Abstract: An ultrasonic sensor for guided wave testing is disclosed. The sensor comprises a flexible circuit board (2), an array of piezoelectric elements (10) on the flexible circuit board and an array of permanent magnets (16). Each piezoelectric element is interposed between a respective permanent magnet and the flexible circuit board.

Abstract: A method of determining a thickness of an elongate or extended structure (2; FIG. 8) using elastic waves is disclosed. The method comprises receiving at least one time-domain signal from a transducer (12), generating a frequency-domain signal in dependence upon the at least one time-domain signal, reducing noise in the frequency-domain signal to provide a de-noised frequency-domain signal, comparing the de-noised frequency-domain signal with at least one reference signal, each reference signal corresponding to a respective thickness; and determining the thickness of the elongate or extended structure in dependence comparing the de-noised frequency-domain signal with the at least one reference signal.

Abstract: An apparatus and method for controlling the production of foamed material in which the material and foam are delivered to a mixer (12) in predetermined relative proportions. The apparatus comprises a mixer (23) for mixing a foam solution and air together, and a foam generator (26) for conditioning the air and foam solution mixture and delivering the resultant foam to the mixer. The foam generator (26) comprises a plurality of foam generating chambers connected in parallel, valves (28) being provided to control the flow of air and foam solution mixture through each of the generator chambers. The volume flow rate at which foam is delivered to the mixer (12) is monitored, and the valves are controlled to direct the air and foam solution mixture through one or more of the generator chambers in dependence upon the volume flow rate such that the flow velocity of the air and foam solution mixture within the chamber or chambers is within predetermined limits.