164 Materials Research Lab
Tel:814-865-4101
Fax:814-865-2321
Email:cao@math.psu.edu
The research activities of Dr. Wenwu Cao center on the physical and mechanical properties of ferroic materials and piezoelectric composites which are used for transducers and actuators. In ferroic materials, such as ferroelectric materials, domain structures are generated at the paraelectric-ferroelectric phase transition due to the existence of degenerate orientational states in the low temperature phase. These domains can be switched from one orientation to the another by electric field or mechanical stress. In ferroelectric materials the domain pattern and the mobility of domain walls determine the level of piezoelectric activity. The understanding on the formation of domains and the mobility of domain walls can provide guidelines for the development and fabrication of better transducer materials. Piezoelectric composites were developed to meet the challenge of underwater acoustics and medical ultrasonic imaging, which are made of piezoelectric ceramics embedded in polymer matrix. The geometry of the ceramic inclusion can be plates, rods, tubes and distributed particles. Most of the current medical ultrasonic imaging transducers are made of piezoelectric composites with 2-2 (plate inclusions) and 1-3 (rod inclusions) connectivities. The structural engineering of the piezocomposites enables the stress transfer between the polymer and the ceramic so as to maintain a high level of piezoelectric activity while substantially reducing the acoustic impedance of the transducer to provide a better impedance match with the human body. Finite element computational methods provide a useful tool for the design of proper composite transducers and other actuator devices. The distribution of stress, electric field, resonance modes and wave propagation characteristics can all be calculated using finite element methods.
Major facilities include two Sun-SPARC workstations with finite element software ANSYS and FLEX installed for structural and piezoelectric analyses and transducer design. A PowerPC with dual operation system. The Intercollege Materials Research Laboratory has many facilities to assist faculty and students on their research activities. Including X-ray diffraction facilities, Chemical Analysis, Scanning Electron Microscope, polishing and cutting facilities for transducers and actuator fabrication, material characterization facilities on dielectric, elastic, and piezoelectric properties.
Cao, W. and L. E. Cross. Theoretical model for the morphotropic phase boundary in lead zirconate-lead titanate solid solution. Phys Rev B 47: 4825, 1993.
Cao, W., Q. M. Zhang and L. E. Cross. Theoretical study on the static performance of piezoelectric ceramic- polymer composites with 2-2 connectivity. IEEE Trans Ultra Ferro and Frequency Control 40: 103, 1993.
Cao, W. Nonuniform surface deformation of piezoelectric composites and the effects of surface plates. Adaptive Structures and Material Systems 35: 197, 1993.
Cao, W., Q. M. Zhang and L. E. Cross. Theoretical study on the static performance of piezoelectric ceramic-polymer composites with 1-3 connectivity. J Appl Phys 72: 5814, 1992.
Cao, W. and L. E. Cross. Theory of tetragonal twin structure in ferroelectric perovskite with first order phase transition. Phys Rev B 44: 1991.