The sound is generated by your active element, travels through some couplant, and is partially reflected where your sound enters your actual part. This reflection goes back through the couplant and is reflected again by your probe. This continues and leads at the beginning of every A-scan to an increased noise level. This is the dead zone. It is the zone where you can not detect anything as the noise, caused by this bouncing back and forth between the active element and the entry surface, is too high. And it is the same effect for conventional and Phased Array probes. On the other hand, the near field is the natural focus point of your beam, which can be calculated. This video can help: ua-cam.com/video/xWRABwg1TB8/v-deo.htmlsi=M8IclHFQWzDRgFhr
@@NDE40Ok thank you very much. In other words the PA transducer has a dead zone like the conventional probes. We are talking about 3-6 mm of dead zone below the surface. From this point of view there are no advantages in using the PA instead of the conventional transducers. Correct? Thank you again. Best Regards. Massimo.
@@MassimoPradetto Exactly - phased array and conventional probes with the same aperture also have a similar deadzone. Actually, I found that the deadzone of phased array probes is a tad longer. This is where TFM can help (but only if done correctly).
Good video. The problem of the TFM is, that it has many propagation modes and whe you choose wrong one, you will not see the imperfection inside the material. So you have to inspect the material with more propagation modes to be sure, that you catch the flaw.
For me that is actually a benefit. In classic UT or PA you never know if the indication was caused by L waves or T waves which can lead to misinterpretations. In TFM you can distinguish and it is not that you have to collect the data multiple times - you only nees to do the data processing with different parameters. And in my eyes a good manual TFM instrument should allow to do multiple reconstructions of the same data set and display them at the same time.
Thank you for the detailed explanation! Your channel is the best in the field of NDE indeed. However, I was wondering if you have ever dealt with NDE for concrete structures and if you have some recommendations for that. I think the most used tool is MIRA, but I couldn't find enough materials that talk about the instrument and how it is used in the best way.
My expertise lies more on the industrial side of NDE - but last year we had a project designing an inspection for a concrete structure - and like everybody we tried the MIRA. In my eyes, the instrument did a pretty good job. It uses something similar to FMC/TFM.
Great Video! In most applications the scanning speed is very important. FMC/TFM is certainly much slower compared with "standard" PAUT. What is your view on this?
Not necessarily. TFM Speed scales linearly with the number of elements and PAUT with the number of focal laws. Moreover, PAUT usually generates more ringing as the beam is directed. Therefore, the PRF of TFM could be higher. The third limiting factor is the speed of data transfer - so You need to be careful which instrument to buy.
I'm intrigued about why you describe as high frequency the A-scans from each capturing elements. I get that we're talking about ultrasonic waves, but shouldn't we reserve such description to frequencies above like 10MHz?
The High Frequency in the A-scans is not about the ultrasonic frequency. So-called HF (high frequency) A-scans are not rectified, are usually not compressed, and use a sampling rate that is at least 5 times the frequency of your ultrasonic frequency.
Brilliant! The future looks bright
very good video. I have a question. What is the dead zone of the phased array transducers? thank you Dr. Vrana!
The sound is generated by your active element, travels through some couplant, and is partially reflected where your sound enters your actual part. This reflection goes back through the couplant and is reflected again by your probe. This continues and leads at the beginning of every A-scan to an increased noise level. This is the dead zone. It is the zone where you can not detect anything as the noise, caused by this bouncing back and forth between the active element and the entry surface, is too high. And it is the same effect for conventional and Phased Array probes.
On the other hand, the near field is the natural focus point of your beam, which can be calculated. This video can help: ua-cam.com/video/xWRABwg1TB8/v-deo.htmlsi=M8IclHFQWzDRgFhr
@@NDE40Ok thank you very much. In other words the PA transducer has a dead zone like the conventional probes. We are talking about 3-6 mm of dead zone below the surface. From this point of view there are no advantages in using the PA instead of the conventional transducers. Correct? Thank you again. Best Regards. Massimo.
@@MassimoPradetto Exactly - phased array and conventional probes with the same aperture also have a similar deadzone. Actually, I found that the deadzone of phased array probes is a tad longer. This is where TFM can help (but only if done correctly).
Good video. The problem of the TFM is, that it has many propagation modes and whe you choose wrong one, you will not see the imperfection inside the material. So you have to inspect the material with more propagation modes to be sure, that you catch the flaw.
For me that is actually a benefit. In classic UT or PA you never know if the indication was caused by L waves or T waves which can lead to misinterpretations. In TFM you can distinguish and it is not that you have to collect the data multiple times - you only nees to do the data processing with different parameters. And in my eyes a good manual TFM instrument should allow to do multiple reconstructions of the same data set and display them at the same time.
What a great video
Thank you so much
very good idear
Thank you
Thank you for the detailed explanation! Your channel is the best in the field of NDE indeed.
However, I was wondering if you have ever dealt with NDE for concrete structures and if you have some recommendations for that. I think the most used tool is MIRA, but I couldn't find enough materials that talk about the instrument and how it is used in the best way.
My expertise lies more on the industrial side of NDE - but last year we had a project designing an inspection for a concrete structure - and like everybody we tried the MIRA. In my eyes, the instrument did a pretty good job. It uses something similar to FMC/TFM.
Great Video! In most applications the scanning speed is very important. FMC/TFM is certainly much slower compared with "standard" PAUT. What is your view on this?
Not necessarily. TFM Speed scales linearly with the number of elements and PAUT with the number of focal laws. Moreover, PAUT usually generates more ringing as the beam is directed. Therefore, the PRF of TFM could be higher. The third limiting factor is the speed of data transfer - so You need to be careful which instrument to buy.
I'm intrigued about why you describe as high frequency the A-scans from each capturing elements. I get that we're talking about ultrasonic waves, but shouldn't we reserve such description to frequencies above like 10MHz?
The High Frequency in the A-scans is not about the ultrasonic frequency. So-called HF (high frequency) A-scans are not rectified, are usually not compressed, and use a sampling rate that is at least 5 times the frequency of your ultrasonic frequency.
@@NDE40, awesome! That makes perfect sense to me now. Thanks a bunch!