Laser Multibeam Differential Interferometric Sensor for Vibration Imaging
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Solution Overview
Problem
Existing vibration imaging systems, such as multiple beam laser Doppler vibrometers, are limited by sensitivity to platform motion and air turbulence, restricting their use to stationary platforms and short measurement distances, and struggle to accurately measure vibrations on moving objects.
Innovation Solution
The laser multibeam differential interferometric sensor (LaMBDIS) projects an array of laser beams with frequency-shifted neighboring beams, which interfere on photodetectors to produce heterodyne signals, allowing for demodulation of relative velocities and displacements, reducing sensitivity to platform motion and air turbulence by using a common Doppler shift and close optical paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multiple beam laser Doppler vibrometer is used to obtain vibration images with high sensitivity and accuracy, then measurement precision is improved, but the system becomes sensitive to platform motion and air turbulence, restricting operation to stationary platforms and short distances
Solution Approach 1:
The system segments the measurement into differential pairs of neighboring beams, where each pair independently measures relative vibration between adjacent points. This segmentation allows the system to reject common-mode platform motion while maintaining sensitivity to local vibrations, resolving the contradiction between measurement precision and reliability in moving platforms
Solution Approach 2:
The patent uses a copy of the beam array (second array) to serve as a reference for differential measurement. By comparing vibrations between corresponding points in the first and second arrays, the system eliminates the effect of platform motion and air turbulence, achieving both high measurement precision and reliability in dynamic environments
2Adaptability or versatility
If the MB LDV operates onboard a moving vehicle to measure vibrations on moving objects, then adaptability is improved, but platform motion causes variation in interference signals that is indistinguishable from object vibration
Solution Approach 1:
The system uses feedback through differential measurement, where the vibration signal from one beam array is compared against the reference array. This feedback mechanism continuously compensates for platform motion effects, enabling accurate vibration measurement on moving objects while operating from moving platforms
Solution Approach 2:
The patent introduces an intermediary reference beam array that mediates between the object and the detector. This intermediary array experiences the same platform motion as the object, allowing differential measurement to isolate true object vibrations from platform-induced signal variations, thus improving both adaptability and measurement precision
3Length of stationary object
If air turbulence is present during measurement, then measurement distance can be extended, but air turbulence changes the phase of reflected light, affecting measurement accuracy
Solution Approach 1:
The system merges the optical paths of reference and measurement beams in close proximity, so that both beams traverse nearly identical atmospheric conditions. By combining these paths and performing differential measurement, the system cancels out phase variations caused by air turbulence, enabling extended measurement distances while maintaining phase measurement accuracy
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 LaMBDIS sensor effectively generates a deformation profile with low sensitivity to motion and turbulence, enabling accurate vibration imaging on moving objects and over longer distances, enhancing applications like non-destructive testing and structural health monitoring.
Implementation Method 1
an interferometer configured to mix radiations reflected from neighboring points on the surface of the object such that the radiations from neighboring points interfere with one another
Implementation Method 2
neighboring beams in the array of laser beams are frequency shifted relative to each other... producing heterodyne signals
Implementation Method 3
neighboring beams in the array of laser beams are frequency shifted relative to each other... allowing for demodulation of relative velocities and displacements
Data Source
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AI summary
A sensor for a vibration imaging system is provided. The sensor includes a transmitter configured to project an array of laser beams onto a surface of an object such that neighboring beams in the array of laser beams are frequency shifted relative to each other, an interferometer configured to mix radiations reflected from neighboring points on the surface of the object such that the radiations from neighboring points interfere with one another, a photodetector array configured to produce output signals representative of the interfering beams, a demodulator configured to demodulate the output signals, and a computing device configured to calculate a deformation profile for the object based on the demodulated output signals.