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  • ItemOpen Access
    A Contrast-Source Inversion-Assisted Attention-Unet for Microwave Imaging
    (IEEE Xplore, 2025-08) Maricar, Mohammed Farook; Zakaria, Amer; Qaddoumi, Nasser
    This paper introduces a physics-based intermediate estimate as input to the Attention-Unet (ATTN-Unet) architecture for solving the electromagnetic inverse scattering problem in microwave imaging. This input is calculated from the tenth iteration results of the conventional contrast source inversion (CSI) algorithm, which is referred to as ITER10. This input incorporates more physical domain knowledge than the widely used backpropagation (BP) estimate, which corresponds to the zeroth iteration of the CSI. While the non-iterative BP estimate is popular due to its simplicity, this work demonstrates that using ITER10 enhances reconstruction accuracy without significantly increasing computational cost. For comparison and the validation of choosing ITER10, the performance of the ATTN-Unet is evaluated using estimates from other intermediate CSI iterations, namely ITER5, 20, 30, and 40. Further, the network outputs are the reconstructed relative complex permittivity values (real and imaginary) of an imaged object. The networks are tested using synthetic and experimental datasets. The results show that the ITER10-ATTN-Unet significantly enhances reconstruction accuracy, outperforming both the BP-ATTN-Unet and the conventional CSI method. Furthermore, the results demonstrate that the ITER10-ATTN-Unet achieves a better balance between accuracy and computational cost compared to the other ITER-based models. These findings highlight the effectiveness of ITER10 as a strong alternative to BP in improving neural network reconstructions in microwave imaging.
  • ItemOpen Access
    Staircase-Enhanced Magneto-Electric Dipole Antenna for Wideband CP 5G Applications with High-Gain Arrays
    (MDPI, 2025-12-16) Malhat, Hend; Zakaria, Amer; Qaddoumi, Nasser
    This paper presents a compact magneto-electric dipole (MED) antenna optimized for wideband circularly polarized (CP) radiation for 5G applications. It incorporates a staircase-shaped electric dipole with trimmed corners to excite orthogonal modes for enhanced CP performance. The proposed single-layer MED antenna achieves a 20.6% wide-impedance bandwidth (|𝑆₁₁| <−10 dB, 22.97–28.12 GHz) and 21.9% CP bandwidth (𝐴𝑅<3 dB, 22.23–27.83 GHz) with a compact footprint of 15×15×1.6mm³. There is a symmetrical radiation pattern with a co-to-cross polarization ratio >23 dB and a stable gain of 8.8 dBi. An equivalent circuit model is optimized via particle swarm optimization (PSO). The optimized MED antenna is utilized to investigate various CP-MIMO configurations and wideband sequential arrays. Next, a 1×2 CP-MIMO antenna system is developed, employing polarization diversity in parallel and mirror configurations. Isolation is improved by etching a ground slot between the MED elements, yielding isolation levels of below −20 dB and −23 dB, respectively. Further, a 2×2 CP-MIMO configuration is designed and evaluated. This arrangement demonstrates an envelope correlation coefficient (ECC) of 1×10‾³ and a diversity gain of approximately 10 dB across the operating bandwidth. Finally, a sequential array is designed that applies a 90∘ sequential rotation and phase excitation to MED elements for high-gain CP 5G communications. Here, various array sizes are evaluated, with an 8×8 MED array providing CP radiation (𝐴𝑅≤1 dB) from 20 to 30 GHz with enhanced impedance and axial ratio bandwidths and stable gain with a peak value of 27.47 dBi.
  • ItemOpen Access
    Detecting Defects in Materials Using Nondestructive Microwave Testing Techniques: A Comprehensive Review
    (MDPI, 2025-03-17) Ghattas, Ahmad; Al-Sharawi, Ramzi; Zakaria, Amer; Qaddoumi, Nasser
    Microwave nondestructive testing (MNDT) has shown great potential in detecting defects in various materials. This is due to it being safe and noninvasive. Safety is essential for the operators as well as the specimens being tested. Being noninvasive is important in maintaining the health of critical structures and components across various industries. In this paper, a review of MNDT methods is given with a comparison against other NDT techniques. First, the latter techniques are described, namely testing using a dye penetrant, ultrasound, eddy currents, magnetic particles, or radiography. Next, an overview of various microwave NDT methods is provided through a review of the applications, advantages, and limitations of each technique. Further, a detailed review of emerging MNDT techniques like microwave microscopy, active microwave thermography, and chipless radio frequency identification is presented. Next, a brief description of current and emerging algorithms employed in MNDT is discussed, with emphasis on those using artificial intelligence. By providing a comprehensive review, this article aims to shed light on the current state of MNDT, thus serving as a reference for subsequent innovations in this rapidly evolving domain.
  • ItemRestricted
    A Wideband Polarization Conversion Absorber for Electromagnetic Cloaking Applications
    (IEEE Xplore, 2026-02-24) Malhat, Hend; Zakaria, Amer; Qaddoumi, Nasser
    This paper presents the design, analysis, and implementation of a wideband polarization conversion absorber (PCA) metasurface for electromagnetic cloaking applications. The proposed unit-cell consists of a centered elliptical slotted ring resonator with four-petal structures printed on an FR4 dielectric substrate. A grounded foam layer is used to improve matching and enhance bandwidth, while providing mechanical support. A wide bandwidth from 3.4 GHz to 10.2 GHz is obtained for an absorption conversion ratio (ACR) ≥ 90%, with practical overlapped RCS reduction and cloaking performance achieved over 4.0–9.5 GHz across planar, curved, and 3D configurations. A theoretical analysis and parametric study are developed to optimize the PCA unit-cell’s performance. The optimized design is fabricated and tested. PCA metasurfaces are designed for radar cross-section (RCS) reduction via co-polarized reflection suppression, achieved through high cross-polarization conversion and minimal co-polarized reflection (evaluated under matched polarization conditions). Next, a sequential arrangement of different sizes of PCA supercells is investigated for RCS reduction from planar and curved surfaces. For the 10×10 supercell, an RCS reduction exceeding −25 dBsm is observed over a broad angular range from −30◦ to 30◦. The 5 × 5 supercell also achieves significant RCS reduction, exceeding −15 dBsm within an angular range of −25◦ to 25◦. The cloaking performance of the PCA metasurface is further investigated when applied to cubical, cylindrical, and rhombus-shaped PEC objects by evaluating the reduction in the RCS from these objects.
  • ItemEmbargo
    Enhanced Brain Source localization using Multimodal signal Fusion
    (2025-12) Chaari, Anas; Al Nashash, Hasan; Mir, Hasan
    The human brain is the most complex organ that controls multiple cognitive, sensory, and motor functions. Understanding its complex dynamics requires precise brain source localization techniques, which are important for diagnosing neurological disorders and studying brain functions. Multimodal neuroimaging can be applied to improve localization accuracy by combining modalities with complementary strengths of each modality. This project proposes an approach for multimodal brain source localization by integrating electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) data using Restricted Maximum Likelihood (REML) model to enhance both spatial and temporal accuracy. The methodology is validated using simulated data, where known neural sources were reconstructed independently using EEG and fNIRS, and then jointly using fNIRS-derived spatial priors. Integration reduced mean localization error (MLE) from 103.46 mm to 22.75 mm, showing the method’s accuracy. The proposed methodology was then applied to experimental data from 20 healthy subjects performing cognitive stress-induction tasks. EEG processing included filtering and ICA-based artifact removal, while fNIRS data underwent motion correction and detrending. The results showed consistent improvements across detection performance metrics, including specificity, accuracy, and MLE. For example, in Subject 10, MLE reduced from 72.601 mm (EEG only) to 16.010 mm (integrated), alongside improvements in specificity (0.3359 to 0.9883) and accuracy (0.3373 to 0.9873). A novel contribution of this work is the inclusion of neurovascular coupling delay compensation prior to multimodal integration, where EEG data are time shifted relative to hemodynamic responses in 2 s increments from 3 to 21 s. Optimal alignment was achieved between 3–5 s, showing enhanced localization performance. Additionally, analysis using frontal-only EEG channels to match the fNIRS cap layout im- proved spatial constraint and reduced interference from unrelated cortical regions.

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