Capacitive Micro Pressure Sensor Gel Isolation for Fluid Environments
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional absolute capacitive micro pressure sensors face issues with stray capacitance, reduced sensitivity, and mechanical property alterations when exposed to fluids, particularly saline, due to direct membrane contact and air bubble formation, leading to sensor drift and inaccurate readings.
Innovation Solution
The sensor incorporates a gel in the open cavity between the base plate and deflectable membrane, minimizing stray capacitance and air bubbles, and uses a biocompatible gel and protective coatings to prevent fluid diffusion and mechanical stress, ensuring improved sensitivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the deflectable membrane is exposed to fluid (saline) for direct pressure sensing, then the sensor can measure pressure in physiological environments, but stray capacitance increases and mechanical properties alter causing sensor drift
Solution Approach 1:
A gel layer is introduced as an intermediary substance between the deflectable membrane and the saline fluid. The gel has low dielectric constant similar to air, minimizing stray capacitance while allowing mechanical pressure transmission. This mediator enables the membrane to sense pressure indirectly through the gel, preventing direct fluid-membrane contact that would cause capacitance interference and mechanical property alterations.
2Productivity
If the open cavity is filled with fluid for pressure transmission, then pressure can be transmitted to the membrane, but air bubbles form causing fluctuation and inaccurate readings
Solution Approach 1:
The gel acts as a flexible continuous medium filling the open cavity between the base plate and membrane. Unlike air-fluid interfaces that create bubbles, the gel forms a homogeneous flexible layer that completely transmits pressure without bubble formation. The gel's flexible nature allows it to conform to the cavity shape and transmit pressure uniformly to the membrane surface.
3Measurement precision
If a gel is introduced to prevent fluid contact with the membrane, then stray capacitance is minimized and measurement sensitivity improves, but the device complexity increases
Solution Approach 1:
The gel layer serves multiple functions simultaneously: (1) It acts as a pressure transmission medium from the saline environment to the membrane, (2) It serves as a dielectric barrier with low dielectric constant to minimize stray capacitance, (3) It prevents direct fluid-membrane contact that would alter mechanical properties, and (4) It eliminates air bubble formation. This multi-functionality achieves improved measurement precision without proportionally increasing device complexity.
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 design minimizes stray capacitance, enhances measurement sensitivity, and reduces mechanical property alterations and air bubble formation, resulting in more accurate and stable pressure readings when exposed to fluids like saline.
Implementation Method 1
A gel is disposed in the open cavity in contact with an exposed surface of the deflectable pressure sensor membrane... minimizing stray capacitance
Implementation Method 2
A gel is disposed in the open cavity in contact with an exposed surface of the deflectable pressure sensor membrane... enhances measurement sensitivity
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An absolute capacitive micro pressure sensor including a pressure sensor element (250) with a mechanically fixed electrode and a deflectable pressure sensor membrane separated from the fixed electrode by a predetermined distance. A packaging defining a chamber is formed by a cover (207) assembled to a base plate (206) with an opening defined therein. The chamber is filed with a fluid and/or a gas at substantially constant pressure. Within the chamber, the pressure sensor element is mounted to the base plate to define an open cavity therebetween substantially aligned with the opening defined in the base plate. A gel (205) is disposed in the open cavity in contact with an exposed surface of the deflectable membrane.