SMASIS2010-3651 ACTIVE VIBRATION ISOLATION SYSTEM USING THE PIEZOELECTRIC UNIMORPH WITH MECHANICALLY PRE-STRESSED SUBSTRATE

ABSTRACT In this paper, a pre-stressed piezoelectric unimorph made by a new fabrication method in room temperature, and an active vibration isolation system using the pre-stressed unimorph actuators are introduced. The fabricated piezoelectric unimorph, called PUMPS (piezoelectric unimorph with mechanically pre-stressed substrate), is an actuator in which actuation level is enhanced by displacement amplification mechanism that converts piezoelectric extension and contraction to large bending/pumping motion without sacrificing the actuation force. Preliminary vibration tests were performed to check the performance of PUMPS as actuators for active vibration control in a lab environment. Two feedback control schemes, the positive position feedback (PPF) and negative velocity feedback (NVF), were applied for active vibration control. Using a smart vibration isolation system with improved load capacity obtained by stacking pre-stressed piezoelectric unimorph actuators, about 10dB vibration reduction of the system was achieved near the resonant frequency region. With the preliminary vibration test results showing promising performance of PUMPS actuator in active vibration control, an integrated active vibration isolation system composed of PUMPS actuators is developed. The developed system contains compact analogue circuits and a sensor for PUMPS actuation and control, and power is supplied by Li-Polymer battery which means the system is completely standalone and portable. In addition, an integrated jitter isolation demonstration system was developed to demonstrate the degrading effect of jitter and the effectiveness of the developed integrated active vibration isolation system in improving the performance of optical payloads. Comparison of image qualities taken before and after the operation of vibration control system indicates that effective suppression of vibration disturbances can be achieved using the developed vibration isolation system with PUMPS actuators

Piezoelectric Characteristics of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr,Ti)O3 Ceramics with Different MnO2 Concentrations for Ultrasound Transducer Applications

In this study, we investigate the piezoelectric characteristics of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr,Ti)O3 (PNN-PZT) with MnO2 additive (0, 0.25, 0.5, 1, 2, and 3 mol%). We focus on the fabrication of a piezoelectric ceramic for use as both actuator and sensor for ultrasound transducers. The actuator and sensor properties of a piezoelectric ceramic depend on the piezoelectric strain coefficient d and piezoelectric voltage coefficient g, related as g = d/εT. To increase g, the dielectric constant εT must be decreased. PNN-PZT with MnO2 doping is synthesized using the conventional solid-state reaction method. The electrical properties are determined based on the resonant frequencies and vibration modes measured by using an impedance analyzer. The MnO2 addition initially improves the tetragonality of the PNN-PZT ceramic, which then saturates at a MnO2 content of 1 mol%. Therefore, the dielectric constant and piezoelectric coefficient d33 steadily decrease, while the mechanical properties (Qm, Young’s modulus), tanδ, electromechanical coupling coefficient k, and piezoelectric voltage coefficient g were improved at 0.5–1 mol% MnO2 content

Analysis of Important Fabrication Factors That Determine the Sensitivity of MWCNT/Epoxy Composite Strain Sensors

Composite sensors based on carbon nanotubes have been leading to significant research providing interesting aspects for realizing cost-effective and sensitive piezoresistive strain sensors. Here, we report a wide range of piezoresistive performance investigations by modifying fabrication factors such as multi-wall carbon nanotubes (MWCNT) concentration and sensor dimensions for MWCNT/epoxy composites. The resistance change measurement analyzed the influence of the fabrication factors on the changes in the gauge factor. The dispersion quality of MWCNTs in the epoxy polymer matrix was investigated by scanning electron microscopy (SEM) images and conductivity measurement results. A configuration circuit was designed to use the composite sensor effectively. It has been shown that, in comparison with commercially available strain gauges, composites with CNT fillers have the potential to attain structural health monitoring capabilities by utilizing the variation of electrical conductivity and its relation to strain or damage within the composite. Based on the characteristics of the MWCNT, we predicted the range of conductivity that can be seen in the fabricated composite. The sensor may require a large surface area and a thin thickness as fabrication factors at minimum filler concentration capable of exhibiting a tunneling effect, in order to fabricate a sensor with high sensitivity. The proposed composite sensors will be suitable in various potential strain sensor applications, including structural health monitoring

Defect Visualization of a Steel Structure Using a Piezoelectric Line Sensor Based on Laser Ultrasonic Guided Wave

We studied the detection and visualization of defects in a test object using a laser ultrasonic guided wave. The scan area is irradiated by a laser generated from a Nd:YAG 532 nm Q-switched laser generator through a galvanometer scanner. The laser irradiation causes the surface temperature to suddenly rise and then become temporarily adiabatic. The locally heated region reaches thermal equilibrium with the surroundings. In other words, heat energy propagates inside the object in the form of elastic energy through adiabatic expansion. This thermoelastic wave is typically acquired by a piezoelectric sensor, which is sensitive in the ultrasonic domain. A single piezoelectric sensor has limited coverage in the scan area, while multi-channel piezoelectric sensors require many sensors, large-scale wiring, and many channeling devices for use and installation. In addition, the sensors may not acquire signals due to their installed locations, and the efficiency may be reduced because of the overlap between the sensing areas of multiple sensors. For these reasons, the concept of a piezoelectric line sensor is adopted in this study for the first time. To verify the feasibility of the line sensor, I- and L-shaped sensors were attached to a steel structure, and the ultrasound signal from laser excitation was obtained. If the steel structure has defects on the back, the ultrasonic propagation image will be distorted in the defect area. Thus, we can detect the defects easily from the visualization image. Three defects were simulated for the test. The results show that the piezoelectric line sensor can detect defects more precisely and accurately compared to a single piezoelectric sensor

Displacement, Strain and Failure Estimation for Multi-Material Structure Using the Displacement-Strain Transformation Matrix

In this study, we propose a method to estimate structural deformation and failure by using displacement-strain transformation matrices, i.e., strain-to-displacement transformation (SDT) and displacement-to-strain transformation (DST). The proposed SDT method can be used to estimate the complete structural deformation where it is not possible to apply deformation measurement sensors, and the DST method can be used for to estimate structural failures where strain and stress sensors cannot be applied. We applied the SDT matrix to a 1D beam, a 2D plate, rotating structures and real wind turbine blades, and successfully estimated the deformation in the structures. However, certain difficulties were encountered while estimating the displacement of brittle material such as an alumina beam. The study aims at estimating the displacement and stress to predict the failure of the structure. We also explored applying the method to multi-material structures such as a two-beam bonded structure. In the study, we used alumina–aluminum bonded structures because alumina is bonded to the substrate to protect the structure from heat in many cases. Finally, we present the results of the displacement and failure estimation for the alumina–aluminum structure