Micromechanics for energy generation

The emergence and evolution of energy micro-generators during the last two decades has delivered a wealth of energy harvesting powering solutions, with the capability of exploiting a wide range of motion types, from impulse and low frequency irregular human motion, to broadband vibrations and ultrasonic waves. It has also created a wide background of engineering energy microsytems, including fabrication methods, system concepts and optimal functionality. This overview presents a simple description of the main transduction mechanisms employed, namely the piezoelectric, electrostatic, electromagnetic and triboelectric harvesting concepts. A separate discussion of the mechanical structures used as motion translators is presented, including the employment of a proof mass, cantilever beams, the role of resonance, unimorph structures and linear/rotational motion translators. At the mechanical-to-electrical interface, the concepts of impedance matching, pre-biasing and synchronised switching are summarised. The separate treatment of these three components of energy microgenerators allows the selection and combination of different operating concepts, their co-design towards overall system level optimisation, but also towards the generalisation of specific approaches, and the emergence of new functional concepts. Industrial adoption of energy micro-generators as autonomous power sources requires functionality beyond the narrow environmental conditions typically required by the current state-of-art. In this direction, the evolution of broadband electromechanical oscillators and the combination of environmental harvesting with power transfer operating schemes could unlock a widespread use of micro-generation in microsystems such as micro-sensors and micro-actuators

Acoustic energy transmission in cast iron pipelines

In this paper we propose acoustic power transfer as a method for the remote powering of pipeline sensor nodes. A theoretical framework of acoustic power propagation in the ceramic transducers and the metal structures is drawn, based on the Mason equivalent circuit. The effect of mounting on the electrical response of piezoelectric transducers is studied experimentally. Using two identical transducer structures, power transmission of 0.33 mW through a 1 m long, 118 mm diameter cast iron pipe, with 8 mm wall thickness is demonstrated, at 1 V received voltage amplitude. A near-linear relationship between input and output voltage is observed. These results show that it is possible to deliver significant power to sensor nodes through acoustic waves in solid structures. The proposed method may enable the implementation of acoustic - powered wireless sensor nodes for structural and operation monitoring of pipeline infrastructure

Power supply based on inductive harvesting from structural currents

Monitoring infrastructure offers functional optimisation, lower maintenance cost, security, stability and data analysis benefits. Sensor nodes require some level of energy autonomy for reliable and cost-effective operation, and energy harvesting methods have been developed in the last two decades for this purpose. Here, a power supply that collects, stores and delivers regulated power from the stray magnetic field of currentcarrying structures is presented. In cm-scale structures the skin effect concentrates current at edges at frequencies even below 1 kHz. A coil-core inductive transducer is designed. A fluxfunnelling soft magnetic core shape is used, multiplying power density by the square of funnelling ratio. A power management circuit combining reactance cancellation, voltage doubling, rectification, super-capacitor storage and switched inductor voltage boosting and regulation is introduced. The power supply is characterised in house and on a full-size industrial setup, demonstrating a power reception density of 0.36 mW/cm3, 0.54 mW/cm3 and 0.73 mW/cm3 from a 25 A RMS structural current at 360 Hz, 500 Hz and 800 Hz respectively, corresponding to the frequency range of aircraft currents. The regulated output is tested under various loads and cold starting is demonstrated. The introduced method may enable power autonomy to wireless sensors deployed in current-carrying infrastructure

Complex impedance matching for far-field acoustic wireless power transfer

In this study, different load matching techniques are analysed to identify the optimum method to deliver power to the receiver for acoustic wireless power transfer systems. Complex impedance matching of the system’s transducers provides an advantage to drive the transmitter off-resonance for cases where there is a resonance mismatch between the transducers due to make, defect or ambient conditions. By studying the effect of impedance matching for different frequencies near the resonance frequency, similar power levels can be achieved for a wider bandwidth of frequencies using complex impedance matching. Thus, increased power can be delivered to the receiver by controlling the frequency of the transmitter, which can be exploited for beam steering along the propagation axis when standing waves are prominent between the transducers. A summary of the power experimentally extracted for the different loading techniques presented in this paper demonstrates a 4 kHz increase in system bandwidth and 140% more power can be delivered by tuning both transducers with complex impedance matching

Shaped coil-core design for inductive energy collectors

Coil design is important for maximizing power density in inductive energy harvesting as well as in inductive power transfer. In this work, we present a study of coil performance, based on simulated flux distributions corresponding to a real aircraft application case. The use of funnel-shaped soft magnetic cores boosts magnetic flux density by flux concentration and allows the use of a smaller diameter coil. This reduces the transducer mass as well as the coil resistance (R COIL ), thereby increasing the power density. Analysis and simulation shows a fifty-fold power density increase from moderate funneling and another two-fold increase by coil size optimization. Results are compared with experimental measurements presented in [1] which demonstrate a 36μW/g(106μW/cm 3 ) power density from alternating environmental magnetic fields in the 10μT/300 Hz range

Inductive power line harvester with flux guidance for self-powered sensors

Self-powered sensors are expected to enable new large-scale deployment and location access capabilities for sensor systems. Energy harvesting devices have been shown to provide adequate power densities but their dependence on very specific environmental conditions restricts their applicability. Energy harvesting from power line infrastructure offers an architecture for addressing this challenge, because such infrastructure is widely available. In this paper an inductive power line harvester concept is presented, based on a flux concentration approach adapted to a closed-loop core geometry. Flux concentration is studied by simulation, showing a 26% flux increase using a 1:3 geometrical concentration ratio in a closed-loop core. A 20×20×25 mm prototype with a U-shaped soft-core sheet and a 200-turn Cu coil around a 5 mm diameter, 20 mm long soft-core rod is introduced. The total device volume is 9.1 cm 3 . Characterization results on a power line evaluation setup for currents up to 35 A RMS and a 50 Hz – 1 kHz range are presented. Power between 2.2 mW (50 Hz) and 233 mW (1 kHz) is demonstrated on an ohmic load, from a 10 A RMS power line current, employing impedance matching with reactance cancellation. The corresponding power densities are 0.24 mW/cm 3 and 25 mW/cm 3 respectively, per total device volume. This performance is adequate for enabling self-powered wireless sensor networks installed along power distribution lines

Clamped closed-loop flux guides for power line inductive harvesting

Inductive harvesting from existing power lines in vehicle, industrial and infrastructure environments offers an opportunity for providing energy autonomy to sensors in a wide range of environments with high sensing interest. Flux funnelling has been shown to improve the power density of such devices by over an order of magnitude. The requirement for retrofitting onto existing power lines leads to a demand for detachable magnetic core interfaces, which introduce gaps and uncertainty to device performance. In this paper, an inductive energy harvesting device design that addresses this challenge is introduced. The design allows the interfaces to be internal to the device housing. Repeatable fixing, with reduced sensitivity to installation practicalities and controllable force is achieved by a screw-pressing mechanism, and the employment of a hard polyoxymethylene housing material. This method is utilized in an inductive power-line prototype, demonstrating power output up to 260 mW from a 40 A RMS, 500 Hz current, emulating aircraft power lines

Linear displacement and force characterisation of a 3D-printed flexure-based delta actuator

Piezoelectric beams provide a fast, high-force and scalable actuation mechanism that could offer precise motion control to medical microdevices including invasive micromanipulators, catheters and diagnosis tools. Their small displacement range can be addressed by motion amplification mechanisms. In this paper, a piezoelectric-actuated delta-robot actuator is proposed for probe-based confocal laser endomicroscopy (pCLE) microsystems. A prototype is designed and fabricated using three-dimensional (3D) polymer compound printing for a multi-flexure compliant motion amplifier and commercial piezoelectric beams. The flexure material is optimised for maximum linear output motion. The overall robot length is 76 mm and its maximum lateral dimension is 32 mm, with 10 g overall mass, including three piezoelectric beams. An axial motion control range of 0.70 mm and a maximum axial force of 20 mN are demonstrated, at 140 V actuation voltage. The proposed actuator architecture is promising for controlling lens, fibre and micromanipulator components for medical microrobotic applications