Hosted at TRW Conekt, this workshop was designed to facilitate the definition of a number of new research challenges and the creation of multidisciplinary teams that would address them. The topic of this workshop was the use of energy harvesting to power the monitoring of structures such as buildings, tunnels, bridges and other fixed infrastructure. The workshop sessions were hence focused on the specific scientific and technology advances necessary to realise the vision of these applications.
Although TRW is mainly involved with components and systems for the automotive industry, the company's involvement in the energy harvesting space takes a step back and doesn't limit itself to vehicle applications for harvesters. Therefore, TRW is researching roadside infrastructure sensors. It is interesting to point out that TRW is one of the world's leading suppliers of tyre pressure monitoring systems (TPMS) but instead of using energy harvesters for those (which could cost several tens of Euros), 60 cent batteries are utilized and perform adequately. According to Dr Roger Hazelden, technology leader on sensors and optoelectronics at TRW Conekt, cost is a major driver in applications such as TPMS's where the use of batteries is not regulated. Energy harvesters would make a lot more sense in applications where there are restrictions on the use of batteries (e.g. aerospace), in which case energy harvesting would be an enabling technology that would be necessary for wireless sensing/monitoring.
Professor of Civil Engineering, Kenichi Soga from the University of Cambridge gave insight on the use of monitoring for structures that were built in the past with a "let's build them and see how long they last..." approach. Several of these structures are by now a few decades old and pose potential risks if their integrity is compromised over time. A very interesting example of use of integrity sensors in a project was during some work undertaken for the London Underground, making sure that tunnel tiles did not shift or move, leading to width changes that could be detrimental to passing trains or even causing fears of collapse. Again, interestingly, batteries were used for these sensors, provided by Tadiran technology. At a cost of about £40 for the battery and £200 for the whole sensor, batteries were considered, the best, most reliable option, with a lifetime of approximately 2 years, and the sensor taking measurements at a rate of 1 measurement/minute.
Professor Soga also talked of advances in energy harvesting technologies that are making them more relevant for the applications in question, mentioning in specific the work of Saito et al in the University of Cambridge, on harvesting UV radiation with a-Se (amorphous selenium) solar cells transparent to visible radiation. On the other hand, he stressed the difficulty in identifying the right kind of energy harvesting technology for some applications (no solar radiation available underground...); simultaneously, in the specific environment of a train tunnel where there are surges of ambient energy that are relatively random in frequency and duration ( e.g air pressure changes, vibrations around a train as it passes through a tunnel) it is difficult to capture and transform this energy into a power source for a sensor.
After presentations from EnOcean (over 160,000 buildings are currently using EnOcean products, from wireless light switches to occupancy sensors) and an overview of the two years of NPL's structure health monitoring (SHM) of a foot bridge, participants at the workshop pooled together their ideas on the needs and requirements, in terms of technical advances, that would be necessary in order to realise the vision that's becoming possible, on the field of SHM, with energy harvesters. Contributions focused on:
- The needs for advances in the different harvesting technologies together with the achievement of low cost solutions in the next decade.
- Simplification of the devices and electronics necessary to incorporate energy harvesters rather than batteries but also, at the same time, education of potential adopters (e.g. civil engineers, construction industry) on the benefits that can outweigh the increase in complexity.
- It was also pointed out that it is important to keep an eye on advances in battery technology that make for harsher competition for energy harvesters which have not yet had the chance to be tested on their long term reliability as well as the older, more mature battery technologies have.
A very fruitful meeting overall, the Energy Harvesting Network will take the participants' contributions, compile them and create a roadmap document that will outline the main challenges and technical advances necessary as well as clarify what collaborations can lead to solutions that will push the technologies forward.
For more read : Energy Harvesting and Storage for Electronic Devices 2010-2020