Papers by Author: Young Sup Lee

Abstract: This paper presents the theory, design, and evaluation of a smart device for the enhanced separation of particles mixed in fluid. The smart device takes advantage of the ultrasonic standing wave, which was generated by the operation of a piezoceramic PZT patch installed in the smart device. The details of the device design including the electro-acoustical modelling for separation and PZT transducer are described at first. Based on this design, the separation device was fabricated and evaluated. In the experiments, an optical camera with a zoom lens was used to monitor the position of particles within the separation channel layer in the device. The electric impedance of the PZT patch bonded on the separation device was measured .The device shows a strong levitation and separation force against 50μm diameter particles mixed with water at the separation channel in the device. Experimental results also showed that the device can work at both heavy and light sand particles mixed with water due to the generated standing wave field in the separation channel.

Abstract: This paper describes a novel tip position sensor for a cantilever beam made of a triangularly shaped distributed piezoelectric PVDF (polyvinylidene fluoride) film. Due to the boundary condition of the cantilever beam and the spatial sensitivity function of the distributed PVDF sensor, the charge output of the PVDF sensor can be shown to be proportional to the tip position of the beam. Experimental result using the triangular PVDF sensor were compared with those using two commercially available position sensors: an inductive sensor and an accelerometer (after double integration). The resonance frequencies of the test beam, measured using the PVDF sensor, matched well with those measured with the two commercial sensors and the PVDF sensor also showed good coherence over wide frequency range, whereas the inductive sensor became poor above 300Hz. However, the measured response of the PVDF sensor showed a bit larger magnitude compared with the two commercial sensors at higher frequencies. The triangular PVDF sensor have a number of advantages over conventional position sensors and could be used as tip position sensors.

Abstract: Structural health monitoring (SHM) is a new technology that has been increasingly evaluated by the industry as a potential approach to improve the cost and ease of structural inspection. Piezoelectric smart active layer (SAL) sensor was fabricated to verify the applicability of finding cracks and conducting source location in a various materials. A crack detection and source location works were done in three kinds of test condition such as aluminum plates with crack for patch type SAL sensor, a smart airplane with embedding SAL sensor, and a concrete beam with real crack for practical application. From this experimental study, the evaluation algorithm for the arrival time delay and decrease of signal amplitude was suggested in this paper. Consequently, it was found that the SAL sensor and detection algorithm developed in this study can be effectively used to detect and monitor damages in the both existing structures and new designed smart structures.

Abstract: This paper describes an array sensor of piezoceramic PZT discs with flexible covering layers, which is designed to detect surface elastic waves in structures, such as Rayleigh waves. The sensor is distinguished from conventional “passive” sensors for elastic waves detection because it possesses an ability to actuate an “active” pulse. This indicates that the function of active pulse generation ensures the diagnosis of the structures, where the sensor attached or embedded into, can be accomplished in a smart way including an easy inspection of faults. Actually the sensor has been inspired from human sensory systems in order to apply for smart structure sensing. They utilized 6mm diameter and 0.25mm thick PZT discs for the active array sensor. The performance of the sensor was demonstrated at various experiments of some metal and composite structures that the sensor can be applied for the health monitoring of the advanced smart structure system.