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A new type of scale that uses microwaves to weigh objects has been developed
by researchers in the US. Microwave-resonant cavities trap microwaves so that
they resonate—in the same way as sound waves resonate when someone sings
in the shower. Stuart Nelson and Andrzej Kraszewski of the US Agricultural
Research Service found that objects moving through these cavities create shifts
in the frequency that correlate with their weight. “As far as we know, no one
else has ever thought to use microwaves to measure mass,” says Nelson.