introduction to utz

Sound

is a form of energy which causes a mechanical disturbance in the form of vibration of molecules within a medium.

Medium

In order to be transmitted, sound requires a _ containing

molecules, and therefore cannot travel through a vacuum.

Vibrating object

The production of sound requires a

Longitudinal Wave

This disturbance will spread through the air as a

TYPES OF UTZ WAVES

1.LONGITUDINAL OR COMPRESSIONWAVES

2.TRANSVERSE WAVES OR SHEARWAVES

3. SURFACE WAVES OR RAYLEIGH WAVES

Ultrasound khz

Above 20,000 hz

Infra sound

Below 16 hz or -20

Compression

The phase of the wave when the molecules are pushed together is called

Rarefaction

When apart

ACOUSTIC VARIABLES

1.Period

2.Wavelength

3.Amplitude

4.Frequency

5.Velocity

Period, T (s or µs)

The time taken for one complete cycle to occur

Wavelength (λ), (m or mm)

Length of space over which one cycle occurs

AMPLITUDE

The maximum displacement that occurs in an acoustic variable

FREQUENCY

1 Hertz= 1Cycle per second

Frequency in a sound wave refers to the rate of the vibration of the sound travelling through the air

SPEED/VELOCITY

A wave speed is the distance traveled by a given point on a wave in a given interval of time

What determines ultrasound speed?

speed changes depending on its MEDIUM frequency doesnt change no matter what medium

Decibels

a unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale. = 10 log(P2/P1)

Power

is the total airborne sound energy radiated by a sound source per unit of time

watts

The intensity of the beam is the power

(measured in ? ) flowing through a unit area

Knowledge of the absolute intensity of ultrasound is required for two Reasons

(i) the output intensity of an ultrasound instrument affects its sensitivity, and hence signal Sizes.

(ii) when one wish to assess the potential biological consequences of exposure to ultrasonic energy, one must have knowledge of the amounts of energy actually dissipated in tissue

INTENSITY SPECIFICATIONS

1.SPATIAL VARIATIONS

2.TEMPORAL VARIATIONS

TP ( temporal peak) intensity

is measured at the time the ultrasound pulse is on

TA ( temporal average) intensity

averaging the intensity over one on off beam cycle

PA ( pulse average) intensity

average overthe duration of a single pulse