Heat sensors were created even before an understanding of IR light and for quite some time, the development of infrared sensor technology was supported mostly by military applications, particularly for detection, surveillance and alert purposes.
However, the introduction of silicon technology in the last few decades has resulted in a dramatic shift in the development of IR sensor technology. From the mid- 20th century on, a variety of IR sensor technologies were created and use to gain knowledge and benefit society.
Infrared light can offer valuable information on physical objects, like their temperature, shape, composition and location. Since IR radiation is absorbed and scattered less by the atmosphere than visible light, IR technology has contributed a great deal to the field of astronomy. Many NASA telescopes include high performance IR imaging systems, which have supplied tremendous amounts of data on galaxies and star clusters. Other applications of IR sensor technology include medical, search and rescue, meteorology, and climatology purposes.
Cutting Edge Medical Uses of IR Sensors
Many of today’s cutting-edge medical uses of infrared technology will become the standard technology of tomorrow.
One of the current cutting-edge uses of IR sensor technology is the identification of blood vessels in laparoscopic surgery. A Chicago-based start-up has found a way to integrate IR sensors in the tips of surgical tools. These sensors can identify the presence and size of nearby blood vessels.
IR sensors are also being used to lower the risk of hospital-acquired infections by detecting bed sores before they appear in the skin. Drexel University researchers have developed a system that is capable of measuring haemoglobin levels and oxygenation just below the surface of the skin, which are indicators of tissue damage.
Another medical technology company based in Philadelphia has developed an IR-sensor system that can assess brain trauma within two minutes.
As our understanding of the body’s systems increases along with IR sensor technology, medical devices will only become more insightful and precise.
Future IR Technology
The future of infrared sensors will mostly depend on the development of technologies behind those sensors, such as quantum dot infrared photodetectors (QDIPs) and Type-II superlattice structures. Also, future IR sensor technology will have photodetectors integrated with highly effective smart algorithms. Experts are also working toward IR arrays with each pixel sensing the entire IR spectrum. This might lead to bio-inspired sensing and production of a complete IR retina.
One current IR sensor technology is quantum-well infrared photodetectors (QWIPs). The technology includes a wide variety of wavelengths and is a relatively low-cost technology. Ideal for large format arrays, QWIP technology has problems with quantum efficiency and an operating temperature that is lower than that of other IR sensor technology. There is also polarization dependence of the incident IR radiation, which calls for fabrication of special grating structures over each pixel.
The creation of QDIP structures was actually triggered by the success of QWIPs. The technology is comparable but with more features resulting from three-dimensional confinement in the quantum dots.
QDIP has emerged as a technology for next-generation IR imaging and there has been a rapid progression of this technology over the last decade. QDIP-based IR sensors are expected to have benefits of low dark current, high operating temperature, normal incidence and multicolour detection.
QDIPs are capable of imaging in mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) ranges. However, the technology has lower absorption quantum efficiency compared to interband photodetectors.
Type II Superlattice
Type-II superlattice structures have recently come forth as a promising material for high-performance IR photodetectors in MWIR and LWIR ranges. Detector devices made by using a Type-II superlattice system are photovoltaic, but there has been a great deal of work on developing more exotic device structures to be able to boost detector performance.
Incidentally, QDIPs with type-II band configuration are anticipated to have all the benefits offered by quantum dot technology, as well, as greater detections efficiencies due to the band-to-band transitions, unlike in QDIP devices. However, the experimentally-demonstrated quantum efficiency values so far are quite low.
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