Frequency Tuning System Research Articles

Machine Learning Approach of Optimal Frequency Tuning for Capacitive Wireless Power Transfer System

Wireless power transmission has become a remarkable research topic due to its enormous application potential. Recent advances in machine learning have been shown to be the most promising approach that offers significant capabilities in the wireless power transfer system (WPTS) for selecting the optimal frequency tuning to achieve high efficiency performance. However, developing an automated frequency-tuned system remains a challenge. In this study, a novel frequency-tuned method is presented that utilises machine learning-based models such as neural networks (NN), support vector regression (SVR), and linear regression (LR) to estimate the best efficiency provided by the frequency level at the most optimal frequency tuning level from the experimental dataset, which is capable of aiding in the selection of the most efficient WPTS design. The results show that the SVR has the highest degree of accuracy, making it a promising option for optimising the tuning of power transfer systems while enhancing their performance efficiency. Keywords—Efficiency, frequency tuning, machine learning, neural network, power transfer

Design, Characteristics and Dynamic Properties of Mobile Plunger-based Frequency Tuning System for Coaxial Half Wave Resonators

Design, Characteristics and Dynamic Properties of Mobile Plunger-based Frequency Tuning System for Coaxial Half Wave Resonators

Control of electromagnetic properties during prototyping, fabrication and operation of low-β 325 MHz half-wave resonators

The general steps for the fabrication of a copper prototype of 325 MHz coaxial half-wave resonator (HWR) with β = 0.21 are presented and discussed in this work. The main features for the control of the electromagnetic properties during the manufacturing process of HWR are described in detail. The resonant frequency sensitivity to the accelerating gap and to the cavity height were experimentally estimated. Bead-pull measurements were performed and the electric field distribution along the beam axis of the manufactured cavity was estimated. The features of the cavity’s response in the critical coupling regime are analyzed. The experimental concept of a slow frequency tuning system (FTS) based on the moving plungers is proposed and tested. The tuning sensibility is experimentally estimated. The measured results agree with the simulations quite well, and the sensitivity for a single plunger configuration kHz mm−1 is achieved. The dynamic properties and operation algorithm of the FTS are studied and experimentally investigated.

High-resolution wavemeter based on polarization modulation of fiber speckles

For speckle pattern-based wavemeters or spectrometers, the intermodal and the chromatic dispersion of the diffusion waveguide are key factors in determining the wavelength resolution. In this study, we propose a new mechanism to modulate the fiber speckles aside from the dispersion related effect. The polarization modulation is introduced in a rectangular core fiber (RCF) by using an in-line polarization rotator (IPR). The IPR can rotate the polarization angle at different wavelengths. Interestingly, it is observed that the modulated speckle patterns appear periodically similar, and they present more variations when compared to unmodulated ones. The theoretical simulation indicates that the polarization exerts an influence on the fiber speckles by modulating the mode coupling coefficients when light is coupled into the RCF. In the demonstration experiment, we first built a precise laser frequency tuning system based on an electro-optic modulator and a microwave source. By comparing the recorded speckles with and without polarization modulation, the former speckles have lower correlations, which are evaluated using the Arc Cosine Similarity algorithm. Reconstructing the spectrum of speckles, the smallest detectable wavelength that can be detected with polarization modulation is 0.2 fm. The experimental results prove that the polarization modulation is a convenient and effective method to enhance the speckle’s wavelength sensitivity. In addition, this study paves a new way to design high-resolution wavemeters with shorter, more compact optical waveguides.

Frequency Tuning System Based on Mobile Plungers For Superconductive Coaxial Half Wave Resonators

Frequency Tuning System Based on Mobile Plungers For Superconductive Coaxial Half Wave Resonators

A Cross-Shape Coil Structure for Use in Wireless Power Applications

This paper presents a novel coil structure employing two parallel-connected subunit rectangular coils. The structure is based on the fact that the rectangular coils are less sensitive to misalignment along its longer side. Therefore, two identical subunit rectangular coils are vertically-oriented to one another and connected in parallel to form a cross-shape coil. The cross-shape coils have the advantage of better misalignment tolerance as compared to circular and square coils with similar footprints at the cost of an increased wire usage. Electromagnetic simulations and experiments on various small-sized coils are performed to verify the advantages of the proposed coil structure. Based on the simulation and measurement results, cross-shape coils exhibit not only better tolerance to misalignment, but also smaller self-inductance values resulting in larger coupling coefficients as compared to square and circular coils. A large cross-shape coil pair consisting of 100 × 70 cm subunit rectangles are fabricated with copper tubes and utilized in a frequency-tuned wireless power transfer system. When coils are separated by 17 cm, a near constant efficiency of more than 89% up to 15 cm misalignment along x- or y-directions and 13 cm along diagonal direction is obtained in the frequency-tuned system.

SYSTEM OF AUTOMATIC FREQUENCY CONTROL OF HETERODYNE OF THE RADAR RECEIVER WITH MAGNETRON TRANSMITTER

At present, pulsed magnetrons are leaders in the use in the radar transmitters which is caused by the need to generate powerful high-frequency oscillations and to provide a given coverage range. The disadvantages of magnetrons include a significant level of noise and difficulties in implementing frequency control. For this reason, when using automatic frequency control (AFC), problems arise in controlling the frequency of the pulsed magnetron. In view of this, the AFC of heterodyne of the receiver rather than the one of the magnetron is most often used. The heterodyne frequency is maintained such that the receiver is always tuned to the frequency of the received signal. The objective of this paper is to analyze the existing methods for tuning the heterodyne frequency of pulsed radars with a magnetron transmitter, to develop a concept for building a functional layout and its practical implementation. The functional layout of the automatic frequency tuning system of heterodyne in radar receiver with a magnetron transmitter is developed and described in the paper. A frequency discriminator is used in AFC. The frequency discriminator combines the advantages of a single-cycle circuit (simplicity of design and tuning) and a two-cycle circuit (an output voltage equal to zero at the given magnetron frequency, as well as compensation of variations in the amplitude of the input voltage and interference). The practical implementation of the developed system is presented upon the example of millimeter-wave band radar (40 GHz), where a Gunn diode oscillator with varactor frequency tuning is used as the receiver heterodyne oscillator. In this paper, the electric scheme of a new frequency discriminator and its amplitude-frequency characteristic are shown. An intuitive method was used to develop an electrical schematic diagram. The analysis of the developed scheme was carried out using the method of mathematical modeling. Conclusions are drawn about the novelty of the proposed concept of constructing the AFC of heterodyne radar receivers with a magnetron transmitter and its advantages in comparison with known solutions.

Frequency-tunable electromagnetic energy harvester using magneto-rheological elastomer

This article proposes an idea for the development of a novel frequency-tunable electromagnetic energy harvester, which mainly consists of a frequency-tuning system component and an electromagnetic energy-harvesting component. A magneto-rheological elastomer, a kind of smart material, was utilized in the design of the frequency-tuning part using its unique rheological characteristic that its shear modulus can be altered by changing the strength of an external magnetic field. When external excitation is provided to the system, the tip magnet oscillates relative to the coil to produce electricity. The stiffness of the system’s equivalent torsional spring composed of magneto-rheological elastomer blocks can be altered by changing the gap distance between two tuning magnets, which results in a shift in the primary natural frequency of the system and significant improvement of energy-harvesting efficiency. This article presents the detailed process for the design, simulation, experiment, and fabrication of the proposed energy harvester. Experiments and numerical simulations were also conducted under band-limited random excitation to support the validity of the present system.

Automatic frequency tuning wireless charging system for enhancement of efficiency

An automatic frequency-tuned wireless charging system is proposed and successfully demonstrated to enhance the power transfer efficiency for different vertical spacings between the charging coils in the presence of proximal metallic objects. The frequency characteristics of wireless power transfer efficiency have been investigated through simulation and experimental measurements. It has been observed that the resonance-based wireless charging system is very sensitive to the imperfect positioning of charging coils and nearby metallic objects. At the operating frequency, the power transfer efficiency of the charging system reduces drastically. However, by allowing the transmitting frequency to adapt to the position of the coils and metallic objects through the automatic frequency-tuned system, the deteriorated power transfer efficiency is further improved.

Design of an Electrically Automated RF Transceiver Head Coil in MRI.

Magnetic resonance imaging (MRI) is a widely used nonionizing and noninvasive diagnostic instrument to produce detailed images of the human body. The radio-frequency (RF) coil is an essential part of MRI hardware as an RF front-end. RF coils transmit RF energy to the subject and receive the returning MR signal. This paper presents an MRI-compatible hardware design of the new automatic frequency tuning and impedance matching system. The system automatically corrects the detuned and mismatched condition that occurs due to loading effects caused by the variable subjects (i.e., different human heads or torsos). An eight-channel RF transceiver head coil with the automatic system has been fabricated and tested at 7 Tesla (T) MRI system. The automatic frequency tuning and impedance matching system uses digitally controlled capacitor arrays with real-time feedback control capability. The hardware design is not only compatible with current MRI scanners in all aspects but also it operates the tuning and matching function rapidly and accurately. The experimental results show that the automatic function increases return losses from 8.4 dB to 23.7 dB (maximum difference) and from 12.7 dB to 19.6 dB (minimum difference) among eight channels within 550 ms . The reflected RF power decrease from 23.1% to 1.5% (maximum difference) and from 5.3% to 1.1% (minimum difference). Therefore, these results improve signal-to-noise ratio (SNR) in MR images with phantoms.

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless non-radiative power-transfer (WNPT) systems. Closed-form expressions for the efficiencies of both types of systems are presented as functions of frequency and system (circuit) parameters. In the frequency-tuned system, the operating frequency is adjusted to compensate for changes in mutual inductance that occur for variations of transmitter and receiver loop positions. Frequency-tuning is employed for a range of distances over which the loops are strongly coupled. In contrast, the impedance-tuned system employs varactor-based matching networks to compensate for changes in mutual inductance, and to achieve a simultaneous conjugate impedance match over a range of distances. The frequency-tuned system is simpler to implement, while the impedance-tuned system is more complex, but can achieve higher efficiencies. Both of the experimental wireless non-radiative power-transfer systems studied employ resonant shielded loops as transmitting and receiving devices.

Comprehensive Analysis and Measurement of Frequency-Tuned and Impedance-Tuned Wireless Non-Radiative Power-Transfer Systems

This paper theoretically and experimentally investigates frequency-tuned and impedance-tuned wireless non-radiative power-transfer (WNPT) systems. Closed-form expressions for the efficiencies of both types of systems are presented as functions of frequency and system (circuit) parameters. In the frequency-tuned system, the operating frequency is adjusted to compensate for changes in mutual inductance that occur for variations of transmitter and receiver loop positions. Frequency-tuning is employed for a range of distances over which the loops are strongly coupled. In contrast, the impedance-tuned system employs varactor-based matching networks to compensate for changes in mutual inductance, and to achieve a simultaneous conjugate impedance match over a range of distances. The frequency-tuned system is simpler to implement, while the impedance-tuned system is more complex, but can achieve higher efficiencies. Both of the experimental wireless non-radiative power-transfer systems studied employ resonant shielded loops as transmitting and receiving devices.

Interferometric diameter determination of a silicon sphere using a traceable single laser frequency synthesizer

To determine the absolute diameter of a silicon sphere for the Avogadro constant project, we present a phase-shifting interferometer based on a flat etalon and a traceable single laser frequency synthesizer. By using an optical frequency comb to calibrate a frequency-tunable diode laser, the single laser frequency synthesizer can produce an arbitrary laser frequency with a relative uncertainty of 9.2 × 10−12 in the range of 4 THz. According to the laser frequency tuning system, the Carré algorithm with arbitrary but equal phase steps is employed to calculate the fractional interference phases. The absolute diameter is obtained by measuring the fractional and integral parts based on the principles of phase-shifting interferometry and frequency-sweeping interferometry, respectively. The uncertainty of a single diameter measurement in air is estimated to be 5 nm, whose uncertainty sources from the laser frequency and the phase-shifting algorithm are negligible.

用于汞原子激光冷却的深紫外激光调谐和锁频系统

用于汞原子激光冷却的深紫外激光调谐和锁频系统

0.8V PLL-based automatic frequency tuning system for current-mode filters

Abstract A wide-range automatic frequency tuning system for current-mode filters is proposed in this paper. The cutoff frequency of the tunable filter is controlled by an external reference signal and is locked in the desired frequency through a current-mode based phase locked loop (PLL) circuit. Although the PLL operates in a relatively narrow band, the total tuning range of the topology is extended by interpolating an automatic frequency detector after the reference input and before the PLL. The use of current controlled oscillator, based on same blocks with those in the filter, offers accuracy and feasible design in the control path. The topology has been simulated using MOS transistor models for a 130 nm CMOS technology in 0.8 V supply voltage. The achieved overall automatic tuning range was from 2.3 MHz to 660 MHz.

A current‐mode automatic frequency tuning system for filters with current mirrors

AbstractA new current‐mode automatic frequency tuning system is proposed in this paper. The system is based on the master–slave technique and is suitable for integrated current‐mode filters based on current mirrors. Automatic control is accomplished by controlling the bias current of the current mirrors employed in the master and slave filters. The proposed scheme has been applied in the leapfrog and wave filters and the corresponding simulation results confirm its validity. Copyright © 2009 John Wiley & Sons, Ltd.

OTA based frequency tuning system with reduced effect of DC offsets

An on-line tuning system based on the master–slave technique is proposed in this paper. Each stage of the system is realized by employing only operational transconductance amplifiers (OTAs). The most significant advantage of the introduced topology is the reduction of the influence of the dc offset terms which are critical about the performance of such systems. In addition, an attractive benefit is the suitability for implementing the resulted configurations in both integrated and discrete-component forms using only the same type of active element. The validation of the proposed topology is achieved through simulation and experimental results.

兰州冷却储存实验环高可靠性低电平控制系统

In order to get an RF electric field which has stable amplitude, phase and frequency, the radio frequency low level control system for HIRFL-CSRe has been constructed at Institute of Modern Physics. To ensure the control of stability, reliability and real-time, analogous modules are mainly used. At the same time, digital module is used to coordinate the modules and compensate for non-linear error of some function modules. The system is consisted of three subsystems-phase stabilizing system amplitude control system and frequency tuning system, and mainly uses the technology as PID, RF phase detect, DSP, FPGA and so on. Low-level control system of HIRFL-CSRe has been tested through a long-term stability experiments and high-power experiments, the control accuracy meeting the amplitude accuracy +or-1% and phase control accuracy +or-3deg, frequency tuning accuracy +or-5deg of the technical requirements.

Resonator tuning accuracy in an automatic frequency tuning system for a passive hydrogen frequency standard

An automatic tuning system for a cavity in a passive hydrogen frequency standard is considered, which uses the excitation signal with phase modulation. Numerical and experimental tests have shown that the performance of this system is dependent on the extent of spectrum distortion resulting from the signal and asymmetry of the resonance curve in the UHF cavity.

A 0.6-V Dynamic Biasing Filter With 89-dB Dynamic Range in 0.18-$\mu$m CMOS

This paper presents a 100-kHz fifth-order Chebychev low-pass filter (LPF) using the proposed dynamic biasing (DB) technique which enables wide dynamic range under a low-supply voltage. The change of state variables in the internal nodes of the filter can be corrected by using a novel simplified scheme, avoiding the output transient owing to dynamic biasing. The filter, including an automatic frequency tuning system based on the voltage-controlled-filter (VCF) architecture and voltage reference circuit, is fabricated in a 0.18-mum standard CMOS technology with a 0.5-V threshold voltage and consumes 443 muW from a power supply of 0.6 V. The output noise and the in-band IIP3 are 575 pArms and 219 muA, respectively. The filter achieves a dynamic range of 89 dB.