Patent ID: 7963165
Filing Date: 2011-06-21
Classification: G01N

Abstract:
1. Apparatus for non-contact detection of features in or on the wall of a hollow pipe having a longitudinal axis, the wall having an inner surface, comprising in combination: an air-coupled transmitting transducer disposed within said hollow pipe for generating ultrasonic waves at a first chosen angle to the normal to the inner surface of the wall, at a chosen first distance from the surface, and at a chosen longitudinal distance along the axis; a sweep generator for exciting said air-coupled transmitting transducer over a selected frequency range, whereby Lamb waves are generated in the wall of said pipe; an air-coupled receiving transducer disposed within said hollow pipe at the same longitudinal position as said transmitting transducer, at a second chosen angle to the normal to the inner surface of the wall and at a second chosen distance from the inner surface of the wall, for receiving ultrasonic waves emitted by the inner surface of said wall, said receiving transducer producing an electrical signal in response to the ultrasonic waves received thereby; a narrow-band tracking filter for receiving the electrical signal from said receiving transducer at the excitation frequency in the selected frequency range and generating a noise-filtered signal therefrom; and a signal processor for receiving the noise-filtered signal from said narrow-band tracking filter and producing a signal containing amplitude and phase information from the Lamb waves in the frequency domain.