Frequency Stability Research Articles

Frequency Stabilizing and Reducing Power Outages of The Islanded Power ‎Network Using a ‎Load Shedding Method in The Presence of Renewable Energy ‎Resources

Frequency Stabilizing and Reducing Power Outages of The Islanded Power ‎Network Using a ‎Load Shedding Method in The Presence of Renewable Energy ‎Resources

Geometry effects in Impact Echo Signals - why traditional time-frequency filtering fails to remove them

Impact Echo signals can sometimes contain a lot of noise, even though the wavelength of the investigated modes is in the order of the specimen thickness. A special type of noise signals are the so-called geometry effects. These effects occur when the lateral dimensions of the investigated structure are not much larger than its thickness. This study compares signals with and without geometry effects using various types of signal processing methods such as classical fast Fourier transform, short-time Fourier transform, and the continuous wavelet transform. Results show that signals without geometry effects have a much more stable resonance frequency, whereas the main frequency content in Impact Echo signals containing geometry effects typically oscillates between two or more discrete frequencies. As this oscillation lasts for the entirety of the signals, traditional time-frequency filters will likely not be capable to remove geometry effects from Impact Echo signals. Resonance frequencies in Impact Echo signals unaffected by geometry effects are much more stable, with no fluctuation or oscillation over time. By comparing time-frequency representations of signals obtained at the same spot with different impactors, it is observed that the peak frequency at the beginning of each signal is similar for all three measurements. This result suggests that, for signals heavily affected by geometry effects, the beginning of the signal, which is usually neglected during Impact Echo inspection, could provide useful information regarding the thickness of the inspected structure. Two ways of obtaining thickness information from the signal beginning are presented and results are compared using a dataset from a reference specimen: one method uses classical Fourier transform of the signal beginning and the other approach uses the maximum frequency determined from the continuous wavelet transform. The results for both approaches show that the Impact Echo signal beginning contains depth information, which could prove valuable for evaluations of noisy datasets.

Linewidth measurement of external cavity lasers

Narrowband laser sources are used in applications that require high-precision or stable optical frequency. Such applications include high-resolution spectroscopy, long-distance measurement, and coherent optical communication. The linewidth of a laser is a direct measure of the laser's stability; therefore, characterization of laser linewidth is essential. In practice, however, determining a laser's linewidth is not a trivial task and typically requires expensive equipment or a complex experimental arrangement. This paper presents a straightforward, low-cost method based on unbalanced interferometry, which allows us to determine the visibility of fringe patterns as a function of the optical path difference and, consequently, the linewidth of the laser. As a test laser, we use a tunable external cavity laser source at around 780 nm, where an interference filter is employed for wavelength selection. Data obtained by applying the interferometric technique to this laser and the analysis of these data, along with the resulting linewidth value, are presented. Given that the described measurement setup is inexpensive, straightforward, and pedagogically accessible, it is well-suited for an instructional physics laboratory experiment and will also be of interest to laboratory researchers.

Laser frequency stabilization for continuous-wave laser enhanced direct frequency comb spectroscopy system

We present the observation of high-precision direct frequency comb spectroscopy excited by an optical frequency comb and a diode laser when each of them drives one step of the two-photon transition in a rubidium vapor system. We demonstrate a stable and low noise system by directly locking the frequency of the continuous-wave laser to the rubidium two-photon transition. The frequency stability of a diode laser via the two-photon transition locking technique is 8 × 10−11 for a 1 s gate time and 3 × 10−12 for 1000 s. It proves to be a potential technique for locking the diode laser with high stability. We chose a suitable optical frequency comb pulse and the frequency of the diode laser to fulfill the double-resonance condition. These techniques eliminate spectrum line overlap and would benefit spectroscopy measurements.

Studying the Optimal Frequency Control Condition for Electric Vehicle Fast Charging Stations as a Dynamic Load Using Reinforcement Learning Algorithms in Different Photovoltaic Penetration Levels

This study investigates the impact of renewable energy penetration on system stability and validates the performance of the (Proportional-Integral-Derivative) PID-(reinforcement learning) RL control technique. Three scenarios were examined: no photovoltaic (PV), 25% PV, and 50% PV, to evaluate the impact of PV penetration on system stability. The results demonstrate that while the absence of renewable energy yields a more stable frequency response, a higher PV penetration (50%) enhances stability in tie-line active power flow between interconnected systems. This shows that an increased PV penetration improves frequency balance and active power flow stability. Additionally, the study evaluates three control scenarios: no control input, PID-(Particle Swarm Optimization) PSO, and PID-RL, to validate the performance of the PID-RL control technique. The findings show that the EV system with PID-RL outperforms the other scenarios in terms of frequency response, tie-line active power response, and frequency difference response. The PID-RL controller significantly enhances the damping of the dominant oscillation mode and restores the stability within the first 4 s—after the disturbance in first second. This leads to an improved stability compared to the EV system with PID-PSO (within 21 s) and without any control input (oscillating more than 30 s). Overall, this research provides the improvement in terms of frequency response, tie-line active power response, and frequency difference response with high renewable energy penetration levels and the research validates the effectiveness of the PID-RL control technique in stabilizing the EV system. These findings can contribute to the development of strategies for integrating renewable energy sources and optimizing control systems, ensuring a more stable and sustainable power grid.

Long-term autonomous time-keeping of navigation constellations based on sparse sampling LSTM algorithm

The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations. This operational mode relies heavily on the support of ground stations. To enhance the high-precision autonomous timing capability of next-generation navigation satellites, it is necessary to autonomously generate a comprehensive space-based time scale on orbit and make long-term, high-precision predictions for the clock error of this time scale. In order to solve these two problems, this paper proposed a two-level satellite timing system, and used multiple time-keeping node satellites to generate a more stable space-based time scale. Then this paper used the sparse sampling Long Short-Term Memory (LSTM) algorithm to improve the accuracy of clock error long-term prediction on space-based time scale. After simulation, at sampling times of 300 s, 8.64 × 104 s, and 1 × 106 s, the frequency stabilities of the spaceborne timescale reach 1.35 × 10–15, 3.37 × 10–16, and 2.81 × 10–16, respectively. When applying the improved clock error prediction algorithm, the ten-day prediction error is 3.16 × 10–10 s. Compared with those of the continuous sampling LSTM, Kalman filter, polynomial and quadratic polynomial models, the corresponding prediction accuracies are 1.72, 1.56, 1.83 and 1.36 times greater, respectively.

D.6 Neurological care and outcomes of pregnant patients with epilepsy in a Canadian tertiary care center (2014-2020)

Background: Limited data exists on neurological care and outcomes of Canadian pregnant patients with epilepsy (PPWE). This study provides Canadian data to inform practice patterns and observed outcomes for PPWE at a tertiary care center. Methods: PPWE receiving care at the University Health Network (Toronto, Canada) epilepsy clinic from January 1, 2014 to November 20 2020 were retrospectively identified with demographics and neurological data and outcomes collected. Results: A total of 195 cases were identified, with a median maternal age of 32 years (SD 4.58), a median age at first seizure of 17 years (range 1 month – 36 years old), 52% were diagnosed with genetic generalized epilepsy and 50% endorsed 6 months of seizure freedom prior to conception. In pregnancy, 93% took ASM(s) with 77% receiving therapeutic drug monitoring (TDM) and drug dose adjustments reported in 69%. Most cases (73%) maintained a stable seizure frequency. Conclusions: This study provides new Canadian data on PPWE at a tertiary care center. PPWE are overall well controlled, more likely to have young adult onset, genetic generalized epilepsy with nearly all taking ASM(s) during pregnancy. While high rates of TDM and drug dose adjustments were observed, most experienced seizure stability in pregnancy.

Frequency multiplexed dual-pulse fiber-optic Φ-OTDR for a fading-free distributed fiber sound sensor

Distributed fiber-optic sensor utilizing optical interference signal detection of the Rayleigh backscattering (RBS) light along the fiber under test (FUT) has greatly progressed over the past 20 years. It can now realize real-time sound signal recovery along the FUT with a good fidelity and high sensitivity. However, the performance of the practical distributed fiber-optic sound sensor is still limited by the fading problem, as invalid spatial channels at unknown positions arise due to the low signal intensity at these positions and the resulting near-zero signal-to-noise ratio (SNR). In this paper, we propose a novel, to the best of our knowledge, fading-free fiber sensor structure by incorporating an acousto-optic frequency shift (AOFS) loop into the light source in a dual-pulse phase optical time domain reflectometry (Φ-OTDR). As a result of stable frequency shifting and feedback within the loop, the loop source can output a high-repetition-rate narrow pulse train consisting of multiple separated frequencies. This pulse train is further shaped into two pulse bursts by an acousto-optic modulator (AOM) and an in-balanced fiber-optic Mach–Zehnder interferometer (MZI). The pulse bursts are then sent into the sensing fiber, while the RBS light is detected using an Avalanche photodiode after an erbium-doped fiber amplifier. The experimental results show that the proposed structure is capable of vibration signal recovery with a good SNR all along the FUT. The fading-free performance is evaluated under different AOFS loop gains, showing significant potential in practical fiber sensor network applications.

Improvement of the Transient Stability of Grid Connected Microgrids Including Inverter Based DGs Using DSTATCOM

Microgrids are becoming popular because they can meet the needs of people who want energy from natural sources and are using more and more energy. Itis important to emphasis on numerous safety and control features of a microgrid. During the change from following the grid to forming the grid, the instability of frequency and voltage due to control problems becomes the main concern. Then, the paper uses a method to control the frequency and voltage of power generators so they can share power efficiently. Furthermore, we are suggesting a way to handle situations when there is not enough control and to keep the system strong. We are proposing a method to prioritize and shed different parts of the system in three stages to help with this. The effectiveness of the method depends on how quickly the system reacts and is calculated based on the changing speed of the frequency. The process combines the battery capacity system and D-STATCOM in the microgrid to provide a reliable power supply to customers for a long time without sudden power cuts. We test the proposed procedures on a smaller version of an IEEE 13-bus microgrid using MATLAB. We recreate the time-domain to see if the procedures work well.

Self-Frequency Tracking for Fixed-Ratio Switch-Capacitors in Data Center Application without Extra Sensors

As research into data centers progresses, the importance of resonant switched-capacitor converters in power supply design becomes more evident. Practical applications reveal that the values of resonant capacitors and inductors may deviate from their nominal values due to various factors, leading to resonant frequency instability. This instability poses a challenge to power electronics technology, affecting system reliability and performance. This paper analyzes the effect of frequency deviation on system functionality, identifies the relationship between output voltage and switching frequency, and proposes a self-tracking frequency strategy to address this issue. Through experimental validation, this approach shows that it maintains synchronization between switching and resonant frequencies, reducing losses associated with frequency misalignment. Simulation and experimental results validate the converter’s stable operation and its ability to achieve zero-voltage and zero-current switching.

Investigation of a dexterous actuator integrated with magnetorheological bearings towards high switching frequency and fast response

Actuators are pivotal for empowering robots to execute a wide array of tasks and adapt to diverse surroundings. However, conventional actuators with a low switching frequency and a prolonged response time significantly comprise the adaptability of robots, restricting them to single operation conditions. This paper presents a solution to this issue by introducing a dexterous actuator integrated with magnetorheological bearings (referred to as MR actuator) for real-time controllable damping. Compared to conventional actuators, the MR actuator boasts exceptional dexterity, featuring a significantly-elevated switching frequency and swifter response time. To validate the remarkable dexterity of this MR actuator, rapid commutation tests and transient response experiments were conducted. Impressively, the MR actuator achieved a stable switching frequency of up to 10 Hz, surpassing that of conventional actuators (2 Hz). Moreover, it demonstrated a reduced response time and a heightened energy efficiency. Beyond robotics, applications of MR actuators are also found in areas requiring an improved machinery precision and production efficiency.

Enhanced energy storage performance, breakdown strength, and thermal stability in compositionally designed relaxor Eu3+ substituted Na0.2K0.3Bi0.5TiO3

Lead-free Eu3+ substituted NKBT ceramics (Na0.2K0.3Bi0.5-xEuxTiO3, x = 0 (Eu 0),0.02(Eu 2),0.04(Eu 4), and 0.06(Eu 6)) were strategically designed via a local random field approach. The structural evolution had been confirmed through X-ray diffraction analysis. The observation of a broad dielectric curve supported the enhanced relaxor nature and the phenomena reflected in the P-E and S-E loops. The diffuse phase transition transforms to the plateau-type feature with excellent thermal stability with ±20 % and ± 40 % variation in dielectric constant over the temperature range of 120 to 500 °C and 90 to 500 °C, respectively in Eu 4. A large recoverable energy density of 1.7 J/cm3 with a high breakdown strength of 188 kV/cm was achieved in the Eu 2 sample at room temperature, making it a potential candidate for energy storage application. Moreover, the frequency stability (0.1 to 500 Hz range), thermal stability (45 °C to 85 °C), and fatigue measurement (10−1 to 106 cycles) were performed from the application point of view. The highest efficiency (82 %) was also achieved in the Eu 6. The negligible Sneg of Eu-rich compositions proves the existence of a relaxor state when the field is removed, and it transforms into the ergodic relaxor state. Furthermore, the SRBRF model is exploited to understand and correlate the transformation from normal to relaxor ferroelectrics with their properties. The current study provides a novel idea for compositional design for energy density, efficiency, and thermal stability ceramics by modifying and creating weakly coupled polar phases with rare earth substitution.

The preparation and magnetic properties of FeSiCr/MoS2 soft magnetic composites

Abstract Two-dimensional layered material MoS2 was used as a high-resistance insulating material and coated on FeSiCr magnetic powder, and FeSiCr/MoS2 composites with low loss and high permeability were successfully prepared. The morphology and magnetic properties of FeSiCr/MoS2 composites were analyzed by XRD, SEM and B-H analyzer. The results show that although the addition of MoS2 will dilute the magnetic properties of FeSiCr, it still has high permeability and obviously reduces the magnetic loss of FeSiCr powder. At the same time, the addition of MoS2 also improves the frequency stability and quality factor of the composite powder cores. Especially, when the MoS2 content is 1.5 wt%, FeSiCr/MoS2 composites show the best magnetic properties after annealing at 500 ℃. with a loss of 330 mW/cm3 and permeability of 66.75 (Bm =20 mT and f =1000 kHz). It can be seen that the MoS2 coating has a good effect on reducing the magnetic loss of powder core, which significantly improves the possibility of application of SMCs at high frequency.

Development of Grid-Forming and Grid-Following Inverter Control in Microgrid Network Ensuring Grid Stability and Frequency Response

This paper proposes a control strategy for grid-following inverter control and grid-forming inverter control developed for a Solar Photovoltaic (PV)–battery-integrated microgrid network. A grid-following (GFL) inverter with real and reactive power control in a solar PV-fed system is developed; it uses a Phase Lock Loop (PLL) to track the phase angle of the voltages at the PCC and adopts a vector control strategy to adjust the active and reactive currents that are injected into the power grid. The drawback of a GFL inverter is that it lacks the capability to operate independently when the utility grid is down due to outages or disturbances. The proposed grid-forming (GFM) inverter control with a virtual synchronous machine provides inertia to the grid, generates a stable grid-like voltage and frequency and enables the integration of the grid. The proposed system incorporates a battery energy storage system (BESS) which has inherent energy storage capability and is independent of geographical areas. The GFM control includes voltage and frequency control, enhanced islanding and black start capability and the maintenance of the stability of the grid-integrated system. The proposed model is validated under varying irradiance conditions, load switching, grid outages and temporary faults with fault ride-through (FRT) capability, and fast frequency response and stability are achieved. The proposed model is validated under varying irradiance conditions, load switching, grid outages and line faults incorporating fault ride-through capability in GFM-based control. The proposed controller was simulated in a 100 MW solar PV system and 60 MW BESS using the MATLAB/Simulink 2023 tool, and the experimental setup was validated in a 1 kW grid-connected system. The percentage improvement of the system frequency and voltage with FRT-capable GFM control is 69.3% and 70%, respectively, and the percentage improvement is only 3% for system frequency and 52% for grid voltage in the case of an FRT-capable GFL controller. The simulation and experimental results prove that GFM-based inverter control achieves fast frequency response, and grid stability is also ensured.

Martian column CO2 and pressure measurement with spaceborne differential absorption lidar at 1.96 µm

Abstract. By utilizing progress in millijoule-level pulsed fiber lasers operating in the 1.96 µm spectral range, we introduce a concept utilizing a spaceborne differential absorption barometric lidar designed to operate within the 1.96 µm CO2 absorption band for remote sensing of Martian atmospheric properties. Our focus is on the online wavelength situated in the trough region of two absorption lines, selected due to its insensitivity to laser frequency variations, thus mitigating the necessity for stringent laser frequency stability. Our investigation revolves around a compact lidar configuration, featuring reduced telescope dimensions and lower laser pulse energies. These adjustments are geared towards minimizing costs for potential forthcoming Mars missions. The core measurement objectives encompass the determination of column CO2 absorption optical depth, columnar CO2 abundance, surface atmospheric pressure, and vertical distributions of dust and cloud layers. Through the amalgamation of surface pressure data with atmospheric temperature insights garnered from sounders and utilizing the barometric formula, the prospect of deducing atmospheric pressure profiles becomes feasible. Simulation studies validate the viability of our approach. Notably, the precision of Martian surface pressure measurements is projected to surpass 1 Pa when the aerial dust optical depth is projected to be under 0.7, a typical airborne dust scenario on Mars, considering a horizontal averaging span of 10 km.

Influence of a magnetic field on the frequency of a laser stabilized to molecular iodine

We report on the effect of a weak magnetic field applied on an iodine cell used to frequency stabilize a laser. A 1.5 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m laser is frequency tripled in order to excite the molecular transitions at 0.51 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m and frequency locked on a hyperfine line. With this frequency reference, we report short-term stability about 3×10-14τ-1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3 \ imes 10^{-14}~\ au ^{-1/2}$$\\end{document}, with a minimum value of 4×10-15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$4 \ imes 10^{-15}$$\\end{document} at 200 s. The lower part of 10-15\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-15}$$\\end{document} frequency stability domain is reached, in our case, only by adding an efficient magnetic shield around the sealed quartz iodine cell. In order to quantify the Zeeman effect, we applied magnetic fields of several ×10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes 10^{-4}$$\\end{document} T on the cell containing the iodine vapour. The Zeeman effect affects the lineshape transition in such a way that we observe a modification of the laser frequency. We have measured this linear Zeeman shift at (1062±6)×104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(1062\\pm 6) \ imes 10^{4}$$\\end{document} Hz/T for the a1 hyperfine component of the R(34) 44-0 transition, near 514 nm by applying a magnetic field along the cell. Thus, in case of uncontrolled magnetic fields of an order of magnitude of 1×10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ imes 10^{-4}$$\\end{document} T, the frequency stability is limited in the upper of the 10-14\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-14}$$\\end{document} domain.

Physics Package Based on Intracavity Laser Cooling 87Rb Atoms for Space Cold Atom Microwave Clock

Abstract This article proposes a new physics package to enhance the frequency stability of the space cold atom clock with the advantages of a microgravity environment. Clock working processes, including atom cooling, atomic state preparation, microwave interrogation, and transition probability detection, are integrated into the cylindrical microwave cavity to achieve a high-performance and compact physics package for the space cold atom clock. We present the detailed design and ground-test results of the cold atom clock physics package in this article, which demonstrates a frequency stability of 1.2 × 10-12 τ-1/2 with a Ramsey linewidth of 12.5 Hz, and a better performance is predicted with a 1 Hz or a narrower Ramsey linewidth in microgravity environment. The miniaturized cold atom clock based on intracavity cooling has great potential for achieving space high-precision time-frequency reference in the future.

Dielectric and energy storage properties of (Ba0.2Sr0.2Na0.2Ca0.2La0.2)(ZrxTi1‐x)O3 high‐entropy ceramics and thin films

AbstractA series of (Ba0.2Sr0.2Na0.2Ca0.2La0.2)(ZrxTi1‐x)O3 (BSNCLZxT1‐x) (x = 0, 0.05, 0.1, 0.15, and 0.2) high‐entropy ceramics were prepared in forms of bulks and thin films by conventional sintering and spin‐coating, respectively. All ceramic bulks and thin films are composed of a single perovskite‐structured solid solution. The introduction of the Zr element reduces the dielectric loss of bulks and thin films and improves the frequency stability of the dielectric constant. The ceramic bulks have a higher dielectric constant and lower loss than their corresponding thin films. As x rises from 0 to 0.2, the breakdown strength Eb of the ceramic bulks increases from 209 to 327 kV/cm, and that of thin films enhances from 890 to 1770 kV/cm. The bulks and thin films of BSNCLZ0.1T0.9 possess the maximum recoverable energy density Wrec (0.82 and 3.48 J/cm3) and energy storage efficiency η (95.8% and 86.8%).

Dark solitons and their bound states in a nonlinear fiber with second- and fourth-order dispersion

We study the excitations of dark solitons in a nonlinear optical fiber with the second- and fourth-order dispersion, and find the emergence of striped dark solitons (SDSs) and some multi-dark-soliton bound states. The SDSs can exhibit time-domain oscillating structures on a plane wave, and they have two types: the ones with or without the total phase step, while the multi-dark-soliton bound states exhibit different numbers of amplitude humps. By the modified linear stability analysis, we regard the SDSs as the results of the competition between periodicity and localization, and analytically give their existence condition, oscillation frequency, and propagation stability, which show good agreements with numerical results. We also provide a possible interpretation of the formation of the existing striped bright solitons (SBSs), and find that SBS will become the pure-quartic soliton when its periodicity and localization carry equal weight. Our results provide the theoretical support for the experimental observation of striped solitons in nonlinear fibers, and our method can also guide the discovery of striped solitons in other physical systems.

The Effect of Sintering Temperature on the Densification and Magnetic Performance of NiCuZn-Ferrites (CuO: 0-6 wt.%).

This article reported on the effect of Cu-content and sintering temperature on the magnetic permeability and power losses of monolithic iron-deficient NiCuZn-ferrite components with low Cu-contents aimed to be used for power applications at frequencies up to 1 MHz. In particular NiαZnb1-xCuxFe1.9O4 ferrite compositions are investigated with a constant Ni/Zn atomic ratio a/b = 0.9 and 0 < x < 0.017. As found, the addition of Cu enables the achievement of good magnetic performance at lower sintering temperatures and, therefore, lower production cost. At all Cu-contents, the initial permeability as a function of the sintering temperature passes through a maximum above which structural deterioration due to asymmetric grain growth occurs. The temperature at which this maximum permeability occurs depends on the Cu content and coincides with the achievement of the maximum density of 5.1-5.2 g cm-3 (relative density ~97%). At Cu-contents x = 0.006-0.012 and sintering temperatures 1200-1100 °C power losses (tan(δ)/μ at 1 MHz, 25 °C) οf 50 × 10-6 could be achieved and initial permeabilities (10 kHz, 0.1 mT, 25 °C) of around 400 with very good frequency and temperature stability. At CuO content higher than 4 wt.% (i.e., x > 0.012) and sintering temperatures higher than 1150 °C, pronounced microstructural disturbances due to asymmetric grain growth result in low permeabilities and high losses. It is suggested that at low CuO contents and low sintering temperatures, the densification enhancement may not proceed through Cu-rich phase segregation but through the creation of oxygen vacancies.