Emat system for detecting surface and internal discontinuities in conductive structures at high temperature

An Electromagnetic Acoustic Transducer (EMAT) (1) for the detection of surface and internal Discontinuities (2) in an electrically conductive Inspected Material (3), comprising:

• a. At least one Magnet (4) or an electromagnet, configured to generate a static or quasi - Static Magnetic Field (SMF) in the Inspected Material (3);
• b. At least one HF Electric Coil (6), the latter being of the type
• i. either, configured as an HF Electromagnetic Transmitter (9) of an Emitted HF Electromagnetic Field (HFEMF), if the EMAT (1) is used in Emission Mode (EM), and then it is connected to the output of at least one AC Current Source (11), driving an HF Alternating Current (AC) in the HF Electric Coil (6) at ultrasonic frequency,
• inducing the Emitted HF Electro-Magnetic Field (HFEMF) in the direction of the Inspected Material (3),
• producing Material Eddy Currents (14) on the surface of the Inspected Material (3),
• generating Lorentz Forces (15) at ultrasonic frequency in the Inspected Material (3), by the interaction of the Material Eddy Currents (14) with the Static Magnetic Field (SMF) and/or a Magnetostriction,
• the disturbance of which generates Primary Ultrasonic Waves (17) directly in the Inspected Material (3);
• ii. and/or, configured as an HF Electromagnetic Receiver (18), if the EMAT (1) is used in Reception Mode (RM), and then it is traversed by a Secondary Ultrasonic Electrical Signal (88) at ultrasonic frequency,
• generated by an Emitted HF Electromagnetic Field (HFEMF),
• Induced by the Material Eddy Currents (14) produced on the Inspected Surface (8) of the Inspected Material (3) by Secondary Ultrasonic Waves (21), under the influence of an ultrasonic source, interacting with the Static Magnetic Field (SMF), and which are representative of the surface and internal Discontinuities (2) of the Inspected Material (3);
• c. At least one Perforated Matrix Laminated Magnetic Core (22), configured to concentrate and direct the Emitted HF Electromagnetic Field (HFEMF) in the direction or coming from the Inspected Material (3);
• of the type comprising a sandwich Matrix (23),
• i. consisting of a multitude of laminated Thin Sheets (24) stacked periodically along the Matrix Axis (25), these Thin Sheets (24) being positioned between the two main Matrix Faces (26) of the Sandwich Matrix (23), parallel to its Stacking Plan (27),
• ii. having multiple adjacent lateral Edge Faces (35), extending substantially perpendicular to the Stacking Plan (27) and perpendicular to the Matrix Axis (25);
• one of them, the First Edge Face (36) of the Matrix (23), facing the Inspected Surface (8) of the Inspected Material (3),
• and the other, the Second Edge Face (37) of the Matrix (23) being situated substantially opposite the First Edge Face (36), and facing the HF Electric Coil (6);
• iii. each laminated Thin Sheet (24) of the Matrix (23)
• having a spatial geometry and lateral dimensions similar to those of the adjacent Thin Sheets (24) in the Matrix (23);
• and,
• having two main lateral Sheet Surfaces (32), parallel to the Stacking Plan (27);
• iv. of which, the combined successive adjacent Peripheral Edges (33) of each Thin Sheet (24) constitute a grooved Edge Surface (34) of the Matrix (23), surrounding the Matrix Axis (25), and,
• v. defining a Core Axis (38) of the Matrix (23), substantially joining the centers of the First Edge Face (36) and the Second Edge Face (37);
• positioned substantially perpendicular to the Matrix Axis (25);
• d. this sandwich Matrix (23) comprising at least one First Multitude (28) of HF Active Laminae (29) (or groups of such laminae), each of them
• i. being isolated from one another,
• ii. externally incorporating an electrically conductive material;
• and/or being covered externally with an electrically conductive layer on its Peripheral Edges (33), and,
• iii. internally incorporating a Magnetic Material of ferromagnetic or ferrimagnetic type, and having a Curie Temperature (TC);
• This Electromagnetic Acoustic Transducer (EMAT) (1) being characterized in combination in that:
• a. It comprises a Grooved Cylindrical Aperture (39),
• i. passing through each Thin Sheet (24) of the Matrix (23), along an Aperture Axis (40) of the Sandwich Matrix (23), substantially parallel to the Matrix Axis (25) and perpendicular to the Core Axis (38), and,
• ii. opening onto each of the two lateral Matrix Faces (26);
• b. It comprises a multitude of Magnetic Via-Holes (41),
• i. of similar cross-sectional dimensions,
• ii. perforated through and substantially at the centre of each of the multiple thus apertured HF Active Laminae (29) of the Matrix (23), along an axis substantially parallel to the Inspected Surface (8),
• iii. having a Via-Hole’s Longitudinal Envelope (42), disposed along the Aperture Axis (40) of the Matrix (23), the lateral perimeter of which being continuously closed, and,
• iv. aligned to form by their alignment the Grooved Cylindrical Aperture (39);
• and,
• c. It comprises a multitude of closed Induced Current Loops (43) which, when the EMAT (1) is in operation, are
• i. induced by the Emitted HF Electromagnetic Field (HFEMF), which is either emitted by the HF Alternating Current (AC) at ultrasonic frequency in the HF Electric Coil (6), and/or emitted by the Material Eddy Currents (14) at ultrasonic frequency in the Inspected Material (3),
• ii. located within the Active Lamina Skin (48) of the periphery of each HF Active Lamina (29) of the Perforated Matrix Laminated Magnetic Core (22),
• iii. arranged according to a Loops Mapping (LM), defining the topology and the relative positions of all the Induced Current Loops (43);
• d. Each Magnetic Via-Hole (41) in each HF Active Lamina (29) is located between - the First Edge Face (36) facing the Inspected Surface (8), and - the Second Edge Face (37) facing the HF Electric Coil (6);
• e. Each Magnetic Via-Hole (41) of the Grooved Cylindrical Aperture (39) is internally free of any hard material, and in particular is free of any electrical conductor passing through it;
• f. The Loops Mapping (LM) is topologically discrete and consists of a multitude of discrete parts of Induced Current Loops (43) of the HF Active Laminae (29), (or groups of such HF Active Laminae) distant from each other;
• g. The remote Induced Current Loops (43) (or group of such Loops),
• i. are induced within the Active Lamina Skin (48) on the Peripheral Edges (33) of the HF Active Laminae (29),
• ii. are each arranged along a plane of loops parallel to the Stacking Plan (27), and substantially perpendicular to the surface of the Inspected Material (3);
• iii. are substantially parallel, and separated from one another, between their respective HF Active Lamina (29),
• iv. encircle the Magnetic Via-Holes (41) of their HF Active Lamina (29) and rotate around it;
• and,
• a. Each Core Spacing Slice (49) of the Perforated Matrix Laminated Magnetic Core (22) and of its surface, located between two adjacent HF Active Laminae (29) (or group), is free of any Induced Current Loops (43);
• Such that a combined and interactive double physical effect occurs within the Perforated Matrix Laminated Magnetic Core (22):
• a. Each of the multiple parallel and topologically discrete Induced Current Loops (43) of each apertured HF Active Lamina (29),
• i. separately generates a high-frequency magnetic field,
• ii. separately and locally increases the discrete and selective high-frequency magnetic coupling between a narrow Local Active Fraction (44) of the Inspected Surface (8) facing the HF Active Laminae (29), and the HF Electric Coil (6), and,
• iii. participates in the mutual reduction of the high-frequency magnetic reluctance of the EMAT (1);
• b. The Inner Perimeter (45) of each Magnetic Via-Hole (41) in each HF Active Lamina (29) of the Matrix (23),
• i. creates a Heat-Conducting and Convective Surface (46) that is free inside the center of its HF Active Lamina (29),
• ii. produces an internal Thermal Cooling effect to dissipate a fraction of the local electrical and calorific energy generated by the specific Induced Current Loop (43) of its specific HF Active Lamina (29), and,
• iii. participates in the improvement of the efficiency of the EMAT (1).