Cross Resonator Research Articles

Free vibration for a micro resonant pressure sensor with cross-type resonator

In this paper, a cross resonator pressure sensor is proposed to improve the detection accuracy of capacitor-detecting sensor. Considering electrostatic force and molecular force, the multi-field coupled dynamic equation of the sensor is established. By solving the dynamic equation, the equations for the mode function and the natural frequencies of the resonator are obtained. Using these equations, the natural frequency and mode function of the sensor are given. Changes of natural frequency of sensor with main parameters are studied. Influence of molecular force on the natural frequency is analyzed. Results show that within a considerable range of pressure, the natural frequencies increase approximately linearly with pressure. Under small pressure, small initial distance between resonator and base, and lower order modes, effects of the Van der Waals force on the natural frequencies are quite obvious.

Ink-jet printed metamaterial microwave absorber using reactive inks

Ink-jet printing technology is one of the most promising printing techniques enabling fabrication of metamaterial absorber (MMA) in a one-step and direct process. In this study and for the first time the metamaterial microwave absorbing structure is proposed using water-based reactive inks and ink-jet printing technique. The MMA based on Unite-Ring-Swastika Cross Resonator (URSCR) is printed on a copy paper. The printed MMA structure is flexible and includes an ink-jet printed silver unit cell, a dielectric layer (copy paper), and an ink-jet printed silver ground plate was formed underneath the substrate. The working principles of the unit cell of MMA and its parametric simulations are evaluated. The performance of MMA with the full-wave simulation at the microwave frequency band is assessed as well, showing great agreement with the results obtained from the measurements. The experimental results indicate that the amount of measured flexible MMA absorption based on URSCR at resonance frequency on a planar surface at 0° to 40° incident angles and on a cylindrical surface at a 0° incident angle stays over 99%.

Demonstration of broadband magnetic polymer composite absorber crossing S- and C-bands

In this paper, an ultra-thin microwave absorber with cross-resonator (CR) exhibiting a broad absorption bandwidth is designed and fabricated. Theoretical and experimental results show that the absorber has a wideband strong absorption in a frequency range from 2.2 to 6.8 GHz and from 2.2 to 5.4 GHz when incident electric field is y-and x-polarized, respectively. The equivalent L–C circuit and energy loss density clarify the mechanism underlying observed absorption. Moreover, the oblique incidence performance of the proposed absorber is also analyzed and shows that the broad bandwidth can be maintained as incident angle increases up to 30 degrees for y-polarized wave and 60 degrees for x-polarized wave, respectively. And when incident angle is fixed at 30 degrees the absorption bandwidth can be achieved from 2.1 to 7.5 GHz with azimuth angle of 90 degrees for x-polarized wave.

Controlling wideband absorption and electromagnetically induced transparency via a phase change material

A terahertz switchable metamaterial is presented with bifunctional properties of absorption and electromagnetically induced transparency based on phase transition of vanadium dioxide. When vanadium dioxide is metal, the designed configuration acts as a wideband absorber consisting of a vanadium dioxide square-shaped array, a dielectric spacer, and a vanadium dioxide continuous film. The working frequency of absorptance larger than 90% ranges from 0.271 THz to 0.592 THz with bandwidth ratio 74.4%. The absorber can work well over a wide range of incident angle for transverse electric polarization and transverse magnetic polarization. When vanadium dioxide is insulator, the designed configuration acts as an analog of electromagnetically induced transparency in the terahertz frequency. The interaction between metallic cross and split ring resonator gives rise to a transparency peak in the transmission spectrum. The performance of electromagnetically induced transparency is robust against polarization and incident angle. This design could provide some prospects in designing switchable terahertz devices, such as the modulator, filter, and optoelectronic components.

Reflection based Strain Sensing using Metamaterials

Resonator arrays of periodicially arranged electromagnetic sub-wavelength resonators show a strong frequency filter behaviour which can be controlled by the geometry, size and arrangement of the resonators. The use of several resonator arrays and their integration into a polymer matrix allows the realisation of metamaterials with a specific resonance behaviour. The resonance behaviour can be influenced by material and structural changes enabling a passive sensor function. The considered sensor approach based on metamaterials is investigated to enable structural health monitoring of lightweight structures. In the present case, a double-layer Jerusalem cross (JC) resonator array (RA) is integrated into a glass fibre reinforced plastic (GFRP) to analyse the change of the resonance behaviour under load (strain) using a reflection measurement. The CST (Computer Simulation Technology) Microwave Studio was used to model the resonator array for operation in the microwave frequency range between 15 GHz and 35 GHz as well as for the numerical analysis of the resonance behaviour under load. The numerical results were validated by a tensile test using a tensile test machine (type TIRATEST 28100, Tira GmbH) and by a reflection measurement using two standard gain horn antennas (type Standard Gain Horn Series 862, ARRA Inc) and a vector network analyser (type ZVA50, Rohde&Schwarz). The reflection measurement shows a reflection minimum at 28.6 GHz which moves to higher frequencies under load of the GFRP laminate. With the shift of the minimum, the quality factor decreases and the dip widens. The investigation shows that it is possible to provide a GFRP laminate with a specific electromagnetic behaviour by integrating resonator arrays. It is also shown that the specific electromagnetic behaviour can be influenced by structural changes and thus opens up the possibility of monitoring the condition of lightweight structures.

Tunable terahertz filters based on carbon nanotubes

Subject of Research. The paper presents the study of optically tunable terahertz filter based on cross resonators coated with a layer of carbon nanotubes (CNT). We show experimentally control capability of the optical spectral characteristics of terahertz devices coated with a layer of single-wall carbon nanotubes. Method. The empirical formulas were used for calculation of the geometrical parameters of a cross-shaped resonator for a given resonant frequency and filter Q-factor. Experimental samples of the notch filter were made by laser engraving. A layer of carbon nanotubes, which were synthesized by aerosol chemical deposition, was deposited on an experimental filter sample. Experimental transmission spectra of an “empty” filter, a filter with a carbon nanotubes layer without pumping, and an optically pumped carbon nanotubes layer filter at a wavelength of 980 nm were measured by terahertz time-domain spectroscopy. Main Results. We have shown by experiments that optical pumping of a filter with carbon nanotubes layer leads to a decrease in the transmittance of the main resonance peak and a shift towards higher frequencies of the side resonance peak. Practical Relevance. Filters coated with carbon nanotubes layer can be used as inexpensive and compact tunable components for terahertz photonics devices

Polarization independent dielectric metasurface for infrared beam steering applications

Over the past years, metasurfaces have been of great interest due to their ability manipulate optical wavefront by introducing a phase gradient across the transverse directions of the wave. This phase gradient was usually realized using plasmonic resonators which had high intrinsic losses. Here, we demonstrate, numerically, a proof of principle of an all-dielectric silicon based metasurface at the infrared (IR) range that manipulates the wave front and achieves beam steering with significantly high transmission. The proposed cross-shaped unit cell design shows high transmission with the ability to fully control the phase of the transmitted wave from 0 to 2π. The metasurface is made of silicon cross resonators, arranged to have a linear phase gradient, on SiO2 substrate which makes the device compatible with most standard semiconductor fabrication techniques.

High-efficiency full-phase modulation of a terahertz wave based on a dielectric metasurface

In this paper, we propose a transmissive terahertz metasurface, consisting of periodically arranged subwavelength silicon cross resonators. Based on the theory of electromagnetic dipole resonance, and changing the structural parameters and directions of cross resonators; the phase modulation of a terahertz wave can be realized at a target terahertz frequency. By employing full-wave finite element numerical simulation, we utilize the metasurface to achieve an almost full phase 2π control in the terahertz band, and the transmission efficiency is over 90%. The proposed transmissive metasurface has potential applications in some terahertz functional devices, such as lenses, wave plates and optical vortex converters.

Electrically Triggered Tunable Terahertz Band-Pass Filter Based on VO2Hybrid Metamaterial

We demonstrate an electrically triggered tunable terahertz (THz) band-pass filter based on vanadium dioxide (VO2) embedded hybrid metamaterials. The unit cell of the filter consists of two cross resonators and a central bar. The phase transition of VO2 is induced by the ohmic heating of the central bar. The transmission can be modulated by the applied currents. The mechanism of tunability is that the conductivity of the VO2 film changes with the applied currents. The relation between the upper cut-off frequency and the geometries is investigated using finite integration time domain method. The sample is fabricated by a thin film process, and characterized using a THz time domain spectroscopy system. The results show that, when the bias current rises from 0 to 0.27 A, the transmission decreases from 0.85 to 0.01. The maximum modulation depth reaches 96%, and the full width at half maximum is about 0.44 THz. This tunable THz band-pass filter has potential applications in THz communication, imaging, and spectroscopy systems.

Multifocal terahertz lenses realized by polarization-insensitive reflective metasurfaces

In this work, we report two multifocal terahertz (THz) lenses (MTLs) based on reflective metasurfaces with focusing efficiencies of 57.3% and 46.3% at a frequency of 3.11 THz, respectively. The reflective metasurfaces were constructed by patterning the polarization-insensitive cross resonator array atop a continuous gold ground plane spaced by a layer of parylene film, which provides a complete 2π phase coverage. The elaborated phase profiles of the two MTLs were arranged based on the Fresnel-Kirchhoff diffraction theory. The two MTLs were theoretically and experimentally verified to converge continuous THz waves into two and four beam spots at their focal planes, respectively. Meanwhile, the MTLs were also experimentally demonstrated with multiple imaging abilities.

Single and multi-band electromagnetically induced transparency-like effects with a four-fold symmetric metamaterial design

In this study classical analogues of single and multi-band electromagnetically induced transparency in metamaterials are numerically and experimentally demonstrated. The unit cells of the two single-band electromagnetically induced transparency-like metamaterials are composed of a Jerusalem cross resonator and four spiral resonators, acting as bright and quasi-dark resonator, respectively. Polarization independent slow light response with transparencies exceeding 80% and group indices more than 100 and 50 are obtained for the proposed first and second electromagnetically induced transparency-like metamaterials, respectively. Supercell method is adopted to achieve polarization independent dual-band electromagnetically induced transparency-like behaviour by combining the unit cells of the designed two electromagnetically induced transparency-like metamaterials in four-fold symmetry. High group indices at the three transmission peaks are obtained with group index values of 114, 127 and 46. Since the third transmission band is not due to classical analogue of electromagnetically induced transparency, a comparison of slow light feature between two transmission bands of different origin is given. The effect of oblique incidence is also investigated and it has been found that the bandwidth and group index properties show opposite behaviour under orthogonal polarizations. Numerical results are supported with experimental measurements for the single and dual-band electromagnetically induced transparency-like metamaterials. The results may be important for practically designing multi-band polarization independent electromagnetically induced transparency-like metamaterials, which have potential applications in multi-frequency filtering, enhanced sensing and multi-band slow light devices.

Broadband multimode antenna and its array for wireless communication base stations

A wideband dual-polarized antenna coupling cross resonator is proposed for LTE700/GSM850/GSM900 base stations. An additional resonance is introduced to obtain strong coupling between the dipole and resonator. Moreover, the input impedance of the proposed antenna is steadily close to $50{\Omega}$ ,...

Enhanced absorption of monolayer molybdenum disulfide (MoS2) using nanostructures with symmetrical cross resonator in the visible ranges

In order to enhance the absorption of monolayer molybdenum disulfide (MoS2), a novel nanostructure with symmetrical cross resonator based on MoS2 in the visible wavelength ranges has been proposed. At a resonant wavelength of 623 nm, the absorption of monolayer MoS2 in the absorption structure is as high as 82%, much higher than the bare MoS2 in the air. The electric field around monolayer MoS2 is enhanced by the guided mode resonance, thereby enhancing the absorption of monolayer MoS2 in the structure. The relevant parameters of the proposed structure are adjusted to achieve the tunability of the resonant wavelength in the visible ranges and the high-efficiency absorption of monolayer MoS2 in the structure, which is of great significance for the applications of MoS2-based optoelectronic devices.

An Ultra-Wideband THz/IR Metamaterial Absorber Based on Doped Silicon.

Metamaterial-based absorbers have been extensively investigated in the terahertz (THz) range with ever increasing performances. In this paper, we propose an all-dielectric THz absorber based on doped silicon. The unit cell consists of a silicon cross resonator with an internal cross-shaped air cavity. Numerical results suggest that the proposed absorber can operate from THz to far-infrared regimes, having an average power absorption of ∼95% between 0.6 and 10 THz. Experimental results using THz time-domain spectroscopy show a good agreement with simulations. The underlying mechanisms for broadband absorption are attributed to the combined effects of multiple cavities modes formed by silicon resonators and bulk absorption in the doped silicon substrate, as confirmed by simulated field patterns and calculated diffraction efficiency. This ultra-wideband absorption is polarization insensitive and can operate across a wide range of the incident angle. The proposed absorber can be readily integrated into silicon-based photonic platforms and used for sensing, imaging, energy harvesting and wireless communications applications in the THz/IR range.

Ultra-broadband terahertz absorption using bi-metasurfaces based multiplexed resonances.

In this paper, we demonstrate an ultra-broadband terahertz (THz) bi-metasurfaces absorber composed of two stacking metasurfaces backed by a metallic ground plane. The bottom metasurface consists of four multiplexed cross resonators with different geometries on a thin parylene layer, achieving a bandwidth of 3.80 THz with the absorption higher than 50% at high frequency. Meanwhile, the top metasurface, including two multiplexed cross resonators with different sizes on a relatively thicker parylene layer, provides a low frequency absorption band with an additional Salisbury screen absorption peak that connects the two absorption bands of the two metasurfaces, therefore enabling an ultra-broadband absorption. The experimental absorption spectrum of the bi-metasurfaces shows a bandwidth of 4.46 THz while the absorption exceeding 50% and a full width at half maxima (FWHM) of 97.7%. The ultra-broadband absorber will be a promising candidate for THz broadband detection.

Wavelength-selective mid-infrared metamaterial absorbers with multiple tungsten cross resonators.

Wavelength-selective metamaterial absorbers in the mid-infrared range are demonstrated by using multiple tungsten cross resonators. By adjusting the geometrical parameters of cross resonators in single-sized unit cells, near-perfect absorption with single absorption peak tunable from 3.5 µm to 5.5 µm is realized. The combination of two, three, or four cross resonators of different sizes in one unit cell enables broadband near-perfect absorption at mid-infrared range. The obtained absorption spectra exhibit omnidirectionality and weak dependence on incident polarization. The underlying mechanism of near-perfect absorption with cross resonators is further explained by the optical mode analysis, dispersion relation and equivalent RLC circuit model. Moreover, thermal analysis is performed to study the heat generation and temperature increase in the cross resonator absorbers, while the energy conversion efficiency is calculated for the thermophotovoltaic system made of the cross resonator thermal emitters and low-bandgap semiconductors.

Transmissive terahertz metalens with full phase control based on a dielectric metasurface.

In this paper, we report a transmissive terahertz (THz) metalens based on a dielectric metasurface that consists of periodically arranged sub-wavelength silicon cross resonators with a spatially hyperboloidal phase profile. By varying arm lengths of the cross resonators, we obtained a full 2π phase coverage with high transmission at target frequency. The fabricated metalens was experimentally demonstrated to focus a continuous THz beam to a spot with a full width at half-maximum of 630μm at a focal length of 28mm, which agrees well with the theoretical calculation. This device has potential for applications in THz imaging and communications, and our work can also easily be extended in the design of other planar THz components, such as beam deflectors or vortex plates.

Design of a wide-angle, polarization-insensitive, dual-band metamaterial-inspired absorber with the aid of equivalent circuit model

We present the design of a wide-angle, polarization-insensitive, dual-band, low-profile metamaterial-inspired absorber for operation at two wireless local area network channels, related to 2.45 and 5 GHz industrial, scientific and medical frequencies. The design synthesis methodology involves equivalent circuit model calculations with the use of analytical expressions of capacitive and inductive elements prior to full-wave electromagnetic optimization, for easily acquiring of very high absorption conditions at the targeted frequencies. The unit cell of the metamaterial-inspired absorber consists of a joint metallic Jerusalem cross resonator with interdigital capacitors and a tetra-arrow resonator printed on top of a grounded 1-mm-thick lossy FR-4 substrate. The proposed absorber shows almost unity absorptivity at the targeted frequencies and a robust absorption characteristic under changes in incidence angle and polarization. The proposed structure can be used for protection of the systems from electromagnetic interference with existing wireless local area network frequencies.

A metasurface for conversion of electromagnetic radiation to DC

We present a metasurface electromagnetic energy harvester based on electrically small resonators. An array of 8× 8 cross resonators was designed to operate at 3GHz. Unlike earlier designs of metasurface harvesters where each resonator was connected to a single rectifier or load, in this work the received power by all resonators is channeled to a single rectifier which in turn channels the DC energy to a single 50Ω resistive load. The critical advantage of the proposed structure is maximizing power density per diode which maximizes the diode turn-on time. We show through simulation and measurements that the proposed metasurface harvester provides Radiation to DC conversion efficiency of more than 40%.

Angle- and Polarization-Insensitive Metamaterial Absorber using Via Array.

In this paper, we propose an angle- and polarization-insensitive metamaterial absorber. We design a metamaterial unit cell that is based on a split ring cross resonator (SRCR). We observe that the absorption frequency and absorption ratio are insensitive to incident angles when a via array surrounds the SRR. We demonstrate the effect of the via array using full-wave simulations by comparing the absorptivity of the SRCR with and without the via array. Because of the symmetric geometry, we also realize polarization insensitivity. We build the proposed absorber on a printed-circuit-board with 30 × 30 unit cells, and we demonstrate its performance experimentally in free space. Under normal incidence, the fabricated absorber shows 99.6% absorptivity at 11.3 GHz for all polarization angles, while for oblique incidence, the fabricated absorber maintains an absorptivity higher than 90% for incident angles up to 70° and 60° for transverse magnetic (TM) and transverse electric (TE) modes, respectively.