Mechanistic insights into ultrasound measurement using CBNP/PVP nanocomposite sensors: Modelling and experimental validation

Conductive nanocomposites exhibit piezoresistivity, enabling their application as sensors for ultrasound measurement. This piezoresistive behaviour originates from nanofiller-formed conductive networks, which evolve under external excitations. Despite this experimentally demonstrated functionality, the mechanism governing the dynamic response of these networks to ultrasonic excitation remains largely unexplored. This work provides mechanistic insights into ultrasound measurement using a carbon black nanoparticle (CBNP)-filled polyvinylpyrrolidone nanocomposite sensor through combined modelling and experimental validation. Using the experimentally measured density and mechanical properties, wave propagation is simulated to calculate the sensor’s nodal displacements induced by guided ultrasonic waves, which dynamically update CBNP distributions within representative volume elements, thereby leading to the evolution of conductive networks. Tunnelling junctions between CBNPs are modelled as resistors to compute the equivalent resistance of the conductive networks over time. The resulting time-dependent resistance variations reveal distinct zero-order symmetric and anti-symmetric waves that closely match the experimentally measured voltage signal. Further analysis of resistance variations in tunnelling junctions with different interparticle distances highlights the critical role of electron tunnelling in the ultrasonic response, showing that junctions near the tunnelling cutoff distance are more sensitive to small distance changes. In summary, this work elucidates the ultrasonic response mechanism of conductive nanocomposites, providing guidance for sensor development.