Flexible Interdigitated Strain Sensor for Large Elongation Detection

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Solution Overview

Problem

Traditional resistive strain gauges and interdigitated electrode capacitive strain gauges face limitations in detecting large elongations due to the low stretchability of metal traces and compatibility issues with high-volume MEMS fabrication.

Innovation Solution

A microfabricated thin-film strain sensor with an interdigitated electrode array supported on a flexible substrate using in-plane trace routing, fabricated using high-volume MEMS manufacturing techniques to enhance stretchability and reduce stiffness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional metal traces are used in interdigitated electrode capacitive strain gauges, then the sensor can measure strain via changing capacitance, but the sensor is limited by low stretchability and cannot detect large amounts of elongation

Engineering Contradiction:

Improvestrain detection capabilityVSAvoidstretchability

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent replaces traditional metal traces with flexible conductive elastomer traces that can be stretched. The interdigitated electrodes are formed using flexible conductive elastomer material deposited on a flexible substrate, enabling the sensor to accommodate large deformations while maintaining electrical connectivity and capacitive sensing functionality.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent employs out-of-plane wavy substrate structures that convert linear stretching into bending deformations. The wavy geometry allows the flat sensor surface to expand and contract like an accordion, significantly increasing the effective stretchability along the elongation axis while maintaining the interdigitated electrode configuration.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Adaptability or versatility

If flexible conductive elastomer traces are used to achieve stretchability, then the sensor can detect large elongations, but the sensor is incompatible with traditional high-volume MEMS fabrication and requires large feature sizes

Engineering Contradiction:

ImprovestretchabilityVSAvoidfabrication compatibility

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent replaces mechanical molding and printing processes with MEMS-compatible thin-film deposition and patterning techniques. The flexible conductive elastomer is deposited using sputtering or evaporation, and patterns are defined through photolithography and etching, enabling integration with standard MEMS fabrication workflows for high-volume manufacturing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent transitions from planar in-plane trace routing to out-of-plane wavy substrate architecture. This dimensional transition allows the sensor to achieve high stretchability through vertical undulations rather than lateral routing, enabling miniaturization while maintaining flexibility and compatibility with MEMS fabrication processes.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Adaptability or versatility

If 3D fabrication of out-of-plane wavy substrates is used to increase stretchability, then the device stretchability increases, but the fabrication complexity and device thickness increase

Engineering Contradiction:

ImprovestretchabilityVSAvoidfabrication complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent pre-forms the wavy substrate structure using standard MEMS release and bonding techniques before depositing the interdigitated electrodes. The wavy geometry is created in advance during substrate preparation, allowing subsequent thin-film deposition to follow conventional planar processing steps, thereby reducing overall fabrication complexity despite the 3D architecture.

Inventive Principle:

Principle #10Preliminary action

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 sensor design significantly increases stretchability along the axis of elongation, enabling effective detection of large deformations while maintaining compatibility with high-volume MEMS fabrication.

Implementation Method 1

interdigitated electrode array (IDE) capacitive strain gauges have been introduced that measure strain via the changing capacitance of interdigitated electrodes as they are moved closer together or further apart

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The sensor uses an interdigitated electrode array supported on a flexible substrate with in-plane trace routing to increase the device stretchability along the axis of elongation

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS20250122073A1Microscale flexible strain sensor

Publication Date: 2025.04.17 CARNEGIE MELLON UNIV

AI summary

Disclosed herein are devices comprising stretchable interdigitated electrode arrays and methods for fabricating the devices. The devices are capable of acting as elongation sensors by sensing a change in the capacitance of the device as the distance between the interdigitated fingers changes when the device is elongated or compressed. The device may be coupled to other devices such as to be able to sense elongation or compression of the coupled device. The interdigitated fingers of the device are supported by a substrate and may be fabricated using traditional microfabrication techniques.