An apparatus, according to various aspects of the present invention, produces contractions in skeletal muscles of a target to impede locomotion by the target. The AP self-pinned layer structure includes a first AP pinned layer having a first thickness; a second AP pinned layer having a second thickness; and an antiparallel coupling layer formed between the first and the second AP pinned layers. Each TR module includes phase shifters, as well as a phase conjugation module for transmitting a return signal to a location along a beam path of an incoming signal.