title: A New High-Temperature Ultrasonic Transducer for Continuous Inspection.
abstract: A novel design of piezoelectric ultrasonic transducer is introduced, suitable for operation at temperatures of up to 700 °C-800 °C. Lithium niobate single crystal is chosen as the piezoelectric element primarily due to the high Curie temperature of 1200 °C. A backing element based on a porous ceramic is designed for which the pore volume fraction and average pore diameter in the ceramic matrix can be controlled in the manufacturing process; this enables the acoustic impedance and attenuation to be selected to match their optimal values as predicted by a one-dimensional transducer model of the entire transducer. Porous zirconia is selected as the ceramic matrix material of the backing element to obtain an ultrasonic signal with center frequency of 2.7-3 MHz, and 3-dB bandwidth of 90%-95% at the targeted operating temperature. Acoustic coupling of the piezocrystal to the backing element and matching layer is investigated using commercially available high-temperature adhesives and brazing alloys. The performance of the transducer as a function of temperature is studied. Stable bonding and clear signals were obtained using an aluminum brazing alloy as the bonding agent.
authors.forename: Mohammad Hossein
authors.initials: MH
authors.lastname: Amini
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Sinclair
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Coyle
mesh_terms: D004867:Equipment Design; D006358:Hot Temperature; D009556:Niobium; D010087:Oxides; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*
chemical_list: D010087:Oxides; D009556:Niobium; C091692:lithium niobate