Frequency Stability Research Articles

The Effect of Temperature Variation on the Performance Parameters of Miniature Atomic Clocks with Similar Frequency Stability Specification

The primary source of error that causes an increase in inaccuracy in determining the location of individual users in a communication network is the lack of synchronization of their time bases. Time synchronisation of the aeronautical communication network should be ensured to the greatest extent possible. Increasing the level of synchronisation would be possible by using a selected type of atomic clocks, which would be placed in the on-board equipment of UAV assets. The paper describes the possibilities of implementing available types of atomic clocks in the instrumentation of different categories of UAV assets. This paper compares the performance of miniature CSAC cesium atomic clocks with a high-performance OCXO quartz oscillator with similar frequency stability specifications and the effect of temperature on their performance parameters. The next section analyses how time, temperature, and initial frequency errors can affect the resulting frequency stability error of each oscillator.

A Sustainable Hybrid Off-Grid System Design for Isolated Island Considering Techno-Economic and Frequency Stability Analysis

Electrifying remote islands presents complex challenges. Currently, most remote areas in Indonesia rely on diesel fuel for their electricity supplies, contributing to escalating generation costs and environmental degradation. Aligned with the global net-zero emission goal, this study proposes the design of a hybrid off-grid system for Kabare Village in the Raja Ampat Islands, integrating techno-economic and frequency stability analyses. HOMER Pro was employed to identify the most optimal system configuration, while DIgSILENT PowerFactory was utilized to assess the frequency stability performance of the system. This study unveils that the optimal system combines existing generators, solar panels, and batteries, with a net present cost of $1.37 million. The optimal system delivers an 11.8% reduction in levelized cost of energy to $0.269/kWh, alongside a 25.6% decrease in both fuel consumption and greenhouse gas emissions compared to the existing system. Moreover, the system meets frequency stability metrics, even under extreme operational conditions. This study demonstrates that implementing a hybrid off-grid system in Kabare Village is not only technically and economically feasible but also a practical option. These findings are anticipated to assist the government in promoting the utilization of renewable energy sources, particularly in remote areas such as the islands of eastern Indonesia.

Latent subtypes of self-injurious urges among adults engaging in disordered eating and non-suicidal self-injury.

Self-injurious urges are arguably the clearest antecedents of engaging in self-injurious behaviors (SIBs; e.g., binge eating, self-induced vomiting, cutting, burning). However, self-injurious urges demonstrate great heterogeneity, and it is unknown which are most closely linked to SIBs. This study aims to identify latent profiles of self-injurious urges and subsequently examine associations between profiles and engagement in SIBs. Adults (N = 124) who reported engaging in at least three SIBs in the past month completed six surveys a day assessing self-injurious urges for 14 days (6600 responses). Latent profiles were constructed using within-person intensity, variability, peak, duration, relative frequency, and overall stability of self-injurious urges over the EMA period. Five distinct profiles were identified: "sustained," "muted," "sudden-onset," "volatile," and "virtually absent." SIB frequency differed across profiles, H(4) = 41.11, p < 0.001; η2 = 0.31, 95% CI [0.19, 0.48], and Dunn's post-hocs indicated those in the "volatile" profile engaged in more SIBs than other profiles. Findings support the presence of meaningful profiles of self-injurious urges and suggest these profiles differ in levels of SIB engagement. Future work should prospectively examine associations between profile membership and engagement in SIBs and identify treatment targets to intervene on SIBs.

Reserve Technique in Integrating Large Sustainable Energy Sources: A Case Study of the Tunisian Grid

The increasing integration of sustainable energy sources, such as wind and solar power, into the national electricity grid presents significant challenges in terms of frequency control and grid stability. Additionally, the imbalance between electricity supply and demand introduces dynamic frequency variations. However, according to the literature, the impact of high penetration of renewable energy sources on the Tunisian grid has not been extensively analyzed using power system simulator for engineering (PSS/E). This research paper explores how the primary reserve technique participates to maintain frequency within acceptable ranges in the Tunisian electrical grid. Individual generators contribute to the total power output, thereby influencing frequency deviation. The primary frequency control action by each generator is proportional to its frequency deviation and inversely proportional to its governing drop, which measures the generator’s sensitivity to frequency changes. This paper analyzes frequency stability in the Tunisian grid under scenarios with and without different rates of sustainable energy source penetration, which barely reached 3.5% in 2023. In Tunisia, the use of sustainable energy is essential not only for ensuring grid stability but for combating climate change and reducing carbon emissions, aligning with the country’s environmental goals. The transition to sustainable energy significantly reduces the carbon footprint of the power sector, offering a sustainable solution for mitigating the adverse effects of climate change. Dynamic simulations were conducted for the isolated Tunisian system, separate from the interconnected grid, focusing on the critical scenario of the loss of a large electricity production unit. This study also examined the absence of sustainable energy integration and the effects of integration of different rates of renewable energy to evaluate the impact of reserves on the continuity of the Tunisian electrical service. Simulation results, which considered a 2023 grid model, show that with an integration trial of 20% renewable energy and, in the worst-case scenario, which represents the loss of the largest production group in the grid, the primary reserve of a given group—defined by the quantity of active energy—can be rapidly deployed to restore the balance between electricity supply and demand. Thus, reserves are a crucial solution for maintaining frequency within reasonable limits and ensuring the continuity of electrical services in Tunisia with varying rates from 10% to 20% integration of different sustainable energy sources.

Control strategy of the novel stator free speed regulating wind turbine generation system.

Building a high-proportion renewable energy power system is a key measure to address the challenges of the energy revolution and climate change. However, current high-proportion renewable energy systems face issues of frequency instability and voltage fluctuations. To address these challenges, this paper proposes a novel topology for a stator free speed regulating wind turbine generation system. The stator free speed regulating machine connects a gearbox and a synchronous generator, forming a flexible drive chain that increases system inertia and enhances frequency stability in high-proportion renewable energy power systems. The synchronous generator at the end of the drive chain can be directly connected to the grid without the converter, thanks to the speed regulation provided by the stator free speed regulating machine, thus avoiding harmonic pollution caused by power electronic devices in traditional wind turbines, enhancing the reactive power support capability, and improving voltage stability in high-proportion renewable energy systems. Given that the proposed stator free speed regulating machine consists solely of a rotating inner and outer rotor without a stator, traditional motor control strategies are not applicable. Therefore, this paper focuses on developing control strategies for the stator free speed regulating machine, employing a dual closed-loop PI control strategy with an outer loop for speed and an inner loop for current, based on flux orientation of the outer rotor. Simulation experiments will validate the feasibility of the proposed stator free speed regulating wind turbine generation system topology and the effectiveness of the control strategy.

Study of control methods to reduce off-grid faults and improve system frequency stability in multi-energy systems based on impedance modeling of electric hydrogen production systems

Study of control methods to reduce off-grid faults and improve system frequency stability in multi-energy systems based on impedance modeling of electric hydrogen production systems

Broad Microbial Community Functions in a Conventional Activated Sludge System Exhibit Temporal Stability.

Wastewater microbial communities within conventional activated sludge (CAS) systems can perform hundreds of biotransformations whose relative importance, frequency, and temporal stability remain largely unexplored. To improve our understanding of biotransformations in CAS systems, we collected 24 h composite samples from the influent and effluent of a CAS system over 14 days, analyzed samples using high-resolution mass spectrometry (HRMS), and conducted a nontarget analysis of our HRMS acquisitions. We found that over 50% of the chemical features in the influent were completely removed, and the daily number of detected features exhibited low variability with a coefficient of variation of 0.07. Additionally, we found 352 Core chemical features present in every sample at both locations. We used chemical features to search for evidence of 19 potential biotransformations and detected 9 of these biotransformations at a frequency of over 80 times per day, where evidence for dehydrogenations, hydroxylations, and acetylations was most frequently detected. The daily number of detections for the 9 biotransformations exhibited coefficients of variation ranging from 0.13-0.20, revealing the broad temporal stability for these wastewater microbial community functions. This stability contrasts with the previously observed temporal variability for micropollutant biotransformations, suggesting that micropollutant biotransformations are linked to specialized microbial community functions.

Kalman filter time scale algorithm based on noise characteristics of optically pumped cesium clock

Abstract The time scale algorithm plays an important role in time keeping. Currently, the time scale algorithm primarily adopts the predictability weighting algorithm for microwave clocks. Due to the different working principles and performance of optically pumped small cesium clocks compared with microwave clocks, a new time scale algorithm must be developed to adapt to optically pumped clocks. Based on the noise characteristics of the optically pumped clocks, the state model is established and the time scale is calculated using the Kalman filtering algorithm. The state model of the optically pumped clocks simultaneously considers the effects of white frequency modulation, flicker frequency modulation, and random walk frequency modulation. The proposed algorithm models the flicker frequency modulation for filtering estimation, which effectively improves the stability of the time scale. Here, the flicker frequency modulation is modeled through the linear combination of Markov processes, and the impact of different numbers of Markov processes on the time scale stability is analyzed. Compared with the predictability weighted algorithm, the results obtained by the proposed algorithm demonstrate that the frequency stability of the Kalman filtering time scale based on the noise characteristics was better than that of the predictability algorithm. Taking rapid Coordinated Universal Time (UTCr) as a reference, the frequency stabilities of the time scale based on three optically pumped clocks obtained by the proposed algorithm were 1.14 × 10−14 for 15 days and 5.50 × 10−15 for 30 days.

Simulation of Voltage and Frequency Stabilization in PV-Based Microgrids Using Virtual Synchronous Generator Control

In recent years, distributed generation technologies and micro-grids have garnered increasing attention, particularly with the rapid growth of renewable energy sources (RESs) integrated via power electronic converters. As the penetration of RESs in modern power systems rises, voltage and frequency support, traditionally provided by synchronous generators, can be effectively managed by Virtual Synchronous Generator (VSG) control. This paper presents the modeling and analysis of voltage and frequency stability enhancement in a PV-based micro-grid system using VSG control. The micro-grid system under study operates at 400V, 50Hz, and is integrated with a 0.4kV power distribution line. Mathematical models of the VSG control strategy are developed in MATLAB/Simulink. Simulation results demonstrate that VSG control significantly improves the voltage and frequency stability of the PV-based micro-grid system.

Estimation of Quantitative Inertia Requirement Based on Effective Inertia Using Historical Operation Data of South Korea Power System

In low-inertia systems with a high penetration of renewable energy, the rotational kinetic energy and inertia constant are significant factors in determining frequency stability. The energy released owing to the frequency decrease during contingency represents a portion of the inertia that a synchronous machine possesses in the normal state. However, when securing inertia or planning additional resources to secure frequency stability, inertia in the normal state is analyzed as the standard rather than the amount of energy released during a fault. Therefore, in this paper, we define the actual energy emitted from a synchronous machine as Effective inertia. In order to evaluate Effective inertia in various operating conditions, we conducted a comprehensive review on approximately 24,627 cases from the years 2019, 2020, and 2021. As a result, in systems with low rotational kinetic energy, both low- and high-frequency nadirs were observed, indicating high uncertainty. However, Effective inertia presented a consistent trend regarding the energy release aligned with the minimum frequency. For instance, the rotational kinetic energy required to satisfy the frequency standard was 23 GWs, while the required Effective inertia was 858 MWs. We emphasize that securing inertia based on rotational kinetic energy includes additional imaginary energy that does not contribute to frequency, resulting in an energy requirement greater than that needed for Effective inertia. Therefore, in order to secure the frequency stability of the future system, the actual required energy amount based on Effective inertia will be presented and utilized in the inertia market and FFR (Fast Frequency Response) resource design.

Record-high power, low phase noise synchronously-pumped optical parametric oscillator tunable from 2.7 to 4.7 μm

Within the domain of optical frequency comb systems operating in the mid-infrared region, extensive exploration has been undertaken regarding critical parameters, such as stabilization, coherence, or spectral tunability. Despite this, certain essential parameters remain inadequately addressed, particularly concerning light source stability at high average powers. This study explores stability limitations of an optical parametric oscillator system when scaling to several watts of average power of the idler. Notably, the highest average power reported in the 3–5 μm region, reaching 10.3 W for the idler output at 3.1 μm, is achieved. Additionally, we analyze the phase noise and beam quality of both idler and signal beams and identify the onset of higher order modes as limiting for stability at high-power operation. Finally, we estimate the free-running optical linewidth of our idler beam to be ∼300 kHz, undermining the high passive temporal stability of our source. These findings represent a significant advancement toward the realization of highly stable high-power optical frequency combs in the mid-infrared region, thereby facilitating applications previously constrained by light source average powers and quality limitations.

Improvement in the Sagnac-loop laser frequency stabilization

Improvement in the Sagnac-loop laser frequency stabilization

High detectivity terahertz radiation sensing using frequency-noise-optimized nanomechanical resonators

We achieve high detectivity terahertz radiation sensing using a silicon nitride nanomechanical resonator functionalized with a metasurface absorber. High performances are achieved by striking a balance between the frequency stability of the resonator and its responsivity to absorbed radiation. Using this approach, we demonstrate a detectivity D*≈3.4×109cm⋅Hz/W and a noise equivalent power NEP≈36pW/Hz that outperform the best room-temperature on-chip THz detectors, such as pyroelectric detectors, while maintaining a comparable thermal response time of ≈200 ms. Our optical absorber consists of a 1-mm diameter metasurface, which currently enables a 0.5–3 THz detection range but can easily be scaled to other frequencies in the THz and infrared ranges. In addition to demonstrating high-performance terahertz radiation sensing, our work unveils an important fundamental trade-off between frequency stability and responsivity in thermal-based nanomechanical radiation sensors.

A digital servo for ultra-stable laser frequency stabilization.

We present a fully digital servo optimized for ultra-stable laser frequency stabilization. Experiments such as optical clock experiments can achieve high laser frequency stability, imposing high bandwidth, high precision, and low noise requirements on servo systems. The laser system utilizes the Pound-Drever-Hall method, employing an ultra-stable cavity to generate an error signal for servo input. The input is separated into two independent channels, with one channel featuring high feedback bandwidth and the other channel featuring high gain in the low-frequency domain. The process is fully digitized using field-programmable gate arrays with custom-made infinite impulse response filters and proportional-integral-derivative algorithms. Thanks to the low latency of 120.5ns and low input noise of 3.22 × 10-12V2/Hz@1Hz, our digital servo can easily lock an external-cavity diode laser to a typical ultra-low expansion ultra-stable cavity. The laser system has a fractional frequency stability of 10-16@1s, with the servo electrical noise contributing only 5.54 × 10-18@1s.

Phase demodulation method for stable long-haul frequency transmission based on the Michelson interferometer.

In this Letter, we present a fiber-optic radio frequency (RF) transmission scheme based on phase modulation with an interferometric detection structure. A self-developed Michelson interferometer (MI) is used to demodulate the frequency signal via an electrically controlled optical shifter. The two complementary outputs from the interferometer are detected using a balanced detector, which suppresses the common-mode noise of the fiber link. The structure is tested in the laboratory using a frequency transfer system over a 560 km fiber link. Experimental results show that a stable 2.4 GHz frequency transmission with a fractional frequency instability of 3.9 × 10-14 at 1 s and 6.2 × 10-17 at 10,000 s is achieved. Compared with the frequency transmission system based on intensity modulation and direct detection, the frequency instability is improved from 7.3 × 10-14 to 3.9 × 10-14 at 1 s. We believe that the proposed method will be useful for the construction of time-frequency synchronous fiber networks.

Copy number variants underlie major selective sweeps in insecticide resistance genes in Anopheles arabiensis.

To keep ahead of the evolution of resistance to insecticides in mosquitoes, national malaria control programmes must make use of a range of insecticides, both old and new, while monitoring resistance mechanisms. The outdoor-biting malaria vector Anopheles arabiensis is of increasing concern for malaria transmission because it is apparently less susceptible to many indoor control interventions, yet knowledge of its mechanisms of resistance remains limited. Furthermore, comparatively little is known in general about resistance to non-pyrethroid insecticides such as pirimiphos-methyl (PM), which are crucial for effective control in the context of globally high resistance to pyrethroids. We performed a genome-wide association study to determine the molecular mechanisms of resistance to the pyrethroid deltamethrin (commonly used in bednets) and PM (widespread use for indoor spraying), in An. arabiensis from 2 regions in Tanzania. Genomic regions of positive selection in these populations were largely driven by copy number variants (CNVs) in gene families involved in metabolic resistance. We found evidence of a new gene cluster involved in resistance to PM, identifying a strong selective sweep tied to a CNV in the carboxylesterase genes Coeae2g - Coeae6g. Using complementary data from another malaria vector, An. coluzzii, in Ghana, we show that copy number at this locus is significantly associated with PM resistance. Similarly, for deltamethrin, resistance was strongly associated with a novel CNV allele in the Cyp6aa / Cyp6p cluster (Cyp6aap_Dup33). Against this background of metabolic resistance, resistance caused by mutations in the insecticide target sites was very rare or absent. Mutations in the pyrethroid target site Vgsc were at very low frequency in Tanzania, yet combining these samples with 3 An. arabiensis individuals from West Africa revealed a startling evolutionary diversity, with up to 5 independent origins of Vgsc-995 mutations found within just 8 haplotypes. Thus, despite having been first recorded over 10 years ago, Vgsc resistance mutations in Tanzanian An. arabiensis have remained at stable low frequencies. Overall, our results provide a new copy number marker for monitoring resistance to PM in malaria mosquitoes, and reveal the complex picture of resistance patterns in An. arabiensis.

Analysis and Control of Frequency Stability in Low-Inertia Power Systems: A Review

Analysis and Control of Frequency Stability in Low-Inertia Power Systems: A Review

An oven controlled piezoelectric MEMS dual-resonator platform with frequency stability of [formula omitted]100 ppb over industrial temperature range

This work demonstrates a piezoelectric MEMS dual-resonator platform with an oven control. The platform includes a micro-oven in-chip, which integrates a frequency output resonator and a temperature sensing resonator. The two resonators operate using a phase-locked loop system, one in width-extensional (WE) mode and the other in width-shear (WS) mode. An equivalent thermal model of the dual-resonator platform is established and both resonators exhibit extremely uniform temperature distributions. The real-time temperature of the resonators is monitored by measuring the frequency difference between the two resonators and a closed-loop oven control is implemented to maintain the dual-resonator platform at an oven-set temperature. The reported oven controlled piezoelectric MEMS dual-resonator platform exhibits a measured frequency stability of ±100 ppb across the industrial temperature range of −40 to 85 °C. This result signifies the promising potential of the device in high-end timing applications.

Temperature and Frequency-Dependent Dielectric Properties Prediction of Oxide Glasses by Machine Learning

The dielectric properties of oxide glasses are essential for telecommunications, where thermal and frequency stability of devices are crucial. However, predicting the temperature and frequency-dependent dielectric properties of glasses is complex using empirical models and computational methods. To address this challenge, machine learning (ML) models with descriptor sets in two different domains—the chemical composition domain and the element physical and chemical properties domain—were employed to predict the dielectric constant and loss of oxide glasses, along with their temperature and frequency dependencies. Additionally, Shapley additive explanations (SHAP) analysis was conducted to interpret the hidden relationships among the data. Compared to experimental values, the ML models perform well in terms of root mean square error (RMSE) and the coefficient of determination (R2). Moreover, the ML models using element physical and chemical properties descriptors demonstrate the potential to predict the dielectric properties of glasses with unknown components.

Research on miniaturized frequency steering system based on atomic clock

In order to generate a high-performance RF signal, by analyzing the traditional frequency steering system, and aiming at the goal of miniaturization and engineering, this paper designs a miniaturized frequency steering system based on dual-atomic clock. In addition, we have carried out research on key technologies such as high-precision frequency deviation measurement and precision frequency regulation. On this basis, a frequency deviation measurement and correction system is designed. And according to the theoretical analysis, the measuring accuracy of the frequency deviation measurement approach can reach 1.0 × 10-14, besides, the step frequency tuning can also reach 1.125 × 10-14. What's more, some related experiments, the RF signal synthesized from a Rb clock and a master has an accuracy of 2.26 × 10-13, and also the frequency stability of 104 s in terms of the Allan deviation reaches 2.36 × 10-14, suggesting that the overall performance of the rubidium atomic clock has been greatly improved.