Stephen C. Butler

A low-frequency directional flextensional transducer and line array

A unique low-frequency (900 Hz) class IV flextensional transducer that produces an enhanced far-field pressure on one side and canceled far-field pressure on the other side has been developed. The transducer radiating surface consists of a thick-walled elliptical aluminum shell and a U.S. Navy type III piezoelectric stack along its major axis with two active sections and one inactive section. The directionality is achieved by simultaneously exciting the shell into an omnidirectional and dipole operation by driving stack into both extensional and bending modes. Both measurements and modeling on this device show a front to back pressure ratio of more than 30 dB, producing cardioid-type radiation patterns over an octave band, for a single transducer element. The transducers measured mechanical Q is 8, coupling coefficient is 0.25, and electroacoustic efficiency is 80% and produced a source level of 215 dB re: 1 μPa at 1 m when driven at a field limit of 394 kV/m (10 kV/in.) at resonance. The uniqueness of th...

Hybrid magnetostrictive/piezoelectric Tonpilz transducer

A self‐tuned magnetostrictive/piezoelectric hybrid Tonpilz transducer which produces enhanced motion at one end and canceled motion at the other is presented. The particular hybrid Tonpilz transducer described here consists of two 5.4 in. (13.65 cm) diameter circular pistons with a central mass separating a Terfenol‐D magnetostrictive tube and a Navy type I piezoelectric ring stack driver. The in‐water mechanical resonance and hybrid electrical self‐tuning occurs in the vicinity of 4.25 kHz where a 15‐dB front‐to‐back pressure ratio was obtained under array loading conditions. As a result of the shared electrical stored energy, an improved effective coupling coefficient is obtained.

A broadband hybrid magnetostrictive/piezoelectric transducer array

Most existing sonar transducer technologies that are capable of producing broadband, high power acoustic signals required for future Navy needs, are only conceptual in design, or very early into their development stage. A high power broadband 16 element array of Hybrid Magnetostrictive Piezoelectric Tonpilz Transducer (MPT) projectors is currently being developed at Naval Undersea Warfare Center (NUWC), Newport, R.I. for these applications. The Hybrid Transducer combines the high strain magnetostrictive material, Terfenol-D, with that of Lead Zieconate Titanate piezoelectric ceramic, to create a double resonant, high power broadband device. This design provides a 1 kHz increase in bandwidth below the low end of the frequency band of a conventional piezoelectric Tonpilz transducers of the same size and weight. The theory of operation, fabrication technique and test results will be discussed for a single element and then compared with a conventional Tonpilz sonar transducer of same size and weight. Modeling and measurement data for the 16-element array will also be discussed.

Unidirectional magnetostrictive/piezoelectric hybrid transducer

The object of the hybrid transducer is to produce enhanced motion at one end and canceled motion at the other end. In the simplest form the transducer consists of a quarter wavelength section of piezoelectric material joined to a quarter wavelength section of Terfenol‐D rare‐earth magnetostrictive material. A 3‐kHz experimental hybrid transducer with a total length of 18 in. was constructed with a small central mass and two small equal end piston masses. Measurements on this device showed an average front‐to‐back ratio of approximately 17 dB. The operating theory, equivalent circuit analysis, and measured results will be presented. The results confirm the original 1984 theoretical prediction [U.S. Patent 4,443,731]. [Modeling effort supported by SBIR.]

Hybrid magnetostrictive/piezoelectric tonpilz transducer

Abstract A combined magnetostrictive/piezoelectric hybrid sonar tonpilz transducer which produces enhanced motion at one end and cancelled motion at the opposite end has been developed. The transducer combines the high strain magnetostrictive material Terfenol-D with that of Lead Zirconate Titanate (PZT- 4) piezoelectric ceramic. The transducer has the ability to electrically self-tune and shows an improved effective coupling coefficient 25% greater than a conventional tonpilz type transducer. The in-water mechanical resonance and electrical self-tuning occur in the vicinity of 4.25 kHz, where a 15 dB front-to- back pressure ratio was obtained under a 12 element array loading condition. The high coupling coefficient and double resonant system makes this transducer attractive for wide bandwidth operation. With simple manipulation of the design parameters analytical results predict a vastly increased bandwidth of the transducer. An increase in bandwidth from the traditional tonpilz value of 20% to over 100%...

Thermal analysis of high drive transducer elements

The increasing demand for high‐power, low‐cost, compact transducer packages for underwater acoustic applications is leading to concerns of overheating in the active driving piezoelectric ceramic (lead zirconate titanate) elements and the associated passive materials (epoxies and polyurethanes). Pushing a design to its thermal limits can lead to reduced acoustic performance and reliability. There is not much guidance to be found in the literature that provides an analytical approach to cope with thermal issues of piezoelectric ceramics in the design phase. An analytic modeling effort is presented that addresses the thermal issues for compact high drive 31‐mode free‐flooded ring underwater sonar transducers. In this particular case, the thermal issues proved to be the limiting design concerns over the field and stress‐limited cases. However, with modeling (analytical and finite element) and bench testing of components, the proper choice of materials and configuration parameters were determined and the perfo...

Thermal model for piezoelectric transducers (L)

A lumped parameter equivalent circuit basis for calculating and allocating heat power sources in a transducer is presented along with experimental results. The simple model allows heat power calculations at resonance based on readily attainable parameters for transducers with uniform fields. Measured and finite element analysis of steady state thermal results are compared for the monopole mode of the single crystal driven modal transducer projector. The model serves as a physical and computational aid in the evaluation of piezoelectric transducer heating and may be used for evaluating highly coupled single crystal as well as ceramic piezoelectric transducers.

Triple-resonant transducers

A detailed analysis is presented of two novel multiple-resonant transducers which produce a wider transmit response than that of a conventional Tonpilz-type transducer. These multi-resonant transducers are Tonpilz-type longitudinal vibrators that produce three coupled resonances and are referred to as triple-resonant transducers (TRTs). One of these designs is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, second central mass, second compliant spring, and a piston radiating head mass. The other TRT design is a mechanical series arrangement of a tail mass, piezoelectric ceramic stack, central mass, compliant spring, and head mass with a quarterwave matching layer of poly(methyl methacrylate) on the head mass. Several prototype transducer element designs were fabricated that demonstrated proof-of-concept.

Thermal behavior of high‐power active devices with the ATILA (analysis of transducers by integration of LAplace equations) finite‐element code

Many active devices using piezoelectric ceramics are driven with very high power densities and long pulse lengths. Due to mechanical and dielectric losses in the materials, this produces heat, causing a temperature rise in the devices, which may lead to their mechanical failure. The thermal issues have been shown to be the limiting device design criteria over electric field and mechanical stress limits, yet the effect of the temperature on performance is generally not considered in the numerical models used during the design stage. A coupled electro‐mechanical thermal analysis is implemented in the ATILA code. For a steady‐state or transient solution, a thermal behavior is weakly coupled to the electromechanical response. The method may take advantage of the order‐of‐magnitude‐greater time constant for thermal effects compared to mechanical behavior. A two‐step analysis is performed whereby the electromechanical behavior is first computed, and the resulting dissipated power is then applied as a heat generator to determine the resulting temperature of the device. A high‐drive, 31‐mode, free flooded ring transducer and a sonar projector serve as validation of the numerical model. The approach addresses both the transient thermal response and the steady temperature profile that results from the high‐power, high‐duty‐cycle drive.

High frequency triply resonant broadband transducer array development at NUWC

Summary form only given. With the Navys current emphasis on detection in littoral environments requires the use of broadband sonar signal processing and frequency agility. This has prompted the need for new classes of broadband sonar transducers that can transmit and receive these complex signals. NUWC has developed and built a new class of novel high-frequency (HF) broadband (electro-acoustic) transducers and arrays that can be configured into conformal arrays for use on the bow or sail of present and future classes of submarines, unmanned undersea vehicles (UUVs), and on torpedo homing sonar systems. This transducer design, the Triply Resonant Tonpilz (TRT), is a mechanical series arrangement of a piezoelectric ceramic stack, two center masses, two compliant springs, and a tail and head mass, all together generating three resonances. The design produces a flat transmitting response of two octaves when in an array-loaded configuration. The increase in operating bandwidth is achieved without the use of exotic and expensive transduction materials. This triply resonant transducer is a very cost competitive approach to introducing broadband into the Fleet. It provides a 5 kHz to 10 kHz increase in bandwidth at the low end of the band over a traditional tonpilz transducer. A traditional tonpilz designed to encompass this lower frequency would be at least 50% to 75% longer, which is unsatisfactory in these applications that require minimal impact on the submarine. The results of two 36 element planar HF arrays that are currently being designed, fabricated, and tested NUWC is presented, modeled results of a more compacted (22% smaller) Triply Resonant Tonpilz using PMN-PT single crystal as the active driver is also presented. A smaller 9 element VHF array design that is three times smaller than the HF design is also presented.