Plucked piezoelectric bimorphs for knee-joint energy harvesting: modelling and experimental validation

The modern drive towards mobility and wireless devices is motivating intensive research in energy harvesting technologies. To reduce the battery burden on people, we propose the adoption of a frequency up-conversion strategy for a new piezoelectric wearable energy harvester. Frequency up-conversion increases efficiency because the piezoelectric devices are permitted to vibrate at resonance even if the input excitation occurs at much lower frequency. Mechanical plucking-based frequency up-conversion is obtained by deflecting the piezoelectric bimorph via a plectrum, then rapidly releasing it so that it can vibrate unhindered; during the following oscillatory cycles, part of the mechanical energy is converted into electrical energy. In order to guide the design of such a harvester, we have modelled with finite element methods the response and power generation of a piezoelectric bimorph while it is plucked. The model permits the analysis of the effects of the speed of deflection as well as the prediction of the energy produced and its dependence on the electrical load. An experimental rig has been set up to observe the response of the bimorph in the harvester. A PZT-5H bimorph was used for the experiments. Measurements of tip velocity, voltage output and energy dissipated across a resistor are reported. Comparisons of the experimental results with the model predictions are very successful and prove the validity of the model

Design Optimization of Piezoelectric Energy Harvesting Cantilever for Medical Devices

Energy harvesting from the human body is considered as an effective solution for powering biomedical systems. In particular, the piezoelectric energy recovery from mechanical vibrations of the human body represents the most promising solution. The harvested power depends on several factors such as the geometry, the size and materials used for the piezoelectric cantilever. In addition, the reduction and the change of the design of the piezoelectric system constitute a process for increasing the output power. In the present paper, the conventional rectangular shape of the piezoelectric energy harvester is studied and different shapes of cantilever are investigated. We introduced thus a triangular and a new shaped cantilever which permits the enhancement of the scavenged power for low frequencies. In addition, simulations result of various structures are compared and performed by employing finite element method (FEM). Simulations results show that the proposed form generates an electric power of 145 µW at resonant frequency of 8.5 Hz. This novel shape provides more efficient performance compared to other designs

Linear Segmented Arc-Shaped Piezoelectric Branch Beam Energy Harvester for Ultra-Low Frequency Vibrations

Piezoelectric energy harvesting systems have been drawing the attention of the research community over recent years due to their potential for recharging/replacing batteries embedded in low-power-consuming smart electronic devices and wireless sensor networks. However, conventional linear piezoelectric energy harvesters (PEH) are often not a viable solution in such advanced practices, as they suffer from a narrow operating bandwidth, having a single resonance peak present in the frequency spectrum and very low voltage generation, which limits their ability to function as a standalone energy harvester. Generally, the most common PEH is the conventional cantilever beam harvester (CBH) attached with a piezoelectric patch and a proof mass. This study investigated a novel multimode harvester design named the arc-shaped branch beam harvester (ASBBH), which combined the concepts of the curved beam and branch beam to improve the energy-harvesting capability of PEH in ultra-low-frequency applications, in particular, human motion. The key objectives of the study were to broaden the operating bandwidth and enhance the harvester’s effectiveness in terms of voltage and power generation. The ASBBH was first studied using the finite element method (FEM) to understand the operating bandwidth of the harvester. Then, the ASBBH was experimentally assessed using a mechanical shaker and real-life human motion as excitation sources. It was found that ASBBH achieved six natural frequencies within the ultra-low frequency range (<10 Hz), in comparison with only one natural frequency achieved by CBH within the same frequency range. The proposed design significantly broadened the operating bandwidth, favouring ultra-low-frequency-based human motion applications. In addition, the proposed harvester achieved an average output power of 427 μW at its first resonance frequency under 0.5 g acceleration. The overall results of the study demonstrated that the ASBBH design can achieve a broader operating bandwidth and significantly higher effectiveness, in comparison with CBH

WearETE: A scalable wearable e-textile triboelectric energy harvesting system for human motion scavenging

In this paper, we report the design, experimental validation and application of a scalable, wearable e-textile triboelectric energy harvesting (WearETE) system for scavenging energy from activities of daily living. The WearETE system features ultra-low-cost material and manufacturing methods, high accessibility, and high feasibility for powering wearable sensors and electronics. The foam and e-textile are used as the two active tribomaterials for energy harvester design with the consideration of flexibility and wearability. A calibration platform is also developed to quantify the input mechanical power and power efficiency. The performance of the WearETE system for human motion scavenging is validated and calibrated through experiments. The results show that the wearable triboelectric energy harvester can generate over 70 V output voltage which is capable of powering over 52 LEDs simultaneously with a 9 × 9 cm2 area. A larger version is able to lighten 190 LEDs during contact-separation process. The WearETE system can generate a maximum power of 4.8113 mW from hand clapping movements under the frequency of 4 Hz. The average power efficiency can be up to 24.94%. The output power harvested by the WearETE system during slow walking is 7.5248 µW. The results show the possibility of powering wearable electronics during human motion

Optimisation and frequency tuning concepts for a vibration energy harvester

With current electronic designs becoming more versatile and mobile, applications that were wired and bulky before have now seen a great reduction in size and increase in portability. However, the issue is that the scaling down in size and cost of electronics has far outpaced the scaling up of energy density in batteries. Therefore, a great deal of research has been carried out to search for alternative power sources that can replace or enhance the conventional battery. Energy harvesting (also known as energy scavenging) is the process whereby ambient energy is captured and stored. The ambient energy here refers to energy that is pre-existing in nature, and is self-regenerating and has extended life time from a battery. After reviewing many possible energy scavenging methods, the conversion of ambient vibrations to electricity is chosen as a method for further research. There are plenty of different methods to transform ambient vibration to electricity, but in this research only piezoelectric and electromagnetic conversions are pursued. In order to harvest the most energy with the harvesting device, the harvester’s fundamental mode must be excited. However, this is not always possible due to fluctuations in the frequency of the vibration source. By being able to change the natural frequencies of the device, the harvester could be more effective in capturing ambient energy. In this thesis, the behaviour of the various types of energy sources is studied and the obtained information is later used to generate a vibration signal for subsequent simulation and experiments. A converter based on a piezoelectric bimorph is investigated. The resultant outputs from the design are compared to the model and the analysis is presented. The mechanical strain distributions on the beam’s surface for five different geometric structures are compared and discussed. This is followed by a discussion of the feasibility of improving the strain distribution by changing the beam’s depth (height) along the cantilever beam length. Lastly, a novel frequency tuning method, which involves applying a different effective electrical damping in different quadrants of the oscillating cycle, is proposed. The results of this analysis are presented, along with experimental results that indicate that the behaviour of the system can be changed over a limited range by changing the effective electrical damping during the oscillation cycle

USING PVDF FILMS AS FLEXIBLE PIEZOELECTRIC GENERATORS FOR BIOMECHANICAL ENERGY HARVESTING

In this paper, a commercial polymeric piezoelectric film, the polyvinylidene fluoride (PVDF) was used to harvest electrical energy during the execution of five locomotion activities (walking, going down and up the stairs, jogging and running). The PVDF film transducer was placed into a tight suit in proximity of four body joints (shoulder, elbow, knee and ankle). The RMS values of the power output measured during the five activities were in the range 0.1 – 10 µW depending on the position of the film transducer on the body. This amount of electrical power allows increasing the operation time of wearable systems, and it may be used to prolong the monitoring of human vital signals for personalized health, wellness, and safety applications

Available Technologies and Commercial Devices to Harvest Energy by Human Trampling in Smart Flooring Systems: a Review

Technological innovation has increased the global demand for electrical power and energy. Accordingly, energy harvesting has become a research area of primary interest for the scientific community and companies because it constitutes a sustainable way to collect energy from various sources. In particular, kinetic energy generated from human walking or vehicle movements on smart energy floors represents a promising research topic. This paper aims to analyze the state-of-art of smart energy harvesting floors to determine the best solution to feed a lighting system and charging columns. In particular, the fundamentals of the main harvesting mechanisms applicable in this field (i.e., piezoelectric, electromagnetic, triboelectric, and relative hybrids) are discussed. Moreover, an overview of scientific works related to energy harvesting floors is presented, focusing on the architectures of the developed tiles, the transduction mechanism, and the output performances. Finally, a survey of the commercial energy harvesting floors proposed by companies and startups is reported. From the carried-out analysis, we concluded that the piezoelectric transduction mechanism represents the optimal solution for designing smart energy floors, given their compactness, high efficiency, and absence of moving parts

Energy harvesting for wearable applications

Energy harvesting, the process of collecting low level ambient energy and converting it into electrical energy, is a promising approach to power wearable devices. By converting the energy of the human body by using piezoelectric and thermoelectric principles, the need for batteries and charging can be avoided, and the autonomy of wearable devices can be significantly increased. Due to the inherent random nature of human motion, however, the energy harvesting devices need to be specifically designed in order to ensure their optimal operation and sufficient power generation. Using several combined approaches, a new class of autonomous devices, suitable for telemedicine, patient monitoring or IoT applications, can be developed

Wearable Energy Harvesting for Charging Portable Electronic Devices by Walking

Wearable energy harvesting technologies will become an everyday part of future portable electronic devices. By generating the energy where the energy is needed and not relying on a main power source to recharge the portable devices battery, wearable energy harvesters will enable future generations to have even more freedoms, travel further, and never run low on battery again. This will reduce the energy consumption of the mains grid and thus in turn reduce CO² emissions generated by this traditional power source making this research important for the whole plant. This research project aims to take another step towards in helping the development of future technologies by investigating novel wearable energy harvesting designs and showing ability to charge current portable electronic devices such as smart phones and tables. This required research into a broad range of topics including, energies from humans, energy conversion mechanisms, the movement of people and the power demands for charging current portable electronic devices. Background research in the human energy levels and how research to date had gone about exacting different energy sources in different ways was the starting point for this research. This leads on to a more detailed look into the exaction methods and optimization of footfall energy harvester designs. Looking into the human gait cycle gave the information required to replicate human footfall motion for use in scientific experiments. From this background research, two bespoke designs of wearable energy harvester have been created. The first novel design showed a promising way of extracting footfall energy and converting it into useable electrical energy producing Watt-Level of power. The second design is an evolution of the first design but expands the extraction method to both feet and relocated the main harvester unit into a backpack worn by the user. The improved design incorporates a novel approach to energy conversion method by introducing a mechanical energy storage system before transduction into electrical energy. This is shown to increased electrical power output from footfall energy, reduced energy consumption of the wearer and is shown to truly be able to charge current portable electronics. The improved design is shown to produce 2.6 Watts average power from normal walking. The experimental set ups, procedures, and their results are shown throughout this thesis. These experimental results are confirmed by using the wearable energy harvesters on a treadmill at the three main walking speeds showing their real-world capabilities. To demonstrate the wearable energy harvester deigns shown in this research project were truly able to charge current portable technologies, endurance testing was also performed. This confirms the harvesters were able to work for longer periods of time. This longer time frame is needed for the charging times of the current portable devices. After researching into wearable energy harvesting from over the last 20 years it was a struggle to compare all the different forms, designs, types and power outputs. It became clear that the existing methods were unable to provide a clear picture of harvester’s scalability, changeability and useability for future design ideas. This is why a new form of comparison was created and is shown to have strong benefits over the existing methods

Energy harvesting from knee motion using piezoelectric patch transducers

This paper presents a piezoelectric energy harvesting device that generates electrical power from knee motion during human gait. The device is composed of two MEMS-based piezoelectric patch transducers optimized for placement around knee joints with minimal footprint. Simulations were performed on COMSOL software to reveal maximum performance that can be achieved under normal walking conditions. The internal capacitance of the patch transducers was measured to be 80 nF, while the resistance was on the order of 470 k. The patch transducers were inserted in a knee brace worn by a volunteer subject, and were characterized for voltage and power generation. During walking, the maximum open circuit voltage and rms power were measured to be 14 V and 6.2 uW, respectively. These values were observed to increase up to 14.4 V and 12 uW during a moderate running activity. The level of power achieved in the experiments shows the potential of this device as an independent onboard power component and as a continuous battery charger for wearable electronic devices.Bu çalışmada insanların yürüyüşleri esnasında diz hareketinden enerji elde edebilen bir piezoelektrik enerji hasadı aygıtının geliştirilmesi ve test edilmesi ele alınmıştır. Aygıt diz çevresine yerleştirmek üzere optimize edilmiş ve minimal ölçülere sahip iki adet MEMS tabanlı piezoelektrik yama dönüştürücüden oluşmaktadır. COMSOL programında yapılan simülasyonlar ile normal yürüme sırasında elde edilebilecek maksimum performans incelenmiştir. Piezoelektrik dönüştürücülerin iç kapasitans ve dirençlerinin 80 nF ile 470 kohm mertebesinde olduğu ölçülmüştür. Dönüştürücüler bir gönüllünün taktığı dizliğe yerleştirilerek, üretilen gerilim ve güç değerleri test edilmiştir. Yürüme sırasında maksimum 14 V ve 6.2 uW rms güç elde edilmiştir. Bu değerlerin orta hızlı koşma esnasında 14.4 V ve 12uW’a çıktığı gözlemlenmiştir. Ölçülen gerilim ve güç değerleri, bu aygıtın giyilebilir elektronik aletleri çalıştırabilme ve bu aletlerin pillerini sürekli şarj edebilme potansiyelini ortaya koymaktadır.No sponso