Non-destructive, non-contact ultrasonic material

Abstract

The invention relates to a method for non-contact, non-destructive testing of a test body of ferromagnetic and/or electrically-conductive material with ultrasound waves, comprising the steps of: producing in a near-surface region of the test body a low-frequency alternating magnetic bias field having flux lines generally parallel to a surface of the test body; producing high frequency alternating magnetic excitation fields in said near-surface region generally parallel to said surface during a time interval when the bias field is at a quasi-static maximum, adjacent excitation fields having opposing polarity and having flux lines lying in mutually parallel directions, whereby ultrasound waves are generated in the test body; and detecting high frequency alternating magnetic fields in said near-surface region during the same time interval when the bias field is at a quasi-static maximum and producing a signal therefrom representative of said ultrasound waves. In this method, the flux lines of said excitation fields lie generally parallel to the flux lines of said bias field, such that dynamic forces are electrodynamically generated in the test body in a direction normal to the surface of the test body, which launch longitudinal waves, Rayleigh waves and Lamb waves, and dynamic forces are magnetostrictively generated in the test body in a direction parallel to said surface, which launch transversal waves, Rayleigh waves and Lamb waves.