Optimal Operating Frequency Research Articles

Selectively enhanced violet and infrared position sensitive photodetectors based on RTA treated ZnO/Si

Position sensitive detectors (PSDs) based on lateral photovoltaic effect (LPE) are extremely versatile in many areas. Generally speaking, it has an optimal operating frequency which corresponding to the best sensitivity. How to effectively adjust a certain operating frequency in a fixed structure and achieve a large sensitivity improvement has always been a challenge. Here, we demonstrate an unusual selectively enhanced violet and near-infrared LPE observed in rapid thermal annealing (RTA) treated ZnO/Si homo-heterostructure. It exhibits excellent performance in the wavelength of 445 nm and 980 nm, and the optimum lateral photovoltage (LPV) sensitivity can be controlled by manipulating the annealing temperature. Notably, the optical response time of the annealed sample is increased by about 25 times compared with the as-deposited one. We attribute this anomalous effect to the defect ionization in ZnO layer, as well as the resistivity change after annealing. This work suggests an effective approach that can selectively enhance the sensitivity of PSDs in violet and infrared region. Moreover, it shows high sensitivity and fast photoresponse speed, which may open new paths toward violet and infrared photoelectric detection.

Design Optimisation of a Current-Fed Solid-State Transformer for MV Grid-Connected Applications

For integrating large batteries in the medium voltage grid, current fed solid-state transformers offer galvanic isolation and a significant weight and size reduction. While the power losses increase with frequency and flux density, the core volume is contrariwise. Therefore, a design optimisation to achieve minimum losses and/or a minimum volume is essential. An optimisation strategy is proposed in this paper to find the optimum operating frequency and core flux density under certain practical constraints such as winding voltage per turn, clearance between transformer windings, saturation flux density and minimum efficiency. Differently from previous works, the proposed strategy provides a holistic approach for the design considering all main power losses from all main components using nonsinusoidal voltage waveforms and different operating conditions. Analytical equations for the power losses calculation and the cores design are derived and validated using ANSYS and MATLAB Simulink software packages. Simulation results of the power loss calculation under different operating frequencies and duty cycles are presented and compared with the analytical results. A case study for designing a 1.0 MW, 0.6/18 kV current fed solid-state transformer is presented. The results of two optimisation objectives, minimum power losses or minimum total cores housing volume are also shown.

Performance analysis of free piston linear generator coupling organic Rankine cycle system for waste heat recovery

• FPLG has been coupled with ORC system for the first time. • ORC-FPLG combined system simulation model is established. • Performance study of combined system have been performed. • Parameter analysis of combined system with different conditions has been studied. As a novel energy conversion device, free piston linear generator (FPLG) has high potential for organic Rankine cycle (ORC) system. In this study, a FPLG simulation model has been established and the accuracy is verified, then the ORC-FPLG combined system simulation model is established for the first time. The performance study and parameter analysis has been performed. The results show that the simulation results are consistent with the experiments, all the relative errors are in the range of ± 10%, which indicates the accuracy of FPLG simulation model. The operation parameters (such as speed, operation frequency and condenser temperature) have significant influence on the ORC-FPLG combined system. The lower the pump speed is, the higher the maximum power output and minimum power input are. The net power output of combined system increases with operation frequency, exhaust temperature, exhaust mass flow rate and cooling water flow rate. Thermal efficiency decreases with condenser temperature and pump speed. There exists an optimal operation frequency achieving the maximum net power output. When operation frequency is 16 Hz, the maximum value of net power output and thermal efficiency can reach up to 2.26 kW and 1.72%.

Improving Output Performance of a Resonant Piezoelectric Pump by Adding Proof Masses to a U-Shaped Piezoelectric Resonator.

This study proposes the improvement of the output performance of a resonant piezoelectric pump by adding proof masses to the free ends of the prongs of a U-shaped piezoelectric resonator. Simulation analyses show that the out-of-phase resonant frequency of the developed resonator can be tuned more efficiently within a more compact structure to the optimal operating frequency of the check valves by adjusting the thickness of the proof masses, which ensures that both the resonator and the check valves can operate at the best condition in a piezoelectric pump. A separable prototype piezoelectric pump composed of the proposed resonator and two diaphragm pumps was designed and fabricated with outline dimensions of 30 mm × 37 mm × 54 mm. Experimental results demonstrate remarkable improvements in the output performance and working efficiency of the piezoelectric pump. With the working fluid of liquid water and under a sinusoidal driving voltage of 298.5 Vpp, the miniature pump can achieve the maximum flow rate of 2258.9 mL/min with the highest volume efficiency of 77.1% and power consumption of 2.12 W under zero backpressure at 311/312 Hz, and the highest backpressure of 157.3 kPa under zero flow rate at 383 Hz.

Coupling Adjacent Microgrids and Cluster Formation Under a Look-Ahead Approach Reassuring Optimal Operation and Satisfactory Voltage and Frequency

Microgrids (MGs) are promising approaches to proliferate distributed energy resources for electrification in remote areas. However, to deal with the uncertainties of renewables and energy demand, special measures are required. Energy storages, controllable loads and reconfigurable networks are some of those measures that improve MGs' flexibility. Another alternative is temporarily coupling the adjacent MGs to support each other and form coupled MGs (CMGs). This paper proposes a look-ahead technique to form CMGs while reassuring the optimal performance of all MGs. Preserving the voltage and frequency of each MG is also another key objective. The proposed optimization approach tries to solve the voltage/frequency problem by forming the CMGs when the local actions (such as energy storages) are inadequate or cost-ineffective. The proposed technique considers the operational cost, technical and environmental aspects, reliability and losses in the CMG formation. This technique is general and can be used for complex topologies and also to form multiple CMGs if deemed more suitable. The performance of the developed technique is validated through extensive numerical analyses in MATLAB.

Optimal Design of LLC Resonant DC Transformer under Adaptive Frequency Tracking Strategy

In recent years, the LLC (inductor–inductor–capacitor) DC transformer has been widely used in communication and computer power supply because of its advantages of zero voltage conduction of primary switch and zero current turn off concerning the output rectifier diode. To obtain higher transmission efficiency and make the LLC DC transformer always run at the optimal operating point, the switching frequency of the LLC DC transformer should work at the resonance frequency of the circuit. In actual conditions, the optimal operating frequency of the LLC DC transformer will be changed due to the influences of the working condition on the circuit parameters and the load change. Therefore, the LLC DC transformer controlled by the fixed frequency mode will not be in the best working condition. In this paper, an adaptive frequency tracking method is used to control the circuit; when the circuit parameters change, the LLC DC transformer can always be in the best working state. Then, the influence of circuit parameters such as output power and excitation inductor on the optimal working point of the LLC DC transformer is analyzed in detail. Finally, a 1 kW LLC resonant converter prototype is designed under laboratory conditions to verify the feasibility of the control strategy.

Metallic Cavity Excitation for Desired z-Component Electric Field

The field patterns in a metallic cavity can be described by eigen modes. These electric field modes are obtained by solving the wave equation with perfect electric conductor (PEC) boundary conditions. In this letter, the authors introduce the relation between the electric field coefficients of a desired excitation function and the cavity modes coefficients, which means that for a given field pattern, we find the amplitude of the excitation modes that yield the best approximation of the desired excitation function in the cavity. This relation is done using the excitation matrix. By minimizing the error function, the optimal frequency of operation can be found and so the amplitudes of the excitations. The proposed analysis has been validated using high frequency structure simulator (HFSS) commercial software simulation.

Detection of Sub-Surface Objects Under Statistically Uneven Soil Surface by Parametric Radar Method

The problem of sensing subsurface objects by the method of excitation of the earth’s surface by Rayleigh seismic waves and obtaining information about the displacement of the ground above the target by radar method, taking into account the electromagnetic parameters of the underlying soil in the frequency range of 10 GHz, is considered. Recommendations are given on the optimal operating frequency of the radar in operating conditions on a statistically uneven ground surface

Optimum Operating Frequency for Electrocoalescence Induced by Pulsed Corona Discharge.

Current oil–water separation methods require a significant power, a high processing time, and costly equipment, which typically yield low treatment efficiency. Pulsed direct current (dc) electric fields and recently nonuniform electric fields caught considerable attention in the petroleum industry research in order to address the most common oil–water separation issues such as chain formation, partial coalescence, and low efficiency in either the energy consumption or coalescence rate. Here, a contact-less charge injection method induced by corona discharge is utilized to investigate the impacts of nonuniform and pulsed dc electric fields on the coalescence of water droplets inside an oil medium. The operating process parameters were experimentally calibrated and optimized with the goal of increasing the effectiveness and energy consumption efficiency of the coalescence process. High-speed imaging and image processing techniques were used in order to investigate the effect of different active forces (i.e., dipole–dipole interaction, migratory coalescence, or electrophoresis, and dielectrophoresis) during the coalescence process. Different pulsed dc frequencies and pure dc waveforms were utilized and their impact on the coalescence of water droplets was investigated. An optimal coalescence recipe was proposed by continuous measurement of the distance, velocity, and acceleration of the coalescing water droplets. The results of this study suggest use of pulsed dc and pure dc electric fields for coalescence of water droplets in concentrated and dispersed emulsions, respectively.

Microporous copper chromite thick film based novel and ultrasensitive capacitive humidity sensor

In this paper we report to have developed a microporous Copper Chromite (CuCr2O4) thick film based capacitive humidity sensor that exhibits excellent response in the range of 1%–98% RH at room temperature. CuCr2O4 spinel nanopowder was synthesized by a facile sol-gel technique. The as prepared CuCr2O4 nanopowder was screen printed to develop a thick film and it was sandwiched between two parallel electrodes of silver and copper to develop a parallel plate capacitive sensor. The CuCr2O4 nanoparticles and the thick film were well characterized by XRD, XPS, FTIR spectroscopy, Raman Spectroscopy, FESEM, TEM, EDX, and contact angle measurement. Various electrical parameters of the sensor, viz. Capacitance (Cp), Dissipation (D), Conductance (Gp), Susceptance (Bp), and admittance (Y) were measured at different frequencies ranging from 100 Hz to 1 MHz. It was observed that the optimum operating frequency is 1 kHz. At this frequency the sensor exhibited very high sensitivity, especially in the low %RH range of 1%–40% (∼640 pF change in capacitance), low dissipation loss (<2 for all %RH range), and fast response (∼3.6 s) and recovery times (128 s). Further, the sensor exhibits long-term stability (at least 6 months). The sensor may find commercial applications in food packaging, tea industry, hospitals, power plants etc.

Optimal Planning and Operation of Multi-Frequency HVac Transmission Systems

Low-frequency high-voltage alternating-current (LF-HVac) transmission scheme has been recently proposed as an alternative solution to conventional 50/60-Hz HVac and high-voltage direct-current (HVdc) schemes for bulk power transfer. This paper proposes an optimal planning and operation for loss minimization in a multi-frequency HVac transmission system. In such a system, conventional HVac and LF-HVac grids are interconnected using back-to-back (BTB) converters. The dependence of system MW losses on converter dispatch as well as the operating voltage and frequency in the LF-HVac is discussed and compared with that of HVdc transmission. Based on the results of the loss analysis, multi-objective optimization formulations for both planning and operation stages are proposed. The planning phase decides a suitable voltage level for the LF-HVac grid, while the operation phase determines the optimal operating frequency and power dispatch of BTB converters, generators, and shunt capacitors. A solution approach that effectively handles the variations of transmission line parameters with the rated voltage and operating frequency in the LF-HVac grid is proposed. The proposed solutions of the planning and operation stages are evaluated using a multi-frequency HVac system. The results show a significant loss reduction and improved voltage regulation during a 24-hour simulation.

Model-Based Analysis and Regulating Approach of Air-Coupled Transducers with Spurious Resonance.

As an essential characteristic of air-coupled transducers, electrical impedance can provide valuable information for quality control during manufacturing of transducers. It is also found feasible to directly read the optimal operating frequency from the impedance plots when the resonance is independent of the others. However, the spurious resonance emerges when two neighboring resonances are closely spaced, resulting in distorted impedance and ambiguous optimal operating frequency. In this paper, the electrical impedance of air-coupled transducers with spurious resonance is modeled using the Butterworth–Van Dyke (BVD) equivalent circuit. Then model-based sensitivity analysis is performed to evaluate the mutual interference between adjacent resonances. Based on the analysis results, the prestress method is proposed to regulate and suppress the spurious resonance by adjusting the equivalent parameters of the BVD model. Experimental study was carried out on the response of the electrical impedance and the vibration velocity of the transducer with spurious resonance to pre-tightening force. The results show that the spurious resonance disappeared when the pre-tightening force was initially loaded. Moreover, the vibration velocity of two main resonance peaks increases about 45.6% and 33.9% as the pre-tightening torque increases to 0.25 N∙m. Hence it is validated that the proposed prestress method is efficient to suppress the spurious resonance and improve the transducers performance.

Inductive Imaging of the Concealed Defects with Radio-Frequency Atomic Magnetometers

We explore the capabilities of the radio-frequency atomic magnetometers in the non-destructive detection of concealed defects. We present results from the systematic magnetic inductive measurement of various defect types in an electrically conductive object at different rf field frequencies (0.4–12 kHz) that indicate the presence of an optimum operational frequency of the sensor. The optimum in the frequency dependence of the amplitude/phase contrast for defects under a 0.5–1.5 mm conductive barrier was observed within the 1–2 kHz frequency range. The experiments are performed in the self-compensated configuration that automatically removes the background signal created by the rf field producing object response.

Compact wireless power transfer system with microstrip-driven coupled dielectric resonators

A compact, low-cost, and highly efficient wireless power transfer (WPT) system is presented. Besides transferring power, this system provides the required bandwidth for data communication; thus, it can be exploited as a wireless digital connector. It utilizes two off-the-shelf cylindrical dielectric resonators with a dielectric constant of 33 and a loss tangent of 2.5×10-4. The mutually coupled dielectric resonators operate in their magnetic-dipole mode. The resonance frequency of this mode determines the optimum operating frequency of the system which is approximately 7 GHz. The power transfer efficiency of more than 43% is maintained for distances up to four times the resonator radius. The maximum power transfer efficiency as a function of distance and misalignment is computed and experimentally verified. Its relative bandwidth renders the proposed WPT system appropriate for high-rate data transmission.

P‐129: Operating Frequency and Sensitivity Prediction of In‐Display Ultrasonic Fingerprint Sensing Systems

This work presents an operating frequency and sensitivity evaluation methodology for an ultrasonic fingerprint on display (FoD). Understanding the underlying physics of the complicated, highly coupled behavior of electromechanical sensors is indispensable for predicting the responses of ultrasonic waves in the multi‐layered system. And predicting the behavior of the ultrasonic waves in a multi‐layered display panel structure is critical for evaluating and optimizing its performance. In this work, we evaluated the optimal operating frequencies from Fabry‐erot resonance and represented acoustic pressure imaging at an operating frequency by developing the Finite Element Method (FEM) based numerical analysis models. This work allows engineers to predict behavior of devices, modify and optimize the designs efficiently

A novel MEMS triboelectric energy harvester and sensor with a high vibrational operating frequency and wide bandwidth fabricated using UV-LIGA technique

A novel triboelectric energy harvesting (TEH) and sensing system scaled down to microelectromechanical systems (MEMS) size is presented. The design is structurally optimized for harvesting the highest average power and power density while ensuring the structural robustness. Unlike traditional triboelectric energy harvesters, this design results in a high operating frequency with a wide bandwidth. Adoption of MEMS fabrication techniques including the use of spin-coated Teflon AF rather than a Teflon sheet, adaptation of UV-LIGA (Ultra-Violet Lithographie, Galvanoformung, Abformung) with modifications and implementation of a thick polyimide sacrificial layer make the fabrication process unique. If excited by ±9.33 g external vibration with a frequency of 1.15 kHz, the TEH can generate 0.179 μW average power and 0.597 μW peak power at an optimum resistive load of 256 kΩ. The peak surface power density, volumetric power density and acceleration-normalized volumetric power density reach 3.98 μWcm−2, 2.64 mWcm-3 and 30.3 μWcm-3/g2, respectively. While the surface power density of the presented TEH is moderate, the volumetric power density and acceleration-normalized volumetric power density are quite competitive among the state-of-the-art designs. The TEH also demonstrates a wide operating frequency bandwidth of 920 Hz. If operated as an accelerometer, the device shows a linear sensitivity of 43 mV/g. Although the simulation predicts the optimum operating frequency and load resistance of the system to be at 800 Hz and 10 MΩ, respectively, the experimental results demonstrate these values to be at 1150 Hz and 256 KΩ. A few fabrication anomalies, most notably the notching in the Teflon layer and bowing of the proof-mass, are responsible for this deviation. In addition, a distortion is observed in the simulated output voltage profile which is not present in the experimental output voltage profile due to the presence of the parasitic capacitance in the experimental circuit. The aforementioned triboelectric energy harvester can have specific applications in the sensor and actuator systems in the aircraft industry as well as in the automobile industry, micro-robotic systems, prosthetic systems, and sensor nodes in the internet of things (IoT) due to its operating frequency and bandwidth range.

Modeling and Simulation of a Micro pump and Its Performance. (Dept. M ( Power ) )

A transient 2D model of Valve-less micro-pump is constructed and used to study pump performance under different conditions through numerical simulation. Operating conditions, design parameters and fluid properties effect on the micro pump net flow rate have been investigated. The operating frequency was found to be a critical operating parameter. Therefore, the effect of other design and operating conditions on the resonance frequency (optimum operating frequency) has been studied. Also, general correlations for the micro pump dimensionless performance characteristics have been deduced with sufficient accuracy, within the studied range.

Performance optimization of test facility for coaxial transmission line components based on traveling wave resonator.

As part of development program for a high power co-axial transmission line component test facility, an existing traveling wave resonator based test stand is modified to improve power gain and ring return loss. The 10 dB directional coupler in the earlier test stand is replaced with a 14 dB directional coupler to couple radio frequency power with the ring. To achieve an improved isolation and return loss, the 14 dB directional coupler design is equipped with two broadside strip-lines with a tunable gap between them. Detailed design and optimization of the 14 dB directional coupler with and without the traveling wave resonator setup is performed using a high frequency simulator Computer Simulation Technology Microwave Studio. The low power test of the fabricated directional coupler is performed at several tuning positions to achieve an optimum operating frequency for the traveling wave resonator. Furthermore, after optimization, the maximum power gain of around 18 dB and minimum return loss of about -22 dB inside the ring are obtained. Finally, a preliminary study of the future 3 MW test facility is discussed.

A misalignment-adaptive wireless power transfer system using PSO-based frequency tracking

One of the major challenges in inductive wireless power transfer (WPT) systems is that the optimal frequency of operation may shift predominantly due to coupling variation as a result of so-called frequency splitting phenomenon. When frequency splitting occurs, two additional resonance frequencies split from the coupler’s resonance frequency. Maximum power levels are observed at these split resonance frequencies; however, these frequencies are strongly-dependent on the coupling coefficient, hence the distance and alignment between the couplers. In addition to that, peak power values at these frequencies can be different from each other due to small impedance differences between the primary and secondary side resonant couplers, forming a local and a global maximum. Therefore, the WPT system should adaptively operate at the correct frequency for achieving maximum power transfer. In this paper, a metaheuristic Particle Swarm Optimization (PSO) based frequency tracking algorithm is proposed for use in WPT systems. The WPT system employs multi sub-coil flux pipe couplers, a full-bridge inverter which is driven by TMS320F28069 controller card and is suitable for high power charging applications. The control algorithm can accurately find the global maximum power point in case of frequency splitting with asymmetric peaks. The proposed frequency tracking algorithm operates only at the primary side based on measurement of the input power level. Therefore, no additional communication link is needed between the primary and the secondary side. Effectiveness of the proposed control method is validated by performing experiments under three different misalignment scenarios and compared to the traditional Perturb and Observe algorithm.

Adaptive Frequency Control of a Sensorless-Receiver Inductive Wireless Power Transfer System Based on Mixed-Compensation Topology

In this article, an adaptive frequency control scheme of a sensorless-receiver inductive wireless power transfer system for battery charging applications is proposed. The mixed-compensation topology is utilized instead of the conventional topologies to deliver power more efficiently. Perturb and observe is proposed to track the optimal operating frequency to achieve maximum transfer efficiency or maximum output power delivery. Moreover, the paper proposes a highly accurate analytical model considering the nonlinear effect of the ac/dc rectifier-stage. Two subsystems are considered: a rectifier based resistive-load, and a rectifier based battery-load. The rectifier based battery-load is represented as a variable ac voltage source. The proposed model is linearized using the first harmonic approximation technique and generalized using the Thévenin's equivalent representation, thus the proposed model can be applied to any compensation topology. Afterward, a systematic approach is developed based on the proposed model to estimate the connected load information including battery voltage based on sender-side measurements only. This results in a smaller size and increased portability of the receiver. A prototype is designed in small-scale with low-power specifications to comply with implantable biomedical applications to demonstrate and validate the proposed model, estimation approach, and frequency tracking experimentally.