Sasan Ahdi Rezaeieh

Microwave System for the Early Stage Detection of Congestive Heart Failure

Fluid accumulation inside the lungs, known as cardiac pulmonary edema, is one of the main early symptoms of congestive heart failure (CHF). That accumulation causes significant changes in the electrical properties of the lung tissues, which in turn can be detected using microwave techniques. To that end, the design and implementation of an automated ultrahigh-frequency microwave-based system for CHF detection and monitoring is presented. The hardware of the system consists of a wideband folded antenna attached to a fully automated vertical scanning platform, compact microwave transceiver, and laptop. The system includes software in the form of operational control, signal processing, and visualizing algorithms. To detect CHF, the system is designed to vertically scan the rear side of the human torso in a monostatic radar approach. The collected data from the scanning is then visualized in the time domain using the inverse Fourier transform. These images show the intensity of the reflected signals from different parts of the torso. Using a differential based detection technique, a threshold is defined to differentiate between healthy and unhealthy cases. This paper includes details of developing the automated platform, designing the antenna with the required properties imposed by the system, developing a signal processing algorithm, and introducing differential detection technique besides investigating miscellaneous probable CHF cases.

Bandwidth and Directivity Enhancement of Loop Antenna by Nonperiodic Distribution of Mu-Negative Metamaterial Unit Cells

The theory, design, analysis, and verification of a wideband and unidirectional loop antenna loaded with mu-negative (MNG) metamaterial unit cells is presented. It is shown that by nonperiodic positioning of MNG unit cells on the loop structure, the amplitude of the surface current can be modified in a desired section of the loop, and hence, unidirectional radiation is achievable at the mu-zero resonance frequency. Moreover, it is demonstrated that as a result of the capacitive MNG loading, a 90° phase difference occurs between the vertical arms of the loop. Therefore, its radiation mechanism can be characterized as an array of two dipole antennas positioned a quarter wavelength apart, thus creating unidirectional radiation. To further improve the performance of the antennas, a quarter-wavelength strip is located in the vicinity of the loop to act as a resonator and director at higher frequencies. With the proposed structure, the final design is at least 50% smaller, in terms of the occupied area, than recent antenna designs of conventional loops, MNG loaded loops, and loop-dipole composite antennas. It also achieves a wide fractional bandwidth of 52% from 0.64 to 1.1 GHz, which is 50% wider than recent MNG metamaterial unit cell loaded loops, with a measured peak front-to-back-ratio and gain of 13 dB and 4.8 dBi, respectively.

Compact Wideband Loop Antenna Partially Loaded With Mu-Negative Metamaterial Unit Cells for Directivity Enhancement

A wideband and unidirectional loop antenna partially loaded with mu-negative (MNG) metamaterial unit cells is presented. To reduce the electrical size of the antenna, its first resonance is formed by capacitively loading a conventional one-wavelength loop antenna to excite the mu-zero resonance that is independent of the resonators size. As a result of partial loop loading using properly designed and distributed slots, the amplitude of the surface current can be engineered to be higher in the feeding arm while achieving a zero phase shift along each arm of the loop structure. Consequently, unidirectional radiation with a moderate front-to-back ratio (FBR) is achieved without using any reflectors. Moreover, as a result of the capacitive loading, the loop antenna is divided into an array of dipoles that are excited with a 90° phase difference, enabling unidirectional radiation at the loop-mode resonance. To both enhance the impedance matching of the antenna at lower frequencies and excite an additional resonance, a strip patch is added in the vicinity of the loop. The proposed structure is smaller by 80% than similar MNG loaded loops and achieves a wide fractional bandwidth of 52% (0.64-1.1 GHz) with a peak FBR and gain values of 12 dB and 3.2 dBi, respectively.

Broadband CPW-fed slot antenna with circular polarization for on-body applications at ISM band

A broadband coplanar waveguide (CPW) fed antenna which has circular polarization is presented. The antenna is designed to operate at the frequency band (2.45 GHz) that is widely used for industrial, scientific and medical (ISM) applications. The proposed antenna has a uniplanar structure. A square slot is created in the ground which is located at the top layer of a printed circuit board. The CPW feeder is connected to a horseshoe shaped radiator inside the square slot. The circular polarization of the antenna is achieved through inserting T- and L-shaped strips inside the slot. The proposed antenna has a 3 dB axial ratio bandwidth from 2.1 GHz to 2.67 GHz, i.e. 20% fractional bandwidth, and impedance matching bandwidth from 1.5 GHz to 3.15 GHz, which is equivalent to 67.5% fractional bandwidth. The whole structure of the proposed antenna has a compact size of 40 mm × 40 mm.

Unidirectional Slot-Loaded Loop Antenna With Wideband Performance and Compact Size for Congestive Heart Failure Detection

A slot-loaded meandered loop antenna for congestive heart failure (CHF) detection system is presented. To meet the requirements for a CHF detection system, the antenna is designed to have a compact size, wideband at the ultra-high frequency band and unidirectional radiation. To that end, several techniques are applied to the main utilized structure, which is a conventional loop antenna. To lower the resonant frequency and enhance the directivity within a compact size, the loop is capacitively loaded using a pair of slots. To compensate for the effect of the capacitive coupling on the input impedance matching, an inductive reactance is added by meandering the loops structure. With the applied modifications, the proposed antenna has a compact size of 0.21 × 0.21 with respect to the wavelength at the lowest operating frequency. The realized dimension represents only a quarter of the size of its counterpart planar designs. The proposed antenna achieves a wide measured fractional bandwidth of 50% (0.66-1.1 GHz), 9 dB peak front-to-back ratio and 4.1 dBi gain. The antenna is then used as part of a CHF detection system that also includes a compact transceiver, scanning platform, and laptop for control and processing. Using a suitable frequency-domain processing and imaging algorithm, the system successfully detects an early CHF in an artificial torso phantom.

Bandwidth and directivity enhancement of metamaterial-loaded loop antennas for microwave imaging applications

Compact, wideband and unidirectional loop antennas are presented, that are based on a conventional planar loop antenna that is loaded in a mu-negative (MNG) fashion with series capacitors, enabling a mu-zero (MZR) resonance to be excited. This, together with the inherent loop resonance and a third resonance introduced by a director element, result in a wide impedance bandwidth and enhanced directivity. Two variants of the MNG-loaded loop antenna are presented; one with a uniform distribution of the MNG-unit cells, and one with a non-uniform distribution. It is shown that both antennas, which have a compact size, achieve a wide operating bandwidth in excess of 50% in the range of 0.6 to 1.1 GHz in the lower UHF band. The uniformly loaded antenna has a measured gain of 3.2 dBi, while the non-uniformly loaded antenna has a higher measured gain of 4.8 dBi. Both antennas have high front-to-back ratios in the range of 10 dB throughout the operating band.

Miniaturization techniques for antennas designed for microwave-based heart failure detection systems

Miniaturization techniques for antennas designed for microwave-based heart failure detection systems are explained. Heart failure is a highly malignant heart disease that causes difficulties for the heart to pump sufficient blood to body organs. Pulmonary edema is one of the most apparent symptoms of heart failure where fluids are accumulated in the lungs and cause a shortness of breath. Hence, a constant monitoring of lungs is one of the most efficient ways to detect heart failure in an early stage. A microwave based detection system can be a reasonable alternative for the current tools, such as CT-Scan and magnetic resonance imaging (MRI) that cannot be used for long term monitoring. Antennas are one of the key elements in any microwave-based detection system. Due to the compromise between the required penetration and resolution, a low microwave frequency band (around 0.5-1 GHz) is used in heart failure detection. Thus, designing antenna arrays, which operate efficiently at that band and occupy the available space for their operation with low level of coupling, requires compact antenna elements. Different miniaturization techniques for antennas specifically designed for microwave-based heart failure detection system are explained in this paper.

Specific absorption rate in human torso from microwave-based heart failure detection systems

Congestive heart failure is a malignant cardiovascular disease which can be detected by monitoring the accumulation of fluids in the lungs and some other parts of the human body. One of the promising techniques to achieve that target is a microwave-based diagnostic system. To assess the safety of using that technique at different frequency bands, power levels and polarization, the specific-absorption ratio (SAR) inside the tissues of the human torso is to be calculated to make sure their peak values are within the safe levels. This paper investigates SAR distributions inside the torso tissues by looking at the main three factors; frequency, polarization, and distance between the antenna and the human torso. The obtained results give a guide on the maximum power levels for microwave-based systems aimed at the detection of heart failure to comply with IEEE regulation for specific absorption rate (SAR) in the specified operating frequency band.