https://www.aeromech.usyd.edu.au/wwwcomp/pzferev.pdf

Advances in piezoelectric finite element modeling of adaptive structural elements: a survey

This paper investigates the behavior of piezoelectric elements as strain sensors. Strain is measured in terms of the charge generated by the element as a result of the direct piezoelectric ef- fect. Strain measurements from piezoceramic (PZT) and piezofilm (PVDF) sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are dis- cussed, along with their limitations. The sensors are surface bonded to a beam and are calibrated over a frequency range of 5-500 Hz. Correction factors to account for transverse strain and shear lag ef- fects due to the bond layer are analytically derived and experimentally validated. The effect of tem- perature on the output of PZT strain sensors is investigated. Additionally, design of signal condition- ing electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of piezoelectric sensors compared to conventional strain gages in terms of sensitivity and signal to noise ratio is demonstrated.

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Fundamental Understanding of Piezoelectric Strain Sensors

HIS article presents an overview and assessment of the technology leading to the development of intelligent structures. Intelligent structures are those which incorporate actuators and sensors that are highly integrated into the structure and have structural functionality, as well as highly integrated control logic, signal conditioning, and power amplification electronics. Such actuating, sensing, and signal processing elements are incorporated into a structure for the purpose of influencing its states or characteristics, be they mechanical, thermal, optical, chemical, electrical, or magnetic. For example, a mechanically intelligent structure is capable of altering both its mechanical states (its position or velocity) or its mechanical characteristics (its stiffness or damping). An optically intelligent structure could, for example, change color to match its background.17 Definition of Intelligent Structures Intelligent structures are a subset of a much larger field of research, as shown in Fig. I.123 Those structures which have actuators distributed throughout are defined as adaptive or, alternatively, actuated. Classical examples of such mechanically adaptive structures are conventional aircraft wings with articulated leading- and trailing-edge control surfaces and robotic systems with articulated manipulators and end effectors. More advanced examples currently in research include highly articulated adaptive space cranes. Structures which have sensors distributed throughout are a subset referred to as sensory. These structures have sensors which might detect displacements, strains or other mechanical states or properties, electromagnetic states or properties, temperature or heat flow, or the presence or accumulation of damage. Applications of this technology might include damage detection in long life structures, or embedded or conformal RF antennas within a structure. The overlap structures which contain both actuators and sensors (implicitly linked by closed-loop control) are referred to as controlled structures. Any structure whose properties or states can be influenced by the presence of a closed-loop control system is included in this category. A subset of controlled structures are active structures, distinguished from controlled structures by highly distributed actuators which have structural functionality and are part of the load bearing system.

Intelligent structures for aerospace - A technology overview and assessment

A finite element model for the static and dynamic analysis of a piezoelectric bimorph

The effective coefe cients of piezoelectric e ber-reinforced composites (PFRC) have been determined through micromechanical analyzes. The method of cells (MOC) and the strength of materials (SM) approach have been employed to predict the coefe cients. A constant electric e eld is considered in the direction transverse to the e ber direction and is assumed to be the same both in the e ber and the matrix. MOC and SM predictions for the effective piezoelectric coefe cient of the PFRC assessing the actuating capability in the e ber direction are in excellent agreement. It has been found for the piezoelectric e bers considered that, when the e ber volume fraction exceeds a critical e ber volume fraction, this effective piezoelectric coefe cient becomes signie cantly larger than the corresponding coefe cient of the piezoelectric material of the e ber. The methods also show the excellent matching of the predictions of the effective elastic constants and the dielectric constant of the PFRC in the useful range of e ber volume fraction.

Effective Coefficients of Piezoelectric Fiber-Reinforced Composites

In this paper, a discrete degrees of freedom model has been formulated for a structural dynamic system consisting of a linear elastic structure, bonded piezoceramic sensors and actuators, and a feedback signal conditioning system. In addition, an optimal control procedure based on the minimization of a quadratic performance index of state and control vectors has been developed that uses output feedback methods. Finally, the application of the model and the control technique has been demonstrated through the example of a linear elastic beam with piezoceramic sensors and actuators occupying discrete subdomains of the beam upper and lower surfaces. A model for the linear elastic beam has been obtained by using test results and a structural dynamic system identification method based on an equation error approach. Results for various weights in the performance index are included, and implications for future applications are discussed. N the past few years, there has been considerable research activity in the field of active and passive control of vibra- tions of flexible structures. One of the methods of active con- trol of vibrations, termed "electronic damping" in some of the early literature,1'6 involves the placement of piezoceramic devices on a structure to sense and control dynamic strains induced by structural vibrations. The deformation of a sens- ing transducer results in an electrical current that is condi- tioned by operations such as amplification and shifting of the phase of the signal. The conditioned signal is then applied to another piezoceramic, electrostrictive, or magnetostrictive device placed at a selected location on the structure. This trans- ducer acts as an actuator and transmits mechanical energy to the structure. Depending on the applied voltage, electrome- chanical coupling of the forcing transducer to the structure, and the location of the transducers, a degree of vibration control of flexible structures can be achieved. To date, applica- tions of the aforementioned scheme have primarily been in the area of large space structures, such as in the work of Crawley and Deluis,7 but the scheme is applicable to any structure with lightweight components. This type of active control offers unique features that are not usually employed for control of structural vibrations. The dynamics of direct contact type sensors and actuators permit a wide frequency range of control. A measure of tunability is provided for the control of structural systems that age or grow. Finally, this method adds little mass to the controlled flexible structure so that the existing plant model does not need to be modified to account for the mass of the transducers. To utilize the advantages of piezoceramic transducers, it is necessary to select appropriate positions of the transducers and to select the sensor signals that are to be fed back to the actuators. The problem of selecting the locations of the transducers is a complete problem in itself and thus will not be addressed in this paper. There has been some work in

M. W. Obal

Papers

Optimal vibration control by the use of piezoceramic sensors and actuators