The human ear can only perceive sound waves up to a maximum of about 20,000 Hz, and sound waves of higher frequencies are ultrasound. Ultrasound is widely used in a variety of technologies.
Ultrasound has two characteristics, one is the energy, one is along the straight line propagation. Its application is in accordance with these two characteristics to develop.
Theoretical studies show that, in the case of the same amplitude, the energy of an object vibration is proportional to the quadratic of the vibration frequency. Ultrasound propagation in the medium, the medium mass vibration frequency is very high, and therefore a lot of energy. In the dry winter in the north of China, if the ultrasonic waves into the water tank, the intense vibration will make the tank of water broken into many small droplets, and then a small fan to the droplets blown into the room, you can increase the humidity of the indoor air. This is the principle of ultrasonic humidifier. For laryngitis, bronchitis and other diseases, it is difficult to reach the diseased part of the medicine. Using the principle of humidifier, the medicine atomization, let the patient inhale, can enhance the therapeutic effect. The use of ultrasound energy can also be used to break up the stones in the body.
Metal parts, glass and ceramic products is a troublesome descaling. If you put these items in the cleaning fluid into the ultrasonic waves, the cleaning fluid of the violent vibration of the impact of the dirt on the items, can be quickly cleaned.
As the saying goes, "walls have ears" (Figure 1), which means that sound waves can bypass obstacles. However, the shorter the wavelength, the less obvious this bypass phenomenon, therefore, ultrasound is basically along the straight line of propagation, can be directed to launch. If the fishing boat carries an underwater ultrasonic generator, it rotates to transmit ultrasound in all directions, ultrasound will be reflected back when it encounters the fish, the fishing boat will know the location of the fish when it detects the reflected waves. This instrument is called sonar. Sonar can also be used to detect reefs in the water, enemy submarines, measure the depth of the sea.
According to the same reason can also use ultrasound to detect metal, ceramic concrete products, and even reservoir dams, check whether there are air bubbles, voids and cracks inside.
The surface of the human body's internal organs on the ultrasound reflection ability is different, healthy and diseased internal organs and reflective ability is not the same. Ultrasound," as it is commonly called, is used to help doctors analyze lesions in the body by imaging the ultrasound waves reflected by the internal organs (Figure 2).
Interestingly, many animals have well-developed organs that emit and receive ultrasound. The insect-feeding braid, which has poor vision, sends out pulses of ultrasound in flight, relying on reflected waves from the insect's body to find food. Dolphins also have a well-developed "sonar" system, which allows it to accurately determine the location of small fish in the distance in murky water. Modern radio locator - radar, the mass of tens, hundreds, thousands of kilograms, the bat ultrasonic positioning system is only a fraction of a gram, but in some important performance, such as determining the accuracy of the target's location, anti-jamming ability are far superior to the modern radio locator. In-depth study of the function and structure of various organs in animals, the knowledge gained to improve existing equipment and create new equipment, which is a new discipline developed in recent decades, called bionics.