The thinnest waist in the world
1. Ultrasonic generator
In order to study and utilize ultrasound, many ultrasound generators have been designed and manufactured. Overall, ultrasonic generators can be divided into two categories: one is to generate ultrasonic waves through electrical means, and the other is to generate ultrasonic waves through mechanical means. Electrical methods include piezoelectric, magnetostrictive, and electric types, etc; Mechanical methods include the Galt flute, liquid whistle, and air flow rotary flute. The frequency, power, and acoustic characteristics of the ultrasound waves they generate are different, so their uses are also different. Currently, the most commonly used type is piezoelectric ultrasonic generator.
2. Principle of piezoelectric ultrasonic generator
The piezoelectric ultrasonic generator actually works by utilizing the resonance of piezoelectric crystals. The internal structure of the ultrasonic generator is shown in Figure 1, which consists of two piezoelectric chips and a resonant plate. When a pulse signal is applied to its two poles with a frequency equal to the natural oscillation frequency of the piezoelectric chip, the piezoelectric chip will resonate and drive the resonant plate to vibrate, producing ultrasonic waves. On the contrary, if no voltage is applied between the two electrodes, when the resonant plate receives ultrasonic waves, it will compress the piezoelectric chip to vibrate, converting mechanical energy into electrical signals, and then it becomes an ultrasonic receiver.
3. The basic principle of ultrasonic rangefinder
The ultrasonic transmitter emits ultrasonic waves in a certain direction and starts timing at the same time. The ultrasonic waves propagate in the air and immediately return when they encounter obstacles. The ultrasonic receiver stops timing immediately when it receives the reflected waves. The propagation speed of ultrasound in air is 340m/s. Based on the time t recorded by the timer, the distance (s) between the emission point and the obstacle can be calculated, which is s=340t/2. This is the so-called time difference distance measurement method.
The principle of ultrasonic distance measurement is to use the known propagation speed of ultrasonic waves in the air to measure the time it takes for sound waves to reflect back from obstacles after being emitted. Based on the time difference between emission and reception, the actual distance from the emission point to the obstacle is calculated. It can be seen that the principle of ultrasonic ranging is the same as that of radar.
