Applications of SWIR Imaging Technology

SWIR is an acronym for Short Wave Infrared, which refers to invisible light with wavelengths roughly between 1400 and 3000 nanometers. The visible spectrum ranges from 400nm to 700nm, so the human eye cannot see SWIR light. To detect SWIR wavelengths, we need specialized sensors made of InGaAs (indium gallium arsenide) or MCT (mercury cadmium telluride), since silicon detectors are no longer sensitive to wavelengths greater than 1100 nm. GaAs sensors are the primary sensors used in the typical SWIR range. MCTs are also an option to extend the SWIR range, but these sensors are generally more expensive and application-dependent.

SWIR light interacts with objects similar to visible light in that it exhibits shadows and contrasts in its images because it is reflective. Images from the SWIR Images camera are comparable to visible images in resolution and detail.

Objects that are nearly the same color when imaged in the visible area can be easily distinguished using SWIR light, making objects easy to identify. This is a tactical advantage of SWIR imaging compared to the visible area. Some of the natural emitters of SWIR are ambient starlight and background radiation, so SWIR is a great application for outdoor imaging. Conventional quartz/halogen bulbs can also be used as SWIR light sources. Depending on the application, some sensors in SWIR cameras can be tuned to have a linear or logarithmic response to avoid saturation.

Using SWIR has many advantages over traditional visible-light sensors. Some applications that cannot be imaged in the visible range can use SWIR range imaging. An example is silicon wafer inspection, which is only possible because silicon is transparent in the SWIR range. Other examples of materials that are transparent in the SWIR region are sodium chloride (NaCl) and quartz (SiO2). Water vapor is also transparent in SWIR, which makes SWIR cameras more popular when imaging through haze or fog. The following sections detail applications of SWIR imaging technology.

The amount of waste generated across developed countries is increasing while available resources are becoming scarce; therefore, it is necessary to develop effective methods to separate high-quality recyclable materials from collected waste.

Since all plastic waste looks similar in the visible spectrum, it is impossible to separate the recyclable material by traditional methods. However, in the short-wave infrared range, the absorption spectra of different plastic materials exhibit different properties. Therefore, SWIR camera technology allows the implementation of automated separation systems to separate materials of similar quality and properties for recycling.

Even more material types can be distinguished by using the latest SWIR cameras with an extended spectral range of up to 2.5µm. To efficiently automate the waste separation process, the material is shredded into small flakes of similar size.

A conveyor belt transports the sheets to the inspection unit, which consists of an illumination system and a SWIR camera with an InGaAs sensor. Since each plastic material exhibits unique spectral properties within SWIR, it is possible to distinguish between different materials and assign spectral properties to the corresponding plastic-type.

The different types of plastic are separated by a series of jets on a conveyor belt. This step can be repeated several times in order to achieve fine screening and thus obtain good recoveries and high-quality results.

Fruits and vegetables contain 80 to 90 percent water. Therefore, their spectral responses are mainly characterized by the water absorption band with a peak of around 1,450nm. Due to its stronger absorption, water appears darker in the SWIR band.

Each food product has a unique chemical composition and therefore has a unique spectral signature in the visible and short-wave infrared spectrum. 

SWIR cameras with InGaAs sensors are used for in-line food inspection via conveyor belts. One of the most common ways to analyze food is spectroscopy. However, recent developments in the food industry show a trend towards hyperspectral and multispectral imaging. The method combines digital imaging with spectroscopy to obtain detailed information across multiple electromagnetic spectral ranges. The reflection and absorption of certain wavelengths depend on the chemical composition and molecular structure of the food. 

SWIR cameras are often used in push-broom imaging systems in combination with spectrometers (hyperspectral imaging). If the number of bands to distinguish certain materials is low (<10), multi-band pass filters or specialized illumination (multispectral imaging) can be used. SWIR cameras have a typical wavelength range of 900nm to 1,700nm and can provide more spectral information than CCD or CMOS cameras. 

An example is the classification of crushed apples. The SWIR camera can detect bruises, which are darker in the image due to the higher water content. This simplifies sorting them for juicing and separating them from those with perfect properties to sell to end customers.

SWIR cameras can be used to thermally image hot objects between 250℃and 800℃. The metal and glass industry integrates SWIR cameras into process and quality control systems.

Compared to CCD and CMOS cameras, typical InGaAs cameras have a spectral range of 900nm to 1,700nm and can be used to detect emission differences between hot metals and slag. This information is used to detect differences in slag during manufacturing. This ensures maximum yield without any contaminating material.

During the bottle manufacturing process, the InGaAs camera can inspect the inside and outside of the glass bottle. With the ability to thermally image hot objects between 250°C and 800°C, the SWIR camera can monitor the temperature uniformity and cooling rate of the glass. As a result, manufacturers can continuously observe production to maximize yield and quality.

Spectral imaging is also used for agricultural purposes, especially in conjunction with unmanned aerial vehicles (UAVs). Farmers can inspect plants from the air, such as their strawberry fields: looking at the SWIR imagery, farmers can identify plants or areas with a lack of water, ideal moisture levels, or too much moisture. The more water detected, the higher the absorption peak at 1,450nm, and the darker the area that appears in the image. Therefore, for such applications, a narrow 1450nm bandpass filter is often used to enhance this effect.

Drones are particularly popular in agriculture, but can also be used for many other purposes; many materials can be inspected from the air. Each inorganic material has a different chemical composition and crystal structure, resulting in a unique spectral response corresponding to its specific light absorption properties.

The unique spectral response enables mineral mapping of every region in the world. Additionally, forestry companies can map woodlands from the air. Hyperspectral imaging aids in geological and mineral inspection through methods similar to food analysis.

The above introduces you to the application of SWIR thermal imaging technology. If you are interested in SWIR thermal imaging camera or want to buy it, please contact us. 

JAVOL provides thermal imaging cameras and infrared imaging solutions, which are widely used in machine vision, autonomous driving, drone payloads, high-end manufacturing, and medical diagnosis. We support OEM/ODM orders. Production according to customer's special requirements.