(Invited) Alternating Current Sensors, Memories and Displays with Ferroelectric Sound

Abstract

Visualization of human senses has been of great interest for developing an emerging interactive display that can artificially stimulate synesthesia with numerous unprecedented applications. Especially, visualization of various daily sound and music in a form of flexible thin film devices can be a great challenge. In this presentation, we first present flexible artificial synesthesia devices that visualize continuous and complicated sounds [1]. The device is made of a thin composite film of a piezoelectric polymer for sound generation and inorganic electroluminescence (EL) microparticles for direct visualization of input sound signals. Field-induced EL of the microparticles in the device depends upon the source sound wave, making their EL synchronized with sound arising from the piezoelectric actuation. We also demonstrate that piezo and ferroelectric sound is capable of sensing, monitoring, and storing the information of various liquids. Our platform utilises sound arising from liquid-interactive ferroelectric actuation, which is dependent upon the polarity of the liquid [2]. Liquid-interactive ferroelectric sound (LIFS) is successfully developed when a liquid droplet is placed on a ferroelectric polymer layer across two in-plane electrodes underneath the ferroelectric layer under an external in-plane AC field. An AC field built up vertically between one of the electrodes and the liquid results in ferroelectric vibration of the device, leading to sound. The sound pressure level (SPL) of the device depends upon the polarity of the liquid, allowing for facile liquid sensing and identification. More importantly, as the SPL arising from LIFS of a liquid is correlated with non-volatile remnant polarisation of the ferroelectric layer, the information of a liquid is readily stored and retrieved even after the liquid is removed, resulting in a sensing memory of the liquid. By programming different LIFSs on a thin film pad, we can also identify the 2D position of a liquid droplet on the pad. Moreover, our device successfully monitored the flow of a human serum liquid passing through channels with their diameters ranging from millimetres to tens of microns and determined its velocity. Mechanically flexible and optically transparent tube-type LIFS AC devices allow for in situ analysis of the flow of a liquid in terms of SPL.