29.08.2019

Dms Classic Analogue Waves

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Dms Classic Analogue Waves 4,2/5 5486 reviews

Analog Modeled Bundles. Tubes, transistors, capacitors and other components work together to give each piece its own unique personality. Waves begins the modeling process by acquiring the very best hardware reference units available. Then, with meticulous attention to detail, we analyze every attribute, behavior, and response of the originals.

Sound- mechanical energy transmitted through a medium.
Wave (Acoustic Waves)- a traveling variation in acoustic variables.
- a traveling variation in one or more quantities such as pressure
-Sound is a traveling variation in pressure, a wave. A longitudinal mechanical wave.
Temperature,Pressure, Density, Particle Motion (distance)
Density-Concentration of mass in a volume
*more about acoustic variables under amplitude & Intensity*
Propagation- transmittal to distant regions remote from the sound source.

Vacuum- a space void of matter. Matter is anything that has mass and takes up space.

Sound cannot travel in a vacuum. Electromagnetic radiation, light/x-ray can travel through a vacuum! Sound waves are not electromagnetic radiation.

Electromagnetic vs. Mechanical Waves

Dms classic analogue waves chart
-Electromagnetic waves do not need a medium for travel.Mechanical waves travel through a medium and cause particle motion of the medium.
Electromagnetic Radiation- consists of alternating electrical and magnetic fields that are at right angles to each other and propagate through a vacuum at the speed of light.

Mechanical waves

-require a elastic deformable medium for propagation. This can be gas, liquid, or solid.
-cause motion of the particles they are moving through
- molecules do not travel from one end to the other it is not a flow of particles. Molecules vibrateback and forth.

-can be either Transverse or longitudinal.

Longitudinal Waves (mechanical)

-propagates by particles of medium vibrating/moving in the same direction (along) the wave propagation direction.*it’s the particles of the medium that are moving*
-Those in which particle motion is along the direction of the wave energy propagation. The molecules vibrate back and forth in the same direction as the wave is traveling.

-sound is a mechanical longitudinal wave

Transverse Waves/Shear Waves/Stress Waves (mechanical)

-propagates by particles of the medium moving perpendicular (across) the wave propagation direction. *particles of medium are what are moving*
- Those in which the motion of particles is perpendicular to the direction of propagation of the wave energy.
-**The only biological tissue that can cause the production of transverse waves is BONE**

Important Terms Describing Sound Waves/The Properties of Sound

Compression- a high pressure region of the wave form. The area of maximum particle density. Also called Compression zone, Peak, Up-hump, Wavefront, Leading edge/Leading portion of a wave.

Rarefaction- a low pressure region of the wave form. The area of minimum particle density. Also called a Trough.

Cycle-one high pressure and one low pressure region of a wave.One complete variation in pressure or other acoustic variable.
- a sequence of changes in molecular motion that recurs at regular intervals.
- periodic changes in the pressure of a medium/sequence of changes in amplitude that recur at regular intervals.

Frequency (f) - The number of cycles that occur in one second; measured in MHz, kHz or Hz

-The number of particular events that occur in a specific duration of time.
- The number of vibrations that a molecule in a wave makes per second.
- The number of times the cycle is repeated per second.
-The number of pressure oscillations (cycles) occurring at a given point in one unit of time. (usually 1 sec.)

(F=1/p)frequency=1/period. or (F= c/λ ) frequency= propagating speed/wavelength

Hertz (Hz) - the unit of measurement for frequency. One cycle per second. Hertz= cycle/second

MHz-1,000,000 cycles/secondor kHz-1,000 cycles/sec

Diagnostic ultrasound frequency Range= 1-16MHz or 1-16 million Hz. 2-10 MHz some 2-16MHz
Period (T)-the time it takes for one cycle (complete pressure variation) to complete itself; measured in seconds(s) or microseconds (us)
- The time between two successive compression zones or rarefaction zones.

(T=1/f )Period=1/frequency

- frequency is important in diagnostic ultrasound because it affects penetration and image quality.
- The dependence of other physical parameters on frequency is called dispersion.
Wavelength (λ) - The distance or length one cycle takes up; measured in meters(m), centimeter (cm), or millimeter (mm).
- The distance between two successive density zones.

λ=c/fwavelength= Propagating speed/frequency

-wavelength and frequency are indirectly related. If frequency goes up wavelength goes down.
-The only parameter determined by both sound source and the medium.
Dms Classic Analogue Waves
Propagation- Changes in pressure conveyed from one location to another.
- The transmittal to distant regions remote from the sound source.
Propagating Speed (P.S. or c)/Acoustic Velocity/Velocity of Sound- The speed thru which sound moves through a medium; measured in mm/us or m/s.
- The speed at which a wave propagates through the medium.
*remember velocity of sound and particle velocity are NOT the same thing!* Particle velocity-the speed at which the particles vibrate back and forth across their mean positions.*

-Determined only by the medium through which it travels.Specifically the density and stiffness of the medium.

-Not operator adjustable

-Thru soft tissue 1.54mm/us or 1540 m/s

-Density and propagating speed are indirectly related so….If Density (D) increases propagating speed(c) decreases.

oDensity (D)↑ Propagating Speed (c)↓

-Stiffness and Propagating Speed are directly related so….If Stiffness increases propagation speed( c ) increases

o Stiffness↑ Propagating Speed (c)↑

* So materials that are very stiff but not dense will have the highest propagating speed.

*Materials that are not very stiff but are extremely dense will have the lowest propagating speed.
Properties of the medium that effect Propagating Speed
Elasticity-the ability of an object to return to its original shape and volume after a force is no longer acting on it. Force applied to an object cause a change in its shape or volume (distortion). The strength of the force determines the amount of distortion.
Ultrasound waves cause elastic deformation by the separation and compression of neighboring molecules. (particle velocity)
Density(d)- The mass of a medium per unit volume.
d=m/v
- larger mass requires more force to cause motion...and more force to stop molecules already in motion.
Particle density is not constant at a particular position but fluctuates with a time dependence imposed by the frequency of the sound wave.

-Density and propagating speed are indirectly related so….If Density (D) increases propagating speed(c) decreases.

Dms
Stiffness (s)/ Bulk Modulus- an objects ability to resist compression. The negative ratio of stress (force or pressure applied) and strain (change in volume). Stiffness is the inverse of compressibility.
-stiffness and propagating speed are directly related.
Compressibility (K) - The fractional decrease in volume when pressure is applied to the material.
- so as stiffness increases compressibility decreases and acoustic velocity increases.
The source is able to determine the Period (T), Frequency (f), Amplitude, Power, and Intensity.
The source does not determine the Propagating Speed(c) *the medium does. Frequency is not related to propagating speed because propagating speed is a constant in soft tissue.
Wavelength (wavelength=c/f) is determined by both the medium and the source.
Pulse “A Burst of Cycles”- collection/group of two or more cycles followed by a resting time. We use pulsed waves for diagnostic ultrasound.

Pulse Duration (PD) -The amount of time from the beginning to the end of a single pulse of ultrasound.The time it takes for one pulse to occur*excludes the resting time*; measured in (us)

PD=nTPulse Duration= number of cycles x Period (time of one cycle)

-Pulse duration is not operator adjustable

Pulse Repetition Period (PRP) - The amount of time from the start of one pulse to the start of the next pulse. *includes resting time, sound on and off time*; measured in us

PRP= 1/PRF

-operator adjustable & determined by sound source

-unrelated to period

Pulse Repetition frequency (PRF) - The number of pulses that occur in a single second; measured in MHz or Hz

PRF=1/PRP

PRF and imaging depth are indirectly related so…imaging depth decreases PRF increases.Imaging depth increases PRF decrease.

PRF is operator adjustable.

Spatial Pulse Length (SPL) - the length of space over which one pulse occurs; measured in mm.

SPL=n x λ Spatial pulse length= number of cycles x wavelength

-Spatial pulse length and frequency.If wavelength increases SPL increases. If wavelength decreases SPL decreases.

-If frequency increases than wavelength decreases so if frequency increases SPL decreases

-shorter pulses=better images

Duty Factor (DF) - The fraction of time that pulsed ultrasound is on.It compares on and off time; unit less

DF=PD/PRP can make a percent if multiply by 100.

-for sonographic systems it averages between .2%-.5%

-If PRP increases than DF decreases.If PRP decreases than DF increases.

-If PRF increases PRP decreases so if PRF increases DF increases.*f and f are alike*
Infrasound-a frequency of less than 20Hz.A sound frequency too low for human hearing. (below)

Dms Classic Analogue Waves

Audible Sound- 20-20,000HzThe range of human hearing.

Dms Classic Analogue Waves 2

Ultrasound- 20,000Hz or higher. A sound frequency too high for human hearing. (beyond)
ultrasound- high frequency mechanical waves that humans cannot hear!

Dms Classic Analogue Waves Meaning

**remember kilo (k)=1,000 and mega (M)=1,000,000** so 20 kHz is 20,000 Hz...ultrasound