OSRAM push health monitoring and fitness tracking field of LED products

With the increasing popularity of quantitative life movement, people are able to integrate into the watch, smart phones or fitness bracelets and other so-called wearable small parts of the medical measurement methods are increasingly interested in. This kind of interest, use acceleration sensor to measure the frequency in the fitness tracker. Now, the optical sensor can directly measure heart rate and oxygen saturation, further expand the possibility of self observation. In addition, it is more convenient to carry out the pulse measurement on the wrist or finger than the chest belt. Last but not least, optical methods have the same advantage in economics, as new technologies for efficient LED can achieve higher efficiency and more compact sensors.

OSRAM Opto Semiconductors provides innovative elements for many kinds of modern fitness tracking and health monitoring, including light emitting diodes with different packaging, size and performance level of the green and red light, photoelectric diode and infrared LED. All the sensor products are based on high efficiency chip technology to ensure the low energy consumption and high signal quality, thus achieving a very reliable measurement. The new SFH7050 is the first integrated optical sensor to be developed for OSRAM semiconductor, which combines three different wavelengths of light emitting diodes and a built-in photodetector. The utility model is suitable for measuring the heart rate and the oxygen saturation of the optical sensor, which is used for the absorption of blood to the light, and more specifically, the absorption of light by the hemoglobin in the blood.

Heart rate monitoring

Light exposure to the body tissue, and then through the transmission, absorption and reflection (Figure 1) and other processes. The greater the amount of radiation received, the lower the amount of light reflected. The amount of blood in the arteries varies with the cardiac cycle, so the heart rate can be calculated from the detector signal cycle (Figure 2). A method for the measurement of the volume of blood in the blood vessels, called optical capacitance tomography (PPG). The sensor is composed of a parallel light source and a detector. In practice, sensors are placed directly on the skin (usually the wrist or finger). Because of the different position, the wavelength used in the measurement is also different: green light has been proved to be the best choice for the wrist, and red and infrared light is the ideal choice of the finger.

Pulse oximetry

Blood oxygen saturation can be measured using infrared light and red light (Figure 3). The so-called pulse oxygen saturation is based on the fact that the absorption behavior of hemoglobin (Hb) and oxygen (HbO2) will change. The concentration of these two variants can be determined by measuring the absorption at two different wavelengths. So you can get the blood oxygen saturation. In this application, red light (660nm) and infrared light (940nm) is the ideal choice, because at these two wavelengths, the absorption behavior of the two hemoglobin molecules is the largest. In contrast to the pulse measurement, which only takes into account the changes in light absorption, the absolute value of the optical absorption of the arterial blood must be measured. In practice, oxygen saturation can be expressed by the ratio function (Imin/Imax) of the minimum and maximum detector signal at the corresponding wavelength.

The SFH7050 sensor emits green light, red light, or infrared light that is absorbed or reflected in the skin or tissue. The amount of reflected light recorded by the detector varies with the volume of blood in the artery (photo electricity volume). For the wrist position, the measurement is carried out by the green light; for the finger part, the red wavelength or the infrared wavelength is used for the measurement.

Fig. 1 optical measurement of biological data

The period of the detector signal I corresponds to the pulsation of the blood volume in the artery. The ratio of the minimum to the maximum signal value (Imin/Imax) is related to the determination of oxygen saturation (pulse oximetry).

Figure 2 measurement of heart rate

The absorption behavior of blood (more accurately, Hb) changes with the amount of oxygen (HbO2). Blood oxygen saturation can be measured by measuring the absorption of red light and infrared light.

Figure 3 Determination of blood oxygen saturation

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