A 2.4GHz Non-Contact Biosensor System for Continuous Monitoring of Vital-Signs

Doppler Radar-Based Non-Contact Health Monitoring for Obstructive Sleep Apnea Diagnosis: A Comprehensive Review

“…This means that the mixed signal is modulated on a non-zero intermediate frequency (IF) rather than being converted directly to baseband. The mixed signal is also filtered by another BPF, followed by a low noise amplifier (LNA), and demodulated directly or mixed down to baseband before demodulation [13,18,24]. An illustration of the heterodyne transceiver topology is shown in Figure 1.…”

“…The advantage of heterodyne topology is that different received frequencies can be converted to the same IF prior to the amplification or filtering processes and the IF is also at a considerably lower frequency than the RF. However, a major disadvantage of heterodyne topology is the high number of circuitry components and passives [13,18,24].…”

“…The gold-standard for OSA diagnosis is the overnight sleep monitoring system using polysomnography (PSG), which records the electric potentials of the brain, heart, eye movement, muscle activity, respiratory effort, airflow, oxygen saturation, and leg movements throughout the night [11]. Despite the quality and reliability of the PSG system, it is not well suited for long-term continuous monitoring usage [12] due to limited mobility as well as causing possible irritation, distress, and discomfort to patients during the monitoring process [13]. These limitations have led to stronger demands for non-contact sleep monitoring systems.…”

“…As documented in literature, the issue with getting an accurate reading from a non-contact monitoring device is due to background clutter, phase-nulling or null point, DC offsets, motion artefacts and electromagnetic interferences [13]. In addition, for continuous sleep monitoring in particular, the challenges are in the complexity of the sleep environment, noises associated with the unpredictability of body movements, body orientations, changes in sleeping posture, multi-subjects cancellation, undesired harmonics, and intermodulation [14,15].…”

A System for Monitoring Breathing Activity Using an Ultrasonic Radar Detection with Low Power Consumption

“…There have been several attempts to devise direct and indirect techniques to monitor breathing activity while minimizing discomfort. These techniques include direct contact such as magnetic induction [14][15][16][17], microphone [18,19], and capacitive [20][21][22][23], and indirect contact (contactless) such as electromagnetic radar detection [24][25][26][27][28][29], laser radar detection [30][31][32][33], ultrasonic radar detection [10,[34][35][36][37], thermographic imaging [38][39][40][41][42][43], and video camera imaging [44][45][46][47][48][49][50]. Each of these techniques, however, requires different process monitoring and has benefits and drawbacks that may make it more or less appealing to use under different circumstances as discussed in reference [51].…”