Omar Ramahi

• Professor at University of Waterloo

Conducting a life cycle assessment (LCA) for technologies used for water heating is crucial for understanding their environmental impacts throughout their entire life cycles. This analysis facilitates the evaluation of resource consumption, energy usage, and emissions associated with each technology. Accordingly, a comparative LCA of a monopole ant...

Honey is a rich source of sugar and is one of the indispensable ingredients in infant foods. Thus, it can be subjected to adulteration due to its cost. Measurement techniques such as liquid chromatography and near-infrared spectroscopy, used for detecting any adulteration, are expensive and need to be conducted by highly trained personnel for off-l...

This paper presents an attractive microwave technique for permittivity (ε<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = ε′ r−jε′′ r) extraction of nondispersive or weakly dispersive dielectric materials. The technique uses amplitude-only transmission | S <sub xmlns:mml="http://www.w3.org/199...

In the present investigation, the impacts of antenna field of view (FOV) on the accuracy of machine learning (ML) models utilized for the classification of various unmanned air vehicle (UAV) types were systematically explored using full-wave electromagnetic simulation software. Initially, similar to many state-of-the-art works, an ML algorithm was...

Unmanned Aerial Vehicles (UAVs) represent a rapidly increasing technology with profound implications for various domains, including surveillance, security, and commercial applications. Among the number of detection and classification methodologies, radar technology stands as a cornerstone due to its versatility and reliability. This paper presents...

Unmanned Aerial Vehicles (UAVs) pose significant security challenges due to their widespread use in various malicious activities, including terrorist attacks and wartime operations where explosives are attached to them. Conventional radar-based detection and classification methods often rely on range-Doppler signatures, which may lead to misclassif...

This work proposes a novel and simple microwave technique for controlling the coupling factor between complementary split ring resonators (CSRRs) and microstrip transmission lines (TLs), which can be applied to the design of highly sensitive dielectric sensors. By varying the areas of the rectangular CSRRs while maintaining a fixed perimeter, the s...

In this study, we present a novel approach for fall detection, leveraging radar-based sensing systems and advanced digital twin simulations. The choice of radar technology is rooted in its capability for high-resolution detection of micro-movements and its inherent respect for individual privacy, as it does not require visual imaging. The integrati...

A de-embedding method for determining all scattering (S-) parameters (e.g., characterization) of a sensing area of planar microstrip sensors (two-port network or line) is proposed using measurements of S-parameters with no calibration. The method requires only (partially known) non-reflecting line and reflecting line standards to accomplish such a...

The detection and classification of Unmanned Aerial Vehicles (UAVs) are disturbing challenges within contemporary radar systems, wherein the physical characteristics of UAVs, including their size and Radar Cross Section (RCS), exert a substantial influence on radar’s detection capabilities. Smaller UAVs, characterized by reduced RCS values, often e...

Coupled-line directional couplers have played a significant role in microwave systems since their introduction by Oliver [1]. This chapter presents a new application of this component: dielectric constant sensing. To this end, the material under test is placed on the top of a microstrip coupled-line section, and by analyzing the coupler’s response,...

A simple and inexpensive microwave measurement setup based on measurements of magnitudes of transmission properties ( $$|S_{21}|_{\text {dB}}$$ | S 21 | dB ) is proposed for industrial-based microwave aquametry (moisture or water content) applications. An easy-to-apply calibration procedure based on normalization is implemented to eliminate systema...

Metasurfaces, promising technology exemplified by their precise manipulation of incident wave properties and exquisite control over electromagnetic field propagation, offer unparalleled benefits when integrated into radar systems, providing higher resolution and increased sensitivity. Here, we introduce a metasurface-enhanced millimeter-wave radar...

A comb spectrum generator based on the substrate integrated suspension line (SISL) is presented. The circuit is placed in an air cavity formed by the stacking of multilayer substrates. The spectrum generator has good structural stability, self-packaging, high electromagnetic shielding, and a small footprint. Moreover, it can achieve high efficiency...

With the recent developments in the field of ultralow-power wearable and portable electronic gadgets and wireless sensor networks, the number of devices and sensors in a system has increased significantly [1] . The emergence of the Internet of Things has added many additional devices and sensors connected via the Internet [2] , [3] . It is al...

This study explores the viability of using the avoided mode crossing phenomenon in the microwave regime to design microwave differential sensors. While the design concept can be applied to any type of planar electrically small resonators, here, it is implemented on split-ring resonators (SRRs). We use two coupled synchronous SRRs loaded onto a two-...

Temporal late-time reflection and transmission natural mode amplitudes ( A_n , B_n , R_n , and Q_n ) of an N -layer multilayer structure are examined by separating the whole structure into left and right regions and middle layer. Due to this separation, some relations among these amplitudes are ana...

Detection and classification of drones have become crucial due to their potential usage in illicit activities. Radar systems can provide a promising solution to this needed task when combined with machine learning (ML) and artificial intelligence (AI) models. Radar datasets that contain drone information are needed to train AI models. Generating ra...

In this paper, we present an entirely simulation-based method to predict the performance of a complete rectenna system that includes all its components: the receiving antenna, the matching circuits between the antenna and the rectification circuit, and the load circuit. Whereas previous efforts to predict the performance of a rectenna system subdiv...

This paper studies the feasibility of a deep neural network (DNN) approach for bone fracture diagnosis based on the non-invasive propagation of radio frequency waves. In contrast to previous “semi-automated” techniques, where X-ray images were used as the network input, in this work, we use S-parameters profiles for DNN training to avoid labeling a...

p>The antennas and metasurfaces designed for biomedical applications operate primarily in the far-field rather than the near-field. Working in the near-field is considerably more intricate in both design and theory. Furthermore, the proposed methodologies are unsuitable for seamless integration with a radar system that seeks to offer an efficient a...

p>The antennas and metasurfaces designed for biomedical applications operate primarily in the far-field rather than the near-field. Working in the near-field is considerably more intricate in both design and theory. Furthermore, the proposed methodologies are unsuitable for seamless integration with a radar system that seeks to offer an efficient a...

Citation: Almuhlafi, A.M.; Ramahi, O.M. A Highly Sensitive 3D Resonator Sensor for Fluid Measurement. Sensors 2023, 23, 6453. Abstract: Planar sub-wavelength resonators have been used for sensing applications, but different types of resonators have different advantages and disadvantages. The split ring resonator (SRR) has a smaller sensing region a...

A time-domain free-space extraction procedure is proposed to uniquely determine the relative complex permittivity ϵr(ω) based on two-sets of natural frequencies of a metal- and air-backed dielectric sample. A graphical analysis is applied for evaluating whether unique ϵr(ω) can be extracted by using such natural frequencies. The method is numerical...

The temporal reflection response of an N -layer composite structure involving bianisotropic behavior is examined for the first time in the literature. Toward this goal, the wave matrix method, which is fundamental, relatively easier to apply, and compact and iterative suitable for analysis of multilayer structures, is first extended to the analys...

A machine learning aided (MLA) method is employed for the direct permittivity retrieval of dispersive and non-dispersive materials. The method requires low-cost measurements since it solely utilizes the amplitude of the transmission response (|S21|) to extract the complex permittivity. This precludes the need for a network analyzer, and therefore,...

For the future application of wireless power transfer on the human body, a wearable directional button antenna, composed of 2×3 artificial magnetic conductor (AMC) cells, is proposed, where the kinetic energy antenna is put on the elbow, which then charges the receiving communication antenna on the upper arm. The radiator of the button antenna is a...

Mathematical and numerical analyses have been performed to examine the close link between Fabry–Pérot resonance and natural-resonance frequencies. For the mathematical analysis, the conditions resulting in minimum magnitudes of reflection coefficients in frequency-domain are derived for air-backed and metal-backed low-loss non-dispersive (or weakly...

A new microwave method is proposed for accurate determination of complex permittivity $\varepsilon _{\textrm {rs}} = \varepsilon _{\textrm {rs}}^{\prime }--j \varepsilon _{\textrm {rs}}^{\prime \prime }$ of soil samples inserted over a holder within the Electronic Industries Association (EIA) 1-5/8” coaxial measurement cell. Such a determination...

A technique based on artificial neural network (ANN) is proposed to extract electromagnetic properties of reflection-asymmetric samples from reference-plane-invariant scattering parameter measurements. It first determines reference plane transformation distances and then extract material properties. The number of neurons in the hidden layer of the...

A new microwave retrieval method is devised to extract complex relative permittivity $\varepsilon_r$ and complex relative permeability $\mu_r$ . It uses reflection-only scattering parameter measurements of direct and revised configurations of a measurement cell, involving an arbitrarily positioned sample, with matched and shorted terminations....

A method for improving the radiation directivity of a dipole antenna is introduced based on placing plasma rings in the close proximity of the antenna. The method is applicable to different types of antennas; however, in this work, extensive investigation is focused on its applicability to dipole antennas. Simulation results show that the plasma ri...

Microwave imaging holds the potential to bring an alternative to ionizing and expensive imaging modalities, such as mammography, magnetic resonance imaging (MRI), and computerized tomography (CT) scan. The absence of a high-resolution and non-model-based image reconstruction technique is one of the reasons that limited microwaves-based imaging. We...

Today, cancer disease is a significant reason for the death of many patients. In many cases, cancer is diagnosed after metastasized during the body. Thus, the earlier detection gives a better opportunity for treatment and cure. A simple 1-D binary photonic crystal with a defect layer is proposed with the structure (Si/SiO2)N/Defect/(Si/SiO2)N as a...

An extraction technique is proposed for electromagnetic characterization of metal-backed multilayer metamaterial (MM) structures demonstrating reflection-asymmetric property. It uses recursive scattering parameters for direct and reversed configurations of a multilayer structure. Its algorithm was validated by comparing the extracted electromagneti...

An extraction technique is proposed for electromagnetic characterization of metal-backed multilayer metamaterial (MM) structures demonstrating reflection-asymmetric property. It uses recursive scattering parameters for direct and reversed configurations of a multilayer structure. The algorithm was validated by comparing the extracted electromagneti...

Simple methods using a microstrip coupled-line directional coupler (CLDC) are presented for dielectric constant measurements. The material under test (MUT) is placed on the coupled-line section of the coupler, and either the coupler’s coupling ( $\lvert S_{31} \lvert $ ) or its isolation level ( $\lvert S_{41} \lvert $ ) is considered as the sens...

Using atmospheric data, which include pressure, temperature, relative humidity and water vapor pressure, the actual refractive index of a specific segment of the atmosphere has been modeled. Based on the refractive index, a numerical method is presented to quickly estimate the propagation path of the radio wave in the troposphere. Utilizing the ter...

This work presents a breast cancer detection modality using a metasurface as the imaging medium and a microwave source. The fundamental concept is to record the electromagnetic energy, which, when transmitted through the breast, scatters differently according to the variation in the electrical properties of the breast tissue. The energy captured by...

This paper introduces a machine learning (ML) measurement method to retrieve the complex permittivity profile of dispersive and non-dispersive materials with high or low loss. The proposed method employs amplitude-only transmission measurements, removing the need for phase and reflection measurements. This approach relies on training a multi-layer...

A microwave method is proposed to determine the forward and backward propagation constants ( $\gamma ^{+}$ and $\gamma ^{-}$ ) and the wave impedance ( $z_{w}$ ) of reciprocal and non-reciprocal microwave networks whose positions are not known within their measurement cells (position-insensitive). The proposed method relies purely on analytical...

Cancer is a fatal disease that leads to the death of many people all over the world. The detection of cancer disease is one of the most challenging in the medical field. A novel sensor based on a one-dimensional ternary photonic crystal is proposed for the detection of cancer cells. The proposed structure consists of a defect layer sandwiched betwe...

In this paper, the characteristics of two different antenna types; metasurface antennas (MSA) and microstrip patch antenna (MPA) array are analyzed. To compare their sensitivity to bending, multiple numerical studies have been performed on both designs at different curvatures. The footprint of each design is $120 \times 90\ \mathbf{mm}^{2}$ . The d...

As a result of the risks that waterborne bacteria bring to the human body, identifying them in drinking water has become a global concern. In this paper, a highly sensitive surface plasmon resonance (SPR) biosensor consisting of prism, Ag, graphene, affinity layer and sensing medium is proposed for rapid detection of the waterborne bacteria. Four S...

A new flexible circularly polarized (CP) wearable antenna is proposed for Wireless Body-Area Network systems (WBAN) operating at 5.8 GHz. The circular polarization is enabled by combining a microstrip-line monopole feed and an inverted L-shaped conformal metal strip extended from a coplanar waveguide. The proposed antenna shows satisfactory perform...

A methodology relying on relating terms of a two-port error network to the scattering (S-) parameters of a two-port network or device is applied to extract its full S-parameters. The new methodology has only one sign ambiguity problem (two solutions) in evaluation of S11 (and thus S22) while the similar methodology in the literature has two sign am...

A new de-embedding line-line method has been proposed for accurate complex relative permittivity (εr) determination of soil samples loaded into a EIA 1-5/8” coaxial transmission line measurement system. The method has three main features. First, it bypasses the requirement of calibration of this system by using only two identical coaxial lines with...

A new deembedding technique is proposed for relative complex permittivity $\varepsilon _{r}$ determination of dielectric materials using gated free-space measurements. Its three main features are 1) it does not require any formal calibration procedure (calibration-free); 2) it is position-insensitive; and 3) it extracts ripple-free $\varepsilon...

Microwave techniques, as an indirect approach, can be applied for analyzing water content in honey by way of permittivity measurements. However, these techniques require proper calibration to accurately perform such indirect evaluation. Improper calibration standards used in this calibration process could naturally result in a reduction in the accu...

Today, cancer disease is a significant reason for the death of many patients. In many cases, cancer is diagnosed after metastasized during the body. Thus, the earlier detection gives a better opportunity for treatment and cure. A simple 1-D binary photonic crystal with a defect layer is proposed with the structure (Si/ SiO 2 ) N /Defect/(Si/ SiO 2...

This study uses a machine learning assisted (MLA) method to determine the complex permittivity profile of high-to-low loss materials. The presented method is based on using the amplitude of the transmission response of the measurement sensor, eliminating the requirement of phase and reflection measurements. We trained a multi-layer artificial neura...

This letter proposes a novel wearable metasurface antenna (MSA) based on electric ring resonators (ERR) for 5.8 GHz wireless body area network (WBAN) applications. All substrates of the proposed design are made from the semi-flexible Rogers RT5880 material. To achieve size miniaturization, 6 × 8 ERR elements are placed on a flat surface connected t...

A machine learning approach is proposed to provide an accurate retrieval of the dielectric properties of materials. In our earlier work, based on a semi-analytic solution of transmission lines, we proposed a method for characterizing dispersive materials having a known dispersion model using amplitude-only transmission measurements. In this work, i...

This paper presents a complex permittivity measurement method for low-dispersive materials as a function of frequency. The introduced method relies only on transmitted power signals which are collected using a spectrum analyzer/power meter, removing the need for phase measurements and a vector network analyzer. This method provides a very good accu...

Today, detecting processes of waterborne bacteria in drinking water is a global challenge because these bacteria can lead to dangerous diseases to the human body. In this paper, we have developed a new sensor for the detection of waterborne bacteria based on a one-dimensional (1D) defective binary photonic crystal. The defect layer is taken as a wa...

A fully automated approach for designing metasurfaces whose unit cell may include metallic vias is proposed. Towards this aim, a ternary version of the particle swarm optimization (PSO) algorithm is employed in order to find the optimal metallic pattern and via-hole positions simultaneously. In the proposed design method, the upper surface of the u...

A circularly polarized, high aperture efficiency antenna based on metasurface (MTS), inexpensively fabricated using a standard printed circuit board (PCB) technology, is presented. An array of 8 × 8 cross-shaped resonators was designed to operate at 3.1 GHz with a 12 cm × 12 cm (i.e., 1.24 λ 0 × 1.24 λ 0 ) footprint size. Each resonator was double...

We propose a surface plasmon resonance (SPR) biosensor that consists of six layers: glass prism (SF 10), chromium, metal, molybdenum disulphide, graphene, and sensing medium. A seventh layer is added between the glass prism and the chromium layer, which is a gap filled with plasma as a dielectric material. The plasma layer is expected to carry the...