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21 November 2009

Answer to Question #6857 Submitted to "Ask the Experts"

Category: Microwaves, Radar, and Radiofrequency — Microwaves and Radiofrequency

The following question was answered by an expert in the appropriate field:

My mother has an old microwave oven with mild visible burns to the plastic interior chamber floor in the area of the seal and cracks where there are screws in the exterior plastic housing in the area of the keypad. I was talking on a cordless phone in the kitchen and extremely loud interference occurred beginning when the microwave was turned on and ending exactly when the microwave was done running. There was interference loud enough to be bothersome to me and the other person I was speaking to even when I moved the headset about 10 to 15 yards away and was partially separated by at least one wall. The base of the phone is in the kitchen and may be running on the same circuit as the microwave. I suspect the interference was coming through the power supply to the phone rather than via microwave leakage, but just wanted your opinion.

The mild visible burns may simply be a case of conventional heating burning liquids and foods that may have splattered onto the interior surface of the microwave oven. The screw burns can be due to a number of things, including lots of use. This oven is probably quite old.

The interference you speak of may have been caused from the power supply or may also have been the very low-level of microwave emissions from the oven. I sometimes get such interference from my own cell phone with my mobile land line.

The microwave oven is shielded to protect the user from the high power in the interior of the oven, which can cook food, from exceeding government emission standards of 5 mW/cm² at a distance of 5 cm from the surface of the microwave oven. Cell phones operate in the microwatt/cm² range, (1,000,000 microwatts = 1 watt = 1,000 mW [milliwatts]) so it is quite possible your phone was getting interference from the low-level emissions from the microwave oven, which are comparable to cell phone emission levels.

In either case, the radiation levels drop by hundreds or thousands of times as you get farther away from the source. You are safe next to the oven; you are much safer 10 to 15 yards away. Don't worry.

Orhan Suleiman, MS, PhD

Answer posted on 22 February 2008. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.