Thermo-magnetic induced monodirectional periodic acoustic emission from free-standing nano-thin film

Abstract

In this article, a thermally and magnetically induced monodirectional acoustic transducer is introduced with applications. An alternating thermal field is aroused by a sinusoidal current on a nano-thin film and an acoustic field is further excited due to the thermo-acoustic effect. A periodic magnetic field at the same frequency is concurrently applied to excite a fresh acoustic field in order to derive an enhanced sound pressure output. An analytical model for the mixed acoustic emitting system is established and the acoustic response is analyzed theoretically. An improved parabolic approximation relationship with only first-order Taylor's expansion is applied on the thermo-acoustic decoupling to obtain the thermo-acoustic propagating wave numbers. In addition, the oscillation of nano-thin film is driven by the magnetically induced Ampère's excitation in magneto-acoustics that introduces an additional mass effect. Moreover, thermo-acoustic and magneto-acoustic responses share the identical frequency but in a distinct phase difference. By designing a proper system configuration on the amplitude and phase of magnetic flux density, the backside acoustic field can be made to disappear. Furthermore, non-dimensionalization and numerical methods are applied to determine the amplitude of magnetic flux density for monodirectional acoustic field in varying parameters.