The attenuation mechanism and regular of the acoustic wave on propagation path in farmland soil

Abstract

Understanding the propagation process of acoustic waves in the soil is very important for designing high-performance acoustic wave detection devices. In this study, the discrete element method was used to simulate the propagation process of acoustic waves in the soil. A single factor experiment was carried out with soil compression ratio, excitation frequency, and excitation amplitude as factors. The influence of various factors on the time and frequency domain were analyzed from the perspective of the received signal and the force signal on the particle. The results showed that: with the increase of soil compression ratio, the speed of the acoustic wave, the amplitude of the received signal's first wave and the dominant frequency increased; with the increase of excitation frequency, the amplitude of the received signal's first wave decreased, and the dominant frequency and speed of acoustic wave remained unchanged; with the increase of excitation amplitude, the received signal amplitude increased, and the dominant frequency and speed of acoustic wave remained unchanged. According to the force signal of the particles on the sound wave propagation path, as the soil compression ratio increased, the dominant frequency of the acoustic wave increased, and the amplitude attenuation coefficient increased; as the excitation frequency increased, the dominant frequency and amplitude attenuation coefficient of the acoustic wave first increased and then decreased; as the excitation amplitude increased, the dominant frequency of the acoustic wave remained unchanged, and the amplitude attenuation coefficient increased. The occurrences of these phenomena were related to the natural frequency of the soil and the sound wave attenuation mechanism. During the propagation process, the dominant frequency of the sound wave would continue to attenuate and eventually reached the natural frequency, resulting in the same dominant frequency of the received signal under different excitation frequencies. Under different parameters, the decay speed of the sound wave amplitude was different, and the initial signal amplitude was different, which led to the various first wave amplitude of the received signal. The conclusion could be drawn through the simulation experiment: the DEM method could well characterize the acoustic wave propagation process in the soil and analyze the acoustic wave propagation law in the soil. Thus, it provides theoretical support and reference for the research and instrument manufacture of the acoustic wave detection of soil characteristics.