Diffraction Grating Non-Contact Temperature Measurement
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Solution Overview
Problem
Current non-contact temperature measurement technologies, such as thermal imagers and fiber Bragg sensors, have limitations in measuring low temperatures and are cumbersome, while direct contact methods like thermistors face issues with heat transfer and electrical interference, making them unsuitable for measuring temperatures in extreme environments or on moving parts.
Innovation Solution
A non-contact temperature measurement system utilizing an optical diffraction grating that changes line spacing with temperature, monitored by a single or multiple light beams and cameras, allowing for accurate temperature measurement over a wide range without heat transfer or electrical interference, suitable for environments like jet engine turbine blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If thermal imagers and IR sensors are used for non-contact temperature measurement, then temperature can be measured without contact, but the measurement range is limited to temperatures above approximately -60°C
Solution Approach 1:
The patent replaces thermal radiation detection (IR sensors) with optical diffraction-based measurement. A diffraction grating attached to the object diffracts light, and the diffraction pattern changes with temperature-induced grating expansion/contraction. This optical-mechanical substitution enables measurement below -60°C where thermal radiation methods fail.
Solution Approach 2:
The patent directly exploits thermal expansion of the diffraction grating structure. As temperature changes, the grating spacing changes, which alters the diffraction angle of light. By measuring the diffraction angle, temperature is determined. This method works across extreme temperature ranges including below -60°C.
2Measurement precision
If fiber Bragg sensors are used for temperature measurement, then temperature can be measured, but the sensors are bulky and cumbersome
Solution Approach 1:
The patent extracts the sensing function from bulky fiber optic components and implements it through a simple diffraction grating pattern that can be directly applied to the object surface. The grating can be as simple as a patterned coating or etched marks, eliminating the need for complex fiber Bragg grating assemblies and their associated mounting hardware.
Solution Approach 2:
The diffraction grating can be implemented as a thin film or surface pattern that conformally attaches to the object. This thin-film approach replaces bulky fiber sensors with a lightweight, flexible sensing layer that can be applied to complex geometries without significant installation complexity.
3Measurement precision
If thermistors are used for temperature measurement, then temperature can be measured, but electrical wiring introduces heat transfer paths and interference
Solution Approach 1:
The patent replaces electrical sensing (thermistors requiring wiring) with optical sensing using diffraction gratings and light sources. This substitution eliminates all electrical connections to the measurement point, removing heat conduction paths through wires and eliminating electrical interference, noise, and grounding issues entirely.
Solution Approach 2:
The patent introduces light as an intermediary between the object and the measurement system. Instead of direct electrical contact, light interacts with the diffraction grating on the object, and the modified light carries temperature information to a remote detector. This intermediary approach isolates the measurement system from the object, eliminating heat and electrical interference.
4Measurement precision
If electrical wiring is used to connect physical sensors, then temperature can be measured, but additional heat transfer paths are created and the system becomes cumbersome
Solution Approach 1:
The patent replaces electrical wiring with optical transmission. Light carries measurement information without conducting heat, eliminating the heat sink effect of wiring. The optical system can be configured to minimize thermal interaction with the measured object while maintaining 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 system provides accurate, non-contact temperature measurement across a wide range, including low temperatures, without heat transfer issues, and is self-calibrating, suitable for moving objects and confined spaces, with enhanced accuracy due to the diffraction grating's thermal expansion properties.
Implementation Method 1
A diffraction grating is an optical component with a periodic structure that diffracts light into several beams propagating in different directions. The directions of the diffracted beams depend on the orientation of the grating, the wavelength of light impinging upon the grating, and the spacing of the periodic structure in the grating, i.e. line spacing.
Implementation Method 2
As the temperature of the grating changes so does its line spacing and therefore it's diffraction characteristics. The density of the grating structure is related to temperature through its coefficient of thermal expansion.
Data Source
AI summary
Methods and systems for non-contact temperature measurement of an object on which is attached or etched a diffraction grating. The diffraction grating expands and contracts as the object expands and contracts upon there being a change in temperature of the object. Upon a light beam being received on the diffraction grating, the diffraction grating produces a pair of complementary light beams and one of the light beams is reflected back onto the diffraction grating and then onto the other light beam in a manner that causes the reflected light beam to propagate alongside and non-parallel to the other light beam. The resultant two light beams are thereafter impinged onto a camera at respective first and second impingement locations. The temperature of the object is then determined based on the separation distance between the first and second impingement locations.