Effects of slits in a patch of omnidirectional Lamb-wave MPT on the transducer output

Abstract

An omnidirectional Lamb-wave magnetostrictive patch transducer (MPT) uses a thin circular magnetostrictive patch excited by the axisymmetric turns of a plane coil placed over it. Since the dynamic magnetic field applied by the coil induces an eddy current only on the top surface due to the skin effect, the mechanical deformation in the patch is confined only near the surface, considerably limiting the transducer output power. This study shows that if a radial slit is introduced in the patch, the circular flow of the eddy current on the top surface only becomes broken, and thus the eddy current flows on both the top and bottom surfaces. As a consequence, there is a substantial increase in the dynamic magnetic field in the patch and, in turn, an increased transducer output power. Interestingly, the material type, either metallic or nonmetallic, of the test waveguide plate affects the magnitude of the eddy current near the bottom surface and the overall magnetic field. If the number of slits is over a certain number, say, 8, and the slits are symmetrically made in the patch, the omni-directivity of the resulting MPT is virtually ensured. Finally, the present findings are verified both numerically and experimentally.

Investigation of the use of uniaxial comb-shaped Galfenol patches for a guided wave-based magnetostrictive phased array sensor

“…Recently, the magnetic shape anisotropy effects on the GW sensing performance and directional sensitivity improvement of a polycrystalline nickel patch have been explored and validated theoretically and experimentally. 13,14 Despite the isotropic magnetostrictive characteristics of the nickel material, the results showed that high-aspect-ratio fingers formed to a nickel disc induced apparent magnetic shape anisotropy feature. Also, we developed a Magnetostrictive Phased Array Sensor (MPAS) using a circular comb-shaped nickel patch and demonstrated its damage detection capability with a thin aluminum plate.…”

Enhanced transduction of MPT for antisymmetric Lamb waves using a detuned resonator

“…[1][2][3]), transducers with higher transduction efficiency levels are becoming more important. Among the various ultrasonic transducers currently available, this study focuses on magnetostrictive patch transducers (MPTs) [4][5][6][7][8][9][10] and aims to increase the transduction efficiency of this type substantially. An MPT consists of a set of magnets and a coil carrying electric signals, along with a thin magnetostrictive patch which is directly bonded onto or coupled with a test waveguide.…”

“…In the case of MPTs, the size of the magnetostrictive patch that is coupled with a test specimen should match the wavelength of the wave excited in a test specimen at the excitation frequency [6,13,14]. As MPTs operate on the magnetostrictive principle, one may also consider optimizing the magnetic circuit to increase the transducer output [5,15].…”

“…For the calculation, we used the material properties of glass (Young's modulus 52.0 GPa, Poisson's ratio 0.33 and density 2500 kg m −3 ). The reason why glass is used to make the resonator is that glass does not disturb the surrounding electromagnetic fields [5], while the electromagnetic field must be used for actuation and sensing using MPTs.…”