To the physicists among us:

I'm in the process of planning a very lightweight mini drone that flies with the help of radio signals that's surrounding it.

I'm targeting 100 MHz.
I calculated the amount of energy (Joules) of it and just when I did change the formula from E=h*f to Power=E/time I realized that time is basically going to be infinite and now I am stuck finding a solution to this.

I can't just use a potential infinite amount of time in this equation and need a workaround.

Any help is appreciated.

E=h*f is a energy of a single photon with that freq. The equation you want is the antena gain equation or eletromagnetic field equations.
Antena deals with longer range electromagnetic waves and ability to extract energy from them (warning it aint easy to get that energy back from rf...) and field equations are more accurate for closer ranges but might be easier to work with (IN THEORY, depends on approach and requirements)
As a rule of thumb, energy decreases with square of distance, that will be good estimate of best case scenario.
It will be the same in both antena or field form. Electromagnetic field equations are basicaly maxwel equations and antena equations are rf isotropic antena equations and other connected to it.
Just dont expect it to get any power at any resonable distance, look that is why wireless charging is shit. That drone is not imposible but i would be looking at the best avaliable gear and the freq is working

dont pick random freq because of it
look at different ones and determine which tech is the: cheapest, easiest, best

@Gregozor2121 ideally you'd use a frequency band that has little, or at least *below average*, noise.

@Parzi Dosent matter in this application, if i understood correctly he wants to send power not just commands so he will have to send A METRIC FUCKTON of power anyway.

Forget about it. It will not run the motor. Not even barely.

@Gregozor2121 no, I don't want to send power. I want to receive power.

@Parzi I first wanted to use gamma rays due to the very high frequency, but I would not be able to find a sufficient amount of gamma rays around me (which is good from a health perspective) thus it is not a reliable source of energy.

If I were to use the visible light from the sun, I would not be able to use it at night (Batteries would come in handy here, but my point is to not use batteries in the drone).

If I use LoRa signals, I would not receive any useful amount of signal energy at all.

It kinda sucks that it all is inversely proportional.

@Gregozor2121 I'm choosing the freq depending on the signal availability and the signal energy. Trying to find the right balance and adjusting the electronics depending on that.

@-ANGRY-STUDENT- The energy density is by far too low. Back when AM was a thing, you could use an antenna and some elementary electronics to directly drive a very small speaker without amplifier, but that's it. This is orders of magnitude less than what you need for motors.

You'd need to send up bundled radio energy from a directed ground antenna and LOTS of radio power - I remember there were experiments with microwaves. Just using what's there anyway won't do, except with solar of course. And even that wouldn't work with a helicopter like drone, only with conventional wings.

Maybe if you use a dish and try to aim at the drone automatically?

@Fast-Nop you're right. I would have to build my own electronics in a much smaller scale of nano to make this type of thing work. Besides of that I see no practical use for a drone of that small size (Medical maybe, but I doubt that). I will ditch the idea of using rf signals as an energy source and maybe use it in a few decades when I have the proper knowledge, time, equipment to experiment on such a small scale and practical use.

But I will still build a lightweight drone :)

@Gregozor2121 thanks for the help

@-ANGRY-STUDENT- I think conventional aviation has some cues.

If you want something that doesn't need a runway or that can stand still in the air, then it's vertical rotor axis like a heli.

If you want something efficient, you need horizontal rotor axis and wings like a plane.

If you want long airtime but don't need range, it's large wing span. That increases air drag, but delivers the same uplift at less speed. Since uplift is (I think) linear with speed, but actual air drag goes with the third power, that works out.

@Fast-Nop Also, if you don't need maneavuerability, speed and you don't mind having less influence on the movement of the craft than wind has, you can always use a balloon.

@Fast-Nop With large enough wings and maybe solar panels, you might even get a better range than a small, fast horizontal axis drone. But for that you would probably have to go full albatros, both in design and flight strategy.

@Lor-inc Yeah or even fixing a balloon with some lightweight fishing line so that it won't just go away.

@Fast-Nop but isn't long airtime proportional to range?

@-ANGRY-STUDENT- No. Airtime * speed = range. Both are design variables.

@Lor-inc so that is the same thing as s=v*t, if I understand it correctly.

@-ANGRY-STUDENT- It is exactly that and nothing more. I think there are more complicated rules where you also consider that planes with a good glide ratio can play seagull and climb to several kilometers at little cost, then proceed to glide for another significant distance.

Oh so you dont even suppy external power but you want to use noise?
It might be possible but if you are asking that question... you wont make it. Even with kW microwave transmitter it would be on the border of posibility and you would still have to have the transmitter nearby. They only thing you can try is nanotech or extremaly light ion engine.construct but you have to find a way to create HV from thin air... Might be possible with microwaves but... you clearly dont have a gear for it yet. Also you will never lift anything useful with it.

Also other people posted some correct things too.
-plane is more efficient, + more space for reciever
-you wont get any serious RF power unless you are under AM tower.
-Solar panels have a lot of efficiency to other solutions. Rf intencity is shit, xrays and gamma too, ionising radiation is VERY difficult to capture because of its ability to fuck with anything. You would need thick insulated plates to extract that energy. Or some kind of molecule with huge crosssection that can use it... but still it would be shit.
Visible spectrum and solar are your best bet + batteries for night.