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Saturday, November 27, 2010

182101 (PH2111) Engineering Physics – I ULTRASONICS Lecture notes ebook

182101(PH2111) Engineering Physics – I  ULTRASONICS Lecture notes ebook

Magnetostriction effect - magnetostriction generator
Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of material's magnetization due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value, ?. The effect was first identified in 1842 by James Joule when observing a sample of nickel


Internally, ferromagnetic materials have a structure that is divided into domains, each of which is a region of uniform magnetic polarization. When a magnetic field is applied, the boundaries between the domains shift and the domains rotate, both of these effects cause a change in the material's dimensions. The reciprocal effect, the change of the susceptibility of a material when subjected to a mechanical stress, is called the Villari effect. Two other effects are thus related to magnetostriction: the Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a torque and the Wiedemann effect is the twisting of these materials when a helical magnetic field is applied to them. The Villari Reversal is the change in sign of the magnetostriction of iron from positive to negative when exposed to magnetic fields of approximately 40000 A/m (500 oersteds). On magnetization a magnetic material undergoes changes in volume which are small - of the order 10-6.

Piezoelectric effect - piezoelectric generator

Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins)[1] in response to applied mechanical strain. The word piezoelectricity means electricity resulting from pressure.
The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry.[3] The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect (the internal generation of a mechanical force resulting from an applied electrical field). For example, lead zirconate titanate crystals will generate measurable piezoelectricity when their static structure is deformed to about 0.1% of the original dimension. Conversely, lead zirconate titanate crystals will change about 0.1% of their static dimension when an external electric field is applied to the material.

Detection of ultrasonic waves- properties

Refer attached document.  Attachments:   detection - Ultrasonics

Velocity measurement – acoustic grating

The ultrasonic waves generated with the help of a quartz crystal inside the liquid in a container sets up standing wave pattern consisting of nodes and anti-nodes. The nodes are transparent and anti-nodes are opaque to the incident light. In effect the nodes and anti-nodes are acts like grating(a setup of large number of slits of equal distance) similar to that of rulings in diffraction grating. It is called as acoustic grating or aqua grating. Hence, by using the condition for diffraction, we can find the wavelength of ultrasound and thereby the velocity of sound in the liquid medium.

Industrial applications
Industrial applications
There are numerous practical applications for ultrasonics. The first widespread use was in underwater exploration. Ultrasonic waves proved to be an excellent method for determining the depth of water. Ultrasonics also are used to map the shape of lake and ocean floors. Submarines use ultrasonic waves to maintain secret contact with each other.
In industry, ultrasonic waves have been used in the testing of machinery and machine parts. Using a narrow beam of ultrasound, engineers can look inside metal parts in much the same way that doctors use X rays to examine the human body. With ultrasonic technology, flaws in machinery can be detected and repaired without having to take them apart.
Similar ultrasonic methods have been used to diagnose problems in the human body. As an ultrasonic beam passes through the body, it encounters different types of tissue such as flesh, bone, and organs. Each type of tissue causes the ultrasonic beam to reflect in a different way. By studying these reflections, physicians can accurately map the interior of the body. Unlike X rays, there is no risk of harmful overexposure with ultrasonics. Therefore, they have become a useful alternative to X rays for diagnosis and are often used on sensitive organs, such as kidneys, as well as to monitor the progress of pregnancies.
Because they can vibrate the particles through which they pass, ultrasonic waves are often used to shake, or even destroy, certain materials. An example of this procedure is ultrasonic emulsification. In this technique, two liquids that normally do not mix with each other (such as oil and water) are made to vibrate until they are blended. This technique is also used to remove air bubbles from molten metals before casting so that the finished piece will be free of cavities. Doctors use ultrasound to break up kidney stones and gallstones, thus avoiding invasive (cutting through the skin with a knife) surgery.
Ultrasonic vibration also can be used to kill bacteria in milk and other liquids. Some inventors are attempting to perfect an "ultrasonic laundry," using high-frequency vibrations to shake dirt and other particles out of clothing.

SONAR - Non Destructive Testing
Sonar (originally an acronym for SOund NavigationAnd Ranging) is a technique that uses soundpropagation (usually underwater, as in Submarine navigation) to navigate, communicate with or detect other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic locationand of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR(an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.
A,B and C –scan displays
Refer document.
ABC Scan

Medical applications - Sonograms

Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public.
In physics, the term "ultrasound" applies to all acoustic energy (longitudinal, mechanical wave) with a frequency above the audible range of human hearing. The audible range of sound is 20 hertz-20 kilohertz. Ultrasound is frequency greater than 20 kilohertz.
Typical diagnostic sonographic scanners operate in the frequency range of 2 to 18 megahertz, though frequencies up to 50-100 megahertz has been used experimentally in a technique known as biomicroscopy in special regions, such as the anterior chamber of eye.[citation needed] The above frequencies are hundreds of times greater than the limit of human hearing, which is typically accepted as 20 kilohertz. The choice of frequency is a trade-off between spatial resolution of the image and imaging depth: lower frequencies produce less resolution but image deeper into the body.
Sonography (ultrasonography) is widely used in medicine. It is possible to perform both diagnosisand therapeutic procedures, using ultrasound to guide interventional procedures (for instancebiopsies or drainage of fluid collections). Sonographers are medical professionals who perform scans for diagnostic purposes. Sonographers typically use a hand-held probe (called a transducer) that is placed directly on and moved over the patient.
Sonography is effective for imaging soft tissues of the body. Superficial structures such asmuscles, tendons, testes, breast and the neonatal brain are imaged at a higher frequency (7-18 MHz), which provides better axial and lateralresolution. Deeper structures such as liver and kidney are imaged at a lower frequency 1-6 MHz with lower axial and lateral resolution but greater penetration.
Medical sonography is used in the study of many different systems:


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