The Electro-Magnetic Acoustic Transducer
(EMAT) system is a computer controlled multi-channel electronic
system used to operate EMAT transducers for couplant-free transmitting
and receiving of oblique incident bulk ultrasonic waves and guided
waves in ferromagnetic materials.
The system serves as signal-generating and
-processing component. It
provides the time delayed RF signals for transmitter stages,
amplification, filtering and summation of the received signals and the
power supply of the electromagnets of the transducers.
System control, such as frequency, beam angle, pulse length
(number of cycles), pulse repetition rate, probe selection, etc., is
performed by the system setup program.
System Characteristics
Base Unit
Synthesizer board
Burst generator
board (frequency range: 0.4 – 2.0MHz); burst length (number of
cycles) and frequency are adjustable via PC
Two transmitter power stages
Receiver board with two delayed receiver channels (time delay
of all channels can be modified separately)
Output amplifier and video unit
Control PC for system control and parameter settings
Power supplies
The burst generator produces burst signals with a center frequency given by the synthesizer. These signals are digitally delayed, then amplified by the
driver stages and transmitted to the transducer(s).
Signals received from the receiver coils are pre-amplified in the
transducer by built-in preamplifiers and transmitted to the
system. There, the signals are further amplified and filtered by the
filter stages and are then time delayed. After the combination unit,
the received RF signals are summarized and transmitted to the video
output. At this stage, it is possible to choose between RF output and
video output.
Technical Data
Frequency Range:
Burst Duration: Pulse Repetition Rate: Time Delay:
Amplification:
0.4 - 2.0MHz, adjustable in 10kHz steps
(2.0MHz upper 3dB cut-off frequency 1 - 15 cycles,
adjustable in steps of 1 2.5 - 20ms, adjustable in 1µs
steps 0 - 10µs, adjustable in 2ns steps (transmitter) 0
- 1.5µs, adjustable in 25ns steps (receiver) Maximum of
50dB; 40dB adjustable in 255 steps
Magnetization Unit
The Magnetization Unit provides the AC power for the transducers and
consists of an electromagnet. Amplitude and frequency of the
magnetization are adjustable. Only transducers with permanent magnets
are operated by the Base Unit.
The components of the
Magnetization Unit are:
Frequency generator and a synchronization board
for synchronizing the trigger signal of the Base Unit with AC
current for the transducer(s) electromagnet
LF amplifier for
amplification of AC current for magnetization
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