Nowadays, it has become a trend for pregnant mothers to swipe their pregnant photos on social media. So what is the principle of the B-ultrasound that every pregnant mother is exposed to? Why can the baby in the belly be seen by the B-ultrasound? This requires an introduction to the hero behind-ultrasound.

Ultrasound is a sound wave with a frequency higher than 20000 Hz, which is usually inaudible to the human ear. Ultrasound has good directivity, strong penetrating ability, easy to obtain concentrated sound wave energy, and spreads far in the water. Because of these characteristics, ultrasound is widely used in daily life, and can be used for distance measurement, speed measurement, cleaning, welding, stone crushing, sterilization and disinfection.

Everyone must have used ultrasound products. For example, go to the hospital to wash your teeth, go to the optician to wash your glasses, and do B-ultrasound during the physical examination. Have you found that ultrasound is still very powerful?

In the Ultrasound Technology Center of the Institute of Acoustics of the Chinese Academy of Sciences, nearly a hundred scientific researchers study ultrasound-related issues every day.

The predecessor of the Ultrasound Technology Center was the ultrasound room founded by the famous Chinese physicist and educator Ying Chongfu. There are currently five major research directions, namely, detection acoustics and non-destructive testing of marine equipment, solid acoustics and deep ocean drilling, micro-acoustics and micro-devices, medical acoustics, computational acoustics and sound energy applications.

The following compound er will take you into the ultrasound technology center, watch and experience ultrasound popular science experiments, and experience how ultrasound shows its magical powers up close.

1. Ultrasonic cleaning

Ultrasonic cleaning refers to the process of using ultrasonic waves to remove dirt on the surface of the sample in the liquid, such as removing oil or dust on the surface of the glasses. Here, ultrasonic waves are mainly used to generate strong sound effects such as micro-jets and shock waves when cavitation occurs in the liquid to peel off the dirt on the surface of the sample to achieve the purpose of cleaning , just like cleaning a car with a high-pressure gun.

At present, ultrasonic cleaning is a mature technology and has been applied in laboratories, hospitals and other occasions. Ultrasonic cleaners have also become one of the household appliances used to clean daily necessities such as glasses and jewelry.

2. Phacoemulsification

Ultrasonic emulsification refers to the mixing of two (or more) difficult-to-phase solutions (such as oil and water) under the action of ultrasonic energy to form a dispersion system, where one liquid is evenly distributed in the other liquid The process of forming an emulsion.

The emulsion formed by phacoemulsification has good uniformity and stability. Therefore, cosmetics such as emulsions that women often use, dairy medicines in hospitals, and dairy foods can be prepared by phacoemulsification. Didn't expect it?

3. Ultrasonic atomization

The weather in the north is relatively dry, and many families use humidifiers. After plugging in the power, the humidifier started to "smoke". In fact, this "smoke" is not real smoke, but mist with very small particles. How does the humidifier turn big water droplets into small mist droplets?

Look at the animation above, is it very intuitive? There is an ultrasonic transmitter at the bottom of the humidifier, which emits ultrasonic waves just like a rocket eruption, breaking the water into many tiny droplets and rushing out of the water surface, which becomes the atomization effect we see. Since it is not heated by water to evaporate, it feels cool to the touch. The nebulizer in the hospital also uses ultrasound for nebulization.

4. Dynamic photoelastic (tán) imaging

We know that sound waves are invisible. But with dynamic photoelastic imaging, we can see the propagation route of sound waves in transparent solids very intuitively.

Ultrasound in the solid has the ability to change the direction of light polarization, that is, the temporary birefringence effect. Some substances (such as glass, plastic, epoxy resin) usually do not have birefringence, but when they are stressed or subjected to an electric field, birefringence will occur. Generally speaking, it is difficult for natural light to pass through two mutually perpendicular polarizers. When a transparent test block with ultrasound is placed between two mutually perpendicular polarizers, due to the temporary birefringence effect, part of the incident light can pass through and be The imaging screen captures and shows the waveform of the ultrasound. By adjusting the time delay of incident light and ultrasonic emission by the time delay synchronization device, the ultrasonic trajectory can be observed.

Compared with analytical and numerical methods, the experimental results provided by the dynamic photoelastic imaging method are more accurate and close to the actual physical model, and the numerical simulation method can be experimentally verified.

5. "Industrial Ultrasound"

When ultrasound encounters unevenness or discontinuities in the propagation medium, reflection and diffraction will occur. Using this feature of ultrasound, researchers have developed medical B-ultrasound (such as taking the first photo of the fetus) and "industrial B-ultrasound."

Medical ultrasound

Ultrasonic diagnostic equipment can be divided into four categories: A, B, C, and F, of which category B is the most commonly used. The usual "B-ultrasound" is to transmit ultrasonic waves to the human body, and at the same time receive the reflected waves from the internal organs, and reflect the information carried on the screen.

Ultrasound, like ordinary sound, can be transmitted in a directional manner. Part of the sound penetrates the object, part of the sound is absorbed by the tissue, and part of the sound is reflected. The B-ultrasound uses the reflected signal to determine the shape of the detected tissue. The principle is the same as that of bats and dolphins. Similarly, the time difference between the transmitted signal and the echo signal is used to determine the location information of the tissue. Especially at the tissue interface, ultrasound has strong reflection, and these strong reflection signals are used to characterize the appearance of reconstructed tissues and organs. Due to the penetration depth of different sound waves and the different wavelengths, the ultrasound used in specific physical examinations is generally determined to be in the range of 2MHz to 15MHz. In clinical imaging, the ultrasound probe will directly contact the skin surface, and the coupling mucus is coated between the probe and the skin to facilitate the transmission of ultrasound signals between the probe and tissues and organs.

Ultrasonic non-destructive testing

The simplest conventional ultrasonic non-destructive testing equipment consists of 3 parts, which are ultrasonic transmitter and receiver module, ultrasonic transducer and oscilloscope.

First, the ultrasonic transmitter and receiver module generates electrical pulses, which become ultrasonic waves after entering the ultrasonic transducer. When the ultrasonic wave propagates inside the tested workpiece, it will reflect and be received by the transducer when it encounters a defect, and finally an abnormal signal will be displayed on the oscilloscope interface. Therefore, by moving the transducer and observing the size and arrival time of the defect echo, we can determine the location of the defect, estimate the shape and size of the defect, and complete the non-destructive inspection of the workpiece.

Facing the major strategic needs of my country’s marine resource exploration and marine equipment safety, the Ultrasonic Technology Center focuses on scientific and technological innovation in deep drilling surveys and resource evaluation, marine equipment non-destructive testing, acoustic detection and sensor technology, and acoustic physics and acoustic energy applications. A series of major scientific and technological achievements have been produced, and it is an important base for scientific research, talent training, and open communication in the fields of deep drilling, sound energy application, medical acoustics, micro-acoustics, and computational acoustics. In the future, we will continue to work hard and forge ahead.