>
> > 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.
+V --- Res -----.-----L-------
| |K
Cap Diode
| |A
-V --- Res -----.-----L-------
Alois, DC4RA
- - - - - - - - - - - - - - - - - - - - - - - - - -
Alois Bauer
WORK Microwave GmbH
Raiffeisenstr. 12, D-83607 Holzkirchen, Germany
Tel. {+49} (0)8024-6408-0 / FAX (0)8024-640840
--
Author: Alois Bauer
INET: [EMAIL PROTECTED]
Fat City Network Services -- 858-538-5051 http://www.fatcity.com
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