Harvesting Energy

New energy-harvesting solutions can cut the dependence on batteries for security systems

• By Curtis Salmon
• Oct 03, 2006

The first security systems used wires and were typically only used for newly constructed buildings. For existing buildings, it is often difficult or too expensive to fish wires through walls. The problem was solved by the introduction of wireless security systems. Wireless security systems provide more flexibility while simplifying installations -- but at a cost. Wireless security systems require batteries, prompting a need for maintenance. Even though batteries must be changed, wireless security is still the best solution in many situations.

With wireless, installation is much faster and easier than hard wiring. Wireless also allows easier extension of existing security systems and makes remodeling simple. What can be done to make wireless security systems even better? The next logical step in wireless security evolution is to lose the dependence on batteries.

With wireless, installation is much faster and easier than hard wiring. Wireless also allows easier extension of existing security systems and makes remodeling simple. What can be done to make wireless security systems even better? The next logical step in wireless security evolution is to lose the dependence on batteries.

A Good Solution
Energy harvesting, the process by which energy is captured and stored, is the next logical step in wireless security evolution. A variety of different methods exist for harvesting energy such as solar power, ocean tides, piezoelectricity, thermoelectricity, magnetic coil and physical motion. In the security industry, energy harvesting has been implemented for use in wireless magnetic contacts. This self-powered security device converts ambient energy into electrical energy and uses it to power sensors and radios. One magnetic contact, developed by a company from Germany, has a tiny solar panel on the device that collects ambient light and generates it into energy. These battery-free wireless devices are a solution that system owners can install and treat like a wired security system, but with all the benefits of wireless.

Energy-harvesting devices are low energy, but not low power. The devices typically output high levels of RF power compared to traditional battery-powered devices. The devices can communicate within 300 meters line-of-site and 30 meters through walls inside buildings. The transmitted data is similar to battery-powered magnetic contacts because there is a unique address for each contact sensor. When the data is received, it is sent to a low-voltage relay receiver, which indicates if the relay is open or closed. An entire security system can be designed around energy-harvesting security devices. Low- voltage relay receivers simplify the task of adding energy-harvesting devices to existing security systems.

Energy-harvesting solutions offer battery-free magnetic contacts that allow the reliability of a wired system and also the ease of installation that comes with wireless.

Energy-harvesting magnetic contacts do not require technical or wiring skills. The battery-free contacts use a simple learning sequence that programs the contact to a low-voltage relay receiver. Also, the contacts are easy to move, making it is easy to add more to the system later.

A Better Solution
Though wireless allows for better and easier installations, it still requires regular maintenance. For most situations, it's not logical to install a system that will require more than 100 batteries. Imagine going on a magnetic contact hunt to replace all of those batteries five years after installation. With battery-free contacts, a facility manager will know that their system is maintenance-free for 20 years.

Another situation where battery-free magnetic contacts are more beneficial is when an existing security system needs to be extended. First, it is smart to use wireless magnetic contacts because it takes away the need for wiring. Second, the system can be easily extended without installing wires while keeping the new contacts maintenance free like the already existing hard wired contacts.

Compatibility with Wireless Sensors
Any system is compatible with the help of a four-channel receiver that communicates with battery-free, wireless magnetic contacts. The combination of a low-voltage relay receiver and battery-free magnetic contacts creates a system that enables home and building owners to enhance existing entry/exit security equipment.

The low-voltage relay receiver is used to connect energy-harvesting wireless switches and sensors to existing security and lighting control systems. The receiver provides four channels of relay output, which mirror the status of battery-free wireless transmitters. The four-channel receiver connects to battery-free transmitters with an ID-learn sequence that stores transmitter IDs in EEPROM, so the receiver knows which devices are connected to which relay output. Each output can be configured with up to 30 battery-free transmitters, allowing a system of up to 120 battery-free, wireless magnetic contacts for each four-channel receiver. The system also can be used with other devices, such as battery-free light switches, which can be used to turn on outside lights when a noise is detected.

By using four-channel receivers, installers can configure security zones based on the location of the battery-free magnetic contacts. If any of the contacts in the area are triggered, a zone response can be generated. The system also allows users to know exactly which transmitter has been activated by programming a single, battery-free contact per relay channel.

Solar-Powered Magnetic Criteria
Step one. The device must work in ambient light, not only the levels of light found near windows. Energy-harvesting magnetic contacts require about 100 lux (10 foot candles). Lighting in a typical office is usually at 400 to 600 lux and grocery stores are normally at 1,000 lux. The magnet contact is able to store enough energy to operate for several days in complete darkness, allowing it to work in just about any environment.

Step two. It must be small enough to be embedded in window wells and doors. Energy-harvesting magnetic contacts are typically smaller than normal wireless contacts because there is no extra space needed to house a battery. With smaller dimensions, the battery-free magnetic contact can fit into more spaces.

Step three. It must be cost effective. With battery-free magnetic contacts, there is only the original fee for the units and installation, and that the system is maintenance-free for 20 years.

Step four. It must operate efficiently, rapidly communicating intrusion and a supervisory signal periodically. Energy harvesting magnetic contacts are constantly renewing energy, outputing more RF power (10 megawatts than typical battery-powered radios at 1 megawatt. Also, the radio used in battery-free contacts transmits quickly at 120 KBps compared to normal magnet contacts at 9.6 KBps. Battery-free magnetic contacts have a range of 50 to 150 feet, and by using repeaters, this range can be increased. In addition, a sign-of-life signal is sent every 15 minutes to ensure that the contact is still communicating.

Energy-Harvesting Technology
Energy-harvesting technology that is used for battery-free wireless magnetic contacts can be integrated into other building monitoring systems such as lighting control or environmental monitoring.

The following are solutions that some manufacturers have come up with:

• Wireless lighting can be used to flash lights if there is an intrusion or to turn lights on when a suspicious noise is heard.

• Leak detectors can possibly use battery-free technology to detect water leaks under sinks, behind refrigerators, in the heater closet, behind the washing machine and many other places where moisture can pose a problem.

• Freeze sensors can use energy-harvesting technology.

Manufacturers are finding multiple ways to use energy-harvesting technology because it has so many benefits. Energy harvesting eliminates the need to replace batteries and is beneficial for situations where changing a battery or installing a wire is too difficult. If a monitoring device needs to be placed inside of a wall to detect moisture, it can be done without worrying that the device will fail and need to be replaced.