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How ultrasonic flaw detectors use ultrasonic to detect
Nov 23, 2018

How ultrasonic flaw detectors use ultrasonic to detect


Ultrasonic flaw detectors now usually emit ultrasound on the object to be measured (such as industrial materials, human body), and then use its reflection, Doppler effect, transmission, etc. to obtain information inside the object under test and process it to form an image.


In the ultrasonic flaw detector, the Doppler effect method is to use the Doppler shift effect that occurs when the ultrasonic encounters a moving object to obtain characteristics such as the moving direction and speed of the object;


The transmission law is to obtain the internal characteristics of the object by analyzing the change of the ultrasonic wave after passing through the measured object, and its application is still in the development stage;


The ultrasonic flaw detector here mainly introduces the most widely used method for obtaining the internal characteristic information of the object by 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. Reflection will occur, and the greater the difference between the media, the larger the reflection will be, so we can emit an ultrasonic wave that is strong and capable of linear propagation to an object. The ultrasonic flaw detector then receives the reflected ultrasonic wave and according to The order and amplitude of the reflected ultrasonic waves can determine the size and distribution of the various media contained in the tissue and the degree of contrast between the various media (the ultrasonic waves reflected back can reflect The distance from the reflection surface to the detection surface, the amplitude can reflect the characteristics of the size of the medium, the degree of contrast difference, etc., and the ultrasonic flaw detector determines 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 and transmit it to a crystal having a piezoelectric effect (such as quartz, lithium sulfate, etc.) to vibrate to generate ultrasonic waves;


When receiving the reflected ultrasonic wave, the piezoelectric crystal is subjected to the pressure of the reflected sound wave to generate an electrical signal and transmitted to the signal processing circuit for a series of processing, and the ultrasonic flaw detector finally forms an image 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 A-type display is to process the received ultrasonic signal into a waveform image. According to the shape of the waveform, it can be seen whether there are abnormalities and defects in the measured object, and how large, etc., the ultrasonic flaw detector is mainly used for industrial detection; The display is to perform a one-dimensional "spatial multi-point motion timing diagram" by illuminating the detected information processed by the luminance, and is suitable for observing an internal moving object, an ultrasonic flaw detector such as a moving organ, an artery, etc. ;


The B-type display is a two-dimensional "anatomical image" that combines a plurality of brightness-processed detection information side by side to reflect the internal tomographic section of the measured object (the B-mode used in hospitals is made by this principle). ), the ultrasonic flaw detector is suitable for observing objects that are static inside;


The C-type display and the F-type display are now used less. Ultrasonic flaw detector detection can not only be very accurate, but also more convenient and faster than other detection methods, and it will not cause harm to the detection object and the operator. Therefore, it is more and more popular and popular. Development prospects.


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