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Precise heart rate measurements
Osram adds new generation of sensors to BioFy family
17.10.2016 | Spotlights
Osram Opto Semiconductors presents two new sensors for monitoring fitness
levels. Their main benefit is the excellent signal quality for heart rate
measurements, which allows the derivation of secondary measurement
parameters such as blood pressure. The SFH 7072 has also been further optimized
for determining the oxygen saturation of blood (SpO ). Samples for the SFH 7070
are expected end of November – for the SFH 7072 end of this year.
The SFH 7070 is a sensor specifically designed for pulse rate measurements at the
wrist. It consists of two green emitters and one photodiode, the sensitivity of which is
very high in the green spectrum and is greatly suppressed for infrared light. This
minimizes the noise signal on the detector, which is created when ambient light
penetrates the part of the body being measured and is dispersed. This effect is
particularly strong for infrared wavelengths. Compared to the previous version, the
SFH 7051, the arrangement of the individual components has also been optimized
with regard to signal quality. The green emitters sit on both sides of the photodiode –
separated by optical barriers. That way more light hits the detector and there are
fewer measurement artifacts caused by the user’s movements. The photodiode is
almost twice the size of the one in the SFH 7051, which significantly increases the
signal strength. What’s more, the emitters in the new sensor produce almost four
times more brightness per chip – an optical output of 11.7 milliwatts at a current of
20 milliampere for each chip. This has been achieved by larger chips and a white
housing which absorbs less light.
Thanks to this, a sensor could be created which ensures excellent signal quality even
at a low operating current. This makes it possible to use the measured data also for
further evaluations to determine blood pressure or heart rate variability, for instance.
The new features described have also been implemented in the SFH 7072. This
sensor has the same dimensions as the SFH 7070. Apart from two green emitters and
one photodiode with an infrared filter, it also contains one red and one infrared
emitter as well as a broadband photodiode. The distance between the three latter
components was increased so that more light is reflected onto the detector. The
improved signal quality of the measurements with infrared and red light simplifies
the calculation of the oxygen saturation of blood (SpO ).
Chris Goeltner is responsible for the BioFy family at Osram Opto Semiconductors. He
sums up the improvements: “At Osram we have all process steps under one roof. This
allows us to focus on all levels, both working on the individual components and
optimizing their interaction in the integrated sensor. That way we keep our finger on
the pulse for our customers – in every sense of the word.”
2
2
SFH 7070 SFH 7072
Dimensions 7.5 mm x 3.9 mm x 0.9 mm 7.5 mm x 3.9 mm x 0.9 mm
Wavelengths 530 nm 950 nm / 660nm / 530 nm
Optical output
(for each green LED)
at 20mA
11.7 mW 11.7 mW
Photo-sensitive area
Broadband detector
n/a 0.801 mm²
Photo-sensitive area
IR-cut detector
3.46 mm² 3.46 mm²
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