Multi-actuators piezoelectric devices consist of a multi-flexible
structure actuated by two or more piezoceramic portions, whose
differing output displacements and forces are tailored according to
the excitation properties of the piezoceramic materials and the
desired working locations and directions of movement. Such devices
have a wide range of application in performing biological cell
manipulation, for microsurgery, and in nanotechnology equipment, and
the like. However, the design of multi-flexible structures is a
highly complex task since the devices have many degrees of freedom
and, employ a variety of piezoceramics, but must carefully tune the
movement coupling among the device parts to prevent motion in
undesirable directions. In prior research, topology optimization
techniques have been applied to the design of devices having minimum
movement coupling among the piezoceramic parts, and in this work a
number of these devices were manufactured and experimentally
analyzed to validate the results of the topology optimization. X-Y
nanopositioners consisting of two piezoceramic portions were
addressed and designs considering low and high degrees of coupling
between desired and undesirable displacements were investigated to
evaluate the performance of the design method. Prototypes were
manufactured in aluminum using a wire EDM process, and bonded to
piezoceramics (PZT5A) polarized in the thickness direction and
working in d31 mode. Finite element simulations were carried out
using the commercial ANSYS software application. Experimental
analyses were conducted using laser interferometry to measure
displacement, while considering a quasi-static excitation. The
coupling between the X-Y movements was measured and compared with
FEM results, which showed that the coupling requirements were
adequately achieved.
Analysis of piezoceramics by using optical systems usually requires reflective surfaces. The usual solution to mirror the piezoceramic surface are the optical polishing with gold deposition, or sticking small rigid mirrors. The former solution is difficult to apply in surface with complex shapes. In the latter solution, by sticking a 200um mirror to the piezoceramic surface, it was detected that when piezoceramic are excited in the kHz range, it behaves as unilaminar actuator. In addition, usually not to much attention is paid to the way the piezoceramic is held in the laser interferometer. However, it was noticed that the measured displacements are also highly affected by the mechanical boundary conditions defined by the piezoceramic holder design. Therefore, in this work, both influences are analyzed by combining experimental and computational techniques, and it is discussed how these problems can be solved by using simple solutions. The experimental results are obtained by using laser interferometer and electrical admittance analysis techniques. These results are compared with computational simulations done by using finite element method in ANSYS software. This comparison was very important since it allowed us not only to detect these problems but also to check and evaluate the experimental set up during tests. Simulations and tests are conducted by considering piezoceramics with and without mirror. These problems are isolated, and separately simulated and studied. Experimental measurements are conducted by considering static and transient (one 10kHz sine cycle) piezoceramic excitation. Experimental and simulated data comparison shows a good agreement, and the effect of the mirror and mechanical holder are successfully understood.
The study of piezoceramic and piezoelectric transducers behavior by finite element method (FEM) shows an important influence of viscous damping. Damping values for piezoceramic materials are not provided by manufacturers. In addition, damping values for non-piezoelectrics materials, such as, resins, steel, aluminum, etc, which are usually applied to assemble these transducers are not appropriately given for FEM simulations. Therefore, the objective of this work is to determine damping values of these materials so they can be used in a FEM software, such as, the ANSYS, which has four different ways for damping input. Damping values are determined by combining experimental and numerical techniques. For piezoceramics the damping is determined through the quality factor (Qm) by measuring the admittance curve which are influenced by damping. By using these damping values, harmonic and transient FEM simulations of piezoceramics and piezoelectric transducers are performed and the simulated admittance curve is compared with the measured one, as well as, displacement results are compared with laser interferometer measurements. Damping determination for non-piezoelectric materials are done by comparing experimental and simulated results. By using the obtained damping values, experimental measurements and simulated results for different piezoelectric transducers show a very good agreement.
A flextensional transducer consist of a piezoceramic connected to a flexible structure which amplifies and changes the direction of generated piezoceramic displacement. In a previous work[1,2] these transducers were designed by using topology optimization method. In this work, some prototypes of these transducers were manufactured and experimental measurements were performed to characterize them. The prototypes were built by bonding a flexible structure manufactured by using a wire EDM machine to a piezoceramic with epoxy. As a result, the displacements obtained through laser interferometry at a given frequency and the electrical impedance curves are presented. The experimental results were compared with simulated results obtained by using a commercial finite element software (ANSYS), and the predicted amplification rate provided by these transducers were verified.
In the present paper a double correlator system is proposed. This double Vander Lugt correlation system uses both dynamic photorefractive and a slow complementary holographic processing. The system shows a good discrimination capacity and employs only one bulk photorefractive sample, the Bi12TiO20 crystal at (lambda) equals 0.633 micrometers , in diffusion-only recording mechanism.
We present the study of surface enhanced second-harmonic-generation in a KDP crystal coated with a very thin silver grating of period a by interpreting the roughness of the silver surface with the Rayleigh Theory. With this configuration, long range surface plasmons (LRSP) are excited and the electromagnetic field is resonantly amplified at the Ag/KDP interface.
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