Ultrafast response of spray-on nanocomposite piezoresistive sensors to broadband ultrasound

We present a nano-engineered thin-film-type piezoresistive sensor, coatable or sprayable on a medium surface for in-situ acquisition of broadband ultrasound up to 1.4 MHz – a trait of nanocomposite-based piezoresistive sensing devices that has until now not been discovered and explored. With polyvinylidene fluoride as the matrix, fabrication of the spray-on sensor is attempted in a comparative manner, with multiscale nanofillers ranging from zero-dimensional carbon black, through one-dimensional multiwalled carbon nanotubes, to two-dimensional graphene nanoparticles. With a morphologically optimal nano-architecture, the quantum tunneling effect can be triggered in the percolating nanofiller network when ultrasound signals traverse the sensor, inducing dynamic alteration in the piezoresistivity manifested by the sensor. In-situ morphological analysis and experiment reveal high fidelity, ultrafast responses, and high sensitivity of the sensor to dynamic disturbance, from static strain to ultrasound in a regime of megahertz yet with an ultralow magnitude (of the order of microstrain or nanostrain). These findings are remarkable as no other investigation has probed the response of nanocomposite piezoresistive sensors over such a broad frequency spectrum.