A new way to find dielectric properties of liquid sample using the quartz crystal resonator (QCR)

A new study by Luis Armando Carvajal Ahumada and colleagues demonstrated how the capacitance C_o changes when a fluid sample is in contact with crystal. The team presented a new way in finding dielectric properties of liquid sample while using quartz crystal resonator (QCR).  The study published in the journal Sensors and Actuators A.

The quartz crystal resonator is traditionally considered to be a mass sensitive sensor that generates response to different thin film samples or liquids in contact with its surface. A lot of researcher had worked on the sensor, obtaining different theoretical model. But the one of Butterworth–Van Dyke (BVD) is found more significant due to its use and ease to understand.

            From the conductance curve, when the QCR electrode is in contact with a sample, the structure of the conductance curve changes. The electrical model BVD add impedance which represents the characteristics of the sample. For liquids in contact with the crystal, the equivalent impedance is the series of an inductance and a resistance. From the experimental result, researcher point out that the zero crossing point of the susceptance curve and the maximum peak of the conductance mismatch when the crystal is in contact with liquid. This occurs because C_o value also depends on the properties of the sample. In other words, in the electrical model BVD, the C_o parameter is not negligible and may even provide additional information about the sample, more specifically, about the electrical permittivity of the liquid.

The research team explain that, the relationship between the series resonance frequency and the frequency at minimum impedance with zero phase when the crystal is in contact with a fluid sample is directly related with the change in capacitance C_o. from their experiment, they were able to note that the change in the capacitance C_o is associated with the dielectric properties of the sample. This is expected to improve the sensor design to characterize viscosity and dielectric properties in different biological fluids. The required quantities of the sample for the proposed system are in order of microliters, while the conventional methods need milliliters of fluid to calculate the viscosity.

This new method, quartz crystal resonator aim to find the dielectric properties of liquid sample will be of potential applications such determining mechanical and electrical characteristic of cells during proliferation.