Ultrasonic Waves PDF

 [Ultrasonic applications]:- --------------------------------------- Properties of ultrasonic waves ------------------------------ 1. Sound waves transmit mechanical energy but light wave electromagnetic energy. 2. The velocity of light in air is a maximum speed (spee...

 [Ultrasonic applications]:- --------------------------------------- Properties of ultrasonic waves ------------------------------ 1. Sound waves transmit mechanical energy but light wave electromagnetic energy. 2. The velocity of light in air is a maximum speed (speed of light) but for sound it is not 3. Just like ordinary sound waves, ultrasonic waves get reflected, refracted and absorbed 4. Sound transmitted by the vibration of the molecules of the medium but 5. They can be transmitted over large distances as its travels slower than EM with no appreciable loss of energy. 6. It can penetrate opaque materials, but EM wave as light can not. 7. They produce intense heating effect when passed through a substance. [The similarity between sound and] [light waves:-] ========================================================================== [The important difference between] [sound and light waves:-] ==================================================================================== [Why ultrasonic waves?] ----------------------------------- Modes of Propagation of ultrasonic waves: ----------------------------------------- [Types of U.S. waves:] ---------------------------------- ### U.S. waves Body wave (bulk waves) Surface waves Types of waves -------------- ### Body waves (bulk waves)  Plate Waves : ============= Lamb waves [Ultrasonic wave physics:-] --------------------------------------- Acoustic Impedance ------------------ - The **acoustic impedance** control the amount of reflected and transmitted energy at the boundary of two materials Angular Transmission and wave transformation ============================================ Reflection and Transmission of Ultrasonic Waves at Interfaces -------------------------------------------------------------  𝑉  [Reflection and refraction for sound] [waves:] ====================================================================== poi (amplitude of  #### r = Z2 Z2 Attenuation of Sound Waves -------------------------- The Decibel Scale -----------------  𝐼0 10 Piezoelectricity: -----------------  [Types of Oscillations] ----------------------------------- t Damped oscillation ### US Instrumentation: The Transducer 1. Damp the oscillation. 2. Mechanical support for the thin crystal. 3. Prevent interfering echoes. ### Sound fields and their characteristics  [Non destructive evaluation (NDE)] [of materials:] ========================================================================== [1) To measure the elastic] ======================================= ##### ℓ #### ℓ ### For solid: *s* ℓ ~2~  0.75 − *R*^2^  To look for defects we will study several techniques: ===================================================== - **Two transducers located on opposing sides of the test specimen are used. One transducer acts as a transmitter, the other as a receiver.** - **Discontinuities in the sound path will result in a partial or total loss of sound being transmitted and be indicated by a decrease in the received signal amplitude.** - **Through transmission is useful in detecting discontinuities that are not good reflectors, and when signal strength is weak. It does not provide depth information.**   Test Techniques - Pulse-Echo ---------------------------- - **In pulse-echo testing, a transducer sends out a pulse of energy and the same or a second transducer listens for reflected energy (an echo).** - **Reflections occur due to the presence of discontinuities and the** **f** - **The amount of reflected sound energy is displayed versus time, which provides the inspector information about the size and the location of features that reflect the sound.**  ### Test Techniques -- Pulse-Echo (cont.)  - **To get useful levels of sound energy into a material, the air between the transducer and the test article must be removed. This is referred to as coupling.** - **In contact testing (shown on the previous slides) a couplant such as water, oil or a gel is applied between the transducer and the part.** - **In immersion testing, the part and the transducer are place in a water bath. This arrangement allows better movement of the transducer while maintaining consistent coupling.** - **With immersion testing, an echo from the front surface of the part is seen in the signal but otherwise signal interpretation is the same for the two techniques.** ### For More Information