Mid-Infrared Plastic Detection Using IR LEDs
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Solution Overview
Problem
Existing methods for recycling plastics, such as those using infrared cameras, are expensive and not suitable for all locations, particularly return stations where individual plastic objects need to be separated, and struggle with reliably distinguishing between dark-colored plastics like carbon black materials.
Innovation Solution
A method and device using mid-infrared (MIR) light in the range of 2.2 µm to 5 µm to detect plastic types by comparing reflected intensities across multiple wavelength ranges, employing a broadband IR light source and IR photodiodes, and optionally incorporating near-infrared and visible light ranges for more accurate differentiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If infrared cameras are used to detect plastic types, then plastic separation can be achieved, but the device cost becomes high and the system becomes complex
Solution Approach 1:
The patent replaces expensive infrared cameras with inexpensive IR LEDs as light sources and simple IR photodiodes as detectors. These components are much cheaper than thermal imaging cameras while providing sufficient functionality for plastic identification through mid-infrared absorption spectroscopy
Solution Approach 2:
The patent substitutes complex mechanical infrared camera systems with a simpler optical system using IR LEDs and photodiodes. The mechanical complexity of thermal cameras is replaced by an optical absorption measurement system that uses standard electronic components
2Reliability
If conventional infrared detection is used, then plastic detection is possible, but dark-colored plastics like carbon black materials cannot be reliably distinguished
Solution Approach 1:
The patent changes the detection wavelength parameter from near-infrared (NIR) to mid-infrared (MIR) range. Plastic materials exhibit characteristic absorption bands in the MIR range (e.g., C=O stretching at 1700 cm⁻¹, C-H bending at 1400-1500 cm⁻¹) that are independent of color, enabling reliable identification of dark plastics including carbon black materials
Solution Approach 2:
The patent transitions from single-wavelength or narrow-band detection to multi-wavelength detection across the mid-infrared spectrum. By measuring absorption at multiple characteristic wavelengths simultaneously, the system creates a spectral fingerprint that enables precise plastic identification regardless of color
3Reliability
If individual plastic objects need to be separated at return stations, then sorting accuracy improves, but existing infrared cameras cannot be used in every location
Solution Approach 1:
The patent uses inexpensive IR LEDs and photodiodes that can be deployed in various locations including supermarket return stations, unlike expensive thermal cameras. The low cost enables widespread deployment at decentralized collection points for individual plastic item sorting
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 reliable and efficient separation of plastic types, including dark-colored plastics, by utilizing MIR wavelengths to differentiate between materials based on absorption and reflection properties, providing sufficient signal strength for reliable differentiation and integration into recycling processes for sorting.
Implementation Method 1
detecting a type of plastic material by means of absorption spectra
Implementation Method 2
emitting excitation light having IR light in an MIR range between approximately 2.2 μm and approximately 5 μm
Implementation Method 3
detecting MIR intensities IR1, ..., IRn of IR light reflected from the plastic material
Data Source
Figure 1~2
Figure 3~4b
Figure 5~6
AI summary
Various devices and methods are provided for identifying different, particularly blackened, plastic materials. According to one aspect, a type or kind of plastic material (200) is determined by detecting the intensities of reflected light in the mid-infrared range at wavelengths above 2.2 µm. Using a heat source (20) that emits particularly in this wavelength range allows for simple excitation across the entire MIR range and detection of reflection at several, for example, five or eight different wavelengths or wavelength ranges. In this way, carbon black materials, in particular, can be reliably distinguished from one another.