Interferometric Material Sensing with Adjustable Reference Arm

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Solution Overview

Problem

Existing optical detection systems for ultrasonic waves in materials face low sensitivity due to diffusely reflecting or scattering surfaces, leading to aberrated and mismatched wavefronts, resulting in weak and imprecise signals.

Innovation Solution

An optical waveguide interferometer with a reference arm and measurement arm, coupled via optical fibers and adjustable couplers, maintains a constant optical path length to improve signal precision by adjusting the reference arm length using a controller, ensuring accurate detection of ultrasonic waves induced in materials.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a laser probe beam is directed onto a diffusely reflecting or scattering material surface, then the surface vibration can be detected optically, but the reflected beam becomes highly aberrated and mismatched with the reference beam, resulting in weak and imprecise signals

Engineering Contradiction:

Improvesignal precisionVSAvoidsurface scattering and aberration

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an optical fiber as an intermediary medium to transmit light from the reference source to the material surface and back. The optical fiber acts as a waveguide that maintains a controlled optical path, isolating the measurement system from the effects of surface scattering and aberration. This mediator enables precise interferometric measurement despite the diffusely reflecting nature of the material surface.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the optical path length between the probe beam and surface fluctuates, then the system can adapt to different material surfaces, but the measurement accuracy deteriorates due to path length sensitivity

Engineering Contradiction:

Improvesurface accessibilityVSAvoidpath length stability

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the optical path length of the reference arm is actively adjusted and controlled. The system monitors the interferometric signal and automatically adjusts the reference arm length to maintain optimal path length matching. This feedback control compensates for fluctuations and ensures stable, accurate measurements while maintaining adaptability to different surface positions.

Inventive Principle:

Principle #23Feedback

3Device complexity

If the reference arm optical path length is fixed, then the device complexity is reduced, but the ability to maintain constant optical path relationship with the measurement arm is compromised

Engineering Contradiction:

Improvereference arm structureVSAvoidoptical path length constant relationship

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent transforms the fixed reference arm into a dynamically adjustable structure. The reference arm incorporates variable optical path length elements that can be adjusted to maintain a constant relationship with the measurement arm. This dynamic capability allows the system to compensate for changes in material surface position and maintain precise interferometric measurements without requiring an overly complex fixed structure.

Inventive Principle:

Principle #15Dynamics

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 configuration enhances the accuracy of material sensing by stabilizing the optical path lengths, reducing the impact of surface irregularities and environmental fluctuations, leading to more precise determination of material properties like thickness and composition.

Implementation Method 1

mixing the reflected probe beam with a stable reference beam and measuring the amplitude and frequency or phase of the photodetector output intensity fluctuations

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 2

When the surface vibrates it imparts a phase shift onto the reflected beam

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 3

an optical waveguide interferometer comprising a plurality of optical couplers and interconnecting optical fibers arranged to define a reference arm and a measurement arm

Methodology Applied

Scientific EffectOptical waveguide: Waveguide (optics)

Implementation Method 4

The ultrasonic waves are typically generated with a piezoelectric transducer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS8675204B2Interferometric material sensing apparatus including adjustable reference arm and associated methods

Publication Date: 2014.03.18 HARRIS CORP

AI summary

A material sensing apparatus includes an excitation source configured to induce waves in a workpiece, and an optical waveguide interferometer configured to sense the induced waves in the workpiece. The optical waveguide interferometer includes a plurality of optical couplers and interconnecting optical fibers arranged to define a reference arm, a measurement arm, and a probe segment coupled to the reference arm and the measurement arm and having a probe segment end to be positioned adjacent the workpiece. An optical path length adjustor is coupled to the reference arm. A controller cooperates with the optical path length adjustor and the first optical detector. The controller is configured to adjust an optical path length of the reference arm to maintain a constant relationship with respect to an optical path length of the measurement arm, and to generate workpiece data based upon the first optical detector.