Physical applications of ultrasound

The so-called ultrasonic is a mechanical wave whose particle vibration frequency is higher than 20 kHz. It is named ultrasonic because its frequency exceeds the audible sound frequency band of 16 Hz to 20 kHz. The ultrasonic frequency range of NDT is 0.2 ~ 25MHz. The most frequently used frequency is 0.5 to 10MHz. The higher frequency is mainly used for fine-grained materials and high sensitivity detection. For example, the detection of ultra-fine materials such as cermet in the 10-200 MHz frequency band, or even higher, and the lower frequency is commonly used in terms of attenuation and coarse-grained material detection. For example, the frequency of detecting concrete structures is usually less than 1MHz. Ultrasound is a member of the family of sound waves, which is consistent with audible sound. Their common point is a kind of mechanical vibration, usually in the form of longitudinal wave propagation in elastic media, is a form of energy and momentum transmission, the difference is that the ultrasonic frequency is high, the wavelength is short, in a certain distance along the straight line propagation, has good beam radiation and directivity. The ultrasonic wave length is much larger than the molecular size, indicating that the ultrasonic itself can not directly affect the molecules, but through the physical effects of the surrounding environment, so the role of ultrasonic is closely related to the environment. Ultrasonic wave is not only a form of wave, but also a form of energy. The interaction between ultrasonic wave and media produces ultrasonic effect in the process of propagation.

Two. Application of ultrasound
Ultrasound is widely used in industrial and agricultural production. Including ultrasonic testing, ultrasonic flaw detection, power ultrasonic, ultrasonic treatment, ultrasonic diagnosis, ultrasonic treatment and so on. Ultrasound can be used in industry to detect and detect materials, can measure the physical parameters of gas, liquid and solid, can measure thickness, liquid level height, flow rate, viscosity and hardness, but also can be used to inspect welding seams, bonding and other materials. Ultrasonic cleaning and processing can be applied to cutting, welding, spray, emulsification, electroplating and other processes. Ultrasonic cleaning is an efficient method and has been used in sophisticated and precision industries. High-power ultrasonic can be used in machining, so that ultrasonic can be used in pipe drawing, wire drawing, extrusion and riveting process. Ultrasound diagnosis has developed rapidly in medicine, and has become one of the three major imaging diagnostic methods in medicine. It has been applied to different occasions with X-ray and isotope, such as ultrasonic physiotherapy, ultrasonic diagnosis, tumor treatment and lithotripsy. In agriculture, the killing effect of ultrasound on organism cells can be used for disinfection and sterilization, and the ultrasonic treatment of crop seeds is conducive to seed germination and crop yield. In addition, ultrasonic liquid treatment and purification can be applied to environmental protection, such as ultrasonic water treatment, fuel emulsification, atmospheric dust removal and so on. Microwave ultrasound focuses on microwave electronic devices, and has been made into ultrasonic delay lines, acoustic amplifiers, acoustic and electrical filters, pulse compression filters and so on.

Three. The specific application of ultrasound in agriculture.
Ultrasonic treatment of seeds has been studied many times in the former Soviet Union. According to foreign literature, a small amount of ultrasound can stimulate cell division, moderate amount of ultrasound can inhibit cell division, a large number of cells can cause death. In the last century, ultrasonic experiments were carried out on spinach and cabbage seeds. The results showed that the germination rate of Chinese cabbage seeds treated with ultrasonic wave for 1 minute and 2 minutes was 92%-96%, while that of non-ultrasonic treatment was 88%. After one minute of ultrasonic treatment, 85% of the spinach seeds were unearthed, while 40% of the spinach seeds were unearthed without ultrasonic treatment. The seeds produced by ultrasonic treatment increased significantly in the future. Low frequency pulsed ultrasound had obvious variation on wheat seedlings. The occurrence rate of water-cultured mutant seedlings irradiated by ultrasonic wave was 8.57  The grain weight per plant of the irradiated Xiannong 68 wheat was 55.17% higher than that of the parents, and the significant level of 1% of the parents was 87.50%. After irradiation, 69.23% of the super-parent families had grain weight per plant, and 77.78% of the super-parent families had reached 1% significant level.
Ultrasonic ploughing. Traditional ploughs require heavy machine traction, which not only compacts deep soil and prevents it from retaining moisture and nutrients, but also erodes the topsoil by wind and rain. This is a big worry for many farmers. In addition, because of ploughing, roots and decaying residues of plants are dug out of the ground, they emit carbon dioxide gas. Jordan's agricultural engineer Nida? Abu hade invented the use of ultrasound to loosen the soil. His experimental results showed that the effect of ultrasonic treatment on plant respiration was achieved by loosening soil. The study of plant respiration has always been a hot topic in plant physiology. Especially for crops, the size of plant respiration has a direct bearing on the yield. Therefore, the study of plant respiration has a very important theoretical and practical significance for the development of agriculture. The Albu E study in 1975 found that the respiration intensity of annual plants (such as tomatoes and cucumbers) decreased and that of biennial plants (such as cabbage and onions) increased after low-frequency ultrasound (25kHz) treatment of vegetables. Since then we can speculate that using ultrasound to treat related crops can increase crop yields. Depth 20cm. This fully meets the general soil loosening depth.

Four, ultrasound in medical aspects