Volume 80, Issue 1-2

We present the design and theoretical study of a defect-acquainted superlattice sensor for detecting hemoglobin levels in blood samples. For the design, a sample cavity is inserted between periodically arranged potassium tantalate niobate and magnesium oxide layers. The sample cavity behaves like a defect. Depending on the optical path provided by the defect layer a resonance peak appears in the optical transmission spectra. The optical response and resonance peak of designed sensor is theoretically analyzed using the electromagnetic wave propagation theory and transfer matrix method. The sensor parameters, sensitivity, quality factor and figure of merit, are examined and optimized for high performance. The limit of detection of the sensor was also monitored. The optimized biosensor provides a real time sensing response for blood hemoglobin levels in the near-infrared range and works well with a detection limit 9.42 × 10 −4 RIU.

This work presents an innovative compact dual-band microstrip sensor based on a complementary split-ring resonator (CSRR) for the precise characterization of water–ethanol mixtures. The sensor, optimized via HFSS, offers high sensitivity and an impressive quality factor through dual-band operation at 3.5 GHz and 4 GHz. The validity of the sensor’s performance is supported by both simulated and measured results, which demonstrate its capacity to extract the complex dielectric permittivity of liquids. The proposed sensor utilizes CSRR and offers dual-band resonance, making it a promising alternative to traditional CSRR. This innovative sensor’s dual-band capability, achieved through its unique use of CSRR, renders it particularly suitable for applications in chemical and biomedical fields.

In this communication, a single-layered (resistive ink-dielectric-metal based) wide-band frequency selective surface microwave absorber using a unique pattern of resistive ink is presented analytically and experimentally for the reduction of radar cross section (RCS) in stealth technology. As compared to multilayer designs, single layer designs are more easy to deploy in practical applications like stealth technology. Further in contrast to other options, resistive ink has numerous benefits, including consistent wideband absorption, uniform resistance distribution, low cost, and material flexibility. In this work four-fold symmetric topology based on resistive ink is imprinted using screen printing technology on a copper-backed FR-4 dielectric substrate to yield polarization insensitive response. Absorptivity over 90 % has achieved over the frequency range of 17.2–26.5 GHz, associated to a fractional bandwidth of 42.5 % for normal incidence of electromagnetic (EM) wave with two absorption peaks at 19.4 GHz and 22.9 GHz covering the K U and K bands. In the entire band, more than 20 dB monostatic RCS reduction is obtained with a maximum RCS reduction of 38 dB at 22.9 GHz. Current distribution on the upper and lower surface, along with the induced electric fields at absorption peaks, and equivalent circuits have presented to examine the absorption mechanism. The proposed design is evaluated for transverse electric (TE) and transverse magnetic (TM) waves under oblique incidence, and for varying polarization angles in TE and TM mode, demonstrating wide angular stability. A prototype has been fabricated, and the measured outcomes are compared and validated against the simulation results. The novelty of the proposed absorber lies in its distinctive single layer λ 1 /11 ( λ 1 corresponding to the lower absorbing frequency) thin topology made from resistive ink, which shows polarization insensitivity and wide angular stability. All the above-mentioned attributes along with 18 % fractional bandwidth of 20 dB RCS reduction make it commercially appropriate for RCS reduction in stealth applications.

This work showcases a low-cost portable Complementary Dual Split Ring Resonator (CDSRR)-based microstrip antenna loaded with defective ground structure particularly designed for liquid sample sensing applications. Utilizing state-of-the-art 3D printing technology and polylactic acid (PLA) as the antenna substrate, the design integrates a unique rectangular ring-shaped channel into the substrate to obtain a highly sensitive microfluidic channel-based antenna sensor. The proposed antenna sensor is designed to operate in the vicinity of ISM frequency bands. The overall dimensions of the proposed sensor are 0.5  λ 0  × 0.5 λ 0 and hence compact in size. The proposed antenna sensor resonates at different frequencies with change in the fluid samples inside the microfluidic channel and hence, it can detect different types of liquid materials. The proposed design provides highest sensitivity of 2.42 % and high Q-factor of 67.89 with a very small volume of 0.723 ml. Additionally, it has the ability to detect several kinds of edible oils, such as olive, mustard, and castor oils, which allows the amount of adulteration to be assessed for food safety purposes. The prototype of the sensor is also fabricated with 3D printing technology and also experimentally tested. This validation of the design highlights the sensor’s effectiveness and dependability, as well as its potential for real-world integration in a variety of applications requiring high sensitivity and accurate detection of liquid samples.

This paper presents the design and performance evaluation of a small-size dual-band 90° coupler optimized for operation at 2.42 GHz and 4.9 GHz, making it suitable for applications in 5G communication systems. The proposed coupler uniquely integrates open-ended stubs and spiral lines to achieve significant harmonic suppression, effectively eliminating unwanted harmonics up to the 7th order. This makes the design highly efficient for 5G bands, where minimizing interference and maintaining signal integrity are critical. The dual-band capability of the coupler is demonstrated with minimal insertion loss, with S21 ​parameters of 0.3 dB at 2.42 GHz and 0.8 dB at 4.9 GHz, and acceptable coupling S31 ​of 0.12 dB and 1.36 dB, respectively. The design also maintains a compact footprint, occupying an overall area of just 91.2 mm 2 ( 0.009   λ g 2 $0.009\hspace{0.17em}{\lambda }_{g}^{2}$ ), making it one of the smallest couplers compared to existing designs. The fractional bandwidths (FBW) achieved are 22.72 % at 2.42 GHz and 12.93 % at 4.9 GHz, indicating robust performance across both frequency bands. The measurement results closely align with the simulated data, confirming the accuracy and effectiveness of the design approach. This work uniquely integrates open-ended stubs and spiral lines, demonstrating a novel dual-band coupler with superior harmonic suppression for 5G.

In this paper, a miniaturized wideband bandpass filter based on transversal signal interference technique is proposed. By introducing two independent signal transmission paths, a highly selective and compact design is achieved. The filter utilizes a combination of two paths to excite four controllable resonant modes, which helps to generate a wide passband. Besides, phase cancellation between the two paths yields five transmission zeros on both sides of the passband, which greatly improves frequency selectivity. The proposed wideband filter has very compact dimensions, where the overall circuit size is only 0.39 λ g  × 0.13 λ g ( λ g is the guided wavelength). The center frequency of the designed filter is 4.38 GHz with 3-dB fractional bandwidth of 71.2 %. The design concept has been effectively validated through the experimental results of the fabricated filter, which are in good agreement with the simulated results.

A bandpass filter (BPF) designed for the 5G N77 band using low-temperature co-fired ceramic (LTCC) technology is presented in this paper. This proposed BPF incorporates a pair of hook-shaped microstrip feeding lines (HSMFLs) on the top layer and a T-junction resonator on the second layer. In order to realize a wider upper stopband, the HSMFL is composed of a stepped-impedance variation microstrip line (SIVML) and a folded microstrip line with enhanced coupling effect at the end. With a compact structure measuring 26.85 × 12.68 × 0.20 mm 3 , which equates to 0.689 × 0.325 × 0.005  λ g 3 , the design achieves an exceptional performance profile. The proposed BPF demonstrates superior performance with an out-of-band suppression higher than 20 dB up to 3.35  f 0 , while maintaining low in-band insertion loss (IL) under 0.3 dB. The proposed BPF offers significant potential for 5G mobile communications due to its wide upper stopband, exceptional out-of-band suppression capability, low in-band IL, simple design, and compact structure.

This paper presents a Fabry–Perot cavity-backed multiple input multiple output (MIMO) antenna for millimeter-wave (n257 band) 5G applications. The proposed design comprises three orthogonally placed rectangular patch antenna elements printed on a single substrate, complemented by three different variants of partial reflecting surfaces (PRSs) used as superstrates. The inclusion of the PRS significantly enhances the antenna gain at the operating frequency 28 GHz, starting from 7.21 dBi (without PRS) to 12.24 dBi (with unprinted PRS), and further to 12.74 dBi (with double-sided printed PRS). The orthogonal placement of antenna elements enables high inter-port isolation without requiring additional decoupling structures, and results in a compact form factor (1.4 λ 0  × 2.7 λ 0 , where λ 0 is the free-space wavelength at 28 GHz). Furthermore, the design achieves high aperture efficiencies of 87.9 % and 91.5 % for the unprinted and printed superstrate configurations, respectively. Both variants of the MIMO antenna are fabricated and experimentally validated, with results confirming that all key performance parameters fall within desirable limits, thereby making the proposed antenna a strong candidate for advanced 5G applications.

This article presents a compact dual-band skin implantable antenna for biomedical applications in the ISM 2.4 GHz band and WMTS 1.4 GHz band. An effective permittivity calculation technique was used to ensure antenna operation at the desired bands. It exhibits a compact volume of 0.0984 λ 0  × 0.082 λ 0  × 0.00468 λ 0 . This study presents a complete system comprised of a Wireless Power Transmitter antenna (WPT X ), a rectifier, and an implantable antenna. The WPT antenna has been designed at 1.4 GHz frequency with dimensions of 6 cm × 6 cm × 0.32 cm. The WPT antenna has been used for wireless charging of a static implant and with the parasitic element (consisting of a triple ring) the coupling between WPT and the implantable antenna is improved by 11.57 dB. The rectifier has been optimized for 1.4 GHz and used a voltage tripler topology, with a high RF-to-direct current rectification efficiency of 58.6 %. The fabricated WPT and implantable antennas are tested and measured to validate their characteristics. For analysis of Specific Absorption Rate (SAR), the bare antenna was studied in the human scalp and skin phantoms. WPT SAR compliance has been studied and goes well with international guidelines for SAR.

Enabling performance improvements provided by reconfigurable intelligent surface (RIS)-assisted wireless communications requires precise channel estimation. However, none of the current techniques account for the impact of synchronization issues such as carrier frequency offset (CFO). To improve the accuracy of channel estimation in large Multiple-input, multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems, especially under rapid subcarrier variation, by developing a novel deep learning-based framework that surpasses traditional interpolation techniques in reliability, scalability, and performance under complex communication scenarios. The proposed ODS-DLRACG-Net SGA integrates multiple orthonormal discrete S-transform for signal reconstruction with a Deformable Long Range Attention Convolutional Graph Network, optimized by the Snow Geese Algorithm, to model nonlinear mappings between pilot symbols and channel responses effectively. Simulation results demonstrate that the proposed model significantly outperforms conventional techniques in large MIMO settings, achieving a lower bit error rate, root mean squared error, mean squared error, and normalized mean squared error (RMSE, MSE, and NMSE), thereby confirming its high accuracy and robustness in dynamic and high-dimensional wireless communication environments. ODS-DLRACG-Net SGA offers a robust and scalable solution for channel estimation in massive MIMO systems, effectively addressing challenges of fast-varying channels and nonlinear relationships, thus enabling more efficient and reliable data transmission in future communication networks.