Earphones or headsets with in the ear-earphones are often used to listen to music, when the user is moving around or exercising. People exercising are often also using heart rate monitors worn around the chest and connected wirelessly or by wire to a running watch or smart phone. Recently, earphones with built-in heart rate monitors are put on the market.
Heart rate can be measured at the ear by using optical plethysmography. With this technique, instantaneous changes in the volume of the blood in the tissue are detected. The detection is obtained by emitting light to the tissue of the ear and measuring changes in reflectance resulting from changes in the volume of blood in the tissue.
WO 2012/103273 (Valencell, Inc.) discloses an earbud with sensing means based on optical plethysmography.
IRiver ON™ is a headphone comprising a pair of earphones, wherein one of the earphones comprises an optical heart rate sensor. The heart rate sensor comprises a light emitter and a light detector. The light is transmitted through a first window in the earphone to the skin of the concha. Some of the light is absorbed by the skin and the underlying tissue. However, some of the light is scattered back by the vascular system of veins and arteries. Some of this light is returned through a second window immediately beside the first window to a light detector. The signal from light detector is processed and the heart rate from the user wearing the earphone can be determined. The signal from the heart rate sensor is processed with information from a motion sensor also arranged in the earphone device in order to subtract signal noise due to the movements caused by the exercising.
In order to obtain a reliable signal, it is important that the first and second sensor windows are positioned precisely in relation to the skin so that false light, which means light from the surroundings, do not reach the heart rate sensor. The first and second windows are arranged on the face of a sensor protrusion extending from earphone device and touching the conchal wall at the antitragus of the ear. The edges of the windows must abut the skin in order to not letting ambient light enter, whereby light scattered from the blood vessels cannot be detected sufficiently.
The IRiver ON™ headphone comprises an earphone device according to the preamble. This headphone comprises a neckband with electronics.