This paper presents a novel non-invasive microwave sensor designed for selective multi-component liquid analysis. The proposed sensor integrates a spoof surface-based whispering-gallery mode resonator coupled to a transmission line, enabling precise detection of volumetric concentrations in liquid mixtures by analyzing spectral responses over a broad frequency range. The study examines five mutually soluble liquids blended in varying proportions while maintaining a constant total volume. A multivariable regression-based machine learning model predicts the volumetric concentration of each component, utilizing resonance frequencies and their corresponding amplitudes as input features. Principal component analysis (PCA) is employed to assess feature significance. The sensor achieves a root mean square error (RMSE) of 0.025 in its predictions. Additionally, an edge computing system incorporating a Raspberry Pi 4 automates real-time data processing, facilitating rapid and efficient liquid composition analysis. The portable setup ensures low-latency making it highly suitable for laboratory environments requiring precise and automated multi-liquid assessment.

This work presents a switchable and tunable dual-band terahertz (THz) metasurface absorber based on vanadium dioxide (VO2), designed for high performance biochemical sensing. The absorber employs a complementary metamaterial geometry consisting of patterned VO2 on a SiO2 substrate with a gold backplane, achieving two narrowband absorption peaks at 4.88THz and 14.80THz with absorption efficiencies of 98.76% and 95.03%, respectively, and polarization insensitivity. Dynamic modulation of VO2 conductivity enables reconfigurable absorption, offering switchable operation between insulating and metallic phases. Parametric analysis confirms strong geometrical tolerance, while sensing studies demonstrate a maximum refractive index sensitivity of 1.65THz/RIU. The device effectively detects biochemical analytes and differentiates malaria-infected red blood cell phases. Furthermore, machine learning-driven regression models were applied for refractive index prediction, with polynomial regression achieving the highest accuracy (R2=0.9809). The proposed design demonstrates compact geometry, dual-band tunability at higher THz frequencies, and enhanced sensitivity, making it a promising platform for biochemical, and biomedical sensing applications.

Orbital angular momentum (OAM) in microwave frequencies introduces a promising new dimension for enhancing channel capacity in future 6G wireless communication systems. However, the practical use of OAM waves for long-distance transmission is limited by their inherent beam divergence, which reduces signal strength over distance. This paper proposes a transmissive metasurface lens designed to reduce the divergence of an OAM beam generated by a multimode uniform circular array (UCA) operating at 6 GHz. The design of the metasurface lens is based on the optical converging axicon concept, which is used to achieve the required phase-shift distribution across the metasurface. The UCA generates OAM modes of l = − 1, + 1, and 0 through distinct feed excitations. Comprehensive evaluations comparing the UCA performance with and without the metasurface lens were carried out based on radiation patterns, S11, electric field amplitude, and phase distribution. The results demonstrate a significant improvement: the beam divergence is reduced from 18° to 10°, and the maximum gain is increased from 10.7 dBi to 14.1 dBi. These improvements indicate a more focused and directional OAM beam, enhancing the practicality of OAM-based communication systems for extended-range applications.

This paper presents a frequency-dependent orbital angular momentum (OAM) mode generation technique using a uniform circular array (UCA) antenna with series-feed proximity coupling. The proposed antenna operates within its specified frequency band, generating the OAM mode (Formula presented.) at the lower functional frequency and (Formula presented.) at the higher functional frequency. This functionality is achieved through proximity coupling and an optimized radius of the UCA circularly polarized (CP) array elements, which enable the required frequency-dependent behavior. The array elements, designed as sequentially rotated CP patches, provide the necessary phase shift for OAM mode generation. A prototype of the design is fabricated using an FR4 substrate with an overall size of 210 mm (Formula presented.) 210 mm. Simulated and measured results confirm the successful generation of OAM modes (Formula presented.) and (Formula presented.) within their respective frequency ranges. The design offers a low-profile structure, compatibility with transceiver circuits, and a simple architecture, making it suitable for advanced vehicular and wireless communication applications.

This paper introduces a tunable terahertz bandstop filter with an operating frequency of 2.11 THz. The filter design incorporates two symmetrically positioned split-ring resonators (SRRs) connected via a transmission line, achieving the desired bandstop characteristics. A graphene layer is employed within the structure to facilitate surface plasmon propagation and enable tunable filter performance. Simulation results validate the proposed filter's capability to achieve the desired frequency response, with tunability over an 80 GHz range by varying the voltage applied across the graphene layer. Furthermore, the filter demonstrates exceptional sensitivity, achieving a maximum value of 0.18 THz/RIU, making it suitable for refractive index sensing applications. Machine learning-based regression models are utilized to predict the refractive index from the filter's frequency response, serving as a reliable indicator of analyte property changes. The polynomial regression model outperformed other models, achieving a minimal mean square error of 0.00064. The proposed design showcases significant potential for advanced terahertz sensing and tunable filtering applications. Impact statement: The proposed tunable terahertz bandstop filter represents a significant advancement in the field of terahertz sensing and tunable filtering applications. By integrating graphene to enable surface plasmon propagation, the design achieves remarkable tunability across an 80 GHz range and exceptional sensitivity for refractive index sensing (0.18 THz/RIU). The use of machine learning regression models, particularly the polynomial regression model with a minimal mean square error of 0.00064, highlights the innovative approach to accurately predict analyte property changes. This work not only demonstrates a highly sensitive and tunable filter design but also bridges terahertz technology with machine learning, opening pathways for precise, real-time sensing solutions in fields such as biomedical diagnostics, chemical analysis, and environmental monitoring.

Orbital angular momentum (OAM) of electromagnetic (EM) waves is characterized by a helical phase front, which is significant for its potential to enhance communication systems through orthogonal modes. This paper explores the generation of an OAM beam using a transmitting-type metasurface. A unit cell is designed with three copper layers cascaded by two dielectric layers of Rogers RT5880 with a permittivity (ϵ) of 2.2 and a loss tangent (tan δ) of 0.0009. This multilayer structure enables a full 360 -degree phase variation for both x and y-polarized EM waves, achieved by varying the length of the metallic element in the unit cell. A horn antenna is designed as the feed source for the proposed metasurface, with an optimized focus-to-diameter (F/D) ratio of 0.81. Using a 21 × 21 array of unit cells, the transmit array metasurface can generate an OAM beam with modes = ± 1 and ± 2 in the 2734 GHz (24.7 % bandwidth) band with a divergence angle of 9.5 and 16 degrees, respectively. Furthermore, the metasurface successfully generates OAM beams with a high mode purity for both polarizations.

This paper presents the design and performance analysis of a compact ultra-wideband (UWB) antenna optimized for smart industrial applications. The proposed antenna achieves broad impedance bandwidth from 2 GHz to 10 GHz with omnidirectional radiation characteristics, making it suitable for diverse industrial environments requiring robust and seamless connectivity. Fabricated on a compact 30 mm × 25 mm FR4 epoxy, the antenna incorporates an L-shaped slot in the ground plane to enhance impedance matching and bandwidth without increasing its physical size. Experimental results demonstrate strong agreement with simulated data, showing |S11| values below −10 dB across the UWB range and stable gain levels from 2 dBi to 4 dBi. Three-dimensional radiation pattern measurements were conducted to assess the antenna’s performance comprehensively, confirming consistent omnidirectional coverage across key frequencies and ensuring reliable device communication in varied orientations. The proposed UWB antenna’s compact size, omnidirectional radiation, and broad bandwidth make it a promising solution for smart industrial systems, where spatial constraints and high-performance wireless connectivity are paramount.

Designing planar antenna with orbital angular momentum (OAM) radiation beam is quite challenging. Adding mode configurability in the OAM antenna further increases the complexity for practical realization. This article presents a novel modified single-fed uniform circular array (UCA) antenna capable of generating three OAM modes (l = −1, +1, and 0). These modes can be controlled electronically using three p-i-n diodes in real-time. A series-fed network with eight circularly polarized (CP) patches generates −1 and +1 OAM modes depending on two possible ways of excitation (i.e., clockwise or counterclockwise). Two-element linearly polarized (LP) array placed at the center of the UCA antenna generates l = 0 OAM mode. The CP elements are rotated sequentially along a circle maintaining 45◦ between two consecutive elements to obtain the desired phase excitation. The final optimized antenna was fabricated on an FR4 substrate with the p-i-n diode switches. The experimental results show that the proposed UCA antenna successfully generates the desired OAM modes at 6 GHz. The proposed concept offers simple OAM mode reconfigurability and can be scaled to operate at other frequencies, making it advantageous for various vehicular and wireless communication applications.

In this paper, a reflectarray composed of 14 × 14 unit elements is proposed for generating orbital angular momentum (OAM) beam (l = +1) at 5.75 GHz with reduced phase errors and side lobe levels. Unlike traditional designs, the proposed reflective surface is made up of two different types of unit cell structures. Together, the two-unit cells can offer a complete 360°phase range with linear slope as a function of the phasing element size. The proposed reflectarray prototype is 350 mm×350 mm in size, it is fabricated on commercial FR4 laminates, and experimentally tested. Additionally, antipodal vivaldi (AV) antenna is considered as the feed for the proposed reflective surface. The experimental results confirm that the OAM vortex beam with l = +1 is successfully generated at 5.75 GHz. The generated OAM beam has a high mode purity, with a gain of 15 dBi and divergence angle of ± 8°.

In this article, a novel compact dual-band uniform circular array (UCA) is proposed to generate the conical-shaped orbital angular momentum (OAM) beam with high azimuthal symmetry for vehicular communication. Most antenna designs proposed in the past for obtaining conical-shaped radiation patterns have complex structures and are very expensive. However, the generation of conical-shaped patterns by an OAM antenna provides simplicity in the structural realization and is compact for integrating with transceiver circuits. By selecting circularly polarized (CP) patches as array elements of a UCA, conical-shaped OAM beams can be generated. The proposed UCA consists of a simple feed network with eight dual-band CP elements. The required phase delay for generating OAM beam ((Formula presented.) = +1 mode) is obtained by rotating the CP elements (Formula presented.) in clock wise direction. The UCA is 150 mm (Formula presented.) 140 mm in size, fabricated on a FR4 substrate, and experimentally tested. The measured results confirm that the generated OAM beam has conical-shaped radiation patterns at 5.3 and 5.77 GHz. The generated OAM beam has a peak gain of 10 dBi with high mode purity and a divergence angle of (Formula presented.) in both simulated and measured findings.

This paper presents a novel approach to generating conical-shaped radiation patterns by utilizing the orbital angular momentum property of electromagnetic waves. Unlike the existing conical beam antennas, the proposed uniform circular array (UCA) uses circular polarization (CP) patches as array elements for generating a conical radiation pattern with high azimuthal symmetry. The UCA is designed at 5.9 GHz with eight-CP antenna elements rotated and positioned at 45 ∘ in a clockwise direction with a uniform feed network. As proof of concept, the designed UCA structure is fabricated on an FR4 substrate of 140 mm × 150 mm in size and tested experimentally. The measurements confirm that the designed UCA possesses conical radiation pattern with high azimuthal symmetry at 5.9 GHz. Due to high azimuthal symmetry in the generated conical-shaped radiation pattern, the proposed UCA antenna could be advantageous for numerous wireless and vehicular communication applications.

This paper presents a new approach to producing a conical beam (CB) with highly azimuthal symmetry through a series-feed uniform circular array (UCA) antenna using circularly polarized (CP) elements and the orbital angular momentum (OAM) technique. Most previously proposed antenna designs for generating CB radiation patterns using mode-combining techniques have complex structures and high costs. The proposed antenna utilizes the inherent properties of OAM waves to generate a conical-shaped beam with simplicity and compactness. The UCA antenna utilizes CP elements, which are rotated to provide the desired far-field phase for generating the OAM beam. This design achieves extensive signal coverage and is highly efficient, with minimal spurious radiation and low insertion losses. The experimental measurements validate that the OAM beam produced by the UCA antenna has high azimuthal symmetry at 6 GHz. The OAM beam generated exhibits high mode purity and a peak gain of 10 dBi, with a divergence angle of ± 22°.

In this paper, a wide band, polarization-insensitive reflectarray composed of 14 × 14 unit elements is proposed to generate vortex beams of different orbital angular momentum (OAM) modes with higher mode purity. The multiple resonance architecture of the unit element is designed and achieved 750°of the reflection phase by varying geometrical dimensions, which contributes to the remarkable increase in linear phase bandwidth. The unit element provides stable responses for different incident angles of electromagnetic wave. The prototype of proposed reflectarray with the size of 350 mm × 350 mm is designed, fabricated using printed board technology, and experimentally tested. The measured results confirms that a OAM vortex beam l = +1 is successfully generated at 5.75 GHz with a high gain of 21.3 dBi and a low divergence angle of 12°.

In this paper, a multilayer uniform circular array (UCA) with circularly polarized (CP) patch elements is proposed to generates dual-mode orbital angular momentum (OAM) beams. To eliminate the dependency of phase excitation on feed length, the proposed UCA is designed with a CP elliptical patch as an array of elements that are geometrically rotated to obtain the desired phase excitation. By providing the input excitation of the feed network strategically, the resultant CP radiating patches can be excited for generating OAM modes l = +1 or +2 respectively. The UCA's performance is determined in terms of S11, radiation pattern, and E-field phase distribution. According to the simulation results, the UCA produces a dual-mode OAM beam at 5.9 GHz. Therefore, the proposed UCA could be advantageous for wireless communication systems.

This paper proposes a 3D printable polylactic acid (PLA) lens to reduce the beam divergence of dual-mode OAM beams generated by a uniform circular array (UCA) at 5.9 GHz. The lens is placed in front of the UCA to modify the phase of the OAM beam, which results in a reduction of beam divergence. The UCA generates OAM modes l=+1 and l=+2 by providing input excitation to the individual feed network. The effectiveness of the PLA lens is compared to the UCA antenna with and without the lens in terms of the radiation pattern, S11, electric field amplitude, and phase pattern. The radiation pattern of the OAM beam with the PLA lens exhibits a more focused and narrower beam than the OAM beam generated without the lens. The proposed PLA lens could be used in future OAM-based communication systems to reduce beam divergence and improve communication range.

In this paper, a single-layer uniform circular array (UCA) antenna is designed to generate the conical beam (CB) using the orbital angular momentum (OAM) technique for vehicular applications. Unlike traditional techniques, the proposed UCA takes advantage of inherent OAM beam property to generate a CB. The proposed UCA is a single layered structure with a simple feed network. The UCA consists of 2×2 circularly polarized (CP) square patch elements, which are geometrically rotated to generate a CB with OAM mode l=-1 at 5.8 GHz. The CP square patches are geometrically rotated to achieve the required phase excitation. The simulation results indicate a cone-shaped radiation pattern in the elevation plane. A good isolation is achieved between co and cross polarization. A peak gain of 10 dB is observed at the operating frequency of 5.8 GHz.

In this paper the uniform circular array (UCA) of triangular patch antennas for generating the orbital angular momentum (OAM) beam is presented. The 8-element microstrip triangular patch UCA is designed to work at the 5.45 GHz which generates the OAM beam of mode l=-1. The sidelobe levels of microstrip triangular patch antenna are considerably lower than the other patch shapes and hence it is used in uniform circular phased array for the generation of OAM beam.