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NIR vs. SWIR sensors - definition, distinctions, applications
Which wavelength range is suitable for what? A comparison with FAQs.
Table of Contents
What is an NIR/SWIR sensor? Definitions and distinctions
The term “NIR” stands for near-infrared and the related term “SWIR” (short wave infrared) are often used differently in industrial practice – usually referring to the entire wavelength range between visible light (VIS) and mid-infrared (MIR).
In sensor technology, however, a more precise distinction is worthwhile within this area, as different sub-areas are used for very different applications: simple presence detection on the one hand, material-specific analysis on the other.
This article clearly defines the terms NIR and SWIR, explains their respective operating principles, and shows which applications are used in which wavelength range.
The wavelength range: from VIS to MIR
For orientation purposes, the relevant area can be divided into four sections:
- VIS (visible light): The area perceptible to the human eye – the reference point from which the following areas begin
- NIR in the narrower sense: directly adjacent to VIS, down to approximately 1,2 µm
- SWIR (Short Wave Infrared): above approximately 1,2 µm
- MIR (mid-infrared): It connects to SWIR, with even longer wavelengths.
In practice, the term "NIR" is often used simplistically to refer to the entire range between VIS and MIR. For a precise understanding of the respective applications, we deliberately distinguish on this page between NIR (up to approximately 1,2 µm) and SWIR (above 1,2 µm) – as the two ranges differ significantly in their operating principle and industrial applications.
NIR in the narrower sense (up to approx. 1,2 µm): Presence detection
In the range up to approximately 1,2 µm, primarily conventional and fiber-optic photosensors are used, which operate outside the visible light spectrum. These sensors do not use this wavelength range to identify material, but rather to reliably detect whether an object is present at a specific location – regardless of ambient light in the visible spectrum.
Classic photosensors
This includes all optical sensors for presence detection that operate according to the well-known principle of transmitter and receiver:
- Diffuse reflection sensor
- One-way light barrier
- Reflective light barrier
- Diffuse laser with background suppression)
They are used wherever robust, established attendance tracking with a larger measuring distance is required.
Fiber optic photosensors
The light is transmitted to the actual measuring point via optical fibers. This enables use even where the actual electronics cannot or should not be placed directly at the measuring point – for example, in confined spaces or harsh environmental conditions such as high temperatures.
On sensorikaustria.com, this area includes practically the entire optoGuard product family (e.g. optoGuard-HT) – with the exception of SensoWeb Guard-mat, which is based on a different, material-specific functional principle in the SWIR area (see below).
-> optoGuards: high-performance sensors and sensor systems for presence detection
SWIR (above 1,2 µm): Material-specific absorption
Above approximately 1,2 µm, the behavior changes fundamentally: In this range, many molecules exhibit a characteristic, material-specific absorption behavior: They are set into stronger vibration by light at certain wavelengths (resonance wavelengths) than at others. Light at these wavelengths is therefore absorbed more strongly than at others – this is also referred to as absorption bands, or the fingerprint of a material.
A sensor in the SWIR range no longer simply measures whether something is present, but can – depending on the absorption pattern – draw conclusions about the type of material or certain material properties. This material-specific absorption – also referred to as a "material fingerprint" – is used by Sensorik Austria for two fundamentally different purposes:
Material moisture measurement (around 1,5 µm or 1,9 µm)
Water exhibits particularly pronounced absorption in the range around 1,5 µm. This effect is used for material moisture measurement – thanks to fiber optic design, especially in and around drying processes, where the sensors must detect moisture development directly at the process site.
At Sensorik Austria, this principle is used, among other things, in -> SensoWeb “moist” (paper web) and -> tri²dent “moist” (material moisture outside the paper industry).
Material characterization in inline process monitoring
In addition to pure moisture measurement, material-specific absorptions in the SWIR range can also be used for the detection and differentiation of materials themselves – this is also referred to as “characterization”.
Typical applications are:
- Material supply monitoring: Monitoring whether the "right" material or the "right" quality is being fed into a process, or whether its "fingerprint" remains constant over time.
- Material identification or differentiation: Which of the learned materials is currently being detected by the sensor? Examples of applications include identifying whether a plastic container has a label or not, or detecting tear-offs in a paper machine when paper and drying screen need to be distinguished.
- Monitoring of material composition: Monitoring of mixing ratios or “recipes”
- Material classification for internal recycling streams: Allocation and separation of different material fractions within the production cycle
- Quality Assurance: Continuous monitoring to ensure that the processed material, or the resulting product, meets the required specifications regarding "material quality".
- Coating monitoring: Detection of whether a coating is present, as well as evaluation of the coating thickness and degree of curing.
Sensorik Austria's SWIR sensors -> polyIdent and the material-sensitive paper web tear sensors -> SensoWeb Guard-“mat” fall into this category.
High-end systems: spectrometers, hyperspectral cameras and spatially resolved sensors
For particularly demanding applications, a measurement at a single point or with a few fixed wavelengths is often insufficient. This is where high-end systems come into play:
- Inline spectrometer They capture a significantly broader and more finely resolved spectrum than SWIR sensors, thus enabling a more differentiated material analysis in the ongoing process.
- Hyperspectral cameras They combine the image information of a camera with a full spectrum per pixel – this allows material composition to be represented not only at specific points, but spatially resolved over an entire area.
- Spatially resolved sensor systems They use this information to detect and classify material across the width of a conveyor belt or sorting line – a typical application is automated sorting in recycling plants, where different material fractions need to be detected and separated in real time.
These high-end systems provide significantly more information than individual point sensors, but are also usually much more expensive and complex to integrate and evaluate – their use is particularly worthwhile where material needs to be differentiated across an area or characterized in a particularly complex way.
This area extends beyond our product range. If you are looking for such solutions, please contact appropriate suppliers.
Advantages and limitations at a glance
NIR (≤ 1,1 µm) – Presence detection | SWIR (> 1,1 µm) – Material-specific absorption | |
What is detected? | Whether an object exists | What material or material property is present? |
Benefits | Robust, established, insensitive to VIS ambient light | Material-specific, enables moisture and composition measurement |
boundaries | No statement regarding material type or properties | Calibration requirements, near-surface or material-dependent measurement |
Typical systems | Classic optical and fiber optic photosensors | Fiber optic SWIR sensors, spectrometers, hyperspectral cameras |
Frequently asked questions about NIR/SWIR sensors
Is NIR the same as SWIR?
No. While both terms are often used synonymously, experts use them to refer to different sub-ranges of the infrared spectrum. NIR in the narrower sense extends to about 1,1 µm and is primarily used for presence detection, while SWIR lies above 1,1 µm and utilizes material-specific absorption for moisture and material analysis.
Why is the term "NIR" still often used more broadly in practice?
In everyday language, "NIR" is often used to refer to the entire range between visible light and mid-infrared, as a precise distinction is often unnecessary. However, for the technical selection of a sensor principle, a more precise distinction between NIR and SWIR is worthwhile.
Which method is suitable for pure presence detection, and which for material detection?
For the simple question "Is something present?", conventional or fiber-optic NIR photosensors are sufficient. However, if it is also necessary to identify the material or its composition, a SWIR-based, material-specific measurement principle is required.
Which method is suitable for measuring moisture?
Moisture measurement, or more precisely material moisture measurement, is essentially a special case of SWIR-based concentration measurement, in which the extent of the presence of the “material” water in another material is determined and quantitatively assessed.
Does Sensorik Austria also offer hyperspectral cameras?
No, Sensorik Austria currently only offers sensors for 1-point measurement.
Solutions from Sensorik Austria in material sensor technology
Sensorik Austria uses different areas of the spectrum depending on the requirements:
- classic and fiber optic NIR sensors for presence detection (optoGuard-family) as well as
- SWIR-based sensors for material moisture measurement (SensoWeb "moist", tr²dent "moist"),
- Demolition recording (SensoWeb Guard-mat) and
- diverse customer-specific applications of material characterization (polyIdent).