Doppler effect on ultrasonic signals for pregnancy determination in sheep

Abstract

Knowing the reproductive status of an animal (sheep in the case of this project) is of utmost importance to the modern farmer. Decisions concerning the management of the flock are influenced by knowledge of the percentage of animals that are pregnant at that specific time. The aim of the project was to gain knowledge for the development of an instrument that is affordable and with which the farmer can do pregnancy determination himself and therefore enables him to make the correct management decisions. Experimental data were obtained from pregnant Dorper ewes with the aid of a portable Doppler instrument. In order to gain insight in the frequency spectrum of the Doppler signal, simulations of Wavelet transforms (WT), Fourier transforms (FT) and short time Fourier transforms (STFT) were done in MathCAD. By using real data as input, simulations of correlation, autocorrelation and a specifically developed filter method were done in MathCAD. In the simulations known levels of noise were added to the Doppler signals. Satisfactory results were obtained from the simulations of autocorrelation and the filter method, which led to a DSP implementation of the two methods. In the DSP implementation of the autocorrelation method signals with a SNR of -6.5 dB was successfully identified and with the filter method the fetal heartbeat with a SNR of -8 dB was also identified successfully. It can thus be concluded that both the filter and the autocorrelation method can be used successfully for the detection of the fetal heartbeat in noisy ultrasonic Doppler signals.