Ortiz, a UPV/EHU engineer and lecturer, pointed out that "the indefinite self-powering of devices seeks to offer an alternative for increasing the use time of batteries and, in some cases, even substituting them. This prompted the movement that emerged 10 to 12 years ago to develop these technologies; they are being applied to a host of portable low-powered electronic devices, mainly sensors, and even biological implants. More recently, research has been stepped up to recharge smartphone batteries using the same radioelectric energy emitted by nearby wifi routers.

Ortiz explained that "all these small devices need power, and when it is easy to access the battery and replace it, there's no problem, but in many cases the cost involved is prohibitive. That is why this alternative, in which the existing ambient energy itself can be captured, stored and used to power these devices, is being sought". In the case in question, research has been conducted into electronic circuits that can harvest or acquire ambient vibratory energy, specifically into circuits that use piezoelectric transducers subjected to vibration.

In response to the question of how energy is obtained from vibration, this is what Ortiz said: "Basically, owing to the properties of certain materials known as piezoelectric ones. The most well-known one is quartz, even though in these applications synthetic ceramics with enhanced piezoelectric properties are used. If these piezoelectric materials are subjected to stress or mechanical movement, a shift of electrical charge takes place, in other words, the positive charges move to one zone and the negative ones to another. It is what in physics is known as ‘electric potential'. If these charges can be captured and stored whenever this movement takes place, it is as if we were charging a battery. In a nutshell, that is how vibration produces energy".

Air, rail transport, etc.

According to Ortiz, most of the research into this subject are oriented towards obtaining greater energy densities by minimizing the dimensions of the generating devices, but there has hardly been any development in devices designed to generate power on the level of tens of milliwatts, for example. It was this lack that prompted the idea to group together piezoelectric transducers making up multiple independent sources for producing energy.
Ortiz says that sufficient levels of power can be obtained by developing new techniques and electronic circuits for managing electrical energy. Right now, these generators are used above all for wireless sensor networks but they could be used in fields such as air or railway transport, where there are plenty of vibrations and the dimensions of generators do not signify a great limitation.

Additional information

Javier Ortiz Álvarez-Cienfuegos —engineer and tenured lecturer of the Faculty of Engineering (UPV/EHU)— wrote up his thesis "Development of electronic circuits to extract the vibration applied to piezoelectric materials and convert it into electrical energy" ("Desarrollo de circuitos electrónicos para la extracción y conversión en energía eléctrica de la vibración aplicada a materiales piezoeléctricos") under the supervision of Prof Gerardo Aranguren-Aramendia. The research for this thesis was carried out at the UPV/EHU in collaboration with AERnnova Engineering Solutions and Boeing Research & Technology Europe with grants in the Etortek calls of the Government of the Basque Autonomous Community and of the Cenit call of the Spanish Government.