Monolithic arrays for monitoring industrial plant at high temperatures

Described here is a piezoelectric linear array to survive at 400°C, for non-destructive testing of steel plant at high temperatures. Arrays could be fixed permanently to test subjects to monitor known defects by comparing images over time. A monolithic array structure was used, based on a single crystal of lithium niobate 0.6-1.0 mm thick. Each array is 45×50 mm overall and has an active area 35×15 mm. There were 60-70 elements, 250 μm wide and on 500 μm pitch, defined by metal film electrodes. The arrays produce longitudinal waves and have centre frequencies in the range 3-8 MHz. Backwall echoes 1.5 μs long have been measured at high temperatures. B-scans of simulated defects in test blocks have been taken at room temperature, to show the arrays´ capability for non-destructive testing