Vacuum-Sealed Cavity Structure for Compact Capacitive Microphones
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Solution Overview
Problem
Conventional microphones face issues such as increased package size, susceptibility to damage from large sound pressures, and noise interference due to gaps allowing particles into the back volume, which affect signal-to-noise ratio.
Innovation Solution
A sealed cavity is formed between the backplate and diaphragm of a capacitive sensing device, with controlled gaps and bump stops to restrict diaphragm movement, reducing package size and preventing damage while improving noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the back volume is increased to enable the membrane to move more freely and increase sensitivity, then the sensitivity of the microphone is improved, but the package size of the microphone increases
Solution Approach 1:
The patent creates a vacuum environment (inert atmosphere without gas molecules) in the back chamber to eliminate air pressure resistance against diaphragm movement. This allows the diaphragm to move more freely and achieve higher sensitivity without requiring a larger back volume, thus resolving the contradiction between sensitivity and package size.
Solution Approach 2:
The patent changes the pressure parameter in the back chamber from atmospheric pressure to vacuum (zero pressure). This parameter change eliminates the counteracting force of air pressure on the diaphragm, enabling improved sensitivity while maintaining a compact package size.
2Ease of operation
If gaps are left in the structure to allow diaphragm movement and acoustic access, then the ease of operation is improved, but particles can enter the back volume and increase noise
Solution Approach 1:
By creating a vacuum environment in the back chamber, the patent eliminates gas molecules that could enter through gaps and cause noise. The vacuum condition prevents particle contamination while still allowing the diaphragm to move freely through controlled gaps, thus resolving the contradiction between ease of operation and noise prevention.
3Strength
If the membrane is made more robust to prevent breaking from large sound pressures, then the strength is improved, but the capacitance sensitivity may be reduced
Solution Approach 1:
The vacuum environment eliminates air pressure that could cause membrane breaking from large sound pressures. This allows the use of thinner, more sensitive membranes without the risk of damage from air pressure, thus improving both strength (by eliminating the threat of breaking) and capacitance sensitivity simultaneously.
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 sealed cavity design reduces microphone package size, enhances noise performance, and prevents diaphragm damage, maintaining signal integrity.
Implementation Method 1
forming a sealed cavity between the backplate and the diaphragm... the sealed cavity comprises a pressure less than 100 pascals
Implementation Method 2
Changes in air pressure cause the membrane to move, which changes a capacitance of a sensing gap between the membrane and the backplate, and generates an electrical signal representing sound sensed by a microphone
Data Source
AI summary
A sealed cavity for a capacitive sensing device is presented herein. A micro-electro-mechanical system sensor comprises a capacitive sense element comprising a backplate and a diaphragm, in which the backplate comprises a first backplate portion and a second backplate portion, the diaphragm comprises a first diaphragm portion and a second diaphragm portion, the first backplate portion comprises an electrode of the capacitive sense element, and the capacitive sense element converts an external pressure that has been applied to the diaphragm into an electrical signal; and a sealed cavity that has been formed between the backplate and the diaphragm.