Broadside-coupled Split Ring Resonators Research Articles

Non‐Hermitian Broadside Coupled Split Ring Resonators with Directional Sensitivity

AbstractDirectional radiofrequency (RF) sensing, also known as radio direction finding, is essential in various applications that involve localizing RF sources. However, existing RF sensing technologies face challenges due to their large antenna sizes and complex RF signal processing circuits, which hinder the realization of miniaturized subwavelength direction sensors. In this article, a non‐Hermitian broadside coupled split ring resonators (BC‐SRRs) are presented, which can identify the direction of an incident RF signal with angles ranging from 0° to 180°. The non‐Hermitian Hamiltonian of the system, which can be interpreted by the temporal coupled mode theory, gives rise to asymmetric resonant modes of the BC‐SRRs. The asymmetry allows the direct measurement of RF wave incident angle by probing the resonant strength of the two BC‐SRRs. For the proof of concept, a one‐stage Dickson voltage multiplier is employed to rectify the RF signals and demonstrate angle sensing ability by relating the rectified voltage to the incident angle. The results showcase the potential of the proposed technique using non‐Hermitian BC‐SRRs as a pathway toward subwavelength antenna‐based radio direction finding.

Enhancing the brain MRI at ultra-high field systems using a meta-array structure.

The main advantage of ultra-high field (UHF) magnetic resonance neuroimaging is theincreased signal-to-noise ratio (SNR) compared with lower field strength imaging. However, the wavelength effect associated with UHF MRI results in radiofrequency (RF) inhomogeneity, compromising whole brain coverage for many commercial coils. Approaches to resolving this issue of transmit field inhomogeneity include the design of parallel transmit systems (PTx), RF pulse design, and applying passive RF shimming such as high dielectric materials. However, these methods have some drawbacks such as unstable material parameters of dielectric pads, high-cost, and complexity of PTx systems. Metasurfaces are artificial structures with a unique platform that can control the propagation of the electromagnetic (EM) waves, and they are very promising for engineering EM device. Implementation of meta-arrays enhancing MRI has been explored previously in several studies. The aim of this study was to assess the effect of new meta-array technology on enhancing the brain MRI at 7T. A meta-array based on a hybrid structure consisting of an array of broadside-coupled split-ring resonators and high-permittivity materials was designed to work at the Larmor frequency of a 7 Tesla (7T) MRI scanner. When placed behind the head and neck, this construct improves the SNR in the region of the cerebellum,brainstem and the inferior aspect of the temporal lobes. Numerical electromagnetic simulations were performed to optimize the meta-array design parameters and determine the RF circuit configuration. The resultant transmit-efficiency and signal sensitivity improvements were experimentally analyzed in phantoms followed by healthy volunteers using a 7T whole-body MRI scanner equipped with a standard one-channel transmit, 32-channel receive head coil. Efficacy was evaluated through acquisition with and without the meta-array using two basic sequences: gradient-recalled-echo (GRE) and turbo-spin-echo (TSE). Experimental phantom analysis confirmed two-fold improvement in the transmit efficiency and 1.4-fold improvement in the signal sensitivity in the target region. In vivo GRE and TSE images with the meta-array in place showed enhanced visualization in inferior regions of the brain, especially of the cerebellum, brainstem, and cervical spinal cord. Addition of the meta-array to commonly used MRI coils can enhance SNR to extend the anatomical coverage of the coil and improve overall MRI coil performance. This enhancement in SNR can be leveraged to obtain a higher resolution image over the same time slot or faster acquisition can be achieved with same resolution. Using this technique could improve the performance of existing commercial coils at 7T for whole brain and other applications.

Complex permittivity measurement technique using metamaterial broadside coupled split ring resonator

A simple and effective method for the determination of complex permittivity of dielectric materials at microwave frequencies using a Broadside Coupled Split Ring Resonator (BCSRR) metamaterial structure is presented. A single BCSRR unit cell placed between the transmitting and receiving probes of a Vector Network Analyzer (VNA) is used as the test probe. Resonance frequencies and bandwidths of transmission curves, measured with and without the sample placed over the BCSRR test probe, are used to determine the real and imaginary parts of the complex permittivity by treating the BCSRR as an LC resonant circuit. Relevant equations connecting equivalent capacitance and resonance frequencies are derived from the basic equivalent circuit parameters of the BCSRR through a quasi-static analysis by considering the fringing fields in its vicinity, especially on the top and bottom. Accuracy of the theoretical formula derived for determining the complex permittivity using the BCSRR is verified through experiments and simulations.

Enhanced radiation characteristics of regular dodecagon split ring resonator (D-SRR)-based microstrip patch antenna employing dielectric superstrate for THz applications

In a world where communication requires ever faster data transmission capable of transmitting high speeds. In order to reach and transmit this high speed, it is necessary to increase the frequency that carries the information. For this, scientists are interested in the terahertz (THz) range which, thanks to its high frequencies between 0.1 THz and 30 THz, offers the possibility of increasing the data rate. This letter presents the inclusion of Dodecagon Split Ring Resonator (D-SRR) in rectangular microstrip patch antenna and its effect in the performance of the proposed antenna. The metamaterial design employs two types of SRRs resonators shapes such as the Dodecagon Broadside Coupled Split Ring Resonator (DBC-SRR) and Dodecagon Split Ring Resonator (D-SRR). The model applied uses a local field approach and allowed to obtain the dispersion characteristics of discrete negative magnetic permeability. The proposed antenna substrate uses Arlon AD1000 material, which helps to attain high gain and good directivity at THz frequency. The antenna performance is investigated with and without superstrate. The operating frequencies of the proposed antenna vary in the range of 0.66 - 0.69 THz and shows maximum gain of 10.4 dB and maximum directivity of 9.84 dB. HFSS software tool helps to simulate the parametric analysis of the proposed antenna design. This novel structure may find applications in terahertz imaging, remote systems and may find manifold possibilities in the medical field.

Dual‐band broadside radiation antenna via near‐field electric and magnetic couplings of nested metamaterial resonators

AbstractIn this paper, we propose a method of designing broadside radiation antennas using metamaterial resonators. The antenna consists of a feeding probe and a nested metamaterial resonator (MR), where the latter is located in the near‐field zone of the former and both of them stand on the metallic ground. The nested MR, where a finite‐length comb structure (CS) is circled by a broadside‐coupled split‐ring resonator (BC‐SRR), is used as the radiator. Excited by the tilted electric fields around the feeding probe, even‐mode spoof surface plasmon polaritons (SSPPs) can be excited on the comb structure, forming standing wave, and leading to broadside radiation at the half‐wavelength frequency. The BC‐SRR is excited by the magnetic fields penetrating through it, leading to broadside radiation at its resonant frequency. A prototype working at 5.4 GHz and 7.0 GHz was designed, fabricated and measured. The measured and simulated results agree well and verify our design.

Stored energy of arbitrary metamaterial inclusions

Electromagnetic metamaterials are generally defined and classified in terms of their effective parameters. They are evaluated in the far-field which limits the evaluation of its near field interaction in some applications such as metamaterial inspired design. An alternative approach proposed in this paper is based on the modal stored energy of metamaterial inclusion. This approach is based on the surface current distribution which would address the challenge of metamaterial near-field application. This paper describes a method for quantifying the modal stored energy of arbitrary-shaped metamaterial inclusions based on the theory of characteristic modes. The theory of characteristic modes is independent of excitation, gives good physical insight into the behaviour of an inclusion and would be helpful for near-field application of metamaterials. The modal stored energy approach is also compared with the common effective parameter approach. It shows similarity in terms of the physical and qualitative analysis when far-field assumptions are accounted for. The broadside-coupled split-ring resonator and the S-shaped inclusion are considered. The physical and qualitative analysis based on the modal stored energy approach shows a good agreement with the effective parameter approach.

Broadside Coupled Split Ring Resonator as a Sensitive Tunable Sensor for Efficient Detection of Mechanical Vibrations

This paper explores the possibility of the precise determination of mechanical vibrations using metamaterial split ring resonator (SRR) structure. The amplitude of the interacting electromagnetic wave in the range of GHz frequency is directly varied in accordance with the amplitude of mechanical vibration, using a Broadside Coupled SRR (BCSRR) acting as a vibration sensor. Dependence of the spacing between the two rings on the resonance frequency of the BCSRR is used for the detection of vibration and it is achieved by allowing the spacing to change in accordance with the amplitude of mechanical vibration. For the effective sensing of mechanical vibration, the electromagnetic wave frequency is chosen at the center of the linear portion of the rising or the falling slope of the resonant curve of the BCSRR. By properly choosing the parameters of the BCSRR along with the effective tuning of the operating frequency, it is possible to detect even very weak vibrations. The chances of various distortions in the detected vibration waveform in connection with selection of the operating frequency and intensity of vibrations are also analyzed. The qualitative formulation of the detection process along with its experimental verification is presented. This novel method may find applications in the detection of mechanical vibrations caused by various man made and natural sources and may find manifold possibilities in the field of communication and instrumentation.

Ultra-thin and light-weight spoof surface plasmon polariton coupler achieved by broadside coupled split ring resonators**Project supported by the National Natural Science Foundation of China (Grant Nos. 61331005, 61471388, and 61501503).

Low profile and light weight are very important for practical applications of a spoof surface plasmon polariton (SSPP) coupler, especially at low frequencies. In this paper, we propose and design an ultra-thin, light-weight SSPP coupler based on broadside coupled split ring resonators (BC-SRRs). The size of BC-SRR can be far less than λ/100 and can extremely well control the reflective phases within a subwavelength thickness. Due to the broadside capacitive coupling, the electrical size of BC-SRR is dramatically reduced to guarantee the ultra-thin thickness of the SSPP coupler. The weight of the SSPP coupler is reduced by a low occupation ratio of BC-SRR in the unit cell volume. As an example, a C-band SSPP coupler composed of phase gradient BC-SRRs is designed, fabricated, and measured. Due to the ultra-small size and low occupation ratio of BC-SRRs, the thickness of the coupler is λ/12 and the surface density is only 0.98 kg/m2. Both simulation and experiment results verify that the coupler can achieve high-efficiency SPP coupling at 5.27 GHz under normal incidence.

Design of S-Band Phased Array Antenna with High Isolation Using Broadside Coupled Split Ring Resonator

Design of S-Band Phased Array Antenna with High Isolation Using Broadside Coupled Split Ring Resonator

A Novell compact multiband broadside‐coupled split‐ring‐resonator metamaterial structure loaded fractal slot antenna for 4G communications and wireless systems

ABSTRACTA Novell compact multiband broadside coupled split ring resonator (BC‐SRR) metamaterial structure fractal loaded slot antenna for 4G and other wireless systems is presented in this article. The radiating elements of the proposed antenna are composed of a Perturbed Sierpinski carpet fractal slot printed on the lower face of an FR4 substrate material (εr = 4.4). The slots are fed by a single L‐microstrip line of 50 Ohms characteristic impedance printed on the upper face of the substrate. The operating frequency bands of this antenna are, respectively, centered at 3.62, 6.244, 14.471, and 19.145 GHz and its total size is 28.5 mm × 40.5 mm × 1.5 mm. The introduction of the BC‐SRR structure in the center of this antenna achieved an additional broadband ranging from 2.48 to 3.35 GHz with other additional frequency bands around 5.91, 6.76, 8.33, 10.38, 13.73, and 16.1 GHz (15.74–16.41 GHz). The gain and radiation pattern plots of the antenna are also included and discussed in this article. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2823–2828, 2016

Voltage-tunable dual-layer terahertz metamaterials.

This paper presents the design, fabrication, and characterization of a real-time voltage-tunable terahertz metamaterial based on microelectromechanical systems and broadside-coupled split-ring resonators. In our metamaterial, the magnetic and electric interactions between the coupled resonators are modulated by a comb-drive actuator, which provides continuous lateral shifting between the coupled resonators by up to 20 μm. For these strongly coupled split-ring resonators, both a symmetric mode and an anti-symmetric mode are observed. With increasing lateral shift, the electromagnetic interactions between the split-ring resonators weaken, resulting in frequency shifting of the resonant modes. Over the entire lateral shift range, the symmetric mode blueshifts by ~60 GHz, and the anti-symmetric mode redshifts by ~50 GHz. The amplitude of the transmission at 1.03 THz is modulated by 74%; moreover, a 180° phase shift is achieved at 1.08 THz. Our tunable metamaterial device has myriad potential applications, including terahertz spatial light modulation, phase modulation, and chemical sensing. Furthermore, the scheme that we have implemented can be scaled to operate at other frequencies, thereby enabling a wide range of distinct applications.

Two-dimensional alignment and displacement sensor based on movable broadside-coupled split ring resonators

This paper proposes a two-dimensional alignment and displacement sensor based on movable broadside-coupled split ring resonators (BC-SRRs). As a basis for this sensor, a one-dimensional displacement sensor based on a microstrip line loaded with BC-SRRs is presented firstly. It is shown that compared to previously published displacement sensors, based on SRR-loaded coplanar waveguides, the proposed one-dimensional sensor benefits from a much wider dynamic range. Secondly, it is shown that with modifications in the geometry of the BC-SRRs, the proposed one-dimensional sensor can be modified and extended by adding a second element to create a high-dynamic range two-dimensional displacement sensor. Since the proposed sensors operate based on a split in the resonance frequency, rather than the resonance depth, they benefit from a high immunity to environmental noise. Furthermore, since the sensors’ principle of operation is based on the deviation from symmetry, they are more robust to ambient conditions such as changes in the temperature, and thus they can be used as alignment sensors as well. A prototype of the proposed two-dimensional sensor is fabricated and the concept and simulation results are validated through experiment.

Compact 2 $\times$ 2 Coupled Double Loop GPS Antenna Array Loaded With Broadside Coupled Split Ring Resonators

The design and nulling capability of a compact 2 × 2 dual-band coupled double loop (CDL) GPS antenna array loaded with broadside coupled split ring resonators (BC-SRR) are presented. The high level of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> band mutual coupling is reduced by utilizing -negative (MNG) BC-SRR metamaterial within the array volume. This metamaterial loading is possible due to the small L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> band electrical size (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> / 8.5 × λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> / 8.5) of the CDL antenna elements. Different than the existing work on coupling reduction of linearly polarized antenna arrays, mutual coupling mechanism within the circularly polarized GPS array is considered and MNG metamaterials are shown to reduce the mutual coupling if they are placed between the antennas in a particular alignment. Specifically, a 2 × 2 array with inter-element spacing is designed to be loaded with BC-SRRs and experimentally verified to exhibit a 10 dB L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> band mutual coupling reduction. Through simulations and experiments, it is also demonstrated that the reduction in L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> band mutual coupling improves the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> band array nulling capability in terms of accuracy and null depth without affecting the already well-behaved L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> band performance. The presented array has an overall footprint size 4.3" × 4.3" of and can be potentially miniaturized further for different inter-element spacing.

Frequency-Agile Bandpass Filters Using Liquid Metal Tunable Broadside Coupled Split Ring Resonators

A fluidic-based approach for designing tunable coupled resonator bandpass filters is presented. These filters employ broadside coupled split ring resonators (BC-SRR) with one of their open loop resonators constructed from liquid metal. The tuning mechanism is based on dynamically moving the liquid metal to reshape the resonator. To demonstrate the concept, a second order Butterworth filter with continuous tuning range from 650 to 870 MHz is designed and experimentally verified by utilizing PTFE tubing filled with liquid metal and Teflon solution. Due to an inductive external coupling mechanism and 180° rotated resonators, the filter exhibits a near constant 5% fractional bandwidth throughout its tuning range with > 10 dB return and <; 3 dB insertion loss. The filter is realized over a 1.27 mm thick Rogers 6010.2LM substrate and has an approximate footprint of 20 × 40 mm2.

A Broadside-Split-Ring Resonator-Based Coil for MRI at 7 T

A coil design termed as broadside-coupled loop (BCL) coil and based on the broadside-coupled split ring resonator (BC-SRR) is proposed as an alternative to a conventional loop design at 7T. The BCL coil has an inherent uniform current which assures the rotational symmetry of the radio-frequency field around the coil axis. A comparative analysis of the signal-to-noise ratio provided by BCL coils and conventional coils has been carried out by means of numerical simulations and experiments in a 7T whole body system.

Frequency tunable terahertz metamaterials using broadside coupled split-ring resonators

We present frequency tunable metamaterial designs at terahertz (THz) frequencies using broadside-coupled split ring resonator (BC-SRR) arrays. Frequency tuning, arising from changes in near field coupling, is obtained by in-plane horizontal or vertical displacements of the two SRR layers. For electrical excitation, the resonance frequency continuously redshifts as a function of displacement. The maximum frequency shift occurs for displacement of half a unit cell, with vertical displacement resulting in a shift of 663 GHz (51% of f0) and horizontal displacement yielding a shift of 270 GHz (20% of f0). We also discuss the significant differences in tuning that arise for electrical excitation in comparison to magnetic excitation of BC-SRRs.

Numerical Estimates of Artificial Magnetic Metamaterial Inclusions at Microwave Frequencies: An Edge-Coupled and a Broadside-Coupled Split-Ring Resonator

Numerical Estimates of Artificial Magnetic Metamaterial Inclusions at Microwave Frequencies: An Edge-Coupled and a Broadside-Coupled Split-Ring Resonator

A TUNABLE LEFT-HANDED METAMATERIAL BASED ON MODIFIED BROADSIDE-COUPLED SPLIT-RING RESONATORS

Based on the broadside-coupled split-ring resonator (BC- SRR), a tunable left-handed metamaterial (LHM) was proposed in this paper.The two rings of BC-SRR are etched on two separate substrates so that the coupling between the two rings can be adjusted by slightly slipping one of the two substrates relative to the other one.Thus, the magnetic resonance frequency of the modified BC-SRR can be tuned. By combining the modified BC-SRR (MBC-SRR) with continuous conducting wires, a tunable LHM can be realized.The tunable LHM can realize both rough and minor tunings by minor slips along and perpendicular to the gap direction of BC-SRR, respectively.The proposed tunable LHM has many potential applications in microwave devices.

Miniaturised self-resonant split-ring resonator antenna

A self-resonant miniaturised antenna composed of a broadside-coupled split ring resonator (SRR) and an excitation arc-shaped monopole is presented. The size of the antenna and its resonance frequency is essentially defined by the SRR dimensions and geometry, while the input resistance at the resonance is governed by the arc length of the monopole. Numerical and experimental results are presented for an antenna configuration of 1/23.4 wavelength in diameter (ka~0.134). The antenna is tuned to 50 Omega without any matching network, and its efficiency is measured to be 17.5%.

Magnetic control of negative permeability metamaterials based on liquid crystals

We report on the tunability, by a magnetic field, of a negative permeability metamaterial consisting of stacked arrays of broadside-coupled split ring resonators infiltrated with liquid crystals (LCs). The resonant frequency shift was numerically assessed by a rigorous anisotropic analysis of the reorientation of LC molecules. Experiments were carried out with a prototype designed and fabricated for X-band operation and infiltrated with a nematic compound with optical birefringence Δn=0.18. Scattering parameters vectorial analysis shows a good agreement between the resonant frequency shifts predicted under anisotropic conditions and those measured under static magnetic control.