Metamaterial Array Research Articles

Dual Band 1x4 Linear Metamaterial Bowtie Antenna Array for Autonomous Vehicle in Public Safety Band Communications

This research presents the design, simulation, and fabrication of a dual-band 1x4 linear metamaterial bowtie antenna array for applications in 5G wireless systems and public safety band communications. The single-element antenna is a compact dual-band structure with a complementary split-ring resonator (TCSRR) element, and it exhibits resonant frequencies of 3.5 GHz and 4.9 GHz, covering the sub-6GHz 5G spectrum and the public safety band. The antenna aray design is optimized for impedance matching and radiation efficiency. The 1x4 linear antenna array is designed with a quarter-wave transformer feed network and carefully controlled mutual coupling to enhance gain and directionality. Simulated and measured results confirm the performance of the array, with a reflection coefficient within -10 dB from 3.2 GHz to 3.85 GHz and from 4.55 GHz to 5.95 GHz and 3.45 GHz to 3.75 GHz and 4.45 GHz to 5.7 GHz, respectively. The array exhibits a peak realized gain of up to 8.7 dBi and efficient radiation patterns. This work offers promising insights into the development of antenna systems for advanced wireless communication applications and vehicle-to-vehicle communication in public safety band.

Optimizing graded metamaterials via genetic algorithm to control energy transmission

Optimization of functionally graded metamaterial arrays with a high dimensional and continuous geometric design space is cumbersome and could be accelerated via machine learning tools. Mechanical metamaterials can manipulate acoustic or ultrasonic waves by introducing significant dispersive and attenuative effects near their natural frequency. In this work, functionally graded structures are designed and optimized to combine the energy attenuation performance of multiple unit cells with varying frequency responses and to reduce the interlayer mismatch effects. Optimization through genetic algorithms avoids many local minima related to high dimensionality of the design space, but requires many iterations. A reduced order model (ROM) is applied, which can reproduce the transmission response traditionally calculated with FEM in a fraction of the time. Pairing GA and the ROM together, an array of 6 unit cells (with a total of 18 independent geometric design variables) is optimized to have stop bands with extended width and sharper boundaries. Symmetric functionally graded structures are determined to have optimal geometric configurations. Measured 3D printed features are projected onto the ROM solutions to quantify the effect of printing uncertainty on array performance. Repeatability error of ±20μm is determined to reduce the mean depth of the transmission stop band by a factor of 102 and introduce small shifts in center frequency and band width. Proposed methods to improve the resolution of accessible points in the ROM space, reduce sensitivity to geometric uncertainty, and add design freedom include introducing out-of-plane perforations and varying constituent materials using tunable filled resin systems.

Spectrum enhancement of extraordinary terahertz transmission through metal-dielectric multilayer compound annular hole array metamaterial

This study presents, what we believe to be, a novel approach to enhance the spectrum of extraordinary terahertz transmission utilizing surface plasmon polaritons (SPPs) mode coupling in metal-dielectric compound annular hole array metamaterial. The transmitting properties of the structure are thoroughly assessed through a combination of theoretical analysis and numerical simulation, with a particular focus on understanding the surface plasmon mode coupling. Our investigation revealed the presence of propagating surface plasmon polaritons (PSPP), localized surface plasmon resonance (LSPR) and Fabry-Perot (FP) resonances within the compound layer. We find that the coupling of PSPP and LSPR modes plays a crucial role in determining the broadband nature of the structure. Interference theory is utilized to mitigate the FP resonance, while further optimization of the transmission bands is attained by implementing the impedance matching hypothesis. By adjusting the structure parameters, the effective coupling of the SPPs modes and numerous reflections in the dielectric cavity produced a remarkably smooth and transparent character, leading to a significant enhancement of transmission spectrum and a reduction in the incident loss of terahertz wave.

Wide incidence angle triple-band metamaterial EM wave absorber at X and Ku frequency band applications

ABSTRACT This paper proposes a novel design for a metamaterial-based polarisation insensitive electromagnetic wave absorber for the X- and Ku-frequency bands. The Structure consists of FR4 substrates with modified split-ring resonators operating across three frequencies. Optimal design was achieved by varying the split gap and unit cell size. The proposed design has three absorption peaks (11.6, 14.04, and 16.56 GHz) with 99.88%, 99.72%, and 96.41% absorption efficiencies, respectively. A metamaterial unit cell prototype as well as an array of 13 x 13 unit cells, measuring 170 x 170 mm, were fabricated. Simulated and measured results have shown good agreement. The performance of the metamaterial absorber array is validated through measurement results. Because of its high efficiency and good quality factor, the proposed metamaterial absorber is suited for electromagnetic shielding and sensor applications. Furthermore, simulation results are used to analyse the scalability of the proposed structure.

High-gain reconfigurable polarization antenna based on metamaterial array for Terahertz applications

This paper suggestsproposes a high-gain reconfigurable polarization antenna using a metasurface polarizaer. The metasurface polarizer is a rectangular array that consists of similar 25 unit-cell elements. Each metamaterial (MM) unit-cell element consists of a circular copper patch attached to two copper arrow-shaped strips installed at its circumference. The circular patch and two arrows are installed between a rectangular superstrate at the top and a rectangular substrate at the bottom, which is backed with a perfect electric conductor with a relative permittivity of εsub = 3.38. The MM characteristics are obtained in a wide range of frequencies from 1.4 to 2.1 THz. The metasurface polarizer array is installed at an optimized height of 25 μm under a linear polarized dipole antenna that operates at 1.81 THz with a bandwidth (BW) of 0.2 THz from 1.75 to 1.95 THz (11.05%, − 10 dB BW) and gain of 2.27 dBi. The incident-plane wave from the antenna can be converted into a reconfigurable left- or right-hand circular polarization according to the directions of the arrow of the MM unit-cell element. Moreover, the operating − 10-dB BW of the dipole antenna increases to 30.93%, and the gain is enhanced to 6.18 dBi at the same operating frequency. A reconfigurable polarization conversion for the dipole antenna can be obtained over wide 3-dB axial ratio BW from 1.45 to 1.95 THz (33.3% BW).

Hyperbolic metamaterial nanoparticles random array for thermoplasmonics in the II and III near-infrared windows

Plasmonic nanostructures capable of converting light to heat have found wide applications, thus giving rise to the field of thermoplasmonics. Among them, the use of gold-based plasmonic structures in near-infrared (NIR) spectral regions has catalyzed substantial research efforts due to the potential impact in clinical therapy applications. However, the photon scattering effect scaling with the square of the nanoparticle volume leads to high scattering and then low absorption efficiency. This limit has hindered the exploitation of gold nanoparticles, especially in NIR II regions above 1000 nm. Here, we make a step forward for overcoming this limitation by introducing hyperbolic metamaterial nanoparticles that are made of multi-layered gold/dielectric nanodisks and exhibit >70% absorption efficiency in the NIR II and III regions. Their high light-to-heat conversion is demonstrated by a much larger temperature increase than that of gold nanodisks with the same amount of gold. Efficient in vitro hyperthermia of living cells with negligible cytotoxicity shows the potential of our platform for versatile bio-medical applications.

Exploration of Wire Array Metamaterials for the Plasma Axion Haloscope

AbstractA plasma haloscope has recently been proposed as a feasible approach to extend the search for dark matter axions above 10 GHz (≈40 eV), whereby the microwave cavity in a conventional axion haloscope is supplanted by a wire array metamaterial. Since the plasma frequency of a metamaterial is determined by its unit cell, and is thus a bulk property, a metamaterial resonator of any frequency can be made arbitrarily large, in contrast to a microwave cavity which incurs a steep penalty in volume with increasing frequency. To assess the actual potential of this concept as a practical dark matter haloscope, the basic properties of wire array metamaterials have been investigated through an extensive series of S21 measurements in the 10 GHz range. This report presents some new systematics of wire array metamaterials themselves including the approach to full plasmonic behavior, the applicability of the semianalytic theory of Belov, and estimates of the loss term which bode favorably for the plasmonic haloscope application. This present work constitutes the first precision test of the semianalytic theory of Belov et al., for which the predicted plasma frequency agrees with the experimental value at the 0.1% level.

Huygens principle for random metamaterial without coupling

In this paper, we present the Huygens principle of transmission spectra for random metamaterials without coupling. We theoretically demonstrate the connection between the Huygens principle and coupled mode theory for the first time, to the best of our knowledge. We theoretically illustrate that transmission spectra without metamaterial coupling can be calculated by the Huygens principle. Without loss of universality, we explain the Huygens principle for randomly selecting two different structures on a two-dimensional metamaterial array and compare the calculated results of the Huygens principle, CST Studio Suite (CST) simulations, and experimental results.

Fundamental/harmonics beam control using 1-bit space time-modulated plasma DMA

This paper investigates a space-time modulated digital metamaterial array (DMA) based on reconfigurable plasma ionization. The DMA consists of 8 × 8 unit-cell elements with total dimensions of 120 × 120 × 3.2 mm3. Each unit-cell consists of a ring container filled with argon gas and is backed with a grounded dielectric substrate. The argon gas is ionized into a plasma state through metallic electrodes. The logic state of the unit cell is controlled via the changing of the plasma frequency, {omega }_{p}. The value of {omega }_{p}=6times {10}^{11}mathrm{ rad}/mathrm{sec} represents logic “0”, and {omega }_{p}=8times {10}^{11} mathrm{rad}/mathrm{sec} represents logic “bit 1”. The periodic time switching of the plasma ionization controls the radiation at the fundamental and harmonic frequencies. The on-time instants and on-time durations control the number of radiated beams, their directions, amplitudes, and side-lobe levels. Different time-switching sequences are investigated for beam steering, dual-sum beams, broadside beams, end-fire beams, multi-beams, and fan-shaped beams for wireless communications applications. The DMA was investigated under different switching sequences for phase-modulation and amplitude-modulation schemes. A full-wave simulation CST Microwave Studio simulator is used to analyze the proposed DMA and the results are compared with ideal point sources array excited with the same switching sequences.

Study on influence of ring hole array metamaterial on performance of pyroelectric terahertz detectors

In order to improve the detection performance of 0.1–1THz terahertz wave, a new lithium tantalate pyroelectric terahertz detector based on ring hole array metamaterial is proposed. The quantitative influences of the characteristic parameters such as inner diameter, outer diameter, period and thickness on the transmission bandwidth and transmittance of ring hole array metamaterials are analyzed by simulation. The mechanisms of the influences of different combinations of ring hole array metamaterials and pyroelectric detectors on the detection bandwidth and detection rate of terahertz waves are clarified. The lithium tantalate pyroelectric terahertz detectors of the ring hole array metamaterial ware are fabricated by the MEMS technology. The transmission of the ring hole array metamaterial and the noise equivalent power of the metamaterial detector at different frequencies are tested. The results show that the transmittance of the fabricated ring hole array metamaterial is greater than 40% at 0.25–0.65 THz, and bandpass filtering is realized. When the ring hole array metamaterial and the pyroelectric detector maintain a sufficient distance, the noise equivalent power of the detector at 0.315 THz is 11.29 μW/Hz<sup>0.5</sup>, which is 6.3% of the 0.1 THz noise equivalent power (outside the bandpass band), so the bandpass detection is achieved. When the ring hole array metamaterial is attached to the detector, the noise equivalent power of the metamaterial detector at 0.315 THz is 4.64 μW/Hz<sup>0.5</sup>, which is 29.4% that of the detector without the ring hole array metamaterial, so the narrowband detection is achieved. The above conclusions show that the pyroelectric terahertz detector based on the ring hole array metamaterial can realize the bandpass and narrowband detection of specific frequency band in applications such as biological imaging and macromolecular detection.

The Computed Tomographic Imaging Spectrometer based on metamaterial surface

Computed Tomographic Imaging Spectrometer (CTIS) has the advantages of both computed tomography technology and snapshot spectroscopy and has potential applications in many fields. However, the development of CTIS has been limited by the volume issues of key components. In consideration of the compact structure of the metamaterial, an all-dielectric metamaterial array is studied as an alternative to optimize the structure of CTIS. The array can be used for snapshot-type optical imaging, with a wide working range of 550 nm∼1000 nm. At the same time, the system design and simulation technology are studied by using the array, which provides a useful reference for the development of micro imaging spectrometer based on metamaterial.

Engineering ultrastrong coupling between Josephson plasmon polaritons and subwavelength microcavity arrays in silicon/van der Waals layered superconductor heterostructure for terahertz hybrid circuit cavity quantum electrodynamics

The realization of the ultrastrong coupling between Josephson plasma waves (JPWs) and terahertz (THz) photons in the subwavelength microcavity array is of interest for manipulating the THz cavity quantum electrodynamics (cQED), ultrahigh-resolution sensing and imaging, and quantum information processing. Here, we describe the engineering of ultrastrong light-matter interactions in a deeply subwavelength microcavity array based on the hybrid silicon and high-temperature superconductor (HTS) ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ (BSCCO) van der Waals (vdW) heterostructure. We perform numerical modeling and analytical calculation to describe Josephson THz cQED and the ultrastrong coupling process between THz radiation and the JPWs in Josephson medium which is naturally present in BSCCO vdW. The resonance frequency of microcavities is swept through the Josephson plasma frequency by altering their width. THz reflection demonstrates the anticrossing behavior of ultrastrong coupling with a normalized Rabi frequency (coupling strength) $2{\mathrm{\ensuremath{\Omega}}}_{\mathrm{R}}/{f}_{\mathrm{c}}=0.29$ for the BSCCO thickness $t=200$ nm, which increases to the value of 0.87 for $t=800$ nm. Furthermore, the thermal behavior of coupling strength shows modulation of Rabi splitting $2{\mathrm{\ensuremath{\Omega}}}_{\mathrm{R}}$ with temperature. We show that the normalized Rabi splitting $2{\mathrm{\ensuremath{\Omega}}}_{\mathrm{R}}/{f}_{\mathrm{c}}$ is independent of the temperature in the BSCCO superconducting regime, while a weak coupling can be observed above the superconducting transition temperature. The proposed chip-scale THz photonic integrated circuit with subwavelength microcavity metamaterial array shall guide the effort in the development of power-efficient coherent THz sources, quantum sensors, ultrasensitive detectors, parametric amplifiers and tunable bolometers based on BSCCO HTS quantum material.

Complementary Vanadium Dioxide Metamaterial with Enhanced Modulation Amplitude at Terahertz Frequencies

One route to create tunable metamaterials is through integration with ``on-demand'' dynamic quantum materials, such as vanadium dioxide (${\mathrm{VO}}_{2}$). This enables modalities to create high-performance devices for historically challenging applications. Indeed, dynamic materials have often been integrated with metamaterials to imbue artificial structures with some degree of tunability. Conversely, metamaterials can be used to enhance and extend the natural tuning range of dynamic materials. Utilizing a complementary split-ring resonator array deposited on a ${\mathrm{VO}}_{2}$ film, we demonstrate enhanced terahertz transmission modulation upon traversing the insulator-to-metal transition (IMT) at approximately $340$ K. Our complementary metamaterial increases the modulation amplitude of the original ${\mathrm{VO}}_{2}$ film from 0.42 to 0.68 at 0.47 THz upon crossing the IMT, corresponding to an enhancement of 62%. Moreover, temperature-dependent transmission measurements reveal a significant redshift of the resonant frequency in a narrow temperature range where phase coexistence is known to occur. Neither Maxwell-Garnett nor Bruggeman effective medium theory adequately describes the observed frequency shift and amplitude decrease. However, a Drude model incorporating a significant increase of the effective permittivity does describe the experimentally observed redshift. Our results highlight that symbiotic integration of metamaterial arrays with quantum materials provides a powerful approach to engineer emergent functionality.

Fractal interwoven resonator based penta-band metamaterial absorbers for THz sensing and imaging

This paper presents a unique penta-band metamaterial absorber platform for terahertz imaging systems.The proposed fractal metamaterial absorber (FMMA) consists of fractal triangle section metasurfaces. By combining fractal resonators posing different operation skills in the same unit cell, the absorber shows multiband spectral response. The proposed unit cell structure operates at five near perfect absorption modes corresponding to the frequency bands of 1.1 THz, 3.4 THz, 4.9 THz, 5.9 THz, and 7.8 THz, respectively. Based on the fractal metamaterial absorber array, we also propose a sensing pixel design for bimaterial cantilever array sensing systems. The single pixel assembles 4x6 fractal resonator array and SiO_2-Al bimaterial microcantilevers. The sensing region of the FMMA pixel can bend the bimaterial cantilevers effectively at multiple modes, enhancing the imaging capacity. The effective medium theory is executed to visualize the constitute parameters during the absorption and reveal the origin of the rising modes. The absorption mechanism is also discussed based on the surface current distributions and electric field profiles. The numerical outcomes prove that the proposed fractal metamaterial unit cell is a promising candidate as an absorbing platform for THz band sensing and imaging applications. The derived iterative formula used in the fractal design procedure is explained for further investigations of microelectromechanical systems (MEMS) compatible compact absorber arrays.

High isolation metamaterial-based dual-band MIMO antenna for 5G millimeter-wave applications

This article presents a high-isolation metamaterial-based dual-band multiple-input multiple-output (MIMO) antenna for 5G millimeter-wave communication networks. The proposed antenna is a pentagon-shaped monopole that provides a dual-band response with a wide operating bandwidth at 5G 28/28 bands. The antenna is printed on 0.508-mm-thick Rogers RT5880 substrate of relative permittivity ɛr = 2.2. It exhibits a small physical size of 5.5 × 5.4 × 0.508 mm3, excluding the feeding line. The MIMO system is constructed of two symmetric radiating elements arranged adjacently with the mutual coupling of −18.5 dB at both resonant frequencies. The dual-band metamaterial is designed and placed between the two radiators to reduce the mutual coupling. Embedding a 3 × 1 metamaterial array enhances the isolation to −39 dB and −38 dB at 28 GHz and 38 GHz, respectively. The proposed system is capable of covering both 28/28 5G bands and has the merits of broad bandwidth, low profile, high gain (>5 dB), improved isolation (−38 dB), low envelope correlation coefficient (ECC) (<0.0001) and channel capacity loss (CCL) (<0.05), and high diversity gain (DG) (>9.99 dB). The system performance is verified experimentally with good agreement between the simulated and measured data. These properties demonstrate the system applicability for 5G millimeter-wave communication networks.

Lattice-induced strong coupling in symmetric and asymmetric split-ring metamaterial arrays.

The intrinsic link between surface plasmon modes (eigenmodes) and lattice modes in subwavelength periodic structures is investigated based on the split-ring metamaterial structure. The paper shows that the strong coupling between the eigenmodes and the lattice modes can be achieved by appropriately adjusting the period of the metamaterial structure, and the emergence of new, to the best of our knowledge, modes at low frequencies is observed, resulting in a lower spectral loss of a single hybrid resonance and an increase in its Q factor up to 110. In addition, an asymmetric double-split-ring structure is proposed, and the Fano resonance is excited, giving rise to a spectral line with three resonance valleys. The coupled harmonic-oscillator model is used to interpret the underlying coupling mechanism in lattice-induced transparent systems, which agrees well with our simulation results. This strong-coupling scheme between the lattice and the mixed modes of the metamaterial unit provides a new avenue to modulate lattice-induced transparency, high-Q resonance, and strong-field confinement, which may find applications in the design of ultrasensitive sensors, slow-light devices, as well as multiple frequency absorbers and other fields.

Terahertz Enhanced Sensing of Uric Acid Based on Metallic Slot Array Metamaterial.

An enzyme-free terahertz uric acid sensor based on a metallic slot array metamaterial was proposed and realized both theoretically and experimentally. The sensing model was verified in simulation and femtosecond laser processing technology was employed to ablate slots in the copper plate to fabricate metamaterials. Analytes were tested with liquid phase deposition on the metamaterial by a terahertz frequency domain spectroscopy system. Gradient concentrations of uric acid, ascorbic acid, and a mixture of them were measured separately with a good linear response. A significant decrease in sensitivity was observed in the ascorbic acid assay compared with the uric acid assay. The test results of the mixture also proved that our device is resistant to ascorbic acid. It is a simple and effective method for monitoring uric acid concentrations and the strategy of eliminating interference while modulating the resonance peak location mentioned here can be rationally projected for the development of other sensors.

Design of broadband high efficiency absorption antenna based on metamaterial nano-ring array

Compared with the traditional solar cells, the nano-optical antenna breaks through the band-gap limitation of semiconductor materials, and provides a new scheme for solar energy collection. In order to solve the problems of complex structure, low efficiency and narrow bandwidth of nano-optical antenna, a novel nano-ring-cylinder based on metamaterials is proposed in this paper. The antenna has an average absorption efficiency of 96.93% in the wide-band absorption range of visible and near-infrared light. First of all, the basic design theory of the antenna was given based on the surface plasma theory. Then, the antenna structure design scheme was determined, the overall structure consists of two layers of metal and an insulating layer formed by Al2O3. Finally, on the basis of the established antenna model, the absorption characteristics were analyzed by simulation. The analysis result shows that the super-absorption ability of the antenna is independent of the polarization of the incident light, and the average absorption ability can be maintained at about 91% when the incident angle is ±60°. The absorption capability of the antenna is mainly due to the synergistic effect of Fabry-Perot resonance and localized surface plasmon resonance enhancement. The conclusion can provide a theoretical guidance for the structural design of nano-optical antenna.

Switchable unidirectional waves on mono- and diatomic metamaterials

We demonstrate switchable unidirectional propagation of slow waves of coupling within a metamaterial array of strongly coupled elements. We predict theoretically and verify experimentally that the direction of propagation of magnetoinductive waves for any chosen excitation pattern is dictated by the dispersion relations, with forward and backward waves propagating in opposite directions along a chain of meta-atoms. We further prove that the same fundamental phenomenon of direction selectivity due to the forward/backward wave nature is not limited to magnetoinductive waves: we predict analytically and verify numerically the same selective unidirectional signal propagation occurring in nanostructured metamaterial arrays with purely electric coupling. Generalising our method of unidirectional waveguiding to a diatomic magnetoinductive array featuring both forward-wave and backward-wave dispersion branches, switchable unidirectional signal propagation is achieved with distinct frequency bands with opposite directions of signal propagation. Finally, by expanding our technique of selective unidirectional waveguiding to a 2D metasurface, a selective directional control of waves in two dimensions is demonstrated opening up possibilities for directional wireless signal transfer via magnetoinductive surfaces. The observed phenomenon is analogous to polarisation-controlled near-field interference for unidirectional guiding of surface plasmon-polaritons.

Broadband directional resonant tunneling emission enhancement via acoustic anisotropic metamaterials

Broadband directional acoustic emission enhancement is essential in practical applications, such as acoustic communication and medical imaging. In this paper, an anisotropic metamaterial array of meta-unit consisting of a straight channel and four symmetrical side branch cavities is proposed, aiming to achieve broadband directional resonant tunneling acoustic emission enhancement via the coupling of the transmission peaks in the y-direction. In the range of 3335–4625 Hz, the broadband anisotropic characteristic is reflected in the opposite transmission capacities of the meta-unit and periodic array in the orthogonal directions, which is caused by the different effective impedances due to resonant tunneling. Numerical simulation shows that for the anisotropic metamaterial array with a monopole source in the center, the broadband directional acoustic emission enhancement phenomenon appears in the y-direction. The experimental results confirm that at a distance of 35 cm from the point source, the SPL gain in the y-direction is 4 dB on average, and the SPL in the x-direction is reduced by an average of 12 dB. Based on the above results, the proposed anisotropic metamaterial array is expected to show significant potential applications in the fields where broadband acoustic signals are required.