As a long time lurker on this website, let me first say that I’ve been a fan of Straight Dope for several years and wish to thank to all who have posted here for many educational, entertaining, and humorous exchanges.
My question involves a cheap ($15) electromagnetic radiation detector I bought from an online retailer. It claims to read and display (in milligauss, I think) the amount of radiation coming from household appliances.
I’m going to assume it works because it actually detects something when it’s near the tv, laptop, dryer, etc., and doesn’t beep or register anything when not near electrical appliances or outlets.
I’ve noticed something peculiar, though, that has me puzzled. When I am measuring radiation with the detector in my hand, it registers much higher radiation levels (2-3x’s) at the same location than it does when I don’t touch the detector. It even registers higher levels when my hand is near the detector.
Now, I’ll admit I’m a simpleton when it comes to stuff like this, but i’d be interested to know just what causes this to happen.
Can you provide a link to to it? I’d like to see what it looks like (physically), so I can see how you’re holding it. My WAG is that the EMR is bouncing off your hand and going through the detector again.
As an experiment, you could see if the level goes down if you put your hand between the detector and the EMR source. In theory, if your hand can reflect EMR, it might also shield some of it.
You are correct. Putting my hand between the radiation source and detector does shield it and I get no readings. I can put a thin phone book between the detector and source and it has the same effect.
But why would my hand reflect the waves back and not other things I’ve tried, like a thin phone book, piece of metal, pocket calculator? The phone book blocked the radiation, but would not reflect it.
It’s not all that different from getting a better picture when you touch a rabbit-ear TV antenna. Or affecting the signal on certain models of iPhones.
The human body can greatly hurt/help the signal a nearby antenna picks up.
That detector is a bit odd, and for the money you would not really expect much.
It claims a frequency response from 50Hz to 2GHz. It also claims two frequency ranges, one measuring volts per unit distance, the other power per unit area. But they don’t say where the breakpoint is.
Overall I would say the device is close to useless.
Low frequency energy is going to be mains power (ie 50 or 60 Hz) and switching power supplies, and the higher frequency stuff internal computer operation or microwave ovens. Of these, the only source that matters is a microwave oven, and only if the shielding is damaged in some way.
You can always measure a field right hard up against a source, but what is never pointed out is that the strength of the source will typically decrease at a precipitous rate (to the forth power of the distance for many sources) and is as close to zero as you wish at meaningful distances.
There is scant evidence that the device is actually usefully calibrated or in any way an actual serious measurement device. The big clue is that is claims to be CE Industrial Standard. No such thing. CE means it is allowed to be sold in Europe, and conforms to a set of standards about the manner in which it is made, and from what it is made, and that it won’t hurt anyone. It does not present a standard for test instruments. There will be an appropriate ISO standard for that. It is common for junk devices to advertise such bogus use of standards to imply some high level quality.