Elastic modulus measurement of thin films coated onto magnetoelastic ribbons

A model is presented to describe the change of the resonant frequency of a magnetoelastic sensor when the sensor is coated with a material of given elasticity. With a mass load coated on the surface of the sensor, its characteristic resonant frequency changes depending on the ratio of the sound velocities in the sensor and the coating. A measurement technique is derived that allows the determination of Young's modulus of elasticity of thin film coatings, with thickness greater than approximately 75 nm, based on the measurement of mass and resonant frequency of a sensor before and after coating. Comparing the measurement to the model delivers the value of Young's modulus of elasticity for a coating of known density.