Multi-element Detector Array for Nyquist Sampling in Cargo Inspection
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Solution Overview
Problem
Existing cargo inspection systems using high energy X-ray scanners are undersampled, leading to inadequate image quality and difficulty in materials discrimination, as they fail to achieve full Nyquist sampling rates, especially when dealing with large containers containing dense loads.
Innovation Solution
The implementation of an enhanced detection array with a first detector region and a second detector region, where the second region receives radiation that has passed through the first, allowing for full Nyquist sampling and materials discrimination by capturing overlapping sets of data using offset detection elements, ensuring sufficient spatial frequency for accurate scanning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single linear array of X-ray detectors is used to create one-dimensional inspection lines, then the system can penetrate large containers with dense loads, but the image collecting process becomes inherently undersampled according to the Nyquist sampling theorem
Solution Approach 1:
The detector array is divided into multiple independent detector regions (first detector region, second detector region, third detector region) arranged in a two-dimensional configuration. Each detector region captures data from different spatial frequencies, and the combined data from all regions achieves full Nyquist sampling rate, resolving the undersampling problem of single linear arrays.
Solution Approach 2:
The system transitions from a one-dimensional linear array of detectors to a two-dimensional array configuration with detectors arranged in multiple regions and directions. This dimensional expansion allows simultaneous capture of multiple spatial frequency components, achieving full Nyquist sampling without increasing scan time or complexity proportionally.
2Measurement precision
If high energy X-ray sources are used to penetrate dense cargo loads, then inspection capability is improved, but materials discrimination becomes difficult due to insufficient sampling
Solution Approach 1:
The detector array is segmented into multiple detector regions that capture different spatial frequency components of the X-ray transmission data. This segmentation allows the system to recover and utilize high spatial frequency information that would otherwise be lost, enabling accurate materials discrimination through complete Nyquist sampling.
Solution Approach 2:
The system changes the sampling parameter configuration by using multiple detector regions positioned at different locations and orientations. This parameter change ensures that the combined sampling rate across all regions meets the Nyquist criterion, preserving spatial frequency information necessary for materials discrimination while using high energy X-rays.
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
This approach provides high-resolution images that meet the Nyquist sampling rate, enabling effective materials discrimination and improved decision-making in cargo inspection, even for large and dense containers, by ensuring that data is captured at a frequency sufficient to accurately scan the object in both directions.
Implementation Method 1
A linear array of X-ray detector elements is then positioned opposite to the X-ray source such that it is irradiated by the fan-beam of radiation after attenuation of the X-ray beam by the object under inspection
Data Source
AI summary
The invention provides methods, systems and detector arrangements for scanning an object moving in a first direction that includes the steps of irradiating the object with radiation having a peak energy of at least 900 keV, providing a first detector region having a thickness of at least 2 mm and a second detector region having a thickness of at least 5 mm where the second detector region is arranged to receive radiation that has passed through the first detector region, and detecting the radiation after it has interacted with or passed through the object in order to provide information relating to the object.