Lead-free sodium potassium niobate based piezoelectric thick film bimorph structure for energy harvesting

Vibrational energy harvesting is a very promising way to replace batteries in many types of application like industry, infrastructure, aeronautic or healthcare. Piezoelectric based energy harvesting are commonly employed to scavenge mechanical energy from environmental vibrations in which resonance frequencies are mostly below 200 Hz. Piezoelectric materials that are generally based on lead zirconate titanate (PZT) are increasingly prohibited in many areas in the world for their toxicity to human health and to the environment. A serious alternative to PZT is the sodium potassium niobate (KNN) which presents appropriate properties like its Curie temperature, its coupling coefficient and its density. In this paper we propose to integrate a KNNSr (strontium doped sodium potassium niobate) ceramic in a bimorph structure in a cantilever beam configuration to scavenge vibrational energy in the frequency range of 25 Hz (for medical application). A thinned bulk approach is chosen for the fabrication of the bimorph in order to maintain the good properties of the bulk ceramic. Vibrational measurements demonstrate a power density of 13 mu W/G(2)/cm(3) and a resonance frequency of 24 Hz which is highly compatible with external vibrations at low frequencies.