Resonant electromagnetic excitation and detection of ultrasonic waves in thin sheets

A unified theory of the simultaneous electromagnetic excitation and detection of ultrasonic waves travelling in the through‐thickness direction in conducting sheets in the presence of a static magnetic field is presented. What to our knowledge are the highest‐frequency room‐temperature measurements of this type are described for aluminium sheets of thickness as low as 20 μm for frequencies up to 120 MHz. Maxwell’s equations are solved for the geometry of a planar current sheet above a conducting sheet with sinusoidal time variation. It is shown how, from the solution of a single fourth‐order differential equation for the magnetic vector potential, the coupled electromagnetic and elastic wave problem can be solved analytically. The effective transfer impedance is evaluated, a measure of the ultimate efficiency of the combined excitation and detection process. At acoustic resonance its amplitude is inversely proportional to the sum of the ultrasonic attenuation of the sample and the attenuation arising from...

[1]  W. P. Mason.  Physical Acoustics and the Properties of Solids , 1956 .

[2]  D. E. Gray,et al.  American Institute of Physics Handbook , 1957 .

[3]  William J. Pardee,et al.  Half-space radiation by EMATs , 1980 .

[4]  D. Chimenti.  Nonlocal electromagnetic generation of acoustic waves in aluminum films , 1976 .

[5]  K. Saermark,et al.  Electromagnetic excitation of elastic modes in aluminium , 1968 .

[6]  Katsuhiro Kawashima,et al.  Nondestructive characterization of texture and plastic strain ratio of metal sheets with electromagnetic acoustic transducers , 1990 .

[7]  B. W. Maxfield,et al.  Experiments Relating to the Theory of Magnetic Direct Generation of Ultrasound in Metals , 1969 .

[8]  ALPHER--RUBIN ULTRASONIC ATTENUATION AND DIPOLAR NUCLEAR-ACOUSTIC-RESONANCE COUPLING IN PURE METALS. , 1971 .

[9]  J. Cochran,et al.  Generation and detection of acoustic waves in metals by means of electromagnetic radiation , 1969 .

[10]  R. Rubin,et al.  Magnetic Dispersion and Attenuation of Sound in Conducting Fluids and Solids , 1954 .

[11]  C. M. Fortunko,et al.  The design and use of electromagnetic acoustic wave transducers (EMATs) , 1983 .

[12]  W. P. Mason,et al.  Phonon and Electron Drag Coefficients in Single-Crystal Aluminum , 1966 .

[13]  B. Abeles.  Electromagnetic Excitation of Transverse Microwave Phonons in Metals , 1967 .

[14]  Y. Goldstein,et al.  Conversion of electromagnetic into acoustic energy using Sn, Au, and Cu films at low temperatures , 1974 .

[15]  K. Kawashima,et al.  Quantitative Calculation and Measurement of Longitudinal and Transverse Ultrasonic Wave Pulses in Solid , 1984, IEEE Transactions on Sonics and Ultrasonics.