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6.6. Iterate: Heart-Rate Detection with Radar
95
d
HR: radar HR: oxim. rel. err std err
5cm
83.28
83.61
2%
1%
10cm
95.90
92.66
8%
8%
4%
39
back
chest left side
chest right side
arm
femoral
(a) Body Placements
placement rel. err. std. dev.
arm
1%
1%
femoral
3%
2%
side l 0cm
4%
3%
side l 5cm
9%
7%
side r 0cm
6%
5%
back
13%
9%
(b) Measurements Results
Figure 6.7: A subject’s heart-rate is measured at di erent body placements by
radar over a time-interval of 30 seconds (a). These radar hear-rate measurements are
compared with simultaneously taken oximeter measurements as a reference. Then,
relative error (rel. err.) and standard deviation (std. dev.) are calculated (b).
second column shows the oximeter results. The third and fourth column show the
mean and standard deviation of the relative error comparing radar with oximeter
measurements. Though radar measurements are obviously less accurate than oxime-
ter measurements it is an interesting result that even at distance of 15cm the relative
error is in a range of 5%. Radar has the important ability of reporting reasonable
heart-rate measurements from a greater distance of the test person. In contrast to
that, if an oximeter or ECG chest strap is moved away for some millimeters it cannot
report any meaningful results anymore. This opens the space for radar heart-rate
detection to support applications were sensors can get ripped o but measurements,
even with less quality, are still important.
Placement Study
We also tested di erent placements of the radar at a test person’s arm, femoral, left
and right side, at the height of the chest, and at the back.
Figure 6.7 shows the results of the placement study. It is remarkable that the
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