Nondestructive evaluation of composite materials using acoustic emissions stimulated by absorbed microwave/radiofrequency energy
First Claim
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1. Apparatus for microwave nondestructive evaluation of specimen comprising:
- (a) microwave means comprised of(1) generating means to generate, at least one microwave pulse of predetermined pulse energy, carrier frequency, and polarization; and
(2) directing means to direct said microwave pulse to a microwave coupling means, said coupling means comprising a chamber and a microwave transition into said chamber, said chamber enclosing said specimen; and
(b) receiving means to detect elastic waves which appear on at least one surface of said specimen wherein said receiving means responds to strain in said specimen from impulsive stress imposed on said specimen by absorbtion of said microwave pulse;
(c) measuring means to read output signals from said generating and receiving means, said measuring means evaluating said output signals corresponding to surface displacement as a function of time;
(d) processing means acting upon said measuring means output signals, said processing means classifying said specimens as members of one of at least two reference groups, said reference groups being predefined by prior tests upon known samples.
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Abstract
A method and apparatus for nondestructive evaluation of a composite material specimen is characterized by exposing the specimen to pulsed radio frequency energy to produce an elastic wave that propagates on the surface of the specimen. The wave is detected by a piezoelectric or electro-optic displacement mode transducer which produces a signal corresponding to the wave. The signal is analyzed by a processor to classify the specimen into one of a plurality of predetermined reference groups defined in accordance with a minimum number of defective and nondefective samples.
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Citations
13 Claims
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1. Apparatus for microwave nondestructive evaluation of specimen comprising:
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(a) microwave means comprised of (1) generating means to generate, at least one microwave pulse of predetermined pulse energy, carrier frequency, and polarization; and (2) directing means to direct said microwave pulse to a microwave coupling means, said coupling means comprising a chamber and a microwave transition into said chamber, said chamber enclosing said specimen; and (b) receiving means to detect elastic waves which appear on at least one surface of said specimen wherein said receiving means responds to strain in said specimen from impulsive stress imposed on said specimen by absorbtion of said microwave pulse; (c) measuring means to read output signals from said generating and receiving means, said measuring means evaluating said output signals corresponding to surface displacement as a function of time; (d) processing means acting upon said measuring means output signals, said processing means classifying said specimens as members of one of at least two reference groups, said reference groups being predefined by prior tests upon known samples. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of nondestructive evaluation comprising the steps of:
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(a) Selecting carrier frequency and pulse parameters to induce heat sources in a specimen under evaluation by absorbtion of at least one microwave pulse; (b) Supporting said specimen in an exposure chamber that encloses said specimen with isolation from external sources of mechanical vibration; (c) Generating, directing, and coupling said microwave pulse into said specimen in said exposure chamber; (d) Receiving surface elastic waves secondary to absorbtion of said microwave pulse; (e) Measuring at least one of surface displacement, surface velocity, or surface acceleration as a function of time following absorbtion of at least one microwave pulse; (f) Processing data generated during said measuring step to classify each specimen by time and frequency domain features extracted from said time function whereby said specimen is identified as a member of one of at least two predetermined reference groups, said reference groups being previously defined by applying steps a through e with controlled pulse parameters and exposure chamber conditions to specimens known to be members of, at a minimum, normal or defective groups.
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Specification