Staggered Magnet Array (SMA) Based Electromagnetic Acoustic Transducer (EMAT)

Abstract

A staggered magnet array (SMA) based electromagnetic acoustic transducer (EMAT) system and method for controlling the direction of the ultrasonic waves in the electromagnetic acoustic transducer (EMAT) using staggered magnet array (SMA) configurations, is disclosed herein. The EMAT device proposed herein comprises at least one conductive racetrack coil and at least two magnet arrays wherein the magnet array comprises of permanent magnets, where each magnet is oriented according to a specific configuration to produce ultrasonic waves in order to form an ultrasonic beam by shifting the position of the magnet arrays up or down creating a SMA configuration.

Claims

1. A staggered magnet array (SMA) based electromagnetic acoustic transducer (EMAT) system, comprising: at least one conductive racetrack coil; and at least two magnet arrays wherein the magnet array comprises of permanent magnets, where each magnet is oriented according to a specific configuration to produce ultrasonic waves in order to form an ultrasonic beam by shifting the position of the magnet arrays up or down creating a SMA configuration.

2. The system as claimed in claim 1 wherein the beam forming technique has been tested with periodic permanent magnet (PPM) configuration.

3. The system as claimed in claim 1 wherein the beam forming technique has been tested with linear Halbach array magnet configuration (HBA).

4. The system as claimed in claim 1 wherein the beam forming technique has been tested with a hybrid configuration (combination of PPM and HBA).

5. The system as claimed in claim 1 wherein the SMA based EMAT allow for a fixed frequency electrical input to provide different ultrasonic or acoustic beams using mechanical movements to stagger the magnet arrays thereby enabling to generate different ultrasonic beams in a wide range of industrial applications.

6. The system as claimed in claim 1 wherein the magnetic configurations in the SMA based EMAT can be dynamically manipulated through the mechanical movement of the magnet arrays, thereby manipulating the ultrasonic beams from the EMAT.

7. The system as claimed in claim 1 wherein the SMA based EMAT allows for the dynamic or static focusing or defocusing of ultrasonic beams and thereby enhance the results or data obtained in the industrial application.

8. The system as claimed in claim 1 wherein multiple magnet arrays EMAT for beam forming comprises: two array EMAT configuration, three array EMAT configuration, four array EMAT configuration, five array EMAT configuration and multi-array EMAT configuration.

9. The system as claimed in claim 1 wherein the SMA based EMAT allows the operator to steer the beam at different angles using a single transducer.

10. The system as claimed in claim 1 wherein the SMA based EMAT can have small footprint, low cost, and offer a universal solution for producing static or dynamic beam forming through simple mechanical movement of the magnets.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] The drawings shown here are for illustration purpose and the actual system will not be limited by the size, shape, and arrangement of components or number of components represented in the drawings.

[0017] FIG. 1 illustrates a graphical representation illustrating the staggered magnet array (2 array) PPM EMAT and the SH waves generated using the staggered 2 array PPM EMAT where 2.sup.nd magnet array is shifted down by wavelength ()/8, in accordance with the disclosed embodiments;

[0018] FIG. 2 illustrates a graphical representation illustrating the staggered magnet array (2 array) HBA EMAT and the SH waves generated using the staggered 2 array HBA EMAT where 2.sup.nd magnet array is shifted down by wavelength ()/4, in accordance with the disclosed embodiments;

[0019] FIG. 3 illustrates a graphical representation illustrating the staggered magnet array (2 array) hybrid (PPM-HBA) EMAT and the SH waves generated using the staggered 2 array magnet array shifted down 5 mm (wavelength ()/4 for PPM and wavelength ()/8 for Halbach), in accordance with the disclosed embodiments;

[0020] FIG. 4 illustrates a graphical representation illustrating multiple staggered magnet array section PPM EMAT and the SH waves generated using multiple staggered magnet array section PPM EMAT, in accordance with the disclosed embodiments; and

[0021] FIG. 5 illustrates a graphical representation illustrating multiple staggered magnet array section HBA EMAT and the SH waves generated using multiple staggered magnet array section HBA EMAT, in accordance with the disclosed embodiments.

DETAILED DESCRIPTION

[0022] The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.

[0023] A staggered magnet array (SMA) based electromagnetic acoustic transducer (EMAT) system and method for controlling the direction of the ultrasonic waves in the electromagnetic acoustic transducer (EMAT) using staggered magnet array (SMA) configurations, is disclosed herein. The EMAT device proposed herein comprises at least one conductive racetrack coil and at least two magnet arrays wherein the magnet array comprises of permanent magnets, where each magnet is oriented according to a specific configuration to produce ultrasonic waves in order to form an ultrasonic beam by shifting the position of the magnet arrays up or down creating a SMA configuration. The beam forming technique has been tested with periodic permanent magnet (PPM) configuration, the linear Halbach array magnet configuration (HBA) and a hybrid configuration (combination of PPM and HBA).

[0024] FIG. 1 illustrates a graphical representation 100 illustrating the staggered magnet array (2 array) PPM EMAT and the SH waves generated using the staggered 2 array PPM EMAT where 2.sup.nd magnet array is shifted down by wavelength ()/8, in accordance with the disclosed embodiments. The scheme of generating shear horizontal ultrasonic waves with EMAT is performed using the PPM configuration as shown in FIG. 1. Alternatively, the Halbach array (HBA) configuration (FIG. 2) can also be used to produce SH waves. In both cases, racetrack coils are required for the AC travel path. The interaction between the bias magnetic field (from the PPM and Halbach arrangement) and the eddy current generated from the AC in the coil create alternating Lorentz forces, forming SH waves.

[0025] FIG. 2 illustrates a graphical representation 200 illustrating the staggered magnet array (2 array) HBA EMAT and the SH waves generated using the staggered 2 array HBA EMAT where 2.sup.nd magnet array is shifted down by wavelength ()/4, in accordance with the disclosed embodiments. The selection of the ultrasonic frequency is dependent on the EMAT wavelength () and the ultrasonic shear wave velocity within the inspected material. Using the Dispersion curve, one can select the EMAT frequency based on the material velocity and wavelength () to generate the desired wave mode. For inspections, a single SH wave mode is desired since it simplifies the post processing and analysis. However, there is always a possibility that multiple SH guided wave modes will be formed due to multiple factors such as ultrasonic frequency, shear wave velocity, material thickness and microstructure.

[0026] When individual magnet arrays, PPM or HBA, in the EMAT transmitter are shifted vertically up or down, a SMA configuration is formed. The bias magnetic field from the SMA interacts with the eddy current generated by the racetrack coil. The alternating Lorentz forces, created by the interaction, are skewed due to the position shifts in the magnet arrays resulting in bi-directional SH waves which are formed along the surface of the specimen, at an angle away from the central axis. We call this phenomenon, “Beam Forming”.

[0027] Note that FIG. 1 & FIG. 2 demonstrates an exemplary arrangement of EMAT using PPM and HBA configurations. The FIG. 1 and FIG. 2 should not be constituted any limited sense. FIG. 1 and FIG. 2 are only exemplary representations demonstrating working of the invention. The staggered magnet arrays can be arranged in a wide range of possibilities for both PPM and HBA configurations and any other EMAT configuration without limiting the scope of the proposed invention.

[0028] FIG. 3 presents a graphical representation of the staggered magnet array (2 array) hybrid (PPM-HBA) EMAT and the SH waves generated using the staggered 2 array magnet array shifted down 5 mm (wavelength ()/4 for PPM and wavelength ()/8 for Halbach), in accordance with the disclosed embodiments. Additional simulation studies were conducted to observe if using a combination of PPM and Halbach array (Staggered Hybrid EMAT) can produce beam forming. In the experiments, the optimum frequency for PPM was found to be 156 kHz while the optimum frequency for HBA EMAT was around 80 kHz. This is because the wavelength of the PPM array is 20 mm while wavelength of the Halbach array is 40 mm. Since the setup contains both PPM and Halbach array, the chosen EMAT frequency was 118 kHz, which is the midpoint frequency between 80 kHz and 156 kHz.

[0029] FIG. 4 illustrates a graphical representation 400 illustrating multiple staggered magnet array section PPM EMAT and the SH waves generated using multiple staggered magnet array section PPM EMAT, in accordance with the disclosed embodiments and FIG. 5 illustrates a graphical representation 500 illustrating multiple staggered magnet array section HBA EMAT and the SH waves generated using multiple staggered magnet array section HBA EMAT, in accordance with the disclosed embodiments. The EMAT configurations presented previously shows the staggered magnet arrays arranged and grouped next to each other in one specific area. FIG. 4 and FIG. 5 demonstrates that the staggered array concept can be applied to EMAT configurations with multiple magnet sections. In both cases, ultrasonic waves are generated within the sample, just beneath the magnet sections.

[0030] Again, note that the configurations illustrated in FIG. 1-5 should not be constituted in any limited sense. The configurations are only exemplary perspectives for working of the invention. Several additional configurations are possible within the scope of the proposed invention. The SMA based EMAT proposed herein allow for a fixed frequency electrical input to provide different ultrasonic or acoustic beams using mechanical movements to stagger the magnet arrays thereby enabling to generate different ultrasonic beams using the SMA based EMAT in a wide range of industrial applications.

[0031] The magnetic configurations in the SMA based EMAT can be dynamically manipulated through the mechanical movement of the magnet arrays, thereby manipulating the ultrasonic beams from the EMAT. The SMA based EMAT allows for the dynamic or static focusing or defocusing of ultrasonic beams and thereby enhance the results or data obtained in the industrial application. The EMAT further allows the operator to steer the beam at different angles using a single transducer. The SMA based EMAT can have small footprint, low cost, and offer a universal solution for producing static or dynamic beam forming through simple mechanical movement of the magnets. As demonstrated in the FIG. 1-5, the beam forming has been observed when using multiple magnet arrays, including EMAT configurations with two, three, four and five magnet arrays.

[0032] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.