Ferrites-by-design for Millimeter waves and Terahertz Technologies (FeMiT)
The FeMiT project explained in 5 minutes Have you ever experienced connectivity issues with your mobile? What will happen if as expected there are much more mobiles, in your watches, your home appliances, your cars and in the machines that produce them in a factory? The huge data traffic would saturate the narrow spectrum of today’s networks. In fact, we are already experiencing an explosion in the data demand.1 That’s why with 5G we are shifting to higher frequencies, into the mm-waves, where plenty of bandwidth is available. A big challenge of mm-waves is that these only allow line-of sight propagation, making the transition to higher frequencies a real paradigm change, with the communications relying on myriads of closely scattered small antennas. Thus, besides working at tens to hundreds of GHz, the new communication devices will have to be cheap, low power and miniaturized. For instance, the circulators isolate emitting antennas from one another, acting as a traffic router for the waves only in one direction. This is an example of the ferrite non-reciprocal devices which will gain importance in this new context However, today, these only operate in the first portion of the mm-wave band, using external magnetic fields which makes them bulky and can only work at one frequency. The aim of FeMiT is Making them work at higher frequencies without external magnetic fields And making them reconfigurable to operate at different frequencies Before explaining how we plan to do this it is important to highlight that these devices exploit the phenomenon of ferromagnetic resonance: at a given frequency, the waves propagate through a ferrite or are absorbed, depending on their direction, and the resonance frequency is higher the larger is the magnetic anisotropy of the ferrite. So, for the mm-waves we need ferrites with very high magnetic anisotropy. The FeMiT Now, my idea is developing a new family of ferrites based on ε-Fe2O3 as it has two unique properties highly suitable for implementing innovative non-reciprocal devices in the mm-waves: First, a Japanese group has shown it displays ferromagnetic resonances well into the mm-waves, which can be increased or decreased by chemical doping.2-3 But the transmission losses, which are key to applications, are not characterized and the possibilities of chemical doping have not been fully explored, with relevant dopants
- verlooked.
On the other hand we discovered that the onset of large magnetic anisotropy is accompanied by a strain of the structure, a thousand times larger than in other magnetic transition metal oxides.4 This tells us that one can expect controlling the ferromagnetic resonance through strain, obtaining much larger responses than with a standard ferrite.