Resonant Frequency

This paper analyzes a high-power (50 kW) high-frequency (150 kHz) voltage-fed inverter with a series-resonant load circuit for industrial induction heating applications, which is characterized by a full bridge inverter made of insulated-gate bipolar transistor and a power control based on pulse density modulation (PDM). This power control strategy allows the inverter to work close to the resonance frequency for all output-power levels. In this situation, zero-voltage switching and zero-current switching conditions are performed, and the switching losses are minimized. An additional improvement of inverter efficiency is achieved by choosing appropriate values of the modulation index. Results are verified experimentally using a prototype for induction hardening applications. A comparative study between the PDM and the classical power control by frequency variation will be made.

A novel optical technique is proposed for the characterization of MEMS resonators. The proposed technique is based on measuring the response of the resonator (resonance frequency and quality factor) optically, which eliminates the electrical parasitic effects. The proposed technique was applied to a comb-drive resonator and the obtained results show good agreement with the standard electrical technique with 2-5% deviation in the resonance frequency and 2-10% in the quality factor.

The RFQ1 accelerator has been modeled using the MAFIA codes. Calculated resonant frequency shifts due to the introduction of components into the accelerator agree reasonably well with measurements. Heating predictions based on calculated results correspond well with observations.

This paper analyzes a high-power (50 kW) high-frequency (150 kHz) voltage-fed inverter with a series-resonant load circuit for industrial induction heating applications, which is characterized by a full bridge inverter made of insulated-gate bipolar transistor and a power control based on pulse density modulation (PDM). This power control strategy allows the inverter to work close to the resonance frequency for all output-power levels. In this situation, zero-voltage switching and zero-current switching conditions are performed, and the switching losses are minimized. An additional improvement of inverter efficiency is achieved by choosing appropriate values of the modulation index. Results are verified experimentally using a prototype for induction hardening applications. A comparative study between the PDM and the classical power control by frequency variation will be made.

SUMMARY A batch-compatible, post-fabrication annealing technique based upon filament-like heating of microstructures is demon-strated as an effective means for trimming the reSonance fre-quencies (fa's) and increasing the quality factors (Q's) of surface-micromachined, ...

The series and shunt inductivity introduced by the probe and shorting pin respectively in a single-feed shorted rectangular microstrip antenna has been evaluated theoretically using transmission line method. The proposed structure provides compact dual band operation using single feed mechanism. The input impedance, VSWR, and return loss are calculated theoretically. It is found that the ratio of the resonant frequencies highly depends on the position of shorting pin.

Microstrip structures are now widely used in microwave systems because of their geometrical simplicity, small size, and ease of fabrication. The microstrip structure is inhomogeneous along several directions, which makes the accurate analysis of the electromagnetic fields very difficult. Hence, the design of microstrip devices is mostly done with approximative and empirical methods of limited accuracy. In this report the Green's function technique is used to analyze rectangular microstrip patches. Scalar Green's functions corresponding to the microstrip geometry were derived earlier by the authors. With the aid of these functions, surface currents and resonance frequencies of a patch located in the air/dielectric interface can be computed using the method of moments (MoM). To make the implementation of MoM as simple as possible, numerical approximations for scalar Green's functions are developed. These approximations are functions of permittivity, the frequency, and the thickness of the substrate. Examples of computed results for resonance frequencies of a microstrip patch are given in the present article.

A flow visualisation study was performed to investigate a periodic flow instability in a bifurcating duct within the tip of the flares at the Shell refinery in Clyde, NSW, to verify the trigger of a combustion-driven oscillation proposed in Part A of this study, and to identify its features. The model study assessed only the flow instability, uncoupled from the

In a thin and large area PZT-ceramics piezoresonator (PR) with relatively low resonance impedance, caused by high-frequency resonance and high PR capacitance, the effect of electrode resistivity and parasitic resistive and inductive elements in the measurement fixture results in significant distortion of the measured thickness-mode (longitudinal TL, shear TS) resonance response-resonance frequency shifts and characteristics deformation. This distortion may not allow the precise measurement of the PR characteristic frequencies, quality factor, and electromechanical coupling coefficient so essential to a complete PR and material characterization. A theoretical description of the "energy-trap" phenomena in a thickness-vibrating PR with resistive electrodes is presented. To interpret electrical measurements, the electromechanical model, including for completeness both the PR with resistive electrodes (as a system with distributed parameters) and the measurement fixture, is dev...