  This paper is concerned with a conceptual gesture-based instruction/input
technique using electromagnetic wave detection. The gestures are modelled as
the shapes of some impenetrable or penetrable scatterers from a certain
admissible class, called a dictionary. The gesture-computing device generates
time-harmonic electromagnetic point signals for the gesture recognition and
detection. It then collects the scattered wave in a relatively small
backscattering aperture on a bounded surface containing the point sources. The
recognition algorithm consists of two stages and requires only two incident
waves of different wavenumbers. The location of the scatterer is first
determined approximately by using the measured data at a small wavenumber and
the shape of the scatterer is then identified using the computed location of
the scatterer and the measured data at a regular wavenumber. We provide the
corresponding mathematical principle with rigorous analysis. Numerical
experiments show that the proposed device works effectively and efficiently.
