Energy harvesting from walking using piezoelectric cymbal and diaphragm type structures

Abstract Many electrical devices already surround us in our everyday life. Some devices monitor car performance and traffic while others exist in handheld devices used by the general public. Electrical devices also control manufacturing processes and protect workers from exposure to hazardous working environment. All these devices require electricity to operate. This exponential growth of low power electronic devices in industry, healthcare, military, transportation and in portable personal devices has led to an urgent need for system integrated energy sources. Many energy harvesting technologies have been developed to serve as a power source in close proximity to the electrical device itself. Solar and magnetic energy harvesters are the most common solutions when conditions are suitable. A more recent technique, called piezoelectric energy harvesting, has raised significant interest among scientists and in industry. Through piezoelectric (ceramic) material mechanical energy can be harvested and converted to electrical energy. This method requires accurate analysis of the kinetic energy experienced by the piezoelectric material so that the mechanics can be suitably designed. At the same time the mechanical design has to protect the piezoelectric material from intense forces that might cause cracks, while still transmitting the kinetic energy efficiently. These requirements usually mean a specific energy harvest design for each ambient energy source at hand. This thesis is focused on energy harvesting from low frequency compressions using piezoelectric ceramic materials. The objective was to manufacture, measure and implement structures that could sustain the forces experienced under the heel of a foot and maximize the harvested energy amount and efficiency. Two different construction designs were developed and optimised with an iterative process. The kinetic energy impulse under the heel part of the foot was studied by measuring the electrical output of the harvester during walking and then analysed with modelling software. The results were used to create a walking profile for a computer controlled piston to study the input energy phase, speed and force influence on the amount of the harvested energy and the efficiency of the harvesting process. Finally, the functionality of the concept was tested in a real environment with an energy harvester inserted inside a running shoe. The developed harvester showed the highest energy density reported in this frequency region.Tiivistelmä Monet elektroniset laitteet ympäröivät meitä jokapäiväisessä elämässä. Ne tarkkailevat auton toimintaa tai liikennettä ja toiset toimivat aina mukana kulkevissa kannettavissa laitteissa. Töissä ne valvovat valmistusprosesseja tai varoittavat työntekijöitä vaarallisista työolosuhteista. Kaikki nämä laitteet tarvitsevat sähköä toimiakseen. Pienitehoisten elektronisten laitteiden eksponentiaalinen kasvu teollisuudessa, terveyssektorilla, puolustusteollisuudessa, kulkuneuvoissa sekä kannettavassa kulutuselektroniikassa on johtanut suureen tarpeeseen kehittää järjestelmiin integroituja energialähteitä. Monia energiankeräystekniikoita on kehitetty toimimaan elektronisten laitteiden läheisyydessä. Aurinkopaneelit ja magneettiset energiankeräysmenetelmät ovat yleisimpiä ratkaisuja, jos olosuhteet antavat siihen mahdollisuuden. Pietsosähköinen energiankeräys on uudempi tekniikka, joka on herättänyt kasvavaa huomiota tutkimusyhteisössä sekä teollisuudessa. Pietsosähköisen materiaalin avulla mekaaninen energia voidaan muuntaa suoraan sähköiseksi energiaksi. Tässä tekniikassa kineettinen energia tulee analysoida tarkasti mekaniikka suunnittelua varten, jotta se saadaan kohdistettua tehokkaasti pietsosähköiseen materiaaliin. Lisäksi mekaniikan tulee suojata materiaalia voimilta, jotka voivat johtaa murtumiin. Näistä vaatimuksista johtuen jokainen ulkoinen energialähde vaatii yleensä yksilöllisen energiankeräysrakenteen. Tämä väitöstyö keskittyy pietsosähköisten keraamien hyödyntämiseen energiankeräyksessä matalataajuisista mekaanisista voimista. Tarkoituksena oli suunnitella, valmistaa, mitata ja asentaa rakenteita, jotka kestävät kantapäähän kohdistuvia voimia kävelyn ja juoksun aikana sekä maksimoida talteen saatava energia ja hyötysuhde. Kaksi erilaista rakennetta suunniteltiin, valmistettiin ja optimoitiin energiankeräystä varten. Kantapäähän kohdistuva kineettinen energia analysoitiin mallinnusohjelmistolla ja mittaamalla sähköinen vaste energiakeräys rakenteesta. Tuloksien avulla suunniteltiin kävelyprofiilia imitoiva mekaaninen männän liike, jonka avulla tutkittiin kohdistettavan voiman nopeuden, vaiheen ja suuruuden vaikutusta energiankeräyksen hyötysuhteeseen ja saatavaan tehoon. Viimeisenä energiankeräysrakenteen toimivuutta testattiin oikeassa ympäristössä asentamalla se juoksukenkään. Kehitetyllä pietsosähköisellä energiakeräimellä saavutettiin korkeimmat raportoidut energiatiheydet käytetyllä taajuusalueella

Piezoelectric energy harvesting from rotational motion to power industrial maintenance sensors

Abstract In industry, forecasting machinery failures could save significant time and money if any maintenance breaks are predictable. The aim of this work was to develop an energy harvesting system which could, in theory, power condition monitoring sensors in heavy machinery. In this study, piezoelectric-cantilever-type energy harvesters were attached to a motor and spun around with different rotational speeds. A mass was placed on the tip of the cantilevers, which were mounted pointing inward toward the center axis of the motor. Pointing a cantilever tip inward and increasing the distance from the center axis of the motor decreased the natural resonance frequency significantly and thus enabled higher harvested energy levels with lower rotational frequencies. Motion of the cantilever was also controlled by altering the movement space of the tip mass. This created another possibility to control the cantilever dynamics and prevent overstressing of the piezoelectric material. Restricting the movement of the tip mass can also be used to harvest energy over a wider frequency range and prevent the harvester from getting trapped into a stagnant position. The highest calculated raw power of 579.2 µW at 7.4 Hz rotational frequency was measured from a cantilever with outer dimensions of 25 mm × 100 mm. Results suggest that an energy harvesting system with multiple cantilevers could be designed to replace batteries in condition sensors monitoring revolving machinery

A vibrational energy harvester based on soft-nonlinearity for truly random excitation

Abstract In this paper, we present a nonlinear energy harvester that is based on a “soft-mode” nonlinearity and is able to work in presence of a truly random excitations. The proposed harvester is configured with a cantilever beam structure, and, at the tip is a cylindrical container filled with freely moving iron balls. The nonlinearity is implemented through the container, as a piecewise function. This structure, in presence of noise, can be assumed as a second order (mass-spring-damper) nonlinear system where the length of the spring changes as a function of external vibration. As will be demonstrated, this nonlinearity will improve the performance of the energy harvester under random excitation. In comparison, the conventional approach based on resonant oscillators is able to collect energy only around its mechanical natural frequency, while the solution pursued here will present a wide spectrum of response. Furthermore, the implemented nonlinearity here does not possess any barrier of potential or mechanical threshold. Because of this, it is able to work at weak signal levels and without mixture of periodic signals. A piezoelectric element has been used to convert the mechanical vibrations into an electrical signal. The system has been modeled and simulated. Experimental validations have been carried out, demonstrating the suitability of the proposed solution

The effects of substrate layer thickness on piezoelectric vibration energy harvesting with a bimorph type cantilever

Abstract In this research four piezoelectric bimorph type cantilevers for energy harvesting were manufactured, measured and analyzed to study the effects of substrate layer thickness on energy harvesting efficiency and durability under different accelerations. The cantilevers had the same dimensions of the piezoelectric ceramic components, but had different thicknesses of the steel substrate (no steel, 30 µm, 50 µm and 75 µm). The cantilevers were tuned to the same resonance frequency with different sizes of tip mass (2.13 g, 3.84 g, 4.17 g and 5.08 g). The energy harvester voltage outputs were then measured across an electrical load near to the resonance frequency (∼40 Hz) with sinusoidal vibrations under different accelerations. The stress exhibited by the four cantilevers was compared and analyzed and their durability was tested with accelerations up to 2.5 g-forces

A single-material multi-source energy harvester, multifunctional sensor, and integrated harvester-sensor system-demonstration of concept

Abstract Single‐source energy harvesters that convert solar, thermal, or kinetic energy into electricity for small‐scale smart electronic devices and wireless sensor networks have been under development for decades. When an individual energy source is insufficient for the required electricity generation, multi‐source energy harvesting is indicated. Current technology usually combines different individual harvesters to achieve the capability of harvesting multiple energy sources simultaneously. However, this increases the overall size of the multi‐source harvester, but in microelectronics miniaturization is a critical consideration. Herein, an advanced approach is demonstrated to solve this issue. A single‐material energy harvesting/sensing device is fabricated using a (K0.5Na0.5)NbO3‐Ba(Ni0.5Nb0.5)O3–Δ (KNBNNO) ceramic as the sole energy‐conversion component. This single‐material component is able simultaneously to harvest or sense solar (visible light), thermal (temperature fluctuation), and kinetic (vibration) energy sources by incorporating its photovoltaic, pyroelectric, and piezoelectric effects, respectively. The interactions between different energy conversion effects, e.g., the influence of dynamic behavior on the photovoltaic effect and alternating current–direct current (AC–DC) signal trade‐offs, are assessed and discussed. This research is expected to stimulate energy‐efficient design of electronic devices by integrating both harvesting and sensing functions in the same material/component

Axle mounted piezoelectric energy harvester for continuous energy harvesting from rotation and vibration

Abstract An axle mounted piezoelectric energy harvester is developed for harvesting energy from rotation. The purpose is to generate power for acceleration sensors, wireless communication and data processing in condition and performance monitoring of rotating machinery. Contrary to many vibration based solutions, in this work the vibrations are not the main source of energy, but the rotation of the shaft itself. The rotation is converted into piezoelectric beam vibrations via gravity and inertial mass. This produces constant and predictable source of power not affected by the unbalance vibrations of the machinery. The prototype was designed using FEM-modeling and manufactured using PZT-5A active material and steel as the passive material. Practical measurements and characterization were carried out using a small motor and data logger for measuring the power output during motor rotation at various speeds

Screen-printed mechanical switch based on stretchable PU-foam film

Abstract A screen-printed mechanical switch based on an electrode structure on stretchable polyurethane (PU)-foam film, Platilon U 4021, combined with a piezoelectric actuator, Smart Material MFC M-4010-P1, is proposed. The minimum actuation voltage of the prepared component is 300 V. The measured resistance was 2 Ω while closed and >0.5 TΩ when open. The electrode structure endured on average of up to 15.5 M cycles with movement ≥100 times greater than the ≤1 μm required for actuation. The results suggest that the switch could be advantageous for various e-textile applications

A game changer:a multifunctional perovskite exhibiting giant ferroelectricity and narrow bandgap with potential application in a truly monolithic multienergy harvester or sensor

Abstract An ABO3-type perovskite solid-solution, (K₀.₅Na₀.₅)NbO₃ (KNN) doped with 2 mol% Ba(Ni₀.₅Nb₀.₅)O₃−δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition—pure KNN—and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O₃, BaTiO₃). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N⁻¹) and a much larger pyroelectric coefficient (≈130 µC m⁻² K⁻¹) compared to the previously reported narrow-bandgap material (KNbO₃)₁₋ₓ-BNNOₓ. The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state-of-the-art hybrid energy harvesters and sensors, and thus significantly increases the unit-volume energy conversion efficiency and reliability of energy harvesters in ambient environments

Current modulation by optoelectric control of ferroelectric domains

Abstract Optoelectric control of domains is likely to pave the foundation for optoferroelectric devices. This work reports the combined effect of light and low-voltage electric bias for optoelectric control of ferroelectric domains in a semiconducting ceramic material—KNBNNO ((K0.5Na0.5)NbO3 doped with 2 mol % Ba(Ni0.5Nb0.5)O3−δ). The effect is utilized to achieve two orders of magnitude amplification in electrical response, asymmetric AC modulation, and domain velocities of 30 000 nm s–1 with ultralarge domain switching areas of over 30 μm in fractions of a second. The charge injection due to light illumination on this material causes the tuning of material conductivity and acts as a virtual electrode. Based on this mechanism, a proof of concept for a monolithic ferroelectric light-effect transistor with a source and drain as electrical contacts with light acting as a virtual gate is demonstrated. This is likely to offer a potential solution to the scaling limit of conventional three-terminal transistors. The same device is also demonstrated to work as a photodiode, a half-wave rectifier, and an electrical output modulator

Is brain MRI needed in diagnostic evaluation of mild intellectual disability?

Abstract Aim: The purpose of our study was to suggest an imaging strategy and guidelines for the selection of the children with mild intellectual disability (ID) for magnetic resonance imaging (MRI), to avoid unnecessary imaging. Methods: The brain MRIs and patient reports of 471 children were reviewed for the imaging findings and ID severity. The correlation between the clinical and brain MRI findings was analyzed in the 305 children with mild ID. Results: Thirty-eight (12.5%) of the children with mild ID had significant abnormal brain MRI findings. Thirty-five of these had other neurological symptoms or diseases in addition to ID, which were an indication for brain MRI. In the logistic regression analysis, seizures (in patients without an epilepsy diagnosis), epilepsy, movement disorders, dysmorphia, encephalitis, traumatic brain injury, and abnormal head size were statistically significant symptoms or comorbidities associated with abnormal MRI findings. Only three children (1.0%) with mild ID had a significant MRI finding without any other clinical symptoms or disease. Conclusion: Routine MRI in children with mild ID without specific neurological symptoms, dysmorphic features, or related diseases is not suggested for revealing an etiology of mild ID. Since children with ID usually need to be sedated for MRI, routine imaging in the diagnostic evaluation of mild ID should be carefully considered. Clinical examination, other symptoms, and related diseases should be carefully assessed to decide the need for MRI