Search Results (1,026)

The mid-wave infrared (MWIR) spectral range can provide a larger bandwidth for optical sensing and communication when the near-infrared band becomes congested. This range of thermal signatures can provide more information for digital imaging and object recognition, which can be unraveled from polarization-sensitive detection by integrating the metasurface of the subwavelength-scale structured interface to control light–matter interactions. To enforce the metasurface-enabled simultaneous detection and parallel analysis of polarization states in a compact footprint for 4-micron wavelength, we designed a high-contrast germanium metasurface with an axially asymmetric triangular nanoantenna with a height 0.525 times the working wavelength. First, we optimized linear polarization separation of a 52-degree angle with about 50% transmission efficiency, holding the meta-element aspect ratio within the 3.5–1.67 range. The transmission modulation in terms of periodicity and lattice resonance for the phase-gradient high-contrast dielectric metasurface in correlation with the scattering cross-section for both 1D and 2D cases has been discussed for reducing the aspect ratio to overcome the nanofabrication challenge. Furthermore, by employing the geometric phase, we achieved 40% and 60% transmission contrasts for the linear and circular polarization states, respectively, and reconstructed the Stokes vectors and output polarization states. Without any spatial multiplexing, this single metasurface unit cell can perform well in the division of focal plane Stokes thermal imaging, with an almost 10-degree field of view, and it has an excellent refractive index and height tolerance for nanofabrication. Full article

A pattern-reconfigurable, vertically polarized (VP), electrically small (ES), Huygens source antenna (HSA) is demonstrated. A custom-designed reconfigurable inverted-F structure is embedded in a hollowed-out cylindrical dielectric resonator (DR). It radiates VP electric dipole fields that excite the DR’s HEM_11δ mode, which in turn acts as an orthogonal magnetic dipole radiator. The HSA’s unidirectional properties are thus formed. It becomes low-profile and electrically small through a significant lowering of its operational frequency band by loading the DR’s top surface with a metallic disk. The entire 360° azimuth range is covered by each of the HSA’s four 90° reconfigurable states, emitting a unidirectional wide beam. A prototype was fabricated and tested. The measured results, which are in good agreement with their simulated values, demonstrate that the developed wideband Huygens source antenna, with its 0.085 λ_L low profile and its 0.20 λ_L × 0.20 λ_L compact transverse dimensions, hence, electrically small size with ka = 0.89, exhibits a wide 14.1% fractional impedance bandwidth and a 6.1 dBi peak realized gain in all four of its pattern-reconfigurable states. Full article

The dielectric constant, or permittivity, is a fundamental property that characterizes a material’s electromagnetic behavior, crucial for diverse applications in agriculture, healthcare, industry, and scientific research. In microwave engineering, accurate permittivity measurement is essential for advancements in fields such as biomedicine, aerospace, and microwave chemistry. However, conventional waveguide resonator methods face challenges when measuring high-loss materials, often leading to reduced accuracy and increased cost. This paper introduces a lightweight, compact system for dielectric constant measurement using a negative-resistance voltage-controlled oscillator (VCO) integrated within a frequency synthesizer. The proposed system employs phase response variations of a planar sensor embedded in the VCO’s gate network to detect changes in oscillation frequency, enabling precise measurement of high-loss materials. The experimental validation demonstrates the system’s capability to accurately measure dielectric constants of lossy organic liquids, with applications in distinguishing liquid mixtures. The contributions include the design of a resonant-network-attached oscillator, comprehensive sensor performance simulations, and successful characterization of organic liquid mixtures, showcasing the potential of this approach for practical dielectric property measurements. Full article

In this paper, a novel dual-band metasurface filter (MSF) designed for accurately differentiating pulse waves (PWs) and continuous waves (CWs) is proposed, which is based on a complementary cross resonator (CSR) structure adhered on a dielectric substrate integrated with a capacitive nonlinear circuit. The unit cell of the designed dual-band MSF comprises two identical CSR structures: one of the capacitive nonlinear circuits is configured in parallel with a capacitor (C₁) within one CSR structure. These structures loaded with nonlinear circuits are fabricated on a dielectric substrate. The simulation outcomes reveal that, for normally incident CWs with an input power of 10 dBm, the transmittance of the designed dual-band MSF reaches as high as 97.1% at 2.0 GHz and 93.9% at 3.45 GHz. In contrast, when it comes to 50 ns short PWs, the transmittance remains consistently below 6% throughout the entire frequency range from 1 GHz to 5 GHz. In addition, the transmittance of the dual-band MSF for normally incident PWs increases significantly as the pulse width widens at the aforementioned two discrete frequencies. The ensuing simulation data corroborates that within the input power range of −15 to 15 dBm, the transmittance difference between CWs and PWs of the dual-band MSF first rises and then falls as the input power increases. Specifically, when the input power is specified as 10 dBm and the angle of oblique incidence ranges from 0° to 60°, in the context of TE and TM modes, the transmittance of CWs exceeds 80% around both 2.0 GHz and 3.45 GHz, while that of PWs remains below 15%. Finally, the effects of resistance and capacitance on the transmittance of the dual-band MSF for the incident PWs and CWs are also studied. The dual-band MSF proposed herein showcases its potential applications in wireless communication as well as in the realm of anti-electromagnetic interference. The electromagnetic (EM) waveform modulation in the frequency band of 1–5 GHz has great development prospects in low-frequency working fields such as radar antennas and EM protection. Full article

In this article, a chip-fed millimeter-wave high-gain antenna system with in-antenna power combining capability is presented. A low-profile resonant cavity antenna (RCA) array is fed by multiple spherical dielectric resonators (DRs), demonstrating its multi-feed capabilities. Each of the DRs is fed by two microstrip resonators on a planar circuit board. A printed superstrate is used in the proposed RCA as the partially reflecting superstrate (PRS), which makes the antenna profile small. To increase the directivity and gain, a 2 × 2 RCA array is developed. The demonstrated design shows a prominent peak gain of 25.03 dBi, a radiation efficiency of more than 80% and 3.38 GHz 3 db gain-bandwidth while maintaining a low profile. To steer the beam of the demonstrated 2 × 2 RCA array in a wide angular range with a low side-lobe-level, two planar all-dielectric passive beam steering metasurfaces have been designed and optimized. A detailed analysis of the optimization procedure is presented in this article. This numerical investigation is vitally important for realizing beam steering metasurfaces with suppressed side-lobe-level, wide bandwidth, excellent efficiency and less complexity. Full article

This article provides a brief overview of the research on localized optical states called Tamm plasmons (TPs) and their potential applications, which have been extensively studied in recent decades. These states arise under the influence of incident light at the interface between a metal film and a medium with the properties of a Bragg mirror, or between two media with the properties of a Bragg mirror. The localization of the states in the interfacial region is a consequence of the negative dielectric constant of the metal and the presence of a photonic band gap of the Bragg reflector. Optically, TPs appear as resonant reflection dips or peaks in the transmission and absorption spectra in the region corresponding to the photonic band gap. The relative simplicity of creating a Tamm structure and the significant sensitivity of TPs to its parameters make them attractive for applications. The formation of broadband and tunable TP modes in hybrid structures containing, in particular, rugate filters and porous distributed Bragg reflectors are considered. Considerable attention is paid to TP designs that include liquid crystals, which allow for the remote tuning of the TP spectrum without the mechanical restructuring of the system. The application of TPs in sensors, thermal emitters, absorbers, laser generation, and the experimental capabilities of TP-liquid crystal devices are also discussed. Full article

Typically, the operating frequency in single-frequency reflective-mode phase-variation permittivity sensors based on semi-lumped resonators (e.g., step-impedance resonators—SIRs) is set to the resonance frequency of the sensing resonator when it is loaded with the so-called reference (REF) material, f_0,REF. For the case of an SIR-based sensor, if the ratio between the inductance and the capacitance is high (corresponding to a high-Q resonator), the sensitivity in the limit of small perturbations of the dielectric constant (in the vicinity of that of the REF material) is also high. However, the optimum frequency for sensitivity optimization in the limit of small perturbations neither corresponds to the resonance frequency nor coincides with the frequency of maximum phase slope. Such frequencies are calculated in this paper, and it is shown that the optimum frequency for sensitivity optimization is located between the frequency of maximum phase slope and the resonance frequency, although such frequencies tend to coincide for high-Q sensing resonators. This aspect is validated in this paper from electromagnetic simulation and experiment. Full article

The manipulation of surface plasmon polaritons (SPPs) plays an essential role in plasmonic science and technology. However, the modulation efficiency and size of the device in the traditional method suffer from weak light–matter interaction. Herein, we propose a new method to enhance the light–matter interaction by controlling the resonance of electrons in a sandwich structure which is composed of an interdigital electrode, dielectric, and doped semiconductor. The numerical results show that the resonance of electrons occurs when their vibrational frequency under electrostatic field matches well with the oscillation frequency of the propagating SPPs. The intensity of the electric field is enhanced about 8%, which can be utilized to improve the modulation efficiency and minimize the footprint of device to a great extent. These findings pave a new way towards higher precision sensor and more compact modulator. Full article

The literature reports highlight the transmission field (B₁⁺) uniformity and efficiency constraints of cardiac magnetic resonance imaging (MRI) at ultrahigh magnetic fields (UHF). This simulation study proposes a 3D Metamaterial (MM) to address these challenges. The study proposes a 3D MM consisting of unit cells (UC) with split ring resonator (SRR) layers immersed in dielectric material glycerol. Implementing the proposed MM design aims to reduce the effective thickness and weight of the dielectric material while shaping B₁⁺ and improving the penetration depth. The latter is dictated by the chosen array size, where small local UC arrays can focus B₁⁺ and larger UC arrays can increase the field of view, at the cost of a lower penetration depth. Designing RF antennas that can effectively transmit at 21.0 T while maintaining patient safety and comfort is challenging. Using Self-Grounded Bow-Tie (SGBT) antennas in conjunction with the proposed MM demonstrated enhanced B₁⁺ efficiency and uniformity across the human heart without signal voids. The study employed dynamic parallel transmission with tailored kT points to homogenize the 3D flip angle over the whole heart. This proof-of-concept study provides the technical foundation for human cardiac MRI at 21.0 T. Such numerical simulations are mandatory precursors for the realization of whole-body human UHF MR instruments. Full article

We introduce a novel approach to study the dielectric permittivity of spin crossover (SCO) molecular materials using a radio frequency (RF) resonant tunnel diode oscillator (TDO) circuit. By fabricating a parallel plate capacitor using SCO particles embedded into a polymer matrix as an integral part of the inductor (L) capacitor (C) LC tank of the TDO, we were able to extract the temperature dependence of the dielectric permittivity of frequency measurements for a wide selection of resonance values, spanning from 100 kHz up to 50 MHz, with great precision (less than 2 ppm) and in a broad temperature range. By making use of this simple electronic circuit to explore the frequency and temperature-dependent dielectric permittivity of the compound Fe[(Htrz)₂(trz)](BF₄), we demonstrate the reliability and resolution of the technique and show how the results compare with those obtained using complex instrumentation. Full article

This article presents a circular polarized enclosed dielectric resonator antenna (DRA), operating at 5.8 GHz. The design consists of a twist DRA, which is enclosed in a box to give stability to the structure. The circular polarization of the antenna depends on the sense of twisting the top with respect to its base to achieve Left Hand Circular Polarization (LHCP) or Right Hand Circular Polarization (RHCP). The antenna was manufactured using 3D printing and low-loss dielectric filament. The measurement results show the two resonance frequencies and an axial ratio below 3 dB at the operational frequency, while exhibiting a bandwidth and gain compatible for unmanned aerial vehicle (UAV) applications. Full article

This paper introduces a novel method for measuring the dielectric permittivity of materials within the microwave and millimeter wave frequency ranges. The proposed approach, classified as a guided wave transmission system, employs a periodic transmission line structure characterized by mirror/glide symmetry. The dielectric permittivity is deduced by measuring the transmission properties of such structure when presence of the dielectric material breaks the inherent symmetry of the structure and consequently introduce a stopband in propagation characteristic. To explore the influence of symmetry breaking on propagation properties, an analytical dispersion equation, for both symmetries, is formulated using the Rigorous Coupled Wave Analysis (RCWA) combined with the matrix transverse resonance condition. Based on the analytical equation, an optimization procedure and linearized model for a sensing structure is obtained, specifically for X-band characterization of FR4 substrates. The theoretical results of the model are validated with full wave simulations and experimentally. Full article

A review of natural materials that exhibit negative permittivity or permeability, including gaseous plasma, metals, superconductors, and ferromagnetic materials, is presented. It is shown that samples made of such materials can store large amount of the electric (magnetic) energy and create plasmonic resonators for certain values of permittivity, permeability, and dimensions. The electric and the magnetic plasmon resonances in spherical samples made of such materials are analyzed using rigorous electrodynamic methods, and the results of the analysis are compared to experimental data and to results obtained with other methods. The results of free oscillation and Mie scattering theories are compared. Similarities and differences between permittivity and permeability tensors for magnetized plasma and magnetized ferromagnetic materials are underlined. Several physical phenomena are explained on the grounds of rigorous electrodynamic analysis and experiments. These phenomena include unequal electric and magnetic energies stored in plasmonic resonators, the small influence of dielectric losses on the Q-factors of magnetic plasmon resonances, the role of radiation and dissipation losses on the properties of plasmonic resonators, and the theoretical possibility of the existence of lightning plasma balls. Full article

This paper presents a hybrid dielectric resonator antenna (HDRA) for circularly polarized (CP) radiation at 5 GHz, designed for WLAN applications. The antenna features a single probe feed that excites a combination of a circular ring patch and a cylindrical dielectric resonator (DR) element, achieving stable gain across a wide bandwidth. The parametric analysis and vector E-field distribution of the proposed antenna presents the optimization, and it is evidence of CP radiation, respectively. The hybrid DRA has a reflection loss (RL) bandwidth of 485 MHz, from 4740 to 5225 MHz, and an axial ratio (AR) bandwidth of 150 MHz, ranging from 4950 to 5100 MHz. It achieves a peak gain of 7.03 dBic at 5 GHz, making it suitable for missile tracking, data link communications, and IEEE 802.11n WLAN systems. Measurements of a prototype in an anechoic chamber show a close match with simulation results. Full article

In recent years, metal surface plasmon resonance sensors and dielectric guided-mode resonance sensors have attracted the attention of researchers. Metal sensors are sensitive to environmental disturbances but have high optical losses, while dielectric sensors have low losses but limited sensitivity. To overcome these limitations, hybrid resonance sensors that combine the advantages of metal and dielectric were proposed to achieve a high sensitivity and a high Q factor at the same time. In this paper, a hybrid hollow cylindrical tetramer array was designed, and the effects of the hole radius, external radius, height, period, incidence angle, and polarization angle of the hollow cylindrical tetramer array on the refractive index sensing properties were quantitatively analyzed using the finite difference time domain method. It is found that the position of the resonance peaks can be freely tuned in the visible and near-infrared regions, and a sensitivity of up to 542.8 nm/RIU can be achieved, with a Q factor of 1495.1 and a figure of merit of 1103.3 RIU⁻¹. The hybrid metal–dielectric nanostructured array provides a possibility for the realization of high-performance sensing devices. Full article