Refractive Index Sensor Using Time-Domain Scanning
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Solution Overview
Problem
Existing refractive index measurement systems are not amenable to harsh environments, such as boreholes, due to limited dynamic range, resolution, and sensitivity to environmental factors like temperature and fluid properties, particularly with high viscosities and particulate loading.
Innovation Solution
A refractive index sensor utilizing a critical angle approach with an adaptive optical element, such as a scanning mirror or Liquid Crystal on Silicon (LCoS) element, that operates in the time domain, providing a large dynamic range and insensitivity to environmental fluctuations, and is compact for use in harsh conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional refractive index measurement systems are used, then measurement capability is provided, but they cannot operate in harsh environments due to thermal issues and fouling
Solution Approach 1:
The patent replaces conventional electronic-based refractive index measurement systems with an optical time-domain reflection system. By using light propagation and time-domain analysis instead of electronic sensors and signal processing, the system eliminates thermal issues and electronic component failures that plague conventional systems in harsh environments. The optical system is inherently more resistant to thermal effects and can operate where electronics would fail.
Solution Approach 2:
The patent changes the measurement parameter from spatial/domain-based detection to time-domain detection. By measuring the time of flight of light through different media and analyzing temporal characteristics, the system achieves refractive index measurement without relying on electronic sensors susceptible to thermal drift and fouling. This parameter transformation enables operation in previously inaccessible harsh environments.
2Measurement precision
If critical angle measurement is used to determine refractive index, then measurement is achieved, but the dynamic range and resolution are limited
Solution Approach 1:
The patent introduces a movable mirror that dynamically varies the angle of incidence of light through the medium. By continuously changing the incident angle and measuring the time-domain reflection characteristics at multiple angles, the system expands the dynamic range of measurable refractive indices while maintaining high precision. This dynamic angular scanning enables measurement across a broader range of materials compared to fixed-angle critical angle methods.
Solution Approach 2:
The patent transitions from measuring a single critical angle to analyzing time-domain reflection characteristics across multiple angles and time points. By adding the time dimension to the measurement and using temporal analysis of reflected light, the system achieves both high precision and expanded dynamic range, effectively moving from a one-dimensional critical angle measurement to a two-dimensional time-angle measurement space.
3Measurement precision
If Fabry-Perot optical cavity systems are used for refractive index measurement, then measurement capability is provided, but they are sensitive to environmental factors and have limited adaptability
Solution Approach 1:
The patent replaces the Fabry-Perot optical cavity system with a time-domain optical reflection system. By eliminating the resonant cavity structure and using simple optical reflection with time-of-flight measurement, the system removes the environmental sensitivities associated with cavity resonance (temperature, pressure, alignment) while maintaining refractive index measurement capability. This substitution enables operation in harsh environments where Fabry-Perot systems would fail.
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 sensor achieves accurate and precise refractive index measurements across a wide range of conditions, reducing errors from environmental factors and offering improved resolution and sensitivity, suitable for use in both laboratory and downhole applications.
Implementation Method 1
A first light ray R 1 passing through the first medium M 1 at some angle of incidence (i.e., θ i ) toward the interface will have a portion that passes through the interface and refracts in the second medium M 2
Implementation Method 2
Light ray R 3 incident at other angles θ TIR beyond this critical angle θ crit will be reflected entirely in the first medium M 1. This is referred to as Total Internal Reflection (TIR)
Implementation Method 3
This first ray R 1 will also have another portion that reflects off the interface back into the same medium M 1
Data Source
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AI summary
A refractive index sensor (10) having one or more sources (12), an adaptive optical element or scanner (16), imaging optics (18a,18b), a sensing optic (22), and one or more detectors (20). The scanner (16) impinges a signal from the source (12) into the sensing optic (22) and onto a sensor-sample interface (24) at sequential angles of incidence. The detector response increases dramatically to signals reflected from the interface at corresponding sequential angles of reflection equal to or greater than a critical angle. The refractive index sensor also uses an input lens (18a) between the scanner (16) and the sensing optic (22) and uses an output lens (18b) between the sensing optic (22) and the detector (20). A processor (21) controls the sensor and can determine index of refraction of the fluid sample based on the detector response and scan rate. The sensor can be used in several operational environments from a laboratory to a downhole tool, such as a formation tester to determine properties in a borehole environment.