Measurement scientists from SIQ, the Slovenian Institute of Quality and Metrology have developed a new energy wave generator to calculate the efficiency of all energy harvesting devices and give the most accurate analysis yet of their performance. Their digital arbitrary waveform generator is able to replicate over a million accurately described energy signals encountered by harvesters in operation, whether they are the waste heat produced by a motor engine or the vibrations of a wind turbine as it spins.
These signals can be injected into new measuring devices and contrasted with their measurement output. The plans for the generator have been published by the proceedings of the Conference on Precision Electromagnetic Measurements 2012. This research is part of the EURAMET joint research project on "Energy Harvesting" which brings together seven measurement institutes around Europe to tackle standardisation and metrology issues around these tiny devices. The project is funded by the European Community's Seventh Framework Programme on the basis of Decision no. 912/20097EC.
The Slovenian team will now take their set up across Europe to calibrate measurement equipment at other institutes. They hope to create the most accurate standardisation infrastructure for energy harvesting in the world and drive European commercial growth and innovation in the sector.
Energy harvesters convert wasted energy from unwanted vibrations and heat produced by machinery into electrical energy at the micro-scale. The technology could make industrial processes more efficient and open up applications in areas such as autonomously powered wireless sensor networks which would reduce reliance on environmentally harmful batteries that are costly to replace. As a result reports from IDTechEx, an independent market researcher specialising in energy harvesting predicted the value of the energy harvesting market to rise from $0.7 billion in 2012, to over $5 billion by 2022.
However energy harvesting is still an immature technology. Realising its potential is dependent on the development of an internationally agreed set of measurement standards or verification tools around new products and their potential power outputs.
The difficulty has been the small energy sources that can be harvested are notoriously unstable and unpredictable due to changes in the local environment. However standard measurement practises to determine the efficiency of today's devices use clean sine wave signals with constant frequencies which are just not realistic. This makes it difficult to assess the true efficiency of different harvesters.
Without these standards, developers are unable to provide meaningful product specifications for commercially available energy harvesting devices, and their customers are forced to buy the products and conduct their own trials, often at great expense and time.
In their paper, the team from SIQ started by capturing energy harvester wave bank of signals that mathematically mimic known harvester sources. A digital to analog converter is then used to generate defined signals like cosine shaped bursts, dumped oscillator waveforms and even parts of real sampled signals which are used for evaluation of each harvester.
The arbitrary waveform generator covers signals with amplitude up to 10 V, frequency up to 100 kHz and dynamic range of 120 dB but are generated arbitrarily i.e with varying amplitude and frequency allowing the wave shape of the signal to vary and move up and down as it does in the real world. With the power to traceably simulate all signals from low frequency harvesters, the generator will allow the team to calibrate all properties of measurement equipment used to measure more accurately each harvester's true efficiency.
Dr Rado Lapuh, who led the SIQ team says: "The energy harvesting industry has recognised by the value of standard measurements and traceability in its output claims in recent years but up to now have been unable to traceably measure the energy sources output which harvesters could mine to produce electricity. Our set up utilises the most comprehensive bank of realistic wave signals so far assembled. What we hope is in the future harvesting devices claims around output are based and can be traced back to more accurate reliable measurement process such as this."
The next step is to verify the accuracy of the signal and then the accuracy of the measurement equipment measuring it. Then finally this standardised metrology set up can be used to calibrate equipment of all the measurement institutes around Europe, starting with PTB in Germany and INRIM in Italy.
Source: Metrology for Energy Harvesting
Top image: PCB view of the prototype arbitrary waveform