Optimated optical sensor can be used in wearables
Described as a further development of the optical sensor SFH 7050, the SFH 7060 from Osram Opto Semiconductors is designed to measure pulse rates and the oxygen saturation level of blood. The signal quality and low energy consumption enables it to be used in wearables such as smartwatches and fitness armbands. The new sensor is available at distributor Rutronik.
The 7.2 x 2.5 x 0.9mm sensor consists of three green LEDs, one red LED, one infra red LED and one large-format photodiode, which is optically separated from the emitters by an opaque barrier.
Green light is best for measuring the pulse at the wrist. The three green LEDs with a wavelength of 530nm are based on the latest high-efficiency UX:3 chip technology from Osram. At a current of 20mA they typically deliver an optical output of 3.4mW at a voltage of 3.2V per chip. The higher light output compared with the earlier model results in better signal quality and more stable pulse measurement, claims the company. The low power consumption extends the battery life of the device.
Oxygen saturation in the blood is calculated from the different absorption rates of red (660nm) and infrared (940nm) light. The quality of the measurements depends to a large extent on the achievable signal-to-noise ratio and on the linearity of the photodetector. Both are achieved by the integrated photodiode with its active surface of 1.3×1.3mm.
The wavelength of the red transmitter is specified with a narrow tolerance of ±3nm. The spectral bandwidth of the infrared and green LEDs is 30nm each.
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