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EMAT Application

EMAT – ElectroMagnetic Acoustic Transducer – Application Fields

• testing of steel bars and rods
• testing of tubes and pipes
• testing of pressure vessels
• survey testing
• testing on the orbit
• testing of non-metallic products
• measuring of modulus of elasticity
• thickness measuring at high temperatures

Advantages of EMAT

• works without need of contact or liquid coupling
• can work at high temperatures
• enables generation of various wave types:

1. SH (shear horizontally polarized)
2. LH (longitudinal horizontally polarized)
3. Rayleigh waves
4. Lamb waves
5. SH plate waves

Disadvantages of EMAT

• works only in conductive environment and in ferromagnetic materials
• very weak signal – low SNR
• great force attracting the transducer with permanent magnet to material

Types of US Waves Generated by EMAT

Shear Wave

Longitudinal Wave

Rayleigh and Lamb Waves

Software DIO 2000

• Is intended for control of ultrasonic units, database and signals display
• Individual activation and deactivation of each channel
• A-scan of ultrasonic signals for each channel can be displayed in one or more windows and by groups
• Graphic display of the measured values process, depending on time or space co-ordinates
• Process of measured and calculated values
• B-scan and its combinations, combined values from several channels, statistics, minimum values, maximum values etc.
• Outputs for automated marking
• Maximum possible number of channels up to 64

EMAT – Parameters for Thickness Measurement

• Dead zone: 15 micro s
• Measuring range: 0,8 mm – 150 mm
• Distance probe to material: 1 to 2 mm !!!
• Protective layer thickness: 0,5 mm
• Protective layer material: corundum plate
• Probe type: shear wave
• Probe frequency: 2-7 MHz

EMAT probes

Results of Measurements

OFF-LINE Signal Processing Methods

• Data export is available with different extent of the measuring parameters, up to the clear matrices non/sampled data
• Saved data are indexed according to the order, or files are marked by the time mark for identification distribution
• Export of the measured data is available in the following formats: Database PARADOX for programming in DELPHI, EXCEL export, ASCII file export, Binary file export, ASCII file in the columns for MATLAB

Results of Development

• Designing the EMAT probes – By optimizing the coil impedance, we have achieved very good signal, even with lead-in cables up to 5 m long.
• Durability tests of probes in real operation – Durability of probes is determined primarily by mechanical destruction by different artifacts on the material under measuring.
• Development of EMAT amplifiers – Amplifiers with power supply from external sources seems to be insufficient from view of noise immunity. We have developed the amplifiers, which are powered dynamically via signal cable.