What Is a SWIR Sensor? 

A Short-Wave Infrared (SWIR) sensor is an optoelectronic device designed to detect and measure electromagnetic radiation in the short-wave-infrared region of the spectrum, typically spanning wavelengths from 1000 to 2500 nanometers. This region falls just beyond visible light, making it invisible to the human eye but rich in information about the molecular composition of materials. These specialized transducers convert short wave-infrared radiation into measurable electrical signals, enabling the non-destructive analysis of various substances based on their interaction with SWIR light.

The fundamental principle behind SWIR spectroscopy sensor technology is molecular absorption spectroscopy, where different molecular bonds (particularly C-H, O-H, and N-H bonds) absorb SWIR radiation at specific wavelengths, creating characteristic spectral fingerprints. These detection systems range from simple single-wavelength detectors to sophisticated SWIR spectrometer sensors capturing detailed spectral information across multiple wavelengths simultaneously.

Short-wave-infrared detection technologies, while still expensive, are critical across numerous industries due to their ability to provide rapid, non-destructive, and chemical-free analysis of materials.

The technology’s significance stems from its ability to analyse internal compositional properties rather than just surface characteristics, allowing inspection of sealed packages, monitoring of chemical reactions in real-time, and identification of molecular constituents without extractive sampling.

How Does a SWIR Sensor Work?

Short-wave-infrared detection systems operate based on the interaction between SWIR radiation and matter. When SWIR light encounters a material, several phenomena can occur: transmission, absorption, reflection, or scattering. The specific interaction depends on the molecular composition and physical properties of the material. Detection devices primarily measure the absorption or reflection patterns, which correspond directly to the vibrational modes of molecular bonds within the sample.

The working mechanism of a typical short wave-infrared system involves several key components:

1. Light Source: These systems employ specialised light sources such as tungsten-halogen lamps, light-emitting diodes (LEDs), or laser diodes that emit radiation in the  SWIR region.
   
2. Sample Interface: The interaction between SWIR radiation and the sample being analysed may involve transmission through the sample, reflection from its surface or a combination of both with absorption and scattering within the material contributing to the diffuse reflection observed..
   
3. Optical System: Lenses, filters, and other optical elements direct the SWIR radiation, isolate specific wavelengths, and focus the light appropriately. Monochromators or interferometers may be incorporated to achieve wavelength selection and separation.
   
4. Detector: The heart of the system is its detector, which converts the SWIR radiation into an electrical signal. Common detector technologies include indium gallium arsenide (InGaAs) photodiodes, lead sulfide (PbS) detectors, and mercury cadmium telluride (MCT) devices, each offering different sensitivity profiles across the SWIR spectrum.
   
5. Signal Processing: The electrical signal from the detector undergoes amplification and conversion from analog to digital format. Advanced signal processing algorithms then extract meaningful information from the spectral data, often employing multivariate analysis techniques.

Calibration is critical for accurate measurements. First, samples with known properties are measured with the device. Then, statistical methods correlate the spectral data with the known properties to create a calibration model. This model is validated using independent samples to ensure accuracy.

Applications of SWIR Sensors

Short-wave-infrared detection technologies have found extensive applications across diverse fields:

Agricultural and Food Industries:

• Quality assessment of fruits, vegetables, grains, and dairy products
• Determination of protein, moisture, fat, and sugar content in foods
• Detection of contaminants and adulterants in food products
• Monitoring crop health and irrigation requirements, where Living Optics’ portable field cameras can detect plant stress well before visual symptoms appear
• Soil analysis for nutrient content and composition

Pharmaceutical Industry:

• Raw material identification and verification
• Process monitoring during drug manufacturing
• Tablet and capsule composition analysis that can detect counterfeit pharmaceuticals with high accuracy
• Moisture content determination in lyophilized products
• Quality control throughout production processes

Medical and Biomedical Applications:

• Non-invasive blood glucose monitoring
• Tissue and blood oxygenation measurement
• Brain activity monitoring through functional short wave-infrared spectroscopy
• Optical coherence tomography for retinal imaging
• Cancer detection through tissue spectroscopy

Industrial Process Control:

• Real-time monitoring of chemical reactions
• Quality control in polymer and plastic manufacturing
• Textile fiber composition analysis
• Paper and pulp industry moisture monitoring
• Petroleum product classification and blending control

Environmental Monitoring:

• Soil contamination assessment aided by Living Optics’ field-deployable systems that can provide rapid, on-site analysis
• Water quality analysis
• Vegetation health monitoring via remote sensing
• Waste sorting and recycling applications

The continuous expansion of these applications is driven by ongoing miniaturisation, cost reduction, and performance improvements in detection technology.

Advantages of SWIR Sensors

These advanced imaging and sensing technologies offer numerous advantages that have fueled their widespread adoption:

Non-Destructive Analysis: These technologies enable examination of materials without altering their physical or chemical properties, making them ideal for quality control and in-process monitoring.

Rapid Measurement Speed: Unlike many traditional analytical methods that require extensive sample preparation, these systems can provide results in seconds enabling real-time monitoring.

Minimal Sample Preparation: Many short wave-infrared techniques require little to no sample preparation, eliminating the need for chemical reagents or complex extraction procedures.

Multi-Component Analysis: A single measurement can simultaneously quantify multiple chemical constituents within a sample, providing comprehensive compositional information from a single scan.

Penetration Depth: SWIR radiation can penetrate several millimeters into many materials, allowing for analysis beyond surface properties and enabling examination of internal composition.

Process Integration Capability: These systems can be directly integrated into production lines, with solutions that enable continuous monitoring without interrupting manufacturing processes.

Packaging Penetration: One significant advantage is the ability to penetrate many common packaging materials, allowing for non-destructive analysis of packaged products without opening containers.

Portability and Field Deployment: Modern technology has increasingly moved toward miniaturisation, enabling the development of handheld and portable devices suitable for field use and in-situ measurements outside laboratory environments.

These advantages continue to drive innovation in SWIR hyperspectral imaging and related technologies, with companies like Living Optics leading developments focused on improving sensitivity, selectivity, miniaturisation, and cost-effectiveness.