Showing papers on "Frequency drift published in 2019"

Probing 10 μK stability and residual drifts in the cross-polarized dual-mode stabilization of single-crystal ultrahigh- Q optical resonators

Abstract: The thermal stability of monolithic optical microresonators is essential for many mesoscopic photonic applications such as ultrastable laser oscillators, photonic microwave clocks, and precision navigation and sensing. Their fundamental performance is largely bounded by thermal instability. Sensitive thermal monitoring can be achieved by utilizing cross-polarized dual-mode beat frequency metrology, determined by the polarization-dependent thermorefractivity of a single-crystal microresonator, wherein the heterodyne radio-frequency beat pins down the optical mode volume temperature for precision stabilization. Here, we investigate the correlation between the dual-mode beat frequency and the resonator temperature with time and the associated spectral noise of the dual-mode beat frequency in a single-crystal ultrahigh-Q MgF2 resonator to illustrate that dual-mode frequency metrology can potentially be utilized for resonator temperature stabilization reaching the fundamental thermal noise limit in a realistic system. We show a resonator long-term temperature stability of 8.53 μK after stabilization and unveil various sources that hinder the stability from reaching sub-μK in the current system, an important step towards compact precision navigation, sensing, and frequency reference architectures. Researchers in California have improved the thermal stability of tiny optical microresonators for use in high-precision timing and global navigation technologies. Ultrahigh-quality whispering gallery optical microresonators work by guiding the light from two differently-polarized lasers around the resonator circumference, which is carefully designed to have particular resonant frequencies. However, microresonators are extremely sensitive to temperature changes, and the impact of laser-induced heating, heat diffusion, and thermal expansion over time is detrimental to performance. Jinkang Lim and Chee Wei Wong at the University of California, US, and co-workers have shown that, by locking the dual-mode beat frequency of the lasers to a radio-frequency clock, the resulting suppression of thermal noise and frequency drift can enhance the long-term thermal stability of optical microresonators. This novel solution could result in microresonators stable enough to be used in space.

Crystalline optical cavity at 4 K with thermal-noise-limited instability and ultralow drift

Abstract: Crystalline optical cavities are the foundation of today’s state-of-the-art ultrastable lasers. Building on our previous silicon cavity effort, we now achieve the fundamental thermal-noise-limited stability for a 6 cm long silicon cavity cooled to 4 K, reaching 6.5×10−17 from 0.8 s to 80 s. We also report for the first time, to the best of our knowledge, a clear linear dependence of the cavity frequency drift on incident optical power. The lowest fractional frequency drift of −3×10−19/s is attained at a transmitted power of 40 nW, with an extrapolated drift approaching zero in the absence of optical power. These demonstrations provide a promising direction to reach a new performance domain for stable lasers, with stability better than 1×10−17 and fractional linear drift below 1×10−19/s.

Analysis of Modal Resonance Between PLL and DC-Link Voltage Control in Weak-Grid Tied VSCs

Abstract: Weak ac grid operation is known to challenge the stability of voltage source converters (VSCs). This paper provides an interpretation for the cause of such instability in view of a particular modal resonance within VSC's control, i.e., the resonance between dc-link voltage control (DVC) and synchronizing control-phase-locked loop (PLL). To characterize this modal interaction, a two degrees-of-freedom mass–spring–damper model is first proposed. Subsequently, based on a multi-modal decomposition approach, the amount of interaction is quantified by the incremental damping and frequency drift superimposed on each individual mode. Analytical results indicate that when the natural frequencies of PLL and DVC mode are close, strong interaction will push the lower-frequency mode to move toward the decreased frequency and damping direction, while causing the higher-frequency mode to go the opposite. Moreover, weaker ac grid operation will amplify such frequency/damping excursion and, thus, will render the lower-frequency mode unstable. Further, when the ac voltage control (AVC) is disregarded, a dynamic stability margin is analytically derived, and operation beyond the margin will result in monotonic drift. With the inclusion of AVC, owing to its introduced additional negative damping, by contrast, instability will occur in the presence of oscillations. Both eigenvalue analysis and simulations are conducted to verify the results.

Improved chemical exchange saturation transfer imaging with real-time frequency drift correction.

Abstract: Purpose To investigate the effects of frequency drift on chemical exchange saturation transfer (CEST) imaging at 3T, and to propose a new sequence for correcting artifacts attributed to B0 drift in real time. Theory and methods A frequency-stabilized CEST (FS-CEST) imaging sequence was proposed by adding a frequency stabilization module to the conventional non-frequency-stabilized CEST (NFS-CEST) sequence, which consisted of a small tip angle radiofrequency excitation pulse and readout of three non-phase-encoded k-space lines. Experiments were performed on an egg white phantom and 26 human subjects on a heavy-duty clinical scanner, in order to compare the difference of FS-CEST and NFS-CEST sequences for generating the z-spectrum, magnetization transfer ratio asymmetry (MTRasym ) spectrum, and amide proton transfer weighted (APTw) image. Results The B0 drift in CEST imaging, if not corrected, would cause APTw images and MTRasym spectra from both the phantom and volunteers to be either significantly higher or lower than the true values, depending on the status of the scanner. The FS-CEST sequence generated substantially more stable MTRasym spectra and APTw images than the conventional NFS-CEST sequence. Quantitatively, the compartmental-average APTw signals (mean ± standard deviation) from frontal white matter regions of all 26 human subjects were -0.32% ± 2.32% for the NFS-CEST sequence and -0.14% ± 0.37% for the FS-CEST sequence. Conclusions The proposed FS-CEST sequence provides an effective approach for B0 drift correction without additional scan time and should be adopted on heavy-duty MRI scanners.

Tunable low-drift spurious-free optoelectronic oscillator based on injection locking and time delay compensation

Abstract: A finely tunable low-drift spurious-free single-loop optoelectronic oscillator (OEO) incorporating injection locking and time delay compensation is proposed and experimentally demonstrated. In the proposed OEO, one mode of a single-loop OEO is injection locked by a tunable electronic oscillator resulting in single-mode oscillation. A time delay compensation system is used to compensate the OEO’s loop length change caused by environmental changes, such as temperature and strain. Tuning of the oscillation frequency is realized by controlling the injection frequency and absolute loop length of the single-loop OEO. In the experiments, when the ambient temperature varies between 22°C and 31°C within 1000 s, an output signal at the frequency of 10.664 GHz with a frequency drift better than −0.1 ppb and side-mode suppression ratio greater than 78 dB has been realized. Also, the OEO can be tuned with a precise frequency step of 10 Hz.

Scalable Feedback Control of Single-Photon Sources for Photonic Quantum Technologies

Abstract: Typically, quantum systems are very sensitive to environmental fluctuations, and diagnosing errors via measurements causes unavoidable perturbations. Here, an in situ frequency-locking technique monitors and corrects frequency variations in single-photon sources based on resonators. By using the classical laser fields used for photon generation as probes to diagnose variations in the resonator frequency, the system applies feedback control to correct photon frequency errors in parallel to the optical quantum computation without disturbing the physical qubit. Our technique can be implemented on a silicon photonic device and with sub 1 pm frequency stabilization in the presence of applied environmental noise, corresponding to a fractional frequency drift of <1% of a photon linewidth. These methods can be used for feedback-controlled quantum state engineering. By distributing a single local oscillator across a one or more chips, our approach enables frequency locking of many single photon sources for large-scale photonic quantum technologies.

Thermal and acoustic noise insensitive Brillouin random fiber laser based on polarization-maintaining random fiber grating.

Abstract: Thermal and acoustic noises are crucial to the long-term stability of fiber lasers, as it introduces the fluctuation of optical path length on laser cavity, and hence imposing undesirable intensity noise and frequency drift, particularly for a random fiber laser with distributed Rayleigh scattering feedback from a long length fiber. In this Letter, we propose and demonstrate a thermal and acoustic noise insensitive Brillouin random fiber laser by utilizing the random feedback from a polarization-maintaining (PM) fiber-based random grating. A theoretical model is developed for the first time, to the best of our knowledge, to analyze environmental perturbation on the randomly induced refractive index modulation via a PM random grating. Both the theory and experiments show that the scattered optical intensity of the PM random fiber grating exhibits a weak dependence on the temperature fluctuation and the acoustic noise perturbation compared to that of the Rayleigh scattering from hundreds of meters of PM fibers, leading to the Brillouin random lasing radiation with a 20 dB relative intensity noise suppression in the frequency range from 10 Hz to 1 kHz.

Improvement of the intensity noise and frequency stabilization of Nd:YAP laser with an ultra-low expansion Fabry-Perot cavity

Abstract: Continuous-wave, single-frequency, solid-state lasers with long-term frequency stability and low-intensity noise are an essential resource to generate squeezed and entangled states of light. In order to obtain the stable, nonclassical states of light, the frequency of the laser has to be stabilized with a stable reference. Due to the zero expansion property at a certain temperature, an ultra-low expansion (ULE) Fabry-Perot (F-P) cavity with a high finesse can be used as one of the best candidates of the frequency reference. We perform a detailed analysis of an extraordinarily high-frequency stability and ultra-low-intensity noise laser based on an improved cascade Pound-Drever-Hall frequency stabilization to a ULE F-P cavity. The frequency drift of the laser is suppressed to 7.72 MHz in 4 hours, and the noise level of the laser is simultaneously reduced to the quantum noise limit in the frequency below 300 kHz, which provides the possibility for the direct generation of a stable, high-level squeezed state in a lower-frequency region.

Sensitivity analysis and correction algorithms for atmospheric CO 2 measurements with 1.57-µm airborne double-pulse IPDA LIDAR

Abstract: In this study, a 1.57-µm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was developed for CO2 measurements. This airborne IPDA LIDAR is integrated with a real-time frequency monitoring system, an integrated sensor for temperature, pressure, and humidity, an inertial navigation system, and a global positioning system. The random errors of the LIDAR system, which are caused by the signal noise, background noise, and detector noise, among other factors, are analyzed for different target reflectivities at a flight altitude of 8 km. After parametric optimization, the signal is unsaturated at high target reflectivity. Further, it can be detected at low target reflectivity by adjusting the detector gain. After the averaging of 148 shots, the relative random error (RRE) was 0.057% for a typical target reflectivity of 0.1 sr-1. Moreover, the systematic errors caused by the laser pulse energy, linewidth, spectral purity, and frequency drift, as well as the atmospheric parameters related to the flight experiments are also investigated. The relative system error (RSE) was 0.214% as determined based on an analysis of the systematic errors, which are primarily caused by the frequency drift. Two methods are proposed to reduce the RSE caused by the frequency drift. The first is the averaging of 148 shots, which can reduce the RSE to 0.096%. The other method involves calculating the integral weight function (IWF) using real-time frequency. However, this is a time-consuming and computationally intensive process. Hence, look-up tables for the absorption cross-section were created to overcome this issue, resulting in a decrease in the RSE to 0.096%. Using actual aircraft attitude angles, velocity, and position data from flight experiments, the relative errors (REs) in the IWF caused by the uncorrected integral path and Doppler shift were determined to be 0.273% and 0.479%, respectively. However, it was found that corrections to the integral path and Doppler shift based on accurate calculations of the IWF cause the airborne platform to turn in such a way that the REs are eliminated. Hence, this study confirms the validity of system parameters and provides a reference for other researchers who study similar IPDA LIDAR systems. Further, the sensitivity analysis of the airborne IPDA LIDAR system can provide a reference to future data inversions. Moreover, the proposed correction algorithms for the integral path and Doppler shift contribute to more accurate inversion results.

Method for suppressing the frequency drift of integrated microwave photonic filters

Abstract: The significant frequency drift of integrated microwave photonic filters (IMPFs) is caused by relatively independent frequency fluctuations of the optical carrier and the photonic integrated filter, which imposes a rigid limitation on the practical application. In this paper, a novel method is proposed for suppressing the frequency drift of IMPFs. The scheme is implemented by utilizing an on-chip high-Q microring resonator as a frequency monitoring unit to track the instantaneous frequency drifts caused by the optical carrier drift and the temperature fluctuations of the photonic integrated chip. And the same frequency tuning is simultaneously applied on the photonic integrated filter to suppress the frequency drift of IMPFs based on the differential scheme. As a proof of concept, the proposed IMPF scheme is demonstrated on the Si3N4 platform, and the frequency drift is measured to be tens of MHz in one hour. Compared with conventional IMPF schemes, the frequency drift is significantly suppressed by 86.3% without using complex laser frequency stabilization and temperature control systems.

Observer-Based Transient Frequency Drift Compensation in AC Microgrids

Abstract: This paper proposes a novel solution for transient frequency compensation in weak 3-phase microgrids (MGs) based on a Luenberger observer and a transient frequency detector. Unlike in conventional grids, the low inertia of the generators coupled to an MG could make their rotor speeds to be affected by load changes, varying the grid frequency and compromising the grid quality and stability. This problem has been approached in the literature by the virtual inertia concept. However, the existing solutions are affected by the decoupling of the grid frequency reference and the frequency estimation bandwidth. The proposed paper addresses these problems by the use of a transient frequency drift estimator based on a transient detector and a Luenberger type observer that provides a nearly zero lag frequency estimation. The proposed alternative is analytically compared with the existing techniques and validated through simulation and exhaustive experimental results in an islanded MG. The developed method enables a 1 Hz reduction in the transient frequency deviation when compared with the existing alternatives and improves the system stability.

Temperature-frequency drift suppression via electrostatic stiffness softening in MEMS resonator with weakened duffing nonlinearity

Abstract: This paper reports a silicon micromechanical resonator with Duffing nonlinearity weakened and temperature-frequency drift suppressed by electrostatic tuning. By operating the resonator in an elastic mode via semicircular beams, we can weaken the instability of amplitude-frequency dependence to linearize the behavior of electrostatic stiffness softening. The mutual independence of linear frequency modulation by temperature and DC bias is theoretically modelled and experimentally verified. Based on this finding, an active temperature compensation model by slightly regulating DC bias voltage is established. The experimental results show that the resonator has a slight Duffing nonlinearity and a maximum frequency inaccuracy of only ±6 ppm during a temperature ramp across a testing span of 70 °C. This active technique does not need additional power consumption and is generic to a variety of electrostatic resonators.

Using an Auxiliary Mach–Zehnder Interferometer to Compensate for the Influence of Laser-Frequency-Drift in Φ-OTDR

Abstract: In phase-sensitive optical time-domain reflectometry (Φ-OTDR), the frequency drift of the laser source induces the fluctuation of signal, which limits the measurement capacity of Φ-OTDR for low frequency severely. In this paper, we propose a method to compensate for the influence of the frequency drift by using an auxiliary Mach–Zehnder interferometer (MZI). In this method, the signal of the auxiliary MZI is received to monitor the frequency drift continuously, and then, to correct the signal obtained from the sensing path. In the experiment, a vibration with a 0.1-Hz frequency on a 6-km sensing fiber is detected with a 10-m spatial resolution and the sensitivity is estimated to be $5.9\;\text{n}\varepsilon $ . This method will expand the scope of application of Φ-OTDR in the fields that require high sensitivity and low frequency response.

High-Resolution Brillouin Optoelectronic Oscillator Using High-Order Sideband Injection-Locking

Abstract: Microwave signals with high frequency, flexible tunability, and low phase noise are highly desired in signal processing and radar systems. In this letter, an optical injection-locking scheme using the high-order phase modulation sideband is introduced to realize a stable Brillouin optoelectronic oscillator (OEO). Pure microwave signals up to 40 GHz with low phase noise are obtained using an electrical drive signal below 5 GHz. A flexible frequency tuning with high resolution of 8 MHz is maintained by controlling the electrical drive signal and the slave laser, and the side mode suppression ratio is higher than 60 dB. The phase noise of the OEO-generated microwave signals under different master lasers is measured and compared to verify the significance of the master lasers with ultralow frequency noise. The maximum frequency drift of a 10.79-GHz signal is 1.4 kHz within 600 s, showing the stability of the proposed Brillouin OEO.

High resolution observations with Artemis-JLS. II. Type IV associated intermediate drift bursts

Abstract: Aims. We examined the characteristics of isolated intermediate drift bursts (IMDs) and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges and the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the IMDs appear and exhibit the above characteristics. Methods. We analyzed sixteen metric type IV events with embedded IMDs. The events were recorded with the Artemis-JLS/SAO high resolution (10 ms cadence) receiver in the 270-450MHz range with a frequency resolution of 1.4 MHz. We developed cross- and autocorrelation techniques to measure the duration, spectral width, and frequency drift of fiber bursts in 47 IMD groups. We also developed a semi-automatic algorithm to track fibers on dynamic spectra. Results. We distinguish six morphological groups of fibers, based on the relative position of the emission and absorption ridges. These included fibers with emission or absorption ridges only, fibers with the absorption ridge at lower or higher frequency than the emission, or with two absorption ridges above and below the emission or with two emission ridges were separated by an absorption ridge. Some borderline cases of IMDs with very high drift rate (~0.30 s-1) or very narrow total bandwidth (~8 MHz) were recorded; among them a group of rope-like IMDs with fast repetition rate and relatively narrow total frequency extent. The whistler hypothesis leads to reasonable magnetic field (~4.6 G), but the Alfven-wave hypothesis requires much higher field. We estimated the ratio of the whistler to the cyclotron frequency, x, to be ~ 0.3 to 0.6 and the average frequency scale along the loop of ~220Mm. We present empirical relations between fiber burst parameters and discuss their possible origin.

A Temperature Compensated RF $LC$ Clock Generator With ±50-ppm Frequency Accuracy From −40 °C to 80 °C

Abstract: This article presents the crystal-less CMOS frequency reference circuit that is suitable for connectivity applications with a relaxed frequency drift requirement. The presented architecture exploits the open-loop LC oscillator while ensuring constant bias condition, temperature-insensitive operation with an on-chip temperature sensor and digital control logics comprising an adaptive frequency calibration circuit and a non-volatile memory (NVM) performing frequency setup and temperature compensation of the LC oscillator. From 4.12-GHz LC oscillator output frequency, the divide-by-2 circuit followed by the multi modulus divider with 8–256 divide ratio provides 8.05–257.6-MHz output frequencies. The prototype circuit is measured at 27.12-MHz output frequency with ten devices under test and achieves ±50 ppm frequency accuracy (drift) over temperature variation from −40 °C to 80 °C. The measured period jitter in root-mean-squared is 1.32 $\text {ps}_{\mathrm{ rms}}$ . Fabricated in the low-cost 0.18 $\mu \text {m}$ CMOS technology, a temperature compensated frequency reference circuit occupies 0.69 mm2 and dissipates 15 mA from a 1.8-V supply voltage.

Tunable optoelectronic oscillator based on a polarization-dependent phase modulator cascaded with a linear chirped FBG

Abstract: A tunable optoelectronic oscillator (OEO) based on polarization controlled frequency response shifting of a dispersion-induced microwave photonic filter (MPF) is proposed and experimentally demonstrated. The MPF consists of a phase modulator (PM), a linear chirped fiber Bragg grating (LCFBG), and polarization multiplexed dual loops. Thanks to the polarization properties of the LiNbO3 crystal, the center frequency of the MPF can be tuned by simply adjusting the polarization state of the optical signal, and a tunable optoelectronic oscillator is established. Compared to the previous structure, the expensive wavelength-tunable laser is not needed in the proposed structure. In addition, the instability of oscillation frequency caused by the bias drifts of the modulator is avoided. A pure oscillation signal with a tunable frequency range from 3.3 to 7.3 GHz is generated. The single-sideband phase noise of the oscillation signal is about −110 dBc/Hz at 10-kHz offset. During more than 30 min observation, the oscillation frequency drift is about 7 kHz.

Multi-wavelength Brillouin erbium-doped fiber laser sensor with high tunable temperature sensing coefficient

Abstract: A multi-wavelength Brillouin erbium-doped fiber laser sensor is proposed and investigated experimentally. It is a linear laser cavity multi-wavelength fiber laser, formed by fixing two high-reflectivity Sangac loop mirrors at both ends. We investigate the laser system output characteristics and test the sensor performance for different temperature. Temperature/humidity and reliable linear-cavity fiber laser sensing operation were successfully achieved. Experimental results show that the temperature sensitivity is $$27.15$$ MHz/ °C and the measurement error caused by frequency drift is about $$\pm 0. 2 8 5$$ °C.

Research on High-accuracy Clock Synchronization Based on IEEE 1588 Protocol

Abstract: With the continuous development of mobile Internet3G/4G/5G, the requirement of time synchronization is becoming higher and higher. The IEEE1588 protocol has received extensive attention and research because it can provide sub-microsecond time synchronization to meet the actual needs. This research is based on Kalman Filter(KF) and Sliding Mode Controller(SMC) to achieve master-slave clock synchronization. Firstly, SMC is used to compensate the frequency drift caused by temperature, thereby reducing the influence of temperature on the frequency drift of crystal oscillator. Then, KF is used to suppress and optimize clock frequency jitter or random error. Through simulation, it is proved that this method can effectively improve the synchronization accuracy and meet the clock synchronization requirements of IEEE1588 protocol.

Magnetic resonance CEST imaging sequence based on frequency stabilization module and device

Abstract: The invention discloses a magnetic resonance CEST imaging sequence based on a frequency stabilization module and a device. The method comprises the steps that first, in the frequency stabilization module, a small flip angle radio-frequency pulse excites a target layer, and three rows of non-phase encoded k-space data are collected; secondly, by calculating the phase difference between the first and second rows of non-phase encoded k-space data, the fine estimate of main magnetic field frequency drift is acquired; the rough estimate of main magnetic field frequency drift is acquired by calculating the phase difference between the second and third rows and the phase difference between the first and second rows; by comparing the difference between the rough estimate, the fine estimate and a threshold value, the value of main magnetic field frequency drift is determined; according to the calculation result of main magnetic field frequency drift, the center frequency of the radio-frequencypulse is adjusted to realize real-time correction of main magnetic field frequency drift; and finally, conventional magnetic resonance CEST imaging is carried out. According to the invention, real-time correction of main magnetic field frequency drift is realized when magnetic resonance CEST imaging is carried out; a fat signal is effectively suppressed; and the magnetic resonance CEST imaging performance is improved.

A 2.4-GHz Frequency-Drift-Compensated Phase-Locked Loop With 2.43 ppm/°C Temperature Coefficient

Abstract: A frequency-drift-compensated phase-locked loop (PLL) with an LC voltage-controlled oscillator (VCO) is fabricated in TSMC 40-nm CMOS process. The proposed frequency drift compensator employs an analog-to-digital converter to monitor the control voltage of the PLL in background. The capacitor banks are adjusted to compensate for the frequency drift of the LC-VCO. The measured reference spur is −65.15 dBc. The measured best phase noise of this PLL is −108.32 and −130.26 dBc/Hz at the frequency offset of 1 and 10 MHz, respectively, among five chips. This chip occupies 0.223-mm2 active area. The power dissipation of this PLL is 6.32 mW from a 0.9-V supply voltage. The average temperature coefficient is 2.43 ppm/°C from 20 °C to 100 °C.

Performance Analysis of Active Anti-islanding Techniques for Photovoltaic Application

Abstract: In this paper some anti-islanding detection methods are evaluated through MatLab/Simulink® models. The methods are embedded into the control system of a voltage source inverter that is used to inject power to the grid from a set of photovoltaic modules. Due to low efficiency of the passive methods in detection of islanding and to the high cost of implementing the remote methods, only the active methods will be evaluated. In that sense, this paper presents comparative analysis regarding Active Frequency Drift (AFD), Slip-Mode Frequency Shift (SMS) and Sandia Frequency Shift (SFS) methods. Commonly, the active methods are implemented combining the passive sub/overvoltage and sub/overfrequency protection methods. The simulations presented comply with the voltage and frequency limits established by IEEE Std 929-2000 and harmonic distortion established by IEEE Std 519-2014.

Secondary phase difference measurement method for compensating frequency drift in phase sensitive optical time domain reflectometer

Abstract: The invention discloses a secondary phase difference measurement method for a phase sensitive optical time domain reflectometer (phi-OTDR), which is used for compensating the effects of frequency drift of laser in phi-OTDR The measuring structure comprises a laser module, a phi-OTDR sensing module, a data acquisition card and a processor The laser module comprises a laser and a first coupler The phi-OTDR sensing module comprises an acousto-optic modulator, a pulse signal generator, an optical amplifier, a circulator, a sensing fiber and a photodetector The measurement method is based on the conventional phi-OTDR, uses a secondary phase difference algorithm to differentiate the phase information in the signal according to a certain interval, and performs phase difference again by selecting two points with certain interval in a non-vibration area in order to eliminate the phase signal drift caused by the frequency drift of the laser, reduce the effect of frequency drift noise on phi-OTDR sensing performance, and improve the accuracy of the system for quantitative measurement of vibration events and the ability to detect low frequency signals

A Temperature-Insensitive CMOS-MEMS Resonator Utilizing Electrical Stiffness Compensation

Abstract: A temperature-insensitive micromechanical resonator that utilizes an electrical stiffness compensation technique was demonstrated. In particular, a 2.92-MHz free-free beam (FF-beam) resonator based on a $0.35-\mu \mathrm{m}$ 2-poly-4-metal CMOS-MEMS process platform cancels the first-order temperature coefficient of frequency $(TCF_{1})$ , from − 70.03 ppm of an uncompensated version to +0.44 ppm, and a $22\times$ lower overall frequency drift from the uncompensated 2120 ppm to 95 ppm from 25°C to 55°C. In contrast to the previously demonstrated electrical stiffness compensated resonator of [1], for which the resonator consists of an out-of-plane overhanging temperature-compensating electrode realized by a CMOS-incompatible poly-Si surface micromachining process, this work employs an in-plane U-shaped compensating electrode design that allows the use of a standard CMOS-MEMS process platform for achieving the device. The FEA-derived thermal expansion of the compensating electrode is used to predict the temperature coefficient of frequency. The measured results is compared with a finite element analysis.

Wireless Telemetry System for Gas Production

Abstract: When developing automated information and measurement systems (AIMS) for scattered automated or controlled facilities, choosing the type of communication channels for system components is an essential issue. The efficiency of communication channels determines the efficiency of the AIMS as a whole, thus affecting the quality of controls. This is especially relevant for gas-production facilities, which are mostly located in the Far North. The unprofitability or immaturity of wired connectivity enforces the exclusive use of wireless channels. Russia has a bandwidth that can be used for unlicensed radio communication. However, this bandwidth is very small (868.7 to 869.2 MHz), which is why various measurement channels might use very close frequencies; this in its turn means that the transmitters and receivers of crystal oscillators must produce very stable frequencies. The temperature and the “aging” of a crystal affect its frequency. The existing frequency stabilization technology only compensates the temperature-related frequency drifts. This paper proposes use of GPS data for frequency adjustment. This method can compensate the frequency drift of a crystal oscillator regardless of why it has occurred, which helps make use of a greater number of channels with the unlicensed bandwidth while keeping them reliably separated. Besides, a GPS receiver does not consume a lot of energy. The usage of the offered system allows to optimize the inhibitor’s flow, to increase reliability of any gas field exploitation, even without full electricity supply system.

A Least Mean Square Algorithm Based Single-Phase Grid Voltage Parameters Estimation Method

Abstract: Grid-synchronization may be the most significant task in order to integrate renewable energy sources (RESs) and electric vehicles (EVs) into the power grid. The popular technique for grid synchronization is the power based phase locked loop (PLL). The major challenges that one encounters to design a robust power based PLL is the filter design inside the power based PLL control loop, and estimating the grid voltage parameters under frequency drift conditions. A wide bandwidth should be considered during filter design if a wide range of frequency variations are predicted in the grid voltage. The traditional filters cause a large phase delay if a wide bandwidth is considered during filter design. As a result, it degrades the transient performance of the power based PLL. In order to improve the transient performance of the PLL, this paper adopted a Fourier linear combiner (FLC) filter inside the PLL control loop. Moreover, a feedback loop is used to make the FLC frequency adaptive in order to estimate the grid voltage parameter when grid frequency drift occurs. Simulation and experimental results are provided to verify the proposed technique.

High resolution observations with Artemis--JLS, (II) Type IV associated intermediate drift bursts

Abstract: Aims. We examined the characteristics of isolated intermediate drift bursts (IMDs) and their morphologies on dynamic spectra, in particular the positioning of emission and absorption ridges and the repetition rate of fiber groups. These were compared with a model in order to determine the conditions under which the IMDs appear and exhibit the above characteristics. Methods. We analyzed sixteen metric type IV events with embedded IMDs. The events were recorded with the Artemis-JLS/SAO high resolution (10 ms cadence) receiver in the 270-450MHz range with a frequency resolution of 1.4 MHz. We developed cross- and autocorrelation techniques to measure the duration, spectral width, and frequency drift of fiber bursts in 47 IMD groups. We also developed a semi-automatic algorithm to track fibers on dynamic spectra. Results. We distinguish six morphological groups of fibers, based on the relative position of the emission and absorption ridges. These included fibers with emission or absorption ridges only, fibers with the absorption ridge at lower or higher frequency than the emission, or with two absorption ridges above and below the emission or with two emission ridges were separated by an absorption ridge. Some borderline cases of IMDs with very high drift rate (~0.30 s-1) or very narrow total bandwidth (~8 MHz) were recorded; among them a group of rope-like IMDs with fast repetition rate and relatively narrow total frequency extent. The whistler hypothesis leads to reasonable magnetic field (~4.6 G), but the Alfven-wave hypothesis requires much higher field. We estimated the ratio of the whistler to the cyclotron frequency, x, to be ~ 0.3 to 0.6 and the average frequency scale along the loop of ~220Mm. We present empirical relations between fiber burst parameters and discuss their possible origin.

Decentralized Frequency Alignment for Collaborative Beamforming in Distributed Phased Arrays

Abstract: A new approach to distributed syntonization (frequency alignment) for the coordination of nodes in open loop coherent distributed antenna arrays to enable distributed beamforming is presented. This approach makes use of the concept of consensus optimization among nodes without requiring a centralized control. Decentralized frequency consensus can be achieved through iterative frequency exchange among nodes. We derive a model of the signal received from a coherent distributed array and analyze the effects on beamforming of phase errors induced by oscillator frequency drift. We introduce and discuss the average consensus protocol for frequency transfer in undirected networks where each node transmits and receives frequency information from other nodes. We analyze the following cases: 1) undirected networks with a static topology; 2) undirected networks with dynamic topology, where connections between nodes are made and lost dynamically; and 3) undirected networks with oscillator frequency drift. We show that all the nodes in a given network achieve average consensus and the number of iterations needed to achieve consensus can be minimized for a given cluster of nodes. Numerical simulations demonstrate that the consensus algorithm enables tolerable errors to obtain high coherent gain of greater that 90\% of the ideal gain in an error-free distributed phased array.

Performance of Optically-Preamplified, Direct-Detection, M-ary PPM for Inter-Satellite Links

Abstract: In this paper, we evaluate the end-to-end performance of optically-preamplified, direct-detection, 16-ary and 64-ary Pulse Position Modulation (PPM) receivers with optical Fabry-Perot and electrical filters for the use in inter-satellite links. Monte-Carlo simulations are used to evaluate the bit error ratio (BER) versus the optical signal-to-noise ratio per bit without the need to assume that the noise at the decision sample is Gaussian. Extensive simulations are carried out to optimize the bandwidths of the optical and electrical filters at the receiver for three different pulse shapes while considering the combined effects of the extinction ratio (ER) of the optical transmitter, the dual-polarized amplifier noise, intra-symbol, and inter-symbol interference (ISI). The performance penalties due to timing jitter and frequency drift at the receiver are also evaluated. The results indicate that for ER > 25 dB, 64-ary PPM systems outperform 16-ary PPM systems by up to 1.2 dB, however, under realistic system imperfections of ER > 20 dB, timing jitter, and frequency drift, the performance of both systems becomes comparable.

Drift frequency of kilometric radio burst type III with solar wind speed and density

Abstract: Solar radio burst is a signature of solar flare generated by plasma emission mechanism. Radio burst is a diagnostic tool to study electron beam evolution and plasma background properties in corona and interplanetary medium. Sudden release magnetic energy up to 1032 ergs due to magnetic connection accelerates electron located at accelerated site to propagate near relativistic. This fast group of electron propagating through plasma background induced high level of Langmuir wave due to bump in tail instability. Non linear wave-wave causing radio burst near the local plasma frequency. In this paper, frequency drift of radio burst is calculated only from 1 MHz to 400 kHz and the data is obtained from Coordinated Data Analysis Web (CDAweb). The data is analysed by identifying time during maximum intensity of burst at the particular frequency range. Only 45 burst observed in September 2017 is considered in this paper. Meanwhile the data of solar wind speed and density is collected from Advanced Composition Explorer (ACE) satellite. Drift frequency of burst then compared to average of solar wind and density. From the analysis, drift frequency of burst decreasing against solar wind speed and solar wind density. But both relationship shows very weak correlation between drift frequency and solar wind properties.