Zero-Power Sensing Based on Inter-Tag Channel Estimations

We demonstrate a new backscatter sensing modality that exploits the measurement of the channel between two backscatter tags. This channel is independent of the channel between the reader and each tag. A theoretical basis of the sensor modality for dipole tags in the near field is derived. A proof-of-concept distance sensor, using commercial RFID tags, exhibits conformity to theory and demonstrates separation measurement with sub-centimetre accuracy.