1-3 connectivity lithium niobate composites for high temperature operation.

Lithium niobate, LiNbO(3), is a piezoelectric material well known for its high Curie temperature. However, it has often been neglected for use in ultrasonic transducers because of its low electro-mechanical coupling coefficients. Recent advances in signal processing have made this disadvantage less significant and we now report an investigation of the potential of LiNbO(3) composites for use in high temperature transducers for non-destructive testing (NDT). LiNbO(3) composites of 1-3 connectivity in room temperature vulcanising (RTV) sealant and cement matrices were fabricated by the dice and fill method. The RTV and the cement are specified to withstand temperatures up to 350 degrees C and 1600 degrees C, respectively. The composites have been characterized by electrical impedance measurement at ambient and elevated temperatures. In array configuration, transmit-receive signals from the back wall of a steel specimen were obtained at room temperature with good signal to noise ratio. High temperature measurements were made at temperatures up to 180 degrees C for the RTV composite and 360 degrees C for the cement composite configured as single element transducers. Temperature cycling has also been investigated and the new composite materials have been demonstrated to withstand several cycles without deterioration. It is concluded that they may contribute toward a solution to presently unsolved problems in NDT at elevated temperatures.