Optical Detection of Electromagnetic Acoustic Admittance
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Two embodiments of a non-contact acoustic impedance measurement technique for examining subsurface delaminations of any conducting surface adhered to a substrate are proposed. A contour map of such delaminations is produced by scanning the conductive surface with a laser doppler vibrometer while the sample substrate is in the presence of a static magnetic field and AC current is applied either directly or by induction to the conducting surface of the sample. Since the directions of the two fields are orthogonal and in the plane of the sample surface, a force normal to the conducting surface is applied thereto. Thus, the conducting surface will vibrate at the excitation frequency at all points where the surface is delaminated. No vibration will be observable at points where lamination is secure.