Capacitive Pressure Sensor Annular Cavity Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive micromachined pressure sensors used in medical instruments for cardiovascular diagnostics often suffer from hysteresis effects, leading to inaccurate pressure readings, especially when operated in collapse mode.
Innovation Solution
A capacitive pressure sensor design featuring a membrane with a central pillar anchoring it to a substrate, forming an annular cavity, which allows operation in a non-collapse mode with improved sensitivity and reduced hysteresis, achieved by maintaining the inner and outer edges of the cavity at substantially the same height and incorporating a rim laterally displaced from the outer edge to minimize contamination impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive pressure sensors are operated in collapse mode to improve sensitivity, then sensitivity is improved, but hysteresis effects occur leading to inaccurate pressure readings
Solution Approach 1:
The patent inverts the conventional operation mode from collapse mode to non-collapse mode. Instead of allowing the membrane to collapse onto the substrate to improve sensitivity, the invention maintains the membrane in a non-collapse state while achieving enhanced sensitivity through a different structural configuration (annular cavity with central pillar), thereby eliminating hysteresis effects while maintaining measurement precision.
Solution Approach 2:
The cavity is segmented into an annular shape with a central pillar rather than a simple circular cavity. This segmentation creates distinct functional zones: the central pillar provides structural support and defines the non-collapse operating region, while the annular cavity maintains capacitive coupling. This structural segmentation enables the membrane to operate without collapsing while preserving sensitivity.
2Length of moving object
If the sensor size is reduced to fit on minimally invasive medical instruments, then the instrument can be inserted into the cardiovascular system, but manufacturing precision becomes more difficult to achieve
Solution Approach 1:
The patent applies local quality by creating an annular cavity with a central pillar rather than a uniform circular cavity. This local structural modification concentrates the capacitive sensing function in the annular region while the central pillar provides localized structural support. This allows the sensor to maintain precise dimensions even at small scales suitable for minimally invasive instruments.
Solution Approach 2:
The sensor structure combines multiple materials with different properties: the membrane material provides flexibility and biocompatibility, the central pillar material provides structural support, and the electrode materials provide capacitive coupling. This composite structure enables the sensor to achieve the required manufacturing precision and mechanical properties at miniaturized dimensions.
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 design enhances sensitivity to levels comparable to pre-collapse mode sensors without hysteresis, providing stable and accurate pressure readings over time, suitable for precise anomaly detection in cardiovascular systems.
Implementation Method 1
The pressure on the membrane defines the degree of deformation of the membrane towards the substrate, which alters the (average) distance between the opposing electrodes. This alters the capacitance of the capacitor formed by the spatially separated opposing electrodes
Implementation Method 2
The pressure on the membrane defines the degree of deformation of the membrane towards the substrate
Data Source
Figure 1
Figure 2
Figure 2
AI summary
A capacitive pressure sensor (10) is disclosed comprising a membrane (21) including a second electrode (23) spatially separated by a cavity (20) from a substrate (11) including a first electrode (13) opposing the second electrode; and a central pillar (22) extending from the membrane to the substrate such that the cavity is an annular cavity enveloping said central pillar. Also disclosed is an invasive medical instrument comprising such a capacitive pressure sensor and a method of manufacturing such a capacitive pressure sensor.