서강대학교

초록/요약

Non-contact measurements using the radar have been studied a lot, but have mainly used low frequency bands (below 10 GHz). However, the lower the frequency, the more difficult it was to miniaturize the overall system due to the length of the wavelength. By measuring the human body in a non-contact with a high level of miniaturization, real time treatment of the elderly and emergency patients can be possible. In addition, since non-contact vital signs are collected, unnecessary contact can be reduced to prevent infection of medical staff due to infectious diseases. In this paper, the human vital signs were measured by Doppler radar using W-band (75-110 GHz) frequency. And the respiration and heartbeat signs of the targets were extracted from the measured vital signs. By using the W-band frequency, we can achieve the high resolution to measure precise vital signs. Also it is unlikely that the measured value will be distorted by the external radio waves, because the W-band is not the frequency band used for communication. The radar was constructed based on the waveguide system to prevent noise from the background. The direct-conversion system which used in this radar also gave an advantage that the phase noise is canceled by sharing the signal source of the local oscillator and the transmission signal. Baseband signals of the radar are the I/Q signals and there is a 90° phase difference between them. The I/Q signals from the mixer were collected through commercial DAQ to extract the vital signs. Various signal processing techniques (filter, outlier removal, arctangent demodulation, …) are applied to remove the noise and extract only the human vital signs from the signal of the radar. The w-band signal is well attenuated inside the human body, but because it has a high resolution, it can measure the heartbeat signals near the chest. The heartbeat signs can be extracted by removing the respiration signs from the original vital signs. As a result, it is possible to make on-chip radar system to measure vital signs in the future.