SENSORS


environmental considerations since batteries are hazardous and must be disposed of properly. With a large number of wireless sensors where, in an office building, this can quickly amount to several thousand, the process of battery replacement and disposal can easily become a full-time job for a facility manager. This ranges from access coordination, device localisation, battery exchange, device testing, documentation, battery storage, and finally to disposal.


Energy harvesting


Modern systems leverage battery-free wireless components, offering a reliable and maintenance-free alternative to traditional wired solutions while retaining the flexibility and easy retrofitting of wireless systems. Products with battery-free wireless technology harness the energy available in their immediate surrounding, a concept known as energy harvesting. Three main forms of energy harvesting have emerged in building automation: kinetic, solar, and thermal energy.


Kinetic energy


Motion is a dependable energy source for various switches. A single press generates enough energy for three wireless messages. An electromechanical energy converter (EnOcean ECO 200) inside the switch housing converts the button press into electrical energy, making it available immediately after activation. The energy converter works similarly to a bicycle dynamo, where a small but powerful magnet drives a magnetic flux through two magnetically conductive anchor plates, which closes in a U-shaped core. An induction coil is wound around this core, which can be put in two positions where it touches the respective opposing anchor plates. This movement results in a sudden change in the magnetic field, thereby producing a voltage pulse in the induction coil.


ECO 200 is an energy converter for linear movement. Possible applications include miniaturised switches and sensors in building technology and industrial automation. A single switch actuation generates an energy amount of 120 µWs, sufficient for three radio messages. At room temperature the


Solar-based energy


Thanks to miniaturised solar modules, it is possible to power radio modules with electricity even with low interior light intensity. Solar- powered sensor modules operate energy efficiently. A temperature reading that is to be transmitted every 15 minutes requires only 3.6 hours of charging time per day at a brightness of 200 lux for uninterrupted operation. At this brightness, the solar cell produces a voltage of 3 V. An additional Poly Acenic Semiconductor (PAS) charging capacitor ensures that the module can bridge periods without ambient energy. When the energy storage is fully charged, the module can operate in complete darkness for about a week without interruptions.


Miniaturised solar modules enable maintenance-free window contacts, temperature, gas, and humidity sensors, as well as light sensors and presence detectors.


Thermal energy


A significant temperature difference, for instance, between a radiator and its surroundings can provide a lot of energy that can be used not only for sensors, but also for actuators. Energy harvesting is done using a Peltier element in combination with a DC/ DC converter (EnOcean ECT 310 Perpetuum). Even a small input voltage of 20 millivolts (mV), which corresponds to a temperature difference of about 2 °C, can be converted into a usable output voltage of over 3 V. The larger the temperature difference, the more energy can be harnessed. This principle is currently mainly used in radiator actuator drives. The


electromechanical energy converter allows over a million switching cycles. The principle of kinetic energy harvesting can also be used for light or blind switches. Additionally, there are battery-less sensors that can warn of water damage. These sensors have swell disks at the bottom that expand when they come into contact with a liquid. This movement triggers the electromechanical converter and sends a radio signal. Due to this message, the line’s valve automatically closes, and the building owner or facility manager receives a corresponding notification, for example on their smartphone.


energy harvested is sufficient for both radio communication and the actuation changes of the valve. Combined with a solar-powered room sensor, a fully energy-autonomous individual room control can thus be realised. With the DC/DC converter ECT 310 Perpetuum, battery-free radio modules can also use heat as a power source. In this process, heat, for example, from warm machine parts, radiators, or the human body, is converted into electrical current.


Products with EnOcean technology utilise, among other things, three different frequency bands that vary depending on the region: 868 MHz in Europe, 902 MHz in North America, and 928 MHz in Japan. Short messages (telegrams) are used for data transmission. These can be verified by the central system using a checksum. Due to the short duration of the telegrams (about one millisecond) and multiple telegram transmissions, the risk of data collisions is minimised. Interference with other systems such as WLAN or DECT is ruled out since frequencies outside the 2 GHz frequency band used by these devices are employed. The range is up to 30 meters within buildings, even through walls, and can also be further improved using repeaters. Communication between devices is secured with a 128-bit AES encryption, and the use of rolling codes prevents unauthorised tampering.


Wireless, maintenance-free, smart technology


Manufacturers worldwide have developed thousands of smart products based on battery-free EnOcean wireless technology, such as room thermostats, wireless window contacts, and solar-powered presence detectors. These products not only increase the energy efficiency of a building, but also offer high flexibility since no wiring is required for installation. This reduces installation costs and enhances comfort, as the wireless switches can be placed anywhere desired. Another significant advantage is interoperability, as all EnOcean-based products can communicate with each other, irrespective of the manufacturer.


Armin Anders, Co-founder & VP Business Development, EnOcean GmbH www.enocean.com


APRIL 2024 | ELECTRONICS FOR ENGINEERS 39


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