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Energy focusing | Time-reversal focusing of waves (Time-reversal targeting of waves)
Energy focusing | Time-reversal focusing of waves (Time-reversal targeting of waves)
Energy focusing by time reversal is used to create the focal point patterns corresponding to targeted microfigurines.
The two videos below show how a specific microfigurine can be targeted, while those in proximity remain unaffected. This can be transposed to a medical setting, where we wish to ablate a tumor using electromagnetic radiation.
Reference: https://news.byu.edu/news/lego-figurines-dont-stand-chance-against-time-reversal
The microfigurine position holds a sound emitter/microspeaker which emits a sound wave. The emitted sound wave is received by a receiver sensor found in a far-away position. If obstacles are present between the emitter and the receiver (e.g. other microfigurines), the sound may perform complicated reflections that will allow it to eventually reach the receiver. The sound may have to follow a complex path in time.
If we wish to focus sound on the microfigurine, or in other words to target it by sending sound from the far-away position, we would have to reverse the above path in time. In other words, we would have to play-back the signal.
This technique is termed time-reversal of waves.
Further reading: Time-reversal acoustics
Figure 1: A microfiguring is a specific position is targeted using sound energy focusing by time-reversal of sound waves.
Time reversal detection and imaging in the electromagnetic domain
Time reversal detection and imaging in the electromagnetic domain
An application where we perform illumination of the target area with the time-reversed returned echo.
https://wwwcp.umes.edu/engineering/time-reversal-detection-and-imaging-in-electromagnetics
Time reversal applications
Time reversal applications
Energy focusing/refocusing using time reversal of waves. Numerous applications including diagnostic/medical.
https://www.youtube.com/watch?v=1WcIejZd__w
"TIME-REVERSED ACOUSTICS"
"TIME-REVERSED ACOUSTICS"
1999, Scientific American
https://www.jstor.org/stable/26058488
(Please refer to the first paragraph)
Related scientific article: https://www.researchgate.net/publication/224026006_Time-reversed_acoustics
Time Reversal in MIMO Radar
Time Reversal in MIMO Radar
When targeting becomes stronger after each iteration (in each back-and-forth) as the transmitted waveform is adapted to the target and the environment and therefore becomes optimal. Improvement of signal-to-noise ratio.
Radar waveform - adaptive transmission scheme
Refocalisation de l'énergie des ondes par miroir temporel instantané
Refocalisation de l'énergie des ondes par miroir temporel instantané
ESPCI* : "Et si on faisait un miroir temporel instantané ? Défi relevé par les chercheurs, toute l'histoire ici !"
https://www.espci.psl.eu/fr/actualites/2016/une-nouvelle-approche-du-retournement-temporel
Dans une cuve remplie d’eau, si l’on vient perturber la surface (par exemple en appliquant un motif en forme de Tour Eiffel ou encore un "smiley") un paquet d’ondes va se propager autour de la perturbation.
Si l’on impose une brusque modification à la cuve, on fera apparaître un groupe d’ondes rétro-propagé, qui se refocalise exactement sur les points de la source, le motif mentionné.
En vidéo :
Motif simple : perturbation « ponctuelle »
Motif complexe : Tour eiffel
Motif complexe : smiley
Référence : Time reversal and holography with spacetime transformations doi:10.1038/nphys3810
*"L'histoire de l'école est marquée par les découvertes de ses sept prix Nobel" (Wikipedia)
Figure 2: Reference "Miroir temporel".
Time reversal in Massive MIMO beamforming
Time reversal in Massive MIMO beamforming
https://youtu.be/XBb481RNqGw?t=61
If a source emits a signal that is detected by our receiver, we can reverse the signal to target the source.
The process is termed source event reconstruction and specifically we refer to a signal processing technique which is called "time-reversal".
It represents a play-back in time and can be considered as a reverse game of pools (billiard). Or even a virtual boomerang.
In this video we have three sources (red, green, blue). They emit an impulse (pilot signal) which may be reflected on different buildings before reaching the receiver antenna. That antenna receives all reflections and registers both their direction and time of arrival. It then reconstructs the combination of direction and time to play-back the signal and reach the source optimally.
Figure 3: Time reversal in Massive MIMO beamforming
Radar - Phase conjugation - Time-reversed waves (TR wave weapons) - Radar TR wave weapons
Radar - Phase conjugation - Time-reversed waves (TR wave weapons) - Radar TR wave weapons
"Phase conjugate mirrors for radar frequency bands".
"Phase conjugate mirrors are capable of producing a time-reversed (TR) wave in direct response to a received ordinary wave. The mirror may be powerfully "pumped" with energy to produce a very large amplification of the time-reversed wave."
Time-reversed wave: "It is a solution to the wave equation and, as such, it applies to every kind of wave."
"Such a wave precisely retraces the path of the ordinary wave that stimulated it to be formed. So it possesses an "invisible wire" through space, back to the original position of whatever emitted its stimulus wave."
"Using several simple schemes (particularly pumped 4-wave mixing), extremely large amplification of the time-reversed (TR) wave can be cheaply and readily accomplished."
"A startling weapons capability therefore emerges when amplified TR waves are generated in response to received signals from a distant target:
(1) If any signal at all can be received from a distant target, a return TR signal of extreme power can be delivered directly to that target. Almost all of the transmitted TR signal energy will arrive at and in the distant target, even through a highly nonlinear medium or under scattering conditions. Hardly any of the energy will be lost enroute. If the target is fast-moving, a "lead correction" signal can be calculated and added to steer the return path.
(2) Since real-time holography can readily be accomplished using TR waves - and without first making holograms - geometrical forms (balls, shapes, hemispherical shells, etc) of energy can be created readily by interferometry (crossed beam techniques). Since the TR wave carriers do not disperse with distance, these interference energy forms can be assembled by crossed TR wave beams at great distances-even hundreds of thousands of miles. The energy appearing in such a distantly created energy form is limited only by the amount one cares to put in at the amplified transmitting end".
http://www.cheniere.org/books/excalibur/part4.htm
Holography (Holographic energy focusing/targeting)
Holography (Holographic energy focusing/targeting)
How do we create a three-dimensional pattern (holographic pattern) to target neurons at specific locations simultaneously.
Excerpts from https://www.simonsfoundation.org/2018/06/14/controlling-the-brain-with-holograms/ (FB)
"A technique called computer-generated holography can better target specific cells by using spatial light modulators to create three-dimensional patterns of light."
“Say there are 30 neurons we want to target; we can instruct our system to activate those neurons and only those neurons".
"The system integrates both optogenetics and calcium imaging, meaning that scientists can simultaneously monitor and control neural activity."
Featured publication: https://pubmed.ncbi.nlm.nih.gov/29713079/
Prior description of the technique (3D-SHOT): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5663714/
Inteference - Two-Point Source Interference Pattern
Inteference - Two-Point Source Interference Pattern
https://www.physicsclassroom.com/class/light/lesson-3/the-path-difference
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