A transponder string comprising multiple transponders is configured for injection into human tissue. In one embodiment, the transponders are sized to move through a needle for injection into the human tissue. Positions of the transponders with reference to one another may be maintained by coupling the transponders via a filament, adhesive backed substrate, shrink tubing, and/or any other suitable substrate. The transponders are configured to transmit data to a mobile computing device, e.g., a wand, smart phone or wireless tablet positioned outside the human tissue such that positions of the transponders are determinable, e.g., during an excision surgery.