I have made this ppt in a way such that it will be able for viewers to understand easily and also have included construction and advantages of EMT and also I have compared it with Piezoelectric Transducers for better gain and videos for testing of EMT.

1. Electro Magnetic
Transducers
-By Group No. 9
-Mechanical Dept.
-4th Semester
-Mechanical Measurements and Metrology

2. Introduction
 In inductive type transducer, the
magnetic characteristic of electric
circuit change due to the motion
of the object.
 Electro-magnetic transducer is the
self generating type inductive type
transducer in which voltage signal
is generated because of relative
motion of conductor and magnetic
field.

3. Construction
 Electromagnetic transducer
contains of a coil is wound direct
on a permanent core as shown in
the figure.
 When a plate of iron or
ferromagnetic material is moved
with respect to the magnet, the
flux field expands or collapse and
a voltage is induced in the coil.

4. Working of EMT
 Practical application of this
transducer lies in the angular speed
measurement.
 When pickup is placed near the teeth
of rotating gear, speed measurements
can be made with great accuracy.
 This transducer is linear only for small
motion as the flux intensity changes
due to change in air gap.

5. Advantages
 Compared to Piezoelectric Transducers, EMT probes
have the following advantages:
1. No couplant is needed. Based on the transduction
mechanism of EMT, couplant is not required. This
makes EMT ideal for inspections at temperatures below
the freezing point and above the evaporation point of
liquid couplants. It also makes it convenient for
situations where couplant handling would be
impractical.
2. EMAT is a non-contact method. Although proximity is
preferred, a physical contact between the transducer
and the specimen under test is not required.

6. Advantages
3. Dry Inspection. Since no couplant is needed,
the EMT inspection can be performed in a
dry environment.
4. Less sensitive to surface condition. With
contact-based piezoelectric transducers,
the test surface has to be machined
smoothly to ensure coupling. Using EMT, the
requirements to surface smoothness are less
stringent; the only requirement is to
remove loose scale and the like.

7. Advantages
5. Easier for sensor deployment. Using
piezoelectric transducer, the wave
propagation angle in the test part is affected
by Snell’s law. As a result, a small variation in
sensor deployment may cause a significant
change in the refracted angle.
6. Easier to generate SH-type waves. Using
piezoelectric transducers, SH wave is difficult
to couple to the test part. EMT provide a
convenient means of generating SH bulk wave
and SH guided waves.

8. Disadvantages
 The disadvantages of EMT compared to
piezoelectric UT can be summarized as follows:
1. Low transduction efficiency. EMAT transducers
typically produce raw signal of lower power
than piezoelectric transducers. As a result,
more sophisticated signal processing
techniques are needed to isolate signal from
noise.
2. Limited to metallic or magnetic products. NDT
of plastic and ceramic material is not suitable
or at least not convenient using EMT.

9. Disadvantages
3. Size constraints. Although there are EMT transducers as small as a
penny, commonly used transducers are large in size. Low-profile EMT
problems are still under research and development. Due to the size
constraints, EMT phased array is also difficult to be made from very
small elements.
4. Caution must be taken when handling magnets around steel products.

10. Comparison of Piezoelectric and
Electromagnetic Transducers

11. Application
 EMT has been used in a broad range of
applications and has potential to be
used in many other applications. A brief
and incomplete list is as follows:
1. Thickness measurement for various
applications.
2. Flaw detection in steel products
3. Plate lamination defect inspection
4. Bonded structure lamination detection

12. Application
5. Laser weld inspection for automotive
components
6. Various weld inspection for coil join,
tubes and pipes.
7. Pipeline in-service inspection.
8. Railroad and wheel inspection
9. Austenitic weld inspection for power
industry
10. Material characterization

13. EMT Plate Testing Procedure