From The Editor | May 14, 2024

Transforming Smart Living with Emerging Infrared Technologies

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By John Oncea, Editor


Infrared tech advances in detection, imaging, and sensors are enhancing applications in ADAS, healthcare, security, IoT, and smart homes, enabling automated, efficient living spaces.

It’s March 27, 1800, and you’re a Fellow attending a meeting of the Royal Society of London. Renowned astronomer and telescope builder William Herschel – who discovered the planet Uranus 19 years earlier – is reading from his paper Experiments on the Refrangibility of the Invisible Rays of the Sun.

Herschel mentions that during his years of solar observations, he used pieces of colored glass to reduce the amount of light and heat coming through the telescope. Through experimentation with different color combinations, he made a surprising discovery: Some color combinations blocked most heat but little light, while others blocked most light but little heat. Additionally, different color combinations produced images of the sun in different colors.

These observations led Herschel to wonder if the heating power of light varied by color. “It occurred to me, that the prismatic rays might have the power of heating bodies very unequally distributed among them,” he wrote.

Herschel conducted a careful experiment to test the distribution of heat. He placed a prism in the window so that sunlight passing through created a rainbow on a nearby table. Then he positioned an adjustable card with a narrow slit between the prism and the table. The card blocked all but a narrow band of color from reaching the table. One thermometer sat in the light, and another sat nearby in the card’s shade. Herschel meticulously recorded the temperature in the light and shade for bands of red, green, and violet light.

“In each case, the temperature inside the light was higher than that in the shadow. Red rose highest, then green, then violet,” writes the American Physical Society (APS). Herschel concluded that the ‘radiant heat’ in sunlight was being refracted by the prism according to the laws of dispersion — just like the light.

Herschel theorized that illuminating power could also be unequally distributed amongst colors, much like radiant heat was. “To test this, he placed small objects under a microscope,” APS writes. “He illuminated them with only one color of light at a time (orange, yellow, green, blue, indigo, and violet), produced as in the first experiment.

“By carefully rating the visibility of different objects in different colors, Herschel concluded, ‘The maximum of illumination lies in the brightest yellow or palest green.’ As we now know, the sensitivity of the eye peaks in exactly this range.”

Herschel told the Royal Society that illuminating power starts low, peaks, and then decreases while radiant heat’s intensity of radiant heat starts low, increases, and continues increasing. This discovery led Herschel to wonder if the peak could be outside the visible range of light.

Herschel’s experiments detailed in his March 1800 paper led him to write, “The full red still falls short of the maximum of heat.” In short, he had discovered infrared radiation.

Herschel went on, suggesting “that if radiant heat peaked beyond the red, ‘radiant heat will at least partly, if not chiefly, consist, if I may be permitted the expression, of invisible light; that is to say, of rays coming from the sun, that have such a momentum as to be unfit for vision.’ It was a novel and seemingly contradictory idea — to think of something invisible as light.”

Herschel’s later papers on the subject revealed a change in his thinking. “He outlined his experimental findings on the similarities and differences between light and radiant heat and concluded that they were likely distinct entities, in part because his results were difficult to correctly interpret given the knowledge of the time,” writes APS. “Herschel returned to observational work, making discoveries for another 20 years before he died in 1822. But it would take generations for the scientific community to realize the full value of his brief trek into the nature of light.”

Though his final thoughts on the matter don’t align with what we know to be true today, Herschel did lay “the foundation on which scientists like Johann Wilhelm Ritter and Wilhelm Conrad Röntgen would uncover the full light spectrum, and others like James Clerk Maxwell and Max Planck would build the framework for electromagnetic radiation.”

Emerging Infrared Technologies

The term infrared was coined later in the 1880s, derived from the Latin word infra meaning below, as infrared has a lower frequency than visible red light, notes American Scientist. After Herschel’s initial discovery, progress in infrared astronomy was slow until the early 1900s when thermopiles and bolometers were developed to detect infrared radiation more sensitively.

A major milestone was the first infrared all-sky survey conducted by the Infrared Astronomical Satellite (IRAS) in 1983, revealing many previously unknown infrared sources in the cosmos. Since then, infrared detectors and imaging systems continued advancing rapidly, especially after the invention of the transistor in 1947 enabled the development of semiconductor infrared photon detectors like InSb, HgCdTe, and Si, SPIE reports.

Modern infrared focal plane array (IRFPA) technology with multiplexed readout circuitry emerged in the second generation, followed by third generation IRFPAs with orders of magnitude more pixels and on-chip features. Infrared imaging finds widespread applications today in military, scientific, and commercial domains.

Infrared detector technologies are rapidly advancing, and new technologies are emerging to address the limitations of existing detectors, according to SPIE. These new technologies are expected to improve performance, reliability, size, weight, and power/cost.

Some new infrared technologies include:

  • SPRITE detectors: These detectors require a long minority carrier lifetime, which has led to improvements in material and fabrication technology.
  • HOT-IR MCT detector technology: This technology can perform at higher temperatures, so the detector doesn't need to be cooled down to 77°K. HOT-IR™ detectors perform better at temperatures above 110°K and use smaller coolers and less power.
  • PRISMA: This hyperspectral imaging system has sensors that can acquire images in about 235 contiguous spectral channels. 

These technological advances have further expanded the uses of infrared and are, according to American Bright LED, enabling applications such as:

  • Automotive: Infrared sensors are being integrated into advanced driver assistance systems (ADAS) for night vision, pedestrian detection, and collision avoidance.
  • Healthcare: Infrared thermography aids in disease diagnosis and vascular health assessment. IR sensors enable non-contact temperature measurement and are used in pulse oximeters.
  • Security/Surveillance: Infrared illumination combined with image sensors enables intelligent surveillance systems with facial recognition and motion tracking capabilities.
  • Internet of Things: Infrared sensors are being integrated into IoT devices for environmental monitoring, motion detection, and energy management in smart homes and industrial settings.

Infrared And Smart Homes

Smart homes are another area in which infrared is being applied. A smart home is a home that contains smart devices that can be controlled remotely using a smartphone or tablet through an internet connection, according to Tech Target. Smart homes can be set up using wireless or hardwired systems. 

A smart home allows homeowners to control appliances, thermostats, lights, and other devices remotely using a smartphone or tablet through an internet connection. Smart homes can be set up through wireless or hardwired systems.

Smart home devices include:

  • Smart TVs
  • Smart lighting systems
  • Smart thermostats
  • Smart door locks and garage door openers
  • Smart security cameras and systems
  • Smart pet and lawn care
  • Smart kitchen appliances
  • Smart household monitors 

Smart homes can provide many benefits, including controlling utilities and features of the home via the internet, increasing home security, and saving money on energy costs and maintenance expenses 

Infrared technology is playing a crucial role in the development of smart homes by enabling various sensing and communication capabilities. Here are some key applications of IR technology in smart home systems:

  • Motion And Occupancy Sensing: IR motion sensors are widely used in smart homes for occupancy detection and home automation. These sensors detect changes in infrared radiation emitted by warm objects (like humans or pets) to determine presence and movement within a space. This allows for automated lighting control, HVAC adjustments, and security monitoring based on occupancy patterns.
  • Remote Control And Device Communication: IR LEDs and receivers enable wireless remote control of smart home devices like TVs, media players, and smart appliances. Many smart home hubs and controllers use IR blasters to integrate legacy devices into the smart home ecosystem.
  • Environmental Monitoring: IR sensors can monitor environmental conditions like temperature, humidity, and air quality by detecting specific infrared absorption bands of gases like CO2, methane, and volatile organic compounds (VOCs). This data aids in optimizing indoor air quality and energy efficiency.
  • Presence Detection And Gesture Control: Advanced IR sensor arrays can detect and track human presence, movement, and gestures within a space. This enables touchless control of smart home systems, enhancing accessibility and convenience. Gesture recognition using IR sensors is also being explored for gaming and entertainment applications.
  • Thermal Imaging And Night Vision: IR thermal imaging cameras can provide night vision capabilities for enhanced home security and surveillance. They can detect heat signatures of people and animals, even in complete darkness, enabling proactive monitoring and alerts.
  • Li-Fi Communication: Li-Fi (Light Fidelity) technology, which uses modulated IR and visible light for high-speed wireless data transmission, is being explored for smart home networking and device communication. IR LEDs could potentially replace Wi-Fi routers in smart homes, offering higher data rates and improved security.

As smart home technology continues to evolve, the integration of IR sensors, detectors, and communication systems will play an increasingly important role in enabling intelligent, automated, and energy-efficient living spaces.