Energy harvesters based upon resonantmass-spring-damper systems can only generate useful power over a narrow range of excitation frequencies. This is a significant limitation in applications where the vibration source frequency changes over time. In this paper, an active electrical load is presented which can overcome the bandwidth limitations by parametrically tuning the overall harvester system. The electrical tuning technique synthesizes an optimum reactive load with high-efficiency switch-mode electronics, which also provides rectification, feeding the energy harvested into a dc store. The method is shown to be effective at increasing the power frequency bandwidth of resonant type harvesters and offers the capability of autonomous operation. The theoretical basis for the technique is presented and verified with experiment results. The paper illustrates the challenges of implementing the power electronic converter for a low-quiescent power overhead and in choosing the control architecture and tuning algorithms.

Wireless sensors have the potential to provide significant insight into in situ physical and biogeochemical processes in sub-ice hydrologic systems. However, the nature of the glacial environment means that sensor deployment and data return is challenging. We describe two bespoke sensor platforms, electronic tracers or 'ETracers', and 'cryoegg', for untethered, wireless data collection from glacial hydrologic systems, including subglacial channels. Both employ radio frequencies for data transmission, are designed to endure harsh environmental conditions and can withstand low temperatures, high pressure, turbulence and abrasion. We discuss the design, optimization and field testing of the ETracers and cryoegg, culminating in test deployments beneath the Greenland ice sheet. The small, low-cost ETracers were able to travel through subglacial drainage channels, from where they returned water pressure measurements through 100 m of ice, and could measure water depth in crevasses. The larger cryoegg was able to return multi-parameter data from moulins through 500 m of wet ice to receivers up to 2 km away, and from 12 m depth in a proglacial lake to a receiver on the shore. The tests demonstrate that the cryoegg and ETracers are low-power, versatile, robust wireless sensor platforms suitable for glacial environments, which may be used with portable, low-cost receiving equipment.

This briefing describes the first deployment of a new electronic tracer (E‐tracer) for obtaining along‐flowpath measurements in subsurface hydrological systems. These low‐cost, wireless sensor platforms were deployed into moulins on the Greenland Ice Sheet. After descending into the moulin, the tracers travelled through the subglacial drainage system before emerging at the glacier portal. They are capable of collecting along‐flowpath data from the point of injection until detection. The E‐tracers emit a radio frequency signal, which enables sensor identification, location and recovery from the proglacial plain. The second generation of prototype E‐tracers recorded water pressure, but the robust sensor design provides a versatile platform for measuring a range of parameters, including temperature and electrical conductivity, in hydrological environments that are challenging to monitor using tethered sensors. Copyright © 2012 John Wiley & Sons, Ltd.

Energy harvesters based upon resonant mass-spring-damper systems can only generate useful power over a narrow range of excitation frequencies. This is a significant limitation in applications where the vibration source frequency changes over time. In this paper an active electrical load is presented which can overcome the bandwidth limitations by parametrically tuning the overall harvester system. The electrical tuning technique synthesizes an optimum reactive load with high-efficiency switch-mode electronics, which also provides rectification, feeding power harvested into a DC store. The method is shown to be effective at increasing the power frequency bandwidth of resonant type harvesters, and offers the capability of autonomous operation. The theoretical basis for the technique is presented, and verified with experiment results. The paper illustrates the challenges of implementing the power electronic converter for a low quiescent power overhead and in choosing the control architecture and tuning algorithms.