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Is it possible to build a transmitter inside of working .45 caliber bullet?

Specifications:

  • The bullet must be fireable from a .45 semi-automatic pistol

  • Transmitter must function after firing

  • Transmitter must function after embedding itself into a human being (assume that the bullet does not impact bone and does not exit the target)

  • The signal from the bullet must be detectable at a range of 30 meters

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    $\begingroup$ What would you like it to transmit and is this line of sight or around corners? $\endgroup$ Commented Apr 6, 2022 at 2:32
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    $\begingroup$ What signal is it transmitting? Is it just "I am here," which can be an extremely low bandwidth signal, or is it trying to transmit data it acquired? $\endgroup$
    – Cort Ammon
    Commented Apr 6, 2022 at 4:13
  • $\begingroup$ @EveninginGethsemane Around corners. $\endgroup$ Commented Apr 6, 2022 at 12:55
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    $\begingroup$ Ah, that excludes light-modulation which would have been very easy comparatively-speaking, thanks for the clarification. $\endgroup$ Commented Apr 6, 2022 at 13:18
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    $\begingroup$ Are you asking in essence if there exists a small, ruggedized transmitter that can handle the acceleration that a bullet is subject to and still function? Does the firearm have to be stock or can it be specialized in some way? Does it have to be fired with the same force as a real bullet, or can it be subsonic? It'll be hard to find electronics which can survive >100,000g. $\endgroup$
    – forest
    Commented Apr 6, 2022 at 19:24

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Yes, it surely is.

The radio proximity fuze as used in the Second World War functioned after being fired from (in the example image at the link) a 40 mm Bofors gun, despite requiring an onboard battery sufficient to operate a cold cathode vacuum tube circuit.

Build the circuit on a chip and power it with a small supercapacitor, and it could easily be made to fit in a .45 Colt or .45 ACP bullet, and being all solid state, should readily survive firing and operate afterward.

Contrary to other answers, the bullet need not be made entirely of plastic -- the shell for the Bofors gun certainly was not, and the fuze transmitted well enough to hear its own echo in order to detect when it was "close enough" to a target to explode the shell. Given modern receiver technology, an antenna in the base of the bullet should readily transmit to a receiver near the gun out to reasonable handgun ranges (< 100 m).

Transmission from inside a body is a little more difficult, but there are "pill cameras" -- the size of a large capsule, these are swallowed to transmit pictures of the digestive tract as they pass through, and the signals are received outside the body (though these are short range, trading off battery life for range would give much more range without the need to run for 24 hours).

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  • $\begingroup$ What material does this bullet need to be made out of? I get that it does not need to be plastic for radio transparency, but you still want to maximize the probability that it will not fragment... copper-jacketed lead seems a bad choice. $\endgroup$
    – John O
    Commented Apr 6, 2022 at 13:45
  • $\begingroup$ Material choice is governed by engineering decisions in design. If this is intended to be a tracking or telemetry device, you also have to be concerned with the "subject" seeking out a hack doctor to get the "bullet" removed and/or wound treated, even if it's not life-threatening. $\endgroup$
    – Zeiss Ikon
    Commented Apr 6, 2022 at 13:48
  • $\begingroup$ I think everyone is a little fixated on making the transmitters contain everything they need within the bullet casing even after deployment. It doesn't have to only use what is in the bullet at the time of firing, for example, ieeexplore.ieee.org/abstract/document/7389359 or ncbi.nlm.nih.gov/pmc/articles/PMC5751732 $\endgroup$
    – ColleenV
    Commented Apr 6, 2022 at 16:37
  • $\begingroup$ @ColleenV That doesn't work if there's no separate ground. You need to have two conductors that are electrically isolated to form the radiating element and ground reference. The body can act as an antenna (you can demonstrate this, sometimes, by grabbing your car radio's aerial), but if you touch the ground (bare body metal or frame) it will blank the signal instead. $\endgroup$
    – Zeiss Ikon
    Commented Apr 7, 2022 at 13:49
  • $\begingroup$ I'm not suggesting a particular solution. The articles were just illustrations to show that if you know the environment bullet transmitter is going to be deployed into, you don't necessarily have to make it self-contained. $\endgroup$
    – ColleenV
    Commented Apr 7, 2022 at 13:57
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If the bullet is not made of metal, and you are willing to interrogate the device with a strong RF signal you could make something like an RFID. However, your performance will vary a lot. You need to be high frequency because the antenna is small, and if embedded in the body, the conductivity is high enough that your signal will be attenuated.

If you want the bullet to transmit, having a small power source is one problem, another is the power needed to transmit, through the body. You can potentially do some things like only broadcast infrequently (a good strategy) or try to use the body itself as an antenna, but power is probably limiting.

There are issues with the acceleration and reliability, but there has been sensors that have been put into 40 and 30 mm munitions.

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https://archive.jsonline.com/news/crime/milwaukee-police-to-deploy-high-tech-gps-trackers-on-fleeing-vehicles-b99551340z1-320827571.html/

I heard about shotgun ammo with same features. Do not think there be big problem to make .45 round. Electronic and power source is not an problem, problem will be with antenas for GPS/GSM/any other emission. You need to deploy them after hit and do not tear them by flesh. You can forget about Bluetooth and WiFi connection - human body is good absorber for used ferequences. Same problem with some RFID - need to have antena next to skin or use lots of power.

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  • $\begingroup$ They use shotguns for this because shotgun bores are considerably larger than 0.45 inches in diameter. $\endgroup$
    – Mark
    Commented Apr 6, 2022 at 22:21
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If you want the transmitter to still work after "embedding" itself into a human, then you'll have several problems.

The powder load should not be too powerful, so the bullet stays in instead of shooting through the target. This will also reduce acceleration and deceleration on the electronics.

Then, the bullet, or at least the part with the electronics, should not deform or mushroom on impact, which means it has to be hard, probably steel... which means it will tend to shoot through the target instead of staying in. You could come up with a compromise, with lead in front so it mushrooms, and the electronics behind, in a hard case.

All of this means it'll be much less deadly than a standard bullet.

Next comes the problem of frequency, antenna, and false comparison with proximity fuzes.

I'll tackle that first. The proximity fuze uses a tiny radar in the front of the shell. The electronics can handle acceleration in the gun barrel, but not deceleration at impact, since it is supposed to explode anyway. In addition, the radar uses a high-frequency directional antenna, which means most of the shell can be made of metal, with the fragile radio-transparent plastic only covering the tip where the fuze is, to let the RF beam out.

None of that applies to your idea, because you want an omnidirectional antenna so the receiver can pick up the signal anywhere, at a frequency that will go through flesh well enough so the RF gets out of the target and can be received.

So, let's look at RF absorption by salt water, which should be good enough to pass for flesh...

enter image description here

From this, it is obvious you will need a frequency below 10MHz, which means a rather large magnetic rod dipole antenna, which is a coil wrapped around a ferrite core. That will barely fit in a .45 bullet, and the ferrite will fracture on impact.

So, i think you will end up with a barbed flechette that stays out of the body. That would also allow to tag a car, for example. Or a bullet that deploys an antenna that stays out of the body, for example a wire coming out of the rear end. That way you can use a frequency high enough to allow for the tiny antenna that you need.

Or you could use an acoustic method: burning hot tracer bullet, and listen to the screams.

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so first of all, your bullet must be built from resin, have the transmitter device fixed in the resin, and the base of the bullet from detachable metal component, and depending on the gun you want to propose, try and find if you can elongate your bullet, optional...more space for transmitter device..

next..

the amount of propellant must be way little than the normal load,

also you must use deflagrating propellant and not explosive propellant. because deflagration propellants burn slower and don't impart a higher shock to the bullet as it's leaving its barrel.

the cartridge needs testing to measure the right amount of propellant to use with the proposed bullet , so that the bullet should not shatter at launch and impact.

I assume that you are talking about a pistol round .45 ACP

And finally considering all of the above and small propellant mass, if you want to launch the bullet..

!Then I suggest a mortar style angle launch, then you should make calculations for a curved ballistic trajectory, for the required range you want to achieve,..

why?..consider that, at the impact the bullet must have the least terminal velocity and energy,..so that the least impact force is achieved, which is necessary if you want your bullet internal device to withstand impact and remain functional.

so the transmitter I think it should be a seismometer sensor, so that way you know if something is approaching the sensor or departing..

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    $\begingroup$ Almost every word of this is wrong, as evidenced by the use of radar proximity fuzes in ordinary anti-aircraft ammunition. $\endgroup$
    – Mark
    Commented Apr 6, 2022 at 22:23
  • $\begingroup$ answer-ing will not allways be resonating with all readers, and how to make such device is out of my knowledge base. $\endgroup$
    – Cris
    Commented Apr 7, 2022 at 5:44
  • $\begingroup$ There is a big difference between a transmitter and a seismometer sensor, the rest is problematic and doesn't seem to have much relation to reality either. $\endgroup$ Commented Apr 7, 2022 at 22:12
  • $\begingroup$ a seismometer is basicly a vibration meter, wich is a very tiny chip found in evry smartphone, i was not implying a 2000 pound equipment.. $\endgroup$
    – Cris
    Commented Apr 8, 2022 at 5:54
  • $\begingroup$ @Mark, nope, read my answer $\endgroup$
    – bobflux
    Commented Apr 8, 2022 at 9:36

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