The ultrasonic phased array imaging technology is sound-wave imaging technology utilizing the sound wave emitted (or received) by each array element, changes the phase relationship by controlling the delays of each transducer array element stimulating or emitting pulse, to change the focal point and beam azimuth. Because the delay of the phased array element can be changed dynamically, the ultrasonic phased array probe inspection mainly uses its two characteristics: controllable acoustic beam angle and dynamic focusing.
Each element in ultrasonic phased array is stimulated by the same pulse with different delays. Changing the delays can control deflection Angle and focus. In fact, the rapid deflection of the focus makes it possible to perform two-dimensional imaging of specimens.
The ultrasonic phased array detection technology has the following characteristics:
(1) It generates controllable acoustic beam angle and focus depth, to test complex structural parts and blind spot defects.
(2) It combines crystals to controls the sound field, which makes high-speed electronic scanning possible. Equipped with mechanical fixture, it tests the specimen through high speed, omnibearing and multi-angle detection.
(3) By driving each array element with the same pulse voltage, it makes the actual sound field intensity of focus area much higher than the conventional ultrasonic testing technology. Therefore, it’s possible to use higher test frequency for materials of the same acoustic attenuation.
Principle of ultrasonic phased array
The digital control technology of phased array ultrasonic imaging system mainly controls the space and time of the beam. With the advanced computer technology, it controls precise phase of the emitting / receiving beam, in order to get the best features of the beam. These key digital technologies include phase control delay, dynamic focusing, dynamic pore diameter, dynamic change trace, coding emission, acoustic beam formation, etc.
Phased array ultrasonic imaging systems makes use of the array transducers, and realizing the beam focusing, deflecting, beamforming and other phased effects by adjusting the phase delay of the transmitted / received signals of each array element and controlling the curvature, orientation, aperture, etc. of the synthetic wave front, so as to form a clear imaging. Therefore, the phase delay (also known as phase-controlled delay) is the core of phased array technology, which is the basis of a variety of phased effects.
Phased focus principle (as Figure): Phased emission and focus principle is shown in Figure. We set array element center distance d, array transducer aperture D, focus point P, focal length f, the media velocity of sound c. According to the geometric path difference, it can be calculated how to make each element emitted wave can be focused at point P.
[激励脉冲 stimulation pulse, 延时 delay]
(A) Launch focus map (B) Receive focus map
Phased focusing principle diagram
Phased array testing equipment
Phased array detection equipment includes parts: hardware and software
The hardware has ultrasonic signal transmitting and receiving device, which transmits the array beam by phased array probe to form a focusing beam. The ultrasonic wave after passing through the object can be received and then the signal is amplified, filtered and detected, then A / D converted for further signal dealing.
The software mainly makes use of the received signal for computer data processing in order to obtain the required image data.
Phased array probe
Phased array probe has a wide variety of specification, including different sizes, shapes, and frequency counts, but their internal structure is to divide an entire piece of piezoelectric ceramic into multiple segments. The modern phased array sensors for industrial NDT inspection are mostly made of piezoelectric composite materials. Most of these sensors are polymer matrices formed from tiny and thin piezo ceramic strips. This structure greatly increased the difficulty of the production of composite materials than the same structure of the piezoelectric ceramic sensor with 10dB -30dB higher sensitivity. The split metal coatings are used to divide the composite strip into individual electronic wafers, which can be excited independently. The segmented wafers are transferred to the same sensor. The sensor also includes a matching layer to protect the wafers, backing material, connected cables, and the probe shell.
[多路同轴控制电缆Multi-Coaxial Control Cables, 晶片线路Wafer Circuit, 背衬材料Backing Materials, 内衬Internal Meterial, 复合压电晶片Composite Piezoelectric Wafer, 匹配层Matching Layer, 金属镀层Metal Plating]
Phased array calibration test block
An artificial reflector specimen with a certain purpose-designed and a simple geometric shape, is usually called the test block. Like the instrument probe, the test block is an important tool in ultrasonic phased array flaw detection. The role of the test block: is to determine the detection sensitivity.
A-type test block diagram
Phased array test image display