Hee-n Seo

Design and Fabrication of a Multimode Ring Vector Hydrophone

Typical underwater acoustic sensors can measure the magnitude of an incoming sound wave but cannot identify the direction. In this paper, a new simple method for detecting the direction of a sound wave with a piezoelectric ring hydrophone is proposed. This method divides the piezoceramic ring of the hydrophone into eight elements and distinguishes the direction of the sound wave by combining the output voltages of the elements in a particular manner. The validity of the design method was confirmed through the fabrication of an experimental prototype of the ring hydrophone with the proposed structure and a comparison of its performance with the design results. The method allows the ring vector hydrophone to operate over a very wide frequency range without being restricted to its structural resonant frequencies.

Design of a Multimode Piezoelectric Spherical Vector Sensor for a Cardioid Beam Pattern

Typical underwater piezoelectric spherical sensors are omni-directional, thus can measure the scalar quantity sound-pressure-magnitude only with the limitation not being able to measure the direction of the incoming wave. This paper proposes a method to simultaneously measure both the magnitude and direction of the sound wave with the spherical sensor. The method divides the piezoceramic sphere of the sensor into eight elements, and distinguishes the magnitude and direction of the sound pressure by combining the output voltage of the elements in a particular manner. Further, through the analysis of the sensitivity variation in relation to the structural parameters like radius and thickness of the piezoceramic sphere, we have suggested the way to improve the sensitivity of the vector sensor.

Design of a Multimode Type Ring Vector Sensor

Typical underwater acoustic sensors can measure the scalar quantity of sound-pressure-magnitude with the limitation of being unable to identify the direction of an incoming wave. This paper proposes a method to detect the direction of the sound wave with a ring sensor. The sensor of the proposed structure has a piezoceramic ring divided into eight elements, and distinguishes the direction of the sound wave by properly combining the output voltages of the piezoceramic elements. Further, through the analysis of the effects of the structural parameters like the ring radius and length, and piezoceramic thickness, we have suggested the way to improve the sensitivity of the vector sensor.

Direction-of-Arrival Estimation for the Ring-Type Multimode Vector Hydrophone based on the Pressure Gradient-Acceleration Relationship

Conventional hydrophones can only measure acoustic pressure. To measure both acoustic pressure and incident direction, various types of vector hydrophones have been researched. In this paper, we deal with a ring-type multimode vector hydrophone divided into 4 elements and present a direction-of-arrival (DoA) estimation method based on the pressure gradient-acceleration relationship. The performance of the presented method is analyzed by the simulation based on the sensor modeling and is verified by the water tank experiment. The proposed method could work under the multi-frequency condition and may be utilized in many applications due to its low computation complexity.

Structural-acoustic Coupled Analysis of Buried Hydrophone System

A study was carried out to investigate the fluid-structure interaction phenomena of buried hydrophone system that exposed complex loads due to handling, transportation and installation. The buried hydrophone system has necessarily neighborhood structures for installation. Because of the neighborhood structure, acoustic field is deformed. We analyze the piezoelectric-structural-acoustic coupled problem and the results to use a finite element analysis software, ANSYS, which has an coupled field analysis capability. The effect of the component of hydrophone system is revealed altogether in pressure distribution. So, we classify and analyze the problem by four different compositions for decomposition.

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 characte...

Investigations of PMN-PT composites for high sensitive ultrasonic phased array probes in NDE

This paper describes the manufacturing and evaluation of a PMN-PT 1-3 composite based phased array ultrasonic probe for nondestructive evaluation (NDE). The electromechanical parameters of PMN-PT based 1-3 composites were measured and the composites were directly used in the acoustic stack manufacturing process (matching layer, etc.) similar to conventional PZT based probes. The performance of the phased array probes was measured by a PCUS® pro phased array electronic front end from Fraunhofer and compared with a PZT composite based phased array probe. The behavior of the single elements as well as the usability for a standard phased array sector scan was evaluated. The PMN-PT phased array probe shows a significant improvement of the sensitivity and a higher bandwidth.

Experimental Study of Radiation Impedance with Effect of Reflected Wave from Sonar Dome

The radiation impedance of arrayed vibrators is analyzed experimentally when the array has a reflector. To verify the effect of the reflector, the radiation impedance with the reflector was calculated. To estimate the radiation impedance change, the input impedance of the vibrator was calculated using an equivalent circuit model. The input impedance was dependant on the location of the vibrators. The experimental results show a similar tendency to the theoretical results. It is noted that the equivalent circuit model for theoretical analysis is useful for estimating the radiation impedance change caused by the reflected wave.

Acoustic Characteristics Analysis of Cylindrical Array for the Directional and Omni-directional mode Using the Boundary Element Method

The transducers used in active sonar on surface ships are packed in a specific geometry in the array drum in order to meet the requirements such as the source level, directional beam pattern, etc. This paper describes the acoustic characteristics of the cylindrical array which is based on a 64 vertical staves arrangement, each stave composed 5 independent transducers. Firstly, the single transducer on the rigid baffle in the water is analyzed with the Finite Element Method. From the result of the FE analysis nodal velocities on the radiation surface is calculated and used with the boundary conditions of the transducers mounted on the array drum. Then the acoustic pressure is calculated in the field points using the Boundary Element Method and the other acoustic informations, the source level, beam pattern, near field and far-field distance, were acquired.

Beam Analysis of Underwater Conformal Array by Using Cylindrical Acoustic Holography

As an experimental technique to analyze the far-field characteristics of underwater cylindrical array sensors, cylindrical acoustic holography is studied. Inside an laboratory water tank, far-field directivity patterns as well as near-field source images are reconstructed from the measured hologram by hydrophone array. Approximate equation for far-field directivity estimation is derived based on stationary phase method. The simulation and experiment show well usefulness of the proposed method in application of underwater array sensors.