Free-flooded Ring Research Articles

A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

An improved lumped parameter model of the single free-flooded ring transducer using Helmholtz–Kirchhoff integral solution

The Helmholtz-Kirchhoff integral (HKI) may be considered as the boundary element method (BEM) used to calculate the acoustic pressure at any position in the 3D-radiation problem from a vibrating surface. This method provides valuable insights into the radiation characteristics of vibrating structures, which may offer significant information and tools to underwater transducer design engineers during the early stages of development. It may save considerable computational costs in the design processes for the underwater transducer such as Hull Mount Sonar. This study illustrates usefulness of the HKI-based approach by developing a simple model of the Free Flooded Ring (FFR) transducer using a piezoelectric ring model and the HKI solution on the surface acoustic pressure of the ring through their physical conditions on their connected interfaces. The FFR transducer is widely utilized as a low-frequency acoustic source in underwater environments due to its broad operating frequency bandwidth and relatively small size. The developed approach aims to construct a precise model that considers the sound-structure interactions between the piezoelectric ring and the acoustic medium around it. To validate the accuracy of the proposed method, the acoustic pressure and electrical admittance are compared with those obtained through finite element method (FEM) simulations.

A new lumped parameter model for the design of the free-flooded ring transducer

The free-flooded ring (FFR) transducer is the well-known low-frequency sound sources in underwater because of its broad operating frequency bandwidth and relatively small size. Many previous studies have been performed that predict the characteristics of an FFR transducer using an equivalent circuit model (ECM), a type of lumped parameter model (LPM) because an ECM is widely used to understand the properties of such transducers in the design process. However, it is quite difficult to predict the characteristics of an FFR transducer because the acoustic field is generated from its top and bottom openings, connected by the inner fluid, as well as the cylindrical ring surface. In this study, the authors investigated an ECM of an FFR transducer. The ECM consists of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. In addition, an LPM which can consider mutual radiation loads was proposed to improve the accuracy of the model. The proposed models were compared and verified using commercial finite element method (COMSOL Multiphysics). We confirmed that LPM can predict characteristics of FFR transducer more accurately than ECM. [This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (Grant No. 2016R1E1A2A02945515).]

A review of single crystal underwater transducers

The unique material properties of lead magnesium niobate-lead titanate (PMN-PT) single crystals enable compact, broadband, high power sound projectors that cannot be realized using conventional ceramics. This paper shall highlight single crystal transducer prototypes developed at the Naval Undersea Warfare Center, Division Newport, and elsewhere demonstrating that the broadband, high power performance promised by single crystal’s material properties can be realized in practical underwater transducers. Various single crystal 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. t will also be shown that these technologies provide stable performance under high drive and duty cycle conditions. Finally, the impact of using these single crystal sources on the drive electronics and power consumption shall also be discussed.

음원 간격에 따른 FFR 트랜스듀서 배열의 송신특성 연구

A free flooded ring (FFR) transducer is a ring type projector which has a open backing, cavity, to the water, and it can be applied to a deep sea sound source. A a vertical line array should be constructed to improve the source level but a height of the vertical array should be limited shortly to ensure the sonar operation at sea. In this compact array case, complex interferences caused by cavity modes and mutual radiation impedances may affect on the transmitting responses of the array. Therefore, effects of the element spacing on transmitting characteristics of the FFR transducer array should be understood since the element spacing is the dominant parameter of those interactions. First of all, the transmitting responses of the arrays are numerically calculated according to the element spacing. Strong interference effects related with transmitting characteristics are expected especially around the cavity mode. Simulated results are verified experimentally by underwater acoustic test. Several practical aspects regarding the interference effects are discussed for a sonar design and an operation in this work.

A new lumped parameter model for the design of the free-flooded ring transducer

The free-flooded ring (FFR) transducer is the well-known low-frequency sound sources in underwater because its operating frequency bandwidth is broad and relatively small size. Previous researches were preformed to predict the characteristics of FFR transducers using ECM which is a type of LPM because ECM is widely used to understand its characteristics in transducer design process. However, it is hardly to predict the characteristics of an FFR transducer because the acoustic field is generated from its top and bottom openings, connected by the inner fluid, as well as the cylindrical ring surface. Here, the authors investigated an ECM of an FFR transducer consisting of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. In addition, an LPM which can consider mutual radiation loads was proposed to improve the accuracy of the model. The proposed models were verified using commercial finite element method (COMSOL Multiphysics). It was confirmed that LPM could predict characteristics of FFR transducer more accurately than ECM. [Work supported by NRF 2016R1E1A2A02945515).]

A lumped parameter model of the single free-flooded ring transducer.

A free-flooded ring (FFR) transducer can generate low-frequency sound in a small device and has a wide operating frequency bandwidth. Many studies have been performed that can predict the characteristics of an FFR transducer using analytical techniques and an equivalent circuit model (ECM), and methods to predict properties using numerical simulations have recently been developed. However, an ECM, a type of lumped parameter model (LPM), is still widely used to interpret the properties of such transducers in the design process. In this study, the authors investigated an ECM of an FFR transducer. The ECM consists of three parts: the piezoelectric ring, the cylindrical cavity, and the radiation load. Moreover, it can be included readily in a circuit to drive an FFR transducer. Additionally, an LPM was proposed, considering the mutual radiation loads, to improve the accuracy of the model. Each model was tested in comparisons with the finite element method; it was confirmed that an LPM could predict the properties of an FFR transducer with much better accuracy than an ECM. The LPM developed can save much time in designing FFR transducers.

소나 시스템 설계를 위한 FFR 트랜스듀서 어레이의 등가회로 모델링

Free-Flooded Ring (FFR) transducer array for use in Sonar system can be driven with large amplitude in a wide frequency band due to its structural characteristics, in which two resonances of a ring mode (1st radial mode) and an inner cavity vibration mode occur in a low frequency band. Since its sound wave generation characteristics are not influenced by the water pressure, the FFR transducer array is widely used in the deep sea. So FFR has been recognized as a low-frequency active sound source and has received much attention ever since. In order to utilize the FFR transducer array for SONAR systems in military and industrial applications, its equivalent electric circuit model is necessary especially to design the matching circuit between the driving power amplifier and the FFR transducer array. Thus this paper proposes the equivalent electric circuit model of FFR transducer array by using measured values of parameter, and suggest the improved method of parameter identification. Finally it verifies the effectiveness of the proposed circuit model of FFR transducer array by experimental measurements.

Thirty years progress of underwater sound projectors in china

Progress in the development of underwater sound projectors over the past thirty years in China is presented in this paper. This progress may be divided into four parts: (i) The development of new underwater sound projectors based on new transducer materials such as rare earth giant magnetostrictive materials, relaxation ferroelectric materials and piezoelectric composite materials. (ii) The design of new structures and energy transfer mechanisms such as flex-tensional transducers, mosaic cylindrical transducers, longitudinal transducers, flexural disk and beam transducers. (iii) The development of new configurations that broaden transducer bandwidth such as free-flooded ring transducers, broadband free-flooded flex-tensional transducers, doubly-excited longitudinal transducers, hybrid longitudinal transducers and matching layer technology. (iv) The development of new transducer design and analysis tools such as finite-element models for complex geometries, structure and fluid coupling mechanisms. These models have been used to optimize the design of a variety of projectors including low-frequency transducers, high power transducers and broadband wide-beam transducers.

Advantage analysis of PMN-PT material for free-flooded ring transducers

The acoustic radiation characteristics of free-flooded ring transducers made of PZT4 and PMN—PT materials are calculated and compared. First, the theoretical formulae for free-flooded ring transducers are studied. The resonant frequencies of a transducer made of PZT4 and PMN—PT materials are calculated. Then, the transmitting voltage responses of the free-flooded ring transducers are calculated using the finite element method. Finally, the acoustic radiation characteristics of the free-flooded ring transducers are calculated using the boundary element method. The calculated results show that the resonant frequencies of the free-flooded ring transducer made of PMN—PT are greatly reduced compared with those made of PZT4 with the same size. The transmitting voltage response of the transducer made of PMN—PT is much higher than that of the transducer made of PZT4. The calculated 3-dB beamwidth of the acoustic radiated far-field directivity of the free-flooded ring transducer made of PZT4 at the resonant frequency 1900 Hz is 63.6° and that of the transducer made of PMN—PT at the resonant frequency 1000 Hz is 64.6°. The comparison results show that the free-flooded ring transducer made of PMN—PT material has many advantages over that made of PZT4. The PMN—PT is a promising material for improving the performance of free-flooded ring transducers.

Numerical acoustic modeling code applied to sonar transducers and arrays: review and perspectives

In this paper a review based on several examples of Thales Underwater Systems (TUS) design and modeling of transducers will be presented: several examples like wide band free flooded ring flextensional and bender transducers, high frequency transducers with thermal analysis modeling included, will be discussed. An approach of the problem of the mutual impedance computation appearing in array modeling will be also presented. Tus used since several decades FEM ‐ BEM codes to design acoustic transducers and arrays. The perspectives in transducer and array modeling will be indicated like the possibility to take into account the non‐linearities in the material, the time dependent problem and the use of new kind of piezoelectric material will be also discussed. Specific aspect of single crystal transducers modeling will be presented. The increase of the computing power will also permit to take into account the complex problem of the interaction between transducers in an array (mutual impedances). We will conclude on complex ultra wide band antenna (based on strong transducers interactions) optimization and the associated modeling architecture issues.

Finite element modeling of radiating structures using dipolar damping elements

The finite element modeling of a radiating structure can be performed by surrounding this structure with a limited fluid domain, upon the external boundary of which a nonreflexion condition is prescribed for the acoustic field. This condition can be implemented with the help of damping finite elements which are attached to the external boundary and are designed to absorb the successive components of the pressure field multipolar expansion [Bayliss et al., ICASE Rep. No. 80/1, NASA, Langley (1980)]. This paper describes an axisymmetrical finite element which damps the monopolar and dipolar components of the radiated field. Then, it provides an original extrapolation algorithm to compute farfield quantities (sound pressure level or transmitting voltage response, directivity patterns,...) from the previously obtained nearfield. Finally, it demonstrates the accuracy of the method in two test cases and describes its application to the analysis of a free-flooded ring transducer used in sonar devices.

Historical highlights of the development of free-flooded magnetostrictive ring transducers

The historical highlights of research activity on magnetostrictive free-flooded ring transducers are presented with emphasis on recent work. The significant achievements of the research, their background, and the ongoing materials research that has been stimulated are summarized. They may have to use at some future time the technology of magnetostrictive ring transducers for high-power active surveillance because of changing conditions affecting undersea surveillance. The highlights include the advantages and disadvantages of free-flooded magnetostrictive transducers. A detailed summary of all of the work done on the subject would be lengthy and far beyond the scope of this. Nevertheless, an attempt is made to present an accurate and complete account of some of the more significant contributions to the technology.

Analytical-numerical method for the treatment of radiation from elastic structures I. General theory. II. Application to free-flooded ring transducers

Finite element methods have been used by several authors to study the problem of acoustical radiation from elastic structures [M.R. Knittel and D. Barach, Naval Undersea Center TP 412 (July 1974), and references contained therein]. The radiation loading of the structure due to the fluid medium can be taken into account either by numerical techniques based on the Helmholtz integral equation, or by additional finite element modeling of some of the liquid out to a separable surface where impedance conditions can be written in closed form. In this work we extend this method to the problem of radiation from multiple structures, either passive or active. Finite elements are used to model the scatterer and/or projector, as well as that portion of the liquid medium between the structure and a sphere completely surrounding it. The multiple-radiation problem is then handled using the methods developed by Twersky and others for conventional boundary-value problems [V. Twersky, “Scattering by Two Objects,” in Electromagnetic Waves, R.E. Langer, Ed., Univ. of Wisconsin P., Madison, WI (1962)]. As an application of the method we have analyzed the radiation from two tangentially polarized, ceramic free-flooded rings. Directivity, source levels, and electrical impedance have been calculated for a range of frequencies. Comparison with experiment show very good agreement over the frequency band of interest.

Low-frequency radiation characteristics of free-flooded ring transducers with application to a low-frequency directional hydrophone

Numerically predicted radiation characteristics of uniformly vibrating free-flooded rings are compared with experiment at frequencies above the monopole region but still below any resonances. Low-frequency velocity distributions for piezoceramic rings for several commonly used drive conditions are derived. Analytical formulas for the monopole radiation resistance, farfield pressure, and free-field voltage sensitivity are presented. A technique is developed for measuring the piezoelectric constants of free-flooded ceramic cylinders. It is predicted and experimentally verified that a free-flooded circumferentially polarized ring has maximum sensitivity in the axial direction for a band of very low frequencies. Thus, such a system may have application as a low-frequency directional hydrophone.

Low-Frequency Acoustic Radiation from Free-Flooded Ring Transducers Driven through the Circumference, Thickness, or Height

The normal velocity distribution of the surface of a free-flooded ring transducer completely determines its radiation characteristics in a given medium. The SHIP program is an algorithm for rapidly predicting the radiation characteristics of a free-flooded ring when the known surface velocity distribution is axisymmetric. The character of the radiation at low frequencies is extremely sensitive to the details of the velocity distribution which, in turn, depends not only on the geometry of the ring, but also on the manner in which the ring is driven and on the electromechanical parameters of the ring material. Gross differences in the directivity patterns predicted for different drive conditions occur at frequencies well below the first radial resonance for typical rings. Directivity patterns were obtained for a number of rings fabricated for different commonly encountered drive conditions (circumference, thickness, or height) and compared with patterns predicted by the SHIP program using simple models for the velocity distribution appropriate to each drive. Good agreement was obtained between the measured and predicted directivity patterns.

Accuracy of Simple Approximations Used to Calculate Axially Symmetric Extensional Vibrations of Elastic Ring Transducer

A complete mathematical model of a free-flooded ring transducer must predict the ring's surface velocity distri- bution when the forces acting on the ring are known. The acoustic radiation from a radially oscillating cylindrical ring is a function of its surface velocity distribution. In particular, the far-field radiation on the axis of the ring is a sensitive func- tion of the difference between the inside and outside surface areas and radial velocities and the axially directed edge veloc- ity. The theoretical determination of the velocity distribution of an unloaded elastic ring oscillating in its lowest order purely radial mode is performed by back of the envelope approxi- mations commonly used by transducer engineers and by a more sophisticated calculation based on the theory of Gustafsson and Kane for high-frequency extensional vibrations of a circular disk with a concentric hole. The results are com- pared and the transducer engineer can utilize this comparison to judge the confidence with which he may apply his easily ob- tained approximate results to the design of a free-flooded ring transducer with a specified velocity distribution.

Underwater Behavior of Free-Flooded Ceramic Ring Transducers

A numerical method is presented for the study of the underwater behavior of piezoelectric ceramic transducers in the shape of a shell of revolution, which are known as free-flooded ring transducers. The ceramic is circumferentially polarized and may be prestressed circumferentially by a layer of fiberglass. The method computes stresses within the transducer, its electrical admittance, and the acoustic radiation pressure field in the water. The theory is compared with experimental results from a circumferentially polarized PZT-4 cylindrical ring, and good agreement is obtained.