ULTRASONICMETHODS
Ultrasonic methods utilize sound waves to inspect the interior of materials. Sound waves are mechanical
or elastic waves and are composed of oscillations of discrete particles of the material. The
process of inspection using sound waves is quite analogous to the use of sonar to detect schools of
fish or map the ocean floor. Both government and industry have developed standards to regulate
ultrasonic inspections. These include, but are not limited to, the American Society for Testing and
Materials Specifications 214-68, 428-71, and 494-75, and military specification MIL-1-8950H.
Acoustic and ultrasonic testing takes many forms, from simple coin-tapping to transmission of sonic
waves into a material and analyzing the returning echoes for the information they contain about its
internal structure. Reference 15 provides an exhaustive treatment of this inspection technique.
Instruments operating in the frequency range between 20 and 500 kHz are usually defined as
sonic instruments, while above 500 kHz is the domain of ultrasonic methods. In order to generate
and receive the ultrasonic wave, a piezoelectric transducer is usually used to convert electrical signals to sound wave signals and vice versa. This transducer usually consists of a piezoelectric crystal
mounted in a waterproof housing that facilitates its electrical connection to a pulsar (transmitter)
receiver. In the transmit mode, a high-voltage, short-duration pulse of electrical energy is applied to
the crystal, causing it to change shape rapidly and emit a high-frequency pulse of acoustic energy.
In the receive mode, any ultrasonic waves or echoes returning from the acoustic path, which includes
the coupling media and part, compress the piezoelectric crystal, producing an electrical signal that
is amplified and processed by the receiver.
pressure (P), and amplitude (a). The following relationship between wavelength, frequency, and sound
velocity is valid for all types of waves For example, the wavelength of longitudinal ultrasonic waves of frequency 2 MHz propagating in steel is 3 mm and the wavelength of shear waves is 1.6 mm.
Ultrasonic waves are reflected from all interfaces/boundaries that separate media with different
acoustic impedances, a phenomenon quite similar to the reflection of electrical signals in transmission
lines. The acoustic impedance Z of any medium capable of supporting sound waves
Ultrasonic methods utilize sound waves to inspect the interior of materials. Sound waves are mechanical
or elastic waves and are composed of oscillations of discrete particles of the material. The
process of inspection using sound waves is quite analogous to the use of sonar to detect schools of
fish or map the ocean floor. Both government and industry have developed standards to regulate
ultrasonic inspections. These include, but are not limited to, the American Society for Testing and
Materials Specifications 214-68, 428-71, and 494-75, and military specification MIL-1-8950H.
Acoustic and ultrasonic testing takes many forms, from simple coin-tapping to transmission of sonic
waves into a material and analyzing the returning echoes for the information they contain about its
internal structure. Reference 15 provides an exhaustive treatment of this inspection technique.
Instruments operating in the frequency range between 20 and 500 kHz are usually defined as
sonic instruments, while above 500 kHz is the domain of ultrasonic methods. In order to generate
and receive the ultrasonic wave, a piezoelectric transducer is usually used to convert electrical signals to sound wave signals and vice versa. This transducer usually consists of a piezoelectric crystal
mounted in a waterproof housing that facilitates its electrical connection to a pulsar (transmitter)
receiver. In the transmit mode, a high-voltage, short-duration pulse of electrical energy is applied to
the crystal, causing it to change shape rapidly and emit a high-frequency pulse of acoustic energy.
In the receive mode, any ultrasonic waves or echoes returning from the acoustic path, which includes
the coupling media and part, compress the piezoelectric crystal, producing an electrical signal that
is amplified and processed by the receiver.
Sound Waves
Ultrasonic waves have several characteristics, such as wavelength (A), frequency (/), velocity (i>),pressure (P), and amplitude (a). The following relationship between wavelength, frequency, and sound
velocity is valid for all types of waves For example, the wavelength of longitudinal ultrasonic waves of frequency 2 MHz propagating in steel is 3 mm and the wavelength of shear waves is 1.6 mm.
Ultrasonic waves are reflected from all interfaces/boundaries that separate media with different
acoustic impedances, a phenomenon quite similar to the reflection of electrical signals in transmission
lines. The acoustic impedance Z of any medium capable of supporting sound waves
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