Heart Rate Detection during Sleep Using a Flexible RF Resonator and Injection-Locked PLL Sensor

Novel non-intrusive technologies for wrist pulse detection have been developed and proposed as systems for sleep monitoring, using three types of radio frequency (RF) sensors. The three types of RF sensors for heart rate measurement on wrist are a flexible RF single resonator, array resonators, and an injection-locked PLL resonator sensor. To verify the performance of the new RF systems, we compared heart rates between pre-sleep time and post sleep onset time. Heart rates of 10 subjects were measured using the RF systems during sleep. All three RF devices detected heart rates at 0.2 to 1 mm distance from the skin of the wrist over clothes made of cotton fabric. The wrist pulse signals of a flexible RF single resonator were consistent with the signals obtained by a portable piezo-electric transducer as a reference. Then we confirmed that the heart rate after sleep onset time significantly decreased compared to before sleep. In conclusion, the RF system can be utilized as a non-contact non-intrusive method for measuring heart rates during sleep.