Coupling element with varying wall thickness for an ultrasound probe

An ultrasonic probe, comprising:

• an elongate rotatable ultrasonic coupling element having a longitudinal axis defining a transducer cavity and having a plurality of ultrasonic transducers disposed within the transducer cavity,
• the plurality of transducers forming an elongate array extending along the longitudinal direction of the coupling element, the coupling element having a circumferential wall thickness that varies with position along the length of the coupling element, wherein the ultrasonic probe comprises end elements with a circularly symmetric roiling surface and the coupling clement is disposed between the end elements that abut the surface of an object under investigation when a force in excess of a predetermined minimum force has been applied to bring the coupling element into contact with the object under investigation, said predetermined minimum force being sufficient to deform the coupling element to produce a longitudinally extending contact footprint greater than the elongate aperture of the elongate transducer array, said end elements are mounted for rotation with the coupling element and engage frictionally with the surface of the object under investigation such that the rolling force required to roll the probe along the surface under test is borne primarily by the end elements.