The absolute bulk modulus has a major effect on the position, power delivery, response time, and stability of virtually all hydraulic systems. A novel sensing technique to determine the bulk modulus of a fluid or hydraulic system is proposed. The constitutive equations of a piezoelectric actuator are coupled to a fluidic system that contains entrained air and mechanical compliance. The model can be used to extract the bulk modulus of the fluid system in real time. The results indicate that matching the stiffness of the actuator to the stiffness of the fluidic system is critical in obtaining a high sensitivity to the bulk modulus measurement.
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