Parametric resonance in microelectromechanical structures

A microelectromechanical device, comprising:

• a substrate;
• a parallel plate actuator incorporating a linear force comb drive actuator, said actuator having selected structural parameters and mounted for in-plane motion at a natural resonant frequency with respect to said substrate;
• at least first and second parallel, capacitively coupled plates on said substrate and on said actuator, respectively;
• and
• a drive signal source connected between said first and second plates, said drive signal having a frequency and amplitude selected to cause said actuator to oscillate with respect to said substrate at a frequency other than said natural resonant frequency, variations in said structural parameters or in the frequency or amplitude of said drive signal causing said actuator to shift between stable and unstable oscillation.

A micromechanical sensor, comprising:

• an actuator mounted for motion with respect to a substrate, said actuator having a mass which produces in said actuator a natural resonant frequency of motion;
• drive electrodes on said actuator and on said substrate;
• and
• a drive circuit connected to said drive electrodes, said drive circuit including a signal generator supplying a drive signal to said electrodes having an amplitude and frequency selected to produce parametric oscillation of said actuator, and wherein a change in the mass of said actuator causes said actuator to shift between stable and unstable regions of oscillation for detection of said change.

A method of detecting changes in a measured parameter, comprising:

• mounting a microelectromechanical actuator for oscillating motion with respect to a substrate at a natural resonant frequency;
• generating a drive signal having a frequency and amplitude selected to cause parametric resonant oscillation of said actuator at a frequency greater than said natural resonant frequency;
• applying said drive signal across fixed and stationary capacitively coupled electrodes on said actuator and said substrate, respectively, to cause said actuator to oscillate at said parametric resonant frequency;
• measuring the amplitude of the oscillation of said actuator;
• and
• detecting changes in the amplitude of said oscillation in response to changes in a measured parameter.

A sensor, comprising:

• a micromechanical actuator mounted for oscillating motion with respect to a substrate at a natural resonant frequency of motion that is dependent on a structural characteristic of said actuator;
• capacitively coupled drive electrodes on said actuator and on said substrate;
• a drive circuit connected between electrodes on said actuator and electrodes on said substrate;
• a signal generator supplying a drive signal across said actuator and substrate electrodes, said drive signal having an amplitude and frequency selected to cause parametric resonant oscillation of said actuator with respect to said substrate at a frequency greater than said natural resonant frequency, whereby said actuator has a sharp threshold between stable and unstable oscillation;
• and
• means for measuring the amplitude of oscillation of said actuator to detect changes in the amplitude of oscillation caused by a change in said structural characteristic of said actuator.

A parametric resonance oscillator comprising:

• an actuator spring-mounted for motion with respect to a substrate at a natural resonant frequency, said actuator having at least one selected structural parameter determinative of said natural resonant frequency;
• at least first and second parallel, capacitively coupled plates on said substrate and said actuator, respectively;
• drive circuitry connected to said actuators and energizable to supply to said plates a drive signal having a frequency and amplitude selected to cause said actuators to oscillate with respect to said substrate at a stable parametric frequency other than said natural resonant frequency, variations in said structural parameter or in the frequency or amplitude of said drive signal causing said actuator to shift between said stable and an unstable oscillation;
• and
• means for detecting a shift between stable and unstable oscillation to detect changes in said structural parameter.