How energy harvesting can make the Internet of Things happen
EP&T MagazineElectronics Engineering Environmental
Energy harvesting wireless is just starting to unfold its potential. The rapid improvement of components and system design setup will open up new applications in many aspects of life. Together with the Internet moving towards IPv6, the batteryless approach can even lay the foundation for an Internet of Things.
Energy is everywhere within reach, it just needs to be harvested: this is the principle of energy harvesting. Today, energy harvesting wireless solutions are already well established in the commercial building automation sector. Here, batteryless sensors, switches and actuators provide the needed data to control a building’s energy consumption for an improved carbon footprint and to increase comfort and security. The self-powered devices demonstrate their benefits by being highly flexible and easy to position or to remove, operating maintenance-free and performing robustly.
But the technology is just getting started. New application fields for batteryless wireless communication will be found to further enhance the world around us. This becomes particularly true in connection with the Internet turning to a new decade. This development is directly related to IPv6, the next generation of Internet protocol that provides an almost unlimited number of IP addresses.
This next wave of Internet usage enables one or both parts of the communication to be machines (sensors, actors, control units) interacting directly with users or other machines on a broad scale over the Internet. Therefore, this phase is called the “Internet of Things.” Having a large network of sensors, actuators and control units all interacting with each other and the user can bring several distinct benefits. More input (sensor) data offers a better insight into the system status. This additional information allows a better decision-making process considering a broad range of criteria.
Unlike the standard approach of one or more sensors being connected to one central control unit, an Internet of Things allows the sharing and reuse of available information between different partners. Thus, the system collects data only once but uses the information for several applications. That way, temperature data from outdoor agriculture sensors, for example, could be reused to generate more precise weather models.
All required base technologies for forming such network already exist today – sensors, actuators, local or cloud-based control units and IPv6 to connect all of them together with an own IP address. The main challenge now is how to deploy large numbers of sensors and actuators and connect them in a practicable way.
The batteryless standard
The solution is energy harvesting. Liberating sensors from external power, making them energy-autonomous, opens up unlimited processing and monitoring applications where cables or batteries represent an insurmountable hurdle. These features make energy harvesting wireless technology the ideal communication standard to easily and reliably interconnect thousands of individual devices in a system and to the Internet.
The specific characteristics of the sensor protocol allow highly energy-efficient communication. Telegrams are just about 1 millisecond in duration and are transmitted at a data rate of 125 kilobits per second. Although transmitted power is up to 10 milliwatts, the wireless transmission used here only has an energy requirement of 50 microwatt seconds for a single telegram. That is about the same as the power needed to lift a weight of 1 gram by 5 millimeters. The short telegram is randomly repeated twice in the space of about 40 milliseconds to prevent transmission errors. Transmitting data packets in random intervals makes the probability of collision extremely small. Due to a radio technology that only needs very little amounts of energy, wireless sensors can be powered by energy converters using motion, light or temperature differences as their only energy source.
The translation between this energy-efficient sensor protocol and IPv6 is provided by dedicated IP gateways that represent the state of each connected sensor node and act as their representative within the IPv6 network. This approach allows exchanging data with individual sensors even while they are sleeping and therefore unavailable for direct communication. Upon wake-up, sensors will then update their state information in the gateway and retrieve messages/commands intended for them.
Improved technology platform
For applications outside the building, the components of energy harvesting wireless technology, consisting of energy converters, wireless transmitters, energy management, software-, and development tools as well as the energy-saving radio protocol, are currently further enhanced.
Radio for longer distances
While state of the art 802.15.4 radio transmission range is up to 300 feet line of sight, current energy harvesting wireless technology bridges up to 900 feet today – which is fine for building applications and keeps the component count low.
The next generation of radio technology will enable up to ten times longer radio ranges to wirelessly transmitted data via a distance of more than 1.7 miles and enabling new outdoor applications with higher range requirements. The increased energy need of such long distance can be realized by the progress of other components at the same time.
Higher efficiency harvesters
The kinetic energy source is almost inexhaustible, as motion can be found anywhere. New types of mechanical energy harvesters will make use of the energy of flowing gases and liquids in particular.
As a second energy source, light will play a significant role. Next miniaturized solar-cell generations will combine better efficiency with improved performance under low light conditions. While the limit of operation is light intensities of about 100 lux at 5% efficiency today, next generation solar cells based on organic material or dye-sensitized technology can operate down to 10 lux light intensity with more than 10% efficiency.
Finally, temperature differences contain a lot of energy and are therefore ideally suited to power devices. Just the cooling of a drop of water by 1 degree Celsius releases energy for about 25,000 energy harvesting wireless telegrams. One new option is to harvest energy from temperature differences between day and night for outdoor applications. These harvesters will allow the building of very robust sensor nodes, independent of light and therefore not sensitive to dirt.
Further reduced energy demand
The lower energy consumption a device has, the better the chances are of applying energy harvesting strategies successfully. So, as the energy demand of sensor modules gets lower from generation to generation, the technology is suitable for outdoor applications working under strenuous environmental conditions. Besides the energy need, research is also evaluating improved storage components. The target is to store harvested energy from weeks to several months up to a year without new ambient energy impulses.
Energy harvesting for outdoor activities
With the technology’s progress and the enhanced abilities of IPv6, new application fields for energy harvesting wireless communication become feasible, particularly outdoor for environmental use cases.
Agriculture and environment
Cloud-based computing resources could be used to combine local temperature data provided from batteryless sensors with an external weather forecast to compute the exact amount of water required for agricultural irrigation. This information would then be sent to a remote actuator controlling the water flow. Similar sensors could measure the degree of humidity or soil nutrients for an optimal supply of water and care for plants.
Energy-autonomous wireless sensors could also be placed over large areas to provide early warnings or to monitor farm animals and plants in order to react very quickly to changing cond
itions. Temperature sensors, for instance, could send position data and an alarm signal when they measure the heat of a fire. Via a central gateway, a notification is immediately sent to the nearest fire station and/or via SMS to a responsible persons’ smart phone. Such an early warning system could prevent forest fires to spread, enabling a prompt extinguishing.
Monitoring of resources
Whether it is water, gas or oil – all resources on earth are limited and therefore need to be protected and used carefully. Batteryless sensor networks can support this by providing the needed data to monitor water in terms of quantity and quality or the movement of shoals of fish. In addition, detectors can use miniaturized solar cells or motion energy converters to power wireless signals that report water, oil or gas leaks to a gateway controller or directly to a valve. The energy harvesting technology prevents system malfunctions that otherwise could be caused by battery failures.
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