Osram Opto Semiconductors GmbH of Regensburg, Germany SFH 7051 has launched an integrated optical sensor that consumes very little power (maximizing battery life and reliability), designed especially for heart rate monitoring in fitness trackers, smart watches and other wearables.
Picture: The compact, integrated SFH 7051 sensor (for measuring pulse rate) consists of three high-efficiency green LEDs and a large-format photodiode.
The SFH 7051 consists of a large-format photodiode and three green LEDs with a wavelength of 530nm. Used for monitoring heart rate by measuring the volume of blood passing through blood vessels, it works by shining light on the surface of the skin. Different amounts of this light are absorbed by blood and the surrounding tissue. The light not absorbed is reflected to the detector. With its green emission spectrum, the SFH 7051 is suitable for measuring pulse rate at the wrist.
The green emitter chips of the SFH 7051 are based on the firm's latest high-efficiency UX:3 chip technology. The sensor uses three of these chips so that they can be operated at the optimum current of 20mA. At this operating current, the efficiency of the emitters is particularly high. Overall, the SFH 7051 produces an optical output of 3 x 3.4mW at a current of 20mA and a voltage of 3.2V. The low power consumption enables long battery life in the device, increasing reliability. With a photo-sensitive area of only 1.7mm2, the photodiode is small enough to enable the sensor to be compact, but sensitive enough to provide the required signal quality. Also, its low capacitance of only 11pF ensures short switching times and high measurement frequency.
The SFH 7051 is Osram's second integrated optical sensor for fitness tracking applications. In 2014, it launched the SFH 7050, a multi-function sensor for measuring heart rate and the oxygen content of blood. "We are keeping a very close watch on the trend for heart rate monitoring in the wearables and medical markets," says product marketing manager Christoph Goeltner. "Wearables are electronic devices that are worn on the body, such as smart watches and fitness wristbands. The SFH 7051 meets our customers' need for a separate solution, specifically for heart rate monitoring," he adds. Users now have a choice between the multi-function SFH 7050 and the SFH 7051, which is optimized for pulse rate monitoring. The housing dimensions of the two sensors are identical (4.7mm x 2.5mm x 0.9mm).
