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In the early 2010s, LightSquared, a multibillion-dollar startup that promised to revolutionize cellular communications, filed for bankruptcy. The company hasn’t figured out how to prevent GPS signals from
In the early 2010s, LightSquared, a multibillion-dollar startup that promised to revolutionize cellular communications, filed for bankruptcy. The company hasn’t figured out how to prevent GPS signals from being jammed. Now Penn engineers have developed a new tool that could prevent such problems from occurring again: a tunable filter that can successfully prevent interference even in the higher frequency ranges of the electromagnetic spectrum.
“My hope is that this will enable the next generation of wireless communications,” says Troy Olsson, associate professor of electrical and systems engineering (ESE) at Penn Engineering and senior author of the new paper. Nature Communicationexplains the filter.
The electromagnetic spectrum itself is one of the modern world’s most valuable resources; Only a small portion of the spectrum, specifically radio waves, which are less than a billionth of a percent of the total spectrum, is suitable for wireless communications.
Bands in this part of the spectrum are closely monitored by the Federal Communications Commission (FCC), which recently introduced Frequency Band 3 (FR3), which includes frequencies from approximately 7 GHz to 24 GHz, for commercial use. (One hertz is equivalent to one oscillation of an electromagnetic wave passing a point every second; one gigahertz, or GHz, is one billion oscillations per second.)
Today, wireless communications mostly use lower frequency ranges. “We are now running from 600 MHz to 6 GHz,” says Olsson. “This is 5G, 4G, 3G.” Wireless devices use different filters for different frequencies, resulting in multiple filters that take up a lot of space to cover all frequencies or bands. (A typical smartphone contains more than 100 filters to prevent signals from different bands from interfering with each other.)
“The FR3 band will most likely be used for 6G or Next G,” says Olsson, referring to next-generation cellular networks, “and the performance of small filter and low-loss switch technologies in these bands is currently highly limited. Having a tunable filter in these bands will be useful with many different switches.” It means you don’t need to install more than 100 filters on your phone. A filter like the one we created is the most convenient way to use the FR3 band.”
One of the complications of using high frequency bands is that many frequencies are already reserved for satellites. “Elon Musk’s Starlink operates in these ranges,” says Olsson. “They’ve already been removed militarily from a lot of the lower echelons. They’re not going to give up radar frequencies or satellite communications in those exact bands.”
As a result, Olsson’s laboratory colleagues Mark Allen, in collaboration with ESE Professor Alfred Fitler Moore and ESE Associate Professor Firuz Aflatuni and their respective groups, designed the filter to be tunable; so engineers can use it to selectively filter different frequencies. It’s better than using individual filters. “Tunability will be very important, because at these higher frequencies you can’t always have a block of spectrum dedicated solely to commercial use,” Olsson continues.
What makes the filter tunable is a unique material called “yttrium iron garnet” (YIG), which is a mixture of yttrium, a rare earth metal, with iron and oxygen. “The thing about YIG is that it emits a magnetic spin wave,” says Olsson, referring to the type of wave created in magnetic materials when electrons spin synchronously.
Under the influence of a magnetic field, the frequency of the magnetic spin wave produced by the YIG changes. “By tuning the magnetic field,” says Xingyu Du, a postdoctoral researcher in Olsson’s lab and first author of the paper, “the YIG filter provides continuous frequency tuning over an extremely wide frequency range.”
As a result, the new filter can be tuned to any frequency from 3.4 GHz to 11.1 GHz, covering most of the new space the FCC has opened up in the FR3 band. “We hope to show that a single adaptive filter is sufficient for all frequency ranges,” Du says.
Besides being customizable, the new filter is also very small; It’s about the size of a quarter, unlike previous-generation YIG filters that resemble large index card packages.
One of the reasons why the new filter is so small and could therefore be installed in mobile phones in the future is that it requires very little power. “For the first time, we have developed a circuit with zero static power and magnetic bias,” says Du, referring to the type of circuit that creates a magnetic field without needing any energy other than random pulses to readjust the field.
Although YIG was discovered in the 1950s and YIG filters have been around for decades, combining the new circuit with ultrathin YIG films micromachined at the Singh Nanotechnology Center significantly reduced the power consumption and size of the new filter. “Our filter is 10 times smaller than existing commercial YIG filters,” Du says.
Source: Port Altele
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