# Can I send an electromagnetic wave to a specific point?

• I
• nlopwer
In summary, the person is asking if it is possible to create and send an electromagnetic wave to a specific point in a room with a margin of error of 1cm, using a frequency range of 250khz - 500khz. However, this is not possible due to constraints in beamwidth and the only feasible option would be to use a laser.

#### nlopwer

TL;DR Summary
I want to know if it is possible to make and send an electromagnetic wave to a specific point in a room.
Since I'm computer engineer and don't have much experiences with electromagnetism, I'd like to know if it is possible to make an electromagnetic signal (250khz - 500khz) and send it to a point (with an error of maximum 1cm) in a room. If yes which devices do I need to setup my experiment?

Your problem is ill-defined. Do you want a single frequency? Do you want signal zero outside yourr 1cm?
Why don't you take a step back and describe what you are actually attempting to do.

Orodruin, topsquark and Ibix
nlopwer said:
TL;DR Summary: I want to know if it is possible to make and send an electromagnetic wave to a specific point in a room.

Since I'm computer engineer and don't have much experiences with electromagnetism, I'd like to know if it is possible to make an electromagnetic signal (250khz - 500khz) and send it to a point (with an error of maximum 1cm) in a room. If yes which devices do I need to setup my experiment?

As Hutch said ... you problem is a bit il-defined
But going on what you have stated so far, the answer would be, no.
A signal somewhere in the range of 250 - 500 kHz, the radio/EM signal is going to
propagate out in many/all directions from the antenna ( depending on the style of antenna)
Making a direction antenna for such a low frequency would be near impossible.
The higher the frequency, the easier it is to make a signal directional, but even up into
the 10's of GHz, it's still going to be a very broad beamwidth over the distance of an average room
between the TX and RX. Really narrow beamwidth wouldn't really come into a usable possibility
till freq's in the 100's of GHz - THz range.

The ONLY way that it would be possible, off the top of my head aware of for such a narrow constraint in beamwidth, a cm or so would be a laser. Anything considerably lower in frequency than that of ""light"" IR, VIS or UV, via a collimating lens, is going to spread out and pretty much fill the room.

cheers
Dave

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berkeman, hutchphd and Ibix
It's rather like shining a light down a microscope to create a small spot. We can't make the spot much smaller than the wavelength, which in the present case is in the order of 1 km.

hutchphd