This paper shows how the energy transfer between electromagnetic waves and elastic waves at the surface of fluid or solid materials could constitute a new way to generate ultrasonic waves without contact for the purpose of nondestructive evaluation and control. When time-gated microwaves strike the surface of a material, there is a generation of ultrasonic waves. The times-of-flight of these elastic waves inside the material decrease when the power of the incident microwaves increases. Therefore, the diminution of the propagation path indicates that the energy transformation appears in a volume close to the surface, the depth of which is increasing along with the power of the microwaves and depends on the material properties. Consequently, the elastic wave generation is attributed to the evolution of the power of the microwave during the gate width that governs the frequency content of the ultrasonic waves. The generation of ultrasound is checked in water and polymers. If the microwaves are not too attenuated in the material, the ultrasonic waves can be generated both at input (air–solid) and output (solid–air) interfaces. These peculiarities can generate new applications in the nondestructive evaluation and control of material.

1.
Proceedings of Review of Progress in Quantitative NonDestructive Evaluation, edited by D. O. Thompson and D. E. Chimenti (Plenum, New York), Vols. 1–16.
2.
R. M.
White
, “
Generation of Elastic Waves by Transient Surface Heating
,”
J. Appl. Phys.
34
(
12
),
3559
3567
(
1963
).
3.
J. C.
Lin
, “
Further Studies on the Microwaves Auditory Effect
,”
IEEE Trans. Microwave Theory Tech.
MTT-25
(
11
),
939
943
(
1977
).
4.
D.
Borth
, “
Theoretical Analysis of Acoustic Signal Generation in Materials Irradiated with Microwave Energy
,”
IEEE Trans. Microwave Theory Tech.
MTT-25
(
11
),
945
953
(
1977
).
5.
R. L. Nasoni, G. A. Evanoff, P. G. Halverson, and T. Bowen, “Thermoacoustic Emission by Deeply Penetrating Microwave Radiation,” in IEEE Ultras. Symp. (1984), pp. 633–638.
6.
D. A. Hutchins, “Ultrasonic generation by pulsed laser,” Physical Acoustics, edited by W. P. Mason and R. N. Thurston (New York, 1988), Vol. XVIII.
7.
C. B. Scruby and L. E. Drain, Laser Ultrasonics Techniques and Applications (Hilger, Bristol, 1990).
8.
K. L.
Telschow
and
R. J.
Conant
, “
Optical and thermal parameter effects on laser-generated ultrasound
,”
J. Acoust. Soc. Am.
88
,
1494
1502
(
1990
).
9.
A. Hénault, A. Cournoyer, F. Enguehard, and J. Bertrand, “A study of dynamic thermal expansion using a laser-generated ultrasound 1-d model,” Proceedings of the 9th International Conference on Photoacoustic and Photothermal Phenomena, edited by S. Y. Zhang, Nanjing, China (1996), pp. 370–374.
10.
F. C. Chen and W. C. Chew, “An impulse radar nondestructive evaluation system,” in Review of Progress in QNDE (Plenum, New York, 1997), Vol. 16A, pp. 709–715.
This content is only available via PDF.
You do not currently have access to this content.