Loss Measurement of High-Finesse Fabry-Perot Cavities

The loss of a high-finesse Fabry-Perot cavity was measured using frequency scan and cavity ring-down techniques.Different transverse modes were examined by sweeping the frequency of the laser across the corresponding resonances.In addition,cavity ring-down technique was used to measure the loss of the Fabry-Perot cavity and a simple model was employed to remove the influence of finite response time of the optical switch and the detection circuit.

Small signal gain and loss measurement of a CW Nd:YAG laser using an antiresonant ring interferometer

An antiresonant ring （ARR） interferometer configuration is introduced for the characterization of a continuous wave （CW） Nd：YAG laser output. The output of the ARR device is precisely characterized to determine the gain and loss of a laboratory CW Nd：YAG laser by using the Findlay-Clay approach. The ARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CW Nd：YAG laser. A coated beam splitter with 50–50% re？ectivity at normal incidence is placed inside the cavity to provide a wide range of re？ectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10？ with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual re？ectivity of ARR arm. Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.

Comparative study on the corrosion behavior of low alloy steels in sulfuric acid solution

The corrosion behavior of a weathering steel SPA-C and two acid resistance steels（ S-TEN1 and ND）in sulfuric acid solution was investigated by using potentiodynamic polarization and weight loss measurement techniques. Both potentiodynamic polarization and weight loss measurement tests indicated that corrosion resistance of these three alloy steels was as follows： ND ~ S-TEN1 〉 SPA-C. Surface analysis of the corroded samples conducted after the immersion test indicated that two layers were formed on the substrates, with the outer layer comprising FeSO4. H20 and the inner layer mainly comprising iron oxides. The addition of Cu, Cr, and Sb refined the corrosion products and improved the adhesion ability between the rust layer and the substrate.

Measurement of insertion loss for underwater acoustic passive materials with the time reversal technique

A method using the time reversal（TR） technique to measure the insertion loss（IL） of passive materials is presented.Firstly the received signals are focused according to the TR theory when there is not a sample between the source and the received array.Then,the sample is placed near the received array and the TR processing is again employed to realize the focus of the received signal.Finally,the IL of the sample is evaluated from these focusing signals.Because the TR processing can focus the energy in spatial domain and time domain,the method can be used to measure acoustic properties of passive materials in a waveguide tank with reflections induced by boundaries or with low source frequencies.Two samples with the same size of 1.1 m×1.0 m×5 mm are tested in the waveguide tank.The method is demonstrated by the comparison of the theoretical and the experimental results in the measured frequency range of 1-20 kHz.

Novel and Simple Calorimetric Methods for Quantifying Losses in Magnetic Core and GaN Transistor in a High Frequency Boost Converter

In design and implementation of a boost converter,information on loss characteristics of switching devices and magnetic materials is a prerequisite,especially in high frequency applications.To gather such information,testing and accurate loss quantification is needed.Previous methods for measuring magnetic core loss are either only suitable for sinusoidal wave excitations or cannot separate winding loss from inductor loss.In addition,existing loss measurement approaches on the newly introduced GaN transistors are not satisfactory.In this paper,we present a new method to distinguish winding loss from inductor loss under practical excitations.This method utilizes a converter to generate the actual excitation waveforms and uses a calorimetric setup to quantify the losses.By splitting up the inductor in a converter into an air-core inductor and a magnetic-core inductor,both equipped with exactly the same winding structure,the air-core inductor loss can be used as the reference of the magnetic-core inductor winding loss.In this way,losses in the magnetic core can be determined in the actual operating condition of a converter in which the inductor is to be used.Moreover,a simple calorimetric approach for obtaining loss information of GaN transistors are is also presented.Both methods require simple setup and are easy and convenient to execute.The methods work well in assessing different high frequency magnetic core materials and measuring losses in GaN transistors at 1MHz.

Overview of Planar Magnetics for High-frequency Resonant Converters

With the continuous development of power supplies toward miniaturization,light weights,and high levels of integration,research on high-frequency resonant conversion based on planar magnetics is becoming extensive.Combining the soft-switching characteristics of resonant converters with those of wide bandgap devices,the switching frequency can be increase to the MHz range,and the power density of the entire system can be improved considerably.However,higher switching frequencies impose new requirements for the structural design,loss distribution,and common mode(CM)noise suppression of passive magnetic components.Herein,a thorough survey of the-state-of-the-art of planar magnetics in high-frequency resonant converters is conducted.Printed circuit board winding-based planar magnetics,magnetic integration,and power-loss optimization strategies are summarized in detail.Suppression methods for CM noise in high-frequency planar magnetics are also clarified and discussed.An insight view into the future development of planar magnetics for high-frequency resonant converters is presented.