Browsing by Author "Pozzi, Michele"
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Item Open Access Characterization of a rotary piezoelectric energy harvester based on plucking excitation for knee-joint wearable applications(Institute of Physics, 2012-05-31T00:00:00Z) Pozzi, Michele; Zhu, MeilingWearable medical and electronic devices demand a similarly wearable electrical power supply. Human-based piezoelectric energy harvesters may be the solution, but the mismatch between the typical frequencies of human activities and the optimal operating frequencies of piezoelectric generators calls for the implementation of a frequency up-conversion technique. A rotary piezoelectric energy harvester designed to be attached to the knee-joint is here implemented and characterized. The wearable harvester is based on the plucking method of frequency up-conversion, where a piezoelectric bimorph is deflected by a plectrum and permitted to vibrate unhindered upon release. Experiments were conducted to characterize the energy produced by the rotary piezoelectric energy harvester with different electric loads and different excitation speeds, covering the range between 0.1 and 1 rev s −1 to simulate human gait speeds. The electrical loads were connected to the generator either directly or through a rectifying bridge, as would be found in most power management circuits. The focus of the paper is to study the capability of energy generation of the harvester for knee-joint wearable applications, and study the effects of the different loads and different excitation speeds. It is found that the energy harvested is around 160–490 {µJ} and strongly depends on the angular speed, the connected electric loads and also the manufacturing quality of the harvester. Statistical analysis is used to predict the potential energy production of a harvester manufactured to tighter tolerances than the one presented here.Item Open Access Experimental characterisation of macro fibre composites and monolithic piezoelectric transducers for strain energy harvesting(2012-07-06) Pozzi, Michele; Canziani, Alfredo; Durazo-Cardenas, Isidro; Zhu, Meiling; Tribikram, KunduCompact and lightweight energy harvesters are needed to power wireless sensor nodes (WSNs). WSNs can provide health monitoring of aircraft structures, improving safety and reducing costs by enabling predictive maintenance. A simple solution, which meets the requirements for lightness and compactness, is represented by piezoelectric generators fixed to the surface of the wing (i.e. the wing skin). Such piezoelectric patches can harvest the strain energy available when the wing is flexed, as occurs, for example, in the presence of gust loading. For this study, monolithic piezoelectric sheets and macro fibre composite (MFC) generators were fixed to plates made of two materials commonly used for aircraft wing skin: Al-2024 aluminium alloy and an epoxy-carbon fibre composite. The plates then underwent harmonically varying loading in a tensile testing machine. The power generation of the harvesters was measured at a selection of strain levels and excitation frequencies, across a range of electrical loads. The optimal electrical load, yielding maximum power extraction, was identified for each working condition. The generated power increases quadratically with the strain and linearly with the frequency. The optimal electrical load decreases with increasing frequency and is only marginally dependent on strain. Absolute values of generated power were highest with the MFC, reaching 12mW (330μW/cm2) under 1170μstrain peak-to-peak excitation at 10Hz with a 66kΩ load. Power generation densities of 600μW/cm2were achieved under 940μstrain with the monolithic transducers at 10Hz. It is found that MFCs have a lower power density than monolithic transducers, but, being more resilient, could be a more reliable choice. The power generated and the voltage outputs are appropriate for the intended applicItem Open Access Harvesting energy from the dynamic deformation of an aircraft wing under gust loading(2012-07-06) Pozzi, Michele; Guo, Shijun J.; Zhu, Meiling; Tribikram, KunduWeight reduction and maintenance simplification are high in the agenda of companies and researchers active in the aerospace sector. Energy harvesters are being investigated because they enable the installation of wireless sensor nodes, providing structural health monitoring of the aircraft without additional cabling. This paper presents both a weight-optimized composite wing structure and a piezoelectric harvester for the conversion of mechanical strain energy into electrical energy. Finite elements modelling was used for the minimum- weight optimisation within a multi-constraints framework (strength, damage tolerance, flutter speed and gust response). The resulting structure is 29% more compliant than the original one, but is also 45% lighter. A strain map was elaborated, which details the distribution of strain on the wing skin in response to gust loading, indicating the optimal locations for the harvesters. To assess the potential for energy generation, a piezoelectric harvester fixed to a portion of the wing was modelled with a multi-physics finite elements model developed in ANSYS. The time-domain waveforms of the strain expected when the aircraft encounters a gust (gust frequencies of 1, 2, 5 and 10 Hz were considered) are fed into the model. The effects of harvester thickness and size, as well as adhesive thickness, were investigated. Energy generation exceeding 10 J/m2in the first few second from the beginning of the gust is predicted for 100μ-thick harvesters. The high energy density, low profile and weight of the piezoelectric film are greatly advantageous for the envisaged applicationItem Open Access Performance testing of a low power consumption wireless sensor communication system integrated with an energy harvesting power source(2012-11-30T00:00:00Z) Marsic, Vlad; Giuliano, Alessandro; Pozzi, Michele; Zhu, Meiling; Williams, Stewart W.; Yurish, S.This paper presents the performance testing results of a wireless sensor communication system with low power consumption integrated with a vibration energy harvesting power source. The experiments focus on the system’s capability to perform continuous monitoring and to wirelessly transmit the data acquired from the sensors to a user base station, completely battery-free. Energy harvesting technologies together with system design optimisation for power consumption minimisation ensure the system’s energy autonomous capability demonstrated in this paper by presenting the promising testing results achieved following its integration with Structural Health Monitoring (SHM) and Body Area Network (BAN) applications.Item Open Access Pizzicato excitation for wearable energy harvesters(2012-07-25) Pozzi, Michele; Zhu, MeilingA new technique based on the plucking of flexible piezoelectric material can be used to boost energy harvested to power portable electronic devices.Item Open Access Plucked piezoelectric bimorphs for knee-joint energy harvesting: modelling and experimental validation(Institute of Physics, 2011-05-31T00:00:00Z) Pozzi, Michele; Zhu, MeilingThe 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.Item Open Access Plucked piezoelectric biomorphs for energy harvesting applications(2011-05-05T00:00:00Z) Pozzi, Michele; Zhu, MeilingThe modern drive towards mobility and wireless devices is motivating intense research in energy harvesting (EH) technologies. In an effort to reduce the battery burden of people, we are investigating a novel piezoelectric wearable energy harvester. As piezoelectric EH is significantly more effective at high frequencies, in opposition to the characteristically low-frequency human activities, we propose the use of an up-conversion strategy analogous to the pizzicato musical technique. In order to guide the design of such harvester, we have modelled with Finite Elements (FE) the response and power generation of a piezoelectric bimorph while it is "plucked", i.e. deflected, then released and permitted to vibrate freely. An experimental rig has been devised and set up to reproduce the action of the bimorph in the harvester. Measurements of the voltage output and the energy dissipated across a series resistor are reported and compared with the FE predictions. As the novel harvester will feature a number of bimorphs, each plucked tens of times per step, we predict a total power output of several mW, with imperceptible effect on the wearer's gait.