> 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?
>
hi Declan,
from my experience sensitivity starts in the milli-watt range if you use a
voltmeter with high R_in, e.g. 10 MOhm impedance.
To be able to give better numbers, I'll build such a beast and test it at home.
More later.
regards
Alois
- - - - - - - - - - - - - - - - - - - - - - - - - -
Alois Bauer
WORK Microwave GmbH
Raiffeisenstr. 12, D-83607 Holzkirchen, Germany
Tel. {+49} (0)8024-6408-0 / FAX (0)8024-640840
--
Author: Alois Bauer
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