Abstract: An EMAT arrangement utilizes separate transmitter and receiver EMATs which may each be connected to a tuning capacitor by a stripline cable. An electrostatic shield may also be provided between the coils and the coils can be offset from each other by 1/2 the pitch distance of sections in the coil. This reduces the duration of main bang, thus making it possible for the EMAT arrangement to detect structures which are very close to the coils.

Abstract: An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal.

Abstract: A method and apparatus of inspecting for flaws in a specular reflector, where the flaws having an expected length and the reflector is electrically conductive. The method includes directing a beam of an electromagnetic acoustic transmitting transducer along a beam axis toward the specular reflector for producing a reflected electromagnetic acoustic beam. The transmitted beam has side lobes with zero points therebetween, at least some of the side lobes being major side lobes. The reflected beam is received using an electromagnetic acoustic receiving transmitter set at an angle to the beam axis, the angle being selected to be at one of the zero points and past all of the major lobes of the transmitted beam to eliminate root and crown signals of the weld, in the reflected signal.

Abstract: In an electromagnetic acoustic transducer or EMAT, a spring release mechanism comprises a frame or carriage and, if necessary at least one movement element for permitting movement across a surface of a workpiece. A magnet is movable against the surface past the frame or carriage and a base supports the magnet. The spring is connected between the frame and the base for biasing the base away from the frame to urge the magnet away from the surface.

Abstract: A flaw detection method and arrangement utilizes electromagnetic acoustic transducers (EMATs) which ultrasonically test a material for cracks or flaws. Four EMATs are used in a pitch-catch configuration, i.e. two pairs of EMAT transmitters and receivers. The EMAT transmitters and receivers are arranged such that a first EMAT transmitter is located on the surface diagonally across from a first EMAT receiver and a second EMAT transmitter is located diagonally across from a second EMAT receiver. The first and second EMAT transmitters transmit ultrasonic signals to the first and second EMAT receivers respectively; and these ultrasonic signals are transmitted orthogonal to each other. A pulser/receiver is operatively connected to the first and second EMAT transmitters and the first and second EMAT receivers for inducing the EMAT transmitters to propagate their respective waves. The pulser/receiver also receives the signal transmitted through the material after being received by the first and second EMAT receivers.

Abstract: A variable power source is provided having multiple power modules each of which can produce a portion of the total range of voltage required for pulsed operation of an electromagnetic acoustic transducer electromagnet. The power modules are connected in series, and controlled by individual potentiometers which are simultaneously adjusted. Selector switches are provided for enabling or disabling each module. The output of the power modules is connected to a pulser/controller for wave forming prior to sending the output signal to the electromagnet. A noise filter can be placed between the power modules and the pulser. LED-type indicators on the selector switches may be used to indicate the operational status of the modules.

Abstract: An enhanced EMAT probe and coil construction takes advantage of heat transfer and magnetic flux principles to permit inspection of workpieces at elevated temperatures of 1200.degree. F. and higher. A ferromagnetic, cup-shaped probe assembly having an end cap and a barrel is provided for carrying a coil assembly, preferably one or more permanent magnets, and a frustoconical focus core. The magnets are located within the barrel and connected to the end cap, and the cup-shaped probe assembly positions the coil assembly proximate the surface of the workpiece. A plurality of passageways may be provided in the end cap and barrel for admitting cooling air to an interior portion of the cup-shaped probe assembly. The cup-shaped probe assembly serves to provide a return path for magnetic flux of the magnetic field back to the permanent magnet means.

Abstract: A fault detecting circuit for use with an electromagnetic acoustic transducer having an electrostatic shield and a wear surface for determining when the wear surface for contacting test surfaces has developed holes.

Abstract: A device for measuring a load on a part and for monitoring the integrity of the part such as a bolt, comprises a socket having walls defining an interior space wherein the socket engages the bolt for transmitting a load to the bolt. An electromagnetic acoustic transducer comprising a magnet and a coil is located in the interior space of the socket near the bolt. The coil provides a current while the magnet provides a magnetic field such that the magnet and the coil generate an ultrasonic signal within the bolt. A detector is used to detect and measure a change in the ultrasonic signal at the bolt for measuring the load on the bolt and for detecting any flaws in the bolt.

Abstract: An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal.

Abstract: A shield for an electromagnetic acoustic transducer (EMAT) has multiple layers of electrically insulating and electrically conductive materials which contain a coil of the EMAT. A first insulating layer lies directly on top of the coil and is attached thereto by a suitable layer of non-conductive adhesive. A second layer having both insulating and conductive portions is provided on a side of the coil opposite the first insulating layer such that the coil is completely encapsulated within and in direct contact only with the insulating portions of the first and second layers. The insulating portion of the second layer has a high electrical resistance. A third, conductive layer having a conductive adhesive side is provided in contact with the conductive portion of the second layer. The third layer is also provided with a window extending completely therethrough having dimensions coextensive with those of the coil; shielding of the coil itself by this third layer is thus prevented.

Abstract: A method for detecting corrosion fatigue cracks in membraned boiler tubes in a membrane tube panel employs at least one EMAT coil generating ultrasonic SH shear waves at a predetermined beam angle. The method of the present invention provides better signal-to-noise ratios than conventional ultrasonic techniques as well as not requiring any couplant.

Abstract: A fast reacting ground fault interrupter circuit particularly suited for use with high current, high voltage DC pulses generated by transistor switched magnet pulsers driving pulsed electromagnets used with electromagnetic acoustic transducers (EMATs). Whenever a ground fault is detected, a digital shut off signal is sent to the transistor switched magnet pulser to shut it off and prevent transmission of the DC pulse. Additionally, the shut off signal is also provided to a DC current interrupter which shuts off power supplied to the transistor switched magnet pulser itself.

Abstract: A preamplification and impedance matching circuit for an electromagnetic acoustic transducer includes an impedance matching section of the circuit having input terminals for receiving radio frequency power from a radio frequency power source. A matching transformer, which is a step-down transformer, is operatively connected to the input terminals. Diode networks are operatively connected to the matching transformer and output terminals which lead to the coil of the transducer. Signal responses emitted by the transducer coil are transmitted to a preamplifier section of the circuit. Choke coils or resistors are used to limit radio frequency power entry into the preamplifier section of the circuit.

Abstract: A device for measuring a load on a part such as a bolt, comprises a socket having walls defining an interior space wherein the socket engages the bolt for transmitting a load to the bolt. An electromagnetic acoustic transducer comprising a magnet and a coil is located in the interior space of the socket near the bolt. The coil provides a current while the magnet provides a magnetic field such that the magnet and the coil generate an ultrasonic signal within the bolt. A detector is used to detect and measure a change in the ultrasonic signal at the bolt.

Abstract: An electrical circuit incorporating an improved diode expander network for an EMAT having a coil and a radio frequency power source which emits radio frequency power, and which blocks noise and interference while having the ability to operate at high frequencies and high current/power levels. A matching transformer having a primary side is operatively connected to the radio frequency source for receiving the radio frequency power. The transformer also has a secondary side having a first leg and a second leg. The matching transformer is normally a step-down transformer. A diode expander network is provided having a first pair of composite diodes connected in parallel with respect to each other to the first leg of the transformer, and a second pair of composite diodes connected in parallel with respect to each other to the second leg of the transformer. Each composite diode has a plurality of diodes arranged in a series and parallel relationship.

Abstract: A shield for an electromagnetic acoustic transducer (EMAT) has multiple layers of electrically insulating and electrically conductive materials which contain a coil of the EMAT. A first insulating layer lies directly on top of the coil and is attached thereto by a suitable layer of non-conductive adhesive. A second layer having both insulating and conductive portions is provided on a side of the coil opposite the first insulating layer such that the coil is completely encapsulated within and in direct contact only with the insulating portions of the first and second layers. The insulating portion of the second layer has a high electrical resistance. A third, conductive layer having a conductive adhesive side is provided in contact with the conductive portion of the second layer. The third layer is also provided with a window extending completely therethrough having dimensions coextensive with those of the coil; shielding of the coil itself by this third layer is thus prevented.

Abstract: A noncontact ultrasonic transducer for studying the acoustic properties of a metal workpiece includes a generally planar magnetizing coil positioned above the surface of the workpiece, and a generally planar eddy current coil between the magnetizing coil and the workpiece. When a large current is passed through the magnetizing coil, a large magnetic field is applied to the near-surface regions of the workpiece. The eddy current coil can then be operated as a transmitter by passing an alternating current therethrough to excite ultrasonic waves in the surface of the workpiece, or operated as a passive receiver to sense ultrasonic waves in the surface by measuring the output signal. The geometries of the two coils can be varied widely to be effective for different types of ultrasonic waves. The coils are preferably packaged in a housing which does not interfere with their operation, but protects them from a variety of adverse environmental conditions.