The world of machine vision is constantly evolving, driven by the demand for faster, more precise, and more versatile inspection solutions. While visible light has long been the workhorse of machine vision, exploring the electromagnetic spectrum beyond the visible range opens up exciting new possibilities. This post explores the advantages of shortwave infrared (SWIR) imaging and how it's transforming various industrial applications.
Beyond the Visible Spectrum: Entering the SWIR Realm: Shortwave infrared (SWIR) occupies the electromagnetic spectrum between near-infrared (NIR) and mid-wave infrared (MWIR), spanning approximately 900nm to 2500nm. This region lies beyond the capabilities of conventional silicon-based sensors, which are highly sensitive to the visible and near-infrared regions but become increasingly insensitive at longer wavelengths. This has traditionally limited SWIR imaging applications. However, advances in sensor technology, particularly with InGaAs and quantum dot sensors, have opened up access to this spectral range, enabling a new frontier in machine vision.
InGaAs and Quantum Dot Sensors: The most common sensor technology currently used for SWIR imaging is InGaAs (Indium Gallium Arsenide). These sensors are cost-effective and mature, offering good sensitivity and speed. They also benefit from not requiring cooling in most industrial machine vision applications, unlike some other SWIR imaging modalities. In contrast to thermal imaging (MWIR and LWIR), SWIR images retain a more visual appearance and higher resolution.
A newer player in the SWIR sensor arena is quantum dot technology. While offering comparable spectral sensitivity, quantum dot sensors currently suffer from lower quantum efficiency (QE) compared to InGaAs, impacting sensitivity. However, ongoing advancements are expected to improve this metric. The cost of quantum dot cameras tends to be higher than that of InGaAs alternatives, though this is likely to change as the technology matures.
The Unique Advantages of SWIR Imaging: SWIR light interacts with materials in ways that differ significantly from visible light. This provides several unique advantages for machine vision:
High Resolution and Contrast: The shorter wavelengths in the SWIR spectrum translate to images with higher resolution and stronger contrast compared to MWIR and LWIR, benefiting applications requiring detailed analysis.
Penetration Capabilities: Certain materials, like silicon wafers, are opaque in the visible spectrum but become translucent in the SWIR region. This property enables non-destructive inspection of internal defects or characteristics. Plastics, often opaque to visible light, can also exhibit translucence in SWIR, aiding in fill-level inspection or analysis of internal structures.
Moisture Detection: Water strongly absorbs SWIR light at specific wavelengths (around 1450nm and 1900nm). This property is highly valuable for inspecting agricultural produce (detecting bruises or assessing ripeness), textiles, and other materials where moisture content is a critical factor.
Lighting Considerations: While broad-spectrum SWIR light sources are effective, more precise illumination is frequently needed for optimal results. The emergence of SWIR LEDs emitting at peak wavelengths in the SWIR spectrum offers efficient and controlled illumination. Smart Vision Lights provides a selection of SWIR LEDs in various form factors (linear, spot, and ring lights) to facilitate optimal integration with SWIR imaging systems.
Practical Applications: SWIR imaging is rapidly expanding into various applications, including:
In sum, SWIR imaging is a rapidly growing area of machine vision, providing unique capabilities for inspection and analysis that visible light cannot replicate. The availability of efficient SWIR LED lighting and the continued advancements in InGaAs and quantum dot sensor technology make SWIR imaging more accessible and practical. Choosing the right SWIR wavelength and employing suitable lighting are critical for realizing the full potential of this technology.
