Vacuum MEMS Accelerometer for Wideband Contact Vibration
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Solution Overview
Problem
Conventional accelerometer designs face a tradeoff between bandwidth and sensitivity, limiting their ability to capture a wide range of vibrations from the human body, particularly in health informatics applications where frequencies from DC to 10 kHz are relevant, and are often bulky due to increased proof-mass size and reduced stiffness.
Innovation Solution
A vacuum-encapsulated MEMS accelerometer with a suspended proof mass and nano-gap capacitive electrodes, providing out-of-plane sensitivity and micro-g resolution, allowing for wideband cardio- and pulmonary-induced vibration capture without sensitivity to air-borne acoustic emissions, and featuring a tunable resonant frequency and tri-axial vibration sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the proof-mass size is increased to achieve higher force sensitivity, then sensitivity is improved, but the device size increases and bandwidth is limited to a few hundred Hertz
Solution Approach 1:
The patent changes the operating environment parameter by placing the accelerometer in a vacuum enclosure, which eliminates air damping and allows the use of smaller proof masses while maintaining sensitivity. This enables micro-scale device size with enhanced sensitivity and extended bandwidth.
Solution Approach 2:
The patent segments the system into two parts: a micro-scale accelerometer with small proof mass for sensitivity, and a vacuum enclosure that provides the necessary damping control. This segmentation allows the small accelerometer to achieve high sensitivity without the bulk of traditional designs.
2Speed
If the resonant frequency is increased to extend operational bandwidth, then bandwidth is improved, but force sensitivity decreases
Solution Approach 1:
The patent changes the damping parameter by introducing a vacuum environment, which allows the resonant frequency to be increased for extended bandwidth while maintaining sensitivity through controlled damping. The vacuum eliminates air resistance, enabling higher frequency operation without sensitivity loss.
3Adaptability or versatility
If the device is made sensitive to air-borne acoustic emissions, then acoustic detection capability is improved, but sensitivity to contact vibrations from the body is reduced
Solution Approach 1:
The patent extracts the accelerometer from the air environment by placing it in a vacuum enclosure, removing its sensitivity to air-borne acoustic emissions. This isolation preserves contact vibration sensitivity from the body while eliminating unwanted acoustic interference from the environment.
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 solution enables high-fidelity capture of heart and lung sounds with constant sensitivity across a broad frequency range, from DC to 10 kHz, in a compact, wearable form factor, unaffected by environmental noise, and suitable for noisy environments like hospitals.
Implementation Method 1
a sensing electrode separated from the suspended proof mass by a sub-micron sensing gap
Implementation Method 2
vacuum-encapsulated MEMS accelerometer
Data Source
AI summary
Small form-factor MEMS devices and methods of using the devices. An exemplary MEMS device includes an ACM. Certain devices comprise nanometer scale sensing gaps in the out-of-plane direction to increase vibration sensitivity in a vacuum casing. Certain devices described herein provide a differential sensing mechanism. Accelerometer contact microphones having an operational bandwidth ranging from 0 Hz and 10,000 Hz are also disclosed. The vibration acceleration sensitivity of certain devices described herein is better 100 μg√Hz.