Four channels fNIRS system design with 35dB dynamic range for monitoring of brain signals

There are different Chromophores such as Oxyhemoglobin and Deoxyhemoglobin in brain cortex that their concentrations are changed in brain diseases and cognitive task. These variation of concentration can be measured by fNIRS. It operates by shining radiation that has a wavelength equal to the wavelength of Chromophore absorption. This paper describes a four channels fNIRS system containing four light sources. The first two sources and second two sources emit light in wavelengths of 730nm and 850nm, respectively. They are modulated in 2130HZ ،3370HZ ،4175HZ ،5765HZ by a square wave shape. On the other hand, four band pass filters are used to separate wave and to delete noises. Subsequently some parameters are selected to produce a device with 35dB dynamic range.