Ultrasound is a sound wave with a frequency higher than 20 kHz, which is beyond the discriminating ability of the human ear and is very penetrating. There are many applications of ultrasound, such as measuring the distance with ultrasound reflection, using high-power ultrasonic vibration to remove the scale attached to the boiler, and using high-energy ultrasound to make an "ultrasonic knife" to destroy and crush the cancer and stones in the human body. Etc., and the use of ultrasonic reflection and other effects such as strong penetrability and linear propagation are also a large application area.
The application of ultrasonic detection mainly includes the detection of various materials in the industry and the medical diagnosis and diagnosis of the human body. Through it, people can detect defects such as bubbles, scratches and cracks in industrial materials such as metals, and can detect people. Whether the body's soft tissue, blood flow, etc. are normal.
So how do people use ultrasound for testing? Nowadays, ultrasound is usually emitted on an object to be measured (such as industrial materials, human body), and then its reflection, Doppler effect, transmission, etc. are used to acquire information inside the object to be measured and processed to form an image. The Doppler effect method is to use the Doppler shift effect of ultrasound when encountering a moving object to derive the moving direction and velocity of the object; the transmission method is to analyze the ultrasonic wave after passing through the measured object. The application of the internal characteristics of the object is still in the development stage; here is the most widely used method to obtain the internal characteristic information of the object through the reflection method.
The reflection method works on the principle that the ultrasound will reflect strongly when the interface is organized by different acoustic impedances. As we know, the sound waves are transmitted from one medium to another at the interface between the two. Reflections will occur, and the greater the difference between the media, the greater the reflection, so we can emit an ultrasonic wave that is strong enough to penetrate straight through an object, and then receive the reflected ultrasonic waves and return them according to these reflections. The order and amplitude of the ultrasonic waves can be used to determine the size and distribution of various media contained in the tissue and the degree of contrast between the various media. The reflected ultrasound can reflect the reflective interface. The distance from the detection surface, the amplitude can reflect the characteristics of the size of the medium, the degree of contrast difference, etc., to determine whether the object to be measured is abnormal.
In this process, there are many aspects involved, including the generation, reception, signal conversion and processing of ultrasonic waves. The method for generating ultrasonic waves is to generate an excitation electric signal through a circuit to transmit a crystal having a piezoelectric effect (such as quartz, lithium sulfate, etc.) to vibrate to generate ultrasonic waves; and when receiving the reflected ultrasonic waves, the piezoelectric crystal is again The electric signal is generated by the pressure of the reflected sound wave and transmitted to the signal processing circuit for a series of processing, and finally an image is formed for observation and judgment.
Here, the type of the image processing method (that is, the image into which the obtained signal is converted) can be further classified into an A-type display, an M-type display, a B-type display, a C-type display, an F-type display, and the like. The type A display processes the received ultrasonic signal into a waveform image. According to the shape of the waveform, it can be seen whether there are any abnormalities and defects in the object to be tested, and how large, etc., mainly used for industrial inspection; the M-type display is A luminance-processed detection information is expanded in chronological order to form a one-dimensional "space multi-point motion timing diagram", which is suitable for observing internal moving objects, such as moving organs, arteries, etc.; Side by side, a series of two-dimensional "anatomical images" that reflect the internal tomographic section of the measured object (the B-mode used in hospitals is made by this principle), which is suitable for observation. The internal is in a static object; the C-type display and the F-type display are now used less.
Ultrasonic testing can not only be very accurate, but also more convenient and faster than other testing methods, and it will not cause harm to the object and the operator. Therefore, it is more and more popular and has a very broad development. prospect.
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Label: Principles of application of ultrasonic detection
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