QCM board impedance matching using transformer

To maximize the power that is absorbed by the QCM from the RF amplifier, the impedance of the connection must be as close to the amplifiers impedance (50 Ohms), at resonance, as possible to minimize loss due to the driving signals reflections.
This is achieved using a transformer to match the impedance to the crystal, as shown in Fig. 6. Impedance was found using the Hewlett Packard Network Analyzer’s (HP3589A) impedance function, to measure and match the QCM impedance at resonance to 50 Ohms. It was found that there is a large difference between the impedance of the QCM measured in gas and liquid; and so separate transformers were chosen for a different environment.

Fig. 6.

Quartz Crystal Microbalance Induced Bond Rupture
Sensing for Medical Diagnostics
M. J. van der Werff, Y. J. Yuan, E. R. Hirst, W. L. Xu, Senior Member, IEEE, H. Chen, and J. E. Bronlun