This article explains how infrared sensors work and the role of materials science in making them possible, and discusses the properties of superconducting materials and their various applications.
It’s a dark and narrow room, but there’s always a good friend waiting for you with a bright smile that helps you not to stumble in this dark room. This friend is called an infrared sensor light, and it is a product of materials science that has helped brighten our lives.
These infrared sensors, which we often see when we walk into a bathroom, hallway, or home entrance, literally work by detecting infrared radiation from our bodies. Infrared light is light that has a longer wavelength than visible light, and our bodies emit infrared light with a wavelength of about 9.4um. However, unlike visible light, it is invisible to the eye, so we are not normally aware of it. However, the sensor works by detecting infrared light when an object with a temperature difference of more than 3 degrees from the ambient temperature approaches the detection zone at a speed of between 30 centimeters and 2 meters per second. If nothing is detected after a certain period of time, it stops working to avoid wasting power. For this reason, in the summer, the difference between our body temperature and the ambient temperature is not as great, so the sensors may not detect as well.
The advent of infrared sensors is more than just a convenience, it’s a huge step forward in safety and efficiency. For example, automated lighting systems in homes, such as porch lights and restrooms, are helping to save energy by reducing unnecessary power waste and providing light only when it’s needed. Furthermore, this technology is also playing an important role in security systems. When an intruder is detected, warning lights automatically turn on or alarms sound, contributing to the safety of residential spaces. As you can see, infrared sensors are improving our lives in many different ways.
But what materials are these sensors made of that allow them to detect infrared radiation from our bodies? These sensors are made possible by “superconducting materials,” which are a product of the materials science we talked about earlier. The different molecules that make up a substance have different properties depending on their shape and the atoms they are composed of. Some of these molecules are crystalline, and when a change in temperature is applied to the crystal, the surface of the crystal changes due to a change in the kinetic state of the atoms due to heat or a change in shape due to thermal expansion. This causes a change in electrical potential. In short, the property that allows electricity to be generated due to temperature changes is called superconductivity, and materials with this property are called ‘superconducting materials’.
To function effectively as a superconductor, the molecules themselves must have a high degree of polarization in their natural state. These materials are called ferroelectrics and are commonly used in superconducting sensors. A typical ferroelectric is ceramics. Most of these ceramic pyroelectric materials are based on PZT (a ceramic molecule with high superconductivity), and various components can be added to it to make it more durable or to form materials with specific properties.
Pyroelectric sensors are made from these materials. Pyroelectric sensors can measure the intensity of incident light by using superconductivity, which is a property that changes the magnitude of electrical polarization (polarization) when light strikes a material and the temperature of the object increases due to the energy of the light. Based on this principle, pyroelectric sensors are used as temperature sensors and infrared sensors. Temperature sensors can detect temperature by direct contact or by measuring the infrared radiation emitted by an object. Infrared sensors measure the light emitted by the object itself. This gives them the advantage of being able to observe at night. Infrared light is also largely penetrating, even through smoke, so it can pick up images even if they are obscured. All of this is made possible by the fact that it is based on super materials.
This is how sensors could greet us at the front door of our homes. Other applications include automatic door systems, human body sensors, intrusion alarms, smoke detectors, and infrared photography. For example, in the case of gas detectors, pyroelectric sensors that detect wavelengths in the vicinity of 4.3um, which is the wavelength of CO2, can be used to determine the concentration of CO2 in the air. Another example is the vidicon. A vidicon is what we call an infrared camera, which uses a pyroelectric material to capture an object in a phase and then acquire a thermal image. The light from the object is then captured by the phase converter and made visible to the human eye, just like the principle of a regular camera.
Furthermore, pyroelectric materials and sensor technology are also being utilized in the medical field. For example, non-contact thermometers use pyroelectric sensors to accurately measure body temperature from a distance, which has been an important tool for contactless temperature measurement, especially during the pandemic. Infrared sensors are also used in smart mattresses to reduce the discomfort caused by temperature fluctuations at night, contributing to improved sleep quality.
The invention of these pyroelectric materials has allowed scientists to build pyroelectric sensors, which have helped us in many ways in our lives, even in places we don’t realize. Even today, when you walk into an empty house after reading this article, you’ll be greeted by a now-familiar pyroelectric sensor, illuminating the ground beneath your feet.
