From the perspective of physics, sound waves belong to the category of sound, which is a kind of mechanical waves. Sound waves that humans can hear have a frequency range of 16Hz to 20KHz. If the frequency of the sound wave is lower than 16Hz, it is called infrasound. If it is higher than 20KHz, we are called ultrasonic sound wave. Ultrasound is named because its lowest frequency is approximately equal to the highest hearing frequency of a person. Ultrasonic direction performance is good, strong penetrating ability, easy to obtain more concentrated sound energy, long distance in water, can be used for measuring distance and speed, cleaning, welding, lithotripsy, sterilization and disinfection. Sound waves are divided according to principles and can be divided into detection ultrasound and power ultrasound. There are many applications in medicine, military, industry, and agriculture. Sound waves are a form of mechanical vibration of an object that transmits energy. The so-called vibration refers to the back and forth movement of the mass point of a substance near its equilibrium position. For example, after the drum surface is struck, the drum surface vibrates up and down, and the vibration state is transmitted to the surroundings through air, liquid or solid, which generates sound waves. Sound waves with a frequency higher than 20KHZ cannot be heard by humans. People call them ultrasound. Ultrasound and audible sound are actually the same. Their main feature is a mechanical vibration, which is a form of energy transmission. The difference is that the ultrasound frequency is high and the wavelength is short. Within a certain range, the straight-line propagation has excellent beam radiation and directivity. At present, the frequency range for abdominal ultrasound imaging is between 2MHz and 5MHz, and the most commonly used is 3NHZ to 3.5 MHz (particles vibrate at 1Hz once per second, 1MHz = 10 ^ 6Hz, which means 1 million vibrations per second)
Characteristics of ultrasound
1. When the ultrasonic wave propagates in the liquid, it can produce strong impact and cavitation on the interface.
2. Ultrasonic waves can be effectively transmitted in gas, liquid, solid, solid-melt and other media.
3. Ultrasonic waves will produce reflection, interference, superposition and resonance.
4. Sound waves can transmit strong energy.
Utilization of the ultrasonic effect
Ultrasonic frequency has high wavelength and short wavelength, has good directivity, and can penetrate opaque materials. Ultrasonic flaw detection, thickness measurement, distance measurement, remote control and ultrasonic imaging technology are made by using this characteristic. Ultrasound imaging is a technique that uses ultrasound to render the internal image of an opaque object. The ultrasonic wave emitted from the transducer is focused on the opaque sample, and the ultrasonic wave transmitted from the sample carries the information of the illuminated part (such as the ability to reflect, absorb, and scatter sound waves), and converges through the acoustic lens. On the piezoelectric receiver, the obtained electric signal is input to an amplifier, and the image of the opaque sample is displayed on a fluorescent screen by a scanning system. The above device is called an ultrasound microscope. Ultrasound imaging technology has been widely used in medical inspection, used in microelectronic device manufacturing to inspect large-scale integrated circuits, and used in materials science to display regions and grain boundaries of different components in alloys. Acoustic holography is an acoustic imaging technology that uses the interference principle of ultrasound to record and reproduce stereoscopic images of opaque objects. Its principle is basically the same as that of light wave holography, except that the recording methods are different (see Holography). The same ultrasonic signal source is used to excite two transducers placed in the liquid, which respectively emit two coherent ultrasound waves: one beam passes through the object under study and becomes the object wave, and the other serves as a reference wave. Object waves and reference waves are coherently superimposed on the liquid surface to form an acoustic hologram. A laser beam is used to illuminate the acoustic hologram. A diffraction effect generated when the laser reflects on the acoustic hologram is used to obtain a reproduced image of the object. Usually, cameras and televisions are used. Machine for real-time observation.
Utilizing ultrasonic mechanical, cavitation, thermal and chemical effects, ultrasonic welding, drilling, solid smashing, emulsification, degassing, dust removal, descaling, cleaning, sterilization, promoting chemical reactions, and biology Research has been widely used in various sectors such as industry and mining, agriculture, and medical care.
Application of ultrasonic flow velocity sensor
Ultrasonic sensors use ultrasonic detection technology to convert detected ultrasonic waves into electrical signals, which are generally divided into two categories:
The first type is a time difference method, a frequency difference method, and a phase difference method that use changes in flow velocity. The basic principle is to reflect the flow velocity by detecting the time difference of the propagation of ultrasonic waves in the forward and backward liquid, so it is also called the propagation speed difference method. The time difference method and frequency difference method eliminate the influence of temperature on the detection, and the measurement accuracy is high, and it is widely used;
The second type is the use of ultrasonic waves that drift with the flow velocity, and the reflected flow velocity is called the Doppler ultrasonic flow velocity method. The ultrasonic wave is transmitted to the liquid in the open channel, and the ultrasonic wave carries a flow velocity in the flowing liquid, and then the receiving probe, that is, the transducer, transmits information to the microprocessor for data processing, and finally obtains the flow velocity.
The ultrasonic sensor is a non-contact measuring instrument that does not hinder the flow of liquid and has high measurement accuracy.