Science
Scientists Say Terahertz Waves Could Revolutionize Daily Life — Here’s What You Should Know
Engineers are unable to traverse a certain area of the electromagnetic spectrum.
The light that reaches our eyes, radio waves, microwaves, X-rays, and gamma rays are all included in the spectrum. And practically all of them can be sent and received by humans, who have perfected the skill.
But there is an exception. A dead zone exists where our technology is ineffective, between the blips of radio static and the beams of visible light. We refer to it as the terahertz gap. Nobody has been able to create a consumer gadget that can send terahertz waves for decades.
“There’s a laundry list of potential applications,” says Qing Hu, an electrical engineer at MIT.
However, a few researchers are gradually making headway. If they succeed, they might unlock a whole new range of technologies, such as a more intelligent skin cancer detection system or the Wi-Fi successor.
The mystery of the terahertz
Consider the terahertz gap to be a border region. Longer radio waves and microwaves are on the left. The infrared spectrum is located on the right side. The terahertz gap is even referred to as “far infrared” by some scientists. Even though infrared is invisible to the human eye, it functions similarly to light in terms of technology.
Radio waves are ubiquitous in today’s electronics because they are essential for communication, particularly between electronic equipment. The optical fibres that support the internet are powered by light. In the current world, these technological domains sometimes operate on separate wavelengths and cohabit in an uncomfortable way.
However, neither domain can penetrate very far into the terahertz neutral zone. The speed at which silicon chips and other standard electronic components operate prevents them from producing terahertz waves. Terahertz waves also don’t operate with light-producing devices like lasers, which are most comfortable with infrared radiation. Even worse, after only a few dozen feet, terahertz vibrations are usually absorbed by the water vapour in the atmosphere.
A small number of terahertz wavelengths are able to pass through water vapour. These bands are particularly useful for observing interstellar dust, and astronomers have constructed telescopes that can pick them up. Those telescopes must be placed in the highest and driest locations on Earth, such as Chile’s Atacama Desert, or in space, away from the atmosphere, for optimal use.
Mist covers the remainder of the terahertz gap. Hu and other researchers are working to address this, but it’s not simple.
Engineering terahertz waves
There is a fundamental issue facing the electronics industry when it comes to harnessing terahertz waves. Our electronics’ silicon chips must pulse rapidly—at trillions of cycles per second, hence the term “terahertz”—in order to bridge the gap. Your computer’s or phone’s chips can function flawlessly at millions or billions of cycles per second, but they have trouble reaching the trillions. The extremely experimental terahertz parts that do function can be as expensive as a high-end vehicle. Engineers are trying to lower the costs.
The goal of the other domain, the world of light, has long been to develop inexpensive equipment, such as lasers, that can produce terahertz waves at particular frequencies. As early as the 1980s, scientists were discussing how to create such a laser. There were others who believed it was impossible.
But MIT’s Hu didn’t think so. “I knew nothing about how to make lasers,” he says. Still, making this kind of laser became his quest.
The quantum cascade laser, which was especially effective at producing infrared light, was then created by scientists in 1994. Hu and his associates only had to direct the laser towards the far-infrared’s longer waves.
They were able to create a terahertz quantum cascade laser about 2002. There was a catch, though: for the system to work, temperatures had to be close to -343 degrees Fahrenheit. Additionally, it needed liquid nitrogen to function, which made it challenging to utilise outside of cryogenic or laboratory environments.
That temperature threshold has gradually increased during the past 20 years. Hu’s lab’s most recent lasers run at a more comfortable 8 degrees Fahrenheit. Although it’s not quite room temperature, it’s warm enough to allow the laser to be transported out of the lab and refrigerated inside a portable refrigerator. In 2019, a group from the US Army, MIT, and Harvard developed a terahertz laser the size of a shoe box that can change molecular gas.
Electronics have advanced in the time it took Hu to perfect his laser. Chips are becoming faster and faster due to improvements in their construction and the materials they use. (In 2020, a team in Switzerland created a nanoplasma chip that, once more, could only transmit 600 milliwatts of terhertz waves in a laboratory setting.) Although greater advancements are desired by electrical engineers, developing terahertz components is no longer a pipe dream.
“Now we can really make really complicated systems on the chip,” says Ruonan Han, an electrical engineer at MIT. “So I think the landscape is changing.”
“What’s happened over the last thirty years is that progress has been made from both ends,” says Mark Sherwin, a physicist at the University of California, Santa Barbara’s Terahertz Facility. “It’s still relatively rare, but I would say, much, much, much more common … and much easier.”
In a world where new technologies come and go in cycles of excitement and disappointment, such decades-long durations are typical. Terahertz is no different among engineers.
The future of terahertz technology
The two realms attempting to enter the terahertz black zone from either end are still mainly isolated for the time being. Nevertheless, they are providing the scientific community with new skills in a variety of fields.
Communication could be accelerated by some of those skills. Microwaves power your Wi-Fi, and terahertz, which has frequencies higher than microwaves, might create a stronger connection that is orders of magnitude quicker. It could also produce a lightning-fast connection between fibre optics and USB via a cable.
Terahertz waves are also ideal for detecting substances. “Almost every molecule has a ‘fingerprint’ spectrum in the terahertz frequency range,” says Sherwin. That makes terahertz waves optimal for picking out chemicals like explosives and the molecules in medicines. Astronomers already use that ability to look at the chemical compositions of cosmic dust and celestial objects. Closer to Earth, Han envisions a terahertz “electronic nose” that could even discern odors in the air.
The far infrared is also perfect for scanning individuals and objects because of their terahertz traces. With the added benefit of avoiding potentially dangerous ionising radiation like X-rays, terahertz waves can see through materials, like clothing, that light cannot. The technology has already piqued the interest of security screeners.
Terahertz waves’ inability to pass through water, air, or the human body is their only scanning property. However, that is not a barrier to medicine. A researcher may use a terahertz device to scan a mouse’s brain, or a doctor could use it to screen for minute signs of skin cancer that X-rays could miss.
Han imagines a terahertz “electronic nose” that may detect airborne scents closer to Earth.
Hu thinks the research is still early days. “If we can develop tools that can really see something and not take forever to scan some area, that could really entice potential practitioners to play with it,” he says. “That’s an open-ended question.”
Equipment that uses the sought-after far-infrared waves is just not yet ubiquitous because a large portion of the terahertz gap is still blank on researchers’ maps.
“Researchers really don’t have a lot of chances to explore what [terahertz waves] can be good at,” says Han. So, for now, the faster, more sensitive world inside the gap remains largely in their imagination.
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