Signal Characterisation
Output oscillations produced by a system at integer multiples of an applied excitation frequency define the structural and electrical behaviour of resonant sensors. The harmonic response of a microelectromechanical resonator reveals changes in mass or stiffness caused by the adsorption of gas molecules. Analysts use these secondary signals to separate the primary resonant action from background electrical noise.
Frequencies Relation
When a sensing element is driven by a sinusoidal electrostatic force, the non-linearities in the suspension or the transducer generate signals at double or triple the driving frequency. The magnitude of this harmonic response depends on both the drive amplitude and the damping forces of the surrounding gas. By measuring these higher-order components, the instrument can extract multiple physical parameters, such as gas density and viscosity, from a single sensing element.
This multi-frequency analysis reduces the need for additional sensor channels, simplifying the instrument architecture and lowering power consumption.
Measurement Accuracy
Operating conditions such as temperature and pressure directly influence the resonant properties, causing shifts in the secondary peaks. This drift must be monitored because it affects the signal-to-noise ratio of the measurement system. To maintain measurement accuracy, the signal processing electronics must employ narrow-band filters that isolate the specific harmonic component of interest from ambient vibrations.
Calibration Standard
Calibration protocols for resonant sensors establish the relationship between the applied excitation voltage and the amplitude of the second harmonic component under reference laboratory conditions. Manufacturers verify this behaviour during production testing to ensure the resonant structure complies with design specifications. The certificate of calibration states the sensitivity of the harmonic response and defines the temperature compensation coefficients used by the sensor microcontroller.
