Fluid Property Sensors

This chapter treats the measurement of physical fluid properties using miniaturized devices. The most practical approach is to measure the frequency response of immersed or partly exposed mechanical resonators. Depending on the technology used, the mechanical response can be measured optically or in the electrical domain utilizing piezoelectric, piezoresistive, or electrodynamic coupling mechanisms. Spurious signal components have to be handled accordingly to enable a proper interpretation of the data. The fluid parameters which are accessible by this method are the mass-density, the complex viscosity at the frequency of oscillation (or equivalently, the linear viscoelastic storage and loss moduli), and the speed of sound if compressibility of the fluid is of relevance in the considered frequency range. The specific form of the fluid-structure-interaction as a consequence of the resonance mode-shape determines how these parameters affect the sensor response function and whether a separation of the individual parameters is possible or not.