Search Results (408)

This article presents a nested split-ring resonator (SRR) metamaterial unit cell which demonstrates dual-resonant double-negative (DNG) behavior for the 5G mmWave and D-band sub-THz region. The proposed geometry contains a scaled inner SRR pair within an outer SRR pair that enables operation at two different resonant frequencies while maintaining a single-layer planar platform. Full wave simulations are performed through a two-port wave excitation set up with proper PEC/PMC symmetry boundaries (normal incidence) to obtain the scattering parameters. The lower resonance is tuned around 28.9 GHz to cover the 5G FR2 (Frequency Range 2) mmWave region and the upper resonance is tuned around 113.3 GHz, in accordance with the allocated D-band window (111.8–114.25 GHz) which is relevant for the emerging 6G sub-THz band. Effective-medium parameters are extracted from the simulated S-parameters by the standard Nicolson–Ross–Weir (NRW) retrieval approach. The simultaneous presence of negative effective permittivity and permeability around the resonance region confirms double-negative (DNG) behavior. The proposed passive unit cell is a compact building block for future planar metasurface/microwave devices and can also be incorporated as a passive loading layer or superstrate in an antenna system. Full article

A novel microwave biosensor operating in the C-band is developed and characterised for enhanced glucose sensing applications. The sensor is based on a single metamaterial asymmetric split-ring resonator (SASR) and has been investigated in two configurations: a single semi-circular design (SASR-S) and a double semi-circular design (SASR-D). The structural modifications were introduced to enlarge the sensing area by creating two high-field hotspots, thereby increasing the interaction between the electromagnetic (EM) field and the sample, which consequently enhances the overall sensor sensitivity. The sensor is fabricated on a Rogers AD350A substrate and is optimised to detect glucose levels in a 1 µL solution applied within each semi-circle sensing region. To characterise the sensor’s enhanced sensitivity, we performed a 3D electromagnetic simulation of a small droplet positioned within a semicircular sensing region, varying the relative permittivity of the droplet from 45 to 65. The resulting shifts in resonant frequency served as a primary indicator of dielectric sensitivity. The sensor’s response was experimentally validated using a vector network analyser to measure the transmission coefficient (S₂₁) of samples with no glucose and at glucose concentrations of 97 mg/dL to 286 mg/dL. The results demonstrate that the resonator configuration strongly influences the resonance frequency shift and sensitivity, with the SASR-D configuration being the most effective design. This has also been confirmed by measurements demonstrating a sensitivity of approximately 2.4 MHz/(mg/dL), representing an approximately two-fold improvement over the SASR-S sensor (sensitivity: 1.27 MHz/(mg/dL)) and a notable enhancement over previously reported sensors. These findings demonstrate the practical potential of the proposed sensor for blood glucose monitoring applications. Full article

In this paper, a mechanically reconfigurable antenna is proposed to overcome the limitations of conventional patch antennas, particularly their static radiation patterns in millimeter-wave (mmWave) 5G applications. The proposed design integrates a physically rotating metasurface above a compact patch antenna, enabling dynamic beam steering through a simple mechanical rotation. A key contribution of this work is the clear and highly predictable relationship between the metasurface rotation angle and the resulting main lobe direction. By rotating the metasurface to specific positions, the main beam is precisely steered to $0^{\circ }$, ${90}^{\circ }$, ${180}^{\circ }$, and ${270}^{\circ }$ in direct correspondence with the metasurface rotation angle. For clarity and conciseness, four representative rotation states are selected and analyzed in this work, although the proposed antenna inherently supports continuous beam steering as a function of the metasurface rotation angle. Full-wave electromagnetic simulations, utilizing a RT/Duroid 5880 substrate, confirm a resonance frequency at 28 GHz with a bandwidth of 1.7 GHz, covering the frequency range from 27.15 GHz to 28.85 GHz. The results confirm notable performance improvements, with the antenna achieving a maximum realized gain of 8.66 dBi and its radiation efficiency increasing from $90\%$ to $94\%$ after metasurface integration. The proposed antenna offers a compact structure, high efficiency, and reliable beam steering without the need for complex feeding networks or active components, making it a promising solution for next-generation wireless communication systems. Full article

Material discontinuities and defects can profoundly impact the structural integrity and overall product quality. In a multitude of industries, ranging from aerospace and automotive to the nuclear sector and manufacturing, even surface discontinuities can pose significant risks to component reliability. This paper presents a planar microwave sensor for non-destructive testing (NDT) to quantify the electromagnetic response to controlled crack-like discontinuities in polylactic acid (PLA) materials. The sensor comprises a host coplanar waveguide (CPW) positioned at the base of an RO3210 substrate and a multiple split-ring resonator (MSRR) on the surface, creating a compact device measuring 30 mm × 50 mm × 1.27 mm. When a discontinuity-free PLA sample-under-test (SUT) is placed above the sensor, the transmission coefficient exhibits a resonance at 1.780 GHz. As the width of the groove-based discontinuity increases, a systematic blue shift in the resonant frequency is observed. The relationship between resonant frequency shift and discontinuity width is established through empirical calibration for both surface and subsurface configurations. The results demonstrate the feasibility of the proposed sensor for calibrated detection and sensitivity-based discrimination of millimeter-scale crack-like discontinuities in PLA within the tested dimensional range. Full article

This paper investigates the viability of utilizing Fused Deposition Modeling (FDM) for the fabrication and follow-up testing of a hemispherical resonator (HR). This form of resonator has several significant applications, including the design of vibratory gyroscopes. While traditional high-precision resonators for this application rely on expensive fused-silica fabrication, this study proposes a macro-scale approach using Polylactic Acid (PLA) to enable accessible lab-scale experimentation. The specimens, featuring a unique central-hole mounting configuration, were designed in SolidWorks and analyzed via finite element methods to establish the modal hierarchy. Experimental Modal Analysis (EMA) was conducted using a Laser Doppler Vibrometer (LDV) to acquire vibration signals, which were then analyzed in NVGate, MATLAB, and MEscope to extract natural frequencies and quality factor. Results for a lab-scale HR specimen identified the n = 2 wine-glass mode with a deviation from theoretical natural frequency predictions largely attributed to inherent defects in the fabrication process. Furthermore, a frequency split of 2.15 Hz was observed due to the inherent asymmetries and mass imbalances of the fabrication method. The quality factor was evaluated via the ring-down method and validated using the half-power bandwidth (HPBW) technique. This work demonstrates that 3D-printed resonators serve as an effective, low-cost platform for isolating modal behaviors and optimizing geometric parameters before advancing to micro-scale fabrication. Full article

A synthesis method for compact dual-band bandpass filters based on split-ring resonators (SRRs) is presented. The method combines coupling-matrix synthesis with an energy-based SRR model with a control technique of the center frequencies and the bandwidth ratio (BWR) of the two passbands. The proposed methodology is experimentally validated for prototypes implemented on Rogers RO3010. Although the synthesis procedure is general in formulation, any change of substrate requires re-optimization of the SRR dimensions, couplings, and achievable bandwidth ratio. Two third-order microstrip prototypes were fabricated on Rogers RO3010 (${ϵ}_r=10.2$, $h=0.64$ mm) to validate the approach. The first prototype operates at 1.9 and 2.4 GHz with measured −3 dB bandwidths of 200 and 100 MHz, insertion losses of 1.0 and 1.95 dB, and BWR ≈ 0.5. The second prototype operates at 1.9 and 2.4 GHz with measured bandwidths of 100 and 200 MHz, insertion losses of 1.8 and 0.6 dB, and BWR ≈ 1.9. The corresponding footprints are 32 × 12.37 ${\mathrm{mm}}^2$ and 27.87 × 12.42 ${\mathrm{mm}}^2$, respectively. The measured responses agree well with electromagnetic simulations and confirm that asymmetric dual-band bandwidths can be achieved in a compact planar topology without additional reconfigurable elements. Full article

This paper presents a compact, single-layer substrate-integrated waveguide (SIW) bandpass filter for 5.8 GHz WiMAX applications. The filter achieves an improved performance trade-off through a novel hybrid design strategy that combines central vertical perturbation vias with symmetrically etched complementary split-ring resonators (CSRRs). This configuration implements a hybrid magnetic–electric perturbation within a single cavity, enabling simultaneous control of electric and magnetic field confinement. The proposed topology achieves an optimized balance among unloaded quality factor Q_u, insertion loss, selectivity, and structural simplicity. Through targeted intra-cavity field manipulation, the filter attains a Q_u of 239.7, a narrow fractional bandwidth of 3.08% (5.75–5.93 GHz), and a low insertion loss of 1.12 dB. It also delivers enhanced selectivity compared to conventional single-cavity designs and performs competitively with multi-resonator architectures. An equivalent circuit model accurately captures the via–CSRR interaction and agrees closely with full-wave electromagnetic simulations. Experimental results confirm excellent return loss and robust performance across the entire WiMAX band (5.725–5.850 GHz). Thus, the proposed filter offers a practical, high-performance, and manufacturable solution for selective RF front-end applications. Full article

In this paper, we propose a single-layer metasurface structure with ultra-wideband operation and high polarization conversion efficiency, capable of transforming linearly polarized waves into cross-polarized waves. This structure excites additional electromagnetic resonance modes by integrating two symmetrical square patches within an anisotropic split-ring resonator (SRR). These new modes couple with the inherent resonance modes of the SRR, forming closely spaced multi-resonance characteristics across a wide frequency band. This multi-resonance capability enables broadband polarization conversion. This metasurface achieves an ultra-wideband performance spanning 10.89 GHz to 30.12 GHz, covering part of the X-band, the entire Ku-band, and the K-band, while maintaining a high polarization conversion efficiency exceeding 90%. Its broadband characteristics are attributed to the resonator’s ability to generate multiple resonances within a single unit cell. Both experimental and simulation results demonstrate the metasurface’s excellent polarization conversion performance. Furthermore, the proposed metasurface maintains acceptable oblique-incidence performance over a large portion of the operating band, although localized degradation appears at some frequencies. This structure offers significant advantages over traditional multilayer or active designs, featuring simple fabrication without assembly or welding. It may be useful for broadband polarization conversion and may also provide potential for scattering-control applications. Full article

This study designs a complementary split-ring resonator (CSRR)-based 5 GHz patch-type microwave resonant sensor for measuring the concentrations of glucose solutions under static and dynamic conditions. Circulating glucose solutions were used to simulate blood glucose, and the CSRR sensor was operated over a frequency range of 4.8–5.0 GHz. The planar microstrip configuration of the CSRR creates a highly confined electric field within the sensing area. When glucose solution covers or flows through the sensing region, the dielectric loading changes, altering the resonance condition and inducing perturbations. Identifiable measurement features can be extracted from data on the scattering parameter S₁₁. Glucose solutions with concentrations ranging from 5% to 65% were used to examine the response of the proposed sensor. The concentrations of these solutions were estimated on the basis of resonant frequency shifts, and variation in S₂₁ at the CSRR’s resonant frequency (or at a fixed frequency corresponding to the maximum slope) was also analyzed. Full article

In this study, we propose a novel approach to enhance upper stop-band attenuation in a split-ring resonator-based bandpass filter by partially inserting W-type hexaferrite films into a strategically placed mechanical hole. The hexaferrite exhibits a substantial increase in magnetic loss tangent in the desired band owing to ferromagnetic resonance, considerably improving attenuation in the upper stop-band while maintaining an acceptable insertion loss in the pass-band. The obtained results indicate that selectively placing the hexaferrite film enhances out-of-band rejection by up to 4 dB, with a slight degradation of 0.84 dB in pass-band insertion loss. Before inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.01 dB at 28 GHz and an attenuation of 20.04 dB at 32 GHz. By contrast, after inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.95 dB at 28 GHz and an attenuation of 24.45 dB at 32 GHz. Full article

Accurate permittivity characterization at terahertz frequencies is important for material analysis and device design, yet it remains challenging for small-volume samples and compact test structures. In this work, a terahertz permittivity sensor based on a spoof surface plasmon polariton (SSPPs) transmission line coupled to a backside split-ring resonator (SRR) is proposed and numerically studied. The SSPPs line is patterned on the top side of the substrate, while the SRR is etched on the backside, with the sample loaded into the SRR gap. The SSPPs mode penetrates through the substrate and excites the SRR, producing a pronounced transmission notch. Changes in the sample permittivity modulate the effective capacitance of the resonator, resulting in a monotonic shift in the notch center frequency. For relative permittivities from 1 to 8, the notch center frequency decreases from 152.1 GHz to 117.8 GHz, corresponding to a total shift of 34.3 GHz and an average sensitivity of about 4.90 GHz/ε_r. The minimum S₂₁ remains within approximately −23.80 to −21.56 dB, while the Q-factor stays in the range of 94.33–108.23, indicating good spectral readability. Tolerance analysis further shows that the resonance frequency is sensitive to critical structural dimensions and layer alignment, and practical implementation is therefore more suitable for single-device calibrated frequency-shift sensing. These results demonstrate the feasibility of the proposed dual-layer SSPPs–SRR configuration for compact permittivity sensing in the terahertz regime. Full article

Planar microwave (MW) sensors offer high-resolution, non-invasive technology for monitoring critical soil properties, serving as a support for modern precision agriculture. While laboratory studies confirm their exceptional sensitivity, the widespread adoption of these sensors is severely impeded by critical translational challenges that constitute a defining “lab-to-field gap”. These barriers include high sensor-to-sensor variability, debilitating thermal cross-sensitivity, soil heterogeneity necessitating unique site-specific calibration, and the enduring tension between high-performance and cost-effective scaling. This review systematically synthesizes the current state of planar permittivity MW technology, moving beyond technical mechanisms to critically assess these operational limitations. We detail advanced architectural strategies designed to bridge this gap, focusing particularly on the transition toward more robust solutions. The key strategies analyzed include the adoption of differential sensor designs using microstrip patch antennas to mitigate common-mode environmental errors, the integration of ultra-compact metamaterial structures such as split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) for enhanced field robustness and deep soil sensing, and the necessity of multi-parameter sensing capabilities (moisture, pH, and salinity). By establishing a comprehensive roadmap that prioritizes field stability, cost efficiency, and seamless IoT integration, this review demonstrates that planar MW sensors are poised to become reliable and scalable tools. Addressing these critical translational hurdles will ensure optimal resource management, significantly enhance crop productivity, and enable sustainable practices within smart farming ecosystems. Full article

This paper presents the design of a compact four-element MIMO antenna based on a metamaterial structure and a reactive load generated by an open-circuit stub. The radiator array, arranged in an axial symmetry configuration, provides high inter-element isolation despite a sub-millimeter separation. The design is optimized for 5G n77/n78 band applications and employs a metamaterial structure composed of embedded octagonal split-ring resonators (SRRs) integrated on a Duroid RT5880 0500 (${ϵ}_r=2.2,h=1.27 \mathrm{m}\mathrm{m}$) substrate. This configuration achieves high miniaturization, with individual radiators of $19\times 9.53 \mathrm{m}{\mathrm{m}}^2$. Furthermore, through a stub-loading technique, the array is enhanced in two significant aspects: (a) it exhibits an increased impedance bandwidth, rising from a 23% fractional bandwidth in the stub-less design to 39% in the final architecture; and (b) a shift of the lower cut-off frequency toward lower values is obtained, resulting in a reduction of the radiator’s electrical length, which translates into physical size diminution. The total array has a size of only $28.8\times 28.8 \mathrm{m}{\mathrm{m}}^2$ ($0.24{\lambda }_0\times 0.24{\lambda }_0$, considering the lower cut-off frequency). Despite the proximity between radiators and the absence of electromagnetic decoupling structures, the design ensures inter-element isolation exceeding 15 dB in the lower band and reaching values above 20 dB in the mid and upper bands. Diversity metric analysis confirms high performance, yielding an Envelope Correlation Coefficient (ECC) $\ll 0.005$, Diversity Gain (DG) close to the ideal value ($\ge 9.9$), Total Active Reflection Coefficient (TARC) below −10 dB (converging in random phase analysis), and a Channel Capacity Loss (CCL) of less than $0.4$ bits/s/Hz. Therefore, the proposed antenna stands as an ideal design for compact 5G communication devices. Full article

This study details the design and development of an ultra-sensitive microwave sensor for non-invasive blood glucose monitoring, achieved by analyzing variations in the response of a split-ring resonator (SRR) through advanced engineering methodologies. There were three design phases in the development process. In the first phase, a standard SRR design was used. It had a resonant frequency of 2.975 GHz in S₂₁ and a sensitivity of only 0.0032 dB/(mg/dL). In the second phase, an interdigital capacitor (IDC) was added to the SRR structure. This made it work better and made it more sensitive, with a sensitivity of 0.015 dB/(mg/dL) at 4.1 GHz. The third phase was to use a fourth-order Moore fractal geometry to improve the resonance properties of the design a lot. From the obtained S₁₁, the maximum sensitivity was 0.042 dB/(mg/dL), which was a huge improvement in sensing efficiency compared to earlier designs. Several resonant frequencies were recorded between 4.84 and 7.56 GHz. The addition of the fractal structure made the electromagnetic field stronger in the resonant space and made the waves interact more with small changes in the biological medium, all without changing the sensor’s size (80 mm × 40 mm). These results show that fractal architecture is a promising way to create non-invasive, accurate, and easily integrated sensors in biological systems that can continuously measure blood glucose levels. Full article

Rapid and real-time monitoring of blood glucose concentration is critical for the diagnosis and management of diabetes, while conventional invasive detection methods suffer from inconvenience and discomfort, making non-invasive detection a research hotspot. In this study, a dual complementary split-ring resonator (DS-CSRR) operating at 3.3 GHz was designed and fabricated for non-invasive glucose concentration detection, aiming to address the problems of low sensitivity and large size of existing microwave glucose sensors. The sensor was fabricated on a low-cost FR4 dielectric substrate with dimensions of 20 × 30 × 0.8 mm³, and two U-shaped slots were incorporated into the traditional DS-CSRR structure to realize cross-polarization excitation. This design not only enhances the interaction between the electric field and glucose solution but also optimizes the quality factor (Q) and electric field distribution of the resonator without changing the overall size. Compared with the traditional DS-CSRR, the Q factor of the modified structure is increased to 130 under no-load conditions. The transmission coefficient Signal Port 2 to Port 1 (S21) of the sensor loaded with glucose solutions of different concentrations was measured using a vector network analyzer (VNA). The experimental results show a good linear frequency shift with the increase in glucose concentration, with a measured sensitivity of 1.95 kHz/(mg·dL⁻¹). In addition, the sensor is characterized by miniaturization, low cost and easy fabrication due to the adoption of standard PCB fabrication processes. This study successfully demonstrates a non-invasive microwave sensor with high sensitivity for glucose concentration detection, which has promising application potential in personal continuous glucose monitoring, and also provides a useful design strategy for the development of miniaturized high-sensitivity microwave biosensors. Full article