Covert Sensor Using Frequency Shifted Light
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Solution Overview
Problem
Existing sensing technologies face a trade-off between covert measurement of a target's position and accuracy, where improving covertness often results in unacceptable degradation of precision.
Innovation Solution
A system utilizing a broadband light source split into two portions, where one portion illuminates the target and the other is frequency shifted, with the reflected light combined and demodulated using an in-phase and quadrature demodulator, allowing for fine range measurement while maintaining covertness through adjustable optical delay and frequency shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the illumination intensity is increased to improve measurement precision, then the target's position can be measured more accurately, but the target may detect the measurement and alert adversaries
Solution Approach 1:
The patent uses pulsed illumination instead of continuous illumination, where the light source emits periodic pulses at controlled intervals. This allows the sensor to accumulate sufficient photons during pulse periods for accurate measurement while remaining covert between pulses when no illumination is present, thus resolving the contradiction between measurement precision and detectability
Solution Approach 2:
The patent dynamically adjusts the illumination intensity and pulse timing based on target characteristics and measurement requirements. By making the illumination regime adaptive rather than static, the system can optimize between providing enough light for accurate position measurement and maintaining low detectability to avoid alerting adversaries
2Object-affected harmful factors
If the illumination intensity is decreased to maintain covertness, then the target remains undetected, but the measurement accuracy deteriorates
Solution Approach 1:
By using periodic pulsed illumination, the system concentrates the illumination energy into brief intense pulses rather than spreading it over continuous time. This allows low average power (maintaining covertness) while achieving high peak intensity during pulses (ensuring sufficient photons for accurate measurement)
Solution Approach 2:
The patent employs continuous integration and accumulation of photon signals over multiple pulses and time periods. This continuous signal processing approach allows the system to maintain covertness with low instantaneous illumination while accumulating sufficient measurement data over time to achieve high position measurement accuracy
3Measurement precision
If the measurement time is extended to improve accuracy, then the position can be measured more precisely, but the target has more time to detect the measurement
Solution Approach 1:
The pulsed illumination scheme allows the system to conduct multiple rapid measurement cycles in sequence. Each pulse provides a quick measurement opportunity, and by rapidly repeating pulses, the system can accumulate accurate measurements quickly rather than requiring one long continuous measurement, thus reducing overall measurement duration while improving precision
Solution Approach 2:
The patent implements continuous signal integration across multiple pulsed measurements, where data from each pulse is accumulated and processed continuously. This allows the system to achieve high measurement precision through rapid repeated sampling rather than extended single measurements, minimizing the time window for target detection while maximizing 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
Enables precise and covert measurement of a target's position with reduced detectability by adversaries, achieving high accuracy and low mean squared measurement error while maintaining covertness.
Implementation Method 1
A broadband light source is split into two portions
Implementation Method 2
a second portion of which is frequency shifted, e.g., by an acousto-optic frequency shifter
Implementation Method 3
Light reflected from the target is combined with the frequency shifted light
Implementation Method 4
detected, and demodulated with an in-phase and quadrature demodulator
Data Source
AI summary
A system for covert sensing. A broadband light source is split into two portions, a first portion of which illuminates a target, and a second portion of which is frequency shifted, e.g., by an acousto-optic frequency shifter. Light reflected from the target is combined with the frequency shifted light, detected, and demodulated with an in-phase and quadrature demodulator. The outputs of the demodulator are filtered and the arc tangent of the ratio is calculated.