QCM Measurement of Highly Dense Fluids, a Measurement Technique Based on Sine Sweep Excitation

Quartz Crystal Microbalance (QCM) is a pivotal technique for analyzing tribological interactions and lubricant performance at both macroscopic and nanoscopic scales. This study explores the limitations of traditional QCM methods when applied to highly viscous lubricants and proposes an innovative measurement method utilizing chirped excitation signals to enhance sensitivity when analyzing highly damped QCMs. The proposed method involves exciting the quartz sensor with a sinusoidal linear frequency sweep and measuring current through and voltage across the quartz with a tailored front-end electronics. This approach allows allowing for more accurate characterization of lubricants with high viscosity coefficients. Experimental validation was conducted using a laboratory testbench with AT-cut 10 MHz quartzes, demonstrating the effectiveness of the new approach in measuring viscoelastic properties exploiting engine oils with different degrees of wear. The results indicate that the chirped excitation method provides a robust and scalable solution for lubricant characterization, overcoming the challenges faced by conventional QCM-D techniques. This approach offers significant improvements in sensitivity and accuracy, particularly in highly viscous regimes, making it a valuable tool for both academic research and industrial applications. The study highlights the potential of modified QCM hardware to expand the range of lubricant characterization, providing deeper insights into the behavior of base oils and additive-enhanced lubricants under various operating conditions.