Principle and application of ultrasonic wave

Transcription

1 Topics on ultrasonic wave Principle and application of ultrasonic wave Writer Handong Li ( ) Emendator: Yabin Zhu ( ) 1 brief introduction to the special subject Ultrasonic wave is an acoustic wave whose frequency ranges from to Hz. The ultrasonic wave widely exists in the natural world and our daily life. For example the languages of dolphins and rats contains ultrasonic wave. The bats navigate and look for food with the help of ultrasonic wave. Besides, the sounds produced by metal striking and the leaking gas of a small fovea contain ultrasonic wave. People begin to research on the ultrasonic wave from F. Savart once tried to create an 4 ultrasonic wave with a frequency of Hz using a multi-gear manually. The scientists came up with the idea detecting the islands of ice using the ultrasonic wave after the Titanic event in The research team headed by P. Langevin studied on the ultrasonic detective which laid the groundwork for the sonar technology during the First World War in R. W. Wood and A. E. Loomis published an experimental report about the ultrasonic energy in The Russian scholar Sokolov came up with the idea that we can detect the internal defects of an opaque substance using the good penetration property of ultrasonic wave. Then, American scientist Firestone made the Ultrasonic Non-destructive Evaluation to be a practical technology. The ultrasonic detection uses the ultrasonic wave as an information carrier and it is widely used in the detection and the development of the ocean, the non-destructive detection and evaluation and the medical diagnosis field and so on. For example, the ultrasonic wave can be used to detect the shoals of fish and the island of ice and can be used for the navigation of submarines, the transmission of information, the drawing of topography and the geological survey in the application of the ocean. In the detection, the ultrasonic wave is used to detect the internal defects of the solid materials, to measure the size of the materials and to measure the physical parameters. In medical field, the ultrasonic wave can be used to image the human internal organs (Ultrasonic B-scanner) and to measure the blood flow velocity (Color Doppler Ultrasound). 2 the arrangement of the special subject

2 Experiment 1: The generation and the transmission of ultrasonic wave 1 measure the delay of the straight probe and the sound velocity of the longitudinal wave in the test sample using the ultrasonic bottom echo 2 measure the delay of the Angle probe and the sound velocity of the shear wave in the test sample using the Quarter-circular R1 R2 3 measure the frequency and the wavelength of pulsed ultrasonic shear wave and longitudinal wave. Experiment 2: The measurement of elastic constants of solid 1 measure the front distance of the Angle probe 2 measure the shear refraction of the angle prob with respect to the Al test sample 3 observe the wave transformation, judge the type of the refraction wave in the text sample and refraction plane of the echo 4 calculate the young's modulus and the Poisson's ratio of the Al test sample Experiment 3: The detection of ultrasonic wave 1 measure the radial angle of the straight probe 2 measure the radial angle of the angle probe 3 measure the depth of the defect C in the test sample 4 measure the depth of the defect D and the distance from the right side of the test sample Experiment 4: The basic principle of ultrasonic imaging 1 Collect and record the scattering data of the test sample imaging 2 Use the computer to do the data processing, C type and 3D display 3 points of the preparation This subject experiment refers to the vibration and wave motion in college physics course. And its focal points are the properties of reflection, refraction and diffraction as well as the similarities and differences of the ultrasonic wave and the electromagnetic wave.

3 Part 1: The generation and the transmission of ultrasonic wave Purpose of the experiment 1 To know the main method of the generation and the receiving of the ultrasonic wave 2 To know the ultrasonic pulsed wave and its properties 3 To understand the reflection, refraction and the wave mode conversion of the ultrasonic wave 4 To preliminarily master the way of sound velocity measurement of ultrasonic wave 5 To master the using method of the ultrasonic experimental instrument and the oscilloscope Laboratory instruments JDUT-2 ultrasonic experimental instrument GOS-620 oscilloscope ( 20MHz) CSK-IB Al test sample steel ruler coupling medium (engine oil) and so on. The principle of the experiment 1 piezoelectric effect Deflection will occur in some solid substance when they are stressed or pulled and they will polarize at the same time. And the positive/negative bound charges are on the surface of the object. We call that piezoelectric effect. The piezoelectric effect of the substance refers to its inner structure. For example, the chemical constituent of quartz is SiO 2 and it can be seen as to be made up of +4 charged Si ions and -2 charged O ions. In the crystal, these two kinds of ions form a regular hexagonal which can be seen in figure In the figure, the three positive atoms make up an equilateral triangle towards to the right side and the center of the positive charge is at the center of gravity of the equilateral triangle. Similarly, three negative atom couples make up an equilateral triangle towards to the left side and the center of the negative charge is at the center of gravity of the equilateral triangle too. When there is no force on the crystal, the two gravities of the triangles are at the same place and the hexagonal electrical neutral. The whole crystal is made up of many hexagons, so the crystal is charge neutral too. f y x p crystal structure polarization by pull macro-polarization of crystal Figure piezoelectric effect of quartz crystal When the crystal is pulled from the direction x or pressed from the direction y, the hexagon above becomes longer in the direction x and that makes the center of the negative charge center and the positive charge center in different places. Though the hexagon is still electrical neutral, the negative charge center and the positive charge center are in different places that can generate the

4 electrical dipole moment p. There are many electrical dipole moments in the whole crystal which due to the polarization of the crystal and the bound charges occur on the right surface and the left surface. When the external force disappears, the crystal recovers to the original shape and the polarization disappears too. According to the same principle, when the crystal is pulled from the direction y or pressed from the direction x, the triangles made up of positive atoms and negative atoms are pressed flat and then the center of the negative charge center and the positive charge center in different places too. But at this time, the direction of electrical dipole moments is contrary to the direction that the crystal is pulled in the direction x and the polarization direction of the crystal is the opposite too. That is the principle of piezoelectric effect. When the external force is in the direction z (Vertical with the paper direction in figure 5.4-1), the centers of the positive and the negative charge have no relative displacement, so there is no piezoelectric effect. From above, the piezoelectric effect of quartz crystal is directive. When the quartz crystal has no external force but is forced by the electric field, the negative and positive ions are moving to the opposite direction, so the shape of the crystal changes. We called this phenomenon converse piezoelectric effect. There are other kinds of crystals. Let s take BaTiO 3 for example; the centers of the positive and the negative charge are not the same but the converse piezoelectric effect and the piezoelectric effect still exits even though the crystal has no external force in the room temperature. Most of them are manmade ceramic materials and we also called them piezoelectric ceramics. The piezoelectric material we used in this experiment is piezoelectric ceramic. 2 the generation and properties of ultrasonic pulse The piezoelectric ceramic is used as ultrasonic transducer and it is produced to Plan view pattern. The positive side and the negative side are silver coated to be the electrode and we call that bimorph. When we add a short voltage pulse to the two electrodes of the bimorph, the elastic deformation will occur in the bimorph and then the elastic oscillation occurs according to the converse piezoelectric effect. The oscillation frequency refers to the sound velocity and the thickness of the bimorph. We can get the elastic wave in the range of ultrasonic wave frequency by choosing the thickness of the bimorph properly. During the oscillation of the bimorph, bimorph oscillation the amplitude decreases gradually because the energy decreases gradually. So, it creates an ultrasonic wave packet which is usually called ultrasonic pulse as is shown in figure When the ultrasonic wave spreads in the material, the tested object creates spurious emission because of interaction. The scattered waves are received by the same piezoelectric transducer. Because of the piezoelectric effect, the oscillatory bimorph creates oscillatory voltage on the two electrodes and the voltage will be displayed on the oscilloscope after being amplified. ultrasonic pulse Figure generation of pulse The figure 5.4-3(a) shows the transmission of the ultrasonic wave in a test sample. The figure 5.4-3(b) shows the ultrasonic wave signal that the oscilloscope received. In the figure, t 0 is

5 the time that the electrical pulse is added to the bimorph, t 1 is the time that the ultrasonic wave arrived to the bottom of the test sample and reflected and received by the same probe. So, the time that the ultrasonic wave spreads to the bottom of the test sample is: ( ) t = t t 1 0 /2 If the test sample is homogeneous material, the ultrasonic sound velocity is certain and then the propagation distance of the ultrasonic wave in the test sample is: S = Ct 3 the wave type of the ultrasonic wave and the types of the transducers If the vibration direction of the bimorph inner particle is vertical with the bimorph plane, the bimorph transmit ultrasonic wave. There are some wave types of the spreading ultrasonic wave in the medium and they are depends on the force on the medium and the way the ultrasonic wave generates. Usually, there are three types of ultrasonic wave. Longitudinal wave type: When the vibration direction of the bimorph inner particle is the same with the spread direction of the ultrasonic wave, the wave type is longitudinal wave. Any solid substance can create longitudinal wave when its volume changes alternately. Shear wave type: When the vibration direction of the bimorph inner particle is vertical with the spread direction of the ultrasonic wave, the wave type is shear wave. The solid substance can endure not only the volume changing but also the shear changing. So, the solid substance can create the shear wave when the shear changing is alternate. Besides, the shear wave can only spread in the solid substances. Surface wave type: It spreads along the surface of the solid and it has the properties of both the shear wave and the longitudinal wave. The surface wave can be seen as to be made up with the longitudinal parallel with the surface and the shear wave vertical with the surface. The path of the vibrating particle is an ellipse which has the strongest amplitude 1/4 of the wavelength from the surface and decreases with the increase of the depth. a b Figure 5.4-3(a) the transmission of the ultrasonic wave in a test sample (b) the ultrasonic wave signal that the oscilloscope received Actually, the amplitude of the vibrating particle is weak when its distance with the surface is larger than the wavelength a 7b 2 (a) (b) 1. shell 1-2. bimorph absorb backing 4-4. electrode a- 7 b- down-lead 5. matching impedance 6.plug 7a. protective film 7b. slanting wedge Figure the structure of straight probe and angle probe. (a) straight probe and (b) angle probe 5 6 4

6 In actual application, we usually call ultrasonic transducer ultrasonic probe. In the experiment, the ultrasonic probes we often used are straight probe and angle probe. Figure shows its structure. The probe transmits the ultrasonic wave to the outside space from the protective film or the slanting wedge. The usage of the absorbing backing is to absorb the sound wave transmitted to the back so that the clutters can be reduced. The usage of the matching impedance is to adjust the shape of the wave packet pulse. Normally, the straight probe is used to create a longitudinal wave and an angle probe is used to create a shear wave or a surface wave. In an angle probe, the sound wave spreads in the probe first and then it arrives at the surface of the test sample after the ultrasonic wave is created and we call this period of time the. In a straight probe, the delay time is very small and can be ignore when the measurement accuracy is not very high. 4 the reflection, refraction and wave mode conversion of the ultrasonic wave In the angle probe, the ultrasonic wave the bimorph creates is longitudinal wave. The ultrasonic wave spreads into the test sample with the help of slanting wedge and the longitudinal wave can be converted into shear wave at the same time. Actually, when the ultrasonic reflect and refract on the surfaces of two solid substances, the longitudinal wave can be reflected and refracted to shear wave, also the shear wave can be reflected and refracted to longitudinal wave. We call this phenomenon of ultrasonic wave the conversion of the ultrasonic wave and figure shows its principle. The reflection, the refraction and wave mode conversion of the ultrasonic wave content with Stirling law of refraction: sinα sin αl sinα = = S (Reflection) C C C 1L 1S sinα sin βl sin β = = S (Refraction) C C C 2L 2S Incident longitudinal wave Reflected transverse wave Reflected longitudinal wave Medium 1 Medium 2 plug probe core Refracted longitudinal wave Η bimorph Refracted transverse wave Figure the reflection, the refraction and wave mode conversion of the ultrasonic wave Figure schematic picture of a variable angle probe

7 In the law above, α is the reflection angle of longitudinal wave, α is the reflection angle L S of shear wave, β is the refraction angle of longitudinal wave and L β S is the refraction angle of shear wave. C1L is the sound velocity of longitudinal wave in medium 1 and C1S is the sound velocity of shear wave in medium 1. C 2L is the sound velocity of longitudinal wave in medium 2 and C 2S is the sound velocity of shear wave in medium 2. In this experiment, we use a variable angle probe which has been shown in figure The core of the probe can rotate and angle probes with different refraction angles can be obtained by changing the incident angle θ. The variable angle probe becomes a straight probe when 0 θ =0, we can observe the process of wave type conversion using the probe. In the angle probe and the variable angle, the sound velocity C in the organic glass or the probe corn of the organic glass is smaller than the shear wave velocity Cs in Al, while the shear wave velocityc is smaller than the longitudinal wave velocity C. So, according to formula S (5.4-3(b)), there is only refractive shear wave in the Al medium when L α C > α1 = arcsin and there are no refractive longitudinal wave and no refractive shear CL C wave in the Al medium when α > α2 = arcsin CS. α1 is called the first critical angle from the organic glass to the interface of organic glass and Al medium. α2 is called the second critical angle. Experiment content 1 the measurement of the delay time of the straight probe and the longitudinal wave velocity in the test sample We should connect the JDUT-2 ultrasonic experimental instrument with the oscilloscope according to Appendix A and connect the straight probe to the ultrasonic experimental instrument, and then put the probe on the right side of the CSK-IB test sample, the radio frequency output of the instrument is connected with the first channel of the oscilloscope, the trigger is connected with the external trigger of oscilloscope, the oscilloscope Figure measurement of the delay time of straight probe

8 adopts the way of external trigger, set the value of ultrasonic wave instrument muffler and the voltage range and the time range of the oscilloscope to make the oscilloscope display the waveform as showed in figure In figure 5.4-7, S is called original wave, t 0 is corresponding with the initial time of the ultrasonic transmission; B 1 is called the primary bottom echo, t 1 is corresponding to the time that the ultrasonic wave spreads to the bottom of the test sample, being reflected and being received by the ultrasonic probe, so t 1 is corresponding to ultrasonic wave s round trip time in the test sample, B 2 is called the second bottom echo of the sample and it is corresponding to the time that the ultrasonic wave starts one round trip and arrives on the surface of the sample and some of the ultrasonic wave are reflected by the upper surface and then reflected by the bottom of the sample. In a word, that is the ultrasonic wave that goes two rounds trip in the inner of the sample. The rest may be deduced by analogy, the third the fourth and multiple bottom echo. Read the parameter t 1 and t 2 from the oscilloscope, the delay time of the straight probe is t = 2t 1 t 2 The longitudinal wave velocity of the sample is: C L = t 2L t The measurement of the delay time of the angle probe and the shear wave velocity of the sample The angle probe is connected with the ultrasonic wave instrument and we should put the probe on the CSK-IB sample near the front of the sample. Then, what we should do is to aim at the arc curved surface to make the sound beams arrive at the arc curved surface R 1 and R 2 at the same time. Figure shows the place that the angle probe placed. We can observe the echoes B 1 and B 2 on the oscilloscope at the same time by setting the value of ultrasonic wave instrument muffler and the voltage range and the time range of the oscilloscope, besides; we can measure the corresponding time t 1 and t 2. The waveform of the echo is similar to that in figure 5.4-7, B 1 is the primary bottom echo of the arc curved surface R 1 and B 2 is the primary bottom echo of the arc curved surface R2. From the formula R2 = 2R1, we can get the delay time of the angle probe: t = 2t 1 t 2 R 2 R 1 Figure measurement of the delay time of angle probe

9 The shear wave velocity of the sample is: C s 2 = t ( R R ) 2 1 t The direct and indirect measurement of the sound velocity When we use a single reflector (interface or manmade reflector) to measure the sound velocity, we can calculate the sound velocity by just measuring the echo time of the reflector. Figure shows the reflective wave of a single reflector. The time of direct measurement contains the spreading time t0 that the ultrasonic wave spreads in the probe which is also called the delay time of the probe. To any type of probe, the delay time is only corresponding to the probe itself but not the material we measured. So, we should measure the delay time of the probe first, and then we can use the probe to measure the echo time directly. What I introduced above is the method of direct measurement of the sound velocity. The calculation method of the longitudinal wave and the shear wave is referring to the formula and the formula If there are two certain reflector in the test sample, the method of relative measurement is to calculate the sound velocity after measuring the time difference of the echoes from the two reflectors. To straight probe, we can do the measurement by using two of the reflective echoes from the uniform of bottom. To the angle probe, we can do the measurement using the echoes on the two arc curved surfaces of the sample. Figure reflector the reflective wave of a single 4. Measurement of pulse wave frequency and wavelength For straight detector and sideling detector, adjust the time position of oscilloscopes respectively, make the first bottom echo of test block shown in the center of the screen, making amplitude is 80% of full screen. At this time press 10 button on the oscilloscope, measure the time interval between two vibrate wavelengths and get the vibrate time of one pulse cycle time. In order to read data precisely during experiment, time interval t of four cycles should be measured, the corresponding pulse wave frequency is f=4/t; calculate the pulse wavelength in Al block with longitudinal wave of sound velocity you got before, the wavelength is?=c/f. Basic requirement 1. Measure the delay of straight detector and longitudinal wave of sound velocity of test block using bottom echo. Test on 45 mm thickness of CSK-IB test block, test three times and do average. 2. Measure the delay of sideling detector and longitudinal wave of sound velocity of test block

10 using arc face R1 and R2. Test on the arc face R1 and R2 of CSK-IB test block, test three times and do average. 3. Measure the frequency and wavelength of pulse ultrasonic longitudinal wave and transverse wave. 4. Use 45mm thickness of CSK-IB test block to test first bottom echo for straight detector, measure the vibrate cycle time t of four pulse wave to get frequency wavelength. Test arc face R1 and R2 of CSK-IB test block to for sideling detector, measure the vibrate cycle time t of four pulse wave to get frequency wavelength. Test three times and do average. Analysis and thinking 1. The electric pulse that stimulating pulse ultrasonic wave is a very sharp and narrow pulse with a rising edge less than 20ns. Judging by the wave shape of ultrasonic pulse wave, the amplitude changes from small to big and becomes small again, not change from big to small directly, and the vibration lasts 1~10µm, do you know why? 2. When you incidence with sideling detector, why is transverse wave instead of longitudinal wave observed? Part 2: The measurement of elastic constants of solids Experimental purpose 1. To understand the relationship between the velocity of ultrasonic wave and elastic constants of solids 2. To master the method of ultrasonic velocity measurement 3. To understand the importance of velocity measuring in applications of ultrasonic waves Experimental principle and content 1. Measuring the incident point of the angle (inclined) probe. It is necessary to detect the incident point of the angle probe (i.e., the point where the incident wave beam intersects with the sample surface) for measuring the distance which ultrasonic wave travels. It s defined as the distance between the front edge of probe and the incident point, named front distance. According to Fig , put the probe on the sample surface and aim the probe to sample circular surface R 2. Move the probe to the position where the reflected signal can reach its maximum then record the distance L between the sample left edge and the front edge of the angle probe by a ruler. The front distance L then can be expressed as: 5.4-8

11 L L 0 R 1 R 2 Figure measuring the incident point of the angle (inclined) probe 2. Measuring the reflection angle of angle probe. The reflection angle can be calculated indirectly by measuring geometric parameters of the two holes A and B on the sample as reference. As to Fig , find out the maximum signal reflected from hole A on CSK-IB with angle probe, and measure the distance X A from the sample edge to the front edge of the angle probe; then move the probe left to find out the hole B and measure the corresponding distance X B as done to the hole A. At last measure the vertical and horizontal distance (H and L, respectively) between A and B. Since the reflection angle can be expressed as: (5.4-9) Thus one can easily calculate the reflection angle. x B x A D A C B L H Figure measuring the reflection angle of angle probe 3. The observation and measurement of wave conversion. Connect the adjustable probe to the JDUT-2 ultrasonic wave generator, as referred to Fig , then aim the probe at the R 2 circular surface of the sample. Change the incident angle of the wave beam by rotating the knob on the probe, at the same time slightly change the position of probe in order to make the reflected signal maximum, referred to Fig As the incident angle increasing, the longitudinal, transverse, and surface wave can be observed respectively.

12 4. The calculation of Young's modulus and Poisson coefficient of Aluminum. D A 2 C B Figure observation and measurement of wave conversion In anisotropic solid materials, the transport equation of ultrasonic wave can be expressed as: (5.4-10), Where is potential function C is the velocity of ultrasonic wave. Figure measuring the shear and longitudinal wave In solids, ultrasonic wave travels as either longitudinal or transverse type wave. The velocity can be expressed as: (5.4-11) Where d means the distance that the wave tranvels, and t is the travelling time. The velocities of longitudinal or transverse wave in one solids are usually not equal, which are generally determined by elastic parameters such as density, Young's modulus and Poisson coefficient. Therefore one can obtain these elastic constants by measuring the

13 velocities of ultrasonic waves travelling in solids. The solids will deform in the direction that force (strain) was put. The ratio between strain and stress is defined as the Young's modulus, represented by letter E. When solids suffer external strain, there will be an elongation in the longitudinal direction while a corresponding shortening in the transverse direction. The ratio of transverse and longitudinal stress is then defined as the Poisson coefficient, named as. Further, in the isotropic solid materials, the velocities of various type waves can be expressed as: (longitudinal wave) (transverse wave) Where E,, and are the Young's modulus, Poisson coefficient, and density of solids, respectively. Accordingly, one can use the above functions to calculate the elastic constants of solid materials if the velocities of the ultrasonic waves that travel in the solids can be measured. The functions to calculate the elastic constants can thus be deduced from the above functions as following: (Young's modulus) (5.4-14) Poisson coefficient Where is the velocity of longitudinal wave in the solid is the velocity of transverse wave in the solid and is the density of the solid, respectively Basic requirements 1. Measure the front distance of angle probe. Utilize the R 2 Circular surface of CSK-IB as reference. 3 times measurements are required then calculate the average value. 2. Measure the angle parameters of refracting transverse traveling from the angle probe into Aluminum. (1) Aim the probe to A, B holes and find out the maximum reflected wave signal in the oscilloscope screen. Measure X A and X A for 3 times, respectively. The lateral and vertical

14 distances (L and H, respectively) between hole A and B need to be measured for 3 times too. (2) Calculate the refracting angle of angle probe. (3) Calculate the incident angle of the incident longitudinal wave by formula :. (4) Calculate by formula:. Comparison between, and is needed. 3. Observe the wave conversions between Transverse wave, Longitudinal wave, and Surface wave. Change the incident angle of adjustable probe, observe and record the corresponding wave signals displayed on the oscilloscope screen at angle range of displayed on screen are needed., respectively. Schematic diagrams of these signals 4. Calculate the Young's modulus and Poisson coefficient of Aluminum. Analysis and Reflection 1. Why can the transverse wave reflected from R 1 circular surface coincide with the one from B 1 when approaching the adjustable probe gradually to the front of the sample? 2. How to measure the delay of surface wave probe by using CSK-IB sample? If it is possible to measure the incident point of surface wave probe the same way as angle probe? Why 3. How to measure the delay and incident point of angle probe by using the hole A and hole B on CSK-IB sample? 4. Is there any difference in measuring the delay and incident point by using steel or aluminium samples with the same size? Why? Part 3: Ultrasonic detecting Experimental purpose 1. To understand the directivity of Ultrasonic probe 2. To grasp the principle of ultrasonic detection and Position method Experiment instrument

15 JDUT-2 Ultrasonic experiment instrument Aluminum test block Steel ruler Coupling agent (machine oil) GOS-620 Oscilloscope 20MHz CSK-IB Experiment Principle The energy of direction lanched by the Ultrasonic probe is directly related to the Geometry and wavelength of the probe. In general, the smaller the wavelength, the higher the frequency, the better the directivity; The larger the size, the better the directivity. Expressed as: λ θ = 2arcsin( 1.22 ) d the relationship between the directivity of ultrasonic probe and its size and wavelength is shown in fig , where r is Radius of circular piezoelectric, λ is Ultrasonic wavelength. To have certain requirements of the ultrasonic probe directivity, using the higher frequency can make the ultrasonic probe size smaller. Because of high frequency, wavelength is smaller, and the chip radius is proportiona to the wavelength. In practice, we usually use the position that the amplitude reduced by half after 2r r=5ℵ/2 r=ℵ/2 r=ℵ/4 r=ℵ/8 Figure the directivity of ultrasonic probe deviating from the center axis to express the boundary of the acoustic beam. As is shown in fig , in the same depth location, the energy of center axis is the largest, When it deviates from the midline to the position of A, A', the energy is reduced to half of the maximum. Where θ is the diffusion angle of the probe. The smaller θ is, the better the directivity, the higher the positioning accuracy. Notice During the defect location, you must find the position that the flaw echo is the largest and make the defects in the central axis of the probe, then measure the corresponding time of the defect echo. According to the speed of sound you can calculate the vertical depth or horizontal distance between the incident points of the probe and the defects. O O Ηℵ Ηℵ A A' A' X A X straight (a) probe angle (b) probe Figure the directivity of ultrasonic probe (a) straight probe and (b) angle probe

16 Experimental content 1. Measurement of the acoustic beam s diffusion angle As is shown in fig , use the straight probe to find the corresponding echo of Channel hole B. Move the probe to make the echo largest, and record the location of the point x 0 and the amplitude of the corresponding echo; Then move left to make the amplitude reduced to half of the maximum, and record the location of the point x1; Use the same method to record the location of the point x 2 when move right. The diffusion angle of the straight probe is: θ = 2arctan x 2 2L x 1, where L is the distance between through-hole and surface. For the Inclined probe, first we must measure the refraction angle β of the probe, then use the same method as the Straight probe,and get the diffusion angle of the Inclined probe by x2 x1 2 θ = 2 arctan cos β 2L. x 0 x 1 x 2 D ξ A C B Figure measuring acoustic beam s diffusion angle of ultrasonic probe 2. Detect the depth of the defect by using Straight probe In ultrasonic detection, straight probe can be used to detect position and equivalent size of internal defects C in thick workpiece. Place the probe in the position shown in fig , and observe the waveform. The bottom wave is the reflection echo of the working bottom. We can use either absolute measurement method or relative measurement method to measure the corresponding time of bottom echo and defects wave (depth). Using the absolute measurement method, you must first measure (or know) the probe s delay and the sound velocity in the measured material, refering to the experiment 1 straight probe delay and the absolute measurement method of sound spreed. When use the relative measurement method, you must have specimen which have the same material as the tested block, and know the thickness of the specimen, referring to the experiment 1 straight probe delay and the relative measurement method of sound spread.

17 tc Hc = CL In absolute measurement, the depth is 2 t 0,where CL is longitudinal wave velocity t C is echo of defect C t 0 is straight probe delay D A C B Figure measuring the depth of defect of straight probe 3. Detect the depth and horizontal distance of the defect by using Inclined probe When you measure with inclined probe, if the measured ultrasonic wave propagation in the material distance is M, the depth H and the horizontal distance L is: H = M tan β L = M cot β Where β is the refraction angle of oblique probe in the test materials. To achieve the positioning of the defect D, you shall measure (or know) the refraction angle and the sound speed in the material, except the probe s delay and Point of incidence. Usually we use two holes at different depths in a test block of the same material as the measured materials to measure the oblique probe s delay, incident point, refraction angle and the sound speed. As is shown in fig , A and B are two holes in the blocks, edge from the test block are L A, L B, horizontal distance between the holes is L AB. Let the inclined probe points A and B,find the maximum echo, and measure the echo time t A, t B, The horizontal distance between the front edge of the probe and the edge of the test block are x A x B, The depths are known as H A H B, then: S = xb xa LAB H = H B H A Refraction angle: β = arctan S H C = 2H sound speed: ( t B t A ) cos β Delay: t 0 = t B 2H B C cos β L ( ) Edge distance: 0 = H B tan β xb LB Then point the probe to hole D, find the maximum echo, and measure xd td, then H D C t = ( ) D t 0 cosβ 2 depth of hole D

18 L D = x D + L H 0 D tan β (the horizontal distance from D hole to the edge of the test block) xb xa 0 D S H A C B Basic requirements 1. Measure the diffusion angle of the straight probe Use the Straight probe to measure hole A and B in CSK-IB respectively, each for 3 times, calculate diffusion angle. 2. Measure the diffusion angle of the inclined probe Use the inclined probe to measure hole A and B in CSK-IB respectively, each for 3 times, calculate diffusion angle. 3. Detect the depths of defect C in CSK-IB Use the straight probe and absolute measurement method, to measure 3 times, get average value. 4. Detect the depths of defect D in CSK-IB and the distance from the right side of the block Measure the oblique probe s delay, incident point, refraction angle and the sound speed, then Detect the depths of defect D and the distance from the right side of the block Analysis and Reflection In the use of the inclined probe, if you can get the same material as the tested materials, and know the depths of two deffetent holes in the block, then you don t need to measure the oblique probe s delay, incident point, refraction angle and the sound speed, and you can also determine the depth of defect. Try to explain the specific detection process of the method. Try to measure the length of the circular arc R2 in CSK-IB using the surface wave