Multifrequency Terahertz Imaging for Skin-Object Differentiation
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Solution Overview
Problem
Passive terahertz imaging systems face challenges in distinguishing concealed objects from human skin due to factors like thermalization, sky glint, and limited resolution, especially in outdoor environments, where the signal-to-noise ratio is low and penetration through clothing is inadequate.
Innovation Solution
A multifrequency terahertz imaging method using at least two receivers adapted to receive radiation at different frequencies, with mixers employing a common local oscillator for down-conversion, allowing for the generation of composite image data that distinguishes skin from non-skin materials by exploiting differences in reflectivity and emissivity across various frequencies, thereby overcoming thermalization and sky glint issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive terahertz imaging is used to avoid physical harm, then safety is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent employs multiple terahertz receivers operating at different frequencies to capture radiation from the same area simultaneously. By analyzing the frequency-dependent reflectivity and emissivity characteristics of skin versus concealed objects, the system distinguishes between them even in passive mode. This multifrequency approach enhances the effective signal-to-noise ratio by exploiting material-specific spectral signatures without requiring active illumination.
2Difficulty of detecting and measuring
If terahertz radiation is used to detect concealed objects, then detection capability is improved, but distinguishing skin from objects deteriorates due to thermalization
Solution Approach 1:
The system utilizes multiple receivers tuned to different terahertz frequencies to capture the frequency-dependent optical properties of materials. Skin exhibits characteristic variations in reflectivity and emissivity across the terahertz spectrum that differ from concealed objects. By simultaneously analyzing these spectral signatures at multiple frequencies, the system can distinguish skin from objects even when they are at the same physical temperature, overcoming the thermalization problem.
3Device complexity
If single frequency terahertz imaging is used, then system simplicity is maintained, but material characterization capability deteriorates
Solution Approach 1:
The patent divides the terahertz spectrum into multiple frequency bands, each captured by dedicated receivers. This segmentation of the spectral information allows the system to exploit the fact that different materials (skin, clothing, concealed objects) have distinct frequency-dependent reflectivity and emissivity characteristics. By processing information from multiple frequency segments simultaneously, the system achieves enhanced material characterization while maintaining a relatively simple parallel receiver architecture.
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 method effectively differentiates skin from concealed objects, even when they are at the same physical temperature, and reduces false alarms caused by sky glint, while maintaining sufficient penetration and resolution for concealed object detection.
Implementation Method 1
respective mixers are configured to provide down-conversion of the different respective frequencies at mixer frequencies that are harmonically related to the frequency of the common local oscillator source
Implementation Method 2
at least two terahertz receivers adapted to receive radiation from a common area of the field of view at different respective frequencies
Data Source
Figure 1
Figure 2A~2B
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AI summary
Terahertz imaging apparatus uses multiple frequencies simultaneously to obtain images of a field of view. The image data obtained at the different frequencies is colour coded and combined to provide a composite image in which differences in properties of materials at the different frequencies give rise to colour differentiation in the composite image.