# What are microwave doors made of? **URL:** \ **Category:** Factual Questions\ **Created:** [June 13, 2003, 11:18am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535 "2003-06-13T11:18:21Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Swoop](https://avatars.discourse-cdn.com/v4/letter/s/b77776/32.png) [@Swoop](https://boards.straightdope.com/u/Swoop)\ **Post date:** [June 13, 2003, 11:18am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/1 "2003-06-13T11:18:21Z")
and how effective are they at trapping the emissions? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 13, 2003, 11:38am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/2 "2003-06-13T11:38:17Z")
They usually contain a metallic mesh, which should be an effective reflector of microwave frequencies. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [June 13, 2003, 11:40am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/3 "2003-06-13T11:40:21Z")
The reason they don’t let the microwaves through is that they’re lined with metal mesh, as you can see inside the glass. The metal reflects the microwaves back into the oven. [Here](http://home.cvc.org/microwaves/eeafs8.htm) is some info: > [@](#): > > In FDA’s experience, most ovens tested show little or no detectable microwave leakage even after years of use in the home. If there is some problem and you believe your oven might be leaking microwaves, contact the oven manufacturer, your state health department, or the local FDA field office. As for the holes in the mesh, don’t worry about them: > [@](#): > > From [here](http://www.hot-house.co.uk/microwave.htm) > Microwaves used in a cooker have a wavelength of around 12 cm, the metal mesh in the glass door has holes of a smaller size, which stops microwaves escaping and cooking people standing in front of it. ---
**Author:** ![postcards](https://avatars.discourse-cdn.com/v4/letter/p/8e8cbc/32.png) [@postcards](https://boards.straightdope.com/u/postcards)\ **Post date:** [June 13, 2003, 12:30pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/4 "2003-06-13T12:30:54Z")
You don’t even need the glass in the door. I suspect it’s there more to give a sense of security. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 13, 2003, 12:35pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/5 "2003-06-13T12:35:06Z")
> [@](#): > > \*Originally posted by postcards \* > \*\*You don’t even need the glass in the door. I suspect it’s there more to give a sense of security. \*\* Eh, not exactly. On it’s own the mesh is fairly fragile and unsturdy, and it would be easy for someone to carelessly kcock into it and tear it or push it out. It isn’t glass, either, it’s plexiglass, or occassionally some other polycarbonate plastic. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 13, 2003, 12:44pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/6 "2003-06-13T12:44:25Z")
The mesh in my microwave is a punched aluminium or steel sheet. It’s not fragile at all. But I’d much rather be able to wipe down a smooth plastic sheet than try and get icky stuff out of a mesh. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 13, 2003, 12:54pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/7 "2003-06-13T12:54:18Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\*The mesh in my microwave is a punched aluminium or steel sheet. It’s not fragile at all. But I’d much rather be able to wipe down a smooth plastic sheet than try and get icky stuff out of a mesh. \*\* The ones I’ve seen have a mesh that’s more of a foil sandwiched between two sheets of plexiglass or similar plastic. On it’s own it couldn’t stand up to an angry housefly, let alone normal kitchen wear and tear. They must make things tougher Down Under. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 13, 2003, 12:58pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/8 "2003-06-13T12:58:31Z")
It’s just an ordinary Panasonic. Anyway the amount of energy that will get through a mesh is given by: 1 - _e_[sup]-2_x_/λ[/sup] where λ = wavelength x = aperture size My microwave has holes 1 mm (0.001 m) in diameter in the mesh. The microwave operates as 2.45 GHz, so: λ = 3 x 10[sup]8[/sup] / 2.45 x 10[sup]9[/sup] = 0.12 m. Plugging the numbers in: 1 - _e_[sup]-(2 x 0.001 / 0.12)[/sup] = 0.017 = 1.7%. So the mesh stops 98.3% of the incident microwave energy from escaping, but 1.7% gets out. A good reason not to stand staring into the microwave while it’s operating. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [June 13, 2003, 3:07pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/9 "2003-06-13T15:07:09Z")
Uh, so as not to be alarmist, I think what **Desmostylus** means by “incident microwave energy” is the stuff that isn’t dissipated anywhere else, like your food. So that 1000w microwave isn’t necessarily going to shoot 17 watts of RF energy at you. Also, **Desmostylus** , that’s a pretty nifty equation and I’d never have though to dig it up. But would there be any difference between a grounded mesh vs. an ungrounded one? I have no idea. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 13, 2003, 3:38pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/10 "2003-06-13T15:38:03Z")
> [@](#): > > \*Originally posted by Balthisar \* > \*\* But would there be any difference between a grounded mesh vs. an ungrounded one? I have no idea. \*\* Doesn’t make any difference. Why would it? We’re talking about e-m waves in space (air, but close enough), the concept of “ground” doesn’t really apply. The equation gives the proportion transmitted vs reflected. It also assumes negligible dissipation in the mesh, which doesn’t affect these calculations terribly much. And “incident microwave energy” just means what it says - the microwave energy hitting the door. ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [June 13, 2003, 4:05pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/11 "2003-06-13T16:05:02Z")
Thanks for the equation, **Demostylus**. That would be why the #%(#!& microwave in the lunchroom wipes out my wireless ethernet connection. 🙂 ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [June 13, 2003, 6:20pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/12 "2003-06-13T18:20:50Z")
Note that the mesh exists only in the door for the purposes of preventing microwaves from going thru the glass. If there were no glass, the microwave would be shielded in unperforated metal like the rest of it. BTW, the 2nd opening of concern is for venting, usually from the side of the chamber out thru the back, with nice turns in between. Usually only messed up by DIY repairs or when the duct gets coated with stuff. The 3rd source of leakage is around the edge of the door. If the door isn’t closing nicely, you’ve got a problem. ---
**Author:** ![Gelaan](https://avatars.discourse-cdn.com/v4/letter/g/bbe5ce/32.png) [@Gelaan](https://boards.straightdope.com/u/Gelaan)\ **Post date:** [June 13, 2003, 7:47pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/13 "2003-06-13T19:47:50Z")
> [@](#): > > The 3rd source of leakage is around the edge of the door. If the door isn’t closing nicely, you’ve got a problem. I am (among other things) an FCC-licensed broadcast engineer (GROL grandfathered from FCROL) and have in my bag of tricks a field-strength meter that functions at microwave oven frequencies and is calibrated, traceable to NIST standards. I can put that meter up to the glass on the door of most microwave ovens and the needle barely budges, but if I move it to the door, the needle pegs. Demonstrations freely available, but you’ll have to come over to my house, as I don’t make house calls. ---
**Author:** ![Gelaan](https://avatars.discourse-cdn.com/v4/letter/g/bbe5ce/32.png) [@Gelaan](https://boards.straightdope.com/u/Gelaan)\ **Post date:** [June 13, 2003, 7:49pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/14 "2003-06-13T19:49:04Z")
> [@](#): > > \*Originally posted by Gelaan \* > \*\*I am (among other things) an FCC-licensed broadcast engineer (GROL grandfathered from FCROL) and have in my bag of tricks a field-strength meter that functions at microwave oven frequencies and is calibrated, traceable to NIST standards. > > I can put that meter up to the glass on the door of most microwave ovens and the needle barely budges, but if I move it to the door crack, the needle pegs. > > Demonstrations freely available, but you’ll have to come over to my house, as I don’t make house calls. \*\* ---
**Author:** ![Swoop](https://avatars.discourse-cdn.com/v4/letter/s/b77776/32.png) [@Swoop](https://boards.straightdope.com/u/Swoop)\ **Post date:** [June 20, 2003, 11:19am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/15 "2003-06-20T11:19:33Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\*It’s just an ordinary Panasonic. > > Anyway the amount of energy that will get through a mesh is given by: > > 1 - _e_[sup]-2_x_/λ[/sup] > > where > > λ = wavelength > x = aperture size > > My microwave has holes 1 mm (0.001 m) in diameter in the mesh. > > The microwave operates as 2.45 GHz, so: > > λ = 3 x 10[sup]8[/sup] / 2.45 x 10[sup]9[/sup] = 0.12 m > > Plugging the numbers in: > > 1 - _e_[sup]-(2 x 0.001 / 0.12)[/sup] = 0.017 = 1.7%. > > So the mesh stops 98.3% of the incident microwave energy from escaping, but 1.7% gets out. A good reason not to stand staring into the microwave while it’s operating. \*\* Thanks for that equation, **Des** , that’s really interesting. I don’t get where you got the one value from: λ = 3 x 10[sup]8[/sup] / 2.45 x 10[sup]9[/sup] = 0.12 m. where does 3 x 10[sup]8[/sup] come from? (apologies if I’ve missed something obvious) ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 20, 2003, 11:32am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/16 "2003-06-20T11:32:05Z")
3 x 10[sup]8[/sup] metres per second is the speed of light. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 20, 2003, 12:12pm UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/17 "2003-06-20T12:12:12Z")
To write the thing out properly: λ = _c_ / f = 3 x 10[sup]8[/sup] ms[sup]-1[/sup] / 2.45 x 10[sup]9[/sup] s[sup]-1[/sup] = 0.12 m. ---
**Author:** ![Swoop](https://avatars.discourse-cdn.com/v4/letter/s/b77776/32.png) [@Swoop](https://boards.straightdope.com/u/Swoop)\ **Post date:** [June 24, 2003, 11:15am UTC](https://boards.straightdope.com/t/what-are-microwave-doors-made-of/181535/18 "2003-06-24T11:15:21Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\*3 x 10[sup]8[/sup] metres per second is the speed of light. \*\* > [@](#): > > \*Originally posted by Swoop \* > \*\* (apologies if I’ve missed something obvious) \*\* :smack: 😃