Loaded Quality Factor Research Articles

Active suppression of microphonics detuning in high QL cavities

Operation of superconducting radio frequency (SRF) cavities with high loaded quality factors is becoming increasingly preferred for applications which involve low beam loading including energy recovery linacs (ERL). Vibration induced microphonics detuning poses a major operational bottleneck in these low bandwidth systems, adversely affecting field stability. Besides passive measures of mitigating the vibration sources, modern SRF cavities are also attached to fast tuners incorporating piezoelectric actuators. We demonstrate the narrow band active noise control algorithm for realizing active resonance control and propose a modification based on the least mean square approach to adaptively tune the control parameters and study its stability and performance. We discuss our experience of using passive mitigation techniques while commissioning the main linac cryomodule of the Cornell-BNL ERL test accelerator and report a net reduction in peak detuning by more than a factor of 2 in its unstiffened cavities. Finally, we demonstrate stable performance of our resonance control system with consistent reduction of peak microphonics detuning by almost a factor of 2 on multiple cavities.

Phase stabilization design for radio-frequency system of the IMP HIRFL-SSC

Abstract The Radio Frequency (RF) system at the Heavy Ion Research Facility in Lanzhou of the Institute of Modern Physics was upgraded to a digital low-level radio frequency system. The key part is the phase and amplitude negative feedback system based on Digital Signal Processing (DSP) and a Field Programmable Gate Array (FPGA). This paper mainly introduces the design of the phase stabilization loop, including the principle designs for phase stabilization, loop filter design, parameter calculation, and hardware. In order to improve the performance and stability of the system, the loop filter was designed by means of zero-pole cancellation. In this paper, the derivation of the “zero pole cancellation method” is introduced in detail. The implementation structure of the loop filter in the FPGA is an ingenious design that can be applied to RF systems with different cavity loaded quality factor ( Q L ) values. For different RF systems, the parameters of proportional integral (PI) algorithm are fixed, and only one parameter Q L needs to be set. An economical compensation method for the temperature drift in the pick-up cables was designed to improve the control accuracy of the system. The phase control system was tested in long-term stability experiments, and the results show that the system has excellent phase stability over the long term, as well as parasitic phase modulation suppression.

Piezoelectric-Based Support Transducer Design to Enable High-Performance Bulk Mode Resonators

An innovative topology to realize high-performance bulk mode devices made up of low-defect material by driving them into resonance using piezoelectric thin-film transduction is proposed and implemented in this paper. Here, the piezoelectric transducer is uniquely positioned at the bulk mode's support location. To realize the resonators, MEMSCAP Inc.'s PiezoMUMPS platform was utilized. Wine-glass and Lamé bulk mode devices are demonstrated to establish the feasibility of the support transducer drive/sense mechanism. Several drive/sense combinations of the balanced-unbalanced setup were measured. For the differential-in differential-out configuration, reduced feedthrough and enhanced stop-band rejection was observed. As a result, the Wine-glass and Lamé mode resonators having a resonance frequency ( f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) of 20.943 and 21.15 MHz with a motional resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of 1.68 and 3.88 kQ and a loaded quality factor (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> ) of 9940 and 6840, respectively, operating in vacuum at 0-dBm driving power are demonstrated. Temperature Coefficient of Frequency of -26.4 and -25 ppm/K is recorded for Wineglass and Lamé mode resonators, respectively. To characterize the closed-loop response of the devices, they were connected to a lock-in amplifier with phase-locked loop, and a phase noise of -122 and -118 dBc/Hz at 1-kHz offset were measured for Wine-glass and Lamé mode resonators, respectively. [2018-0092]

Rapid Characterization of Powder Mixtures through High Q Dielectric Resonator

In this research work a high quality factor cylindrical dielectric resonator is used to determine the dielectric properties of powder mixtures. The setup is based on resonant perturbation theory and it has a potential to quickly and accurately characterize samples in quantities as small as a tens of milligrams. The loaded quality factor of the proposed dielectric resonator is 19,217, which is operated in TM01δ mode at 10.57 GHz. The measured results are compared with the calculated values obtained from different mixing models. The worst case measured dielectric constant error of 9.4% and 9.95% has been observed for mixtures of boric acid – titanium dioxide and baking soda – titanium dioxide respectively with variable concentrations of weight. The proposed technique is suitable to be deployed in industries in order to rapidly assess the mixture concentration before subjected to the detail investigation.

Electrostatic tuning of mechanical and microwave resonances in 3D superconducting radio frequency cavities

We implement a non-contact, external method of simultaneously fine-tuning a mechanical resonator and a superconducting radio frequency (SRF) cavity using a capacitor formed between a silicon nitride membrane and a copper electrode at cryogenic temperatures. The silicon nitride membrane forms a variable boundary condition for the SRF cavity thereby creating the optomechanical cavity. By controlling the DC voltage applied between an external electrode and the silicon nitride membrane we are capable of tuning the resonance frequency internal to the SRF cavity up to 25 kHz for a cavity with loaded quality factor of 2.5 million, corresponding to six cavity linewidths. At the same time we observe the electrostatic frequency shift of the membrane. This approach has the unique benefit of avoiding any dielectric insertion or added gaps due to a moving end-wall thereby limiting the loss of the cavity. Furthermore, this design avoids applied pressure typically used with piezoelectric devices in accelerator cavities. This work seeks to have strong impact in tuning high-Q cavities due to its ability to maintain low losses.

A Low-Voltage Low-Phase-Noise 25-GHz Two-Tank Transformer-Feedback VCO

This paper presents a low-voltage low-phase-noise LC voltage-controlled-oscillator (VCO) with a novel two-tank transformer-feedback topology. The flicker noise up-conversion is suppressed by making the drain impedance of the cross-coupled transistors to be a real number at the second harmonic of the oscillation. The loaded quality factor is boosted and the noise contribution from the transconductor of the VCO is reduced by introducing a negative source impedance. A prototype VCO based on this topology is demonstrated in a 65 nm digital CMOS process. The VCO is operated from 23.9 to 26.9 GHz at a low supply voltage of 0.6 V, while achieving an ultra-low 1/ $f^{3}$ phase noise corner from 170 to 240 kHz across the tuning range. The phase noise is −110 dBc/Hz at 1 MHz frequency offset. The power consumption is 4.8 mW. The measurement results demonstrate that the VCO achieves a state-of-the-art phase noise performance in both the 1/ $f^{2}$ region and the 1/ $f^{3}$ region.

Load Mismatch Sensitivity of Class-E Power Amplifiers

Class-E RF power amplifiers (PAs) are very power efficient under nominal operating conditions. Due to incorporating two tuned tanks, the dependence on the load impedance is, however, relatively large, resulting in, e.g., load-dependent output power, power efficiency, peak voltages, and peak (and average) currents which can lead to reliability issues. This paper presents load–pull analyses for class-E RF PAs from a mathematical perspective, with analyses and discussions of the effects of the most common nonidealities of class-E PAs: the limited loaded quality factor ( $Q_{\mathrm {loaded}}$ ) of the series filter, switch ON-resistance, the limited quality factor of the dc-feed inductor, load mismatch-dependent switch conduction loss, and the limited negative voltage excursions (due to, e.g., the reverse conduction of the switch transistor for negative voltage excursions). The theoretical findings are backed up by extensive circuit simulations and load–pull measurements of a class-E PA implemented in 65-nm CMOS technology. The PA provides 18.1-dBm output power and 72% efficiency at 1.4 GHz under nominal operating condition employing an off-chip matching network.

Blue Microlasers Integrated on a Photonic Platform on Silicon

The main interest of group-III-nitride nanophotonic circuits is the integration of active structures and laser sources. A photonic platform of group-III-nitride microdisk lasers integrated on silicon and emitting in the blue spectral range is demonstrated. The active microdisks are side-coupled to suspended bus waveguides, and the coupled emission is guided and outcoupled to free space using grating couplers. A small gap size of less than 100 nm between the disk and the waveguide is required in the blue spectral range for optimal evanescent coupling. To avoid reabsorption of the microdisk emission in the waveguide, the quantum wells are etched away from the waveguide. Under continuous-wave excitation, loaded quality factors greater than 2000 are observed for the whispering gallery modes for devices with small gaps and large waveguide bending angles. Under pulsed excitation conditions, lasing is evidenced for 3 $\mu$m diameter microdisks integrated in a full photonic circuit. We thus present a first demonstration of a III-nitride microlaser coupled to a nanophotonic circuit.

An Energy-Efficient Wirelessly Powered Millimeter-Scale Neurostimulator Implant Based on Systematic Codesign of an Inductive Loop Antenna and a Custom Rectifier.

In this work, a switched-capacitor-based stimulator circuit that enables efficient energy harvesting for neurostimulation applications is presented, followed by the discussion on the optimization of the inductive coupling front-end through a codesign approach. The stimulator salvages input energy and stores it in a storage capacitor, and, when the voltage reaches a threshold, releases the energy as an output stimulus. The dynamics of the circuit are automatically enabled by a positive feedback, eliminating any stimulation control circuit blocks. The IC is fabricated in a 180nm CMOS process and achieves a quiescent current consumption of 1.8 μA. The inductive coupling front-end is optimized as a loaded resonator, in which the input impedance of the custom rectifier directly loads the inductive loop antenna. The loaded quality factor and the rectifier's efficiency determine the reception sensitivity of the stimulator, while a balance should be achieved for the robustness of the system against dielectric medium variations by increasing the reception bandwidth. The finalized stimulator adopts a 4.9mm × 4.9mm inductive loop antenna and achieves an overall assembly dimension of 5mm × 7.5mm. Operating at the resonant frequency of 198MHz, the stimulator works at a 14cm distance from the transmitter in the air. An animal experiment was performed, in which a fully implanted stimulator excited the sciatic nerve of a rat that consequently triggered the movement of the limb.

Evaluation of YBa2Cu3O7-δ-based microwave kinetic inductance detectors with rewound spiral resonators

We propose a YBCO-based microwave kinetic inductance detector with rewound strip structure (spiral-MKID) suitable for imaging applications. The superconducting rewound strip acts as a microwave resonator and broadband antenna. A 25-pixel MKID array with a width of 10 μm and slightly varying length of each of the resonators was fabricated on a 10×10 mm2-MgO substrate. Microwave resonance characteristics of the array were evaluated by measuring one of the scattering-matrix elements, S21, using a vector network analyser. The 25 resonance dips were clearly observed around 5 GHz; the frequency spacing between adjacent pixels was 13 MHz, with a standard deviation of 5 MHz. Each resonance frequency was shifted by 170 MHz, owing to the temperature change from 11 K to 50 K. We showed that the YBCO-based spiral-MKIDs with 200 nm-thick films have loaded quality factors of 1,200 at 11 K and 700 at 50 K. We irradiated visible light to a single pixel on the array. The obtained noise equivalent power was on the order of 10−9 W/Hz1/2, while the response time was smaller than 30 ms at 13 K. The responsivity of the array at 70 K was six times larger than that at 13 K.

Flux-tunable heat sink for quantum electric circuits

Superconducting microwave circuits show great potential for practical quantum technological applications such as quantum information processing. However, fast and on-demand initialization of the quantum degrees of freedom in these devices remains a challenge. Here, we experimentally implement a tunable heat sink that is potentially suitable for the initialization of superconducting qubits. Our device consists of two coupled resonators. The first resonator has a high quality factor and a fixed frequency whereas the second resonator is designed to have a low quality factor and a tunable resonance frequency. We engineer the low quality factor using an on-chip resistor and the frequency tunability using a superconducting quantum interference device. When the two resonators are in resonance, the photons in the high-quality resonator can be efficiently dissipated. We show that the corresponding loaded quality factor can be tuned from above 105 down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.

Detuning related coupler kick variation of a superconducting nine-cell 1.3 GHz cavity

Superconducting TESLA-type cavities are widely used to accelerate electrons in long bunch trains, such as in high repetition rate free electron lasers. The TESLA cavity is equipped with two higher order mode couplers and a fundamental power coupler (FPC), which break the axial symmetry of the cavity. The passing electrons therefore experience axially asymmetrical coupler kicks, which depend on the transverse beam position at the couplers and the rf phase. The resulting emittance dilution has been studied in detail in the literature. However, the kick induced by the FPC depends explicitly on the ratio of the forward to the backward traveling waves at the coupler, which has received little attention. The intention of this paper is to present the concept of discrete coupler kicks with a novel approach of separating the field disturbances related to the standing wave and a reflection dependent part. Particular attention is directed to the role of the penetration depth of the FPC antenna, which determines the loaded quality factor of the cavity. The developed beam transport model is compared to dedicated experiments at FLASH and European XFEL. Both the observed transverse coupling and detuning related coupler kick variations are in good agreement with the model. Finally, the expected trajectory variations due to coupler kick variations at European XFEL are investigated and results of numerical studies are presented.

Compact titanium dioxide waveguides with high nonlinearity at telecommunication wavelengths.

Dense integration of photonic integrated circuits demands waveguides simultaneously fulfilling requirements on compactness, low loss, high nonlinearity, and capabilities for mass production. In this work, titanium dioxide waveguides with a thick core of 380 nm exhibiting a compact mode size (0.43 μm2) and a low loss (5.4 ± 1 dB/cm) at telecommunication wavelengths around 1550 nm have been fabricated and measured. A microring resonator having a 50 μm radius has been measured to have a loaded quality factor of 53500. Four-wave mixing experiments reveal a nonlinear parameter for the waveguides of 21-34 W-1 m-1 corresponding to a nonlinear index around 2.3-3.6 x 10-18 m2/W, which results in a wavelength conversion efficiency of -36.2 dB. These performances, together with the potentially simple dispersion engineering to the fabricated waveguides by the post processes, yield a strong promise for the titanium dioxide waveguides applied in photonic integrated circuits, especially for nonlinear implementations.

Lumped element kinetic inductance detectors based on two-gap MgB2 thin films

Lumped element kinetic inductance detectors (LEKIDs) are made from a single layer superconducting thin film. Because of their low noise and highly multiplexibility, LEKIDs provide a sensitive technology for the detection of millimeter and submillimeter waves. In this work, a 5-pixel 50-nm-thick MgB2 array is made. The microwave properties of the array are measured under dark conditions. We show that the loaded quality factor Q of the resonant circuit is 30 000 at 7.5 K, which is comparable to that of lower-operating-temperature (usually several hundred mK) LEKIDs made from superconductors such as Al and Nb. Moreover, the temperature dependence of resonance frequency gives the two-gap character of MgB2, Δπ (0) = 2.58 meV and Δσ (0) = 8.26 meV. The gap frequency (f = 2Δ/h) indicates that MgB2 LEKIDs have a promising application on terahertz detection.

Theory of Double Ladder Lumped Circuits With Degenerate Band Edge

A conventional periodic LC ladder circuit forms a transmission line that has a regular band edge between a pass and a stop band. Here for the first time we develop the theory of simple yet unconventional double ladder circuit that exhibits a special degeneracy condition referred to as degenerate band edge (DBE). The degeneracy occurs when four independent eigenstates coalesce into a single eigenstate at the DBE frequency. In addition to possible practical applications, this circuit may provide insight into DBE behavior that is not clear in more complex systems. We show that double ladder resonators exhibit unusual behavior of the loaded quality factor near the DBE leading to a stable resonance frequency against load variations. These two properties in the proposed circuit are superior to the analogous properties in single ladder circuits. Our proposed analysis leads to analytic expressions for all circuit quantities thus providing insight into the very complex behavior near degeneracy points in periodic circuits. Interestingly, here we show for the first time that DBE is obtained with unit cells that are symmetric along the propagation direction. The proposed theory of double ladders presented here has potential applications in filters, couplers, oscillators, and pulse shaping networks.

The analysis and design of a 50MHz Colpitts low phase noise crystal oscillator

Crystal oscillators have huge demand in medical filed especially in building medical devices. They are used in diagnostic equipment, monitoring devices, hearing aids, etc. Since they are widely used in medical devices, it is essential to maintain accurate requirements for the output phase noise of reference frequency source. At the same time it is important to find out new ways to reduce the phase noise which is the major problem in designing crystal oscillators. The importance of loaded quality factor QL is analyzed on the basis of Leeson model and the formula of QL is derived from the analysis of Colpitts oscillator circuit. According to the results, we can draw a conclusion that QL is explicitly related to circuit parameters. The phase noise of the 50MHz Colpitts crystal oscillator is simulated by the Agilent Advanced Design System (ADS). Based on the simulation results, a design of the prototype crystal oscillator is presented. The crystal resonator we use is AT-cut 3rd overtone crystal resonator with 49 U resistance welding package, its unloaded quality factor Q0 is about 1.45 × 105. The measured results of phase noise are -107 dBc/Hz@10Hz, -134 dBc/Hz@100Hz and -152 dBc/Hz@1KHz. Experimental results show that it is feasible to design low phase noise crystal oscillators on the basis of improving QL.

A Frequency Adaptive Phase Shift Modulation Control Based LLC Series Resonant Converter for Wide Input Voltage Applications

This paper presents an isolated LLC series resonant DC/DC converter with novel frequency adaptive phase shift modulation control, which suitable for wide input voltage (200–400 V) applications. The proposed topology integrates two half-bridge in series on the primary side to reduce the switching stress to half of the input voltage. Unlike the conventional converter, this control strategy increases the voltage gain range with zero-voltage-switching (ZVS) to all switches under all operating voltage and load variations. Adaptive frequency control is used to secure ZVS in the primary bridge with regards to load change. To do so, the voltage gain becomes independent of the loaded quality factor. In addition, the phase shift control is used to regulate the output voltage as constant under all possible inputs. The control of these two variables also significantly minimizes the circulating current, especially from the low-voltage side, which increases the efficiency as compared to a conventional converter. Experimental results of a 1-Kw prototype converter with 200–400-V input and 48-V output are presented to verify all theoretical analysis and characteristics.

Design and Optimization of SHF Composite FBAR Resonators.

We propose an apodization technique-based composite thin-film bulk acoustic wave resonator (c-FBAR) design to enable the displacement and strain energy confinement at the central section of the resonator while in operation at the resonance mode. Sinc-shaped AlN on Silicon on Insulator apodized c-FBARs is designed to attain close to 90% energy localization. In this paper, a single crystal silicon as the mechanical layer and an AlN piezoelectric material as the transducer layer of the resonator implemented by InvenSense Inc.'s AlN MEMS-CMOS platform renders an asymmetric feature to the traditional FBAR resonator. The nature of composite thin-film piezoelectric on substrate FBAR resonators in the super high-frequency (SHF) range is studied in detail. Furthermore, a complete deembedding procedure to extract the resonator parameters from the CMOS + MEMS measured data is also explained meticulously. A complete equivalent circuit modeling for c-FBAR operating in the SHF is provided. Measurement data statistics show that sinc c-FBAR features superior electromechanical coupling coefficient ( ) than that of pentagon c-FBAR. As a result, we successfully demonstrate a sinc c-FBAR resonator operating at 3.264 GHz with an electromechanical coupling coefficient of 2.12%, a loaded quality factor ( ) of 790 and an unloaded of 2507.

Design of X-Cut and Z-Cut Lithium Niobate Whispering-Gallery-Mode Disk-Resonators With High Quality Factors

We demonstrate the fabrication process of millimeter-size lithium niobate (LiNbO $_3$ ) whispering-gallery-mode (WGM) disk-resonators. We fabricate both $x$ - and $z$ -cut disk-resonators, starting from commercially available LiNbO $_3$ disks with diameters of 12 mm and thicknesses of 1 mm. We characterize these two WGM resonators using a prism coupling configuration. We find that both resonators feature high loaded quality factors, in both cases higher than $10^7$ at 1550 nm. We also investigate the polarization and thermal effects in these disk-resonators. The design of high- $Q$ LiNbO $_3$ disk-resonators with different orientations using the same platform will allow for a wide variety of potential applications in nonlinear and quantum photonics.

A Compact Balanced-to-Balanced Filtering Gysel Power Divider Using $\lambda _{g}$ /2 Resonators and Short-Stub-Loaded Resonator

In this letter, a compact balanced-to-balanced filtering power divider (FPD) is presented. It is composed of three half-wavelength resonators and a short-stub-loaded resonator (SSLR). Due to the intrinsic resonance characteristic of the half-wavelength resonator, the bandpass response and power dividing function for differential-mode signal are realized and the suppression for common-mode signal is also achieved. The SSLR is utilized as an extra isolation resonator to achieve high isolation between two output ports. A resister is also needed to load on the SSLR for adjusting its loaded quality factor $(Q_{e})$ . For the demonstration of the design method, an FPD operating at 2.405 GHz has been fabricated and measured. The measured results validate the design method.