Authors: Simon Aliwell, Zartech and Costis Kompis, Vodera
There was a good cluster of presentations on heat energy harvesting with some new technologies or advances in production capability.
Nextreme described their microscale thin film thermoelectric technology and high volume semiconductor manufacturing processes. They made the very strong case that the predicted large markets ($6bn by 2020) for thermoelectric devices will require very substantial cost reductions and widespread wireless sensor network deployment. Their process uses 400x less Te than conventional TEGs and this could become key with the trend to rapidly increasing Te costs. Interesting practical solutions e.g. harvesting off the hot and cold pipes under a sink or on the waste trap as well as turbine bearing condition monitoring were described.
described a completely new thermal harvesting approach using bimetals which snap up and down around specific pre-defined temperatures. A significant potential advantage is that the devices would be able to work without the need for a heatsink - usually a rather bulky element of a thermal energy harvester. The harvesting devices are constructed by combining the bimetal with a piezoelectric
material in a shock layout or by direct patterning of the bimetal on the piezoelectric. The snap temperature does not change with scale and scaling laws seem to work in favour of scaling down in size - several small matrixed bimetals can replace one large on resulting in increases in power and be surface and shape adaptive at the same time. Concerns of fatigue lifetime were claimed to not be a problem having demonstrated thousands of cycles although this may still not address the issue of lifetime of the piezoelectric components. It was also claimed that the matrixed approach could be used to address different temperature ranges in a single device by coupling bimetal with different snap temperatures.
Marlow Industries also covered thermal energy harvesting and power management but the presentation was more tutorial in style so did not reveal much detail on their own developments.
Piezoelectric energy harvesting received a fair bit
of attention this year.
work in the area of mechanical push button or vibration energy harvesting and their key USP appears to be a very high claimed conversion efficiency (some 13x better than their competition). No information was however supplied to explain how this was achieved. They demonstrated their usual batteryless TV remote control based on 2-way radio developed for Philips
. This is still a prototype rather than having started achieving product sales. Arveni now also appear to be working on using their technology for powering industrial wireless sensor networks
Meggitt Sensing Systems
talked about the performance of fully integrated vibrational energy harvesters based on PZT. They have taken a thick film manufacturing approach by screen-printing on micro-machined silicon cantilevers. Through their internal spin-off company, InSensor, they offer various mass-beam geometries including unimorphs and bimorphs and can manufacture in high volumes. Their focus would appear to be devices that are designed to operate with relatively modest acceleration levels achieving something like 15-20 microwatts at 0.5g.
One of the main criticisms of piezoelectric materials is their brittle nature that results in failure after repeated bending. Algra have come up with a piezoelectric switch design that works without displacement. Greater than 5N pressure on the piezoelectric material is sufficient to activate the device as a handheld remote control. The use of a laminated multilayer casing with support rather than clamping for the piezo layer appears to be an important aspect of the design. It has been applied to light switching, garage door openers and other home automation applications. Further applications are envisaged in push stop buttons on buses, batteryless pH meters, e-ink display, various industrial push buttons etc.
Low power electronics and energy management was also a major area of focus.
Infinite Power Solutions
, well known for their THINERGY Micro-energy thin film rechargeable cells, made the case that Bluetooth Low Energy is the protocol
to enable personal sensor networks that are powered using energy harvesting. The claim is that it can increase battery run time up to 10x over traditional sensor network protocols.
Imperial College London
focused on power electronic interfaces for energy harvesting devices. They criticised the approach of many researchers in measuring the power output of EH devices. Three research questions relating to power conditioning, adaptability (improving electromagnetic
coupling of piezoelectric harvesters) and damper strength (electronics tuning of resonant harvesters) were highlighted with some (at least partial) solutions suggested.
There were a number of presentations on microcontrollers addressing various issues. Anagear
presented a new controller for smart power management in both battery supplied and self-powered wireless sensor nodes. It was claimed that this could provide a solution to the 'cold start' problem. The circuit is in prototype form with manufacturing expected shortly. Microchip
presented another family of microcontrollers that can operate with as low as 45μA/MHz @ 3V. Energy Micro
presented on a new 32Bit microcontroller claimed to be the world's most efficient at 32bit. By taking an industry standard ARM
Cortex-M3 processor and integrating modules they have managed to increase its power efficiency by a factor of 4. The microcontroller is provided as a developer toolkit.
There were also a series of presentations that related more to the wireless sensor network aspects than energy harvesting itself.
described some quite largescale wireless sensor network deployments (up to 1,000 nodes) in a smart cities project. They have been taking a horizontal and modular approach and can accommodate over 60 sensors and interface all key protocols (ZigBee
, Bluetooth, 3G, GPRS
Linear Technology / Dust Networks
claimed that the two major WSN challenges (battery lifetime and reliability) are no longer an issue. By using time synchronised channel hopping battery lifetime can be extended to 5-10 years and reliability to 99.99% for a network that has 50 motes, 7 hops over 3 floors exchanging 100,000 packets a day. With regards larger deployments, examples were given e.g. a 700 acre oil refinery of Chevron instrumented by Emerson
. Also it was reported that NTT was able to cut significantly the energy costs in their data centres. They praised the arrival of WirelessHART.
, who have developed their own ultralow power radio protocol and a very successful ecosystem of smart building product suppliers around this standard, addressed issues of security in their early systems. A rolling code has been proposed to offer fraud resistance against reply attacks. Encryption
has been added as a protection against eavesdroppers.
, a small technical consulting company in the field of wireless communications showed 'WibiSol' a concept antenna
with an integrated dye sensitised cell which harvests energy from ambient light or the sun and simultaneously transmits and receives RF signals.
There was more representation of the academic community in the poster sessions with academic groups from across Europe including Germany, UK, Sweden, France, Czech Rep., Poland, Latvia, Italy and Belgium presenting. The posters covered mainly basic research but several also had a clear focus on applications of energy harvesting
. Some highlights include:
Riga Technical University
, Latvia featured flat inductors for energy harvesting, investigated the creation of electromagnetic
harvesters with flat architecture and evaluated their performance. The key advantage of such design is avoiding a rigid construction for the harvester, where an empty space for the magnet's motion must be ensured. The ultimate goal is to use such harvesters in wearable systems integrated in clothes. Theoretical results for 3 shapes (square, rhombic and circumference) of inductors were compared.
, UK presented a range of on-chip solutions for voltage sensing and voltage monitoring. Their work is motivated by the need to have non-invasive operations. Their voltage sensors and monitors avoid using conventional analogue to digital
converters that are power costly, slow and occupy a large area. The proposed sensing method is based on sampling energy into storage and mapping this energy into a code. The implementation uses elastic digital circuits leading to a low energy solution because they only consume power when they actively perform conversions. Using UMC 90nm technology node the conversion time was 1.2μs, the dynamic power consumption 76μW with cell leakage power 7μW.
Università degli Studi di Modena e Reggio Emilia
, Italy presented an autonomous wireless sensor to enhance safety in vehicles equipped with tow bars by taking into account if a trailer is connected to the vehicle. Overturning vehicles lead to preventable fatal accidents. The device scavenges energy from the vehicle's vibration using a piezoelectric
module. Data are transmitted to the stability control algorithm
running on the vehicles ECU so as to dynamically adjust the vehicle's model parameters to consider the current real operative conditions.
Cranfield University, UK presented the advances in self-powered wireless sensor nodes for structural health monitoring. The system is designed to harvest energy from wing vibrations of aircraft in active service and should be able to use that energy to measure aircraft wing fatigue and inflight loading. The system features a novel piezoelectric harvester based on a macro-fibre composite. A patent pending solution integrates impedance matching, power management and smart switching. The power harvested is 1.8-12mW at 1-10Hz and 230-570 μStrain representing one of the best performances reported.
The Best Poster award was given to Erasmus University College, Belgium for the topic Ambient Energy Powered Smart Meters. The poster presented initial yet promising results on a micro-turbine based energy harvester that could be added to water pipes in order to autonomously measure and transmit to the utility companies the amount of water used. The authors had used a 3D printer to produce models of the turbine and compared several ways to retrofit them on existing water pipe installations.
And that folks is the highlights as we saw them. If there are any inaccuracies in the above please feel free to let us know. If you would like to know more about what is reported here or would just like some help in finding out more about energy harvesting in general do get in touch.