Quantitative evaluation of directivity patterns and sensitivities for electromagnetic-ultrasonic transducer design

A formalism is presented which allows to evaluate directivity patterns and sensitivities of electromagnetic-ultrasonic transducers for bulk waves and Rayleigh waves from the electrical, magnetic and elastic material properties and the geometrical and electrical properties of the transducer. The sensitivity is calculated in terms of the transfer impedance of a transmitter-receiver-pair. Expressions for signal-tonoise ratio and insertion loss are derived from this quantity. The calculations are based on a physical model of electromagnetic-ultrasonic transduction which makes use of a complete suitable description of the transduction mechanisms that determine the interaction between electromagnetic field and elastic matter in an electrically conductive, ferromagnetic material. These are Lorentz forces, magnetic forces and magnetostriction. The theoretical results have been verified in an experimental study concerning electromagnetically excited shear waves in iron. Thereby it has been prov ed that the transducer model can successfully be applied to the design of electromagnetic-ultrasonic probes. (IZFP)