page_title: Energy harvesting
section_title: Energy from smart roads and piezoelectricity
hierarchical_section_title: Energy harvesting / Devices / Energy from smart roads and piezoelectricity
caption_attribution_description: English: sketching shows the behaviour of a piezoceramic Italiano: schema che mostra il comportamento di un cristallo piezoelettrico
context_page_description: Energy harvesting is the process by which energy is derived from external sources, captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.
  Energy harvesters provide a very small amount of power for low-energy electronics. While the input fuel to some large-scale generation costs resources, the energy source for energy harvesters is present as ambient background. For example, temperature gradients exist from the operation of a combustion engine and in urban areas, there is a large amount of electromagnetic energy in the environment because of radio and television broadcasting.
  One of the earliest applications of ambient power collected from ambient electromagnetic radiation is the crystal radio.
  The principles of energy harvesting from ambient EMR can be demonstrated with basic components.
context_section_description: Brothers Pierre Curie and Jacques Curie gave the concept of piezoelectric effect in 1880. Piezoelectric effect converts mechanical strain into voltage or electric current and generates electric energy from motion, weight, vibration and temperature changes as shown in the figure.
  Considering piezoelectric effect in thin film lead zirconate titanate  PZT, microelectromechanical systems (MEMS) power generating device has been developed. During recent improvement in piezoelectric technology, Aqsa Abbasi (also known as Aqsa Aitbar, General secretory at IMS, IEEE MUET Chapter and Director Media at HYD MUN) diffentiated two modes called  and  in vibration converters and re-designed to resonate at specific frequencies from an external vibration energy source, thereby creating electrical energy via the piezoelectric effect using electromechanical damped mass.
  However, Aqsa further developed beam-structured electrostatic devices that are more difficult to fabricate than PZT MEMS devices versus a similar because general silicon processing involves many more mask steps that do not require PZT film. Piezoelectric  type sensors and actuators have a cantilever beam structure that consists of a membrane bottom electrode, film, piezoelectric film, and top electrode. More than (3~5 masks) mask steps are required for patterning of each layer while have very low induced voltage.  Pyroelectric crystals that have a unique polar axis and have spontaneous polarization, along which the spontaneous polarization exists. These are the crystals of classes 6mm, 4mm, mm2, 6, 4, 3m, 3,2, m. The special polar axis—crystallophysical axis X3 – coincides with the axes L6,L4, L3, and L2 of the crystals or lies in the unique straight plane P (class “m”). Consequently, the electric centers of positive and negative charges are displaced of an elementary cell from equilibrium positions, i.e., the spontaneous polarization of the crystal changes. Therefore, all considered crystals have spontaneous polarization . Since 
  piezoelectric effect in pyroelectric crystals arises as a result of changes in their spontaneous polarization under external effects (electric fields, mechanical stresses). As a result of displacement, Aqsa Abbasi introduced change in the components  along all three axes . Suppose that   is proportional to the mechanical stresses causing in a first approximation, which results  where Tkl represents the mechanical stress and dikl represents the piezoelectric modules.
  PZT thin films have attracted attention for applications such as force sensors, accelerometers, gyroscopes actuators, tunable optics, micro pumps, ferroelectric RAM, display systems and smart roads, when energy sources are limited, energy harvesting plays an important role in the environment. Smart roads have the potential to play an important role in power generation. Embedding piezoelectric material in the road can convert pressure exerted by moving vehicles into voltage and current.
caption: A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated)