led that sensors based on MEMS microphones recorded the highest-quality bronchopulmonary sounds. The microphones were installed into a sound-detecting head of the binaural stethoscope. Signals detected by the sensor were transmitted to a notebook's microphone input, where they were digitized by a sound AD converter (16 bit, 44.1 kHz) and recorded on a PC hard drive in the form of WAVE files without any loss of quality.
Figure 1 demonstrates a graphic representation of breath sounds obtained by means of the acoustic sensor based on the MEMS microphone.
As it is seen from Figure 1 that demonstrates the graphic representation of breath sounds produced by the bronchopulmonary system, the acoustic sensor based on the MEMS microphone allows recording high-quality acoustic signals of the human bronchopulmonary system. Signals contain a maximum volume of useful information and minimum volume of noises hindering the diagnosis making process in case of auscultation. In this case, the acoustic sensor was placed in the area of the right second intercostal space. The frequency range of the signal recorded was 60-140 Hz .
Bronchopulmonary signals recorded by means of the sensor designed by the authors can be used for further mathematic processing. It will allow singling out signal fragments corresponding to patients' inspiratory/expiratory sections. They can be analyzed further to automatically diagnose patients' disease.
Unlike the noises of the human bronchopulmonary system, most sound vibrations reasoned by heart sounds and noises are beyond the limits of sound perception. Therefore, during the registration of phonocardiograms an acoustic sensor should register sound vibrations beyond perception by ear. It is possible to make up the complete picture of heart noises by analyzing phonocardiograms obtained in each frequency range. As for the diverse filtration schemes, the Maass and Weber scale (Table 2) used in the modern phonocardiographs has the greatest practical importance nowadays.
In order to perform the long-term monitoring of cardiac activity (in both adults and fetuses during their intrauterine growth), it is more preferable to record phonocardiograms within a low-frequency band (40-90 Hz), which allows avoiding the overlapping of breath sounds with heart sounds down to the limit. Thus, on the basis of the required frequency characteristics and the analysis of the modern market of heart noise and tone registration devices, the authors have chosen a piezoelectric converter [4,11]. The required coherence of resistances was provided by the electronic part of the sensor designed by the authors. The sensor was fastened with an elastic band at the standard points of hearts auscultation. The signal was recorded by analogy with the recording of bronchopulmonary noises. The sensor has allowed obtaining the recording of the human cardiovascular system tones (Figure 2) with a certain number of extraneous noises concerned with the activity of the human respiratory system (its low-frequency constituents) and ambient noises.
The structure used provides the quality of the signal in the required frequency band that is sufficient for the future discrimination of heart sounds. The sensor of such a type can be successfully used to register heart sounds in adults and fetuses (during their intrauterine growth). However, such peculiarities of fetus heartbeat registration as low amplitude, source movement, and a significantly noisy signal determine the need to modernize the sensor and its loading, so that it can be used for fetus heartbeat registration in the future.
In order to eliminate noises from the acoustic signal obtained, the authors used the designed and software-based Type 1 Cherbyshev low-frequency filter, and its performance result is presented in Figure 3.
The further mathematic treatment of the human heart sounds obtained will allow calculating the heart rate (both in real time and in a delayed mode) and performing the noninvasive diagnostics of the patient's cardiovascular system by analyzing the first and second heart sounds derive