Abstract: A change in a surface of a wall is detected by transmitting a pulse of input ultrasonic vibrations into a proximal surface of the wall and then receiving ultrasonic vibrations from that proximal surface. The received ultrasonic vibrations are compared with a previously detected pulse of output ultrasonic vibrations that have been received from the proximal surface in order to identify, for example, a time of arrival of a current pulse of output ultrasonic vibrations. The time of arrival of this current pulse of output of ultrasonic vibrations may be used to detect a change in the surface of the wall, such as a change in the thickness of the wall. Other embodiments can detect a change in the roughness profile of the wall using changes in the received ultrasonic vibrations other than arrival time.

Abstract: An electromagnetic acoustic transducer includes a flux guide surrounded by one or more permanent magnets abutting side faces of the flux guide. The magnetic field from the permanent magnets enters the flux guide where repulsion between the magnetic fields directs at least a portion of the magnetic fields toward a test face abutting a test object. The flux density at the test face is greater than the flux density within the originating permanent magnets. An active portion of a coil disposed between the flux guide and the test object contains conductors that are substantially straight, parallel and carry current in the same direction in order to provide substantially mode pure and uni-directionally polarised excitation of shear waves within the test object.

Abstract: A change in a surface of a wall is detected by transmitting a pulse of input ultrasonic vibrations into a proximal surface of the wall and then receiving ultrasonic vibrations from that proximal surface. The received ultrasonic vibrations are compared with a previously detected pulse of output ultrasonic vibrations that have been received from the proximal surface in order to identify, for example, a time of arrival of a current pulse of output ultrasonic vibrations. The time of arrival of this current pulse of output of ultrasonic vibrations may be used to detect a change in the surface of the wall, such as a change in the thickness of the wall. Other embodiments can detect a change in the roughness profile of the wall using changes in the received ultrasonic vibrations other than arrival time.

Abstract: A change in a surface of a wall is detected by transmitting a pulse of input ultrasonic vibrations into a proximal surface of the wall and then receiving ultrasonic vibrations from that proximal surface. The received ultrasonic vibrations are compared with a previously detected pulse of output ultrasonic vibrations that have been received from the proximal surface in order to identify, for example, a time of arrival of a current pulse of output ultrasonic vibrations. The time of arrival of this current pulse of output of ultrasonic vibrations may be used to detect a change in the surface of the wall, such as a change in the thickness of the wall. Other embodiments can detect a change in the roughness profile of the wall using changes in the received ultrasonic vibrations other than arrival time.

Abstract: An electromagnetic acoustic transducer includes a flux guide surrounded by one or more permanent magnets abutting side faces of the flux guide. The magnetic field from the permanent magnets enters the flux guide where repulsion between the magnetic fields directs at least a portion of the magnetic fields toward a test face abutting a test object. The flux density at the test face is greater than the flux density within the originating permanent magnets. An active portion of a coil disposed between the flux guide and the test object contains conductors that are substantially straight, parallel and carry current in the same direction in order to provide substantially mode pure and uni-directionally polarised excitation of shear waves within the test object.