What are the modern methods to produce ultrasonic waves?

Answer 1

A piezoelectric crystal gives off electricity when compressed (used in gas grill igniters) but will also change volume when an electrical current is applied. When a high frequency alternating current is applied to the crystal, it expands and contracts at the same frequency as the current. If the frequency is high enough, it produces sound waves above the range that people can hear- ultrasonic.

Answer 2

DEFINITION:

Piezoelectric effect is exhibited by certain asymmetric crystals like quartz, tourmaline, Rochelle salt etc. If one pair of opposite faces (mechanical axis) of the crystal is subjected to pressure the other pair of opposite faces (electrical axis) of the crystal develop opposite charges .i.e, if stress is applied to the mechanical axis ,positive and negative Charges are developed on the electrical axis.

The converse of this effect is also true and is used to produce ultrasonics.

When an alternating potential difference is applied along the electric axis, the crystal is set into elastic vibration along the corresponding mechanical axis.

Fig. A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated)

PRINCIPLE:

Langevin, in 1917, developed a method for producing ultrasonic waves by using piezoelectric effect .He used a value oscillator to produce the necessary alternating potential difference.

X-cut quartz Crystals are used here to produce ultrasonic waves because they produce longitudinal waves. Y-cut Crystal produce shear waves which can travel only in solids.

WORKING:

The X-cut quartz crystal Q is placed within two metallic foils which are connected to the anode A and grid G of the triode value. An oscillatory tuned circuit LC is also connected to A .High tension battery H. T is shunted by a by-pass Capacity G to prevent high frequency currents from passing through the battery. Grid leak Resistor Rg is used to regulate the action of the grid.

When a high frequency current flows in anode circuit, an alternating potential difference of the same frequency is applied on the faces of the crystal. Consequently, Crystal undergoes linear expansions and contractions or is set into mechanical vibrations.

The frequency of alternating potential difference can be varied by varying the capacity of capacitor 'C'. When this frequency becomes equal to the fundamental natural frequency of crystal, crystal is set into resonant mechanical oscillations producing ultrasonic waves .Ultrasonic waves of frequencies of the order of 500 KHz can be produced by this method.The piezoelectric generator delivers maximum power when it is operated at fundamental frequency of the crystal .Higher frequency ultrasonics can be produced by making the L-C circuit oscillates at frequency which is equal to one of the odd harmonics of the crystal .Only odd harmonics of the crystals are used because piezoelectric effect can be occur only when opposite changes appear on the electrodes

Answer 3

Modern methods to produce ultrasonic waves include using piezoelectric transducers, magnetostrictive transducers, or capacitive micromachined ultrasonic transducers. These devices convert electrical energy into mechanical vibrations at ultrasonic frequencies, generating ultrasonic waves. This technology is commonly used in various applications such as medical imaging, industrial cleaning, and distance sensing.

Answer 4

1.piezo electric method, 2.megnetostriction method,

3.galton's whistle...

Answer 5

ultrasonics are produced by either magnetostructure or piezoelectric, which causes vibrations at a high frerquency

Answer 6

Some crystalline materials (quartz for example) resonate at ultrasonic frequencies when an electric field is applied to the material.