Scott D. Moss

A low profile vibro-impacting energy harvester with symmetrical stops

This paper reports on an investigation into the use of a vibro-impact approach to construct a relatively broadband kinetic energy harvester. Potentially, the vibro-impacting process may be exploited as an autotuning mechanism for energy harvesting in an environment where the source vibration spectrum varies in time, such as an aircraft in flight. The energy harvester examined in this paper is based on a vibro-impacting oscillator with double-sided, symmetrical, piezoelectric bimorph-stops. The energy harvester operates in the frequency range of 100–113 Hz and has a (non-optimized) maximum energy of 5.3 mW from an rms host vibration of 450 mG.

Scaling and power density metrics of electromagnetic vibration energy harvesting devices

A review of the vibration energy harvesting literature has been undertaken with the goal of establishing scaling laws for experimentally demonstrated harvesting devices based on electromagnetic transduction. Power density metrics are examined with respect to scaling length, mass, frequency and drive acceleration. Continuous improvements in demonstrated power density of harvesting devices over the past decade are noted. Scaling laws are developed from observations that appear to suggest an upper limit to the power density achievable with current harvesting techniques.

A broadband vibro-impacting power harvester with symmetrical piezoelectric bimorph-stops

The certification of retrofitted structural health monitoring (SHM) systems for use on aircraft raises a number of challenges. One critical issue is determining the optimal means of supplying power to these systems, given that access to the existing aircraft power system is often problematic. Previously, the Australian Defence Science and Technology Organisation has shown that a structural strain-based energy harvesting approach can be used to power a device for SHM of aircraft structure. Acceleration-based power harvesting from airframes can be more demanding than a strain-based approach because the vibration spectrum of an aircraft structure can vary dynamically with flight conditions. A vibration spectrum with varying frequency may severely limit the energy harvested by a single-degree-of-freedom resonance-based device, and hence a frequency agile or (relatively) broadband device is often required to maximize the energy harvested. This paper reports on an investigation into the use of a vibro-impact approach to construct a piezoelectric-based kinetic power harvester that can operate in the approximate frequency range of 29?63?Hz.

Hybrid rotary-translational vibration energy harvester using cycloidal motion as a mechanical amplifier

This paper reports on a hybrid rotary-translational vibration energy harvesting approach that exploits cycloidal motion to achieve a relatively high power density from an oscillatory kinetic energy harvester operating at frequencies below 10 Hz. The approach uses a rolling magnetic sphere. The rolling motion mechanically amplifies the velocity at which the magnetic pole of the sphere passes a nearby coil transducer, inducing a proportionally larger electro-motive force across the coil. A prototype cycloidal energy harvester is shown to produce a peak power of 201 mW from a host vibration of 500 mg rms at 5.4 Hz.

Development of structural health monitoring systems for composite bonded repairs on aircraft structures

The application of bonded composite patches to repair or reinforce defective metallic structures is becoming recognized as a very effective versatile repair procedure for many types of problems. Immediate applications of bonded patches are in the fields of repair of cracking, localized reinforcement after removal of corrosion damage and for reduction of fatigue strain. However, bonded repairs to critical components are generally limited due to certification concerns. For certification and management of repairs to critical structure, the Smart Patch approach may be an acceptable solution from the airworthiness prospective and be cost effective for the operator and may even allow some relaxation of the certification requirements. In the most basic form of the Smart Patch in-situ sensors can be used as the nerve system to monitor in service the structural condition (health or well-being) of the patch system and the status of the remaining damage in the parent structure. This application would also allow the operator to move away from current costly time-based maintenance procedures toward real-time health condition monitoring of the bonded repair and the repaired structure. TO this end a stand-alone data logger device, for the real-time health monitoring of bonded repaired systems, which is in close proximity to sensors on a repair is being developed. The instrumentation will measure, process and store sensor measurements during flight and then allow this data to be up-loaded, after the flight, onto a PC, via remote (wireless) data access. This paper describes two in-situ health monitoring systems which will be used on a composite bonded patch applied to an F/A-18. The two systems being developed consists of a piezoelectric (PVDF) film-based and a conventional electrical-resistance foil strain gauge-based sensing system. The latter system uses a primary cell (Lithium- based battery) as the power source, which should enable an operating life of 1-2 years. The patch health data is up- loaded by the operator using an IR link. The piezoelectric film-based sensing system is self-powered and has been designed to operate using the electrical power generated by an array of piezoelectric films, which convert structural dynamic strain to electrical energy. These transducers power the electronics which interrogate the piezoelectric film sensors, and process and store the patch health data on non-volatile memory. In this system the patch health data is up-loaded by the operator using a magnetic transreceiver. This paper describes the development and evaluation of the two systems, including issues such as system design and patch health monitoring techniques.

Wideband vibro-impacting vibration energy harvesting using magnetoelectric transduction

This article reports on proof-of-concept experimental work carried out to demonstrate a wideband vibro-impacting energy harvesting approach based on a magnet/bearing arrangement coupled with a magnetoelectric transducer. The harvesting arrangement uses a Terfenol-D/Pz27 laminate transducer (disc with radius 5 mm) positioned between an oscillating spherical chrome-steel bearing and a rare earth magnet. The oscillating bearing steers magnetic field through the magnetoelectric transducer, generating an oscillating charge that can be harvested. A vibro-impacting arrangement between the oscillating bearing (radius 12.7 mm) and a pair of aluminium mechanical stops is designed to produce a wideband frequency response. For a 434 mG host acceleration, the vibro-impact mechanism produced a bandwidth of ∼7.2 Hz (between 6 and ∼13.2 Hz). The issue of damage to the mechanical stops caused by the vibro-impacting process is also explored and was demonstrated experimentally and theoretically to be inconsequential. This non-optimized wideband harvesting approach has demonstrated a generated power of 3.3 µW from a root mean square host acceleration of 180 m-g at 8.0 Hz.

Energy harvesting from heavy haul railcar vibrations

Vibration energy harvesting has shown promise as technique for powering sensor networks and wireless devices. Previously, a biaxial vibration energy harvester approach was reported that used a wire-coil transducer and a permanent magnet/ball-bearing arrangement. In response to host accelerations the ball-bearing (i.e. proof mass) oscillates with two translational degrees of freedom, hence producing a varying magnetic field across the coil and therefore inducing an electromagnetic force (EMF) that could potentially be used to power a sensor. Vertical host accelerations, somewhat stochastic in nature, were measured from the bogie of a heavy haul railcar. The measured railcar accelerations were filtered, and replicated in a laboratory environment using a vibration shaker arrangement. The shaker arrangement was used to excite a non-optimised prototype energy harvester which employed a steel ball-bearing proof-mass with 31.8 mm diameter. The harvester, when excited by stochastic vibrations similar to those found on a railcar (and having an RMS acceleration of 4.16 ms-2), produced a peak power of 1.71 mW and a longer term RMS power of 874 μW.

Detachable acoustic electric feedthrough

This paper outlines the development and characterisation of a detachable acoustic electric feedthrough (DAEF) to transfer power and data across a metal (or composite) plate. The DAEF approach is being explored as a potential means of wirelessly powering in-situ structural health monitoring systems embedded within aircraft and other high value engineering assets. The DAEF technique operates via two axially aligned piezoelectric-magnet structures mounted on opposite sides of a plate. Magnetic force is used to align the two piezoelectric-magnet structures, to create an acoustic path across a plate. The piezoelectric-magnet structures consisted of Pz26 piezoelectric disk elements bonded to NdFeB magnets, with a standard ultrasonic couplant (High-Z) used between the magnet and plate to facilitate the passage of ultrasound. Measured impedance curves are matched to modeled curves using the Comsol multi-physics software coupled with a particle-swarm approach, allowing optimised Pz26 material parameters to be found (i.e. stiffness, coupling and permittivity matrices). The optimised Pz26 parameters are then used in an axi-symmetric Comsol model to make predictions about the DAEF power transfer, which is then experimentally confirmed. With an apparent input power of 1 VA and 4.2 MHz drive frequency, the measured power transfer efficiency across a 1.6 mm Al plate is ~34%. The effect of various system parameters on power transfer is explored, including bondline thickness and plate thickness. DAEF data communication is modelled using LTspice with three-port one-dimensional piezoelectric models, indicating that data rates of 115 kBit/s are feasible.

Vibro-impacting power harvester

The certification of retro-fitted structural health monitoring (SHM) systems for use on aircraft raises a number of challenges. One critical issue is determining the optimal means of supplying power to these systems, given that access to the existing aircraft power-system is often problematic. Previously, the DSTO has shown that a structural-strain based energy harvesting approach can be used to power a device for SHM of aircraft structure. Acceleration-based power harvesting from airframes can be more demanding than a strain based approach because the vibration spectrum of an aircraft structure can vary dynamically with flight conditions. A vibration spectrum with varying frequency may severely limit the power harvested by a single-degree-of-freedom resonance-based device, and hence a frequency agile or (relatively) broadband device is often required to maximize the energy harvested. This paper reports on an investigation into the use of a vibro-impact approach to construct an acceleration-based power harvester that can operate in the frequency range 29-41 Hz.

Non-linear dynamics of a vibration energy harvester by means of the homotopy analysis method

This article reports on the modelling and experimental validation of a vibration energy harvesting approach that uses a permanent-magnet/ball-bearing arrangement and a wire-coil transducer. The harvester’s behaviour is modelled using a forced Duffing oscillator modified with quintic non-linearity, and the primary first-order steady-state resonant solutions are found using the homotopy analysis method. These solutions found are shown to compare well with measured ball-bearing displacements and harvested output power and are used to predict the wideband frequency response of this type of vibration energy harvester. A prototype harvester was found to produce a maximum output power of 16.4 mW from a 14.2 Hz, 400 milli-g excitation.