Measuring respiration through the wall by passive RFID tag

The perception of respiratory status of targets behind walls is highly significant in areas such as isolation monitoring, medical monitoring, and emergency rescue. Nevertheless, existing through-wall sensing technologies face many challenges in their deployment and application due to high costs, high power consumption, and low accuracy. Accordingly, this article proposes a fine-grained through-wall target state sensing system based on passive radio frequency tag, which offers the unique advantages of passivity and low cost. We construct a high-precision respiratory signal perception model based on tag phase information for complex through-wall environments. In the method, the phase signal is directly correlated with the measured respiratory signal, effectively suppressing the severe signal noise caused by wall penetration. Furthermore, based on an in-depth analysis of the propagation model, a novel analysis method for complex phase signal is proposed. Based on our method, respiratory feature information can be accurately extracted from strong interfering raw phase signal without restricting the normal movement of the measured personnel. Ultimately, we achieve effective detection of the respiratory rate and waveform of each breath of the tested personnel.