Miniaturised SH EMATs for Fast Robotic Screening of Wall Thinning in Steel Plates

Abstract

Electromagnetic acoustic transducers (EMATs) are well suited to generating and detecting a variety of different ultrasonic wavemodes, without the need for couplant, and they can be operated through some coatings. EMATs can be used to generate shear horizontal (SH) waves, which show promise for fast screening of wall thinning and other defects. However, commercial SH-wave EMATs are not suitable for robotic implementation on ferritic steel due to the large magnetic drag force from the magnets. This paper describes the design and characterisation of miniaturised SH guided wave EMATs, which significantly reduce the magnetic drag and enable mounting onto a small crawler robot for sample scanning. The performance of the miniaturised EMATs is characterised and compared to a commercial EMAT. It is shown that signal to noise ratio is reduced, but remains within an acceptable range to use on steel. The bandwidth and directivity are increased, depending on the exact design used. Their ability to detect flat bottomed holes mimicking wall thinning is also tested.

Influence of Magnetostriction Induced by the Periodic Permanent Magnet Electromagnetic Acoustic Transducer (PPM EMAT) on Steel

“…EMATs are rapid and economical sensor solutions for detecting significant thickness reductions due to corrosion, as they consume little power and do not require direct contact with the inspected medium. For inspecting plate structures, using a periodic permanent magnet (PPM) EMAT has been a popular choice [2][3][4][5][6] due to their high signalto-noise ratio and ability to generate shear horizontal (SH) ultrasonic waves. SH waves are useful for nondestructive testing (NDT) since all particle displacements are parallel to the plane, reducing the influence of surface coatings and fluid contact.…”

“…Hirao and Ogi have developed an EMAT technique utilizing the PPM EMAT for detecting corrosion defects on steel pipelines by measuring the amplitude and phase of the detected SH wave signals [3]. Trushkevych et al, used miniaturized PPM EMATs with a robot to detect wall thinning on steel [4]. Shi et al, proposed a method for detecting circumferential cracks on a pipe with SH waves produced by a PPM EMAT by analyzing the reflections from the edges of the defect [6].…”

Unidirectional Shear Horizontal Wave Generation With Side-Shifted Periodic Permanent Magnets Electromagnetic Acoustic Transducer

“…HEAR horizontal (SH) are widely used for defect inspection in plates and pipes [1,2,3,4,5,6] due to its advantages, such as simple dispersion relationship, the possibility of readily operating with a single non-dispersive mode and no energy loss to non-viscous liquid loading. SH waves can be generated either by a periodic permanent magnet (PPM) electromagnet acoustic transducers (EMATs), shearpolarized piezoelectric strips [7,8], or by magnetostrictive patch transducers [9].…”

Desenvolvimento De Um Manipulador Para Varreduras Angulares Com Transdutores Emat

“…Servo myservo; // create servo object to control a servo //int servoPos = 0; // variable to store the servo position // Recommended PWM GPIO pins on the ESP32 include 2,4,[12][13][14][15][16][17][18][19][21][22][23][25][26][27][32][33] void prepareRelativeMove(int positions [5] move, will return \"ok\" or \"wait\"</p>\n\ <p>.../trig</p>\n\ <p>.../set_MaxSpeed?=value -in steps/sec</p>\n\ <p>.../set_MaxAccel?=value -in steps/sec&sup2;</p>\n\ <p>.../get_ready -will return \"ready\" or \"wait\"</p>\n\ <p>.../get_pos -will return \"x=value1 y=value2 z=......\" current position in absolute steps (sinse reboot)</p>\n\ <p>.../stop -stops as soon as possible (acording to deceleration) will always return \"ok\"</p>\n\ <p>...target_pos -will return\"x=value1 y=value2 z=......\" the target position in absolute steps (sinse reboot)</p>\n\ ";…”

“…Em específico, são guiadas em uma placa de metal, se propagando nas direções indicadas na Figura 2-2 (a) de maneira não uniforme. Existem direções principais, nas quais a intensidade de propagação é a maior, e direções não-principais[12]. Um dos objetivos principais das varreduras é construir um diagrama de radiação que indica essa intensidade em cada direção.…”