Aaron T. Crumm

Design of piezocomposite materials and piezoelectric transducers using topology optimization— Part III

SummaryCurrently developments of piezocomposite materials and piczoelectric actuators have been based on the use of simple analytical models, test of prototypes, and analysis using the finite element method (FEM), usually limiting the problem to a parametric optimization. By changing the topology of these devices or their components, we may obtain an improvement in their performance characteristics. Based on this idea, this paper discusses the application of topology optimization combined with the homogenization method and FEM for designing piezocomposite materials. The homogenization method allows us to calculate the effective properties of a composite material knowing its unit cell topology. New effective properties that improves the electromechanical efficiency of the piezocomposite material are obtained by designing the piezocomposite unit cell. This method consists of finding the distribution of the material and void phases in a periodic unit cell that optimizes the performance characteristics of the piezocomposite. The optimized solution is obtained using Sequential Linear Programming (SLP). A general homogenization method applied to piczoelectricity was implemented using the finite element method (FEM). This homogenization method has no limitations regarding volume fraction or shape of the composite constituents. The main assumptions are that the unit cell is periodic and that the scale of the composite part is much larger than the microstructure dimensions. Prototypes of the optimized piezocomposites were manufactured and experimental results confirmed the large improvement.

Topology optimization applied to the design of piezocomposite materials and piezoelectric actuators

Currently developments of piezocomposite materials and piezoelectric actuators have been based on the use of simple analytical models, test of prototypes, and analysis using the finite element method (FEM), usually limiting the problem to a parametric optimization. By changing the topology of these devices or their components, we may obtain an improvement in their performance characteristics. Based on this idea, this work discusses the application of topology optimization combined with the homogenization method and FEM for designing piezocomposite materials and piezoelectric actuators. The homogenization method allows us to calculate the effective properties of a composite material knowing its unit cell topology. In the design of piezocomposites, new effective properties that improves the electromechanical efficiency of the piezocomposite material are obtained by designing the piezocomposite unit cell. Prototypes of the optimized piezocomposites were manufactured and experimental results confirmed the improvement. In the design of piezoelectric actuators, we focus on the low frequency flextensional actuators which consist of a piezoceramic connected to a coupling structure that converts and amplifies the piezoceramic output displacement. By designing new kinds of coupling structure flextensional actuators for different tasks can be obtained.

New microfabrication technique for electroactive ceramic and electrode materials

Several mechanical designs capable of amplifying the performance of electroactive ceramic actuators and sensors have been presented in the smart materials and structures literature. The realization of these designs on the microscale requires a fabrication technique capable of producing intricate ceramic and electrode structures. Microfabrication by coextrusion (MFCX) provides a simple and inexpensive method to produce axially symmetric structures. It allows concurrent shaping of both the electroactive ceramic and electrode materials, thereby removing the necessity of performing complex electroding procedures after sintering the ceramic. Typically these post firing procedures are difficult, if not impossible, with microdevices. The MFCX technique is a two step process. The first is the use of coextrusion to shape powder-filled thermoplastic compounds into green microsized parts. The second is a co-firing step to achieve binder burnout and densification of both the ceramic and electrode materials. Electroactive ceramic and silver palladium parts with 5 micron feature sizes have been fabricated using this method. This article includes a description of this new microfabrication technique and results of efforts to fabricate microsized ceramic objects including a fenestrated electrostrictive ceramic-silver palladium electrode structure and a piezoelectric hydrophone.