Authors: C-H Wang and R.J. Weber
Affilation: Iowa State University, United States
Pages: 310 - 313
Keywords: MEMS, pull-in voltage, microstrip line, MUMPs
The reflection coefficient (S11) of a one-port device is most sensitive to its input impedance if a matched condition is obtained. This implies two methods to measure the deflection-induced impedance change for a 1-port device such as micro-cantilever in our case: 1) selecting an operating frequency at which the input impedance is closest to the characteristic impedance of the measurement system; 2) inserting a matching network to obtain a matched condition at a preferred operating frequency. Using the first method, the capacitance change can be measured at various DC bias voltages. Using the second method, the input impedance of a DUT is matched to 50 ohms at a desired frequency. Because of this matched condition, the reflection coefficient is very sensitive to DC bias on a DUT. A 20 dB change of |S11| in 2 Volts range without amplification was obtained. Both methods are quite simple and can be very useful for characterizing the capacitance change for a capacitive sensor and/or sensor application.
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