MEMS Contact Stress Sensor with Piezoresistive Thermal Compensation

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Solution Overview

Problem

Current methods for determining contact stress between surfaces are challenging due to complex geometries and material properties, making analytic and computational approaches difficult, and often require direct measurement for validation, highlighting a need for effective contact stress measurement instrumentation.

Innovation Solution

A minimal thickness contact stress sensor using silicon sensing elements with excellent elasticity and stability, configured as a single sensor or array, employing MEMS processing technology, including a non-recessed and recessed portion with a pressure-sensitive element and an electric circuit for thermal compensation, to provide accurate static or dynamic measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If analytic or computational methods are used to determine contact stress, then modeling capability is provided, but the methods become extremely difficult and computationally intensive due to complex geometries and material properties

Engineering Contradiction:

Improvemodeling capabilityVSAvoidcomputational complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent replaces complex analytic and computational mechanical stress analysis with a direct electrical measurement system. The sensor uses electrical fields and resistance measurements to directly determine contact stress, bypassing the need for complex FEA modeling and material property characterization.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the measurement parameter from mechanical stress analysis to electrical resistance measurement. By monitoring changes in electrical resistance of the sensor element under contact stress, the system achieves accurate measurement without complex computational modeling.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If direct measurement instrumentation is developed for contact stress, then measurement capability is improved, but the instrumentation becomes complex and difficult to manufacture

Engineering Contradiction:

Improvecontact stress measurement capabilityVSAvoidinstrumentation manufacturing

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The sensor element serves multiple functions: it is both the structural component experiencing contact stress and the measurement element. The sensor's own electrical resistance changes provide the measurement signal, eliminating the need for separate complex measurement instrumentation.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The sensor element is designed to perform multiple functions simultaneously: structural support, stress transmission, and electrical measurement. This multi-functionality simplifies the overall system and reduces manufacturing complexity compared to separate measurement instruments.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If sensor thickness is reduced to minimal levels, then the sensor can measure contact stress more accurately, but manufacturing precision requirements increase

Engineering Contradiction:

Improvecontact stress measurement accuracyVSAvoidsensor thickness control

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent employs thin-film fabrication techniques to create the minimal thickness sensor element. By using standard semiconductor thin-film processes, the sensor achieves minimal thickness with controlled precision, enabling accurate contact stress measurement while maintaining manufacturability.

Inventive Principle:

Principle #30Flexible shells and thin films

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 contact stress sensor enables precise measurement of contact stress with high sensitivity and long-term stability, overcoming the limitations of existing methods by providing a reliable and efficient means for determining contact stress in complex scenarios.

Implementation Method 1

The sensor includes a piezoresistive element configured to change resistance in response to contact stress

Methodology Applied

Scientific EffectPiezoresistive effect: Piezoresistive Effect

Implementation Method 2

The circuit includes a thermal compensator and further includes a pressure signal circuit element configured to provide a signal upon movement of the pressure sensitive element

Methodology Applied

Scientific EffectThermal compensation: Thermal Expansion

Data Source

PatentUS8109149B2Contact stress sensor

Publication Date: 2012.02.07 LAWRENCE LIVERMORE NAT SECURITY LLC

AI summary

A contact stress sensor includes one or more MEMS fabricated sensor elements, where each sensor element of includes a thin non-recessed portion, a recessed portion and a pressure sensitive element adjacent to the recessed portion. An electric circuit is connected to the pressure sensitive element. The circuit includes a thermal compensator and a pressure signal circuit element configured to provide a signal upon movement of the pressure sensitive element.