Metamaterial Filter Research Articles

Experimental and numerical study of a broad pass-band low-loss optical metamaterials filter

We present the simulation, and fabrication of an optical metamaterial filter. It consists of two silver layers and one SU-8 layer perforated with periodic sub-wavelength holes arrays which are prepared by optical lithography. Measured results indicate that a broad pass-band with over 96% transmittance across 90.0–105.0THz frequency range can be obtained. Effective permeability, permittivity, and impedance are retrieved by applying S parameter retrieval method. These retrieved effective parameters show that the fabricated metamaterial filter can be modulated from a double negative material to a normal material in pass-band. Real parts of effective permeability and permittivity follow a similar slope results in well-matched impedance to free space, which leads to the broad pass-band. Furthermore, effects of nano-hole sidewall length (w2) and thickness of dielectric layer (h1) are experimental surveyed. The pass-band is expanded with w2 increasing or h1 reducing due to the reduced of strength of electromagnetic resonance.

Tunable metamaterial bandstop filter based on ferromagnetic resonance

Tunable wideband microwave bandstop filters have been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance frequency which can be influenced by the demagnetization factor of the ferrite rods. For the filter composed of two ferrite rods with different size, it exhibits a -3 db stop bandwidth as large as 500 MHz, peak absorption of -40 db and an out-of-stopband insertion loss of -1.5 db. This work provides a new way to fabricate the microwave bandstop filters.

Ultra compact CPW dual band filter based on π-generalized metamaterial NRI transmission line

This paper presents an ultra compact dual-band coplanar waveguide metamaterial filter based on generalized metamaterial transmission line. The detailed theoretical design steps of the filter are explained. The dual-band filter design performance has been validated using equivalent circuit modeling, electromagnetic full wave simulations, and practical measurement. The results illustrate the filter has dual passbands centered at 0.82 and 1.48 GHz with approximately 1 dB insertion loss and minimum 12 dB return loss. Good agreements between the circuit modeling, electromagnetic full wave simulations, and practical measurements are achieved. Moreover, the filter size is only (18 × 28 mm2) which is only less than (0.2λg × 0.31λg) at the center frequency of the first passband and (0.36λg × 0.56λg) at the center frequency of the second passband.

Design, fabrication and characterization of resonant metamaterial filters for infrared multispectral imaging

We present the design of infrared filters for multispectral imaging applications, based on square annular aperture arrays in a thin gold film. These structures function as band pass filters with large bandwidth and high transmission at resonance. A modal analysis based on the Finite Element Method (FEM) is performed to obtain quickly the features of this resonance. The center wavelength can be tuned in the 7–12μm range while keeping constant the quality factor and maximum transmission by scaling all transverse dimensions of the apertures, which allows to obtain filters with different centering on the same substrate in a single fabrication step. Large area samples have been fabricated on a silicon wafer by electronic lithography. Spectrophotometric measurements are in rather good agreement with numerical predictions. In addition, angle resolved measurements show that the filters are quite tolerant to the incidence angle up to 30° for both polarizations which is consistent with our FEM simulations. Finally, a complete sensitivity analysis allows us to evaluate acceptable opto-geometric tolerances of fabrication and thus to improve reproducibility on large areas. The impact of fabrication defaults (rounded corners, aperture anisotropy, aperture edge roughness, sloping aperture edges) on the filtering performances is analyzed. The simulations of realistic structures allow to explain and reduce the differences between measured and simulated spectra.

Numerical demonstration of compound structure broad pass-band optical metamaterial filter

We have presented a systematic numerical study about a compound structure to obtain a broad pass-band optical metamaterial filter at terahertz frequency. The designed structure consists of periodic composite metallic arrays and dielectric layer. In order to increase the pass-bandwidth of such metamaterial filter, the sidewall length of square hole is increased. The availability of bandwidth enhancement is verified by our simulation in this paper, which is performed through full-wave method by using the commercial software Ansoft HFSS 13.0. Based on analysis of this rich optical response, we found that the effective impedance matched to free space leads to the pass-bandwidth increased. We hope these results are useful to modulate the electromagnetic wave in optoelectronics, such as sensor and spectroscopy in the future.

Improved RF Metamaterial Band-Pass Filter Design Using CSRR Structures on LCP Substrate

In the past decade, the emergence of man-made structures with unusual electromagnetic properties not seen in nature—commonly known as “metamaterials”—has generated much interest in designing filters, antennas, lenses, and other devices based on negative values of permittivity (ε) and permeability (μ). Manipulating negative values of these electromagnetic parameters has found applications in communication technology and cloaking research by taking advantage of interesting phenomena such as a negative index of refraction and the reverse Doppler Effect. RF and microwave filters with different frequency responses (low-pass, high-pass, band-pass, and band-stop) can be realized by varying microstrip signal line shapes at a frequency of interest due to the fact that the metamaterial frequency response is dependent on the physical dimensions of the structures. For example, the center frequency of a filter can be determined by adjusting the physical dimensions of metamaterial building blocks called split-ring resonators (SRR) or their duals, complementary split-ring resonators (CSRR). To further metamaterial applications, however, non-planar surfaces and effects of curvature on frequency response must also be considered. In this work, an RF metamaterial filter is presented to demonstrate an improvement in the band-pass frequency response from a previous design at Auburn University by enhancing the upper band behavior of the filter. This is achieved by modifying the metamaterial design on the microstrip device to incorporate new additions to the signal line to combine both high-pass and low-pass metamaterial design concepts, resulting in a band-pass response. The filter is designed using a liquid crystal polymer (LCP) slab as a substrate due in part to its dielectric properties, but also to investigate the filter's performance on a flexible structure. An exploration into the roles of different signal line and CSRR dimensions in filter design is given, and a microstrip filter designed using ANSYS HFSS is shown along with simulation results to verify band-pass filter response. LCP was selected due to its excellent RF properties, its resistance to moisture absorption, and its ability to be micromachined.

The development of a wideband and angle-insensitive metamaterial filter with extraordinary infrared transmission for micro-thermophotovoltaics

This study demonstrates a metamaterial filter with coaxial ring structure for the micro-thermophotovoltaic system with improved system efficiency.

Post-processing approach for tuning multi-layered metamaterials

We propose a post-processing approach to efficiently tune the resonance frequency in double-layered terahertz metamaterials separated by a bonding agent. By heating the bonding agent, it is possible to move one metamaterial layer laterally with respect to the other. This changes the coupling between adjacent layers, thereby shifting the resonance frequency. The resonance frequency of the stacked layers continuously shifts as a function of the lateral displacement, reaching a maximum shift of 92 GHz (31% of the center frequency). We discuss the effects of vertical separation on the tunability of the two-layered structure. The post-processing approach is rather general and can be applied to different paired metamaterials in various wavelength ranges, paving the way to efficiently assemble and fine tune metamaterial sensors and filters.

New π –T generalised metamaterial negative refractive index transmission line for a compact coplanar waveguide triple band pass filter applications

This study presents, for the first time, a novel π − T generalised negative refractive index (NRI) transmission line (TL) configuration. It is innovated for increasing the possible passbands in designing microwave components. It is proved that the proposed transmission line can introduce up to seven passbands for completely unbalanced transmission line condition. The detailed mathematical analysis of that configuration based on the periodic network analysis and equivalent circuit model is introduced. As an application for the novel π − T generalised NRI TL configuration, a new compact triple band coplanar waveguide (CPW) metamaterial filter is introduced. The proposed triple bands CPW filter design steps are introduced and its performance is validated using equivalent circuit model simulation, electromagnetic full wave simulation and experimental measurements. Good agreements between the circuit modelling, electromagnetic full wave simulation and practical measurement results are achieved. All the results confirm that the proposed filter has triple passbands from 900 to 960 MHz, 1.4 to 1.48 GHz and 2.4 to 2.45 GHz. Moreover the filter size is compact whose length is only 12.1% λg at first passbands, 18.2 λg % at second passbands and 31.7 λg % at third passbands.

Graphene-based tunable metamaterial terahertz filters

We propose and describe a micro-machined tunable metamaterial terahertz filter based on graphene. The device structure consists of periodic metallic rings with several gaps where tunable graphene stripes are located. We demonstrate that the filter resonance frequency can be adjusted easily by varying the conductivity of graphene and implement this by changing the number of stacked graphene layers. Moreover, the proposed design is scalable, in the sense that the resonance frequency tuning can be controlled by scaling the inner and outer radius of the metal rings. Using numerical simulations and terahertz time-domain spectroscopy measurements of the fabricated samples, we show that the resonance frequency of the structure can be altered by 40% (i.e., from ∼0.2 THz to ∼0.12 THz) by simply tuning the conductivity of graphene. Importantly, the active area of the device is ≪0.1% of the total unit cell area, which can boost the device speed upon electrostatic actuation.

A novel metamaterial filter with stable passband performance based on frequency selective surface

In this paper, a novel metamaterial filter based on frequency selective surface (FSS) is proposed. Using the mode matching method, we theoretically studied the transmission performance of the structure. Results show that, by rotating its neighboring elements 90 degree, the novel filter has a better stability to angle of incidence than traditional structures for TE and TM polarization. As the incident angles vary from 0 to 50 degrees, the metamaterial filter exhibits a transmittance higher than 0.98 and the center frequency slightly shifts downward (from 10 GHz to 0.96 GHz) for TE polarization. For TM polarization, a transmittance of 0.98 is achieved and the center frequency retains 0.96 GHz with the varying of the incident angles. Furthermore, an experimental prototype fabricated was tested in a microwave chamber, and the measured results show good agreement with the simulated ones.

Analysis and Design of Complementary Ring Type Metamaterial Filter in THz Wave Domain

In this paper, the complementary ring type metamaterial unit is theoretically analyzed by using the spectral domain approach. A terahertz bandpass filter is designed, which consists of triple-layer complementary ring metamaterial. The center frequency of the filter is 338GHz, the transmission rate in pass band reaches 97%, the maximum insertion loss in pass band reaches 0.62dB and 3dB bandwidth reaches 75.9GHz. The filter shows stable filtering properties at different polarization wave and the same polarized wave at different incident angles within the scope of 20°. The range of operating frequency matches the first terahertz atmosphere communication window, so it can be used in the field of terahertz atmosphere communication.

Compact quad-band superconducting metamaterial filter based on split ring resonator

In this Letter, a multi-resonant split ring resonator (SRR) is proposed for multi-band application. Its equivalent circuit model and even/odd-mode analysis are investigated. To verify this design methodology, a quad-band high-temperature superconducting (HTS) metamaterial structure is designed and fabricated with a compact size of 11.1 mm × 14.95 mm (about 0.149 λg by 0.2 λg). The insertion losses at each passband are 0.13, 0.07, 0.135, and 0.2 dB, respectively. The temperature effects and power handling capability of the quad-band HTS filter are also studied and the results show that the device has both perfect quad-band bandpass performance (temperature < 77 K) and perfect bandstop performance (temperature > 100 K) for the multi-band communication and superconductor switch applications.

Metamaterial composite bandpass filter with an ultra-broadband rejection bandwidth of up to 240 terahertz

We present a metamaterial, consisting of a cross structure and a metal mesh filter, that forms a composite with greater functional bandwidth than any terahertz (THz) metamaterial to date. Metamaterials traditionally have a narrow usable bandwidth that is much smaller than common THz sources, such as photoconductive antennas and difference frequency generation. The composite structure shown here expands the usable bandwidth to exceed that of current THz sources. To highlight the applicability of this combination, we demonstrate a series of bandpass filters with only a single pass band, with a central frequency (f0) that is scalable from 0.86–8.51 THz, that highly extinguishes other frequencies up to >240 THz. The performance of these filters is demonstrated in experiment, using both air biased coherent detection and a Fourier transform infrared spectrometer (FTIR), as well as in simulation. We present equations—and discuss their scaling laws—which detail the f0 and full width at half max (Δf) of the pass band, as well as the required geometric dimensions for their fabrication using standard UV photolithography and easily achievable fabrication linewidths. With these equations, the geometric parameters and Δf for a desired frequency can be quickly calculated. Using these bandpass filters as a proof of principle, we believe that this metamaterial composite provides the key for ultra-broadband metamaterial design.

Low-loss flexible bilayer metamaterials in THz regime

Low insertion-loss single-layer and bilayer metamaterial filters in terahertz (THz) frequency regime were demonstrated on top of low cost flexible Scotch tape by utilizing pattern transfer method. The transmittance of the flexible 51-μm-thick Scotch tape was found out to be higher than 0.85 in the range of 0.2 to 3 THz, which is excellent for the substrate materials for THz applications. Free standing filters exhibited record low insertion loss of 0.6 dB and band rejection ratio as high as 30 dB. The resonance reflection characteristics of the bilayer filters were maintained when they were attached on top of curved PET bottle or metallic surfaces, providing promising application in THz identifications.

Study the Effect of SRRs on Broadband Microwave Parallel-Coupled Band-Pass Filters

 Abstract—  In this paper, broadband microwave parallel-coupled band-pass filters for wireless microwave technology are presented. Two designs of filters with center frequency of 10.5GHz and 9.5GHz are proposed. A metallic split ring resonator (SRR) as a basic building block for planar filters with dual-band band-pass frequency response, which exhibits simultaneously negative permittivity and permeability as a metamaterial without resorting to additional metallic wires is numerically investigated. The effect of SRRs on these filters to get new two metamaterial dual-band microwave filters is also presented. The dimensions of the second filter are reduced compared to the first filter with better results. Numerical results for all designs are obtained, then the filters are simulated using computer aided design (CAD) in microwave applications (Ansoft HFSS) and implemented on the Roger RT/duroid 6010, Metamaterials (MTMs) are defined as artificial (fabricated by human), effectively homogeneous (p << λg) and exhibiting highly unusual properties (er, µ r < 0) not readily available in nature, where p is the average cell size and it is much smaller than the guided wavelength (λg) (4). Split-ring resonators (SRR) were one of the first particles proposed for metamaterial construction. Metallic metamaterials comprising double split-ring resonators (SRRs) are the main artificial structures to realize magnetic responses at an electromagnetic spectrum above gigahertz frequencies (5)-(8). The realization of backward wave propagation using split ring resonator (SRR) and thin wire (TW) and several other electrically small resonators was considered by Pendry (5), ( 9). The split ring resonator shown in Fig. 2 is used to obtain a negative value of effective permeability over a desired frequency range.

Design, measurement, and characterization of dual‐band left‐handed metamaterials with combined elements

AbstractWe report on a new kind of planar left‐handed metamaterial with both simulations and experiments in this article. Dual electric and magnetic resonance frequency bands are experimentally realized by introducing two different metallic elements in one unit cell, which offers a convenient approach in building dual‐band or multiband negative‐index metamaterials. The effective electromagnetic parameters obtained from the measured S‐parameters indicate that negative refractive indexes are verified near 8.5 and 12 GHz with both negative permittivity and negative permeability. Field and current distribution at the dual resonances are also examined. At last, we calculated the radiated power of the magnetic dipole moments along y‐axis. The idea can help us to fabricate dual‐band or multiband metamaterial absorbers, filters, and antennas. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:493–497, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27399

Metamaterial filter for the near-visible spectrum

We demonstrate metamaterials operating in the near-visible regime based on two-dimensional arrays of gold-coated silicon nanopillars. The nanopillar arrays demonstrate a cutoff response at the metamaterial plasma frequency in accordance with theory and can be utilized for filtering applications. A plasma frequency in the near visible region of λ = 1 μm is calculated numerically for an array with a lattice constant of 300 nm and wire radius of 50 nm, with reflection measurements in agreement with numerical calculations. Such structures can be utilized for achieving negative-index based metamaterials for the visible spectrum.

메타재질구조의 UWB 전력 분배기를 이용한 광대역 배열 안테나를 위한 급전부 설계

In this paper, a new method is suggested to reduce the size of a wide-band array antenna. The power-divider for the feeding structure is made compact as with the help of a novel Metamaterial UWB bandpass filter. This power divider is clearly different from others in that the proposed design uses microstrip structured Composite Right and Left-Handed (CRLH) filters, while others use two dielectric layers or long tapered transmission lines. In order to validate the proposed design method, the circuit and full-wave simulated results of the power divider with the Metamaterial UWB filters are compared to each other, and the Metamaterial properties of the structure are shown with the electric field at the ZOR and dispersion diagram. Furthermore, the antenna performance of the fabricated antenna with the power divider is measured and compared with the prediction. Also, the size reduction effect by the proposed scheme is addressed.

An approach for mechanically tunable, dynamic terahertz bandstop filters

Theoretical and experimental work was carried out on a terahertz metamaterial bandstop filter comprising an array of identical subwavelength resonators, each formed by fusing a pair of printable metallic U-shapes that have their openings pointing in opposite directions. Linear frequency tunability of the stopband electromagnetic response can be achieved by altering the overlap distance between the two fused shapes. Tuning does not significantly affect the strength or quality factor of the resonance. An approach to create mechanically tunable, dynamic terahertz filters is thereby suggested, with several functional advantages. Meanwhile, an effective equivalent circuit model based on self-inductance, mutual inductance, and capacitance has been proposed.