Temelev: mechanical tuning electronically emulated for vibrational energy harvester

Due to their resonant nature, vibration harvesters can efficiently operate only when the frequency of the vibrations is coincident with their mechanical resonance frequency. Once, after the manufacturing, a vibration harvester has been tuned to a predefined mechanical resonance frequency, it should be used only in those applications with a dominant frequency that is coincident with such a resonance frequency and that does not vary during time. Unfortunately, in the most practical cases, exploitable vibration frequencies vary during time and, hence, a resonant harvester may not always be able to extract power. Mechanical tuning techniques are essentially aimed at adjusting the mechanical resonance frequency of a vibration harvester, in real time during its operation, so that it is always coincident with the vibration frequency. Currently, the proposed mechanical tuning techniques change the mechanical resonance frequency by acting on quantities that are strictly related to the mechanical harvester parameters (the stiffness of a spring, the position of the center of gravity, the physical distance among magnets systems etc.). In all these cases, it is very difficult to obtain smart autotuned and self-supplied systems.

The proposed invention refers to a mechanical tuning technique that is electronically applied by acting on an electrical current, paving the way for automatic and accurate resonance frequency tracking.

The product that can be offered by exploiting the proposed invention is an energy harvester equipped with a mechanical tuning technique characterized by an increased efficiency at vibration frequencies different from its mechanical resonance frequency.

The mechanical tuning technique is implemented by adding a fixed external coil to a standard electromagnetic vibration harvester (that is equipped with a magnet that moves with respect to an internal coil). A proper current is injected into the additional external coil, by means of a power electronic circuit, in order to emulate, at the same time, the equivalent effects of a suitable stiffness, a suitable mass and a suitable damping coefficient. In this way, the magnetic force exerted on the harvester magnet by the current flowing into the external coil becomes the mechanical force that would be exerted by a “virtual” spring (with the desired stiffness) on a “virtual” magnet (with the desired mass) vibrating in a “virtual” fluid (with the desired viscous damping coefficient). In this way, the resonance frequency of the harvester can be changed by proper controlling the current flowing into the external coil. A significantly higher efficiency at a desired vibration frequency, even if different from the harvester resonance frequency, can be obtained.

With the PoC project the proposed invention have reached the TRL 3 level. The follow-on activities, planned for the immediate future, concern the further increase of the TRL to reach levels that can get us closer to the production and commercialization of a product. Fundamental for the further future advancement of the patent TRL is the implementation of the mechanical system including the magnet, the spring system, the internal coil and the additional external tuning coil. Therefore, the follow-on activities mainly concern the search for funding to be used for the implementation of such a mechanical system.