We have reported previously on the use of a novel Electric Potential Sensor, developed and patented at the University of
Sussex, for remote monitoring of life signs and through-wall sensing of movement and proximity. In this paper we
present the data obtained using a sparse (4-element) array of sensors to image a volume of space for target movements.
This is achieved by passive monitoring of the disturbances which result from the movement of a dielectric object through
the ambient electric field. Numerical computation is used to simulate the expected sensor responses for a given pattern of
movement and comparison with these simulations allows the trajectory to be followed. With this 4-element array, it is
possible to track the movement of a single subject, for example an intruder, or the lone occupant of a room. However,
with the addition of just a few extra sensors, it is possible to resolve the ambiguities caused by multiple targets. The
advantage of this approach over competing technologies such as radar, for through-wall surveillance and tracking, is that
the method is passive. It requires no excitation field or probe signal and relies instead on the ambient static electric field
which exists between the ionosphere and the surface of the Earth. It therefore only works well if the array is not
obstructed by earthed conducting materials, in common with the other technologies. On the other hand, the passive
nature of the technique provides a low power system which is potentially undetectable.