Vibration converters based on piezoelectric materials are currently becoming increasingly important for powering low-power wireless sensor nodes and wearable electronic devices. Piezoelectric materials generate variable electrical charges under mechanical stress, requiring an energy management interface to meet load requirements. Resonant interfaces like Parallel Synchronized Switch Harvesting on Inductor (P-SSHI) are highly efficient and robust to energy sources and loads variations. Nevertheless, SSHI circuits require synchronous switch control for efficient energy transfer. At irregular excitation, SSHI circuits may not perform optimally because the resonant frequency of the circuit is typically tuned to match the frequency of the energy source, which in the case of footsteps can be irregular and unpredictable. In addition, the circuit may also be susceptible to noise and interference from irregular excitations, which can further affect its performance. The aim is to design a self-powered energy management solution that can operate autonomously even at low frequencies and for irregular chock excitations, while at the same time allowing higher energy flow to the energy storage device and maintaining high levels of energy efficiency. To evaluate the performance of the proposed circuit, a piezoelectric shoe insole is designed and used for testing with different storage capacitance values and loads as a proof of the circuit’s adaptability to various loading conditions.:1 Introduction 2 Theoretical background 3 State of the art of piezoelectric energy harvesting interfaces 4 Novel approach of SP-PSSHI piezoelectric energy harvesting interface 5 Experimental investigations 6 Conclusions and Outlook

Materiais piezocompósitos laminados são compostos por camadas de material piezelétrico, metálico e compósito (matriz epóxi com fibras de carbono ou de vidro), que possibilitam obter vantagens em relação aos materiais piezelétricos convencionais, permitindo obter características superiores que não podem ser conseguidas pelos seus componentes de forma isolada como, por exemplo, maior flexibilidade e resistência mecânica ou menor peso. Sob esse enfoque, este trabalho tem por objetivo o desenvolvimento de Estruturas Piezocompósitas Laminadas (EPLA) que consistem basicamente em estruturas multicamadas, através do projeto da sua resposta transiente e harmônica visando aplicações dinâmicas. Entre as potenciais aplicações dessas estruturas, tem-se atuadores, motores, sonares e dispositivos de coleta de energia (\"energy harvester\"), sendo de muito interesse a melhora das suas características dinâmicas e o seu desempenho. O projeto dinâmico de uma EPLA é complexo, porém pode ser sistematizado utilizando o Método de Otimização Topológica (MOT). O MOT é um método baseado na distribuição de material num domínio de projeto fixo com o objetivo de extremizar uma função de custo sujeita às restrições inerentes do problema, combinando algoritmos de otimização e de elementos finitos. A formulação de MOT para o projeto dinâmico de EPLA pretende determinar tanto a topologia ótima dos materiais nas diferentes camadas quanto o sinal de polarização do material piezelétrico e o ângulo da fibra na camada compósita, tendo como finalidade a maximização da amplitude de vibração em pontos determinados (em atuadores) ou da geração de energia elétrica a partir de excitações mecânicas (em coletores de energia). Além disso, é formulado um problema combinando os enfoques harmônico e transiente com o intuito de customizar a resposta da EPLA, de modo que, o nível da resposta seja o mesmo perante diferentes tipos de onda de excitação (transdutores multi-entrada). O trabalho inclui as etapas de projeto, simulação, fabricação e caracterização de protótipos. / Laminated piezocomposite materials are composed by layers of piezoelectric, metal and composite material (epoxy matrix with carbon or glass fiber), which have advantages over conventional piezoelectric materials, because of their superior characteristics, which cannot be achieved by any of its components isolated, for example, more flexibility and strength and less weight. Under this approach, this work aims at the development of Laminated Piezocomposite Structures (LAPS) what primarily consist of multi-layer structures, through the transient and harmonic response design aiming at dynamic applications. Among the potential applications of these structures it can be cited actuators, motors, sonar devices and energy harvester, being of great interest the improvement of its dynamic characteristics and performance. The dynamic design of a LAPS is complex however it can be systematized by using the Topology Optimization Method (TOM). The TOM is a method based on the distribution of material in a fixed design domain with the aim of extremizing a cost function subject to constraints inherent to the problem by means of combining the optimization algorithms and the finite element method (FEM). The TOM formulation for the LAPS dynamic project aims to determine together the optimal topology of the materials for different layers, the polarization sign of the piezoelectric material and the fiber angle of the composite layer, in order to maximize the vibration amplitude at certain points (in actuators), or the generation of electrical energy from mechanical excitations (in energy harvesters). In addition, a TOM problem combining harmonic and transient approaches is formulated with the purpose of customizing EPLA response so that the response level is the same for different excitation waveforms (multi-entry transducers). The work includes design, simulation, manufacturing and characterization of prototypes.

Low-power requirements of contemporary sensing technology attract research on alternate power sources that can replace batteries. Energy harvesters function as power sources for sensors and other low-power devices by transducing the ambient energy into usable electrical form. Energy harvesters absorbing the ambient vibrations that have potential to deliver uninterrupted power to sensing nodes installed in remote and vibration rich environments motivate the research in vibrational energy harvesting. Piezoelectric bimorphs have been demonstrating a pre-eminence in converting the mechanical energy in ambient vibrations into electrical energy. Improving the performance of these harvesters is pivotal as the energy in ambient vibrations is innately low. The present work is organized in three major sections: firstly, audit of the energy available in a vibrating source and design for effective transfer of the energy to harvesters, secondly, design of vibration energy harvesters with a focus to enhance their performance, and lastly, identification of key performance metrics influencing conversion efficiencies and scaling analysis for MEMS harvesters. Typical vibration levels in stationary installations such as surfaces of blowers and ducts, and in mobile platforms such as light and heavy transport vehicles, are determined by measuring the acceleration signal. The frequency content in the signal is determined from the Fast Fourier Transform. A method of determining the energy associated with the vibrating source and the associated power using power spectral density of the signal is proposed. Power requirements of typical sensing nodes are listed with an intent to determine the adequacy of energy harvesting. Effective transfer of energy from a given vibration source is addressed through the concept of dynamic vibration absorption, which is a passive technique for suppressing unintended vibrations. Optimal absorption of energy from a vibration source entails the determination of absorber parameters such as resonant frequency and damping. We propose an iterative method to obtain these parameters for a generic case of large number of identical vibration absorbers resembling harvesters by minimizing the total energy absorbed by the system. The proposed method is verified by analysing the response of a set of cantilever absorber beams placed on a vibrating cantilever plate. We find, using our method, the values of the absorber mass, resonant frequency and damping of the absorber at which significant amount of energy supplied to the system flows into the absorber, a scenario which is favourable for energy harvesting. We emphasize through our work that monitoring energies in the system and optimizing their flow is both rational and vital for designing multiple harvesters that absorb energy from a given vibration source optimally. Enhancing the performance of piezoelectric energy harvesters through a multilayer and, in particular, a multistep configuration is presented. Partial coverage of piezoelectric material in steps along the length of a cantilever beam results in a multistep piezoelectric energy harvester. We find that the power generated by a multistep beam is almost twice of that generated by a multilayer harvester made out of the same volume of polyviny-lidine fluoride (PVDF), further corroborated experimentally. Improvements observed in the power generated prove to be a boon for weakly coupled, low pro le, piezoelectric materials. Thus, in spite of the weak piezoelectric coupling observed in PVDF, its energy harvesting capability can be improved significantly by using it in a multistep piezoelectric beam configuration. Besides, the effect of piezoelectric step length and thickness in a piezoelectric unimorph harvester and performance metrics such as piezoelectric coupling factor and efficiency of conversion are presented. Modeling of a hybrid energy harvester composed of piezoelectric and electromagnetic mechanisms of energy conversion motivated by the need to determine the contribution of each domain to the power generated by the harvester is presented, particularly, when multiple domains exist in a single harvester. Two exclusive schemes of energy transduction are represented using equivalent circuits, which allow modeling any additional transduction scheme employed in the hybrid harvester with relative ease. Furthermore, a method of determining optimal loads in the respective domains using the equivalent circuit of the hybrid harvester is presented. Four different hybrid energy harvesters were fabricated and evaluated for their performance in comparison with that estimated from the proposed models. Additionally, scaling laws for hybrid energy harvesters are presented. The power developed by both piezoelectric and electromagnetic domains is observed to decrease with width and length cubed. Power indices and figures of merit in a hybrid harvester are proposed and are used to estimate the efficiencies of the four fabricated hybrid harvesters. The important design parameters for micro scale harvesting are identified by performing scaling analysis on MEMS piezoelectric harvesters. Performance of energy harvesters is directly related to the harvester attributes, viz., size, material, and end-mass. Depending on the contribution from each attribute, the power developed by MEMS harvesters can vary widely. A novel method of delineating the power developed by a harvester using five exclusive factors representing scaling, composition, inertia, material, and power (SCIMP) factors is presented. Although the proposed method can be extended to bi-morph and multilayer harvesters, in the present work, we elucidate it by applying it to a MEMS unimorph. We also present a unique coupling factor that ensures maximum power factor in a harvester. As any tiny increment in the power generated would considerably improve the power densities of MEMS harvesters, we focus on enhancing the power developed by maximizing each of the five exclusive factors irrespective of material and size. Furthermore, we demonstrate the competence of the proposed method by applying it on nine different MEMS harvesters reported in the literature. Considering the close match between the reported and predicted performance, we emphasize that monitoring the proposed factors is sufficient to attain the best performance from a harvester.

Materiais piezocompósitos laminados são compostos por camadas de material piezelétrico, metálico e compósito (matriz epóxi com fibras de carbono ou de vidro), que possibilitam obter vantagens em relação aos materiais piezelétricos convencionais, permitindo obter características superiores que não podem ser conseguidas pelos seus componentes de forma isolada como, por exemplo, maior flexibilidade e resistência mecânica ou menor peso. Sob esse enfoque, este trabalho tem por objetivo o desenvolvimento de Estruturas Piezocompósitas Laminadas (EPLA) que consistem basicamente em estruturas multicamadas, através do projeto da sua resposta transiente e harmônica visando aplicações dinâmicas. Entre as potenciais aplicações dessas estruturas, tem-se atuadores, motores, sonares e dispositivos de coleta de energia (\"energy harvester\"), sendo de muito interesse a melhora das suas características dinâmicas e o seu desempenho. O projeto dinâmico de uma EPLA é complexo, porém pode ser sistematizado utilizando o Método de Otimização Topológica (MOT). O MOT é um método baseado na distribuição de material num domínio de projeto fixo com o objetivo de extremizar uma função de custo sujeita às restrições inerentes do problema, combinando algoritmos de otimização e de elementos finitos. A formulação de MOT para o projeto dinâmico de EPLA pretende determinar tanto a topologia ótima dos materiais nas diferentes camadas quanto o sinal de polarização do material piezelétrico e o ângulo da fibra na camada compósita, tendo como finalidade a maximização da amplitude de vibração em pontos determinados (em atuadores) ou da geração de energia elétrica a partir de excitações mecânicas (em coletores de energia). Além disso, é formulado um problema combinando os enfoques harmônico e transiente com o intuito de customizar a resposta da EPLA, de modo que, o nível da resposta seja o mesmo perante diferentes tipos de onda de excitação (transdutores multi-entrada). O trabalho inclui as etapas de projeto, simulação, fabricação e caracterização de protótipos. / Laminated piezocomposite materials are composed by layers of piezoelectric, metal and composite material (epoxy matrix with carbon or glass fiber), which have advantages over conventional piezoelectric materials, because of their superior characteristics, which cannot be achieved by any of its components isolated, for example, more flexibility and strength and less weight. Under this approach, this work aims at the development of Laminated Piezocomposite Structures (LAPS) what primarily consist of multi-layer structures, through the transient and harmonic response design aiming at dynamic applications. Among the potential applications of these structures it can be cited actuators, motors, sonar devices and energy harvester, being of great interest the improvement of its dynamic characteristics and performance. The dynamic design of a LAPS is complex however it can be systematized by using the Topology Optimization Method (TOM). The TOM is a method based on the distribution of material in a fixed design domain with the aim of extremizing a cost function subject to constraints inherent to the problem by means of combining the optimization algorithms and the finite element method (FEM). The TOM formulation for the LAPS dynamic project aims to determine together the optimal topology of the materials for different layers, the polarization sign of the piezoelectric material and the fiber angle of the composite layer, in order to maximize the vibration amplitude at certain points (in actuators), or the generation of electrical energy from mechanical excitations (in energy harvesters). In addition, a TOM problem combining harmonic and transient approaches is formulated with the purpose of customizing EPLA response so that the response level is the same for different excitation waveforms (multi-entry transducers). The work includes design, simulation, manufacturing and characterization of prototypes.

This thesis is focused on design of piezoelectric energy harvester with additional nonlinear stiffness. Linear generator has very narrow resonance frequency bandwidth. It makes the resonance mechanism very sensitive to tuning up of the resonance frequency and it can be tuned only for one narrow vibration peak. The main idea for using of the vibration energy harvester with nonlinear stiffness is to make resonance frequency bandwidth wider, so the generator will be useable for more excitation frequencies. In this thesis is used generator Midé V21BL and additional nonlinear stiffness is realized with permanent magnets.

Diphenylalanine peptide (Phe-Phe or FF) is a very promising bio-material in the future wearable electronics application due to its self-assembly into nanotubes and nanoribbons with high shear piezoelectric coefficient which is comparable to traditional inorganic piezoelectric materials. In order to efficiently harvest piezoelectric response, alignment and unidirectional polarization of FF nanotubes are required. Most prior works show that there mainly two methods to achieve the alignment and unidirectional polarization. They are epitaxial growth and meniscus-driven dip-coating. However, they still have some disadvantages like low productivity or harsh conditions. In this work, we use inkjet printing technology to develop a scalable, programmable and patterns designable process for the fabrication of FF nanotubes. Most prior works use toxic solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to dissolve FF peptide. In our work, the ink only contains sustainable and ecofriendly solvent like acetic acid and ethylene glycol. In the inkjet printing process, patterns can be perfectly printed on the substrate of graphene and ethyl cellulose. The direction and length of FF nanoribbons are controllable. Aligned FF nanoribbons can be observed in the printed devices. Orthorhombic crystal structure is characterized by SEM and XRD. The piezoelectric performance of the device with aligned FF nanoribbons is much higher than the random FF based devices. The FF piezoelectric nanogenerator generates voltage, current, and power density of up to 1.49 V, 10.5 nA, and 4.4 nW/cm2, respectively, under a force of 50 N. Our results show the promising future of FF-based piezoelectric devices in self-powered and wearable electronics application. / Diphenylalanine peptide (Phe-Phe eller FF) är ett mycket lovande biomaterial i den framtida bärbara elektronikapplikationen pågrund av dess självmontering till nanorör och nanorband med hög piezoelektrisk koefficient som är jämförbar med traditionella oorganiska piezoelektriska material. För att effektivt skörda piezoelektrisk respons krävs inriktning och enkelriktad polarisering av FF-nanorör. De flesta tidigare arbeten visar att det huvudsakligen finns tvåmetoder för att uppnå inriktning och enkelriktad polarisering. De är epitaxiell tillväxt och menisk-driven dopp-beläggning. Men de har fortfarande vissa nackdelar som låg produktivitet eller svåra förhållanden. I detta arbete använder vi bläckstråleutskriftsteknik för att utveckla en skalbar, programmerbar och mönsterdesignbar process för tillverkning av FF-nanorör. De flesta tidigare verk använder giftigt lösningsmedel 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) för att lösa upp FF-peptid. I vårt arbete innehåller bläcket endast hållbara och miljövänliga lösningsmedel som ättiksyra och etylenglykol. I bläckstråleutskriftsprocessen kan mönster tryckas perfekt på substratet av grafen och etylcellulosa. Riktningen och längden på FF nanoband är kontrollerbara. Justerade FF-nanoband kan observeras i de utskrivna enheterna. Ortorhombisk kristallstruktur kännetecknas av SEM och XRD. Den piezoelektriska prestandan hos enheten med justerade FF-nanoband är mycket högre än de slumpmässiga FF-baserade enheterna. FF piezoelektriska nanogeneratorn genererar spänning, ström och effekttäthet på upp till 1,49 V, 10,5 nA respektive 4,4 nW/cm2 med en kraft på 50 N. Våra resultat visar den lovande framtiden för FF-baserade piezoelektriska enheter i sig själv -driven och bärbar elektronikapplikation.

Diphenylalanine peptide (Phe-Phe or FF) is a very promising bio-material in the future wearable electronics application due to its self-assembly into nanotubes and nanoribbons with high shear piezoelectric coefficient which is comparable to traditional inorganic piezoelectric materials. In order to efficiently harvest piezoelectric response, alignment and unidirectional polarization of FF nanotubes are required. Most prior works show that there mainly two methods to achieve the alignment and unidirectional polarization. They are epitaxial growth and meniscus-driven dipcoating. However, they still have some disadvantages like low productivity or harsh conditions. In this work, we use inkjet printing technology to develop a scalable, programmable and patterns designable process for the fabrication of FF nanotubes. Most prior works use toxic solvent 1,1,1,3,3,3-hexafluoro2-propanol (HFIP) to dissolve FF peptide. In our work, the ink only contains sustainable and ecofriendly solvent like acetic acid and ethylene glycol. In the inkjet printing process, patterns can be perfectly printed on the substrate of graphene and ethyl cellulose. The direction and length of FF nanoribbons are controllable. Aligned FF nanoribbons can be observed in the printed devices. Orthorhombic crystal structure is characterized by SEM and XRD. The piezoelectric performance of the device with aligned FF nanoribbons is much higher than the random FF based devices. The FF piezoelectric nanogenerator generates voltage, current, and power density of up to 1.49 V, 10.5 nA, and 4.4 nW/cm2, respectively, under a force of 50 N. Our results show the promising future of FFbased piezoelectric devices in self-powered and wearable electronics application. / Diphenylalanine peptide (Phe-Phe eller FF) är ett mycket lovande biomaterial i den framtida bärbara elektronikapplikationen på grund av dess självmontering till nanorör och nanorband med hög piezoelektrisk koefficient som är jämförbar med traditionella oorganiska piezoelektriska material. För att effektivt skörda piezoelektrisk respons krävs inriktning och enkelriktad polarisering av FFnanorör. De flesta tidigare arbeten visar att det huvudsakligen finns två metoder för att uppnå inriktning och enkelriktad polarisering. De är epitaxiell tillväxt och menisk-driven dopp-beläggning. Men de har fortfarande vissa nackdelar som låg produktivitet eller svåra förhållanden. I detta arbete använder vi bläckstråleutskriftsteknik för att utveckla en skalbar, programmerbar och mönsterdesignbar process för tillverkning av FF-nanorör. De flesta tidigare verk använder giftigt lösningsmedel 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) för att lösa upp FF-peptid. I vårt arbete innehåller bläcket endast hållbara och miljövänliga lösningsmedel som ättiksyra och etylenglykol. I bläckstråleutskriftsprocessen kan mönster tryckas perfekt på substratet av grafen och etylcellulosa. Riktningen och längden på FF nanoband är kontrollerbara. Justerade FF-nanoband kan observeras i de utskrivna enheterna. Ortorhombisk kristallstruktur kännetecknas av SEM och XRD. Den piezoelektriska prestandan hos enheten med justerade FF-nanoband är mycket högre än de slumpmässiga FF-baserade enheterna. FF piezoelektriska nanogeneratorn genererar spänning, ström och effekttäthet på upp till 1,49 V, 10,5 nA respektive 4,4 nW/cm2 med en kraft på 50 N. Våra resultat visar den lovande framtiden för FF-baserade piezoelektriska enheter i sig själv -driven och bärbar elektronikapplikation.

This work studies the influence of field effect on large area 2 dimensional ribbons of fluids. A fluid of choice is confined in the channel of a metal-insulator-channel-insulator-metal architecture and is subjected to constant (d.c) or alternating (a.c) fields (de-pending on the application) along with a pressure drive flow. A general fluid would be composed of molecules having certain polarizability and be a dispersion of non-ionic and ionic particulates. The field effect response under pressure driven flow for this fluid would result in electrophoresis, electro osmosis, dielectrophoresis, dipole-dipole interaction and inverse electro osmosis phenomena. Using some of these phenomena we study applications related to desalination and energy harvesting with saline water as the ex-ample fluid for the former case, and solution processed poly vinyldene fluoride (PVDF) for the latter case. The geometrical features of \large area" and the \ribbon shape" can be taken advantage of to influence the design and performance for both applications. With regards to desalination, it is shown via experiments and theoretical models that the presence of alternating electric fields aid in ion separation along the flow when the saline water is subjected to laminar flow. Moreover, the power consumption is low due to the presence of the insulator. An average of 30% ion removal efficiency and 15% throughput is observed in the systems fabricated. Both performance parameters are discussion can be improved upon with larger channel lengths. The \2-D ribbon" and alternating field effect aid in achieving this by patterning the randomly distributed ions in the bulk into a smooth sheet charge and then repelling this sheet charge back into the bulk. The electric field exhibited by this sheet charge helps trap more ion sheets near the interface, thereby converting a surface ion trapping phenomena (when d.c is used) to a bulk phenomena and thereby improving efficiency. With regards to energy harvesting, a solution of PVDF in methyl ethyl ketone and 1-methyl-2-pyrollidone is confined to the \2-D ribbon" geometry and subject to high d.c fields. This aids in combining the fabrication, patterning and poling process for PVDF into one setup. Since the shape of the ribbon is defined by the shape of the channel, the ribbons (straight or serrated) can be used to sense forces of various magnitudes. More importantly experiments and theoretical models are studied for energy harvesting. Since the ribbon geometry defines the resonant frequency, large PVDF ribbon can be used to harvest energy from low frequency vibrations. Experiments show that up to 60 microwatt power can be harvested at 200 Hz and is sufficient to supplement the power for ICs.

This thesis explores the viability of various energy harvesting technologies for powering micro-scale IoT devices in outdoor environments, specifically for products developed by Thule Sweden AB. Through a comprehensive literature review and experimental testing, we evaluated the performance of solar panels and piezoelectric systems to identify sustainable power solutions that could replace or reduce dependence on traditional battery power. Our methodology involved controlled laboratory tests and real-world applications on car roof boxes and bike trailers to assess the technologies under practical conditions. The experiments aimed to achieve a minimum daily energy output of 20 Joules. This target was chosen with reference to the energy consumption data of a specific IoT device used by Thule. The results demonstrated that while both solar and piezoelectric technologies have their possibilities and limitations, they hold promise for integration into IoT applications, offering a step towards more sustainable product designs. These findings contribute to a broader understanding of energy harvesting’s potential to reduce environmental impact and enhance the self-sufficiency of energy production in outdoor IoT applications. / Denna avhandling undersöker genomförbarheten av olika teknologier för energiutvinning för att driva mikroskaliga IoT-enheter i utomhusmiljöer, specifikt för produkter utvecklade av Thule Sweden AB. Genom en omfattande litteraturöversikt och experimentella tester utvärderade vi prestandan hos solpaneler och piezoelektriska system i syfte att identifiera hållbara energilösningar som kunde ersätta eller minska beroendet av traditionella batterier. Vår metodik inkluderade både kontrollerade laboratorietester och praktiska tillämpningar på takboxar och cykelkärror för att bedöma teknologierna under praktiska förhållanden. Experimenten syftade till att uppnå en minsta daglig energiproduktion på 20 joule. Detta mål baseras på energiförbrukningsdata från en specifik IoT-enhet som används av Thule. Resultaten visade att även om både sol- och piezoelektriska teknologier har sina fördelar och begränsningar, har de potential för integration i IoT-applikationer, vilket erbjuder ett steg mot mer hållbara produktdesigner. Dessa fynd bidrar till en bredare förståelse för energiutvinningens potential att minska miljöpåverkan och förbättra självförsörjningen av energiproduktion för IoT-applikationer utomhus.