Transponder

A device that receives a signal and automatically transmits a response signal. In RTLS, typically refers to tags that respond to reader interrogation signals. Common in active RFID and some UWB implementations.

A transponder is a wireless communication device that receives a signal and automatically transmits a response, combining the functions of transmitter and responder. The term transponder originates from 'transmitter-responder,' describing devices that respond to interrogation signals. Transponder operation typically involves: an anchor/reader transmitting an interrogation signal or command, the transponder receiving and decoding the signal, processing the request (eg., preparing ID, sensor reading, or ranging response), and transmitting a response back to the interrogator. This bidirectional communication enables capabilities beyond passive broadcasting including: guaranteed delivery through acknowledged protocols (transponder confirms receipt of commands), selective addressing (interrogating specific transponders rather than broadcast reception), dynamic reconfiguration (updating transponder parameters remotely without physical access), and interactive applications (workers triggering transponder features via mobile apps or buttons). Passive transponders derive operating power from the interrogation signal itself (classic RFID principle) enabling battery-free operation but limiting range (typically under 10 meters) and functionality. Transponder selection considerations include: application requirements (is two-way communication necessary or would simpler transmit-only tags suffice), power budget (can battery support receiver power consumption at required duty cycle), range requirements (interrogation signal must reach transponder at required distance), latency tolerance (response time may be longer than broadcast systems due to protocol overhead), and cost constraints (transponders typically cost more than equivalent transmit-only tags). Sewio's RTLS solutions primarily use transmit-optimized tags for maximum battery life and capacity, though TWR positioning mode where implemented would use transponder capabilities for range measurement dialogues, selecting appropriate tag type based on application requirements and performance priorities.