technology sources to power circuitry. Tiny energy sources are captured and converted to electricity, and stored in durable storage cells, such as supercapacitors or micro-energy cells (MECs – a form of thin-fi lm lithium solid-state battery). The system generally includes circuitry to condition and manage the power, protecting both the storage device and other circuitry. Common sources of readily available energy with potential to be harvested from the environment include: light, captured by solar photovoltaic cells (which o er the highest power density and output of the various energy harvesting methods); kinetic energy, in the form of mechanical vibration, stress or pressure (for instance, vibration from motors or aero-foils), captured by piezoelectric elements; or temperature di erentials, captured by thermo- electric generators that convert heat into electric- A drone in agriculture - a smart farmer using his drone for terrain scanning and monito- ity. Currently, integrating solar cells, usually on the ring soil hydration. Source: Shutterstock / Monopoly 919) wings to maximize the scope for receiving sunlight, and piezoelectric elements, to harvest energy from the vibrations in the wings or body, o er the great- providing services such as Earth observation or est potential. telecommunications relay in support of a range of defense, security and civil requirements. Researchers are also working on UAVs for road- The role of photovoltaic cells based or maritime tra c monitoring, border secu- rity, weather monitoring and environmental impact Advances in photovoltaic cell technology over the studies – with airborne sensors o ering mobility past few decades have given rise to lighter, thin- and measurements from multiple perspectives. ner solar cells. Traditional solar panels contain Disaster response use cases also include drones with crystalline silicon, the active material in solar cells, infrared cameras for night-time search operations, encapsulated into individual cells housed in a metal relaying information to emergency services on the frame and protected with a glass cover – making ground. n them rigid and heavy. But now, thin-fi lm solar cell technology allows amorphous silicon to be painted or rolled onto very thin substrates to achieve light- weight, fl exible solar cells. And new compound semiconductor materials are also making it easier to cost-e ectively mass produce e cient thin-fi lm solar cells. Typically, the amount of energy capable of being harvested by piezoelectric elements is orders of accelerometers accéléromètres magnitude less than that of solar cells. However, ambient énergie ambiante piezoelectric elements are less dependent on envi- ronmental conditions than solar cells. Anytime the amorphous amorphe drone is in fl ight, piezoelectric elements can harvest capture, to capter energy; however, solar cells can only harvest energy circuitry les circuits when exposed to light. This gives piezoelectric harvesting an advantage when fl ying at night, or in deploy, to déployer cloudy conditions. encapsulate, to emprisonner gyroscopes gyroscopes From defense to disaster relief harvest, to capter maneuverability maniabilité Applications that can particularly benefi t from integrating these technologies include high-altitude perfect storm véritable tempête long-endurance (HALE) drones (also known as scavenge, to fouiller Sources: “atmospheric satellites” or “pseudo-satellites”). substrate substrat Mark Patrick, HALEs remain in fl ight for extended periods of time, Mouser Electronics 19