Laser interferometry is recognized as an extremely sensitive measurement technique, capable of detecting quantities that conventional sensors usually cannot. However, such advantage also brings a challenge, the interferometer detects, beyond the interest measurements, the environmental disturbances, causing the signal fading which usually leads to a nontrivial process to extract the relevant signal, making the interferometer operation more difficult. Thus, the challenge of interferometry is to be able to measure physical quantities whose values are extremely small, in the presence of external environmental disturbances whose magnitudes are several orders of magnitude higher. Objecting to mitigate this drawback, this work presents the implementation of a digital controller based on variable structures and sliding modes (VS/SM) method, applied to two beams interferometry. The VS/SM technique is a powerful technique in the nonlinear control area because it is simple to implement, presents high performance and provides robustness characteristic. In this work, its digital implementation is made by using the myRI0-1900 (National Instruments) embedded platform, which allows easy configuration and the visualization of system when working online. The results showed that the proposed digital implementation allows the system to log the data from experimental tests, which enables the assembly of an embedded system. As additional advantages, it allows to digitally configure the control gain, allowing high gains, and consequently, a fast response. Applications of this closed loop interferometer to piezoelectric actuators are presented.
Piezoresistive sensors, which have been widely studied and applied to several applications, are usually made of
a piezoresistive membrane attached to a flexible substrate, a plate. A topology optimization formulation for
the design of piezoresistive plate-based sensors, for which the piezoresistive membrane disposition is optimized
together with the substrate, is proposed in this work. The objective is to maximize the sensor sensitivity to
external loading, as well as the stiffness of the sensor to particular loads. A material model for the piezoresistive
membrane based on the Solid IsotropicMaterial with Penalizationmodel, and perfect coupling conditions between
the plate and the membrane based on the "layerwise" theory for laminated plates are employed. Results for an
AFM probe suggest that the performance of the sensors can be improved by using the proposed approach.
One of the properties of composite materials is the possibility of having phononic band gaps, within which
sound and vibrations at certain frequencies do not propagate. These materials are called Phononic Crystals
(PCs). PCs with large band gaps are of great interest for many applications, such as transducers, elastic/
acoustic filters, noise control, and vibration shields. Most of previous works concentrates on PCs made
of elastic isotropic materials; however, band gaps can be enlarged by using non-isotropic materials, such as
piezoelectric materials. Since the main property of PCs is the presence of band gaps, one possible way to
design structures which have a desired band gap is through Topology Optimization Method (TOM). TOM is
a computational technique that determines the layout of a material such that a prescribed objective is maximized.
Functionally Graded Materials (FGM) are composite materials whose properties vary gradually and
continuously along a specific direction within the domain of the material. One of the advantages of applying
the FGM concept to TOM is that it is not necessary a discrete 0-1 result, once the material gradation is part
of the solution. Therefore, the interpretation step becomes easier and the dispersion diagram obtained from
the optimization is not significantly modified. In this work, the main objective is to optimize the position and
width of piezocomposite materials band gaps. Finite element analysis is implemented with Bloch-Floquet theory
to solve the dynamic behavior of two-dimensional functionally graded unit cells. The results demonstrate
that phononic band gaps can be designed by using this methodology.
As storage data density in hard-disk drives (HDDs) increases for constant or miniaturizing sizes, precision positioning
of HDD heads becomes a more relevant issue to ensure enormous amounts of data to be properly written
and read. Since the traditional single-stage voice coil motor (VCM) cannot satisfy the positioning requirement of
high-density tracks per inch (TPI) HDDs, dual-stage servo systems have been proposed to overcome this matter,
by using VCMs to coarsely move the HDD head while piezoelectric actuators provides fine and fast positioning.
Thus, the aim of this work is to apply topology optimization method (TOM) to design novel piezoelectric HDD
heads, by finding optimal placement of base-plate and piezoelectric material to high precision positioning HDD
heads. Topology optimization method is a structural optimization technique that combines the finite element
method (FEM) with optimization algorithms. The laminated finite element employs the MITC (mixed interpolation
of tensorial components) formulation to provide accurate and reliable results. The topology optimization
uses a rational approximation of material properties to vary the material properties between 'void' and 'filled' portions. The design problem consists in generating optimal structures that provide maximal displacements, appropriate structural stiffness and resonance phenomena avoidance. The requirements are achieved by applying formulations to maximize displacements, minimize structural compliance and maximize resonance frequencies. This paper presents the implementation of the algorithms and show results to confirm the feasibility of this approach.
The advances in miniaturization techniques over the last decades has made the widespread of electronic devices greater than ever and the rate of growth increases each day. Research has been carried out all over the world aiming at developing devices capable of capturing ambient energy and converting it into useable energy in this very promissing field of energy harvesting. Piezoelectric laminates have been used in the design of energy harvesting systems. While most of current research considers traditional assemblies with bimorph transducers and proof masses, this work involves the design of novel energy harvesting devices and other laminate piezoelectric structures by applying topology optimization, which combines Finite Element Method with optimization algorithms. The finite element employs a robust formulation capable of representing both direct and converse piezoelectric effects, based on the MITC formulation. The topology optimization uses the PEMAP-P model (Piezoelectric Material with Penalization and Polarization) combined with the RAMP model (Rational Approximation of Material Properties), where the design variables are the pseudo-densities that describe the amount of piezoelectric material at each finite element. A multi-objective function is defined for the optimization problem, which aims at designing eigenvalues and eigenvectors and maximizing the electromechanical coupling of a specific mode. This paper presents the implementation of the finite element and optimization software and shows results achieved.
Precision flow pumps have been widely studied over the last three decades. They have been applied in the areas of
Biology, Pharmacy and Medicine in applications usually related to the dosage of medicine and chemical reagents.
In addition, thermal management solutions for electronic devices have also been recently developed using these
kinds of pumps offering better performance with low noise and low power consumption. In previous works was
presented the working principle of a pump based on the use of a bimorph piezoelectric actuator inserted in a
fluid channel to generate flow. This work presents a novel configuration of piezoelectric flow pumps using a
bimorph piezoelectric actuator of different aspect ratio. Sensibility studies of the rectangular cross-sectional area
channel are conducted computationally (CFD) and three parameters are investigated: resonance frequency and
oscillation amplitude of the piezoelectric actuator, and pressure inside the channel. Also, experimental tests are
conducted to verify the influence of clamps' rigidity and actuator's insulator. The experimental results show
that improving these two aspects it is possible to achieve higher flow rates.
Precision flow pumps have been widely studied over the last three decades. They have been applied in the areas of
Biology, Pharmacy and Medicine in applications usually related to the dosage of medicine and chemical reagents.
In addition, thermal management solutions for electronic devices have also been recently developed using these
kinds of pumps offering better performance with low noise and low power consumption. In a previous work, the
working principle of a pump based on the use of bimorph piezoelectric actuators inserted in a fluid channel to
generate flow was presented. The present work aims at the development of novel configurations of piezoelectric
flow pumps based on the use of bimorph actuators with biomimetic tip geometries that are inspired in fish caudal
fin shapes, such as ostraciiform, subcarangiform, carangiform and thunniform. The pump development consists
in designing, manufacturing and experimental characterization steps. In the design step, computational models of
pump configurations are built to perform sensitivity studies and to apply optimization techniques using ANSYS
finite element analysis software. The prototype manufacturing is guided by the computational simulations.
Electronic circuits for pump electrical excitation and control are developed and implemented. Comparisons
among numerical and experimental results are also made.
Sensors and actuators based on piezoelectric plates have shown increasing demand in the field of smart structures,
including the development of actuators for cooling and fluid pumping applications and transducers for novel energy
harvesting devices. This project involves the development of a finite element and topology optimization
software to design piezoelectric sensors, actuators and energy harvesting devices by distributing piezoelectric material
over a metallic plate in order to achieve a desired dynamic behavior with specified vibration frequencies.
The finite element employs a general formulation capable of representing both direct and converse piezoelectric
effects. It is based on the MITC formulation, which is reliable, efficient and avoids the shear locking problem. The
topology optimization formulation is based on the PEMAP-P model (Piezoelectric Material with Penalization
and Polarization), where the design variables are the pseudo-densities that describe the amount of piezoelectric
material at each finite element. The optimization problem has a multi-objective function, which can be subdivided
into three distinct problems: maximization of mean transduction, minimization of mean compliance and
optimization of Eigenvalues. The first one is responsible for maximizing the amount of electric energy converted
into elastic energy, the second one guarantees that the structure does not become excessively flexible and the
third one tunes the structure for a given frequency. This paper presents the implementation of the finite element
and optimization software and shows preliminary results achieved.
The microchips inside modern electronic equipment generate heat and demand, each day, the use of more
advanced cooling techniques as water cooling systems, for instance. These systems combined with piezoelectric
flow pumps present some advantages such as higher thermal capacity, lower noise generation and miniaturization
potential. The present work aims at the development of a water cooling system based on a piezoelectric flow
pump for a head light system based on LEDs. The cooling system development consists in design, manufacturing
and experimental characterization steps. In the design step, computational models of the pump, as well as the
heat exchanger were built to perform sensitivity studies using ANSYS finite element software. This allowed us
to achieve desired flow and heat exchange rates by varying the frequency and amplitude of the applied voltage.
Other activities included the design of the heat exchanger and the dissipation module. The experimental tests of
the cooling system consisted in measuring the temperature difference between the heat exchanger inlet and outlet
to evaluate its thermal cooling capacity for different values of the flow rate. Comparisons between numerical and
experimental results were also made.
Functionally Graded Materials (FGMs) possess continuous variation of material properties and are characterized
by spatially varying microstructures. Recently, the FGM concept has been explored in piezoelectric materials
to improve properties and to increase the lifetime of piezoelectric actuators. Elastic, piezoelectric, and dielectric
properties are graded along the thickness of a piezoceramic FGM. Thus, the gradation of piezoceramic properties
can influence the performance of piezoactuators, and an optimum gradation can be sought through optimization
techniques. However, the design of these FGM piezoceramics are usually limited to simple shapes. An interesting
approach to be investigated is the design of FGM piezoelectric mechanisms which essentially can be defined as a
FGM structure with complex topology made of piezoelectric and non-piezoelectric material that must generate
output displacement and force at a certain specified point of the domain and direction. This can be achieved by
using topology optimization method. Thus, in this work, a topology optimization formulation that allows the
simultaneous distribution of void and FGM piezoelectric material (made of piezoelectric and non-piezoelectric
material) in the design domain, to achieve certain specified actuation movements, will be presented. The method
is implemented based on the SIMP material model where fictitious densities are interpolated in each finite element,
providing a continuum material distribution in the domain. The optimization algorithm employed is based on
sequential linear programming (SLP) and the finite element method is based on the graded finite element concept
where the properties change smoothly inside the element. This approach provides a continuum approximation
of material distribution, which is appropriate to model FGMs. Some FGM piezoelectric mechanisms were
designed to demonstrate the usefulness of the proposed method. Examples are limited to two-dimensional models,
due to FGM manufacturing constraints and the fact that most of the applications for such FGM piezoelectric
mechanisms are planar devices. An one-dimensional constraint of the material gradation is imposed to provide
more realistic designs.
Precision flow pumps have been widely studied over the last three decades. They have been applied in the areas of
Biology, Pharmacy and Medicine in applications usually related to the dosage of medicine and chemical reagents.
In addition, thermal management solutions for electronic devices have also been recently developed using these
kinds of pumps offering better performance with low noise and low power consumption. In a previous work, the
working principle of a pump based on the use of a bimorph piezoelectric actuator inserted in a fluid channel to
generate flow was presented. In this work, a novel configuration of this piezoelectric flow pump that consists
of a flow pump using two bimorph piezoelectric actuators in parallel configuration has been studied and it is
presented. This configuration was inspired on fish swimming modes. The complete cycle of pump development
was conducted, consisting in designing, manufacturing, and experimental characterization steps. Load-loss and
flow rate characterization experimental tests were conducted, generating data that allows us to analyze the
influence of geometric parameters in the pump performance. Comparisons among numerical and experimental
results were made to validate the computational results and improve the accuracy of the implemented models.
Precision flow pumps have been widely studied over the last three
decades. They have been applied as essential components in thermal
management solutions for cooling electronic devices offering better
performance with low noise and low power consumption. In this work,
a novel configuration of a miniature piezoelectrically actuated flow
pump with the purpose of cooling a LED set inside a head light
system for medical applications has been studied and it will be
presented. The complete cycle of pump development was conducted. In
the design step, the ANSYS finite element analysis software
has been applied to simulate and study the fluid-structure
interaction inside the pump, as well as the bimorph piezoelectric
actuator behavior. In addition, an optimization process was carried
out through Altair Hyperstudy software to find a set of
parameter values that maximizes the pump performance measured in
terms of flow rate. The prototype manufacturing was guided based on
computational simulations. Flow characterization experimental tests
were conducted, generating data that allows us to analyze the
influence of frequency and amplitude parameters in the pump
performance. Comparisons between numerical and experimental results
were also made.
Functionally Graded Materials (FGMs) possess continuous variation of material properties and are characterized by spatially varying microstructures. Recently, the FGM concept has been explored in piezoelectric materials to improve properties and to increase the lifetime of bimorph piezoelectric actuators. Elastic, piezoelectric, and dielectric properties are graded along the thickness of a piezoceramic FGM. Thus, the gradation of piezoceramic properties can influence the performance of piezoactuators. In this work, topology optimization is applied to find the optimum gradation variation in piezoceramics in order to improve actuator performance measured in terms of output displacements. A bimorph type actuator design is investigated. The corresponding optimization problem is posed as finding the optimized gradation of piezoelectric properties that maximizes output displacement or output force at the tip of the bimorph actuator. The optimization algorithm combines the finite element method with sequential linear programming. The finite element method is based on the graded finite element concept where the properties change smoothly inside the element. This approach provides a continuum approximation of material distribution, which is appropriate to model FGMs. The present results consider gradation between two different piezoceramic properties and two-dimensional models with plane stress assumption.
The micro-tools considered in this work consist essentially of multi-flexible structures actuated by two or more piezoceramic devices that must generate different output displacements and forces at different specified points of the domain and on different directions. The multiflexible structure acts as a mechanical transformer by amplifying and changing the direction of the piezoceramics output displacements. Micro-tools offer significant promise in a wide range of applications such as cell manipulation, microsurgery, and micro/nanotechnology processes. Although the design of these micro-tools is complicated due to the coupling among movements generated by various piezoceramics, it can be realized by means of topology optimization concepts. Recently, the concept of functionally graded materials (FGMs) has been explored in piezoelectric materials to improve performance and increase lifetime of piezoelectric actuators. Usually for an FGM piezoceramic, elastic, piezoelectric, and dielectric properties are graded along the thickness. Thus, the objective of this work is to study the influence of piezoceramic property gradation in the design of the multiflexible structures of piezoelectric micro-tools using topology optimization. The optimization problem is posed as the design of a flexible structure that maximizes different output displacements or output forces in different specified directions and points of the domain, in response to different excited piezoceramic portions: while minimizing the effects of movement coupling. The method is implemented based on the solid isotropic material with penalization (SIMP) model where fictitious densities are interpolated in each finite element, providing a continuum material distribution in the domain. As examples, designs of a single piezoactuator and an XY nano-positioner actuated by two FGM piezoceramics are considered. The resulting designs are compared with designs considering homogeneous piezoceramics. The present examples are limited to two-dimensional models because most of the applications for such micro-tools are planar devices.
Piezoelectric actuators offer significant promise in a wide range of applications. The piezoelectric actuators considered in this work essentially consist of a flexible structure actuated by piezoceramics that must generate output displacement and force at a certain specified point of the domain and direction. The flexible structure acts as a mechanical transformer by amplifying and changing the direction of piezoceramics output displacements.
The design of these piezoelectric actuators are complex and a systematic design method, such as topology optimization has been successfully applied in the latest years, with appropriate formulation of the optimization problem to obtain optimized designs. However, in these previous design formulations, piezoceramics position are usually kept fixed in the design domain and only the flexible structure is designed by distributing only some non-piezoelectric material (Aluminum, for example). This imposes a constraint in the position of piezoelectric material in the optimization problem limiting the optimality of the solution. Thus, in this work, a formulation that allows the simultaneous search for an optimal topology of a flexible structure as well as the optimal positions of the piezoceramics in the design domain, to achieve certain specified actuation movements, will be presented. This can be achieved by allowing the simultaneous distribution of non-piezoelectric and piezoelectric material in the design domain. The optimization problem is posed as the design of a flexible structure together with optimum positions of piezoelectric material that maximizes output displacements or output forces in a certain specified direction and point of the domain. The method is implemented based on the SIMP material model where fictitious densities are interpolated in each finite element, providing a continuum material distribution in the domain. Presented examples are limited to two-dimensional models, once most of the applications for such piezoelectric actuators are planar devices.
Electrical Impedance Tomography (EIT) seeks to recover the impedance distribution within a body using boundary data. More specifically, given the measured potentials, the model of the body - an elliptic partial differential equation - and the boundary conditions, this technique solves a non-linear inverse problem for the unknown impedance. In this work, an algorithm called Topology Optimization Method (TOM) is applied to EIT and compared to the Gauss-Newton Method (GNM). The Topology Optimization has solved some non-linear inverse problems and some of its procedures were not investigated for EIT, for instance, the use of Sequential Linear Programming. Assuming a pure resistive medium, the static resistivity distribution of a phantom was estimated using a 2-D finite element model. While the first method (GNM) essentially solves several algebraic systems, the second (TOM) solves several linear programming problems. Results using experimental data are shown and the quality of the images obtained, time and memory used are compared for both algorithms. We intend to use these methods, in future works, for the visualization of a human lung subjected to mechanical ventilation.
Piezoresistive materials, materials whose resistivity properties change when subjected to a mechanical stresses, currently have wide industry application for building MEMS, such as, pressure sensors, accelerometers, inclinometers, and load cells. A basic piezoresistive sensor consists of piezoresistive material bonded to a flexible structure, such as a cantilever, membrane, or compliant mechanism, where the flexible structure transfers pressure, force, or inertial force (due to acceleration), thereby causing a stress that changes the resistivity of the piezoresistive material. By applying a voltage to the material, its resistivity can be measured and correlated with the degree of applied pressure or force. The performance of the piezoresistive sensor is closely related to the design of its flexible structure which can be achieved by applying systematic design methods, such as topology optimization. Thus, in this work, a topology optimization formulation has been applied to the design of piezoresistive sensors. As an initial problem, a piezoresistive force sensor design is considered. The optimization problem is posed as the design of a flexible structure that bonded to the piezoresistive material generates the maximum response in terms of resistivity change (or output voltage) when a force is applied.
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.
Plate and shell laminates that include piezoelectric layers have found
increasing use in the field of smart structures. The present work focuses on
the design of plate and shell piezoelectric actuators such as bimorph and
C-block actuators. In this work, a method for designing piezoelectric
plate and shell actuators is proposed which uses topology optimization. The
approach is based on the SIMP (Solid Isotropic Material with Penalization)
material model, which was extended to piezoelectric materials allowing the
change of sign of the polarization of the piezoelectric material. This new
material model is called PEMAP-P (Piezoelectric Material with Penalization and
Polarization). The design problem consists in finding an optimal distribution of
piezoelectric material in a multi-layer plate or shell structure to accomplish
the maximum displacement in a given direction at a given point of the domain,
when an electric charge is applied. Different and novel types of plate and shell
actuators can be obtained for a desired application. For the modelling of the
piezoelectric layers, newly developed piezoelectric plate and shell elements are
employed, which are free of locking and allow an accurate modeling of thin
piezoelectric actuators of arbitrary geometry and number of layers. To illustrate
the potential of the proposed method, the optimal distributions of piezoceramics
in different layered piezoelectric plates and shells actuators are shown.
Micro-tools can have a wide range of
application such as cell manipulation, microsurgery, nanotechnology
equipment,etc. Micro-tools considered in this work consist of a multiflexible structure
actuated by two or more piezoceramics that must generate different output
displacements and forces in different specified points of the domain and
directions, for different excited piezoceramics. The multiflexible structure
acts as a mechanical transform by amplifying and changing the direction of
the piezoceramics output displacements. Thus, the development of micro-tools requires to design
micromechanisms with many degrees of freedom that perform complex movements
without presence of joints and pins, due to manufacturing constraints of
MEMS scale. In addition, when many piezoceramics are involved the
coupling among movements becomes critical, that is, undesired movements
may appear. This makes the design task very complex, which
suggests that systematic design method, such as topology optimization, must
be applied. Thus, in this work the topology optimization formulation was
applied to design micro-tools actuated by many piezoceramics with minimum
movement coupling. Essentially, the topology optimization method consists of
finding the optimal material distribution in a design domain to extremize
some objective function. The topology optimization method implemented is
based on the CAMD approach where the pseudo-densities are interpolated
in each finite element, providing a continuum material
distribution in the domain. The optimization problem is posed as the
design of a flexible structure that maximizes different output displacements
(or grabbing forces) in different specified directions and points of the
domain, for different excited piezoceramics. Different types of micro-tools
can be obtained for a desired application. Among the examples, designs of
a XY nanopositioner and a micro-gripper are considered.
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.
In the MEMS scale the presence of joints and pins must be avoided due to manufacturing constraints. This makes difficult to design micromechanisms with many degrees of freedom to perform complex movements, such as micromanipulators or micro-robots. However, these microdevices can have a wide range of application such as cell manipulation, microsurgery, nanotechnology equipment,etc. Therefore, in this work, a method for designing multiflexible micromanipulators is proposed by using topology optimization technique based on the homogenization design method. Micromanipulators considered in this work consist of a multiflexible structure actuated by two or more piezoceramics. A multi-flexible structure must generate different output displacements and forces in different specified points of the domain and directions, for different excited piezoceramics. It acts as a mechanical transform by amplifying and changing the direction of the piezoceramics output displacements. The multiflexible structure design is obtained by distributing flexibility and stiffness in the design domain, which can be achieved through topology optimization. Essentially, the topology optimization method consists of finding the optimal material distribution in a perforated design domain with infinite microscale voids. The material in each point can vary from void to full material, also assuming intermediate materials. The optimization problem is posed as the design of a flexible structure that maximizes different output displacements (or grabbing forces) in different specified directions and points of the domain, for different excited piezoceramics. Different types of micromanipulators can be obtained for a desired application depending on the multiflexible structure design connected to the piezoceramics. A linear behavior of piezoceramics is considered. To illustrate the method, the design of some micromanipulators are presented.
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.
Piezoelectric motors consist essentially of a coupling structure actuated by two or more piezoceramics excited with different phases. The actuated piezoceramics deform the coupling structure which moves due to friction over a fixed structure, called stator. The motor performance is related to the displacement generated by the motor in the moving direction and clamping force between the coupling structure and stator. Both quantities depend on the distribution of flexibility and stiffness in the coupling structure domain, which is related to coupling structure topology. By designing other types of coupling structures connected to the piezoceramics, novel types of piezoelectric motors with enhanced performance can be obtained. In this work, topology optimization is applied to design piezoelectric motors. Topology optimization is a general computer design method applied to design optimal structural topology that improves a specified objective function in according to some constraints. The optimization problem is posed as the design of a flexible structure coupled to the piezoceramics that maximizes the output displacement and clamping force in a specified point of the domain and direction. The design of a quasi-static inchworm-type piezoelectric motor is presented to illustrate the implementation of the method.
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.
Flextensional transducers consist of a piezoceramic (or a stack of piezoceramics) connected to a flexible mechanical structure that converts and amplifies the output displacement of the piezoceramic. Among the applications, they can be used as actuators and sonars. The transducer performance in these application depends on the distribution of mass, stiffness, and flexibility in the coupling structure domain, which is related to the coupling structure topology. By designing other types of coupling structures connected to the piezoceramic, we can obtain new types of flextensional transducers with enhanced performance for a desired application. In this work, we extended the method for designing flextensional transducers in static and low-frequency applications to dynamic applications by introducing the inertia effect in the optimization problem. The method applies topology optimization technique based on the homogenization design method, which consists of finding the optimal material distribution in a perforated design domain with infinite microscale voids. The problem is posed as the design of a flexible structure coupled to the piezoceramic that produces high output displacements in a specified point of the domain and direction, in a specified frequency. Therefore, it consists of designing a flexible structure with a specified mode shape in a desired resonance frequency. As a result, designs of flextensional transducers are presented.
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.
In this paper, a design methodology for enhancing the acoustic power radiated from fluid-loaded piezoelectric transducers at a particular operating frequency is developed. For many applications the operating frequency is fixed by the absorption of the material and the desired depth of penetration (e.g., therapeutic ultrasound). For therapeutic ultrasound and other industrial applications, the acoustic power is the critical figure of merit. The acoustic power radiated from the transducer system is computed from a finite element formulation of the coupled acoustic, elastic, piezoelectric equations of motion. The sensitivities of the acoustic power to two design variables: the length of the piezoelectric element and the thickness of the matching layer, are derived. Using these sensitivities, a novel design methodology in which remeshing is avoided is developed and the effectiveness of the method is studied. Results from the application of this framework for transducer design demonstrate the dramatic increase in radiated power possible from this two member design space.
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.
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