A parasitic cavity is used to increase the bandwidth of the antenna, resulting in a fractional bandwidth of 30 % (737-1001 MHz). The antenna has a gain that varies between 3 to 5.25 dBi through this band. Due to its broadband characteristics, compact size and suitable gain, the proposed antenna is a good candidate for the detection of fluids accumulation in the lungs, which is an indication of heart failure.

Loop-Dipole Composite Antenna for Wideband Microwave-Based Medical Diagnostic Systems With Verification on Pulmonary Edema Detection

A unidirectional and compact antenna for wideband microwave-based medical diagnostic applications is presented. The main part of the antenna is formed from the combination of loop and dipole interleaved structures. To enable the antenna to resonate at a low frequency within a compact substrate area, a pair of slots is created on the loops vertical arms, whereas the dipoles structure is tapered to compensate for the negative effect of the capacitively loaded slots. With the proposed configuration, the antenna acts as an array of two dipoles and a quasi-Yagi antenna at lower and higher frequencies, respectively, and thus radiates mainly in one direction. The antenna has a compact size (with respect to the wavelength at the lowest operating frequency) of 0.23 × 0.23, making it 50% smaller than similar designs. It has a measured fractional bandwidth of 55% at 0.65-1.15 GHz and peak gain and front-to-back ratio of 3.8 dBi and 11 dB, respectively. To verify the practicality of the antenna, it is applied in an array configuration and successfully tested in detecting pulmonary edema in realistic simulation and experimental environments.