Received widespread domestic microwave ovens are certified manufacturers KVK safe for the user. Indeed, the level external microwave radiation of their overwhelming majority when shipped from the factory significantly below the maximum permissible sanitary norms. However, after long-term operation of fastening the door into the heating chamber of the furnace is waning, between it and the housing gaps appear. Contribute to the growth and radiation sticking to the point of contact of the door with the housing food remnants. Finally, radiation may increase dramatically after unauthorised repair.
Offer simple indicator it is impossible, of course, to accurately assess the degree matching microwave oven health standards. However, early detection the increased level of radiation it will help.
Scheme of the indicator shown in the figure.
The VD1 diode is the detector signal induced on the findings of the microwave radiation. The inductance and capacitance of a twisted pair of wires connecting the diode with the rest the elements of the device, it is sufficient to filter high frequency component of the detected signal. Its envelope enhances the cascade of op-amp DA1.1. The use of IC LM324 (you can replace it on COD, and CRUD other similar) capable of operating with an input voltage close to the potential of the negative power bus, helped to avoid bias network zero and to simplify the scheme of the sensor.
The magnetron of the microwave oven generates packets of oscillations, following with a frequency of 50 Hz, a similar frequency of the pulses at the output of op-amp. If their amplitude exceeds certain threshold value, the led flashes HL1 connected to the output of op-amp through smithery follower transistor VT1. Feed the device from the battery galvanic cells GB1 voltage of 9 - "Krona" or similar. Button SB1 is the power switch.
When checking household microwave oven detector is located in the near zone of its radiation. The field here is different irregularity and lack of flat wave front. In this situation is optimal for the indicator is electrically short (significantly less than one wavelength) antenna. For this reason, as an antenna used conclusions the diode VD1. It is fixed in the housing of a ballpoint pen and connected with the actual indicator two-wire flexible cord.
I must say that the proposed indicator is very broadband. It sensitive not only to the primary (frequency - 2450 MHz, the wavelength is approximately 12 cm), but also higher harmonics of the radiation of the magnetron, up to the fourth and fifth (frequency, respectively 9800 12250 MHz). Higher harmonics always present in the spectrum and often give a significant contribution to the overall leakage. Microwave oven, radiating harmonics, can create serious interference to the reception satellite television.
As VD1 fit a variety of detection and mixing of microwave diodes, designed to operate at frequencies above 1000 MHz. For each of them useful to find the optimal load resistance (resistor R1), providing the highest sensitivity. The results showed good diode DSB. Test the stand is equipped with a generator G4-79 horn antenna and meter power MZ-54, showed that HL1 led begins to glow with a density of power flow 2...mkvt/cm2.
About the sensitivity obtained with mixing diode D. However with time, the detector properties are degraded, and at a low frequency or a constant current, checking, for example, a diode with an ohmmeter, to notice impossible.
According to the American standards, the power flux density 2.5 mW/cm2 valid at a distance of 70 cm from the furnace, and at a distance of 5 cm it should not be more than 1 mW/cm2. National standards require that the figure is nowhere exceed 10 µw/cm2. Practically the led indicator flashes in the distance 5... 10 cm from a working furnace.
Author: A. Kontsevich, St. Petersburg