Method and apparatus for low complexity ultrasound based heart rate detection

A heart rate monitoring system comprising:

• a bandpass filter adapted to:
• receive a demodulated Doppler ultrasound signal;
• filter the demodulated Doppler ultrasound signal to generate a filtered demodulated Doppler ultrasound signal;
• a signal-to-noise-ratio (SNR) estimator coupled to the bandpass filter, the SNR estimator comprising a first low-pass filter and adapted to:
• determine a peak in the filtered demodulated Doppler ultrasound signal;
• determine, using the first low-pass filter, an average of the filtered demodulated Doppler ultrasound signal;
• and
• estimate a SNR based on the peak and average of the filtered demodulated Doppler ultrasound signal;
• a frequency adapter coupled to the SNR estimator and adapted to modify a lower cutoff frequency of the bandpass filter based on the estimated SNR when the estimated SNR is below a pre-determined SNR threshold;
• the modified bandpass filter further adapted to filter the filtered demodulated Doppler ultrasound signal to generate a double-filtered demodulated Doppler ultrasound signal;
• a rectifier coupled to the frequency adapter and adapted to rectify the double-filtered demodulated Doppler ultrasound signal to generate a rectified filtered demodulated Doppler ultrasound signal;
• a second low-pass filter coupled to the rectifier and adapted to filter the rectified filtered demodulated Doppler ultrasound signal to generate a resulting signal;
• a microcontroller coupled to the second low-pass filter and adapted to:
• detect peaks in the resulting signal;
• and
• compute a heart rate based on the detected peaks.