A Remote Compact Sensor for the Real-Time Monitoring of Human Heartbeat and Respiration Rate

Abstract:
A remote compact sensor system for the detection of human vital signs (heartbeat) and respiration rate is presented. By transmitting the RF signal to the heart and receiving the reflected waves, the heartbeat and the respiration rate can be detected. Inorder to extract the heartbeat and respiration rate from the received RF signal, the peak detection of the power spectral density (PDP) with the tracking algorithm is utilized. For the compact size of the antenna, a frequency band of 24 GHz can be employed. Circular polarization with a single antenna has to be developed for the compact sensor. The sensor system is composed of radio-frequency circuits, a signal conditioning block, a data acquisition unit and a signal-processing part.
Circularly polarized RADAR sensor: A 2x1 patch antenna is used inorder to improve the sensitivity of the sensor. The sensor is composed of circularly polarized antennas, a Lange coupler, a Wilkinson power divider, a voltage-controlled oscillator (VCO), a low noise amplifier (LNA) and a mixer. The Lange coupler operates as a polarizer and a duplexer simultaneously. The transmitter block is implemented at one input port of the Lange coupler and the receiver is constructed at the other one. The left-hand circularly polarized (LHCP) antenna is formed at the transmitter, whereas the RHCP antenna is formed at the receiver. A free running oscillator produces a high stable oscillating signal, thus supporting the high accuracy of a heartbeat and respiration signal.
RF front-end circuits: The VCO is designed by employing negative resistance with capacitive feedback. For the tuning of the oscillator frequency, the base-collector junction of the heterojunction bipolar transistor (HBT) is used. The oscillation frequency is 27.345 Ghz. The tuning range of the oscillation frequency was from 25.5 Ghz to 27.81 Ghz. The received signal is amplified in the LNA and downconverted to the intermediate frequency (IF), 100 Khz, in the mixer circuit. The differential outputs of the VCO are used to drive the mixer circuit.
Signal conditioning and Data acquisition: To extract the human vital signs from the mixer output, the baseband signal-processing blocks have to be developed. It consists of a signal conditioning block (SCB), a data-acquisition (DAQ) unit and a digital signal processing (DSP) program.
SCB: The output signal of the RF front end is very weak and corrupted by noises. It has to be properly conditioned with the SCB. SCB consists of a highpass filter (HPF), a lowpass filter (LPF), and a baseband amplier. The HPF was employed to remove the dc component of the IF signal and block the dc leakage from the mixer. The HPF has a cutoff frequency of 0.02 Hz. The signal is filtered with the LPF to prevent the frequency components over half of the Nyquist sampling frequency. The anti-aliasing LPF has a cutoff frequency of 50 Hz.
The output signal of the SCB is then converted to digital data with the DAQ card. The collected digital data with the DAQ card are processed with the DSP program.
Digital signal processing: The algorithm of DSP is mainly dedicated to detect the periodic signal component from the conditioned signal. For that the PDP with tracking algorithm is used.

Ful report:
http://filesonicfile/18761859/ A Remote Compact Sensor for the Real-TimeMonitoring of Human Heartbeat and Respiration Rate.pdf