This idea came out of the interest of exploring another area of the electromagnetic spectrum (outside the visible spectrum) more directly. Microwave ovens are so readily available, and a microwave ray could potentially have some destructive potential to electronic items. Thus I undertook it as an experiment, partly to see how well it would work and how destructive it would be, and partly just out of the curiosity of doing so. However, with the high voltages and currents involved any builders who do not pay uttermost care to safety have a serious risk of injury from working with the circuits and devices described here. If you still want to build a similar project, please read the warnings in the rest of the article and then make sure you are fully aware of the risks involved.
Most of the supplies you will need come from any microwave oven. Use an old one lying around, or look at dumpster sites and there will surely be some throw-away microwaves which are in perfect working condition. It is rare for any of the crucial components to break, so even a really old looking microwave should work but you might have to replace a fuse or something.
The guts of the microwave are taken out, and the circuit is kept intact. The transformer, capacitor, diode, and switches are then attached to the handle. Be sure that the cases of the transformer (and magnetron) are grounded (attached to the ground wire (third prong) on the power cable) to avoid a floating voltage that could hurt you when it is in close proximity to your body. To be on the safe side, design the handle so that conductive metal parts are very well insulated. My design has three layers - the coating on the wires, rated for the full voltage, covered by tape and air, followed by plastic insulation of the handle, followed by additional tape around the part of the handle where my hand will actually touch the gun. The transformer and magnetron are exposed but both are grounded, and would be hard to touch during operation. The wire going to the electrical outlet should contain a small knot inside the handle, that will prevent the wire from being pulled out of the handle during use.
The inside of the old remote control handle now contains the voltage doubler circuit and a pushbutton switch attached to the trigger. The magnetron will eventually be attached to the side.
Now that the handle is complete, it is necessary to work with the magnetron. It is necessary to consider microwave propagation, that is which way the microwaves will travel when exiting the magnetron. At first, I incorrectly thought that the microwaves would travel straight out of the magnetron, and I mounted the magnetron on top of the handle as seen below.
The magnetron in this photo is attached to the top of the handle, with the assumption that microwaves would travel out of it along the central axis. This is incorrect!
After further research on this topic I realized that the microwaves actually exit the magnetron in radial directions, that is in directions perpendicular to the pink ceramic insulator. The magnetron mounting shown in the above photo then is pretty useless as a directed energy device, because microwaves are going in all directions except where they are expected to go. To overcome this difficulty, it is first necessary to mount the magnetron so the metal tip is pointing upwards (thus microwaves are traveling in the same plane as the shooting direction), and also to install a horn antenna that will give the microwaves some directionality (so the microwaves travel mostly towards the target). After doing some reading on the subject, I designed the horn antenna to have an opening of 3.5x1.7 inches, length along the side of 2.88 inches, and outer rectangle dimensions of 5.34x4.33 inches. This is supposed to provide some sort of gain for 2.45GHz, which is the magnetron frequency. This horn also needed to be coupled to the magnetron through a wave guide, and for this I used the horn opening dimensions for one cross-section, while the length was determined by the magnetron size, so that the magnetron output tip would be in the center between the back wall of the wave guide and the opening of the horn. I made a draft of the design in CAD, and then combined parts so they could be cut out from a single sheet of stainless steel and then bent to shape to create the horn and waveguide. A waterjet cutter was used to make the design, which required an 8x18 inch sheet.
The freshly cut pieces for the combined wave guide and horn antenna. These will be bent to lock in place with each other, and then bolted on to the magnetron.
The completed horn antenna is attached to the magnetron.
The change in magnetron mounting required some modifications to the handle, so it could be attached along its side rather than on top. After this was done, the magnetron gun is now ready for testing. It is a good idea to double-check the electrical circuit at this point. Be sure that you are using a fuse!
Final version of the microwave gun, with properly mounted magnetron and horn antenna for proper microwave directionality.
The microwave gun was an interesting concept, but it has not proven to be very useful. I have been able to reset the time on my alarm clock by shooting it with microwaves from about 5 feet away, so there is potential for interference with electronic systems. It is also possible to reset calculators or other digital devices, although I have not tried it on my laptop or cell phone for risk of ruining something. However no permanent damage was done to either the alarm clock or calculator, they were simply reset. If the gun is pointed away from the cell phone, there is no interference with call quality (as opposed to standing in front of a microwave oven, suggesting this project actually has less undesired leakage than a consumer device). As an additional feature, the gun can be used to light fluorescent bulbs (even ones without the attached starting circuitry). This is also a way to test a microwave oven for leakage, although be aware that it takes quite significant leakage to light the bulb, that is similar levels would be more easily noticeable through heating of your body. I made a short recording of the microwave gun used to light up a fluorescent bulb that is not connected to anything - you can download it here. The video was necessary because my camera did not adjust quickly enough to the light, you can see in the video that when the bulb lights up it is just a white blur.
The above findings suggest that the gun may have some use in attacking an electronic access control system, such as RFID scanners, where the scanning device is within reach. The extent of the attack would be dubious though, since I was not able to destroy or permanently affect any electronic devices. It would be difficult to use the gun against a camera, since cameras can see farther than 5 feet, and security cameras usually have a metal case that would reflect microwaves (on the other hand, if microwaves can be delivered inside the metal case this would reflect them towards the camera circuits). The gun would not be useful for any sort of long-range attacks, unless a better antenna is used, such as a parabolic reflector. However the large antenna would make this a stationary device, and with a much better antenna it makes sense to use better microwave generation techniques than a consumer microwave circuit, for instance discharging capacitors through the magnetron to create a powerful pulse. The final conclusion is that creating any significant EMP activity is not practical using a regular microwave oven circuit. A better approach for a portable device may be to use very large capacitor banks and an exploding coil inside the horn antenna, and I might explore this possibility in the future.