Metamaterial Research Articles

Terahertz metamaterial biosensor for diagnosis of hepatocellular carcinoma at early stage.

We propose a method for diagnosis of cirrhosis and hepatocellular carcinoma (HCC) by using a terahertz (THz) metamaterial (MM) biosensor. The biosensor has a resonance frequency at about 0.801 THz and can measure the concentration of alpha-fetoprotein (AFP) in serum. The sensitivity of the sensor is 124 GHz/refractive index unit (RIU), and the quality-factor (Q) is 6.913, respectively. When the surface of the biosensor is covered with healthy serum (AFP≤7ng/mL), the maximum resonance frequency shift is 50 GHz. However, when it is covered with serum from patients with cirrhosis and early HCC (AFP>7ng/mL), the resonance frequency shift is more than 59 GHz. Positive correlation exists between the frequency shift of the biosensor and serum levels of the AFP in the HCC patients. This study provides a method for quick diagnosis and prediction of cirrhosis and HCC.

Polarization insensitive dual band metamaterial with absorptance for 5G sub-6 GHz applications

A couple ring enclosed circular geometric resonator (CRECGR) based dual-band polarization insensitive metamaterial (MM) with high effective medium ratio (EMR), and excellent absorptance is proposed in this study, which can be utilized as a sensor and absorber in the 5G sub-6 GHz frequency range. A circular geometry-based unique patch has been introduced in the proposed unit cell to achieve high polarization insensitive properties with excellent absorption for the 5G sub-6 GHz spectrum. The distinctive feature of this proposed CRECGR unit cell is its simple and unique structure with a high EMR of 11.13, polarization insensitive up to 180°, and epsilon negative (ENG) properties, including a negative refractive index and near-zero permeability for 5G sub-6 GHz applications. Furthermore, this designed unit cell yields excellent absorption properties with high quality factor. The designed MM unit cell is fabricated on low loss Rogers RT5880 printed media with an electrical dimension of 0.089λ × 0.089λ × 0.017λ. The performance of the designed CRECGR metamaterial is determined using Computer Simulation Technology (CST), Advanced Design Software (ADS), and measurements. The CRECGR unit cell offers dual resonances at 3.37 GHz and 5.8 GHz, covering the 5G sub-6 GHz band with ENG, near-zero permeability and negative index. The polarization insensitive properties of the unit cell were also investigated for maximum angle of incidence, which confirmed the identical response. The simulated outcome is verified by experiment with excellent accordance. Moreover, the unit cell performance with a complete backplane is explored, noting a maximum absorption of 99.9% for all normal and oblique incidence waves, suitable for sensing and antenna systems. In addition, the suggested unit cell sensing performance is evaluated using the permittivity-based sensing model. The proposed MM outperforms recent related studies in terms of polarization insensitivity up to 180°, high insensitive absorptivity, high EMR, and sensing applications. These features prove that the proposed CRECGR metamaterial is perfect for 5G Applications.

An SIC-Fed Low-Profile Wideband Metamaterial-Based Antenna Array for 5G Wireless Cellular Networks

In this paper, we propose a metamaterial (MTM)-based low-profile wideband antenna and its array using a substrate integrated cavity (SIC) feed structure for 5G wireless cellular networks. The proposed wideband antenna consists of two sets of square mushroom-like arrays; a semi-ground plane and a microstrip line-fed bow-tie radiator. Due to the unique in-phase reflection characteristic of the mushroom-like metamaterial, the bow-tie antenna wideband performance is maintained while the distance between the bow-tie radiator and the metamaterial-based semi-ground is considerably reduced to 0.014λ0 (λ0 is the operating wavelength at 5 GHz in free space), thereby satisfying the compact size requirement desirable in many wireless communication systems. The in-phase reflection of the mushroom unit cell is applied to analyze and explain the wideband performance of the presented antenna. The proposed dielectric-filled (εr=3.55) MTM-based wideband antenna element has an overall size of 1.0λ0 × 0.8λ0 × 0.054λ0 and attains a measured (|S11|<−10 dB) bandwidth of 31.3%. Subsequently, an SIC feed structure is employed to form an array antenna, and a measured (|S11|<−10 dB) bandwidth of about 17% is obtained. Across the operating bandwidth, which partly covers the 5G wireless communication in the sub-6 GHz band and 5-GHz WLAN, the antenna array achieved an average gain of 6.6 dBi and a radiation efficiency greater than 73%.

Gap coupled symmetric split ring resonator based near zero index ENG metamaterial for gain improvement of monopole antenna.

In this article, a symmetric split ring resonator (SRR) based metamaterial (MTM) is presented that exhibits three resonances of transmission coefficient (S21) covering S, C, and X-bands with epsilon negative (ENG) and near zero index properties. The proposed MTM is designed on an FR4 substrate with the copper resonator at one side formed with two square rings and one circular split ring. The two square rings are coupled together around the split gap of the outer ring, whereas two split semicircles are also coupled together near the split gaps. Thus, gap coupled symmetric SRR is formed, which helps to obtain resonances at 2.78 GHz, 7.7 GHz and 10.16 GHz with desired properties of the MTM unit cell. The MTM unit cell's symmetric nature helps reduce the mutual coupling effect among the array elements. Thus, different array of unit cells provides a similar response to the unit cell compared with numerical simulation performed in CST microwave studio and validated by measurement. The equivalent circuit is modelled for the proposed MTM unit cell in Advanced Design System (ADS) software, and circuit validation is accomplished by comparing S21 obtained in ADS with the same of CST. The effective medium ratio (EMR) of 10.7 indicates the compactness of the proposed MTM. A test antenna is designed to observe the effect of the MTM over it. Numerical analysis shows that the proposed MTM have an impact on the antenna when it is used as the superstrate and helps to increase the gain of the antenna by 95% with increased directivity. Thus, compact size, high EMR, negative permittivity, near zero permeability and refractive index makes this MTM suitable for S, C and X band applications, especially for antenna gain with directivity enhancement.

Design of a wideband metamaterial absorber for optical wavelength applications based on the quantum-inspired Hadamard matrix

Attaining broadband absorption with a simple-designed photonic absorber is still considered a complex and daunting task. The Hadamard matrix has been a well-known concept for designing quantum gates in quantum mechanics and computing. Despite a series of noteworthy works being done with regard to the design of metamaterial absorbers, very few works exist in literature where a quantum-inspired design has been employed to design a metamaterial-based photonic absorber. In this work, we have demonstrated a polarization-insensitive ultrathin and wideband metamaterial (MM) absorber based on the pattern distribution of the Hadamard matrix. Within the optical domain, the demonstrated MM absorber showcases absorption of over 91% for both transverse electric (TE) mode and transverse magnetic (TM) mode. To explore the angular dependence on absorption features of our Hadamard matrix meta-absorber (HMMA), both TE and TM modes have been used at numerous incident-angles. Finite integration technique has been utilized to simulate the demonstrated MM absorber design and validated using the interference theory model to assure the simulated data. Moreover, electric and magnetic field characteristics, current distributions, and a plethora of parametric sweeps have also been investigated in order to better understand the suggested HMMA absorption mechanism. Because of its wideband absorption and polarization-insensitive characteristic, this MM absorber based on the Hadamard matrix arrangement permits a variety of applications such as light detectors, optical-sensors, magnetic resonance imaging, plasmonic-sensors, and thermal imaging applications.

Modular-topology optimization of structures and mechanisms with free material design and clustering

Topology optimization of modular structures and mechanisms enables balancing the performance of automatically-generated individualized designs, as required by Industry 4.0, with enhanced sustainability by means of component reuse. For optimal modular design, two key questions must be answered: (i) what should the topology of individual modules be like and (ii) how should modules be arranged at the product scale? We address these challenges by proposing a bi-level sequential strategy that combines free material design, clustering techniques, and topology optimization. First, using free material optimization enhanced with checkerboard suppression, we determine the distribution of elasticity tensors at the product scale. To extract the sought-after modular arrangement, we partition the obtained elasticity tensors with a novel deterministic clustering algorithm and interpret its outputs within Wang tiling formalism. Finally, we design interiors of individual modules by solving a single-scale topology optimization problem with the design space reduced by modular mapping, conveniently starting from an initial guess provided by free material optimization. We illustrate these developments with three benchmarks first, covering compliance minimization of modular structures, and, for the first time, the design of non-periodic compliant modular mechanisms. Furthermore, we design a set of modules reusable in an inverter and in gripper mechanisms, which ultimately pave the way towards the rational design of modular architectured (meta)materials.

A carbon nanotube coated metawall with ultra-wideband perfect wave absorption utilizing cement dielectric

Metamaterials (MMs) have attracted intense attention owing to their unprecedented control over the propagation of electromagnetic waves. Researches on MMs usually concentrate on the metallic resonators layer, while the carbon materials-based resonators and the dielectric layer of MMs are relatively overlooked. Here, a novel and simple “metawall” perfect MM absorber based on carbon nanotube (CNT) is conducted, which enables ultra-wideband perfect absorption, showing three peaks with 99% absorption and yielding over 97% absorption in 5.6–11.0 GHz. A reproducible and cost-efficient fabrication method is proposed, using CNT paste as the resonator and the combination of lossy cement board and lossless ceramic fiberboard as the dielectric. Moreover, only one kind of one-dimensional gratings CNT pattern is required to achieve multi-band perfect absorption. Through the control experiments to investigate the roles of the components of the metawall structure, it is found that the wideband perfect absorption of the metawall can be attributed to its unique structure and the absorption performance of the cement board. The proposed metawall provides a new perspective for achieving wideband perfect absorption and may serve as a promising platform to combine carbon nanomaterials with practical load-bearing engineering components.

A Review on Metamaterial Absorbers: Microwave to Optical

Metamaterials (MM) are artificially designed materials that possess unique properties due to their geometrical design. They also display some peculiar properties, such as negative refractive index, Snell’s law reversal, Doppler effect reverse, and left-handed behavior. MMs are used in a myriad of applications, including invisibility cloaking, perfect lensing, perfect absorption, and sensing. In this review article, the property of electromagnetic absorption by structures known as metamaterial absorbers (MMAs) is discussed. An MMA is a composite made up of many layers of metallic patterns separated by dielectric. This novel device helps in achieving near-unity absorption by various mechanisms, which are investigated in this article. The MMAs are classified based on their absorption characteristics, such as polarization tunability, broadband operation, and multiband absorption, in different frequency regimes.

Can a terahertz metamaterial sensor be improved by ultra-strong coupling with a high-Q photonic resonator?

When a metamaterial (MM) is embedded in a one-dimensional photonic crystal (PC) cavity, the ultra-strong coupling between the MM plasmons and the photons in the PC cavity gives rise to two new polariton modes with high quality factor. Here, we investigate by simulations whether such a strongly coupled system working in the terahertz (THz) frequency range has the potential to be a better sensor than a MM (or a PC cavity) alone. Somewhat surprisingly, one finds that the shift of the resonance frequency induced by an analyte applied to the MM is smaller in the case of the dual resonator (MM and cavity) than that obtained with the MM alone. However, the phase sensitivity of the dual resonator can be larger than that of the MM alone. With the dielectric perturbation theory - well established in the microwave community - one can show that the size of the mode volume plays a decisive role for the obtainable frequency shift. The larger frequency shift of the MM alone is explained by its smaller mode volume as compared with the MM-loaded cavity. Two main conclusions can be drawn from our investigations. First, that the dielectric perturbation theory can be used to guide and optimize the designs of MM-based sensors. And second, that the enhanced phase sensitivity of the dual resonator may open a new route for the realization of improved THz sensors.

Nonlinear elastic metamaterials as pulse shaping devices for shock test applications

Metamaterials (MM) have become a very active research topic in numerous domains of engineering because of their promise to create structures and devices that can control wave propagation in ways that exceed the capabilities of conventional homogeneous and composite materials. Most research on acoustic and elastic MM has been focused on linear behavior. However, linear MM suffer from notable drawbacks, for example, (i) the effective material properties for the application of interest are often limited to narrow frequency bands, and (ii) they have limited usefulness in applications where nonlinearity is unavoidable or essential, e.g., shock testing or high-intensity focused ultrasound. Nonlinearity has therefore been explored to expand the palette of accessible dynamic response of synthetic materials. In this work, we investigate applications for nonlinear elastic MM as pulse shaping materials for shock testing. By using high-resolution finite element methods in concert with direct numerical simulations of reduced-order dynamic models, we examine the propagation of elastic pulses under the influence of various types of nonlinear elastic response and identify means to obtain them. These simulations demonstrate the potential for nonlinear elastic MM to significantly expand the space of accessible excitations for shock testing, using a relatively small number of design parameters.

Broadband stop filters for THz waves using H-shaped metamaterials with dual electronic-plasmonic functionality

Terahertz (THz) waves have attracted extensive attention recently owing to their spectral specificity and transmission properties. For developing THz technologies, filters are significant devices because they can manipulate waves transmission. Metamaterials (MMs) possess unique optical characteristics that are not available in natural materials, have been developed for THz filters. However, reported MMs with separated units only excite plasmonic resonances, which limits their application. Here, broadband stop filters based on H-shaped MMs (H-MMs) for THz waves were proposed. The H-MM has two continuous metallic arms that can flow the electric current, allowing it to benefit electronic applications meanwhile keeping the plasmonic characteristics. A stopband with a central frequency of 0.65 THz and a −10 dB bandwidth of 458 GHz was experimentally demonstrated. Moreover, this filter can freely tune its bandwidth and central frequency by designing its geometry, which provides it with potential in wide THz applications such as THz communications.

Surface-Functionalized Terahertz Metamaterial Biosensor Used for the Detection of Exosomes in Patients.

Owing to their stability in bodily fluids, exosomes have attracted increased attention as colorectal cancer (CRC) biomarkers for early diagnosis. To validate the potential of the plasma exosomes as a novel biomarker for the monitoring of CRC, we demonstrated a terahertz (THz) metamaterials (MMs) biosensor for the detection of exosomes in this work. The biosensor with two resonant frequencies is designed using full wave electromagnetic simulation software based on the finite integration time domain (FITD) method and fabricated by a surface micromachining process. The biosensor surface is first modified using Au nanoparticles (AuNPs), and then, anti-KRAS and anti-CD147, which are specific to the exosomes, are modified on the AuNPs assembled with HS-poly(ethylene glycol)-COOH (HS-PEG-COOH). Exosomes used in the experiment are extracted via the instructions in the exosomes isolation and purification kit and identified by using transmission electron microscopy (TEM), Western blot (WB), and nanoparticle tracking analysis (NTA). The biosensor covered with plasma-derived exosomes of CRC patients has a different resonance frequency shift compared to that with healthy-control-derived exosomes. This study proposes an emerging and quick method for diagnosing the CRC.

High Sensitivity and Label-Free Detection of the SARS-CoV-2 S1 Protein Using a Terahertz Meta-Biosensor

High sensitivity and quantitative detection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein (S protein) is of great significance for the diagnosis and treatment of coronaviruses. Here, we utilized terahertz time-domain spectroscopy (THz-TDS) integrated with a metamaterial (MM)-based biosensor and biological modification technology to demonstrate a high accuracy and label-free detection of the SARS-CoV-2 S1 protein by comparing the changes of the dielectric environment before and after binding the S1 protein. To confirm the sensing characteristics observed in the experiments and provide a further insight into the sensing mechanisms, we performed numerical simulations through varying the thickness, quantity, position, and refractive index of analyte aggregates. The sensitivity increases with the increase of the number of gaps and the amount of analyte near the gaps, which convincingly proves that the frequency shift and sensing performance are strongly influenced by the field enhancement and near-field coupling at the gap area.

CPW-fed metamaterial inspired compact multiband antenna for LTE/5G/WLAN communication

Abstract In this work, metamaterial (MTM) inspired a compact CPW-fed antenna with triple operating band is proposed. A rectangular Split Ring Resonator (SRR) is unified in a circular slot of the polygon-shaped radiator in MTM inspired antenna. The antenna exhibits three operating band which are based on metamaterial characteristics of unit cell. The CPW-fed antenna is ensuing 10 dB impedance bandwidth varies from 2.28 to 2.38 GHz, 3.07 to 3.78 GHz, and 5.05 to 7.03 GHz, whereas notch band exist from 2.39 to 3.06 GHz frequency. Metamaterial behaviour leads into the bandwidth enhancement as well as miniaturization in lower operating band with electric length of 0.14λ 0 × 0.21λ 0. The antenna archives the peak gain of 1.49 dB at 2.34 GHz, 2.04 dB at 3.32 GHz, and 4.14 dB at 6.5 GHz frequency. The measured results authenticate the simulated outcomes and consequently the proposed antenna can be pertinent in LTE, WLAN, and 5G communications.

Parametric Experimentation to Evaluate Chiral Bars Representative of Granular Motif

The recent wide-ranging interest in chiral materials motivates the need to understand the mechanisms that underlie mechanical chirality. This paper investigates the emergent chiral mechanical behavior of bars in relationship to microscale deformation mechanisms. The focus is upon (meta)material systems with granular motif that exploit couplings between stretch, shear and rotation such that the designed bar exhibits non-standard transverse motion under extension. To this end, a 1D-micropolar model is derived using the granular micromechanics paradigm to predict macroscale chirality based upon grain-scale interactions. The model provides micro-macro links necessary for designing the physical (meta)material system conceived as a granular bar. The validity of the derived model is then investigated through parametric experimentation using the designed system fabricated through 3D printing. The granular bar is varied with regard to two geometrical parameters that describe the interaction between two adjacent grains, thereby providing parametric spaces with respect to the considered geometrical parameters. Tensile experiments on the granular bar are analyzed using digital image correlation (DIC) to extract multiscalar deformation fields. The DIC results serve as the basis for investigating the unusual motions predicted by the 1D model by comparing the predicted displacement and rotation fields with those obtained experimentally.

Negative Index Metamaterial-Based Frequency-Reconfigurable Textile CPW Antenna for Microwave Imaging of Breast Cancer.

In this paper, we report the design and development of a metamaterial (MTM)-based directional coplanar waveguide (CPW)-fed reconfigurable textile antenna using radiofrequency (RF) varactor diodes for microwave breast imaging. Both simulation and measurement results of the proposed MTM-based CPW-fed reconfigurable textile antenna revealed a continuous frequency reconfiguration to a distinct frequency band between 2.42 GHz and 3.2 GHz with a frequency ratio of 2.33:1, and with a static bandwidth at 4–15 GHz. The results also indicated that directional radiation pattern could be produced at the frequency reconfigurable region and the antenna had a peak gain of 7.56 dBi with an average efficiency of more than 67%. The MTM-based reconfigurable antenna was also tested under the deformed condition and analysed in the vicinity of the breast phantom. This microwave imaging system was used to perform simulation and measurement experiments on a custom-fabricated realistic breast phantom with heterogeneous tissue composition with image reconstruction using delay-and-sum (DAS) and delay-multiply-and-sum (DMAS) algorithms. Given that the MWI system was capable of detecting a cancer as small as 10 mm in the breast phantom, we propose that this technique may be used clinically for the detection of breast cancer.

Tailoring the terahertz far-field radiation pattern based on asymmetric transmission of linearly polarized waves in metasurface tiles

Asymmetric transmission (AT) of linearly polarized electromagnetic (e-m) waves is a well-known phenomenon in metamaterial (MTM) structures, where transverse electric (TE) to transverse magnetic (TM) polarization conversion (and vice versa) is not the same for forward (FW)/backward (BW) excitations. In this work, we explore the linear AT phenomenon of a metasurface (MS) for controlling terahertz (THz) far-field radiation patterns. An MS formed by a bi-layered metal design exhibits strong linear AT with the magnitude of 0.5 in the frequency range of 4.4 THz to 5.1 THz, and a maximum AT of 0.67 is observed at 4.953 THz. Through full-wave e-m simulations and surface current analysis, the mechanism for the observed linear AT is validated for the proposed MS structure. Based on the linear AT, three different MS tiles are constructed for controlling THz far-field radiation patterns. It is found that the proposed tiles significantly alter the electric field pattern, 3 dB angular bandwidth, and sidelobe levels of THz far-fields for FW/BW excitations. We indicate that simultaneous controlling of the amplitude and polarization of far-field radiation patterns is essential for THz imaging, communication, and spectroscopic applications.

Dispersion Control and Size Enlargement of Helical Slow-Wave Structure by Double-Positive Metamaterial Assistance

A novel dispersion control technique, using I-shaped double-positive metamaterial (MTM) as the helical slow-wave structure (SWS) support, exhibiting low-loss, broadband response, has been proposed for wideband traveling-wave tubes (TWTs). The proposed SWS provided the desired flat-to-negative wideband dispersion characteristics giving higher interaction impedance than that is obtainable by conventional vane-loaded helical SWS. A coaxial transmission line-based simulation model has been used to retrieve the effective relative permittivity and permeability of the I-shaped MTMs. The electromagnetic analysis in the sheath-helix model was validated against the CST Microwave Studio simulation with respect to the dispersion characteristics within 14%–16% and interaction impedance versus frequency characteristics within < 12%. Moreover, the proposed structure can be made to exhibit positive, flat, or negative dispersion characteristics by controlling the dimensions of the I-shaped metal strips without altering the dimensions of the helical SWS and metal envelope of the structure. Furthermore, with the help of the proposed structure, the diameter of the structure could be increased without adversely affecting the shape of the dispersion characteristics and reducing the value of the interaction impedance. The structure will reduce the fabrication complexity at higher frequencies and make the structure suitable for high-power, high-gain, and high-efficiency wideband TWTs.

Metamaterial-Inspired Electrically Compact Triangular Antennas Loaded with CSRR and 3 × 3 Cross-Slots for 5G Indoor Distributed Antenna Systems.

In this article, two distinct kinds of metamaterial (MTM) antennas are proposed for fifth-generation (5G) indoor distributed antenna systems (IDAS). Both antennas operate in the sub-6 GHz 5G band, i.e., 3.5 GHz. The antenna’s radiating structure is based on a combination of triangular and rectangular patches, as well as two complementary split-ring resonators (CSRR) unit-cells etched on the top layer. The bottom layer of the first MTM antenna is a complete ground plane, while the bottom layer of the second MTM antenna is etched by a 3 × 3 cross-slot MTM structure on the ground plane. The use of these structures on the ground plane improves the antenna bandwidth. The proposed antennas are designed using two different substrates i.e., a high-end Rogers thermoset microwave materials (TMM4) substrate (h = 1.524 mm/εr = 4.5/tan δ = 0.002) and a low-end flame-resistant (FR4) epoxy glass substrate (h = 1.6 mm/εr = 4.3/tan δ = 0.025), respectively. The antenna designs are simulated using CST microwave studio, and in the end, the antenna fabrication is performed using FR4 substrate, and the results are compared. Furthermore, parametric analysis and comparative studies are carried out to investigate the performance of the designed antennas. The simulated and measured results are presented for various parameters such as return-loss, gain, and radiation pattern. The two MTM antennas have an overall dimension of 18 × 34 mm2, demonstrating that the proposed design is 60 percent smaller than a standard microstrip patch antenna (MPA). The two proposed MTM antenna designs with complete ground plane and 3 × 3 cross-slot MTM on the bottom layer using FR4 substrate have a measured gain/bandwidth characteristic of 100 MHz/2.6 dBi and 700 MHz/2.3 dBi, respectively.

E-shape metamaterials embedded implantable antenna for ISM-band biomedical applications

This paper presents a compact antenna based on two different metamaterial resonators, the E-shape resonators and the interdigital resonators, suitable for biomedical implant applications. The proposed antennas operate in the industrial, scientific, and medical (ISM) bands in the frequency band of 2.4–2.5 GHz. The integration of metamaterial (MTM) into the design led to the reduced size of these antennas and gaining enhancement. The overall size of the proposed antennas is $$8\times 7\times 1.27{\mathrm{mm}}^{3}$$ . The implantable antennas contain two layers of the substrate; the lower layer comprises the MTM resonators and the upper, superstrate layer. The antennas are designed and simulated by the software simulator HFSS. To study the performance of the proposed antennas, the reflection coefficient and gain are determined. In order to observe the exposure of electromagnetic energy to human tissues, the specific absorption rates (SARs) of the proposed antennas are also calculated in the layer model. The results of the proposed antennas are acceptable and suitable for biomedical applications and human body safety through the values obtained from SARs.