Gas accidents such as toxic gas leaks in factories, carbon monoxide leaks from boilers, or suffocation of toxic gases while cleaning manholes continue to claim lives and injuries. The development of a sensor capable of rapidly detecting toxic gases or biochemical products remains an important issue in the sectors of public health, environmental and military surveillance. Recently, a POSTECH research team developed an ultra-compact and inexpensive portable hologram sensor that immediately alerts the user to the detection of volatile gases.
A joint research team led by Professor Junsuk Rho from the Departments of Mechanical and Chemical Engineering and Dr Inki Kim from the Department of Mechanical Engineering with Professor Young-Ki Kim and a PhD. Candidate Won-Sik Kim from the Department of Chemical Engineering at POSTECH integrated a metasurface with a gas-reactive liquid crystal optical modulator to develop a sensor that provides an immediate visual holographic alarm when noxious gases are detected. The results of this study were published in Scientific progress April 7, 2021.
For those who work in hazardous environments such as petrochemical plants, gas sensors are life. However, conventional gas detection devices are not widely used due to their high cost of manufacture with complex machines and electronic devices. In addition, commercial gas sensors have limitations in that they are difficult to use, and have poor portability and reaction speed.
To solve these problems, the research team used the metasurface, well known as a future optical device known to have the effect of an invisible cloak by making visible objects disappear by controlling the refractive index of light. The metasurface is used in particular to transmit bidirectional holograms or 3D video images by freely controlling the light.
Using the metasurface, the research team developed a gas sensor capable of floating a holographic image alarm in space in seconds using the polarization control of transmitted light that turns into due to the change in orientation of liquid crystal molecules in the liquid crystal layer. inside the sensor when exposed to gas. In addition, this gas sensor developed by the research team does not require any support from external mechanical or electronic devices, unlike other conventional commercial gas sensors. Researchers used isopropyl alcohol as a dangerous target gas, known as a toxic substance that can cause stomach pain, headaches, dizziness, and even leukemia.
The newly developed sensor has been confirmed to detect even the tiny amount of gas of around 200 ppm. In an actual experiment using a chalkboard marker, a source of volatile gas in our daily lives, a visual holographic alarm went off instantly the moment the marker was brought to the sensor.
Additionally, the research team developed a one-step nanocomposite printing method to produce this flexible and portable gas sensor. The metasurface structure, which was previously processed on a hard substrate, was designed to enable rapid production with a one-step nanocast process on a curved or flexible substrate.
When the flexible sensor made using this method attaches like a sticker to safety glasses, it can detect gas and display a holographic alarm. It should be integrable with the glass-type AR display systems under development at Apple, Samsung, Google and Facebook.
Going further, the research team is developing a high-performance environmental sensor capable of displaying the type and level of gas or biochemical concentration in the environment with a holographic alarm, and investigating optical design techniques capable to encode various holographic images. If these studies are successful, they can be used to reduce accidents caused by biochemical or gas leaks.
“This newly developed ultra-compact portable gas sensor provides a holographic visual alarm that is more intuitive than conventional or simple auditory alarms,” noted Professor Junsuk Rho. “It is expected to be particularly effective in more extreme work environments where acoustic and visual noise is intense.”