An omnidirectional shear-horizontal guided wave EMAT for a metallic plate

An Improved Design of the Spiral-Coil EMAT for Enhancing the Signal Amplitude

“…Differently, the magnetic flux density will focus on the surface of the magnet in the case of the improved EMAT configuration, as shown in Figure 1e. This analogical configuration combined with a wound coil has been used to generate omnidirectional SH waves, but not yet combined with the spiral-coil to generate bulk waves [11]. …”

“…Electromagnetic acoustic transducer (EMAT) is a type of non-contact ultrasonic transducer, which is the core component of ultrasonic excitation and acceptance in UT [1,2,3,4,5]. Due to a plenty of outstanding advantages such as non-contact operation, requiring no coupling fluid, the flexibility to generate and detect multiple wave modes, and the capability of operating in high temperature, isolation layer and other harsh environment, EMATs are particularly useful and active in nondestructive evaluation (NDE) and internal structure evaluation (ISE) [6,7,8,9,10,11,12]. Besides, EMATs have be distinctively attractive in thickness measurement for their good penetration ability.…”

“…Obviously, it can be obtained from Equation (1) that the square of the magnetic flux density is proportional to the SNR of EMATs with the mechanism of Lorentz force [7,8,9,10,11,12,13,14,15]. The SNR can be given as $\frac{V_{\mathrm{EMAT}}}{V_{\mathrm{noise}}}=\frac{\sqrt{P_0}{N}^2{B}^{2}A}{2Z_S\sqrt{KT\beta }{R}_{\mathrm{EMAT}}}\exp \left(-\frac{\alpha h}{D}\right)$ where $V_{\mathrm{EMAT}}$ is the received voltage across the terminals of the coil (V), $V_{\mathrm{noise}}$ is the received noise level (V), $P_0$ is the power of the EMAT (W), $N$ is the number of turns per unit length, $B$ is the magnetic flux density (T), $A$ is the active area of EMAT (${\mathrm{m}}^2$), $Z_S$ is the acoustic impedance of the part ($\mathsf{\Omega }$), either longitudinal or shear wave, $K$ is Boltzmann’s constant times electronic charge (Meter-Kilogram-Second units), $T$ is temperature in degrees Kelvin (K), $\beta$ is the bandwidth of the amplifier (Hz), $R_{\mathrm{EMAT}}$ is the resistance of EMAT coil ($\mathsf{\Omega }$), $\alpha$ is a geometry dependent constant, $h$ is the lift-off distance between EMAT coil and the surface of the part (m), and $D$ is the diameter of the coil (m).…”

“…Xie et al proposed a wholly analytical modelling method to study the Rayleigh waves’ beam directivity on the surface of the material [10]. Seung et al presented a new EMAT for generation and measurement of omnidirectional shear-horizontal (SH) guided waves in metallic plates [11]. There have been previous studies of SH wave EMAT, but they mainly focused on the meander-line-coil (MLC) EMAT for surface wave generation and detection in the metallic plate or pipe [7,8,9,10].…”

Direction-Controllable Electromagnetic Acoustic Transducer for Sh Waves in Steel Plate Based on Magnetostriction

“…Seung et al proposed an omnidirectional SH wave EMAT using a pair of ring-type permanent magnets [20]. Wilcox et al designed an omnidirectional EMAT array for the fast inspection of metallic plate [21].…”