Ferroelectric PiezoCrystal Underwater Transducers

Harold C. Robinson

Naval Undersea Warfare Center Division Newport, 1176 Howell Street, Newport, RI, United States

harold.c.robinson@navy.mil

Abstract: The unique material properties of lead zinc niobate-lead titanate (PZN-PT), lead magnesium niobate-lead titanate (PMN-PT) and lead magnesium niobate-lead indium niobate-lead titanate (PMN-PIN-PT) ferroelectric PiezoCrystals enable compact, broadband, high power sound projectors that cannot be realized using conventional ceramics like lead zirconate titanate (PZT).  Because of their reduced stiffness compared to conventional ceramics, PiezoCrystal transducers are inherently smaller in volume and weigh less than their ceramic counterparts.  Since the strain energy density of PiezoCrystal is much higher than PZT, PiezoCrystal transducers can produce significantly higher acoustic source levels at a given electric field level than ceramic transducers.  Finally, since the electromechanical coupling factor of ferroelectric PiezoCrystals is significantly greater than conventional ceramics, properly designed PiezoCrystal transducers exhibit a flat response and are ideally matched to drive electronics over an octave or more of frequency, thereby dramatically reducing power requirements over the band of operation.  This paper shall highlight PiezoCrystal transducer prototypes developed at the Naval Undersea Warfare Center, Division Newport, and elsewhere demonstrating that the broadband, high power performance promised by PiezoCrystal’s material properties can be realized in practical underwater transducers.  Various PiezoCrystal transducer designs for underwater applications, including longitudinal vibrators, fully active and active-passive air-backed cylinder transducers, free-flooded ring transducers and bender bar transducers, will be shown.  These transducer designs cover a wide span of frequencies, and utilize both 33- and 32- operating modes.  Tuned bandwidths of up to 2.5 octaves of frequency, as well as source level increases of up to 15 dB at the band edges, will be demonstrated.  A PiezoCrystal segmented cylinder projector, four times smaller than its ceramic counterpart, set world records in terms of power per unit volume and power per unit mass in 2004.  A Low Frequency Range Tracking Transducer, developed in 2014, is 90% smaller and lighter than its legacy counterpart and effectively covers 3 tracking bands with a single unit.  It will also be shown that these technologies provide stable performance under high drive and duty cycle conditions.  Finally, the impact of using these PiezoCrystal sources on the drive electronics and power consumption shall also be discussed.

Harold C. Robinson received his Ph.D. in Physics from the University of Connecticut, Storrs, CT in 1990.  He has been employed at the NAVSEA Undersea Warfare Center Division Newport (NUWCDIVNPT) and its predecessor laboratories since 1990.  He is currently the Technical Program Manager for NUWCDIVNPT’s Science & Technology Transduction Materials Program and a Program Officer in ONR’s Acoustic Transduction Materials and Devices Program.  He has been a Principal Investigator in a variety of programs to determine transduction material properties under Naval sonar operating conditions, including electrostrictive ceramics and ferroelectric single crystals.  Since 2000, Dr. Robinson has been the NUWCDIVNPT technical lead in the development, characterization and testing of ferroelectric single crystal transducers for Naval applications including torpedo homing, countermeasures, acoustic communications, swimmer defense and non-traditional ASW.  He was a recipient of the 2001 NUWC Excellence in Developmental Engineering Award, the 2007 NUWC Excellence in Basic and Applied Research Award and the 2014 Assistant Secretary of the Navy Research, Development and Acquisition’s Dr. Delores M. Etter Top Scientists and Engineers of the Year Award for his work in single crystal transduction.  Dr. Robinson is author or co-author of 20 journal articles on transduction material properties and transducer performance.