# us physics

 Sound waves are? A mechanical wave in which particles in a medium move. Sound travels in a stright line. Sound waves are longitudinal wave Acoustic propagation properities are? The effects of the cound wave upon the biological tissue through which it passes. The acoustic variables? Pressure ( pascals), density (kg/cm^3), and distance (cm,mm) Acoustic parameters Help describe the waves features The 7 acoustic parameters? Period, frequency, amplitude, power, intensity, wavelegnth, propogation speed. Tranverse waves? Particles move in a direction that is perpendicular (right angles) to the direction that the wave popagates.(string shakeing up/down) Longitudinal waves? particles move in the same direction that the wave propagates. (example sound). Inphase waves? Peaks occur at the same time and at the same location Out of phase waves? Peaks occur at different times. (out of step) Interference? When multiple beans arrive at same location and the waves loose their individual characteristic at that moment to combine to form a single wave Constrictive Interference? Intereferance of a pair of inphase waves results in the formation of a single wave of greater amplitude than either of its componets Destructive Interference? Interference of a pair of out of phase waves resulting in the formation of a single wave of lesser amplitude than either of its componets. Parameters? Describe features of a sound wave Period? Time it takes a wave to vibrate a single cycle/ time from start of one cycle to the start of the next cycle. Units of period? untis of time: seconds, ms, hours, days Period is determined by? Sound source. It is not adjustible by sonographer Frequency? The number of events that occurs in a sepcific duration of time. Units of frequency? units per second, 1/second,hertz(per second). Frequency is determined by? Sound source/ It is not adjustible by spnpgrapher Infrasound? less than 20Hz. Audible sound? between 20Hz and 20kHz. Ultrasound? Greater than 20kHz. Period and frequency are Reciprocals of each other The three parameters that describe the bigness of a sound wave? Amplitude, power, intensity Amplitude? Is the bigness of a wave. Units of amplitude? Pressure(pascals), density(g/cm^3), particle motion(cm,inches,any) Amplitdue is determined by? The sound source. It is adjustible by the sonographer Peak to peak amplitude If the difference between maxium and minimun values of an acoustic variable. Power? Is the rate of energy transfer or th rate at which work is performed Units of power? Watts Power is determined by? Sound source. It is adjustable by sonographer Power and amplitude? Power is porportional to amplitude squared Intensity? The concentration of energy in a sound beam. Intensity ='s? Intensity(W/cm^2)= power(w)/area(cm^2). Units of intensity Watts/square centimeter, or W/cm^2 Intensity is determined by? Sound source.It is adjustable by sonographer Intensity is? Poroprtional to power and amplitude squared. Wavelegnth? The distance or legnth of one complete cycle. Units of wavelegnth? mm,meters, any other unit of legnth. Wavelegnth is determined by Both the source and the medium. It is not adjustable by sonographer. To calculate wavelegnth 1.54mm/us(wavelegnth of sound in soft tissue)/ frequency(MHz). Propogation speed? The distance that a sound wave travels through a medium in 1 second. Units of propogation speed? meters per second, mm/us, or any dstance divided by time Propogation speed is determined by? The medium in which it is traveling. It is not adjustable by sonograpger Speed of sound in soft tissue 1,540 m/s Sound travels? Fastest in solids(bone, tendon, muscle), Slower in liquids( blood,liver,soft tissue), slowest in gases(fat,lung,air). Two characteristics of a medium that affects the speed of sound? stiffness, density. Stiffness? The ability of an object to resist compression. Higher stiffness faster speed. Density? The relative weight of a meterial. Higher the density the lower the speed. What is determined by the sound source Period, frequency, amplitude, power ,intensity. Pulse duration.PRP.PRF. Duty factor What is determined by medium? Speed What is determined by both source and medium? Wavelegnth. Spatial pulse legnth. What can be changed by sonographer Amplitude, power, intensity. Pulse duration? The actual time from the start of a pulse to the end of that pulse. Units of pulse duration units of time, us,ms,seconds Pulse duration is determined by? The sound source. It is not adjustable by sonographer To calculate pulse duration? pulse duration(us)= #cycles x period(us) pulse duration(us)=#cycles/frequency(MHz) Spatial pulse legnth? The distance that a pulse occupies in space from the start to the end of a pulse. Units of spatial pulse legnth? Units of distance, mm Spatial pulse legnth is determined by? Both the source and the medium. It is not adjustable by sonographer. Pulse repetition period? The time from the start of one pulse to the start of the next pulse. Units of PRP? time,ms. PRP is determined by The sound source. It is adjustable by sonographer Pulse repetition frequency? The number of pulses than an ultrasound system transmits into the body each second Units of PRF? Units of HZ or per second. PRF is determined by? The sound source. It is adjestable by sonographer Duty factor? The percentage or fraction of time that a system is transmitting a pulse. Units of duty factor? A %. Duty factor is determined by? Sound source. It is adjustable by sonographer Spatial? Refers to distance or space. Peak? The maximun value. Average? The mathamatical middle Temporal? Refers to all time, transmit(pulse duration) and revieve Pulsed? Refers to only to the trnasmit time only(pulse duration). SPTA Intensity that is most revelant to tissue heating. Attenuates? As sound travels in the body it weakens(attenuates Decibel notation? Is used to report chnges of attenuation Logarithms A method of rating numbers. Log represents the number of 10's that are multiplied to create the origional number 3db'S? Means the intensity was doubled its origional value 10db's? Means the intensity has become ten times larger than its origional value. -3db's? Means the intensity has become half its origional value. -10db's? Means the intensity has become 1/10 its origional value. Attenuation? The decrease in intensity, power, and amplitude as sound travels . Attenuation is determined by? Path legnth and frequency of sound. Attenuation coefficient? The number of decibels of attenuation that occurs when sound travels one centimeter Units of attenuation coefficent? dB/cm Total attenuation is calculated by? attenuation coeffieient(db/cm) x distance(cm) Attenuation coefficient is? one half of the frequency. Half value thickness? Is the distance that sound travels in a tissue that reduced the intensity of sound to one half its origional value Units of half-value layer centimeters Half value thickness depends on? the medium, the frequency of sound Impedance is the acoustic resistance to sound traveling in a medium Impedance='s? density(kg/m^3 x prop. speed (m/s) Units of impedance? rayls, Z Impadance is determined by? Medium only. 4 Angles? acute(less than 90degrees), right(90degrees),obtuse(greater than 90 degrees), oblique(any other than 90degrees Two conditions for refraction? oblique incidance and propogation speeds of the two media are different. Go return time(time of flight)? The elapsed time from pulse creation to pulse reception Time of flight is directly related to? depth. 13microsecond rule for every 13us of go return time, the object creating the reflection is 1 centimeter deeper ins oft tissue. ez 13us has a depth of 1 cm and the total distance traveled would be 2cm PRP='s? Imaging depth(cm) x 13us/cm. Axial resolution? describes the measure of detail in a image Piezoelectrice effect? describes the property of certain materials to create a voltage when they are mechanically deformed Authormonkies ID22842 Card Setus physics Descriptionreview Updated2010-06-09T19:48:50Z Show Answers