Sound Beams

Key vocabulary and concepts related to ultrasound sound beams, including near and far zone characteristics, Huygen's Principle, and focusing.

what is the sound beam?

A representation of a sound beam from a single element

What transducer is drawn

CW transducer

T/F? Is intensity is not uniform throughout?

True

What does the sound beam represent

Majority of Power & intensity

What a small amount of the intensity travels out in some direction off the main axis?

These are call side lobes

What image is this ?

a pulsed ultrasound beam looks like this

in reality, an ultrasound image is created by?

many small sound beams or scan lines put together.

What is Near Zone also call?

Also called the near field or Freznel zone.

Beam diameter decreases in?

In the near zone

Near Zone Length (NZL)

The distance from the transducer element to the minimum beam diameter.

NZL Formula (using wavelength)

$$NZL = \frac{[\text{transducer diameter (mm)}]^2}{4 \times \text{wavelength (mm)}}$$

NZL Formula (using frequency)

$$NZL = \frac{[\text{transducer diameter (mm)}]^2 \times f (\text{MHz})}{6}$$

Beam Diameter

The width or diameter of the sound beam, which depends on wavelength/frequency, element diameter, and distance from the transducer.

1 NZL Beam Diameter

At $1\,NZL$, the beam diameter is equal to $\frac{1}{2}$ of the element diameter.

2 NZL Beam Diameter

At $2\,NZL$, the beam diameter is equal to the element diameter.

Far Zone

Also called the far field or Fraunhofer zone, representing the distance from the minimum beam diameter to beyond.

Beam Divergence

The increase in beam diameter in the far zone, this is where beam divergence or diffraction occurs.

What is the reason an unfocused sound beam acts in this manner is because of the ?

Huygens principle

Huygen’s Principle state that?

States that each small portion of the surface of a transducer may be considered as a separate source and the beam results from combining all these small wavelets.

What principle is this ?

Huygens principle result in this

Focusing

A technique that decreases beam diameter in the near field to improve lateral resolution.

Focusing by using ?

curved element (internal focusing)

Electronic focusing( phasing)

Electronic Focusing

A method of focusing that utilizes phasing.

What is Focal point

The point where the beam diameter is at its minimum.

Focal region

The distance between equal beam widths on both sides of focus.

Focal length

The distance from the transducer to the center of the focal region; it cannot be greater than the NZL.

What is this showing ?

Focal zone

Continuous Transmit Focus On or off

Off

Continuous Transmit Focus On or off?

On