Aluminum Cavity Research Articles

Electrowetting lens based on a conical aluminum cavity

A tunable liquid lens based on the electrowetting-on-dielectric effect is demonstrated using a machined aluminum substrate. A metallic substrate eliminates the need for deposited electrodes inside the droplet cavity and simplifies the fabrication procedures required to produce an electrowetting optic. Sloped sidewalls at 45° produce a large optical tuning range, with back focal length tuning from [−134, −18.5 mm] and [+11.3, +134 mm]. An input-shaped overdriven actuation voltage yields a response time of 149 ms. The aluminum substrate is machined using standard processes that allow the device geometry to be customized. A complete lens package is sealed with fluoroelastomer O-rings, enabling applications beyond the laboratory environment.

Precision measurements of the zero-temperature dielectric constant and density of liquid He4

The resonant frequencies of three-dimensional (3D) microwave cavities are explicitly dependent on the dielectric constant of the material filling the cavity, making them an ideal system for probing material properties. In particular, dielectric constant measurements allow one to extract the helium density through the Clausius-Mossotti relation. By filling a cylindrical aluminum cavity with superfluid helium, we make precision measurements of the dielectric constant of liquid $^{4}\mathrm{He}$ at saturated vapor pressure for range of temperatures 30 to 300 mK and at pressures of 0 to 25.0 bar at 30 mK, essentially the zero temperature limit for the properties of $^{4}\mathrm{He}$. After reviewing previous measurements, we find systematic discrepancy between the low and high frequency determination of the dielectric constant in the zero-temperature limit and moderate discrepancy with previously reported values of pressure-dependent density. Our precision measurements suggest 3D microwave cavities are a promising choice for refining previously measured values in helium, with potential applications in metrology.

Ac losses in field-cooled type I superconducting cavities

As superconductors are cooled below their critical temperature, stray magnetic flux can become trapped in regions that remain normal. The presence of trapped flux facilitates dissipation of ac current in a superconductor, leading to losses in superconducting elements of microwave devices. In type II superconductors, dissipation is well-understood in terms of the dynamics of vortices hosting a single flux quantum. In contrast, the ac response of type I superconductors with trapped flux has not received much attention. Building on Andreev’s early work (Andreev 1967 Sov. Phys. JETP 24 1019), here we show theoretically that the dominant dissipation mechanism is the absorption of the ac field at the exposed surfaces of the normal regions, while the deformation of the superconducting/normal interfaces is unimportant. We use the developed theory to estimate the degradation of the quality factors in field-cooled cavities, and we satisfactorily compare these theoretical estimates to the measured field dependence of the quality factors of two aluminum cavities. We also identify a regime in which the dissipated power depends weakly on the Ginzburg-Landau parameter; this makes it possible to apply our findings to cavities made of other materials, such as niobium.

Absorption kinetics of vacancies by cavities in aluminum: Numerical characterization of sink strengths and first-passage statistics through Krylov subspace projection and eigenvalue deflation

Modeling the microstructural evolution of metal and alloys, specifically under irradiation, is essential to predict the aging properties of materials. Many models are based on a transition rate matrix describing the jump frequencies of defects and involve a master equation governing the time evolution of a state probability vector. Here, we present non-stochastic numerical techniques to characterize the motion of individual defects migrating over long distances prior to recombining or being absorbed by another defect, resorting to the theory of absorbing Markov chains. These important events are fully determined by their first-passage time distribution to distant locations, no-passage distribution, and walker fluxes to the sinks. We show that these functions can be efficiently computed using a method combining Krylov subspace projection and eigenvalue deflation. For a model system describing the absorption of a vacancy by a cavity in aluminum, the use of a small Krylov subspace deflated by the unique eigenmode corresponding to the quasi-stationary distribution is sufficient to capture the kinetics of the defect absorption faithfully. This method can be used in kinetic Monte Carlo simulations to perform stochastic non-local moves or in cluster dynamics simulations to compute sink strengths.

Magnet Strength Dependence of Levitated Magnets in a Microwave Cavity

We report on the behavior of a superconducting microwave cavity containing levitated permanent magnets having a range of magnet strengths. By observing the changes in the cavity’s loaded quality factor and resonance frequency as functions of temperature and magnet remanence, we gain an understanding of the transient motion of the magnet as well as its steady-state levitation height when the temperature drops below 1 K. Experimental measurements of Meissner-effect levitation within a 10 GHz superconducting aluminum coaxial quarter-wave stub cavity are performed for a sequence of identically shaped millimeter-scale neodymium magnets having varying strengths. Magnet levitation within the cavity is accompanied by both gradual and abrupt shifts in the resonance frequency (with a height sensitivity as large as 400 MHz/mm) as well as changes in the total quality factor (8%-17%) as a function of temperature during the superconducting transition of the aluminum cavity. Prior to magnet motion and levitation, the Q of the cavity changes quadratically with temperature, as expected, as the walls of the cavity undergo the superconducting transition. We observe, however, a deviation from the quadratic trend which is attributable to magnet movement within the cavity. Such an electromechanical system is a transducer between mechanical and microwave oscillators enabling coupling of low-frequency mechanical motion of the magnet to other quantum objects, such as magnons and transmons, which are used for sensing and quantum information processing.

Stability of superconducting resonators: Motional narrowing and the role of Landau-Zener driving of two-level defects.

Frequency instability of superconducting resonators and qubits leads to dephasing and time-varying energy loss and hinders quantum processor tune-up. Its main source is dielectric noise originating in surface oxides. Thorough noise studies are needed to develop a comprehensive understanding and mitigation strategy of these fluctuations. We use a frequency-locked loop to track the resonant frequency jitter of three different resonator types—one niobium nitride superinductor, one aluminum coplanar waveguide, and one aluminum cavity—and we observe notably similar random telegraph signal fluctuations. At low microwave drive power, the resonators exhibit multiple, unstable frequency positions, which, for increasing power, coalesce into one frequency due to motional narrowing caused by sympathetic driving of two-level system defects by the resonator. In all three devices, we identify a dominant fluctuator whose switching amplitude (separation between states) saturates with increasing drive power, but whose characteristic switching rate follows the power law dependence of quasi-classical Landau-Zener transitions.

Surface stress calculations for nanoparticles and cavities in aluminum, silicon, and iron: influence of pressure and validity of the Young-Laplace equation

This study is dedicated to the determination of the surface energy and stress of nanoparticles and cavities in presence of pressure, and to the evaluation of the accuracy of the Young-Laplace equation for these systems. Procedures are proposed to extract those quantities from classical interatomic potentials calculations, carried out for three distinct materials: aluminum, silicon, and iron. Our investigations first reveal the increase of surface energy and stress of nanoparticles as a function of pressure. On the contrary we find a significant decrease for cavities, which can be correlated to the initiation of plastic deformation at high pressure. We show that the Young-Laplace equation should not be used for quantitative predictions when the Laplace pressure is computed with a constant surface energy value, as usually done in the literature. Instead, a significant improvement is obtained by using the diameter and pressure-dependent surface stress. In that case, the Young-Laplace equation can be used with a reasonable accuracy at low pressures for nanoparticles with diameters as low as 4 nm, and 2 nm for cavities. At lower sizes, or high pressures, a severely limiting factor is the challenge of extracting meaningful surface stress values.

RF Antenna Design for 3D Quantum Memories

A quantum memory has to meet the conflicting requirements of strong coupling for fast readout and weak coupling for long storage. Multimode rectangular superconducting 3D cavities are known to satisfy both properties. Here, we systematically study the external coupling to the two lowest-frequency modes of an aluminum cavity. First, we introduce a general analytical scheme to describe the capacitive coupling of the antenna pin and validate this model experimentally. On this basis, we engineer an antenna which is overcoupled to the first mode, but undercoupled to the second mode.

Identification and time-resolved study of ferrimagnetic spin-wave modes in a microwave cavity in the strong-coupling regime

Recently, the hybridization of microwave-frequency cavity modes with collective spin excitations attracted large interest for the implementation of quantum computation protocols, which exploit the transfer of information among these two physical systems. Here, we investigate the interaction among the magnetization precession modes of a small YIG sphere and the MW electromagnetic modes, resonating in a tridimensional aluminum cavity. In the strong coupling regime, anti-crossing features were observed in correspondence of various magnetostatic modes, which were excited in a magnetically saturated sample. Time-resolved studies show evidence of Rabi oscillations, demonstrating coherent exchange of energy among photons and magnons modes. To facilitate the analysis of the standing spin-wave patterns, we propose here a new procedure, based on the introduction of a novel functional variable. The resulting easier identification of magnetostatic modes can be exploited to investigate, control and compare many-levels hybrid systems in cavity- and opto-magnonics research.

High-Resolution X -Band Frequency Synthesizer Using SILPLL Optoelectronic Oscillators.

Optoelectronic oscillators (OEOs) with their demonstrated low phase noise are popular due to the increasing demand of very clean local oscillator and clock signal sources. A forced technique of self-injection locked and phase-locked loop (SILPLL) reduces phase noise and suppresses side mode observed in long fiber delay of the standard OEO. A frequency synthesizer working at X -band is developed using an electrically coarse-tuned YIG filter cascaded with an optical wavelength fine-tuned dispersive optical transversal filter by tuning the oscillation frequency of the synthesized OEO frequency, as a replacement for fixed-frequency narrowband filter using high- Q aluminum cavities. A close-to-carrier phase noise of -115 dBc/Hz at 1 kHz is reported by the Vπ/2 operation of a Mach-Zehnder modulator (MZM) over 8-12 GHz with a frequency tuning step as small as 2.6 kHz. Phase noise introduced by a photodetector is also explored at a very close-to-carrier frequency. It shows 10-dB phase noise degradation at PD reverse bias voltage of 3 V compared with 6 V at close to the Vπ operation of an MZM. A 19-in rack mount frequency synthesizer system is also realized at X -band with a demonstrated long-term (up to 60 min) frequency drift stability of 3 kHz over whole X -band working frequencies.

Behaviour analysis of a capacitive loaded RF cavity for the Iranian Light Source Facility (ILSF)

Synchrotron radiation has numerous applications in science and technology and is considered as one of the most significant research facilities required in Iran in the next 10 years. A key part in each synchrotron machine is its RF cavity. Improving the operation characteristics of the RF cavity will result in radiation quality enhancements. The cavity structure should be designed in a way that not only it can maintain the beam energy to the desired value, but also minimizes the collective instabilities on the beam. The development of the 100 MHz capacitive loaded RF cavity for the Iranian Light Source Facility was initiated in 2016. The main idea was to design a simple structure avoiding complicated fabrication technologies and to put more focus on applying different methods to control and also to minimize the effect of higher order frequency modes. Before engaging in fabrication of the main copper cavity, it was decided to manufacture a smaller aluminum cavity prototype in order to verify our simulations and moreover, improve the measurement methods and investigate the characteristics of the higher order frequency modes. In this paper, the design, simulations, and measurement results of this aluminum cavity prototype is described, two different methods for frequency tuning of the cavity are applied and the effects of these methods on the higher order frequency modes are studied. Contrary to previous experiences in other RF cavities, we propose to use a plunger as a tool for damping or shifting the HOMs instead of tuning the fundamental mode.

A High-$Q$ Quadruple-Mode Rectangular Waveguide Resonator

This letter presents a high- ${Q}$ quadruple-mode rectangular waveguide resonator. The resonator has a ${Q}$ better than 14 500 in all the four modes at 3.7 GHz using an aluminum cavity. Two narrowband filters (fourth and eighth order) at 3.7 GHz with a bandwidth (BW) of 50 MHz (1.35%) are realized using the proposed resonator as a proof of concept. Due to the high- ${Q}$ nature of the resonator, the filters exhibit very low insertion loss which is better than 0.3 and 1 dB for the fourth- and eighth-order filters, respectively. Furthermore, a transversal coupling scheme is also explored to enhance the spurious performance.

Short-Circuit Degradation of 10-kV 10-A SiC MOSFET

The short-circuit behavior of power devices is highly relevant for converter design and fault protection. In this paper, the degradation during short circuit of a 10-kV 10-A 4H-SiC MOSFET is investigated at 6 kV dc-link voltage. The study aims to present the behavior of the device during short-circuit transients as it sustains increasing short-circuit pulses during its lifetime. As the short-circuit pulse length increases, degradation of the device can be observed in periodically performed characterizations. The initial degradation seems to be associated with the channel region, and continuous stressing leads to an overall increase in device on-state resistance at the end of the degradation study. Thermal simulation shows that the surface aluminum metalization reached its melting temperature and the top part of the device reaches temperatures above the rated junction temperature. Scanning electron microscope investigation shows aluminum reconstruction and cavities at the contact interface between the aluminum surface metalization and source contacts.

Analysis of a MEMS Tuned Cavity Oscillator on $X$ -Band

This paper reports on the analysis of a radio frequency microelectromechanical systems (RF-MEMS) tuned cavity oscillator on $X$ -band based on a GaN-HEMT monolithic microwave integrated circuit reflection amplifier. The RF-MEMS-switches are mounted on a low-loss printed circuit board (PCB) intruded in an aluminum cavity that is coupled to a microstrip line connected to the reflection amplifier. This paper investigates the influence of the number of switches as well as their positions with respect to phase noise and tuning range. Vertical and horizontal positions of the switches are varied with target on optimum trade-off between phase noise and total tuning range. For a three-row MEMS-configuration at 1-mm depth from the end cavity wall, a tuning range of 4.9% is measured. The center frequencies are ranging from 9.84 to 10.33 GHz with measured phase noise of −140 to −129 dBc/Hz at 100-kHz offset. A similar three-row MEMS setup at 2.5-mm depth provides a tuning range of 12.3% with measured phase noise of −133 to −123 dBc/Hz at 100-kHz offset.

Study of the hydrodynamics of the formation of flows caused by the interaction of a shock wave with two-dimensional density perturbations on the Iskra-5 laser facility

The hydrodynamics of the flow formation due to the interaction of a shock wave with two-dimensional density perturbations is experimentally investigated on the Iskra-5 laser facility. Shadow images of a jet arising as a result of the impact of a shock wave (formed by a soft X-ray pulse from a target-illuminator) on a flat aluminium target with a blind cylindrical cavity are recorded in experiments with point-like X-ray backlighting having a photon energy of ~4.5 keV. The sizes and mass of the jet ejected from the aluminium cavity by this shock wave are estimated. The experimental data are compared with the results of numerical simulation of the jet formation and dynamics according to the two-dimensional MID-ND2D code.

RF-MEMS Tuned GaN HEMT based Cavity Oscillator for X-band

This letter presents a radio frequency micro-electromechanical systems (RF-MEMS) tuned cavity oscillator for X-band. The active part of the oscillator is implemented in GaN-HEMT MMIC technology. The RF-MEMS-switches are realized on a quartz substrate that is surface mounted on a low loss PCB. The PCB is intruded in an aluminum cavity acting as an electrically moveable wall. For a three-row RF-MEMS setup, a tuning range of 5 % around an oscillation frequency of 10 GHz is demonstrated in measurements. The phase noise is as low as −140 dBc/Hz to −129 dBc/Hz at 100 kHz from the carrier, depending on the configuration of the RF-MEMS.

Setup for microwave stimulation of a turbulent low-swirl flame

An experimental setup for microwave stimulation of a turbulent flame is presented. A low-swirl flame is being exposed to continuous microwave irradiation inside an aluminum cavity. The cavity is designed with inlets for laser beams and a viewport for optical access. The aluminum cavity is operated as a resonator where the microwave mode pattern is matched to the position of the flame. Two metal meshes are working as endplates in the resonator, one at the bottom and the other at the top. The lower mesh is located right above the burner nozzle so that the low-swirl flame is able to freely propagate inside the cylinder cavity geometry whereas the upper metal mesh can be tuned to achieve good overlap between the microwave mode pattern and the flame volume. The flow is characterized for operating conditions without microwave irradiation using particle imaging velocimetry (PIV). Microwave absorption is simultaneously monitored with experimental investigations of the flame in terms of exhaust gas temperature, flame chemiluminescence (CL) analysis as well as simultaneous planar laser-induced fluorescence (PLIF) measurements of formaldehyde (CH2O) and hydroxyl radicals (OH). Results are presented for experiments conducted in two different regimes of microwave power. In the high-energy regime the microwave field is strong enough to cause a breakdown in the flame. The breakdown spark develops into a swirl-stabilized plasma due to the continuous microwave stimulation. In the low-energy regime, which is below plasma formation, the flame becomes larger and more stable and it moves upstream closer to the burner nozzle when microwaves are absorbed by the flame. As a result of a larger flame the exhaust gas temperature, flame CL and OH PLIF signals are increased as microwave energy is absorbed by the flame.

Using helium as the working fluid in thermoacoustic engines

The efficiency of thermoacoustic engines can be improved by using helium as the working fluid because it reduces viscous losses, has a higher thermal conductivity and speed of sound. The engine in this study has a bottle-shaped resonator. The neck consists of a brass cylinder, closed at the top end and a copper cylinder, open at both ends, with copper mesh screens heat exchangers between them (ID of 1.91 cm and total length of 5.24 cm). A small amount of steel wool (20 mg) functions as the stack. The neck opens into an aluminum cavity (10 cm long with an ID of 4.13 cm). A combination of two types of heat-shrink tubing and Teflon were used to connect the brass and copper pieces. The engine was evacuated of air and backfilled with helium as much as the setup would tolerate. Using an input power of 14.8 W over intervals of 0.5–3 h, it was observed that the frequency decreased in time, indicating that the helium was leaking out slowly. From the frequency data, the volume fraction of helium was calculated, indicating that the engine was able to achieve 64% volume fraction of helium and decreased to 6%. The intensities of the sound over this range of volume fractions averaged at 155 W/m2 compared with air at an average of 118 W/m2.

Generating Microwave Spatial Fields With Arbitrary Patterns

Resorting to the temporal excitation synthesis of a time-reversal mirror (TRM), we develop a method of how to physically generate the desired microwave fields in a predefined area. The new method composes the desired field patterns with a number of the time-reversal (TR) focusing fields generated by a TRM. We first decompose the region of the desired pattern into a number of spatial grids and then probe the system by situating a probe antenna at these grids one by one. After all TRM elements capture their responses to the probing signals emitted from all grids, we synthesize the TRM excitation with these responses based on the TR method. Thanks to the space-time focusing property of TR, a set of TR focusing fields is simultaneously generated when the TRM is excited by the synthesized excitation. These focusing fields are spatially distributed with their focal spots spaced by the grids. If the grids are closely spaced, the focal spots will overlap with each other and eventually produce a smooth microwave field of the desired shape. We successfully demonstrate the generation of different desired microwave fields in an aluminum cavity. Theoretically, this method can be exploited to generate arbitrary electromagnetic fields.

Phase-Noise Analysis of an X-Band Ultra-Low Phase-Noise GaN HEMT Based Cavity Oscillator

This paper reports on an ultra-low phase-noise oscillator based on a GaN HEMT monolithic microwave integrated circuit reflection amplifier and an aluminum cavity resonator. It is experimentally investigated how the oscillator’s phase noise depends on the cavity coupling factor, phase matching, and bias condition of the reflection amplifier. For the optimum bias and cavity position phase noise of $-{\hbox{145}}$ dBc/Hz and ${-{\hbox{160}}}$ dBc/Hz at offsets of 100 and 400 kHz, respectively, from a 9.9-GHz carrier frequency is reached. This is, to the best of the authors’ knowledge, a record in reported performance for any oscillator based on a GaN HEMT device. The optimum performance at 400-kHz offset corresponds to a power normalized figure of merit of 227 and compensating for finite efficiency in the reflection amplifier, the achieved result is within 7 dB from the theoretical noise floor, assuming a linear theory.