Final Exam - Pressure Profiles

Single Point Source

Multi-Point Source

Wavefronts

Undergo constructive and destructive interference

Result in complex wavefront

Huygen's Principle

Increased distance from wave source & superposition of wavelets

Results in planar front that represents even pressure distribution

Hydrophone

Very small TX (0.5mm)

Can send and receive sound energy - interested in received energy

Calculate intensities at different points in beam

Reflector

Measures the amount of received sound at different

points of the beam

TX is moved to different distances from target

Axial Pressure Profile

Different bandwidths

Maximum pressure variations

Along the central beam axis

More frequencies

CW Axial Profile

Very strong null points

May reach zero

Single frequency

Long PW Axial Profile

Narrow bandwidth

Short PW Axial Profile

Broad bandwidth

More uniform echoes

Sum of all frequency components

Transverse Pressure Profile

Infinite number of transverse sections per beam

Maximum pressure value plotted against transverse coordinate x at a fixed axial coordinate value of z

CW Trans Profile

Single frequency

Expect lobulations

Increased variations in amplitude

PW Trans Profile

More frequencies

Less lobulations

Profile smooths out

LAM - Last axial maxima

Corresponds with focal point

Near field boundary (NFB) extends to the focal point

Focal point in focal plane

Polar Plots

Considers energy along the central beam and to the side of the beam

Plots maximum pressure against an angle theta

Examines side lobes of pressure energy

Due to constructive and destructive interference

Polar Paper

Spherical plot

Relationships between beam and side lobes

For each line there is a radius, angle, and LAM

Side Lobes

Significant energy outside of main beam

Create artifacts or noise i

"Grating lobes" in linear transducers

Best seen in anechoic structures

More in CW transducers

Increasing TX diameter & Frequency

Increases # of side lobes

Increases directionality

Rreduced divergence

May increase related artifacts

Low Q TX

Broader bandwidth

Fewer and less intense side lobes

Main lobe intensity pattern is widened

Apodizing

Process in electronic arrays to reduce side lobes