The present invention provides a modular bumper shell comprising an attachment member adapted for attachment to an energy-absorbing vehicle bumper substructure, and at least one outer member affixed to and at least partially covering the attachment member. The system improves throughput by allowing flexibility in the operation and multitasking. The measuring gap containing an element that is sensitive to a magnetic field is located between the ends. A relative position of a first active device in a first pixel cell among the pixel cells is different from that of a second active device in a second pixel cell among the pixel cells.