Quarter-wavelength Resonators Research Articles

Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on α-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of α-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter-wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0 × 106 in the single photon region. The Qi of most devices are higher than 2.0 × 106. Moreover, most of them are still over 1 × 106 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability.

Impact of stack length on performance of standing wave thermoacoustic refrigerator

The low coefficient of performance of thermoacoustic refrigerators has limited their development. The goal of this paper is to investigate the effect of different stack lengths on standing wave thermoacoustic refrigerator (TAR) performance. The stack is essential in TAR because it expands the gas-solid interface, allowing for a greater temperature difference between the warm and cold regions. Hence literature studies on stack length, geometry, plate spacing, and material have been investigated. A quantitative analysis was performed to determine an effective TAR design by numerically modelling three geometries using COMSOL Multiphysics 6.0. A quarter wavelength resonator tube was designed using a 2D axisymmetric model. The acoustic wave and energy fields in solids were studied using conjugate heat transfer, with the fluid flow considered laminar and helium as the working gas. The optimal TAR design was chosen based on the lowest temperature difference between the three simulated geometries. Seven numerical models were simulated for stack lengths ranging from 15 mm to 45 mm, revealing that COP increased as stack length decreased, while the temperature difference decreased.

Extremely tortuous sound absorbers with labyrinthine channels in non-porous and microporous solid skeletons

An assembly of additively-manufactured modules to form two-dimensional networks of labyrinthine slits results in a sound absorber with extremely high tortuosity and thereby a relatively low-frequency quarter wavelength resonance. Fully analytical modelling is developed for the generic design of such composite acoustic panels, allowing rapid exploration of various specific designs. In addition to labyrinthine channels in a non-porous solid skeleton, a case is also considered where the skeleton has microporosity such that its permeability is very much lower than that due to the labyrinthine channels alone. The analytical modelling is verified by numerical calculations as well as sound absorption measurements performed on several 3D printed samples of modular composite panels. The experimental validation required overcoming the non-trivial difficulties related to additive manufacturing and testing samples of extreme tortuosity. However, due to the two-dimensionality and modularity of the proposed design, such absorbers can possibly be produced without 3D printing by assembling simple, identical modules produced separately. The experimental results fully confirmed the theoretical predictions that significant sound absorption, almost perfect at the peak, can be achieved at relatively low frequencies using very thin panels, especially those with double porosity.

Eigenfrequency Shift of Piezoelectric Backplate in Vibro-Acoustic Energy Harvesting

Noise is increasingly recognised as a serious, worldwide public health concern. Noise is a type of occupational hazard that can cause damage to hearing and other health effects in workers who are exposed to high levels of noise in their work environment. Traditionally, noise can be controlled and suppressed but recently, noise can be useful and converted into electrical energy. The process of converting noise or acoustic waves into electrical energy by using a quarter wavelength resonator tube embedded with a flexible piezoelectric backplate was used in this study. The results show the maximum output voltage of 1.41 V/Pa at 112 Hz and 0.44 V/Pa at 225 Hz in the experiment, and 1.44 V/Pa at 106 Hz and 0.41 V/Pa at 226.5 Hz with incident sound waves at 90 dB. A parametric study was then performed by adjusting the lumped pointed mass at the piezoelectric backplate to tune the resonant frequencies of the system and the optimal power output. The point mass has given significant change in the acoustic properties. The maximum output power increased from 20.4 at 112 Hz using a flexible back plate to 711 at 119.75 Hz. Various small power applications can benefit from the approach by reducing and absorbing specific low-frequency bandwidths of continuous noise in the environment.

High performance selective light absorber based on nickel nanopillar array for photothermal conversion

Efficient absorption of solar radiation holds the key to photothermal utilization; however, realizing solar absorber designs with high absorption efficiency remains challenging. Herein, a nickel-based metamaterial selective solar absorber with a nanopillar array structure was proposed to realize nearly perfect optical absorption over a broad spectrum. The average absorbance is up to 96% in the 300–2033 nm wavelength range. Notably, a reasonably detailed analysis of the physical mechanism of the proposed absorber was performed in this paper, attributing the exceptional broadband absorption to the concurrent interaction with surface plasmon resonance, quarter-wavelength resonance, and electric dipole resonance. The absorption efficiency declines significantly when λ > 2.5 μm, with only 20% absorptivity at λ = 6 μm in the radiation-absorbing transition region. This decline is desirable, as it contributes to reducing the emissivity in the mid-infrared range and, therefore, prevents self-radiation. The results demonstrate that the selective absorber possesses the potential to capture solar energy within a broadband, while avoiding undesirable self-radiation, thereby enhancing the integral efficiency of the solar energy conversion system. Moreover, the absorption spectrum shows insensitivity to polarization and angle of incidence. The selective solar absorber proposed here offers excellent performance with a simple structure, showing great promise in the field of photothermal conversion.

WiFi Sensor Node With High Sensitivity and Linearity Based on a Quarter-Wavelength Resonator for Measuring Crack Width

WiFi Sensor Node With High Sensitivity and Linearity Based on a Quarter-Wavelength Resonator for Measuring Crack Width

High fidelity analysis and optimization of a quarter wavelength thermo-acoustically driven refrigerator

High fidelity CFD analysis is done to investigate the coupling of a thermoacoustic engine and refrigerator (TAE & TAR) within a straight tubular quarter-wavelength resonator under high pressure conditions. A parametric study aims to optimize TAE efficiency (η) and TAR coefficient of performance (COP). Firstly, the TAE is modelled to ascertain the optimum position of the TAE stack based on the acoustic power (Ẇ) and efficiency (η). The TAE achieved a drive ratio near 20 %. It was found that the optimum normalized position (xn) for the TAE stack is at 0.43 for highest Ẇ of 78.3 W and 0.25 for highest η of 9 %. Secondly, Thermo-Acoustically Driven Refrigerator (TADR) is developed by incorporating both TAE and TAR stacks in tandem following optimal positioning of the TAR stack. Finally, the performance of the TADR is optimized by altering the TAR stack material, the TAE hot end temperature, and the working fluid. The optimal TAR stack position was found to be the closest to the TAE stack. The material with lower thermal conductivity (Mylar) outperformed the higher conductivity (Steel). Furthermore, Increasing the TH from 1,000 K to 1,200 K significantly increased the cooling power. Argon demonstrated the highest η and COP compared to Air and Helium, however, the highest cooling power was achieved using Helium. Two TADR configurations were considered: a) Helium with stacks at xn = 0.43 (TAE) and xn = 0.77 (TAR), prioritizing cooling power, achieving 60.87 W at 5 K temperature difference; b) Argon with stacks at xn = 0.25 (TAE) and xn = 0.58 (TAR), favoring efficiency, achieving up to 22.815 % overall efficiency at 5 K temperature difference, and a maximum temperature drop of 34 K below ambient (300 K).

Flux-Driven Josephson Parametric Amplifier Fabricated Using the Nb/AlO x /Nb Trilayer Process

In this paper, we report a flux-driven Josephson par-ametric amplifier (JPA) fabricated using the Nb/AlOx/Nb Josephson junction process. The JPA consists of a parallel-plate type coupling capacitor and quarter-wavelength resonator terminated with a DC-SQUID. We adopt a simple 4-layer process using well-estab-lished Nb trilayer technology. The overall configuration time of the Nb-based JPA can be shortened by measuring resonant frequency and its bias dependence in liquid helium. Amplification of the pre-tested device was demonstrated, showing a gain of 20 dB in a -3 dB bandwidth of 17 MHz in a 10 mK dilution fridge.

Extremely large Lamb shift in a deep-strongly coupled circuit QED system with a multimode resonator

We report experimental and theoretical results on the extremely large Lamb shift in a multimode circuit quantum electrodynamics (QED) system in the deep-strong coupling (DSC) regime, where the qubit-resonator coupling strength is comparable to or larger than the qubit and resonator frequencies. The system comprises a superconducting flux qubit (FQ) and a quarter-wavelength coplanar waveguide resonator (lambda /4 CPWR) that are coupled inductively through a shared edge that contains a Josephson junction to achieve the DSC regime. Spectroscopy is performed around the frequency of the fundamental mode of the CPWR, and the spectrum is fitted by the single-mode quantum Rabi Hamiltonian to obtain the system parameters. Since the qubit is also coupled to a large number of higher modes in the resonator, the single-mode fitting does not provide the bare qubit energy but a value that incorporates the renormalization from all the other modes. We derive theoretical formulas for the Lamb shift in the multimode resonator system. As shown in previous studies, there is a cut-off frequency omega _{textrm{cutoff}} for the coupling between the FQ and the modes in the CPWR, where the coupling grows as sqrt{omega _n} for omega _n/omega _{textrm{cutoff}}ll 1 and decreases as 1/sqrt{omega _n} for omega _n/omega _{textrm{cutoff}}gg 1. Here omega _n is the frequency of the nth mode. The cut-off effect occurs because the qubit acts as an obstacle for the current in the resonator, which suppresses the current of the modes above omega _{textrm{cutoff}} at the location of the qubit and results in a reduced coupling strength. Using our observed spectrum and theoretical formulas, we estimate that the Lamb shift from the fundamental mode is 82.3% and the total Lamb shift from all the modes is 96.5%. This result illustrates that the coupling to the large number of modes in a CPWR yields an extremely large Lamb shift but does not suppress the qubit energy to zero, which would happen in the absence of a high-frequency cut-off.

Wideband Bandpass Filters Based on Eighth-Mode Substrate Integrated Waveguide and Microstrip Resonators

A class of wideband bandpass filters (BPFs) with two eighth-mode substrate integrated waveguides (EMSIW) and two microstrip resonators is presented in this brief. The quarter-wavelength microstrip resonator is connected to the hypotenuse side of EMSIW resonator, which is different from these filters with two EMSIW resonators sharing vias or iris windows. By introducing the quarter-wavelength microstrip resonators, the design flexibility can be improved with a compact size. Based on the proposed topology, a BPF centered at 4 GHz is designed and fabricated with fractional bandwidth (FBW) of 25%. The measured insertion loss within the passband is only 0.9 dB, while the return loss is better than 14.1 dB. To further improve the roll-off skirts and attain a better out-of-band rejection, a transmission zero (TZ) is generated with the mixed electric and magnetic coupling between two microstrip resonators. The measured FBW of the BPF with one TZ is 26.6%, whose center frequency is also at 4 GHz. The measured stopband rejection above the passband is better than 34 dB from 5.02 to 8.31 GHz. Good agreement between simulated and measured results validates the feasibility of the proposed BPFs.

Coiled quarter wavelength resonators for low-frequency sound absorption under plane wave and diffuse acoustic field excitations

To reduce their space requirement, quarter wavelength resonators are coiled up into a spiral to have the shape of a flat cylinder. The practical implementation of these resonators is tested using 3D printing, laser cutting and machining. Numerical simulations and impedance tube measurements are first compared for a normally incident plane wave excitation. This step allows to evaluate the effect of the resonator’s inlet diameter, internal wall thickness, overall height as well as its constitutive material. A series of samples are then 3D printed following the identified optimal geometrical configuration. An array of resonators is tested alone and in combination with a glass wool layer under diffuse acoustic field excitation in a small reverberation chamber. The obtained results show that coiled quarter wavelength resonators can provide large sound absorption at their lowest resonance frequency and under both considered excitations, even if the largest external dimension of the resonators is only 1/18th of the targeted acoustic wavelength.

Quarter-Wavelength Two-Section Coaxial Stepped Impedance Resonators With Parallel Central Sections for Constraint Reduction in Compact Tx Bandpass Filters

This paper presents a novel two-section coaxial stepped impedance resonator based on the integration of parallel coaxial sections in the central part of the structure. Compared with the classical approach, this topology adds a new degree of freedom to the design, allowing an improvement of the quality factor, multipactor threshold and fabrication tolerances. To demonstrate these advantages, we designed an example of a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order filter in L band. This filter was fabricated in aluminum and measured. The experimental results are presented and discussed.

Dual-band Bandpass Plasmonic Filter Based on Effective Localized Surface Plasmon Resonators

A dual-band bandpass plasmonic filter based on quarter-wavelength effective localized surface plasmon resonators (ELSPRs) is proposed in this work. Compared with conventional microstrip resonators, ELSPRs have a larger unloaded quality factor and compact size, which can be flexibly designed. Since the harmonics of quarter-wavelength ELSPRs are located only at odd times of their dominant mode frequency, we can not only miniaturize the filter but achieve excellent out-of-band rejection performance. For demonstration, we design and fabricate a dual-band bandpass plasmonic filter, whose size is only 0.0396λ2 0 the center frequency is 3.1 GHz and 3.6 GHz, and the relative bandwidth is 10.7% and 7.7% respectively. Measurement results show excellent agreement with the simulations. Our results provide a route for realizing ultra-compact and high-performance functional devices for the fifth generation (5G) applications

Metamaterial based miniaturized broadband acoustic absorber

A miniaturized, broadband (800–5000 Hz) absorber with &amp;gt;95% absorption is proposed and realized. The absorber is designed using quarter-wavelength resonator tubes coiled as a rectangular “meta-atom.” The study describes the basic theoretical aspects of the absorber and compares it with the numerical simulations, fabrication, and experimental validation. The meta-atom, simple in design and made with fabrication-friendly materials, can provide greater spatial coverage through tiling over large surfaces.

Four Subbands from Dual Mismatched Wideband Bandpass Filter for 5G/WAS/Wi-Fi/WiMAX/WLAN Applications

Based on the simplicity of the design method, this paper presents a new approach for developing matched subbands when splitting two mismatched dual-wideband bandpass filters (BPFs) for the fifth generation (5G), wireless access systems (WAS), wireless fidelity (Wi-Fi), worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN), radar, and other communication devices. The method’s novelty involves using identical quarter-wavelength resonators terminated by alternated short-and-open stub configurations. Both configurations alternate and describe a perfect symmetry by their location from each other to make the subbands possible in the low-frequency and its harmonic (high-frequency) bandwidths (BW). A stub admittance Y 1 is defined and associated with the mainline section characteristic impedance Z 0 and an operating frequency f 0 . A quality factor Q a p is connected to Y 1 and f 0 to approach the BPF global quality factor Q g initially fixed. The stub characteristic impedance and the mainline one differ, while electric lengths (stub and mainline section) are identical. Using the operating frequency determines physical dimensions, creates harmonic frequencies and the rejected BW, mismatches the main frequency BW, matches the subbands, and creates transmission zero (TZ). Hence, a 28.118-dB stopband that separates the two bandpasses at 9.373 GHz is made. At the same time, the unmatched dual ultrawideband (UWB) covers a large panel of communication systems. The lowest (3.146–5.431) and highest (11.891–14.749) GHz BW exhibit a minimum insertion loss (IL) of 0.656 dB and 3.027 dB. The subbands return losses (RL) are better than 28 dB and 19 dB, respectively, and a flat group delay of 0.205 ns is obtained in the upper band. All subbands adaptation methodology is read from 10 dB of the RL. In that case, the four matched subbands in its lower wideband are 3.327–3.709 GHz and 4.442–5.048 GHz, and in its higher wideband are 11.922–12.486 GHz and 14.281–14.653 GHz. The 2275/2858 MHz is the dual-wideband with a fractional BW 53.282/21.456%. The fabricated prototype has validated the EM-simulations, and Anritsu MS4642B 20 GHz vector network analyzer (VNA) has been used for experimental results by scanning the frequency range 3 GHz–15 GHz. The tested prototype is made with a 1 mm FR4 HTG-175 thickness by considering a dielectric constant of 4.4, and its overall size occupies 22.45 × 5.72 m m 2 ( 0.32 λ 0 × 0.082 λ 0 mm 2 ).

Quasi-perfect and wideband absorption with gradient non-uniform micro-slit array absorber via a hierarchical optimization method

Gradient micro-slit array absorber, a kind of acoustic metamaterial, made of multiple quarter-wavelength resonators, is holding a promising future in industrial utilization due to its flexible adaptation and simple structure. However, designing a perfect and broadband absorber remains a huge challenge because of the larger number of the design parameters and complicated coupling effect between different resonators. In this study, a hierarchical optimization method is developed for gradient micro-slit array absorber. First, a prior test based on two-slit absorber is conducted using transfer matrix method (TMM) to give directions on designing a multi-slit absorber. And then an original absorber model is constructed in the range of 1000–1800 Hz. For the first step, the optimal width of the slit is obtained through the analysis of the quality factor. For the second step, the spacings between slits is optimized by maximizing absorption and minimizing the total length of the waveguide. After optimization, the absorption performance of the optimized model increased by 15.6% and the length decreased by 46% compared with the original model. Finally, the gradient micro-slit array absorber is experimentally investigated and achieves a quasi-perfect and flat absorption ranging from 1000 Hz to 1800 Hz.

Study of the impact of boundary conditions on acoustical behavior of granular materials and their implementation in the finite difference method

Granular materials display significant differences in their acoustical response when tested in a standing wave tube, compared with the behavior of more traditional sound absorbing materials such as fibrous webs and foams. The latter materials can often be modeled as an equivalent fluid with the further assumption that the material properties do not depend on the input signal level. In contrast, the level dependence of the acoustical behavior of granular materials has been observed in measurements of glass bubbles, as reported in previous studies, for example. When the input level is low, the absorption coefficient of the glass bubble stack shows solid-like behavior with multiple peaks associated with modal response of the stack. On the other hand, when the input level is high, glass bubble stacks show fluid-like behavior, with the quarter wavelength resonance in the direction of the tube axis dominating the response. In the current work, the boundary conditions at the air/granule interface and the granule/tube wall boundary are studied, as is the mechanism causing the variation of the apparent stiffness of the granule stack. The proposed model is implemented with a finite difference approach, and the model predictions are compared with acoustic measurements of granule stacks.

Compact Dual-Band Filtenna With Controllable Radiation Nulls for Vehicle Application

This paper presents a compact dual-band filtenna with controllable radiation nulls for Shark-Fin scenarios. The proposed filtenna is composed of three quarter-wavelength dual-band resonators. The resonator in the middle is fed by the probe. The other resonators on both sides of the middle resonator are coupled by the mixed electromagnetic (EM) field. Since the electric and magnetic couplings can be cancelled, the mixed EM coupling can be used to obtain more radiation nulls with less order than the other coupling mechanisms. Thus, the proposed antenna is straightforward and compact. Furthermore, the dual-band Quasi-elliptical responses are realized. Four radiation nulls are realized on both sides of two pass-bands, and the positions can be flexibly adjusted in dual bands. Without extra filtering circuits, high radiation efficiency can be achieved. To analyze and guide antenna design, the RLC equivalent circuit and extraction method are provided. For demonstration, the proposed filtenna is implement-ed. Radiation efficiency is about 64% and 83% within 2.4-2.5 GHz and 5.0-5.88 GHz, respectively. Moreover, the out-of-band supp-ression is over 20 dB. Compared with the traditional antenna, the in-band radiation performance of the proposed antenna is almost maintained, whereas out-of-band suppression is significantly enhanced. The proposed filtenna is suitable for Shark-Fin scenar-ios where multiple antennas operating at different frequency bands coexist. The interference from antennas at adjacent bands is reduced significantly due to the out-of-band suppression. Specially, the isolation between the proposed dual-band filtenna and antennas operating at the other bands can be improved by about 21dB.

A Passive Noise Attenuation Earplug Designed to Minimise Unwanted Air Turbine Driven High-Speed Dental Drill Noise.

Air turbine dental drill noise contains high-frequency components that are of concern for patients and dental staff. Meanwhile, verbal communication between the dentist and patient is essential. Conventional active noise-cancelling headphones are ineffective for dental drill noise and simply suppress all sound and hinder communication. A compact passive earplug device was designed specifically to attenuate broadband high-frequency noise ranges from 5 to 8 kHz employing an array of quarter wavelength (QW) resonators. This device was 3D printed and tested against white noise to enhance the objectivity of analysis, using a calibrated ear and cheek simulator to effectively measure its performance. The results showed that the resonators produced an average reduction of 27 dB across the targeted frequency range. When compared with two proprietary passive earplugs, this developed passive device prototype was able to attenuate an average of 9 dB more across the target frequency range whilst delivering louder speech signals of 14 dB more. The results also show that using an array of resonators exhibits an accumulated effect of individual resonator performance. This low-cost passive device could have a place in the dental clinic to reduce unwanted drill noise equivalent to the white noise high frequency spectra tested.

Quarter-wavelength E‖H Beltrami cavity resonators

In this paper, we present the design and implementation methods of quarter-wavelength resonators accommodating Beltrami standing waves with parallel electric and magnetic (E‖H) fields. The resonator is bounded by the quarter-wavelength longitudinal electromagnetic conductor (LEMC), the circumferential electromagnetic conductor (CMEC), and the radial electromagnetic conductor (REMC). The LEMC, CEMC, and REMC boundaries are artificially implemented by the circumferentially aligned corrugation, concentrically aligned circular fins, and axisymmetrically aligned radial fins, respectively. The coupling control methods by introducing slots in the CEMC and REMC with the external TM01 and TE01 circular waveguides are presented. We design the quarter-wavelength resonators with the implemented LEMC, CEMC, and REMC boundaries with controlled external couplings and numerically demonstrate their E‖H properties, which confirms the validity of the proposed design method.