Acoustic wave generation by microwaves and applications to nondestructive evaluation

Area of Science:

• Physics
• Materials Science
• Engineering

Background:

• Acoustic wave generation by electromagnetic waves is well-studied for lasers, but sparse for microwaves.
• Mechanisms include radiation pressure, electrostriction, and thermal expansion; thermal expansion due to microwave absorption is now recognized as primary.
• This research addresses the gap in understanding microwave-generated acoustic waves for material characterization.

Purpose of the Study:

• To review recent theoretical and experimental advances in generating ultrasonic waves using microwaves.
• To introduce a novel non-contact method for ultrasonic wave generation applicable to nondestructive evaluation (NDE).
• To demonstrate the potential for evaluating material properties using microwave-generated acoustic waves.

Main Methods:

• Developing a unidirectional theory integrating Maxwell's equations, heat equation, and thermoviscoelasticity.
• Utilizing pulsed or burst electromagnetic microwaves to excite materials across a broad or narrow frequency range.
• Conducting experiments on water, viscoelastic polymers, and composite materials (rods and plates).

Main Results:

• The theory predicts acoustic wave generation at interfaces and within stratified materials.
• Experiments successfully generated acoustic waves in diverse materials like water, polymers, and composites.
• Computed and measured accelerations correlate with material properties, enabling evaluation.

Conclusions:

• Microwave-induced thermal expansion offers a viable non-contact method for generating ultrasonic waves.
• This technique facilitates the evaluation of viscoelastic and electromagnetic properties of materials for NDE.
• Preliminary applications demonstrate the potential of this method in non-destructive testing.