MEMS Tunable Capacitor Active Damping Control
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Solution Overview
Problem
MEMS tunable capacitor devices are inherently slow, especially when the actuation voltage is close to the closing voltage, due to dominant damping effects over inertial effects, leading to significant capacitance changes just below the closing voltage.
Innovation Solution
A micro-electromechanical device with a controller that applies electrical power in the form of pulses at a higher voltage than necessary to hold the movable element in an intermediate position, followed by a lower voltage to stabilize it, and uses active damping to suppress ringing, allowing for faster tuning and reduced settling delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a voltage close to the closing voltage is applied to achieve large capacitance change, then the capacitance tuning range is improved, but the response speed deteriorates due to dominant damping effects
Solution Approach 1:
The patent applies periodic voltage pulses to the movable electrode to exploit resonant oscillations. By timing the voltage application to coincide with the natural resonant frequency of the MEMS structure, the system achieves large capacitance changes through resonant amplification rather than relying solely on static voltage levels, thereby improving both tuning range and response speed
Solution Approach 2:
The patent dynamically changes the voltage parameter from a static approach to a time-varying pulsed approach. By modulating the voltage amplitude and timing according to the resonant characteristics of the system, the patent overcomes the damping effects that limit response speed while maintaining the desired capacitance tuning range
2Speed
If the actuation voltage is increased to speed up the response, then the response speed is improved, but the risk of electrode breakdown and device damage increases
Solution Approach 1:
Instead of applying a continuous high voltage that would risk breakdown, the patent uses periodic voltage pulses timed to resonant frequencies. This allows the system to achieve fast response through resonant amplification at lower voltage levels, avoiding the electrode breakdown issues associated with sustained high voltage application
Solution Approach 2:
The patent transitions from a static voltage application approach to a dynamic pulsed approach that adapts to the real-time mechanical state of the MEMS structure. By synchronizing voltage application with the mechanical resonance, the system achieves fast response without requiring continuously high voltage levels, thereby improving reliability
3Stability of the object's composition
If the movable element is driven to an intermediate position using standard voltage control, then the device operates stably, but the tuning speed is limited by damping effects
Solution Approach 1:
The patent applies periodic voltage pulses at resonant frequencies to drive the movable element to intermediate positions. The resonant oscillations amplify the displacement response, allowing the element to reach intermediate positions faster than conventional step-response methods, thereby reducing settling time while maintaining stability through controlled pulse timing
Solution Approach 2:
The patent employs feedback control to monitor the position and velocity of the movable element, adjusting the timing and amplitude of voltage pulses in real-time. This feedback mechanism ensures that the element reaches intermediate positions quickly through resonant amplification while preventing overshoot and maintaining operational stability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables faster tuning of MEMS devices by overdriving the movable element with high voltage and applying active damping to reduce oscillations, thereby overcoming the inherent slowness and damping issues, resulting in improved speed and efficiency in reaching the desired capacitance state.
Implementation Method 1
The first and the second electrode are mutually separated by an air gap. The first electrode can be moved towards the second electrode by application of an actuation voltage to provide an electrostatic force.
Implementation Method 2
The spring force is used to move the first electrode away from the second electrode.
Implementation Method 3
uses active damping to suppress ringing, allowing for faster tuning and reduced settling delays
Data Source
AI summary
A micro-electromechanical device has a substrate (60), a movable element (15), a pair of electrodes (40) arranged on the substrate and on the movable element to move the movable element, and a controller (50) to supply the electrodes. To move the movable element to an intermediate position one or more pulses are applied during the movement, timed to compensate for under or over damping of the movement. This can reduce a settling delay. It can be applied to tunable RF capacitors. To control a decrease in the gap, a single pulse of a maximum supply level compensates for the inherent slowness of the device and over damping. To compensate for under damping, the pulses have a period corresponding to a resonant frequency, and comprise peaks and troughs above and below the final supply level, such that successive ones of the peaks and troughs are closer to the given supply level.