Signal Strength Enhancement of Magnetostrictive Patch Transducers for Guided Wave Inspection by Magnetic Circuit Optimization

Abstract

Magnetostrictive patch transducers (MPT) with planar coils are ideal candidates for shear mode generation and detection in pipe and plate inspection with the advantages of flexibility, lightness and good directivity. However, the low energy conversion efficiency limits the application of the MPT in long distance inspection. In this article, a method for the enhancement of the MPT was proposed by dynamic magnetic field optimization using a soft magnetic patch (SMP). The SMP can reduce the magnetic resistance of the magnetic circuit, which increases the dynamic magnetic field intensity in the magnetostrictive patch during wave generation and restricts the induced dynamic magnetic field within the area around the coils for sensing during wave detection. Numerical simulations carried out at different frequencies verified the improvement of the dynamic magnetic fields by the SMP and influence of different affecting factors. The experimental validations of the signal enhancement in wave generation and detection were performed in an aluminum plate. The amplitude magnification could reach 12.7 dB when the MPTs were covered by the SMPs. Based on the numerical and experimental results, the SMP with a large relative permeability and thickness and close fitting between the SMP and coils were recommended when other application conditions were met.

Defect Detection and Imaging in Composite Structures Using Magnetostrictive Patch Transducers

“…The introduction of a conductive thin film then facilitates both Lorentz forces and magnetostriction to be used to generate elastic waves. Various authors have investigated ways of enhancing the efficiency of magnetostriction in this application, involving, for example, magnetic circuit optimization [ 19 ], the use of periodic permanent magnets [ 20 ], the enhancement of longitudinal guided waves [ 21 ], and the use of materials exhibiting giant magnetostrictive properties [ 22 ].…”

The Effect of Changes in Magnetic Field and Frequency on the Vibration of a Thin Magnetostrictive Patch as a Tool for Generating Guided Ultrasonic Waves

“…The magnetostriction phenomenon is widely used for different applications, such as the active element in ultrasonic transducers used to generate elastic waves for nondestructive testing and inspection [ 28 , 29 , 30 , 31 ], microelectromechanical systems or MEMS [ 29 ], positioning sensors [ 32 ], level-gauging sensors [ 33 ] and accurate actuation mechanisms [ 34 ].…”

Experimental Study of the Guided Wave Directivity Patterns of Thin Removable Magnetostrictive Patches

“…The degree of strain induced depends on the specific sample properties, including material composition and microstructure [ 26 ]. When an external magnetic field is applied, the change in dimensions that occurs is known as the Joule effect; conversely, when an external strain is applied, the change in magnetization is known as the Villari effect [ 24 , 27 , 28 , 29 , 30 , 31 ]. There is a non-linear relationship between the applied field ( H ) and λ , as illustrated in Figure 1 for an iron–cobalt alloy.…”