ULTRASOUND
In physics, 'ultrasound' refers
to sound waves with a frequency too high for humans to hear.
Ultrasound images Ultrasound is an oscillating sound pressure
wave with a frequency greater than the upper
limit of the human hearing
range. Ultrasound is thus not separated from
'normal' (audible) sound by differences in physical properties, only by the
fact that humans cannot hear it. Although this limit varies from person to
person, it is approximately 20 kilohertz (20,000
hertz) in healthy, young adults. Ultrasound devices operate with frequencies
from 20 kHz up to several gigahertz.
Among the various fields of Application the most common
application of Ultrasound are detecting objects and measuring distances.
Sonography is the
most common form of Ultrasound Technique used in medical Science.
Diagnostic Sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used for visualizing
internal body structures including tendons, muscles, joints, vessels and internal
organs for possible pathology orlesions. The practice of examining pregnant women using ultrasound is called obstetric Sonography, and is widely
used. It provides images in real-time (rather
than after an acquisition or processing delay), it is portable and can be
brought to a sick patient's bedside, it is substantially lower in cost, and it
does not use harmful ionizing
radiation. Drawbacks of ultrasonography include
various limits on its field of view including difficulty imaging structures
behind bone and air, and its relative dependence on a skilled
operator.
Images for Ultrasonography.
History of Ultrasound
The credit of “Acoustics-the Science
of Sound” goes back to Pythagoras, the great Mathematician from 6th
Century BC who worked on the mathematical properties stringed instruments. Sir
Francis Galton constructed a
whistle producing ultrasound in 1893. The first technological
application of ultrasound was an attempt to detect submarines by Paul
Langevin in 1917.
Applications
of Ultrasound:-
Detection and ranging
Non-contact sensor
An ultrasonic level or sensing
system requires no contact with the target. For many processes in the medical,
pharmaceutical, military and general industries this is an advantage over
inline sensors that may contaminate the liquids inside a vessel or tube or that
may be clogged by the product. Both continuous wave and pulsed systems are
used. The principle behind a pulsed-ultrasonic technology is that the transmit
signal consists of short bursts of ultrasonic energy. After each burst, the
electronics looks for a return signal within a small window of time
corresponding to the time it takes for the energy to pass through the vessel.
Only a signal received during this window will qualify for additional signal
processing.
A popular consumer application of ultrasonic
ranging was the Polaroid SX-70 camera which included a light-weight
transducer system to focus the camera automatically. Polaroid later licensed
this ultrasound technology and it became the basis of a variety of ultrasonic
products
Motion sensors and flow measurement
A common ultrasound application
is an automatic door opener, where an ultrasonic sensor detects a person's
approach and opens the door. Ultrasonic sensors are also used to detect
intruders; the ultrasound can cover a wide area from a single point. The flow
in pipes or open channels can be measured by ultrasonic flowmeters, which
measure the average velocity of flowing liquid. In rheology, an acoustic rheometer relies on the principle of ultrasound.
In fluid mechanics, fluid flow
can be measured using an ultrasonic
flow meter.
Ultrasound Technology is widely
used for the principle of flaw detection in solid material. A void in the solid
material reflects back to the transducer, which is detected and displayed.
Non-destructive testing
Ultrasonic testing is a type of nondestructive
testing commonly used to find flaws in materials and to measure
the thickness of objects. Ultrasound inspection of welded joints has been an
alternative to radiography for non-destructive
testing since the 1960s. Ultrasonic inspection eliminates the use
of ionizing radiation, with safety and cost benefits. Ultrasound can also
provide additional information such as the depth of flaws in a welded joint.
Ultrasonic inspection has progressed from manual methods to computerized
systems that automate much of the process. An ultrasonic test of a joint can
identify the existence of flaws, measure their size, and identify their
location. Not all welded materials are equally amenable to ultrasonic
inspection; some materials have a large grain size that produces a high level
of background noise in measurements
Non-Destructive Testing of
swing Shaft showing spine cracking.
Ultrasonic range finding
A common use
of ultrasound is in underwater range
finding; this use is also called Sonar.
An ultrasonic pulse is generated in a particular direction. If there is an
object in the path of this pulse, part or all of the pulse will be reflected
back to the transmitter as an echo and can be detected
through the receiver path. By measuring the difference in time between the
pulse being transmitted and the echo being received, it is possible to
determine the distance. A common use of ultrasound is in underwater range finding; this use is also called Sonar.
An ultrasonic pulse is generated in a particular direction. If there is an
object in the path of this pulse, part or all of the pulse will be reflected
back to the transmitter as an echo and can be detected through the receiver path. By
measuring the difference in time between the pulse being transmitted and the
echo being received, it is possible to determine the distance.
Principle of Active Sonar
Ultrasound Identification (USID)
Ultrasound Identification (USID) is a Real
Time Locating System (RTLS) or Indoor
Positioning System (IPS) technology used to automatically track and identify
the location of objects in real time using simple, inexpensive nodes
(badges/tags) attached to or embedded in objects and devices, which then
transmit an ultrasound signal to communicate their location to microphone
sensors.
Ultrasonic cleaning
Ultrasonic cleaners, are used at frequencies from 20 to 40 kHz for jewellery, lenses and other optical parts, watches, dental
instruments, surgical
instruments, diving
regulators and industrial parts. An ultrasonic cleaner works mostly by energy
released from the collapse of millions of microscopic cavitations near the dirty surface. The bubbles made by cavitation
collapse forming tiny jets directed at the surface.
Ultrasonic humidifier
The ultrasonic humidifier, one
type of nebulizer (a device that creates a very fine
spray), is a popular type of humidifier. It works by vibrating a metal plate at
ultrasonic frequencies to nebulizer (sometimes incorrectly called
"atomize") the water. Because the water is not heated for evaporation,
it produces a cool mist. The ultrasonic pressure waves nebulizer not only the
water but also materials in the water including calcium, other minerals,
viruses, fungi, bacteria,and other impurities. Illness caused by impurities
that reside in a humidifier's reservoir fall under the heading of
"Humidifier Fever".
Safety to
be observed
Occupational exposure to
ultrasound in excess of 120 dB may lead to hearing loss. Exposure in excess of
155 dB may produce heating effects that are harmful to the human body, and it
has been calculated that exposures above 180 dB may lead to death. The UK's independent Advisory Group on
Non-ionizing Radiation (AGNIR) produced a report in 2010, which was published
by the UK Health Protection Agency (HPA). This report recommended an exposure
limit for the general public to airborne ultrasound sound pressure levels (SPL)
of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above