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EETE SEPTEMBER 2012

Piezo wireless switch: No battery, no cable, no wear By Dr. Venkatesh Sivasubramaniam The principleS BehinD using piezoelectric materials for materials can be energy harvesting are well known since the early 70’s. Despite circumvented with various patents on such energy harvesting implementations, two proprietary barely few inventions have been crystallized into industrial technologies known products. The primary limitation of deploying a piezoelectric as Dynapic and Dy- material is related to its poor mechanical reliability while it is nasim. The Dynapic Fig. 1: Expanded view of the Dynapic often bowed and clamped in a certain manner so as to gener- technology offers an technology showing the multilayer ate the required voltage by mechanical deformation. in reality innovative solution laminate construction with the the deflection of most piezoelectric cantilevers easily exceeds where a disc- piezoelectric disc. a millimetre. Additionally the piezoelectric cantilever suffers shaped piezoelec- inhomogeneous stress concentrations due to clamped bound- tric material is bent within a controlled range from 100 to 300 ary conditions. A larger deflection with inhomogeneous stress µm through the use of a multilayered sandwich construction - states has a negative influence on the mechanical integrity of see figure 1. Figure 2 shows side by side the stress analysis of a the piezoelectric energy harvesting source. typical cantilever bending and the Dynapic piezo key. A homog- As early as the 1990’s, the Swiss-based company Algra enous stress distribution ensures the mechanical integrity of the demonstrated that the reliability issues of bending piezoelectric Dynapic piezo keys, enabling such implementations to exceed 10 million switching cycles. Algra’s latest innovation, Dynapic Dr. Venkatesh Sivasubramaniam is Material Scientist Wireless - as shown in figure 3, demonstrates that energy at Algra AG – www.algra.ch from the Dynapic piezo switch alone is sufficient to be used


EETE SEPTEMBER 2012
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