Closed-loop Oscillator Research Articles

Design and characterization of a self-matching photonic lantern for all few-mode fiber laser systems

We model and demonstrate a self-matching photonic lantern (SMPL) device, which is designed to address the constraint of limited transverse modes generated by fiber lasers. The SMPL incorporates a FMF into the array at the input end of a traditional photonic lantern. The few-mode fiber at the output end is specifically configured to align with the few-mode fiber at the input, therefore named as SMPL. This paper details the design and fabrication of the SMPL device, validated by both simulation and experiment. The 980nm fundamental mode, injected via 980nm single-mode fibers, selectively excites corresponding higher-order modes at the few-mode port of the SMPL. Additionally, 1550nm fundamental and higher-order modes injected at the input end into the SMPL device demonstrates mode preservation and low-loss transmission characteristics. The SMPL is well-suited for developing a ring laser system, enabling selective excitation of 980nm pump light modes and facilitating closed-loop oscillation and transmission of 1550nm laser.

A Closed-Loop VCO-based 1-1 SMASH CT ΔΣ ADC Architecture

A novel closed-loop voltage-controlled oscillator (VCO)-based 1-1 sturdy multistage noise-shaping (SMASH) continuous-time ΔΣ ADC is presented in this paper. The proposed architecture uses VCOs as integrators and puts them in a closed loop to suppress the VCO nonlinearity. The multi-bit quantization is employed in the proposed architecture so that the requirement of a high over-sampling ratio (OSR) is relaxed while maintaining a high resolution. The architecture has been verified in MATLAB Simulink.

A Filter-Free Third Overtone Quartz Oscillator Based on Micromachining Technology.

This work investigates an AT-cut quartz crystal oscillator (XO) operating at its enhanced third overtone thickness shear (TS) mode while suppressing the fundamental TS mode by micromachining technology. A unique quartz plate structure has been proposed to alleviate the strong resonant signal from the first mode. A finite-element method (FEM) was used to characterize the first mode suppression while improving the performance of third overtone in terms of Q -factor and motional resistance ( Rm ) of the proposed device. In measurement, the unloaded Q -factor of the fundamental TS mode is from several tens of thousands (the reference design) to only several hundred (the proposed design). Meanwhile, the unloaded Q -factor of the third overtone response for the proposed design could reach Q ∼95 000 with a decent Rm . The Q -factor ratio attains 170-180 between the third overtone and fundamental modes. With the feature of low Q -factor on the fundamental mode, the oscillator system could successfully oscillate at a higher frequency without the help of bandpass filtering. Finally, the closed-loop oscillation measurement is performed for the phase noise (PN) characterization. The PN performance could reach -154.5 dBc/Hz at a 1-kHz offset at the carrier frequency of ∼ 60 MHz. This technique has proven its potential as a future solution of high-frequency quartz oscillator technology.

Atomic Comagnetometer with a Closed-Loop Optically Aligned 87 Rb Dual-Frequency Oscillator

Comagnetometers have been widely used in fundamental research, such as tests of spin-gravity coupling and searches for permanent electric dipole moments (EDMs). Here, we report a comagnetometer that consists of simultaneous closed-loop oscillation of the $F=1$ and $F=2$ hyperfine Zeeman transitions of optically aligned ${}^{87}$$\mathrm{Rb}$ atoms. The Allan deviation of the $F=2$ and $F=1$ oscillation-frequency ratio reaches $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ after running continuously for 2 days, corresponding to a sensitivity of approximately $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\phantom{\rule{0.2em}{0ex}}\mathrm{eV}$ for the measurement of the hypothetical spin-dependent gravitational energy of the proton. The long-term stability of the comagnetometer can be further improved by system-level thermal control and optimization of the experimental parameters.

Density functional theory based computational investigations on the stability of highly active trimetallic PtPdCu nanoalloys for electrochemical oxygen reduction.

Activity, cost, and durability are the trinity of catalysis research for the electrochemical oxygen reduction reaction (ORR). While studies towards increasing activity and reducing cost of ORR catalysts have been carried out extensively, much effort is needed in durability investigation of highly active ORR catalysts. In this work, we examined the stability of a trimetallic PtPdCu catalyst that has demonstrated high activity and incredible durability during ORR using density functional theory (DFT) based computations. Specifically, we studied the processes of dissolution/deposition and diffusion between the surface and inner layer of Cu species of Pt20Pd20Cu60 catalysts at electrode potentials up to 1.2 V to understand their role towards stabilizing Pt20Pd20Cu60 catalysts. The results show there is a dynamic Cu surface composition range that is dictated by the interplay of the four processes, dissolution, deposition, diffusion from the surface to inner layer, and diffusion from the inner layer to the surface of Cu species, in the stability and observed oscillation of lattice constants of Cu-rich PtPdCu nanoalloys.

Modulation effect of mouse hippocampal neural oscillations by closed-loop transcranial ultrasound stimulation

Objective. Closed-loop transcranial ultrasound stimulation (TUS) can be applied at a specific time according to the state of neural activity to achieve timely and precise neuromodulation and improve the modulation effect. In a previous study, we found that closed-loop TUS at the peaks and troughs of the theta rhythm in the mouse hippocampus was able to increase the absolute power and decrease the relative power of the theta rhythm of local field potentials (LFPs) independent of the peaks and troughs of the stimulus. However, it remained unclear whether the modulation effect of this closed-loop TUS-induced mouse hippocampal neural oscillation depended on the peaks and troughs of the theta rhythm. Approach. In this study, we used ultrasound with different stimulation modes and durations to stimulate the peaks (peak stimulation) and troughs (trough stimulation) of the hippocampal theta rhythm. The LFPs in the area of ultrasound stimulation were recorded and the amplitudes and power spectra of the theta rhythm before and after ultrasound stimulation were analyzed. Main results. The results showed that (a) the relative change in amplitude of theta rhythm decreases as the number of stimulation trials under peak stimulation increases; (b) the relative change in the absolute power of the theta rhythm decreases as the number of stimulation trials under peak stimulation increases; (c) the relative change in amplitude of the theta rhythm increases nonlinearly with the stimulation duration (SD) under peak stimulation, and; (d) the relative change in absolute power exhibits a nonlinear increase with SD under peak stimulation. Significance. These results suggest that the modulation effect of closed-loop TUS on theta rhythm is dependent on the stimulation mode and duration under peak stimulation. TUS has the potential to precisely modulate theta rhythm-related neural activity.

Optically pumped NMR oscillator based on 131Xe nuclear spins

A 131Xe nuclear magnetic resonance (NMR) oscillator can be used in the measurement of rotation rates, CPT and Lorentz violation tests, etc. To improve the measurement precision of devices based on a 131Xe NMR oscillator, its characteristics need to be fully understood. Under the conditions where the Zeeman interaction is much larger than the quadrupolar interaction, the characteristics of the 131Xe NMR oscillator involving the magnetic resonance, free induction decay, and closed-loop oscillation are investigated both experimentally and theoretically. The main findings are as follows. The 131Xe NMR oscillator consists of six oscillators, three of which can be directly observed by a magnetometer. When the polarization of the 131Xe spin ensemble can be described by a spin temperature, the ensemble exhibits both spin orientation and spin alignment. The spin alignment breaks the symmetry of the three main oscillators. The free induction decay signal of 131Xe depends on parameters such as the spin alignment and the driving magnetic field, which make the measurement of the relaxation time difficult. In the closed-loop mode under self-excitation, the 131Xe NMR oscillator may oscillate with more than one frequency at certain feedback gain and phase. If the quadrupole splitting is much smaller than the spin relaxation rate, then the 131Xe oscillator can be described by the Bloch equations, and the 131Xe oscillator will have a large amplitude. The oscillation frequency of the closed-loop oscillator depends on the quadrupole splitting, polarization, and various relaxation times, which should be considered in designing a high-precision NMR sensor. The results are significant for optimizing and improving the performance of the 131Xe NMR oscillator as a sensor for precision measurement.

A Closed-Loop Controlled CMOS MEMS Biaxial Scanning Mirror for Projection Displays

This work presents a biaxial electromag- netically-driven piezoresistively sensed scanning mirror fabricated in a CMOS (complementary metal oxide semiconductor) process. The structure containing the CMOS metal/dielectric layers and underlying silicon is released after back- and front-side etch. The drive coil and piezoresistive sensors are implemented by the metal and polysilicon thin films. Biaxial resonances at 1.13 kHz and 41.5 kHz, and an optical angle of 50° for horizontal scan under a drive current of 12.5 mA are measured. Closed-loop control and oscillation for vertical and horizontal scans are also demonstrated for practical applications.

Stability of Small-Gain Closed-Loop System and Its Applications in VSC-Based DC/AC Power Systems

In a VSC-based HVDC/AC power system, dynamic interactions introduced by the HVDC system are usually weak. Hence, the small-signal stability of the HVDC/AC system is not affected significantly by the HVDC system. This paper presents a description of a weakly coupled VSC-based HVDC/AC power system by a small-gain closed-loop model that consists of two open-loop subsystems interconnected by a small gain. A special condition of open-loop modal proximity of the HVDC/AC system is examined, i.e., in the small-gain closed-loop model, an oscillation mode of one open-loop subsystem is close to an oscillation mode of the other open-loop subsystem on the complex plane. Our analysis indicates that when the open-loop modal proximity occurs, the corresponding closed-loop oscillation modes repulse each other. The closed-loop modal repulsion results in strong dynamic interconnection of the open-loop subsystems, thereby degrading the closed-loop system stability. Two examples are presented to demonstrate the applications of the proposed small-gain closed-loop model. Finally, the utility and accuracy of the closed-loop modal repulsion are evaluated from the viewpoint of the stability of HVDC/AC power systems.

<inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 NEMS Oscillator for Real-Time Middle Ultraviolet (MUV) Light Detection

We report on the first beta gallium oxide (\beta-Ga2O3) crystal feedback oscillator built by employing a vibrating \beta-Ga2O3 nanoresonator as the frequency reference for real-time middle ultraviolet (MUV) light detection. We fabricate suspended \beta-Ga2O3 nanodevices through synthesis of \beta-Ga2O3 nanoflakes using low-pressure chemical vapor deposition (LPCVD), and dry transfer of nanoflakes on microtrenches. Open-loop tests reveal a resonance of the \beta-Ga2O3 device at ~30 MHz. A closed-loop oscillator is then realized by using a combined optical-electrical feedback circuitry, to perform real-time resonant sensing of MUV irradiation. The oscillator exposed to cyclic MUV irradiation exhibits resonant frequency downshifts, with a measured responsivity of $\mathscr{R}$ = -3.1 Hz/pW and a minimum detectable power of \delta Pmin = 0.53 nW for MUV detection.

Thermal characteristic and analysis of closed loop oscillation heat pipe/phase change material (CLOHP/PCM) coupling module with different working media

Aimed to understand the thermal characteristic of closed loop oscillation heat pipe/phase change material (CLOHP/PCM) coupling module filled with different working media for thermal energy storage and thermal management application, experimental investigation on the heat charge and discharge process of the coupling module under different conditions was carried out. The main result shows that the CLOHP filled with self-rewetting fluid (SRWF) and not placed horizontally has better thermal transfer performance relative to the water case as the heat load is low. But, the CLOHP filled with water has better thermal transfer performance than the SRWF case in horizontal condition especially under low heat load. The rise speed of temperature in the heating section increases when the phase transition completes. The highest temperature of the PCM locates in the middle region. Standard deviation (STD) of PCM temperature keeps relative stable for a long time and then increases rapidly and the rise speed has a positive correlation with the heat load. The uniformity of PCM temperature has been greatly improved for those three cases compared to that without working medium. During the discharge process, the fluctuation occurs only when the temperature of evaporation exceeds about 60 °C.

Enhanced Quality Factor Label-free Biosensing with Micro-Cantilevers Integrated into Microfluidic Systems.

Microelectromechanical systems (MEMS) have enabled the development of a new generation of sensor platforms. Acoustic sensor operation in liquid, the native environment of biomolecules, causes, however, significant degradation of sensing performance due to viscous drag and relies on the availability of capture molecules to bind analytes of interest to the sensor surface. Here, we describe a strategy to interface MEMS sensors with microfluidic platforms through an aerosol spray. Our sensing platform comprises a microfluidic spray nozzle and a microcantilever array operated in dynamic mode within a closed loop oscillator. A solution containing the analyte is sprayed uniformly through picoliter droplets onto the microcantilever surface; the micrometer-scale drops evaporate rapidly and leave the solutes behind, adding to the mass of the cantilever. This sensing scheme results in a 50-fold increase in the quality factor compared to operation in liquid, yet allows the analytes to be introduced into the sensing system from a solution phase. It achieves a 370 femtogram limit of detection, and we demonstrate quantitative label-free analysis of inorganic salts and model proteins. These results demonstrate that the standard resolution limits of cantilever sensing in dynamic mode can be overcome with the integration of spray microfluidics with MEMS.

Strong Dynamic Interactions of Grid-Connected DFIGs With Power Systems Caused by Modal Coupling

This paper establishes a closed-loop interconnected dynamic model of a power system with a doubly fed induction generator (DFIG) for wind power generation, wherein, the DFIG and power system are modeled as two open-loop interconnected subsystems. The established model indicates that the impact of the dynamic interactions introduced by the DFIG on the power system's small-signal angular stability is the difference between the closed-loop and open-loop electromechanical oscillation modes (EOMs). The analysis conducted in this study reveals that when an open-loop DFIG oscillation mode (DOM) is close to an open-loop EOM on the complex plane, the modal coupling of the open-loop EOM and DOM can cause strong dynamic interactions between the DFIG and the power system; thus, the DFIG has a significant impact on the power system's small-signal angular stability. An example multimachine power system with grid-connected DFIGs is presented to demonstrate and validate the analysis and conclusions made in the paper.

A Closed-Loop Readout Configuration for Mode-Localized Resonant MEMS Sensors

This letter presents the first experimental results on the closed-loop characterization of a mode-localized microelectromechanical resonator system. Comparisons between the closed-loop oscillator approach and the open-loop frequency sweep approach show good agreement of output metrics including the amplitude ratios and mode frequencies. This new approach enables real-time measurements using emerging mode-localized resonant sensors and represents an important step toward realizing sensors based on this measurement principle.

Experimental investigations of effect of sound waves on oscillation and startup characteristics of oscillating heat pipe at different orientations

This research deals with the effects of working fluid and use of sound waves on the startup and heat transfer characteristics in terms of thermal resistance of a closed loop oscillating heat pipe. The performance of the oscillating heat pipe is checked for different orientations as 90? (vertical position), 60?, and 30?. Initially water is used as working fluid and performance of the oscillating heat pipe is checked with and without sound waves. Then 0.1 wt.% Al2O3-water nanofluid is utilized as working fluid in oscillating heat pipe and its performance is analyzed with and without sound waves. In this work, sound waves of 1 kHz frequency are passed through the evaporator section of closed-loop oscillation heat pipe. Application of sound waves improved the oscillation characteristics of the CLOHP with reduced startup time and enhanced thermal performance at all orientations. In comparison between working fluids, 0.1 wt.% Al2O3-water nanofluid showed better oscillation characteristics at all orientations of CLOHP except at 90? where use of sound waves leads to dry-out condition.

Phase Noise Reduction in an MEMS Oscillator Using a Nonlinearly Enhanced Synchronization Domain

We investigate the phase dynamics of a closed-loop MEMS-based oscillator and demonstrate how one can exploit nonlinear behavior to improve oscillator phase noise characteristics by synchronizing the oscillator with a weak harmonic drive. Analytical predictions are based on an oscillator model that incorporates a resonator element with a weak cubic (i.e., Duffing type) nonlinearity, weak coupling to a clean external harmonic drive, and both thermal and frequency noise terms. The method of stochastic averaging is used to derive an expression for the rate of phase diffusion induced by the noises, and the results predict a remarkable phase noise reduction of three order of magnitude when the oscillator is synchronized to the weak external field. The predictions are experimentally demonstrated using a closed-loop oscillator with a double-anchored double-ended-tuning-fork MEMS resonator with coupling to a small external sinusoidal signal from a signal generator, demonstrating a 30 dB/Hz drop in phase noise. The results show how one can generate a clean high-power signal from a relative noisy oscillator by synchronizing it with a low-power external signal. The results also confirm recent studies showing that the parameter range of synchronization is significantly expanded when the resonator operates in its nonlinear regime. [2016-0067]

Predicting the closed-loop stability and oscillation amplitude of nonlinear parametrically amplified oscillators

This work investigates the closed-loop operation of microelectromechanical oscillators in the presence of both cubic (Duffing) nonlinearities and parametric amplification. We present a theoretical model for this system that enables us to predict oscillation amplitude and instability and experimentally verify it using a silicon disk resonator with a quality factor (Q) of 85 000 and a natural frequency of 251 kHz. We determine that, contrary to previous understanding gained from analyzing the open-loop system, the presence of cubic nonlinearities does not limit the maximum stable oscillation amplitude if the resonator is operated in a closed loop. In addition, the stability and amplitude behavior predicted by our theoretical model are independent of the presence or severity of cubic nonlinearities, or on drive amplitude.

Study of the Composite Oscillator of Particulate Monitoring Instrument Based on TEOM

The effects of atmospheric particulates were more prominent in recent years, so accurate monitoring of particulate matter was a problem needed to resolve. In the existing particulate monitoring instrument based on the principle of Tapered Element Oscillating Microbalance method (TEOM),the particle concentration detection system was tapered quartz tube simple harmonic oscillator. Due to the oscillator relying mainly on analog circuit closed-loop self-excitation oscillator to drive, loop resonance frequency, oscillation stability and Q value was greatly influenced by the oscillator physical characteristics and the interference of mechanical structure and circuit design parameters. And oscillation frequency must be read by the digital circuit frequency detection system, then figured out the corresponding quality. In this paper, we studied a kind of composite oscillator tube which can overcome the lack of stability in the existing technology and reduce the impact of coexistence at the same time of digital circuit and analog circuit. And oscillator frequency step precision raised almost an order of magnitude compared with the national standard detection accuracy of 10ug.

Designing of a micromachined gyroscope system with a closed-loop DC biased interface ASIC

In this paper, a micromachined gyroscope system composed of a vibratory gyroscope with its interface ASIC is presented. The system adopts a DC sensing method to detect the capacitive motion, which is insensitive to the mismatch of the gyroscope capacitors and can eliminate high frequency signals from the chip. Therefore it offers a commendable noise performance with simplified topology. Low noise design can be achieved by a continuous-time charge sensitive amplifier with the input-referred noise voltage of 9.833 nV/rtHz at 10 kHz. A novel high voltage (HV) buffer is adopted in the drive mode to strengthen its drive signal, so that the common-mode voltage of it is made at 5 V that is compatible with the gyroscope. The HV buffer utilizes two sets of power supply to achieve both good noise performance and HV output. The ASIC chip is fabricated in the 0.35 μm 2P4M BCD HV process, and is 2.5×2.0 mm2 in dimension. The test results prove that the system achieves a stable closed-loop oscillation in the drive mode. Furthermore, the in-phase demodulation result of the gyroscope system achieves a nonlinearity of 0.14% within the sense range of 0°–500°/s.

A Self-Oscillating System to Measure the Conductivity and the Permittivity of Liquids within a Single Triangular Signal

We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes. The principle consists in the generation of a current square wave and its application to the sensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic segment. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a system which consists in a closed-loop current-controlled oscillator and only requires DC power to operate. The system interface is portable and only a small number of electrical components are used to generate the expected signal. Conductivities of saline NaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype. The results show excellent linearity and prove the repeatability of the measurements. Experiments on water-glycerol mixtures validate the proposed sensing approach to measure the permittivity and the conductivity simultaneously. We discussed and identified the sources of measurement errors as circuit parasitic capacitances, switching clock feedthrough, charge injection, bandwidth, and control-current quality.