Design of a Contactless Vital-Signal Sensor based on Six-Port Technology and Experiment of WiFi Interference

This paper presents a contactless vital-signal sensor based on the six-port concept. A prototype including the digital signal processing (DSP) is designed and implemented. The RF hardware consists of an in-house produced six-port junction and power detectors. The DSP involves the empirical mode decomposition (EMD) from the Hilbert-Huang transform (HHT) to acquire the vital signals from the measured raw data. The operation frequency is in the unlicensed 2.4 GHz industrial, scientific, and medical (ISM) band, where it coexists with other communication standards, e.g. WiFi and Bluetooth. The WiFi communication link in particular occupies a wide spectrum in this band due to high data rate. Therefore, a series of experiments regarding the interference of WiFi with the prototype is carried out, and studied. Maximum measured distance between the sensor and a person under test is ≈4 m. According to our experiment, the sensor can still extract the vital signal when the WiFi communication is nearby.