Lighting up the wearable tech industry

The global wearables market is estimated to be worth $30bn in 2016, and expected to grow to $100bn by 2023, according to analysts IDtechEx. Opto semiconductor technology is core to many applications within this sector, from infrared light for precise heart rate measurements to iris scans, Biofy sensors, finger print recognition and also the visible light e.g. display lighting.


Fitness trackers led the trend many years ago, using acceleration sensors to count the number of paces a person took. Since then, optical sensors have provided more ways of monitoring fitness by offering simple methods of measuring heart rate and oxygen levels in the blood. Osram Opto Semiconductors has been at the forefront of these technological advances, providing esp IRED technology with higher efficiency and needing less space and energy.


The new IR Topled D5140 photodiode from Osram Opto Semiconductors requires considerably less pc board space than before, enabling more compact sensors to be produced for monitoring fitness levels, for example in fitness armbands. The spectral sensitivity of the D5140 has been optimised for visible light and allows precise heart rate measurements using red or green light. The component is also ideal as an ambient light sensor.


The proven SFH 2440 and the new extremely compact IR Topled D5140 are ideal for optical sensors for pulse rate measurements, on the wrist for instance. Chris Goeltner, expert for infrared products at Osram Opto Semiconductors, explains:

“It works by shining visible light on the surface of the skin, some of which is absorbed or reflected to the detector. As arterial blood absorbs more light than the surrounding tissue, the strength of the detector signal changes with the volume of blood through which the light passes. The periodicity of the signal indicates the heart rate. However, infrared light which shines onto the measuring point from the surroundings and disperses in the body also reaches the photodiode. In practice, the sensor consisting of juxtaposed light source and detector is located directly on the skin, usually on the wrist or fingers. Due to the location the measurement is made at different wavelengths – green light has established itself as the best option for the wrist, red and infrared light for the finger.”


The Topled D5140 offers an outstanding signal-to-noise-ratio because it registers the reflected light particularly well while at the same time suppressing the infrared light. Thanks to its short switching time, the light signal modulated with the heart rate can be time-resolved perfectly. The IR Topled D5140 allows customers to design more compact sensors, preserving the high signal quality offered by the SFH 2440.

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