Conventional Resonator Research Articles

High-Q spiral-based coupled-resonator device on a Si3N4 platform for ultrasensitive sensing applications

We demonstrate high-Q Si3N4 racetrack-spiral and spiral-spiral coupled-resonator devices for sensing applications. The coupled-resonator architecture resolves the confusion caused by small free spectral range (FSR) in conventional long resonators. The sensitivity of the racetrack-spiral coupled-resonator device for sodium chloride (NaCl) and biomolecule detection is numerically achieved at around 199 nm/RIU (bulk sensitivity) and 183 pm/nm (surface sensitivity), respectively. We fabricate a racetrack-spiral coupled-resonator device with intrinsic Q of 560,000 (263,000) at near-infrared wavelengths, at around 1300 nm, for air (water) cladding. We extract an experimental bulk sensitivity of around 131 nm/RIU for this device from the wavelength shift of the device with different concentrations of the NaCl solution. The performance of the spiral-spiral coupled-resonator device for NaCl and biomolecule detection is theoretically calculated. For biomolecular detection, this device is self-referenced, and its FSR increases almost linearly with the refractive index of biomolecular layer in a certain range. A theoretically defined FSR sensitivity of 74 nm/RIU is extracted from the experimental data. We fabricate a spiral-spiral coupled-resonator device with intrinsic Q of 276,000 (112,000) at around 1300 nm for air (water) cladding, and a bulk sensitivity of 167 nm/RIU for NaCl detection.

A New Class of Wideband MS-to-MS Vialess Vertical Transition With Function of Filtering Performance

A new class of wideband microstrip (MS)-to-microstrip (MS) vialess vertical transition with function of filtering performance is proposed and demonstrated on coplanar waveguide (CPW) resonator in this brief. Initially, a higher unloaded quality factor ( Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ) in the proposed CPW resonator than a conventional slotline resonator shows that the CPW resonator is a better choice for design of the proposed transition than its counterpart on slotline resonator. Meanwhile, to give an insight into the Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> of the CPW resonator, the underlying working mechanism how the proposed CPW resonator is provided with higher Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> than the slotline resonator is elaborated. Then, resonant mode in the proposed CPW resonator will be properly investigated. After that, to facilitate design process, a synthesis design method is introduced for design of the proposed transition. Finally, one design example, i.e., a three-pole vertical transition, is designed, constructed, and experimentally verified. The three sets of results, i.e., expected, simulated and measured results of the proposed transition match well with each other.

Dielectric Resonator Antenna Geometry-Dependent Performance Tradeoffs

A flexible shape generation technique (Surface Contour Shape Generation) is combined with multiobjective evolutionary optimization algorithms in order to synthesize geometrically-diverse dielectric resonator antennas and explore the impact geometry has on relevant performance metrics. It is shown that noncanonical shapes can improve gain and bandwidth when compared to conventional dielectric resonator antenna geometries. Previously described free-form techniques (such as the superformula) have demonstrated improved performance over canonical shapes, but are difficult to integrate with inverse-design. In contrast, the proposed shape generation technique is coupled with multiobjective optimization in order to illustrate the solution space tradeoffs between the various design goals. This technical approach is compatible with various feed designs, antenna performance parameters, and 3D printing techniques.

A simple electrically small microwave sensor based on complementary asymmetric single split resonator for dielectric characterization of solids and liquids

The article presents an asymmetric single split resonator (ASSR) unit cell, its resonant properties, and an electrically small microwave sensor employing the complementary asymmetric single split resonator (CASSR) structure with high quality factor (Q) on the FR4 substrate. The structure is compared with the conventional symmetric split ring resonator. The CASSR sensor designed and fabricated on a substrate of dielectric constant 4.4 and a thickness 1.6 mm has an electrically small size of 0.127λ0 × 0.127λ0 × 0.007λ0 at 1.27 GHz, which yields ka = 0.56 < 1 with low radiation efficiency. The properties and performance of the proposed CASSR for extracting the permittivity of both solid and liquid samples using amplitude and phase sensing in a simple lab-in-touch approach are validated with full-wave simulations and experimental results.

Study in circular auxetic structures for efficiency enhancement in piezoelectric vibration energy harvesting

Piezoelectric (PZT) components are one of the most popular elements in vibration sensing and also energy harvesting. They are very well established, cost effective and available in different geometries however there are still several challenges in their application particularly in vibration energy harvesting. They are normally narrow-band elements and work in high-frequency range. Their efficiency and power extraction density are also generally low compared with different electromagnetic techniques. Auxetic structures are proposed here to enhance efficiency of the piezoelectric circular patches in vibration energy harvesting. These kinds of patches namely PZT buzzers are inexpensive (less than 10 USD) elements and easily available. Two novel circular auxetic substrates are proposed to improve power extraction capacity of the conventional piezoelectric buzzers. Negative Poison’s ratio of the proposed meta-structure helps in efficiency enhancement. The concept is introduced, analyzed and verified through the finite element modeling and experimental testing. The idea is proved to work by comparing the harvested electrical power in the auxetic design against the conventional plain system. A parametric study is then carried out and effects of important electrical and geometrical parameters as well as the material property on the power extraction efficiency are assessed to arrive at optimum parameters. It is shown that by employing the auxetic design, a remarkable improvement in the harvested power is achievable. It is shown that for the two proposed auxetic designs, at the resonance frequency, we could reach to 10.2 and 13.3 magnification factor with respect to the plain energy harvester. Another important feature is that the resonant frequency in these new designs is very much lower than the conventional resonators. Results of this study can open a new path to application of inexpensive PZT buzzers in large-scale vibration energy harvesting.

Multi-mode metamaterial-inspired resonator for near-field wireless power transfer

The modern development of wireless power transfer (WPT) technologies brings various products that improve the lives of users. It has become an urgent demand to simultaneously charge multiple mobile devices operating under different WPT standards on a charging platform regardless of their position and orientation with respect to each other. Recent advances in metasurfaces make it possible to control the near electromagnetic fields with much more degrees of freedom in comparison to conventional resonators. Here, we develop a compact multi-mode metamaterial-inspired resonator formed as an array of sub-wavelength parallel strip conductors. This resonator aims to replace conventional flat coil resonators and offers multiple modes with different profiles of electromagnetic field distribution for various near-field WPT applications. The first three eigenmodes are numerically and experimentally studied, and their potential applications for design of multi-mode WPT systems capable of charging multiple receivers simultaneously are discussed.

Efficient random lasing in topologically directed assemblies of blue-phase liquid crystal microspheres

Controlling light flow in the directed-assembly of blue-phase liquid crystal (BPLC) microspheres with curvature boundaries and random domain of cubic lattices is a highly interesting photonic phenomenon. A strategy of efficient random lasing with resonant feedback based on a microemulsion comprising of BPLC, laser dye and block copolymer is presented here. BPLCs are produced with a microfluidic apparatus and confined in microspheres. These spatially-assembled dye-doped BPLC microdroplets are used as a source for the generation of laser light. Recurrent light flow inside the droplets comprising of face-centered cubic blue-phase boundaries provides omnidirectional lasing with efficient coherent feedback which is not supported by conventional resonators. The topologically directed assemblies of BPLC microspheres with explicit shape and symmetry are essential for reducing threshold and increasing Q-factor of laser emission. These results provide new avenues for a wide range of photonic applications.

Coupled ring split ring resonator (CR-SRR) based epsilon negative metamaterial for multiband wireless communications with high effective medium ratio

In this paper, coupled ring split-ring resonator (CR-SRR) based epsilon negative (ENG) metamaterial with high effective medium ratio (EMR) is designed and investigated for microwave applications. The metamaterial unit cell is a modification of the conventional split-ring resonator, which consists of three major outer split rings with two face to face horizontal E segments placed at the center. All the rings are intercoupled with each other to increase the electrical length. The coupling effect is clearly observable as it provides multi-frequency resonances and a higher value of the effective medium ratio. The electrical length of the proposed unit cell is 0.064λ × 0.064λ, where λ is the wavelength calculated at the lowest resonance frequency (2.24 GHz). The designed unit cell is fabricated on a FR-4 substrate, having a thickness of 1.5 mm. Negative permittivity is observed at frequencies ranging from 2.15 to 2.3 GHz, 4.4–4.95 GHz, 5.7–6.1 GHz, 8.46–9.2 GHz, and 10.6–10.98 GHz. It also exhibits near-zero refractive indexes in the vicinity of these frequency ranges. The equivalent circuit is also designed for the proposed unit cell. The values of the lumped components are optimized by using Advanced Design Software (ADS). This circuit also demonstrates similar multi-band resonances. A high effective medium ratio (EMR) of 16.74 at 2.24 GHz indicates the compactness of the proposed unit cell. Array performance is also investigated by using 1 × 2, 2 × 2, and 16 × 16 array of unit cells. Multiband resonances of the transmission coefficient, |S21| are also noticed from these arrays. For high EMR and small size, the proposed metamaterial is suitable for S, C, and X-bands applications in wireless communications.

Biotoxoid Photonic Sensors with Temperature Insensitivity Using a Cascade of Ring Resonator and Mach-Zehnder Interferometer.

The great advances in silicon photonic-sensing technology have made it an attractive platform for wide sensing applications. However, most silicon photonic-sensing platforms suffer from high susceptibility to the temperature fluctuation of an operating environment. Additional complex and costly chemical signal-enhancement strategies are usually required to improve the signal-to-noise ratio (SNR). Here, a biotoxoid photonic sensor that is resistant to temperature fluctuation has been demonstrated. This novel sensor consists of a ring resonator coupled to a Mach-Zehnder interferometer (MZI) readout unit. Instead of using costly wavelength interrogation, our photonic sensor directly measures the light intensity ratio between the two output ports of MZI. The temperature dependence (TD)-controlling section of the MZI is used to eliminate the adverse effects of ambient temperature fluctuation. The simulation and experimental results show a linear relationship between the interrogation function and the concentration of an analyte under operation conditions. The thermal drift of the proposed sensor is just 0.18%, which is a reduction of 567-fold for chemical sensing and 28-fold for immuno-biosensing compared to the conventional single-ring resonator. The SNR increases from 6.85 to 19.88 dB within a 2 °C temperature variation. The high SNR optical sensor promises great potential for amplification-free detection of nucleic acids and other biomarkers.

High spectro-temporal purity single-photons from silicon micro-racetrack resonators using a dual-pulse configuration.

Single-photons with high spectro-temporal purity are an essential resource for quantum photonic technologies. The highest reported purity up until now from a conventional silicon photonic device is 92% without any spectral filtering. We have experimentally generated and observed single-photons with 98.0±0.3% spectro-temporal purity, an upper bound of the stimulated emission tomography, using a conventional micro-racetrack resonator and an engineered dual pump pulse.

Multi-Wideband Band Pass Filter Using Quad Cross-Stub Stepped Impedance Resonator

This simulation study involved the use of a QC-SSIR (quad cross-tub stepped impedance resonator) to examine the behavior and performance of the MW-BPF (multi-wideband band pass filter). To evaluate the performance of the proposed model, it was compared to the case of the conventional resonator. In the results, MW-BPF was found o exhibit a superior performance in terms of the ease of fabrication, good transmission coefficients, and a wider fractional bandwidth. For the filter structure analysis, this study incorporated the ABCD matrix, with the design of the MW-BPF also based on the FR4 microstrip. The experimental conditions and parameters were set in such a way that for the substrate, tan δ = 0.0265, thickness = 1.6 mm, andεr =4.4, and thicknessh= 1.6 mm. at 2.58 GHz, 1.71 GHz, and 0.81 GHz, the proposed QC-SSIR-based MW-BPF achieved transmission coefficients/fractional bandwidths of 1.93 dB/13.9%, 1.49 dB/18.7%, and 0.60 dB/49.3%, respectively. Relative to the filter size reduction, the FQC-SSIR (folded quad cross-tub impedance resonator) was incorporated. The resultant observations indicated a possibility of BPF size reduction up to 46%. Also, the proposed framework was found to yield (at 2.62, 1.80, and 0.82 GHz) 1.76 dB/12.5%, 1.21 dB/17.7%, and 0.57 dB/49.6% transmission coefficient/fractional bandwidths, respectively. It is also worth indicating that the filter employed LTE2600, WCDMA1800, and GSM800. Therefore, the model exhibited a good agreement, which was depicted by the comparison outcomes between the measured values and the simulated values. Hence, the proposed design was found to be valid and reliable.

Multilayered additive-manufactured half-wavelength coupled line filters

This work presents the design, fabrication and measurements of third-order multilayered filters by additive manufacturing technology. The filters are fabricated using conventional half-wavelength line resonators and a low-cost 3d polylactic acid polymer additive manufacturing process, which allows rapid prototyping and fabrication of complex topologies. The designs, performed at a centre frequency of 2.0 GHz, aim to provide fast manufacturing and get enhanced performances when compared to conventional coupled line third order filters using microstrip technology on commercial substrates. The simulated and measured responses of the fabricated prototypes are in all cases in good agreement.

Design and Optimization of Bidirectional Tunable MEMS All-Silicon Evanescent-Mode Cavity Filter

This article presents a bidirectional electrostatic MEMS tuner that enables active voltage compensation of integrated evanescent-mode cavity-based tunable filters. Unlike conventional tunable resonators tuned by unidirectional electrostatic diaphragms, the bidirectional design can compensate for residual displacement errors. This corrective tuning can successfully counterbalance long-term viscoelastic relaxation commonly found in large-displacement MEMS diaphragms. Consequently, it can significantly improve stability and reliability without introducing fabrication complexity. A detailed RF-MEMS codesign and a specific optimization design flow are also discussed. A proof-of-concept, two-pole filter is fabricated, which demonstrates a measured bidirectional tuning range of 18.9–39.6 GHz. The forward (main) actuation tunes the filter from 21.3 to 39.6 GHz with 120 V, whereas the reverse (corrective) actuation tunes it from 21.3 down to 18.9 GHz with 2 V. The measured filter insertion loss varies from 3.14 to 0.78 dB. The extracted unloaded quality factor is 265–510, which is comparable with the state-of-the-art unidirectional filters of this type.

Enhancement of the low-frequency acoustic energy harvesting with auxetic resonators

A new concept to enhance efficiency of the acoustic energy harvesting is presented and experimentally tested in this paper. An auxetic latticed resonator backed by an acoustic rectangular tube is proposed for this purpose. The concept is tested and proved by comparing the extracted power against performance of a conventional cantilever resonator at resonant-resonant condition. The problem is modeled by the Finite Element Method. The models are validated using experimental tests. The energy harvesting performance is numerically evaluated in different sound powers, geometrical aspects and electrical properties. In a parametric study, performance of the proposed auxetic resonator is compared with a plain one. It is shown that employing the concept can remarkably enhance performance of the acoustic energy harvesting system. At low frequencies, 138 Hz in this study, at an optimum situation we could arrive at a large magnification factor around 10.5 for 100 dB sound pressure level.

Enhanced toroidal localized spoof surface plasmons in homolateral double-split ring resonators.

In this paper, toroidal localized spoof surface plasmons (LSSPs) based on homolateral double-split ring resonators is proposed and experimentally demonstrated at microwave frequencies. By introducing a new split in the conventional single-split ring resonator, the magnetic field in resonator is locally modified. The double-split ring resonator can create the mixed coupling in the structure, leading to the enhancement of magnetic field. Both numerical simulations and experiments are in good agreement. Compared with traditional toroidal LSSPs based on the single-split ring resonators, the imperfection of toroidal LSSPs is resolved, the intensity of toroidal resonance and the figure of merit (FoM) are significantly enhanced. To understand and clarify the enhanced magnetic field phenomena, we analyze the role of the double-split ring resonator. The effect of location of source and spacing between two splits on the resonance intensity are also discussed. A higher intensity of toroidal LSSPs resonance could be achieved by changing the spacing between two splits. Additionally, it is experimentally demonstrated that the enhanced toroidal LSSPs resonance is sensitivity to the background medium. The results of our research provide a new idea for exciting the enhanced toroidal dipole.

Numerical Investigations into Higher Order Axial Modes of Terahertz Gyrotron Resonator with Significantly Up-Tapered Midsection

This article presents the effect of significant up-tapering of the resonator midsection on diffractive quality factor, resonant frequency, axial field profile shift, and axial separation between peaks of higher order axial modes (HOAMs) in a gyrotron resonator. Significant up-tapering of the resonator midsection causes the quality factor curves of HOAMs to come close to each other and eventually crossover. This allows HOAMs to have comparable or even higher quality factor value than the lower axial modes—a situation which is not possible in a conventional resonator. Due to this, the operating current for all axial modes can keep an order of magnitude. The up-tapering also shifts the axial field profile toward the output section of the resonator and leads to the loss of spatial symmetry that exists in the axial separation between the peaks of HOAMs in a conventional resonator. Computations have been performed for 0.2-, 0.5-, and 1-THz resonator using single-mode cold cavity solver code developed at CSIR-CEERI. Numerical validation with published results, for 0.2- and 0.5-THz conventional resonators, has also been carried out.

Negative Piezoelectric-Based Electric-Field-Actuated Mode-Switchable Multilayer Ferroelectric FBARs for Selective Control of Harmonic Resonances Without Degrading Keff².

Mode-switchable ferroelectric thin-film bulk acoustic resonators (FBARs) are presented. Such resonators operate based on a dynamic nonuniform effective piezoelectricity in composite multilayer ferroelectrics with large electrostriction coefficients, like barium strontium titanate (BST). Harmonic resonance modes ( nfo ) of a multilayer ferroelectric bulk acoustic wave (BAW) resonator can be selectively excited with an electromechanical coupling coefficient ( Keff2 ) equal to the fundament mode, which is contrary to the trend Keff2 ∝ 1/n2 exhibited by conventional piezoelectric BAW resonators. Such a device can selectively be set to resonate at its different resonance harmonics by generating a pattern of nonuniform piezoelectric coefficient proportional to the stress field of each mode with an application of a proper set of dc control voltages applied across the ferroelectric layers. Such a resonator allows for the design of a new class of band-switching filters. As an experimental validation, a mode-switchable FBAR and a band-switching ladder-type filter based on a bilayer ferroelectric BST structure are designed and fabricated for the first time. The bilayer BST FBARs not only can be switched ON or OFF but also by choosing different bias configurations, two resonance modes at 2 and 3.6 GHz can be selectively excited having Keff2 of 8% and 7%, respectively.

Development of a composite polymer-dye medium for tunable laser emission

We demonstrate optically pumped laser medium with emission in the visible spectral range from binary solutions of Rhodamine 6G and Rhodamine B in epoxy resin as matrix without appending additional scattering centers. A frequency doubled Q-switched Nd: YAG laser was used for pumping. The generation’s behavior is similar to random laser (RL) with no external optical resonator. The influence of the nanostructured morphology of the medium on the laser properties was investigated by means of SEM, AFM, TEM, SAED, Spectrofluorimetry and Spectrometry. The laser emission is characterized by high intensity – energy per pulse – 300 µJ, threshold pump energy 1.7 mJ, relatively low beam divergence of 70 mrad (for RL) and spectrally narrowed major peak at 597 nm. The new gain medium was also investigated in a conventional tunable resonator. Generation with continuous tuning in the spectral range 590–610 nm was obtained. This new effective nanostructured medium, which shows with high optical and energy parameters, can be used in speckle-free laser imaging, time-resolved microscopy, high speed optical converters and others photonics applications.

A new type of the air‐filled substrate integrated gap waveguide resonator

This article presents the design and analysis of an air-filled substrate integrated gap waveguide (ASIGW) resonator. The electromagnetic field of each resonant mode in the resonator is studied by theoretical modeling and EM simulation. Besides, the relationship between the dimensions and Qu is analyzed and the Qu of the resonator can be as high as 2080 at Ku band. Compared with conventional rectangular waveguide resonator and gap waveguide (GW) resonator, the proposed ASIGW resonator can be fabricated more easily. Compared with the substrate integrated waveguide resonator, the ASIGW resonator is more tolerant with dimensional errors and with less degenerate modes. As an example, a fifth-order band-pass filter based on the ASIGW resonators is presented to verify the previous conclusions.

Numerical investigation of liquid metamaterial-based superstrate microstrip radiating structure

In this paper, we present a novel microstrip antenna system that combines liquid and metamaterial properties to achieve higher gain, higher operating bandwidth, and multiple operating frequency bands. This is achieved by stacking multiple liquid-based-metamaterial superstrate passive structures over the active patch. The circular active microstrip patch antenna is loaded with two layers (stacked one-above-the-other) of passive superstrate patches to improve the antenna system performance. Initially, to test and compare the concept-hypothesis, the superstrate is loaded with a conventional copper-based multiple split-ring resonators superstrate passive patch, followed by the liquid counterpart - liquid-based multiple split-ring resonators (liquid-metamaterial) superstrate passive patch, to achieve higher antenna system performances. The study shows that; compared to the copper-based superstrate, the liquid-based superstrate loading increases reflectance response, Gain, the operational bandwidth, and also open vistas for multiple frequency operation of the antenna system. Attention is drawn to the fact that the antenna system gain is enhanced by the liquid-based multiple split-ring resonators superstrate incorporated microstrip patch antenna system with high gain. Position of patches is arranged in two ways. Firstly arranged in center position one another and in secondly they are arranged in one-sided. By shifting patches in one-sided reflectance response will enhance that covers different strategic applications in the Wearable, Bio-monitoring, C-band and other extended wireless communication applications.