EMAT: Frequently Asked Questions.....Innerspec Technologies, Inc.

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1. What is Ultrasonic Testing (UT)?

2. How is ultrasound generated with a piezoelectric transducer?

3. How is ultrasound generated with an EMAT?

4. What kind of waves and what frequencies can you generate with EMAT?

5. What are the advantages of EMAT?

6. What is horizontally polarized shear energy used for?

7. In summary, what is a good application for EMAT?

8. What materials can be inspected with EMAT?

9. Why aren't EMATs used more frequently?

10. Are there standards for EMAT inspection?

11. Is EMAT equipment expensive?

12. Can you have fast inspection with EMAT?

13. Is EMAT safe?

14. Can EMAT transducers be used in phased array?

15. Are EMAT systems difficult to use?

16. Do you also sell EMAT sensors?

17. I have an application that is not on your list of products, how do I find out if you can do it?

18. Do you sell equipment worldwide?

1. What is Ultrasonic Testing (UT)?

Ultrasonic Testing is the use of high-frequency sound waves to detect imperfections, take measurements or to locate changes in material properties of solid objects. Because of its capabilities and reliability, UT is one of the fastest growing Non Destructive Testing techniques. It is the method of choice for critical applications where full volumetric inspection is required, especially when there is only limited access to the object being inspected.

2. How is ultrasound generated with a piezoelectric transducer?

The piezoelectric crystal creates a mechanical disturbance (ultrasonic wave) when subjected to voltage. This ultrasonic wave is “steered” from the transducer into the object to perform the inspection. Because ultrasonic waves do not transmit easily through air due to differences in impedance, the transducer needs to be “coupled” to the solid being inspected using a liquid between the crystal and the solid being inspected.

3. How is ultrasound generated with an EMAT?

An EMAT or Electro Magnetic Acoustic Transducer consists of a magnet and a coil of wire and relies on electro-magnetic acoustic interaction for elastic wave generation (ultrasound). Using Lorentz forces and Magnetostriction, the EMAT and the metal test surface interact and generate an acoustic wave within the material. The material being inspected is its own transducer and there is no need to couple the EMAT with thematerial. For more information see EMAT Technology.

4. What kind of waves and what frequencies can you generate with EMAT?

EMATs can easily generate any wave mode available with piezoelectric UT (Rayleygh, Creeping, Shear Vertical, Longitudinal) plus others that are very difficult to generate with conventional methods (Shear Horizontal, Lamb). Also, EMATs can generate Shear waves at any angle and sweep the material from 0o to 90o using the same transducer by simply modifying the frequency. In terms of frequencies available, Innerspec has deployed systems ranging from 100 KHz to 12 MHz.

5. What are the advantages of EMAT?

Because the sound is generated in the part inspected, EMAT has several unique advantages:
a. It doesn’t require couplant (dry inspection)
b. It is not affected by surface conditions
c. It permits easier deployment of probes (especially important for automated inspections)
d. It can generate wave modes (i.e. horizontally polarized shear energy and lamb waves) that are practically impossible to reproduce with piezoelectric transducers (the energy does not transmit through normal couplant). For more information see EMAT Technology.

6. What is horizontally polarized shear energy used for?

Because of the specific particle motion, horizontally polarized shear energy is the only practical means to ultrasonically inspect austenitic welds and materials with dendritic grain structures (e.g. some cast stainless steels). Moreover, as a guided or plate wave, horizontal shear waves fill up the thickness of the material and provide complete, thru-thickness inspection in one pass of the transducer. Guided waves can be normalized, essentially providing continuous self-calibration of the signal.

7. In summary, what is a good application for EMAT?

EMAT is especially well suited for real-world, industrial applications where speed and accuracy of inspection are paramount and the conditions of the material and process are not always ideal.

8. What materials can be inspected with EMAT?

EMAT works with materials that are either magnetic or conduct electricity (low resistivity). Overall, EMAT works with almost all metals, however some metals are better suited to the technique than others.

9. Why aren't EMATs used more frequently?

EMAT is a relatively new technique still unexplored by many potential users. EMAT transducers also require specific electronic equipment that is not widely available. As industry discovers the advantages of EMAT its use will spread to an increasing number of applications.

10. Are there standards for EMAT inspection?

In terms of wave propagation and response to defects, the same standards that apply to conventional UT apply to EMAT. In addition to this, there are recognized ASTM standards on EMAT inspection. See E MAT Technology.

11. Is EMAT equipment expensive?

Because EMAT requires more power to generate the ultrasound, EMAT instruments are generally more expensive than piezoelectric UT instruments. However, because EMATs don’t require couplant delivery and disposal, and are less affected by process and material conditions, they are significantly more cost effective in integrated inspection systems. In general, integrated EMAT systems are normally equivalent to or less expensive than piezoelectric UT systems.

12. Can you have fast inspection with EMAT?

Real-time inspection at production speeds is one of EMAT´s most powerful characteristics. We currently have weld inspection systems operating at 1m/s, and some applications have reached inspection speeds of 26m/s.

13. Is EMAT safe?

Yes. There are no health risks associated with either the technology or the equipment.

14. Can EMAT transducers be used in phased array?

Yes, EMAT transducers can be used in phased array. In addition to this, the ability of horizontal shear waves to fill up the volume of the material allows some applications of EMAT to perform the equivalent of phased array inspection with just one transducer. This is one of the reasons why there is no equivalent piezoelectric UT solution for most of our systems.

15. Are EMAT systems difficult to use?

Most of our systems are designed to work automatically and do not require specific Non Destructive Testing knowledge or training. Moreover, because EMAT can use guided waves, many applications are self-calibrated and don’t require any human intervention.

16. Do you also sell EMAT sensors?

Yes. Innerspec Technologies sells sensors and has research capabilities to develop custom solutions for specific applications. However, it is important to note that most EMAT sensor designs require high-power instrumentation that is not widely available. For these cases, we can also provide specific instrumentation modules to meet individual requirements.

17. I have an application that is not on your list of products, how do I find out if you can do it?

Contact us with the details of the application. Once we receive this information, we will immediately let you know if it is a good application for EMAT. We might also ask you to send samples to perform a proof-of-principle or feasibility test. Unless specific equipment is required (e.g. custom sensors), Innerspec Technologies will perform this initial test completely free of charge. If the results of the test are positive, we will provide you with a complete quotation. Once we quote your application, the final system will have the same 100% performance guarantee as our existing products.

18. Do you sell equipment worldwide?

Most of our systems are available worldwide through our network of representatives, distributors and partners, although some restrictions apply. Contact us to inquire about availability in your country.