  We measured the electromagnetic stress-induced local strain distribution on a
centimeter-sized parallel-plate metallic resonant unit illuminated with
microwave. Using a fiber interferometer, we found that the strain changes sign
across the resonant unit, in agreement with theoretical predictions that the
attractive electric and repulsive magnetic forces act at different locations.
The enhancement of the corresponding maximum local electromagnetic stress is
stronger than the enhancement of the net force, reaching a factor of >600
compared to the ordinary radiation pressure.
