The field of “green technology” encompasses a continuously evolving group of methods and materials, from techniques for generating energy to non-toxic cleaning products.

The present expectation is that this field will bring innovation and changes in daily life of similar magnitude to the “information technology” explosion over the last two decades. In these early stages, it is impossible to predict what “green technology” may eventually encompass.

The goals that inform developments in this rapidly growing field include:

Sustainability - meeting the needs of society in ways that can continue indefinitely into the future without damaging or depleting natural resources. In short, meeting present needs without compromising the ability of future generations to meet their own needs.

Source reduction - reducing waste and pollution by changing patterns of production and consumption.

Viability - creating a center of economic activity around technologies and products that benefit the environment, speeding their implementation and creating new careers that truly protect the planet.

Concept of Energy harvesting

Energy harvesting is a technology that allows to capture otherwise unused ambient energy (such as vibration, strain, temperature gradients, energy of gas and liquid flows) and convert  into usable electrical energy which is stored and used for performing sensing or actuation. Energy harvesting is a perfect match for wireless devices and wireless sensor networks that otherwise rely on battery power.

Benefits of Energy harvesting

Energy harvesting provides numerous benefits to the end user. Energy harvesting solutions can:

1. Reduce dependency on battery power. Harvested ambient energy may be sufficient to eliminate battery completely. The device can be powered only from by the harvester and rely on internal energy storage to smooth out variations in available ambient energy.
2. Reduce installation costs. Self-powered wireless sensors do require wires, conduits and are very easy to install.
3. Reduce maintenance costs. Energy harvesting allows for devices to function unattended and eliminates service visits to replace batteries.
4. Provide sensing and actuation capabilities in hard-to-access in hazardous environments on a continuous basis.
5. Provide long-term solutions. A reliable self-powered device will remain functional virtually as long as the ambient energy is available. Self-powered devices are perfectly suited for long-term applications looking at decades of monitoring.
6. Reduce environmental impact. Energy harvesting can eliminate the need for millions on batteries and energy costs of battery replacements.

Types of energy harvesting

The type of energy harvesting depends on the kind of energy that is tapped into for powering the device. Usually the following types of energy harvesting are distinguished:

Radiant energy harvesting. Harvesting solar energy is probably the oldest way for powering of electronic devices.

Mechanical energy harvesting. Mechanichal energy of vibration or strain is converted into electrical through various techniques.

Thermal energy harvesting. Relies of thermoelectric effect to convert thermal gradients into useful energy.

Electromagnetic energy harvesting

An electromagnetic harvester uses the principle of a spring-mass system to convert energy of vibration into electrical energy.
The same principle is used in our electromagnetic harvester for highway  bridges .
In this specific example, vibration of a highway bridge or overpass is  created by traffic passing over on top.
Mass and geometry of the structure dictated that the strongest vibration occurs at low frequencies that are on the order of few Hz.
Nevertheless, displacement of structural element is not that great and need to be amplified through the resonance.
The frequency of the harvester is finely matched to the vibration frequency of the bridge by adjusting the spring's parameters.
Mechnical motion of the mass is converted into electrical energy by electromagnetic coupling between the magnet(s) attached to the mass and stationary coil(s).