Finite Element Analysis of Smart Structures with Piezoelectric Sensors/Actuators Including Debonding

In vibration active control of composite structures, piezoelectricsensors/actuators are usually bonded to the surface of a host structure. Debonding of piezoelectricsensors/actuators can result in significant changes to the static and dynamic response. In thepresent paper, an novel Enhanced Assumed Strain(EAS) piezoelectric solid element formulation isdeveloped for vibration active control of laminated structures bonded with piezoelectric sensors andactuators. Unlike the conventional brick elements, the present formulation is very reliable, moreaccurate, and computationally efficient and can be used to model the response of shell structuresbesides thin plates. Delaminations are modeled by pairs of nodes with the same coordinates butdifferent node numbers, and numerical results demonstrate the performance of the element and theglobal and local effects of debonding sensors/actuators on the dynamics of the adaptive laminates.

BIMORPH PIEZOELECTRIC ACTUATOR FOR SMALL PIPE ROBOT

An experimental bimorph piezoelectric element (PZT) actuator for small piperobot is developed. The robot can move in φ20 mm pipe, and can carry a CCD camera for detectingcracks or fine holes on inner surface of pipe. The velocity of the robot can reach 17～22 mm/s forvertical pipe up/down, respectively. Moving principle and its performance characteristics arepresented.

Vibration Control of a Composite Beam Using Self-sensing Semi-active Approach

Structural vibration control was an active research area for the past twenty years because of their potential applications in aerospace structures,civil structures,naval structures,etc.Semi-active vibration control methods based on piezoelectric actuators and synchronized switch damping on inductance（SSDI） techniques attract the attention of many researchers recently due to their advantages over passive and active methods.In the SSDI method,a switch shunt circuit is connected to the piezoelectric patch to shift the phase and amplify the magnitude of the voltage on the piezoelectric patch.The most important issue in SSDI method is to control the switching actions synchronously with the maximum vibration displacement or maximum strain.Hence,usually a displacement sensor is used to measure the vibration displacement or a collocated piezoelectric sensor is needed to measure the strain of the structure near the piezoelectric actuator.A self-sensing SSDI approach is proposed and applied to the vibration control of a composite beam,which avoids using a separate sensor.In the self-sensing technique,the same piezoelectric element functions as both a sensor and an actuator so that the total number of required piezoelectric elements can be reduced.One problem in the self-sensing actuator,which is the same as that in the traditional collocated piezoelectric sensors,is the noise generated in the sensor signal by the impact of voltage inversion,which may cause extra switching actions and deteriorate control performance.In order to prevent the shunt circuit from over-frequent on-and-off actions,a simple switch control algorithm is proposed.The results of control experiments show that the self-sensing SSDI approach combined with the improved switch control algorithm can effectively suppress over-frequent switching actions and gives good control performance by reducing the vibration amplitude by 45%,about 50% improvement from the traditional SSDI with a separate piezoelectric element and a classical switch.

Static shape control of a flat shell structure

The eight-node and forty-DOF piezoelectric shell element were applied to shape control of a flat shell structure. By the direct and converse effects, a distributed piezoelectric sensor layer was used to monitor the shape deformation and a distributed actuator layer was used to suppresse the deflection. A finite element model was for static response of laminated shell with piezoelectric sensors/actuators was derived. The model was verified by calculating piezoelectric polymeric PVDF bimorph beam. The results are in good agreement with those obtained by theoretical analysis of Tzou and Hwang . A case study of the static shape control of a flat shell structure is presented.

Development of an Ultrasonic Motor That Uses an Inchworm Shaped Deformation of a Metallic Plate

At the present time, ultrasonic motors have been developed for a variety of purposes such as linear motion drives and rotational drives. The elaboration of an ultrasonic motor is time-consuming, because it is developed adapting on its application. In this study, a new ultrasonic motor structure that combines a piezoelectric element and a metallic plate is elaborated. The driving principle of this motor is that the metal plate is bent to an inchworm shape and rotates the rotor when the piezoelectric element is stretched. The objective of this study is to verify the functioning of the new motor experimentally.

Algorithm for the layout of a piezoelectric element in an elastic medium providing the maximal piezoelectric effect within a specified frequency range

An algorithm for the layout of a piezoelectric that provides the most efficient performance within a specified range of vibration frequencies is proposed in this paper.This algorithm is based on the consideration of a special parameter within the area of a piezoelectric element’s possible location.This parameter characterizes the superposition of electromechanical coupling coefficients’for all the natural vibration frequencies included in a specified frequency range.The condition for defining the best option for location of the piezoelectric element in the case of several equivalent positions is specified.The efficiency of the proposed algorithm is shown numerically.The electromechanical coupling coefficients were calculated numerically based on solution to the problem of natural vibrations for electroelastic bodies using a finite element method.The calculations were performed to define the best location for a single piezoelectric element at the surface of a thin-walled shell having a half-cylindrical shape.The results are presented for natural vibration frequencies within the frequency range from 0 up to 1100 Hz.The numerical results were obtained by solving the problem of natural vibrations with a finite element method using the ANSYS software package.

Study on precision piezoelectric rotary step motors with inner anchor/loosen and outer drive

A new precision rotary piezoelectric(PZT)actuator is proposed to improve its drive performance.Based on piezoelectric technology,the actuator adopts the principle of bionics,with a new method of stator inner anchor/loosen/rotor outer drive and a distortion structure of a thin shelf flexible hinge.This structure improves the stability of the anchor/loosen and step rotary.Its characteristics are evaluated by finite element analysis.The experiment shows that the new rotary PZT actuator works with higher frequency(40 Hz),higher speed(325 mrad/s),wider movement(360u),high resolution(1 mrad/step)and high torque(30 N?cm).The novel actuator can be applied in wide movement and high resolution driving devices such as those for optics engineering,precision positioning and some other micro-manipulation fields.

A variable step-down conversion ratio switched capacitor DC-DC converter for energy harvesting systems working in intermittent mode

Energy harvesting systems stimulate the development of power management for low power consumption applications. Improving the converter efficiency of power management circuits has become a significant issue in energy harvesting system design. This paper presents a variable step-down conversion ratio switched capacitor （SC） DC-DC converter to advance the converter efficiency of charge on the stored capacitor in a wireless monitoring system of orthopedic implants. The converter is designed to work at 1 MHz switching frequency and achieves 15 to 2 V conversion. Measurement results show that the converter efficiency can reach 42% including all circuit power consumption, which is much higher than previous work.

An approach to determination of shunt circuits parameters for damping vibrations

This paper considers the problem of natural vibrations of a deformable structure containing elements made of piezomaterials.The piezoelectric elements are connected through electrodes to an external electric circuit,which consists of resistive,inductive and capacitive elements.Based on the solution of this problem,the parameters of external electric circuits are searched for to allow optimal passive control of the structural vibrations.The solution to the problem is complex natural vibration frequencies,the real part of which corresponds to the circular eigenfrequency of vibrations and the imaginary part corresponds to its damping rate(damping ratio).The analysis of behaviour of the imaginary parts of complex eigenfrequencies in the space of external circuit parameters allows one to damp given modes of structure vibrations.The effectiveness of the proposed approach is demonstrated using a cantilever-clamped plate and a shell structure in the form of a semi-cylinder connected to series resonant RL circuits.