Vahid Nayyeri

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• PhD
• Professor (Associate) at Iran University of Science and Technology

A simple yet accurate free-space microwave method is proposed for the determination of the dielectric constant (ε<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub>) of solid materials from uncalibrated reflection measurements (metal termination only and sample terminated in the same metal terminat...

This study presents a very thin wideband linear polarization converter in transmission mode with near-unity conversion efficiency. The suggested converter consists of a periodic array on a single-layer substrate, two metallic layers and six vias. Metallic vias connect the upper and lower layers of the construction. The radiated electromagnetic wave...

This study aims to investigate dispersion engineering mechanisms within unilateral and bilateral metasurface-based leaky-wave antennas, presenting methodologies focused on space-time modulation of impedance boundary conditions. Utilizing the generalized framework based on the Floquet-wave expansion method, the research precisely investigates the ef...

This paper presents an alternative solution for higher frequency power amplifier design. Using a plasticpackaged GaN transistor and high-efficiency design techniques, a power amplifier for the space-to-earth satellite was designed and fabricated. The proposed design approach relies on determining an appropriate design space for the matching network...

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...

For electromagnetic stealth against radar digital signal processing systems, real-time adjustable impedance of the platform is urgently needed under the guaranteed instantaneous tracking capability. In this study, a multifunctional metasurface (MMS) based on dynamic resistance loading (DRL) technology is proposed to dynamically modulate the scatter...

This work presents the application of a planar microstrip metamaterial (MM)- motivated sensor in the form of a split-ring resonator (SRR) for the detection and quantification of water adulteration in honey samples. The proposed sensor utilizes inexpensive software-defined radio (SDR) measurements, offering a cost-effective solution. Unlike previous...

This paper proposes a modified quasi-TEM horn antenna incorporating corrugated reactive impedance surfaces to enhance performance across a wide frequency band. The introduction of corrugated surfaces significantly improves both impedance matching and radiation characteristics, enabling a highly miniaturized physical aperture without compromising pe...

In this article, two anisotropic holographic metasurfaces with ultralow profiles are proposed to produce wideband high-intensity self-bending Bessel-like beams with customized propagation trajectories in the microwave band. The phase distribution for generating Bessel-like beams with arbitrary paths is obtained by appropriately modifying the conica...

In this article, a rasorber with energy-selective passband and ultrawideband absorptive out-of-band is proposed, which combines the advantages of conventional frequency-selective absorber (FSA) and energy-selective surface (ESS). The proposed design consists of an upper lossy layer and a lower active layer. By analyzing the equivalent circuit model...

Digital predistortion (DPD) has proven to be an efficient method of linearizing power amplifiers (PAs). In recent years, the use of neural networks (NNs) for DPD has gained momentum. This development can be attributed to the general attention NNs have gotten in recent years, but more importantly, to their ability to find efficient solutions to prob...

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...

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...

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...

This article introduces an ultrawideband antenna with stable phase center and circular polarization. The proposed antenna is a low-profile cavity-backed spiral antenna measuring 58 × 58 × 50 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , where the cavity is partially filled with an absorb...

A dual-band frequency-selective (FS) linear rotation polarizer leveraging a substrate-integrated waveguide cavity technology equipped with two perturbation techniques is introduced. The FS polarization rotator consists of a square cavity divided into two subcavities: a triangular cavity positioned next to an irregular pentagon cavity, connected by...

A novel thin, optically transparent microwave metamaterial absorber (TMMA) is presented. The proposed structure utilizes a 3-mm-thick polycarbonate (PC) main substrate coated on both sides with 8-nm-thick gold thin films deposited via thermal evaporation. To achieve maximum absorption bandwidth, polarization insensitivity, and angular stability, th...

This paper presents a novel and accurate procedure for designing a Doherty power amplifier (DPA) for wireless systems. The method is based on a systematic approach to designing the matching networks of both Main and Auxiliary devices, which employs an optimization process to set their input impedance in the corresponding optimal regions obtained fr...

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...

In this article, two 3-D-printed all-dielectric meta-structures that can produce diffraction-free self-acceleration beams with different transverse intensity profiles are proposed in the microwave frequency band. The first single-layer meta-structure, combining the Fourier lens phase and cubic phase distributions, is engineered to generate Airy bea...

In this paper, a novel technique for detecting female breast anomalous tissues is presented and validated through numerical simulations. The technique, to a high degree, resembles X-ray mammography; however, instead of using X-rays for obtaining images of the breast, low-frequency electromagnetic fields are leveraged. To capture breast impressions,...

This research explores the application of an artificial intelligence (AI)-assisted approach to enhance the selectivity of microwave sensors used for liquid mixture sensing. We utilized a planar microwave sensor comprising two coupled rectangular complementary split-ring resonators operating at 2.45 GHz to establish a highly sensitive capacitive reg...

This study explores the properties and potential of magneto-dielectric (MD) material Ni0.25Cu0.25Zn0.50Fe2O4–BaTiO3 as an antenna substrate for miniaturization and bandwidth enhancement. The MD material was synthesized using a solid-state method and different amounts of BaTiO3 (0, 5, 10, 15 and 20%) were added to improve its relative permittivity....

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,...

In this contribution, a workflow procedure adopted to design a Doherty Power Amplifier (DPA) for broadband Sub-6 5G frequency applications is presented. The approach developed accounts for loading effects of the auxiliary amplifier on the main amplifiers in back-off condition. Moreover, an improved version of optimum region (as opposed to optimum p...

This study presents a novel approach to decrease the radar cross-section (RCS) by integrating and expanding the phase cancellation and polarization conversion methods. In this proposed technique, only one unit cell, akin to the polarization conversion method, is utilized. The RCS reduction surface is comprised of arrays of this unit cell; each arra...

A wideband energy capturing adapter based on 3-D meta-structure is presented in this article for wireless power transmission (WPT) system. Compared with conventional planar resonant structure, the proposed 3-D meta-structure for energy collection is designed first. After analyzing the magnetic field magnitude and power loss density distribution of...

This article introduces a novel design for a thin, single-layer, optically transparent microwave metamaterial absorber. The proposed structure is composed of a polycarbonate (PC) substrate with two sides coated with gold films of a few tens of nm thickness via thermal evaporation. A specific periodic pattern is etched onto the upper side of the sub...

This paper proposes a thin multiband reflective polarization converter surface capable of transforming a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in frequency bands of 8.14-8.25 GHz, 10.23-10.60 GHz, 13.90-14.08 GHz and 16.59-16.71 GHz, while, it reflects a circularly polarized (CP) wave in f...

A special medium-density fiberboard (MDF) has been fabricated in order to electromagnetic shielding composite by adding iron oxide nanoparticles (NF) to wood fiber (WF). The aim of this work was to study the panel properties with different loadings (1, 3, 5, 7, and 10 wt %) of Fe3O4 nanoparticles. The mechanical, physical, and Electromagnetic (EM)...

Planar microwave sensors have become increasing developed in recent decades, especially in material characterization (solid/liquid) as they provide regions highly sensitive to the surrounding medium. However, when it comes to deciphering the content of practical biological analytes or chemical components inside a host medium, even higher sensitivit...

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...

This article presents an active second harmonic injection technique for linearizing power amplifiers (PAs). In this method, a second harmonic signal with adjustable amplitude and phase, which is generated by a differential pair network, is injected into the input of a PA in a forward path. The tunable input and output matching circuits of the propo...

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...

In this paper a simple implementation of a radial N-way power combiner based on the Wilkinson power combiner is presented. The design only makes use of printed circuit board technology and as a result has a relatively simple, lightweight and inexpensive manufacturing process. As a proof of concept, a 6-way radial power combiner in the center freque...

Carbon fiber (CF) filled fiberboard for electromagnetic (EM) shielding applications was produced in this study by mixing CF with wood fiber (WF). The aim of this work was to study the panel properties with different loadings (1%, 2%, 3%, 5%, and 10%) of CF. The mechanical, physical, and electromagnetic interference (EMI) shielding properties of the...

A planar implementation of N-way radial power combiners with isolated input ports is presented. While keeping the design simple, the presented combiner can be manufactured solely using printed circuit board technology, and as a result, has a low weight and manufacturing cost. As proof of concept, two power combiners are designed and built. First, a...

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...

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...

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 new generation of reprogrammable multi-functional bias encoded metasurfaces for dynamic wave manipulation using liquid crystals (LC). This metadevice is an array of unit-cells based on LCs to provide the desired phase steps based on its large birefringence property. The presented 3-bit coding metasurface (CM) use 8 states of "000"-"111...

A wideband and highly-efficient power amplifier (PA) is designed using a simple and systematic approach. This method employs an optimization process to set the input impedance of the matching networks in optimal regions on the Smith chart, obtained using conventional load-pull/source-pull simulations, in both the fundamental and second harmonics. T...

The compressed sensing (CS) technique is applied to the diffraction tomography (DT) method for through-the-wall radar imaging (TWRI), which leads to significantly decreasing the number of measurements and, consequently, reducing the data acquisition time. A large amount of required measurements is a real difficulty in TWRI, which is addressed in ou...

A simple and effective method for linearization of power amplifiers (PAs) is proposed. The method is based on the second harmonic injection into the input of the PA. The second harmonic is generated in a feedback path by taking the low-power transistors of a pseudo-differential pair amplifier to their nonlinear regime. The amplitude and phase of th...

This paper presents an inexpensive transmission line approach to reconstruct the dielectric properties of dispersive and non-dispersive materials, with low or high loss. This method uses amplitude-only transmission measurements, namely power measurements, thereby removing the need for phase measurements. The proposed method only requires a signal g...

A wideband, thin, and multilayer (planar) microwave absorber is designed in this paper. The absorber is a periodic array of cells which includes three patterns of a resistive film on two dielectric substrates. To design the array’s cell, a pattern optimization procedure based on applying a binary optimization algorithm was utilized. The outcome of...

This letter proposes the application of the nonuniform fast Fourier transform to the diffraction tomography (DT) image reconstruction method for 3-D through-the-wall radar imaging which leads to a significant speed-up of the image reconstruction procedure. This speed-up is of critical importance in real-time imaging systems since during a long time...

This letter introduces a systematic procedure to reduce the mutual coupling (MC) between microstrip antennas. The method is based on using parasitic elements between the antennas. The shape of the parasitic element, which impacts the MC and other radiation properties, is determined in a systematic pattern optimization procedure based on pixelizatio...

This article presents a new concept for sensitivity enhancement of dielectric sensors by loading a microstrip line with multiple coupled resonators. The concept is based on the interresonator coupling mechanism, which is represented as a mutual capacitance in an equivalent lumped circuit model. This mutual capacitance increases the sensitivity of t...

This paper presents a novel ultracompact narrow bandpass filter with high selectivity. The proposed filter is composed of cascading two basic cells. Each cell is basically a microstrip line loaded with a quasiplanar resonator and series gaps which can be fabricated using a standard multilayer printed circuit board technology. The structure is analy...

This paper presents the design process, fabrication, and measurement results of a 1-3 GHz, efficient, 90-watt power amplifier (PA). Our design method is based on the source-pull / load-pull and the X-parameter models of the transistor which were obtained using its nonlinear compact model. According to the measurement results, the fabricated PA prov...

The effect of different loading profiles of a conductive nanofiller on the electromagnetic absorption of a gradient nanocomposite (NC) absorber is studied. First, the relative permittivity of a polymer matrix loaded with different contents of the conductive nanofiller is obtained using a theoretical model and experimentally measured data. Then, gra...

This paper presents a concept of an intelligent sensing technique based on modulating the frequency responses of microwave near-field sensors to characterize material parameters. The concept is based on the assumption that the physical parameters being extracted such as fluid concentration are constant over the range of frequency of the sensor. The...

A highly sensitive microwave near-field sensor based on electrically-small planar resonators is proposed for highly accurate characterization of dielectric materials. The proposed sensor was developed in a robust complete-cycle topology optimization procedure wherein first the sensing area was pixelated. By maximizing the sensitivity as our goal, a...

A two-dimensional (2-D) metasurface design for backward leaky wave suppression in microwave regime is proposed based on the theory of holography. The so-called Rabbit’s ears phenomenon describes that the backward mode in the reference wave plays the destructive role and makes the holography principle to behave properly mainly in an only narrow freq...

This paper presents design, fabrication and measurement results of a high-power Doherty power amplifier (DPA) with a fractional bandwidth of wider than 90%. An inverter-less architecture was used to overcome the intrinsic bandwidth limitation of conventional DPA in which a quarter wavelength impedance inverter is utilized. Thanks to the use of a re...

This work presents two approaches to design and implement three-dimensional (3D) graded index (GRIN) flat lenses consisting of concentric annular segments. Generally, the design of GRIN flat lenses calls for segments with very specific tailored permittivity which makes the realization of the lens challenging. To meet this challenge, each segment of...

This paper presents a new approach to design and implementation of a wideband microstrip radial power combiner with a planar structure in a way that it can be simply and inexpensively fabricated using a standard multilayer printed circuit board (PCB) technology. A 14-way power combiner with a two-octave bandwidth (1.5-6 GHz) is designed and fabrica...

For the first time, an unconditionally stable finite-difference time-domain (FDTD) method for 3-D simulation of dispersive nonlinear media is presented. By applying a new adopted alternating-direction implicit (ADI) time-splitting scheme and the auxiliary differential equation (ADE) technique, the time-step in the FDTD simulations can be increased...

A novel finite-difference solution of the time-domain three-dimensional wave equation with a stability criterion relaxed from the discretization space steps in two directions is presented. This method is particularly useful and efficient for electromagnetic simulation of structures having fine details in two Cartesian directions. During the algorit...

In this paper, a novel complementary split-ring resonator (CSRR)-based sensor for full characterization of magneto-dielectric materials is proposed. In general, the operation of microwave resonance-based sensor hinges on the shift in the resonance frequency and the change in the quality factor of the loaded structure. However, both the electric per...

This paper presents a new 3-D hybrid implicit explicit (HIE) finite-difference time-domain (FDTD) method with a stability criterion relaxed from the discretization space steps in one direction. The proposed method is particularly useful and efficient for electromagnetic (EM) simulation of structures having fine details in one Cartesian direction su...

A dual-band and polarization-independent electromagnetic energy harvester composed of an array of pixelated unit cells is proposed. The pixelated unit cell is basically a dual-band resonator loaded with two resistors which model the input impedance of a power combining circuit in a complete harvesting system. To design the unit cell, a topology opt...