Energy Harvesting

Energy harvesting means generating energy from environmental energy.
This allows, for example, wireless data transfer to be performed without requiring batteries.

Piezoelectric energy harvesting makes use of the direct piezoelectric effect.

Sketch: Energy Harvesting
Sketch: Energy Harvesting

This means that a deformation of the piezoceramic or a deformation of the piezoelectric component is used for generating energy.

In the simplest case, when a piezoceramic disc is pressed or pulled in the direction of its thickness, energy is generated. Piezoelectric bending elements as well as torsion elements can also be used. Energy harvesting by piezoceramic means that an electrical charge at the electrodes of the surface of the piezoceramic is generated as a result of a distortion of the lattice structure by deforming the piezoceramic.

Piezoceramic surface

The energy resulting from the deformed piezoceramic, the mechanical strain and the parameters of the piezoelectric components allow the following consideration under open loop conditions:

Wel = ½ . C . U²

When pressure is applied to the surface of a piezoceramic disc in the direction of its thickness where h = thickness, d = diameter, g33 = piezoelectric voltage constant, the generated voltage is

U = - g33 . h  . F/A = - g33  .  h   .  (F/ (d² . pi /4))

Particular attention must always be paid to ensuring that the mechanical strain arising during deformation of  the piezoceramic shows the same orientation overall.

Only in this case will the generated electrical charges be of the same polarity and a maximum generation of energy be achieved.

Mechanical deformation energy is a result of the mechanical strain T introduced into the piezoceramic. The mechanical strain T is the quotient of force and area and the elastic constant sD33.

Wmech = ½ . sD33 . V . T²

Therefore, it is clearly perceptible that only the material parameter, piezoceramic volume and mechanical strain are relevant.

When deformation is in direction of thickness, electrical energy Wel stands in following relation to the coupling coefficient  k33 and the inserted mechanical strain energy :

Wel = k²33 .  Wmech

The generated electrical energy in above case must be stored and dissipated by the user.

Attention must always be paid to ensuring that the impedances of the electronic and piezoelectric networks are matched together.

Piezoelectric energy harvesters can be built as piezoceramic monolayer or piezoceramic multilayer components. To optimize the individually required features,  these may be combined  with metal layers as well as plastic layers.

With optimized energy harvesters and their appropriately adjusted electronic circuits, it is possible to generate several 100 µW per operating cycle. At the same time, several million cycles  are possible under various environmental conditions.

Applications of piezoelectric energy harvesters are:

energy autarkic radio systems, including systems for battery-free mains switches and control systems and tire pressure radio systems.

We are pleased to assist you in developing your energy harvesting system.

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