Shaping complex microwave fields in reverberating media with binary tunable metasurfaces
Shaping complex microwave fields in reverberating media with binary tunable metasurfaces
The resonant unit cell (middle) and its two operating states
The resonant unit cell (middle) and its two operating states
Standard deviation of the transmission between antennas (S) and (R) for 11000 random configurations and 10 positions of (S)
Standard deviation of the transmission between antennas (S) and (R) for 11000 random configurations and 10 positions of (S)
Mathias Fink and his team at the Langevin Institute have managed to rise nearly 10 times, or more precisely by 8.5 dB, the signal received by an antenna.

"We have, in some way, recycled the reverberating waves in a room," says Mathias Fink in an article in a Scientific Reports article published by the Nature review.

There is no amplification, so no increase in the background noise, but just a better use of the existing resource.

The signal received by an antenna is the sum of all the waves arriving on it, coming from, among others, multiple reflections from walls, furniture, etc. All these waves do not arrive in phase, some are offset. Instead of strengthening, they can even annihilate like sound waves. As these offsets are random, the resulting signal is, on average, lower.

It is nearly impossible to put all these waves in phase. But the team from the Langevin Institute realized that, by correcting only a portion, the reception improving was impressive.

For this purpose, 3 x 4.5 cm copper rectangles reflect the waves without modification, or delay them by half a period. An area of 0.4 m², with 102 of these pellets, is enough for a room.

How to choose which copper parts must be activated? Through the receiver which measures the received power: if it is too low, it controls the activation of some copper rectangles to achieve optimal focus on the antenna.

Consumption is minimal since a low signal is enough to switch a rectangle in a condition or the other.

According to Ping Sheng from the Hong Kong University of Science and Technology, we could apply this principle to sound waves. In a noisy room, a person will be able to talk to another at the other end, as if they were neighbors.
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What they think about

Ce procédé inventé par Mathias Fink n'est pas récent, il remonte presque à une vingtaine d'années. Il avait nommé cela "le miroir à retournement temporel", le procédé consistant à remettre en phase un certain nombre d'ondes réverbérées avec l'onde directe grâce à des lignes à retard. Au début, il avait conçu le système avec des ondes acoustiques, mais cela s'applique à n'importe quel type d'ondes vibratoires, y compris électromagnétiques.
En toute modestie, je signale que j'ai utilisé le miroir à retournement temporel dans un roman que j'ai publié en 1999, "Cosmic Blues", (Flammarion), qui expliquait comment on pourrait détruire un satellite ou une station spatiale avec ce système. C'est Mathias Fink lui-même qui m'avait expliqué la chose...
Ceci dit, avec le diversity, y a-t-il encore vraiment des problèmes de réception HF ?

Rating: 4 of 5 Stars!