Capacitive MEMS Microphone Linkage to Reduce Pull-In and Energy Loss
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Solution Overview
Problem
Capacitive detection microphones suffer from energy losses due to deformation of the piston, transmission device, and frame, leading to reduced sensitivity and resonant frequency, and are prone to the 'pull-in' phenomenon, which limits the bias voltage.
Innovation Solution
An electromechanical system with a movable element featuring a membrane and rigidifying structure, incorporating a first opening and a first island connected via pivot hinges, and transmission devices with reduced deformation through rotatable shafts and arms, minimizing energy loss and pull-in effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the piston, transmission device, and frame are made more rigid to reduce deformation, then energy loss is reduced and sensitivity is improved, but the resonant frequency decreases
Solution Approach 1:
The transmission device is divided into multiple rigid transmission arms connected by flexible pivot hinges. This segmentation allows each arm to be rigid (reducing energy loss) while the flexible hinges maintain the overall system's ability to respond quickly (preserving resonant frequency). The flexible hinges act as compliant joints that decouple the rigid segments from each other.
Solution Approach 2:
Flexible pivot hinges are used to connect the rigid transmission arms. These flexible hinges provide the necessary compliance to maintain resonant frequency while allowing the transmission arms to remain rigid for minimizing energy loss. The flexible hinges act as compliant elements that enable the system to vibrate at higher frequencies.
2Measurement precision
If the bias voltage is increased to improve sensitivity, then the signal detection capability is enhanced, but the pull-in phenomenon occurs which limits further voltage increase
Solution Approach 1:
The flexible pivot hinges are designed to provide preliminary counter-action against the electrostatic pull-in force. The flexibility of the hinges creates a mechanical counter-force that opposes the electrostatic attraction between the movable electrode and fixed electrode, preventing the pull-in phenomenon even at high bias voltages. This allows the system to operate at higher voltages for improved sensitivity without experiencing the harmful pull-in effect.
3Loss of energy
If the transmission device is made more rigid to reduce deformation, then energy loss is reduced, but the device complexity increases
Solution Approach 1:
The transmission device is segmented into multiple rigid arms connected by flexible pivot hinges. This segmentation allows each arm to be simple and rigid (minimizing energy loss) while the overall structure remains relatively simple due to the modular nature of the segments and standardized hinge connections.
Solution Approach 2:
The flexible pivot hinges serve multiple functions: they connect the rigid transmission arms, provide flexibility to maintain resonant frequency, and offer mechanical counter-action against pull-in. This multi-functionality reduces the need for additional separate components, thereby reducing overall device complexity while achieving energy loss reduction.
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
The system enhances sensitivity and maintains resonant frequency by reducing energy loss and preventing pull-in, while maintaining a compact design and efficient signal detection.
Implementation Method 1
The capacitive detector 15 makes it possible to measure displacement of the piston 13, and therefore the difference in pressure between its two faces. They comprise a movable electrode 151 and at least one fixed electrode facing the movable electrode 151. The electrodes form the plates of a capacitor whose capacitance varies as a function of the displacement of the piston 13.
Implementation Method 2
This pull-in phenomenon is caused by the electrostatic force, which tends to bring the movable electrode closer to the fixed electrode (or to one of the fixed electrodes) and which depends on the square of the bias voltage.
Data Source
AI summary
An electromechanical system includes a frame; an element movable relative to the frame, the movable element comprising a membrane and a rigidifying structure for the membrane; a capacitive measurement or actuation device; a first transmission device for a movement between the movable element and the capacitive measurement or actuation device, the first transmission device being rotatably movable relative to the frame by a plurality of first pivot hinges; in which system: a first opening is arranged in the movable element; the frame includes a first island extending into the first opening; and the first transmission device is connected to the first island via one of the first pivot hinges.