Descriptions of NDT Projects Fall 2004 October 31, 2004

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1 Descriptions of NDT Projects Fall 2004 October 31, 2004 Introduction There are two separate NDT labs in Magister: ULTRA for ultrasound and EDDY for eddy current. Both labs are equipped with mechanical scanners capable of computer assisted scanning probes over the inspected sample. In ULTRA we have also a Network Analyzer for measuring impedance of piezoelectric transducer as a function of frequency. Projects 1. Transducer characterization- electrical model 2. Transducer characterization - beam pattern 3. Attenuation in solids 4. Defect characterization using eddy current Projects 1, 2 and 3 will be carried out in ULTRA while the project 4 in EDDY. Requirements: Full report Each group must write one full report. The report should have an abstract page, table of contents, an introduction section, a theory section etc. Oral presentation There is no exam, instead each group must perform an oral presentation of the project (at the date for the final exam ). Experiments Make a series of measurement to acquire data. Present the results in the report and oral presentation. This task is to be successfully performed to obtain the highest mark (mvg). Abstract A one page abstract (which contains one overview figure) should be written for presentation on the course web-page. Groups/Projects 2 groups per project, 2 pers ons per group

2 1. Transducer characterization electrical model Description Ultrasonic transducers are electro-mechanical devices that generate vibrations when excited with an electric pulse. Electrical parameters of a piezoelectric transducer can be characterized by measuring its electrical impedance or admittance as a function of frequency. Transducer's frequency response is characterized by resonances occurring at frequencies corresponding to different vibration modes of the piezoelement used in the transducer, and their multiples. A suitable electrical equivalent circuit can be used to model this impedance; the simplest is an RLC model. The mechanical part of the transducer can be modelled using a suitable field generation model; the simplest is the piston model. The purpose of this project is to investigate time and frequency responses of piezoelectric transducers. Transducers: T1-2 MHz contact transducer from PANAMETRICS T2-40 khz air coupled transducer MURATA Network Analyzer Agilent Technology Oscilloscope Ultrasonic instrument HP wave generator Measure the electrical admittance Y(f) of both transducers using Agilent Network Analyzer in a frequency band around main resonances. Measure pulse-echo responses of both transducers using digital oscilloscope and - ultrasonic instrument for T1, measurement on steel block V1 - HP wave generator for T2, measurement of an echo in the air Calculate spectra of the transducer responses Compare the calculated spectra with the impedance characteristics Estimate parameters of the RLC model for the MURATA transducer using the MATLAB routine provided by us. HINT: Acquire frequency characteristics of the T2 in a small frequency band located around of its 40 khz resonance. 1. Theory of piezoelectric transducers: operation principle, transducer as electro-mechanical device, RLC model, electrical parameters (frequency, bandwidth), role of backing for temporal (axial) resolution. 2. Experimental setups: impedance measurements, pulse response measurement. 3. Results: impedance plots (Re(Y), Im (Y), abs(y)), pulse responses in time, spectra of pulse responses. 4. Discussion: comparison of the impedance measurement and spectra of pulse responses, relative bandwidths (B/f 0 ), temporal resolutions in µs. 5. : RLC model, estimation results (numerical values), plots of the real and imaginary parts of the measured and estimated admittance. 6. Abstract: A one page abstract (which contains one overview figure) should be written for presentation on the course web-page.

3 2. Transducer characterization - beam pattern Description Ultrasonic transducers are electro-mechanical devices that generate vibrations when excited with an electric pulse. The mechanical part of the transducer can be modelled using a suitable field generation model; the simplest is the piston model. The model approximates sound field measured by a real transducer. The sound field takes the form of a main lobe and side lobes with geometry depending on the transducer geometry, frequency and medium parameters. Frequency response of the electrical part is characterized by resonances occurring at frequencies corresponding to different vibration modes of the piezoelement used in the transducer and their multiples. It is the purpose of this project to investigate methods for characterizing transducer s beem patterns in pulse-echo mode. Transducers (immersion testing): T1-10 MHz immersion transducer from PANAMETRICS, and T2-10 MHz immersion focused transducer from PANAMETRICS PC based ultrasonic instrument and XY-scanner Point target (small diameter drill) Measure and save in computer pulse-echo responses of both transducers to the point target immersed in water. The responses are to be measured in C-mode with resolution 0,5 mm both in X and Y axis for 3 to 5 different distances transducer point target. NOTE: For transducer T1 perform the measurements close to its near field limit. For transducer T2 perform the measurements close to its focal point. HINT: For any z start measurements from finding coordinates corresponding to the transducer center (x=0, y=0) by finding the point where the received echo has the largest amplitude. This position will be constant only if the drill bottom is parallel to the scanning plane. Define a square scanning region round this point. Measure and save in PC responses of the transducer in A-scan mode on its symmetry axis (Z-axis) for 20 different distances transducer point target. Plot images of the measured field showing echo amplitude in the XY plane in color code. Plot values of max pulse amplitude from A-scans in function of the distance form the transducer on Z-axis Simulate acoustic field of the transducer T1 at a chosen distance using MATLAB tool DREAM. 1. Theory of piezoelectric transducers: operation principle, transducer as an electro-mechanical device, piston model, acoustic parameters (near and far field, beam pattern), focused transducers. 2. Experimental setups: pulse-echo A-scan and C-scan measurements, 3. Results: C-scan illustrating transducers beam patterns at different z, transducers field on the axis. 4. Discussion: comparison of acoustic fields radiated by both transducers, influence of the transducer size on its beam pattern 5. : Simulated field for the transducer T1 presented in the form of C-scan (same as the measured ones), comparison of the measured and simulated results. 6. Abstract: A one page abstract (which contains one overview figure) should be written for presentation on the course web-page.

4 3. Attenuation in solids Ultrasonic attenuation is the rate of decay of mechanical radiation at ultrasonic frequency as it propagates through a material. The attenuation is measured in nepers per unit length 1 or in decibels per unit length. Ultrasonic attenuation α is a measure of the relative amplitudes of a wave at two locations in space. Attenuation, itself, is not relative, however. Attenuation is a definite quantity for a particular mode of wave motion at a certain frequency in a given material under specific conditions. One can make absolute measurements of the quantity α using the correct method of experimentation. It is the purpose of this project to investigate methods for measuring ultrasonic attenuation in materials on an absolute basis and with accuracies of plus-or-minus a few percent. Transducer (immersion testing): T1-5 MHz immersion transducer from PANAMETRICS, and T2-10 MHz immersion focused transducer from PANAMETRICS PC based ultrasonic instrument and XY-scanner 2 copper specimens Measure and save in computer pulse-echo responses of both transducers for the specimens immersed in water. The responses are to be measured for T1 and T2 in B-mode with the resolution of 1 mm for 2 different distances transducer specimen for both specimens. If the difference in the amplitudes of the front and bottom echoes is large perform two measurements with two different gains. HINT: Place the specimen on a tripod table. Start measurements from setting the specimens parallel to the scanners XY plane by finding angles where the received echo has the largest amplitude. In this position the obtained echoes will be horizontal and they will have constant amplitude. Plot amplitudes of the front echo A, first bottom echo B and the second bottom echo C in function of scanning direction (see Papadakis) 2. Calculate diffraction corrections for both transducers for the chosen distances (see Papadakis). Calculate the normalized values of echo amplitudes and the value of attenuation α (see Papadakis). Simulate acoustic field of the transducer T1 on its symmetry axis using MATLAB tool DREAM. 1. Theory: definition of attenuation, description of attenuation measurement setups, sources of errors, diffraction corrections required to transform raw data to absolute measurements 2. Experimental setups: buffer rod method, pulse-echo A-scan, 3. Results: B-scans illustrating the obtained measurements, calculations of diffraction correction and attenuation 4. Discussion: comparison of values obtained by both transducers, influence of the transducer frequency 5. : Simulated field for the transducer T1 presented and its diffraction correction term, comparison with the Papadakis diagram. 6. Abstract: A one page abstract (which contains one overview figure) should be written for presentation on the course web-page. 1 One neper is a decrease of a factor of exp(-1.0) or 1/e in amplitude. 2 E.P. Papadakis, The Measurement of Ultrasonic Attenuation, in Physical Acoustics, vol XIX, Academic Press, Ins.

5 4. Defect characterization with eddy current Description Eddy current probes used for surface inspection have limited penetration depth due to the skin effect. Specially designed deep penetrating probes operated at low test frequencies (below 1 khz) are capable of detecting voids in copper located up to 3-4 mm under the surface. Eddy current response contains information that can be used for the estimation of void's depth and size. Phase angle of the EC response is used for depth estimation and its amplitude gives a measure of void size. It is the purpose of this project to investigate methods for characterization deep defects using amplitude and phase of their EC response. Deep penetrating probe MDF 10 EC instrument PL.E and a PC based XY-scanner Copper plate with drilled holes Estimate test frequency f t suitable for the detection of defects in the plate Measure and save in PC eddy current 2D response of the probe to 2mm hole located at the depths of 1 mm under the surface of the copper plate. The responses are to be measured in C- mode with resolution 0,5 mm in both axes so that the hole response is in center of the acquired image. Measure and save in PC eddy current responses of the probe to the holes in copper plate. The measurement is to be performed from the upper plate side so that bottoms of the holes are at different depths under the plate surface (see figure below). The responses are to be measured in A-mode with resolution 0,5 mm along the one axis depending on the plate location. NOTE: MDF 10 is a double-differential transducer with pick-up coils in the form of cross pattern. Its response strongly depends on orientation of its coils, choose the scanning direction along one of the cross arms. HINT: For any line, start measurements from finding coordinates corres ponding to the transducer center by finding the point where the received response has the largest amplitude. Plot an image of the measured 2D response showing real and imaginary parts as well as amplitudein the XY plane in color code. Plot values of the responses phase in function of depth (hole diameter as a parameter) Plot values of the responses amplitude in function of hole diameter (hole depth as a parameter) Estimate analytical relationships defining the hole depth as a function of phase and hole diameter at given depth as a function of amplitude. Acquire transducer 2D response for - frequency f t and the 2mm deep hole - frequency 1.5f t and the 1mm deep hole. 2. Theory of eddy current testing: eddy current principle, probe operation, responses of absolute and differential probes, information contained in the response s phase and amplitude 3. Experimental setups: measurements of probe signature (2D response) and 1D responses to different holes 4. Results: C-scan illustrating probe signature, tables and diagrams including results obtained for different holes. 5. Discussion: transducer s signature, influence of hole depth and size. 6. : 2D responses obtained for the deeper hole and the higher frequency.

6 Abstract: A one page abstract (which contains one overview figure) should be written for presentation on the course web-page. EC probe Scanning Hole depth Holes COPPER PLATE 1 Φ 1,0 mm Φ 1,0 mm Φ 1,0 mm 2,5mm 2,0 mm 2,5 mm Φ 1,0 mm 1,5 mm Φ 1,5mm Φ 1,5mm Φ 1,5mm Φ 1,5mm 2,0 mm 1,5 mm 1,0 mm 0,5 mm Φ 2,0 mm Φ 2,0 mm Φ 2,0 mm Φ 2,0 mm 2,0 mm 1,5 mm 1,0 mm 0,5 mm Φ 2,5mm Φ 2,5mm Φ 2,5mm Φ 2,5mm 2,0 mm 1,5 mm 1,0 mm 0,5 mm