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Broader contextSelf-powered electronic devices that utilize energy harvesting technology for scavenging ambient energy are highly desirable for next generation wireless and wearable devices since it enables them to work without an external power source and eliminates the need for replacement and management of batteries. Flexible piezoelectric and piezo-composite materials have been directly used as self-powered sensors, but their poor piezoelectric properties and difficulty in achieving various sensing modes, such as the shear sensing mode, limit their performance and applications. In this work, we develop a flexible and highly active piezoelectric polymer composite material using a freeze casting method. The connected piezoelectric phase in the polymer matrix and the combined effect of compression and flexure allow the composites to achieve a high effective piezoelectric coefficient. The unique structure of the ceramic-polymer composite also allows the self-powered sensor to maintain high activity after bending to a small radius. The freeze casting method allows the production of complex device architectures. Using such piezo-composites, we manufacture self-powered sensors that operate in various sensing modes (d 31 , d 33 , and d 15 ) and tested with tire, shaker and light finger tapping. This work further expands on the potential applications of freeze casting and provides new opportunities for the manufacture of future electronics.

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The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or 'snap-through', is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2mW, comparing well with the needs of typical wireless senor node applications.