Filters with adjustable frequencies make phones less crowded

     In modern communication, wireless devices use different filters for different frequencies, such as 5G, 4G, 3G, in order to cover all frequencies or bands need to use a large number of filters, and these filters will take up a lot of space. With the continued evolution of communication standards, 6G will also enter commercial use in the future, which means that more filters need to be added to communication equipment, occupying the limited space in the equipment.

     To solve this conundrum, the University of Pennsylvania research team has designed an adjustable filter that can be used to selectively filter different frequencies without having to use a separate filter.

     The key to making the filter adjustable is a unique material, a mixture of the rare earth metal yttrium and iron oxide - "yttrium iron garnet" (YIG). YIG is special in that it propagates magnetic spin waves, the type of wave that is generated in a magnetic material when electrons rotate in a synchronous manner.

     When exposed to a magnetic field, the magnetic spin waves generated by YIG change frequency, so as long as the magnetic field is adjusted, the YIG filter can achieve continuous frequency tuning over an extremely wide frequency band. The researchers said that the filter frequency can be arbitrarily adjusted between 3.4GHz and 11.1GHz, which basically covers most of the civilian communication spectrum opened up by the FR3 band (7.125-24.25GHz).

     In addition to being adjustable in frequency, the filter is also very small, about the size of a quarter, 10 times smaller than the YIG filter currently commercially available, and because the researchers designed a zero-static power magnetic bias circuit for it, the circuit does not require any energy to generate a magnetic field, only the occasional pulse to readjust the field, so the power consumption is extremely low.

     In fact, YIG was discovered as early as the 1950s, YIG filter has existed for decades, and the innovation of this research team is that not only with the characteristics of YIG filter has adjustable functions, but also greatly reduce the power consumption and size of the filter, so the future filter is very expected to be applied to mobile phones and other types of communication equipment.