Capacitance-based system health monitoring system, apparatus and method for layered structure

Inventors

Nadel, Adam Ian • EHRMANTRAUT, ADAM SCOTT

Assignees

Aurora Flight Sciences Corp

Abstract

The present disclosure endeavors to provide an SHM system and method using a conductive material (e.g., CNT) to measure changes in a layered structure. Change in capacitance of a layered structure may be measured over time thereby indicating a change in the structural integrity of the material. The SHM system may be embedded with, or within, the layered structure such that the system is effectively part of the material. Alternatively, it may be external to the layered structure such that the system is a separate device used to measure the capacitance. The SHM system may also localize any changes in a layered structure by using, for example, strips or panels of conductive material on opposite sides of the layered structure being measured. Damage within overlapping portions of the conductive material provides localization capability where varying the size of the strips or panels may be use to vary the sensitivity and resolution of both the locations and size of the defect.

Core Innovation

The invention detects an amount of residual strength remaining in a layered structural component by using embedded conductive layers on at least two opposite surfaces. The conductive layers are electrically isolated from the layered structural component, so dielectric changes in the material between the conductive layers are detected through electrical capacitance measurements. A signal waveform is applied to a conductive layer, and capacitance rise time is measured to reflect changes associated with damage.

The measured electrical capacitance is compared to a reference value, and deviation from the reference value quantifies an amount of damage in the layered structural component. The quantified damage is then correlated to an amount of residual strength remaining in the layered structural component by relating changes in structural integrity to the residual strength. The approach enables detection of damage and estimation of remaining structural capacity using the same capacitance-based sensing principle.

A system implementation includes a device for detecting changes in the dielectric to measure electrical capacitance using signal waveform excitation and capacitance rise time measurement, a monitoring device for comparing the measured electrical capacitance to the reference value, and a correlating device for correlating the amount of damage in structural integrity to the amount of residual strength remaining. Damage localization is supported by conductive patterns such as conductive strips on at least two surfaces that are not parallel, and the reference value can be established using a baseline capacitance measurement after fabrication but prior to substantial use, or by using capacitance from a reference layered structural component.

Claims Coverage

The independent claims are directed to a method, a system, and additional variants centered on capacitance-rise-time detection between electrically isolated conductive layers on opposite surfaces and correlation of deviation from a reference value to quantified damage and residual strength. Across the independent claims, the core inventive approach contains four main inventive elements: electrically isolated embedded or surface conductive layers, dielectric-change detection via electrical capacitance with signal waveform and capacitance rise time, comparison to a reference value to quantify damage, and correlation of quantified damage in structural integrity to residual strength remaining.

Across the independent claims, residual strength remaining is determined by detecting dielectric changes between electrically isolated conductive layers using electrical capacitance measured via signal waveform excitation and capacitance rise time. The measured capacitance is compared to a reference value, and deviation quantifies damage, which is then correlated to residual strength remaining. System claims implement this as separate devices for dielectric-capacitance measurement, reference comparison, and damage-to-residual-strength correlation.

Stated Advantages

Documented Applications