A History of Ultrasound Physics and the Properties of the Transducer - Research Paper Example

This paper explores the history of piezoelectric crystals and how they have found their use in ultrasound non-invasive medical technique. The article traces it back from the Greeks to the Nobel Laureates emphasizing on the importance of each step which has ultimately lead to the present form of the technique. Keywords: Piezoelectric crystals, ultrasound, attenuation. Nature was among the first teachers of Man and the forefathers of science were lucky enough to be on the receiving end of classes which enriched them with the knowledge of the universe, first-hand and raw.

The study of ‘Acoustics’, as first called by Joseph Sauveur, was a precursor to the world of ultrasound which appeared later in the timeline (W.N.Beck, 1957). The phenomenon with its potential for modern day applications can be accredited to the rich scientific history and background resulting from intense research and philosophical curiosity of the gifted minds. The birth of this curiosity can be dated back to ancient Greek, where the philosopher Pythagoras experimented and toyed with the idea of creating controlled sound by vibrating strings which later came to be known as the Sonometer.

Later Aristotle the intellectual, quite rightly, came up with the notion that sound travelled due to the motion of air. The exploitation of sound continued down the timeline when Lord Raleigh’s work “Theory of Sound” (1877) further provided solid ground for future experiments and endeavors in the field. In this regard Jean-Daniel Colladon was particularly notable, as he quite accurately calculated the speed of sound in water, during an experiment in the waters of Lake Geneva (Brent, 1939).

Acoustic research found a strong base in the making and so discoveries followed suit. The Italian biologist Lazzaro Spallanzani was responsible for discovering high frequency inaudible sound waves which he said helped bats maneuver their way in the dark of the caves, in 1794. This marked the initiation of ultrasonic research and experimentation. As a parallel plot, sonar waves found their usage on ships for the determination of approaching vessels. Early 19th century ships boasted a system of an on-deck foghorn and an underwater gong which sounded simultaneously, to be received by the crew on the other ship and a hydrophone on the hull.

Thus transmission and reception of sonar waves majorly assumed a function for the navy and ships around the globe, initially. The groundbreaking discovery of the Curie’s soon led to rapid actualization that the reverse of the piezo-electric effect would produce alternating rapid relaxation and stress in the crystal to produce high frequency sound waves. This, in close partnership with the introduction of the diode and triode in the world of science made the production of ultrasound available for underwater sonar detection systems (Nobelprize.org). These systems which were used in submarines especially during the First World War were instrumental in the detection of approaching vessels and icebergs.

Reginald Fessenden can be rightly credited with the development of the first sonar system in the United States in 1914, the year of lukewarm international relations and ignition of militaries worldwide. Fessenden’s device consisted of an electromagnetic moving-coil oscillator which emitted a low frequency noise and then switched on a receiver to listen for echoes. In the following years as the war bore down on them, France proved fruitful in the combination of the diode and triode for amplification purposes to develop a powerful high frequency ultrasonic echo-sounding device for which the physicist Paul Langevin and Russian scientist Constantin Chilowsky were responsible(W.N.Beck, 1957).

Such developments soon found their applications for other scientific purposes such as radars for the calculation of the height of the ionosphere in 1924. These turnovers were the bases for ultrasound metal-flaw detectors which followed 4 years later. As more life-scaled applications were realized for ultrasound and echo detection, it did indeed wind its way into the medical world as a therapeutic technology rather than diagnosis, initially, making use of the property of ultrasound to heat and damage disruptive animal tissue.

But increased and much more vigorous experimentation throughout the mid-twentieth century assured that it was bound towards a diagnosis pathway. H Gohr and Th. Wedekind presented a paper on the possibility of the usage of ultrasound in 1940 and so became the first to suggest this possibility, using an echo-detection based system similar to metal-flaw detection. The present day transducer is a hand-held device which is placed over a gel which reduces the loss of energy through quick transmission of sound through the liquid.

It still consists of a the subjection of a piezo-electric crystal to alternating potential difference which produced sound waves by creating areas of compression and rarefaction in the adjacent media. The same wave is bounced back to different extents from different media and falls on the same transducer which acts as a receiver now. The connection of the transducer to a Cathode ray oscilloscope which producer high and low intensity waves. Its connection to a screen can form a very clear image which is clinical to non-invasive diagnosis techniques (NDT Resource Center) Relevant Formulas: Attenuation of an ultrasound pulse: The ultrasound is a wave like any other wave, hence it also suffers from the reduction in power as it moves in space.

It is a natural phenomenon which needs to be reduced to its minimum during its medical use. This loss in power of the ultrasound pulse is known as the attenuation. Attenuation firstly depends on the medium in which it is travelling. Each medium has an intrinsic property named as the acoustic impedance. The power lost depends on the ratio of the acoustic impedances between the two mediums. The greater the ratio the more is lost. a(x,t) = ao.e-px.ej(wt-kx) where a is the wave, p is the damping coefficient, k is the wavenumber.

Works Cited Brent, J. (1939). Pythagoras: Music and Space. Retrieved Dec 22, 2011, from Harmony and Proportion: http://www.aboutscotland.com/harmony/prop.html NDT Resource Center. (n.d.). Characteristics of Piezoelectric Transducers. Retrieved Dec 22, 2011, from http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/characteristicspt.htm Nobelprize.org. (n.d.). Pierre Curie - Biography. Retrieved Dec 22, 2011, from Nobel Prize: http://www.nobelprize.org/nobel_prizes/physics/laureates/1903/pierre-curie-bio.html W.N.Beck. (1957).

Ultrasonic recording of the bones in Human arm. The Journal of the Acoustical Society of America , 865.