The device consists of optical sensors and a processor unit. The whole structure is fixed on the head of the person.

IMG 3933     IMG 3995

The optical sensor is a small unit with a wide-band photodiode and IR LED, located in such a way as to effectively collect data from an area of approximately 1 square cm. The sensor itself occupies an area of about 4 square meters. cm.

The processor unit is connected to the control computer or mobile device via the Bluetooth interface, receiving commands and data from it. The power is supplied from a small Li-Ion battery, which is enough for the device to continuously work for 2.5-3 hours. The device is charged through the microUSB interface, like most modern mobile devices. The processor unit controls the LEDs and data collection from the photodiodes via the high-speed ADC. The use of a multichannel ADC with a speed of up to a million samples per second, as well as the oversampling (multiple measurements with summation and averaging of the result) and matched filtering methods, make it possible to obtain high-bit data with a good signal-to-noise ratio.

IMG 4345   IMG 4376

The equivalent depth of the obtained data is 26-28 bits, which corresponds to the sensitivity of the photo-sensor at the photo-EMF level of the order of tens of nanovolts. This makes possible a reliable detection of the photo-EMF signal. The subsequent statistical processing of the data on the computer allows to filter the background noise and contaminating signals and helps to identify some patterns.

The speed of data acquisition from the photosensors ranges from several dozen measurements per second to one measurement for a long time period (almost unlimited); this period cab be specified by an external control command.

The data is transferred by a packet carrying information from all sensors. At long measurement times, the "dynamics" is lost, i.e. the device is not able to record fast signal fluctuations. On the other hand, longer measurement times increase sensitivity and improves the signal-to-noise ratio. The specified equivalent bit depth (26-28 bits) is achieved at speeds of about 1-10 samples per second. The switching (multiplexing) of the sensors during the measurement with speeds of several thousand switching per second provides (quasi-)simultaneity of data acquisition in the case of multiple channels, with the data packet acquisition frequency for all sensors of the order of 1-10 packets per second.

This data acquisition dynamics can be considered satisfactory, given the inertia of biological processes in the IR region, where the obtained data mainly carry information about the change in blood flow.

Device features:
• number of channels – 4;
• heart rate monitor;
• position sensor (accelerometer);
• the nominal resolution at the photo-EMF sensor level is not worse than 50 nV;
• the nominal wavelength of the first IR emitter in a photosensor – 880 nM;
• the nominal wavelength of the second IR emitter in a photosensor – 700 nM;
• the total pulse power of the IR emitters in a photosensor is not more than 250 mW;
• the bandwidth of an IR emitter in a photosensor (level 0.5) – +/- 20 nM;
• the speed of reading and data acquisition on all four channels (quasi-simultaneous), with the nominal resolution – not worse than 1 four-channel measurement per second;
• interface with a controlling PC or mobile device – Bluetooth v.4.0, with BTLE support (it is possible to use a wired interface USB 2.0 or higher for a PC);
• supply voltage - 5V;
• average current consumption – not more than 200mA;
• weight – not more than 100g.