Cheeyoung Joh

Bio-inspired piezoelectric artificial hair cell sensor fabricated by powder injection molding

A piezoelectric artificial hair cell sensor was fabricated by the powder injection molding process in order to make an acoustic vector hydrophone. The entire process of powder injection molding was developed and optimized for PMN–PZT ceramic powder. The artificial hair cell sensor, which consists of high aspect ratio hair cell and three rectangular mechanoreceptors, was precisely fabricated through the developed powder injection molding process. The density and the dielectric property of the fabricated sensor shows 98% of the theoretical density and 85% of reference dielectric property of PMN–PZT ceramic powder. With regard to homogeneity, three rectangular mechanoreceptors have the same dimensions, with 3 μm of tolerance with 8% of deviation of dielectric property. Packaged vector hydrophones measure the underwater acoustic signals from 500 to 800 Hz with −212 dB of sensitivity. Directivity of vector hydrophone was acquired at 600 Hz as analyzing phase differences of electric signals.

Determination of the complex material constants of PMN–28%PT piezoelectric single crystals

The accurate characterization of piezoelectric crystals should include the loss properties of the materials, which are represented as the imaginary parts of the material constants. The full complex properties of PMN‐PT single crystals have never been evaluated. This paper proposes an automated iterative method to determine the complex material constants of PMN‐28%PT single crystals. The PMN‐28%PT single crystals were grown using the Bridgman method and were poled along the [001] direction to have 4mm effective symmetry. Five different resonators suitable for 4mm symmetry were used to analyze the impedance and admittance spectra of the distinctive resonant modes. The complex material constants were determined by the nonlinear regression of the impedance and admittance spectrum equations for each resonator through the iteration process to fit the measured spectra of the corresponding modes. The efficacy of the characterization method and the accuracy of the complex material constants determined using this method were verified by a comparison of the immittance spectra from the measurements with those from the calculation using the complex constants. (Some figures may appear in colour only in the online journal)

Optimal design of an underwater piezocomposite ring transducer

The structure of an underwater multi-mode ring transducer was optimized to achieve the maximum bandwidth by means of the finite element method. The design scheme developed in this paper can be applied to optimize the structure of general underwater transducers to have a wider bandwidth at various operation frequencies. The designed transducer showed the -6-dB bandwidth of as much as 105%.

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.

Analysis of the Resonant Characteristics of a Tonpilz Transducer with a Fixed Tail Mass by the Equivalent Circuit Approach

In this paper, the resonant characteristic of a Tonpilz transducer with a fixed tail mass has been studied by means of an equivalent circuit approach. An equivalent circuit has been designed to describe the characteristic of a Tonpilz transducer that has an additional resonance because of its fixed tail mass. The transmitting voltage response of the transducer calculated by the designed circuit has been compared with that by the FEA (finite element analysis) to confirm the validity of the circuit. This equivalent circuit approach produces identical results with the FEA, in which the variation of resonant frequencies and TVR has been clearly figured out in relation to the stiffness of the mounting fixture and the mass of the tail mass. The suggested equivalent circuit can be utilized to figure out the characteristics of the Tonpilz transducer more efficiently than FEA that requires much calculation time and revision of the models in accordance with the variation of design variables.

Fabrication and characterization of artificial hair cell sensor based on MWCNT-PDMS composite

The aim of this work is to design and fabricate a flow sensor using an artificial hair cell (AHC) inspired by biological hair cells of fish. The sensor consists of a single cilium structure with high aspect ratio and a mechanoreceptor using force sensitive resistor (FSR). The cilium structure is designed for capturing a drag force with direction due to flow field around the sensor and the mechanoreceptor is designed for sensing the drag force with direction from the cilium structure and converting it into an electric signal. The mechanoreceptor has a symmetric four electrodes to sense the drag force and its direction. To fabricate the single cilium structure with high aspect ratio, we have proposed a new design concept using a separated micro mold system (SMS) fabricated by the LIGA process. For a successful replication of the cilium structure, we used the hot embossing process with the help of a double-sided mold system. We used a composite of multiwall carbon nanotube and polydimethylsiloxane (MWCNT-PDMS). The performance of the mechanoreceptors was measured by a computer-controlled nanoindenter. We carried out several experiments with the sensor in the different flow rate and direction using the experimental test apparatus. To calibrate the sensor and calculate the velocity with direction based the signal from the sensor, we analyzed the coupled phenomena between flow field and the cilium structure to calculate the deflection of the cilium structure and the drag force applying to the cilium structure due to the flow field around sensor.

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.