(a) ECG data. (b) HRV signal as a function of time.
FFT spectrum of the HRV signal.
Schematic diagram of the microwave reflectometer.
Flowchart of the stress-evaluation algorithm.
(a) Comparison between the microwave reflectometer signal and the ECG, (b) selected peak waveforms and a template, and (c) calculated cross-correlation function.
HRV reconstructed from each signal.
(a) FFT spectrum of the HRV in relaxed state and (b) FFT spectrum of the HRV in the stressful state.
(a) Time evolution of the microwave reflectometer signal, (b) the first cross-correlation function, (c) the second cross-correlation function, and (d) the third cross-correlation function.
FFT spectra of the HRV obtained by the cross-correlation technique and the ECG signal: (a) first, (b) second, and (c) third cross-correlation.
FFT spectra of the HRV obtained by the MEM technique and the ECG signal.
Time change rates of the LF/HF.
Heartbeat signal model.
Relationship among the heartbeat frequency, the length of data window, and the estimated model order.
Relationship between the length of data window and the average of the estimated model order.
Relationship between the length of data window and the average of standardized error rates of LF/HF values.
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