A Novel Active/Passive Dual-Mode Sensing Technique for Detecting Vital Signs

Most conventional vital-sign sensing techniques are incompatible with the circuits in commercial wireless communication devices. In addition, conventional techniques cannot easily provide both active and passive sensing. This article presents a novel active/passive dual-mode sensing technique for detecting vital signs. The proposed technique simply combines the error vector magnitude (EVM) algorithm with the demodulation of wireless communication to detect vital signs. Therefore, any wireless device can be used as a vital-sign sensor without any modification of their circuits. The proposed technique can switch between active and passive modes as desired. The experimental results show that the developed sensing technique is very effective in detecting vital signs. In active mode, the maximum vital-sign detection distances of the developed 2.4-GHz sensor are 4.3 and 9 m with and without a 15-cm-thick reinforced concrete wall as a barrier, respectively. In passive mode, the developed sensor can penetrate a 15-cm-thick reinforced concrete wall to detect human vital signs within a range of 6.3 m.