# Ultrasound Phy

Topics: Sound, Hertz, Wavelength Pages: 7 (1652 words) Published: May 11, 2013
CHAPTER 1
Graphs are used to study the relationship between 2 things so you can see what the relationship is.

Unrelated: 2 items that are not associated. Ex. Hair color is unrelated to shoe size

Directly related/proportional: 2 items that are associated such that when one item increases, the other increases. The graph of 2 directly related items extends from lower left to upper right. Ex. Clothing size is directly related to one’s weight.

Related/ proportional: Is a relationship but can’t be measured. 2 items that are associated or affiliated however the relationship between the items does not have to be specified.

Inversely related/proportional: 2 items are associated such that when one item increases, the other decreases. The graph of 2 inversely related items extends from upper left to lower right. Ex. Golf score is inversely related to skill.

Reciprocal relationship: 2 numbers multiplied together, the result is 1. This is a special form of inverse relationship. Reciprocal numbers are inverse because when one increases, the other decreases. Ex. 10/1 x 1/10=1

All numerical values must have corresponding units. A number alone, without units, is ambiguous and can create uncertainty. Percents (%) don’t have units. To change units from one form to another is called unit conversion.

Metric System-Powers of Ten
EXPONENT| PREFIX| SYMBOL| MEANING|
109| Giga| G| Billion|
106| Mega| M| million|
103| Kilo| k| thousand|
102| Hecto| h| Hundred|
101| Deca| da| Ten|
10-1| Deci| d| Tenth|
10-2| Centi| c| Hundredth|
10-3| Milli| m| Thousandth|
10-6| Micro| μ| Millionth|
10-9| Nano| n| billionth|

Exponents tell how many 0’s, tells “meaning”

Hz: cycle per second

Complementary Metric Units
PAIRS| PREFIXES| ABBR.|
Billions and billionths| giga & nano| G & n|
Millions and millionths| mega & micro| M &|
Thousands and thousandths| kilo & milli| k & m|
Hundreds and hundredths| hecto & centi| h & c|
Tens and tenths| deca & deci| da & d|

Think of the pairs as belonging together. If we speak of frequency in megahertz, then we will speak about period in microseconds.

Chapter 2

Media/medium: what sound is traveling thru. Ex. Water, tissue, etc

Sound is a mechanical wave in which particles in the medium move; carries energy from one location to another. Mechanical makes something happen in media

Acoustic propagation properties: effects of the medium upon sound wave. Biologic effects: what effect sound will have on medium; the effects of sound wave upon the biologic tissue through which it passes.

Acoustic variables: Components of media that can be affect by mechanical nature of sound. Pressure, density and distance (particle motion) are used to distinguish between sound waves and other types of waves.

Pressure: concentration of force in an area. Units are pascals (Pa) Density: concentration of mass in a volume. Units are kg/cm3 Distance: measure of particle motion. Units are cm, feet, mile

Transverse wave (sound is not): energy goes away from source Longitudinal wave: sound moves in straight line from source; particles move in the same direction that the wave propagates. Sound travels in a straight line. Sound waves are longitudinal waves.

Compressed: squeezed together (change to positive)
Rarefied: Stretched apart (change to negative)

In-phase: Pair of waves are considered in phase when their peaks occur at the same time and at the same location. Out of phase: Peaks occur at different times and so do their troughs.

Interference: More than one sound beam may travel in a medium and, on occasion, multiple beams may arrive at an identical location at exactly the same time. The waves lose their individual characteristics at that moment and combine to form a single wave; this combination is called interference.

Constructive interference: where the resulting wave is larger than either of its...