Active fence structures and toppings

Fences have traditionally been of rigid and stable structure. The resulting rigidity gives Perimeter Intrusion Detection Systems (PIDS) a stable background energy to work against. Such a structure can be used for mounting enhancements designed to impede escapes or intrusions. There are, however, advantages in making a fence less rigid. A fence that in some way reacts to an attack (an active fence) absorbs a proportion of the energy from an impact from an imparted blow, making it more difficult to penetrate. A swaying fence should also be more difficult to climb. PSDB has tested a range of active fences in non-rigid or `floppy´ form ranging from those made of glass reinforced plastic (GRP) tubes to composite fences made of chain link and mesh. These have been tested for cutting, climbing and impact attacks. Collapsing toppings have been made using shear brackets and floppy toppings made using rubber mountings. More recently, PSDB has experimented with a variety of springy toppings using the natural spring in coils of barbed wire and the inherent spring in steel bars. These have been designed with substantial overhangs to impede climbing. This paper reports the findings of tests on both floppy fences and on toppings and discusses the merits and drawbacks of this type of approach. It suggests directions in which active fence technology may be moving