On Fri, Dec 12, 2003 at 08:54:29AM -0800, Alois Bauer enlightened us
thusly
> >
> > > An interesting idea for testing your microwave cooker was passed
> > > to my wife. If you want to test your Microwave oven for leakage,
> > > put your mobile phone inside, and call it. If it rings, the
> > > microwaves got in, so they could get out, therefore it's leaking.
> >
> maybe this test does not prove low or high leakage at the MW cooker's
> working frequency of typically 2.45 GHz. As it is not neccessary and
> more expensive to make broadband (in frequency) RF gaskets for a
> single-frequency application, often resonant structures are used. For
> example the width of the overlap of the oven's door is made lambda/4
> wide and the contacting zone is only in the inner edges. The
> surrounding gap acts like a waveguide (like a slotline) which an open
> end around the outer edges of the door. This open is transformed into
> a short, in reality in a very low impedance after one quarter of
> wavelength. Low impedance means that the electric field there is quasi
> shorted and so nearly no energy can escape althoug there may be a
> mediocre ohmic contact between door and housing. As the mobile phone
> works at a significantly longer wavelength (f = ca. 900 MHz) this
> trick with resonant RF gaskets does not work any longer. So little
> isolation at 900 MHz does not neccessarily mean little isolation at
> 2450 MHz. It depends on the design principle of the RF gasket.
>
> A simple detector could be built, to check if and where microwave
> energy escapes. You only need e.g. a Schottky diode with < 1pF
> capacitance (hp 5082- 8035) and a blocking capacitor of 10 to 100 pF
> in preferably chip outline (size 0805, 1206) and two resistors of some
> kilo-ohms plus a voltmeter as indicator. The probe should be mounted
> e.g. at the tip of a wooden rod. The both leads of the diode between
> capacitor and diode body should be about 1 cm in length and act as
> magnetic antenna (shown as "L" in the schematic below). The resistors
> decouple the detector from the connecting wires to not perturb the
> electromagnetic field to much.
Does a voltage develop, or does the diode leak (more)? How sensitive
would the thing be?
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
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