EP UNIT-2 Ultrasonics Flashcards
What are the different methods of producing Ultrasounds?
1) Mechanical Generator or Galton Whistle
2) Magneto-restriction Generator
3) Piezo-electric Generator
What is the principle of the Magnetostriction Generator?
When an alternating magnetic field is applied to a ferromagnetic material rod it is thrown into a longitudinal vibration which produces ultrasonic waves when it resonates
What are the parts of an Magnetostriction Generator?
- A Ferro-magnetic rod connected by two ends to coil L1 and L2. L1 is connected to the collector of the transistor and L2 is connected to the base of the transistor.
How does the Magnetostriction Generator work?
After the passing of direct current, the rod is permanently magnetized. After the battery is switched on, the current is produced by the transistor, which is passed through the coil L1. This causes a change in the rod’s magnetization, causing it to vibrate due to the magnetostriction effect.
What is the Converse Magnetostriction effect?
The effect is when EMF is induced due to a coil being wrapped around the rod.
Why is the current built up in the transistor and How is the vibration of the Rod being maintained?
Due to the induced EMF being fed into the base of the transistor, this acts as a continuous feed-back which leads to the current being built up in the transistor and the vibration of the rod being maintained.
How are Ultrasonic waves produced in the Magnetostriction generator?
The frequency of the circuit can be adjusted using the condenser C1 and when the frequency of the circuit is equal to the frequency of the rod resonance occurs where the rod vibrates logitudinally with a larger amplitude producing ultrasonic waves at both ends in high frequencies.
1/2π√(L1C1) = √(e/l)/2l
What are the Advantages and Disadvantages of using Magnetostriction generators for producing Ultrasonic waves?
Advantages
- Mechanically versatile
- Low cost
- Production of large acoustic power with high efficiency
Disadvantages
- Only able to produce up till 3 Million Hertz
- Not possible to get a constant single frequency because it depends on the degree of magnetization and the temperature
What is the Piezo-electric effect?
When a mechanical force is applied along a certain axis with respect to the optic axis of a crystal, like quartz or tourmaline, then an equal and opposite charge is produced along the perpendicular axis.
What is the Inverse Piezo-electric Effect?
When an EMF or Potential difference is applied along a certain axis concerning the optic axis and the crystal starts vibrating along the perpendicular axis.
What is the principle for the Piezo-electric Oscillator?
The main principle is the Inverse Piezo-electric effect where an ultrasonic wave is made at the resonance of the frequencies of the oscillating circuit and the vibrating crystal when they are equal.
What are the parts of a Piezo-electric Oscillator?
It has a primary and secondary circuit.
The Primary circuit has two coil ends L1 & L2, L1 is connected to the collector of the transistor. The capacitor C1 is used to vary the frequency of the circuit.
L2 is inductively coupled to the secondary circuit which has Coil L3 and two metal Plates, A and B.
How does the Piezo-electric oscillator work?
The battery is switched on and then the current is produced by the transistor and is passed through L1 and L2 then is transferred to the secondary circuit due to the transformer action and is fed to the coil L3 and then the inverse piezo-electric effect takes place after the frequency of the oscillating circuit is adjusted by the Capacitor C1 and when equal to the frequency of the vibrating crystal resonance occurs and the crystal starts to vibrate and then ultrasonic waves are produced along the ends of the rod.
1/2π√(LiC1) = P√(e/p)/2l
p - density of material
P - Overtone
E - Young’s Modulus of crystal
l - length of crystal
Properties of Ultrasonic Waves
- Highly energetic
- Travel through long distances
- Can be reflected, refracted and absorbed
- When passed through water, produces a stationary wave pattern and makes the liquid behave as an acoustic grating.
- Has a heating effect on objects that have long exposure to Ultrasonic waves
What is the principle of Acoustical Grating?
When an ultrasonic wave is passed through a liquid, the density of the liquid varies layer by layer due to the variation of the pressure hence the liquid acts as a diffracting grating, Acoustical Grating.
How can the velocity of ultrasonic waves be determined in an Acoustical Grating?
When a monochromatic source of light is passed through the grating and gets diffracted, the condition for diffraction can determine the velocity.
How are the parts of an Acoustical Grating arranged?
A Piezo-electric oscillator is set on the water of a water tank and the ultrasonic waves are emitted into the surface of the water and an incandescent lamp, a monochromatic source of light, and a telescope are arranged to view the diffraction pattern.
A collimator consisting of two lenses L1 and L2 is used to focus the light effectively onto the tank.
What are the different stages in the Acoustical Grating Experiment?
1) The piezo-electric oscillator isn’t switched on and the light is passed through and a single image or vertical peak is seen which shows that there isn’t any diffraction.
2) The Crystal is set into vibration and ultrasonic waves are produced and pass through the liquid and are reflected by the wall of the tank and form a stationary wave pattern with nodes and antinodes.
When the light passes through now it gets diffracted into a diffraction pattern consisting of a central maxima, Cm, and a principal maxima, Pm.
How is the velocity of an ultrasonic wave found in an Acoustical Grating?
2dsinθ = nλ
d - distance between nodes
θ - Angle of diffraction
n - Order of Spectrum
λ - Wavelength of Monochromatic source
λ(u) = 2d
and if we substitute that, we get:
λ(u)sinθ = nλ
and the velocity would be:
v = ⱴnλ/ sinθ
ⱴ - frequency of ultrasonic
What are the applications of Ultrasonic?
- Drilling & Cutting
- Welding & Smoldering
- Cleaning & Drying
- Echo-sounding principles are used to find the depth of the sea
- NDT - testing materials without harming them
What is the principle for an Ultrasonic Flaw Detector?
Whenever there is a change in the medium then the ultrasonic waves will be reflected and once a pattern is formed a flaw can be detected. This is an NDT so it wont harm the product.
