Scichology

My major, as defined in my personalized study program application to the Colleges of the Arts & Sciences, will be, "Scichology"Beloved thanks to my bride, Linda, for her efforts as my primary lexicographer. (She is definitely in the descriptive camp)

x to the nth Dharma Gates, I vow to enter them,

Geoff

Abstract

A heterodyne velocimetry system based on the work of Strand and others [1][2][3] was constructed in the Materials Science and Engineering Department at Ohio State University, under the direction of Glenn S. Daehn. The system was used successfully to measure ring expansion velocities of electromagnetically driven samples. The methodology can contribute data useful in determining material properties under high strain rates and benchmarks for numerical analysis of EM forming [4].

Introduction

As a non contact technique capable of measuring the velocity and acceleration of shock wave propagation, deformation, ejection, or displacement, PDV(Photonic Doppler Velocimetry) is likely to be useful in a variety of experimental settings [5][6]. Recent advances and cost reductions in high speed data acquisition and fiber laser light sources have made such systems feasible. PDV systems now compliment or replace VISAR (Velocity Interferometer System for Any Reflector) and Fabry-Perot Interferometry in analyzing the response of materials subjected to dynamic loading.[6] Pioneering work in the development of PDV systems is attributable to Paul T. Sargis of Lawrence Livermore National Lab from as early as 1999 [3].

Electromagnetically launched ring expansion as a materials characterization test was well developed by Gourdin [7][8]. The technique was restricted by several significant technical challenges at the time [4]. Gourdins’ work attempted to limit resistive heating in the sample and used the operationally cumbersome VISAR. Furthermore his materials analysis is restricted to the decelerating expansion of the sample after removal of the driving solenoid current [7]. The more contemporary technologies of PDV and finite element analysis modeling can accommodate the dynamic nature of the technique by considering the specimen heating and changing magnetic pressure.

The Photonic Doppler Velocimeter

PDV is sometimes known as heterodyne velocimetry [1][2]. As the naming implies, a mixing or superposition of signals creates a heterodyne or beat frequency. In this method of optical interferometry, a stable reference light source interacts with frequency shifted light reflected from a target object of interest. The frequency of light reflected from a moving object will be shifted according to the Doppler effect. Superimposing the reference and reflected light yields a variable frequency signal representing the velocity and acceleration of the target. As the target surface is displaced through a distance equal to one-half the laser wavelength, a full cycle is generated in the heterodyne signal, resulting in a full beat cycle for every 775 nm of motion.