Browse Prior Art Database

Quality Control of Round or Elliptical Objects by Detecting Multiply Reflected and Refocused Photoacoustic Signal

IP.com Disclosure Number: IPCOM000045514D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Caufal, H: AUTHOR [+3]

Abstract

A technique is provided which produces non-destructive testing of round or elliptical objects for structural homogeneity.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Quality Control of Round or Elliptical Objects by Detecting Multiply Reflected and Refocused Photoacoustic Signal

A technique is provided which produces non-destructive testing of round or elliptical objects for structural homogeneity.

Round objects that need critical quality controls are frequently encountered in production. Examples where ideal controls of the mechanical qualities of the round objects would significantly improve production reliability and efficiency are: round sputtering targets used in thin film magnetic head production, aluminum substrates used for magnetic recording disks, optical recording disks, silicon wafers used in making integrated circuits and other micro-devices. In the production of these high-precision products, uncontrolled porosity variations, inhomogeneities, elasticity changes, etc., in the round disk (used as a starting material or as a substrate) may cause excessive product variations or dimensional defects. The present technique of detecting multiply reflected and self-refocused pulsed photoacoustic signals (generated and detected at the center of the disk) provides an unsurpassed quality-control method, being non- destructive, non-contact and/or non-contaminating, reliable and fast.

The pulsed photoacoustic (PA) effect in solids is well known, as can be seen from the recent review paper of Patel and Tam (C. K.
N. Patel and A. C. Tam, Pulsed Optoacustic Spectroscopy of Condensed Matter, Review of Modern Physics 53, 517-550 (1981). However, the present special novel feature applicable to a round (or elliptical in general) geometry for quality control purposes is previously unknown. (Note that a circle is a degenerate ellipse; the present discussion deals mainly with circles, but an extension to general elliptical cases is trivial.)

The special feature in a round geometry is "refocusing" of the pulsed PA signal excited at the center, allowing multiply reflected PA signals to be observed at the center for many reflections at the rim or circumference. In a homogeneous and isotropic disk, the PA pulse produced initially at the center propagates with a strictly circular wavefront, arriving at the circumference of the disk simultaneously; the reflection at the rim results in a strictly circular,...