Paulo H. Nakasone

Dynamic Design of Piezoelectric Laminated Sensors and Actuators using Topology Optimization

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 topology optimization formulation for dynamic design of piezoelectric laminated plates aiming at piezoelectric sensors, actuators and energy-harvesting applications. It distributes piezoelectric material over a metallic plate in order to achieve a desired dynamic behavior with specified resonance frequencies, modes, and enhanced electromechanical coupling factor (EMCC). The finite element employs a piezoelectric plate 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 combined with the RAMP model, where the design variables are the pseudo-densities that describe the amount of piezoelectric material at each finite element and its polarization sign. The design problem formulated aims at designing simultaneously an eigenshape, i.e., maximizing and minimizing vibration amplitudes at certain points of the structure in a given eigenmode, while tuning the eigenvalue to a desired value and also maximizing its EMCC, so that the energy conversion is maximized for that mode. The optimization problem is solved by using sequential linear programming. Through this formulation, a design with enhancing energy conversion in the low-frequency spectrum is obtained, by minimizing a set of first eigenvalues, enhancing their corresponding eigenshapes while maximizing their EMCCs, which can be considered an approach to the design of energy-harvesting devices. The implementation of the topology optimization algorithm and some results are presented to illustrate the method.

Design of piezoelectric energy harvesting devices and laminate structures by applying topology optimization

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.

Design of quasi-static piezoelectric plate based transducers by using topology optimization

Sensors and actuators based on piezoelectric plates have shown relevance in the field of smart structures. Recently, modern design techniques such as the topology optimization method have been applied to design laminated piezoelectric transducers, and design requirements such as maximizing static displacements (actuator design) and output voltages (sensor design) have been employed. However, it may be desirable to keep the transducer working range before its first resonance frequency. In this case, the (displacement or voltage) amplitude is expected to be constant with excitation frequency, which may not be the case when only static design requirements are employed. Thus, considering sensor design, if the amplitude is constant, an undetected change in the excitation frequency would cause a small measurement error. Regarding actuators, on the other hand, if the first resonance frequency is small, oscillations in the response to a step excitation (which is usually applied in quasi-static applications, i.e. applications in which the transducer operates under the first resonance frequency) could be high, ultimately causing overshoot, for instance. Thus, in this work, the topology optimization method has been applied to design piezoelectric transducers considering quasi-static operation, by distributing piezoelectric material over a metallic plate and by selecting the material polarization sign, in order to fulfil quasi-static design requirements. This is achieved by maximizing an objective function that depends on both displacements (for actuators) or output voltages (for sensors), and first resonance frequencies. The applied methodology, which encompasses the optimization problem formulation and numerical implementation, is presented. The achieved computational results, corresponding to the design of different types of transducers, clearly show the potential of the proposed methodology to increase the quasi-static working frequency range.

Water cooling system using a piezoelectrically actuated flow pump for a medical headlight system

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.

Design of piezoelectric sensors, actuators, and energy harvesting devices using topology optimization

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.

A miniature bimorph piezoelectrically actuated flow pump

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.

Study of oscillatory piezoelectric flow pumps using bimorph actuators with different tip geometries

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.

Design of piezoelectric laminated shell structures with material gradation and fiber orientation using topology optimization

Sensors and actuators based on piezoelectric laminated shell have shown increasing demand in the field of smart structures. This project involves the development of methodology using topology optimization techniques for static design of piezoelectric laminated composite shell structures aiming at piezoelectric energy harvesting applications. The objective is to find the optimum distribution and polarization of piezoelectric material in the structure in order to achieve enhanced electromechanical coupling factor (EMCC). The optimization of piezoelectric material distribution is done in two ways, finding the best size and location of piezoelectric patches over a base layer, or finding the best location inside the base layer using the functionally graded materials (FGM) concept. This work also investigates an approach where the fiber orientation of orthotropic materials is optimized together with the piezoelectric material distribution. The finite element employs the laminated piezoelectric shell theory, using the degenerate solid approach based on Reissner-Mindlin assumptions which allow the shear deformation and rotary inertia effect to be considered. Reduced integration is used to overcome membrane locking and shear locking and the numerical integration is carried out in all three directions to obtain accurate results. The topology optimization formulation is implemented using three approaches: the first one is based on the PEMAP-P model (Piezoelectric Material with Penalization and Polarization), where the design variables describe the amount of piezoelectric material at each finite element and the polarization variables that determine the sign of polarization; the second approach is based on the Discrete Material Optimization (DMO), where orientation variables determine which fiber angle best suits the problem optimization; finally the third approach considers the material distribution using the FGM concept. Examples of energy harvesting designs are shown using these approaches.

Viability study of oscillatory flow pumps using bimorph piezoelectric actuators

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.