Laser ultrasonics-based material analysis system and method utilizing lamb modes

• US 5,956,143 A
• Filed: 02/14/1997
• Issued: 09/21/1999
• Est. Priority Date: 09/19/1994
• Status: Expired due to Fees

• Current Assignee: Brown University
• Original Assignee: Textron Systems Corporation (Textron Inc)
• Inventors: Kotidis, Petros Amestis
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): MERLINO, AMANDA H
• Application Number:
  US08/800,835
• Time in Patent Office: 949 Days
• Field of Search: 356/432, 356/358, 356/357, 356/351, 73/655, 73/657
• US Class Current: 356/502
• CPC Class Codes: G01N 21/1717 with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• CPC Class Codes: G01N 2291/011 Velocity or travel time
• CPC Class Codes: G01N 2291/015 Attenuation, scattering
• CPC Class Codes: G01N 2291/0237 Thin materials, e.g. paper, membranes, thin films
• CPC Class Codes: G01N 2291/0251 Solidification, icing, curing composites, polymerisation
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/045 External reflections, e.g. on reflectors
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 2291/2697 Wafer or (micro)electronic parts
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/228 related to high temperature conditions
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046
• CPC Class Codes: G01N 29/2456 Focusing probes focusing arrangements G01N29/221
• CPC Class Codes: G01N 29/326 : compensating for temperature variations
• CPC Class Codes: G01N 29/348 : with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/4427 : with stored values, e.g. threshold values
• CPC Class Codes: H01S 3/08004 : incorporating a dispersive element, e.g. a prism for wavelength selection H01S3/0811, H01S3/08022 take precedence
• CPC Class Codes: H01S 3/106 : by controlling devices placed within the cavity H01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 5/02208 : characterised by the shape of the housings
• CPC Class Codes: H01S 5/02255 : using beam deflecting elements
• CPC Class Codes: H01S 5/141 : using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence

Abstract

An interferometric system for measuring a property of interest of a target, such as temperature, by detecting the velocities of the symmetric S_o) lamb modes and anti-symmetric (A_o) lamb modes.

Claims

1. A system for determining a characteristic of a target having a thickness suitable for supporting Lamb modes, comprising:

means for launching an elastic wave within the target;

an interferometer for detecting a displacement of a surface of the target in response to said launched elastic wave;

means, responsive to said detected displacement, for determining a velocity of an elastic wave corresponding to a symmetric (S_o) Lamb mode and a velocity of an elastic wave corresponding to an anti-symmetric (A_o) Lamb mode within the target; and

means for correlating said determined S_o Lamb mode and said A_o Lamb mode velocities with a property of interest of the target.

2. A system as set forth in claim 1 wherein a frequency of the elastic wave is made a function of the thickness of the target so as to substantially eliminate a dispersive characteristic of the elastic wave.

3. A system as set forth in claim 1 wherein said property of interest is temperature.

4. A system as set forth in claim 3 wherein the target is comprised of a silicon wafer.