In one aspect, an electromagnetic or capacitive sensing position system for determining the relative position of at least one void in a conductive material is provided. In one example, the system includes a sensor (or probe) having at least two probe elements (e.g., tips or plates). The position of the probe relative to the at least one void is determined in response to an electrical signal (e.g., a differential signal) measured across the two probe elements that varies in response to interaction of the probe elements with the at least one void. The system may be used, e.g., to servo a magnetic head assembly relative to a magnetic storage tape.