Flashcards in Array Transducers Deck (21)

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1

## How are the far-field directivity, and distance tot he axial maxima and minima related to the frequency?

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Far field directivity is inversely proportional to frequency.

Axial max and min a directly proportional to frequency.

2

## After the last axial maxima, how does the axial pressure profile change?

### Drops off as 1/wavelength.

3

## What is the equation for the axial pressure?

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p=2p_0*|sin{(k/2)*(sqrt(z^2+a^2)-z)}|

where p0 is the pressure at z=0,

z is the depth in tissue,

a is the radius of the transducer,

k is the wavenumber.

4

## What is the equation for the location os the last axial maxima and minima?

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z=a^2/(n*lambda)

n=odd, max

n=even, min

5

## What is the equation for the far-field directivity of a circular transducer?

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D(0,k)=|[2*J_1*(kasin0)]/kasin0|

where k is the wavenumber,

a is the half aperture, and

J_1 is a first order Bessel function.

6

## How does the axial profile of a pulsed wave differ from that of a continuous wave?

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- The final axial maximum is further out.

- Fewer axial minima

- Shallower minima.

7

## How does the axial profile of a square transducer differ from that of a circular one?

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- The final axial maximum is shifted outwards.

- Incomplete destructive interference (non-zero minima)

8

## What is the equation for the far-field directivity of a square transducer?

### D(0, phi, k)=|sinc{0.5*kL_xsin(0}*sinc{0.5kL_ysin(phi)}|

9

## What is the equation for the axial pressure of a circular focused transducer?

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p=2p_0*(A/A-z)*|sin{(k/2)*(B(z)-z)}|

Where B(z)=sqrt(z^2+2b(A-z)),

and b = A-sqrt(A^2-a^2)

A is the radisu of curvature of the spherical trnasducer.

10

## What is the equation for the focal gain?

### G=(pi*a^2)/F*lambda

11

## How does the last axial maxim change with increased focal length?

### Gets further out and lower in amplitude.

12

## What is the equation for the -6dB beam width at the focus?

### w=0.7F*lambda/a

13

## Describe the construction of a mechanical sector transducer?

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- Mechanically scanned single element transducer.

- The element is on a motor and is waggled side-to-side to produce the image.

- Only used in simple devices today (e.g. bladder scanners)

14

## Describe the construction of an annular array transducer?

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- Mechanically scanned annular array transducers.

- Typically 4-8 equal area, concentric, ring-shaped elements.

- One electrical connection for each element.

15

## What are the advantages and disadvantages of an annular array transducer?

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+ Beam is radially symmetrical.

+ Scan plane focusing and slice thickness focusing are identical.

- Moving parts make them less reliable.

16

## Describe the construction of a simple linear array transducer.

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- Flexible printed circuit attaches to lower surface of the crystal.

- Flexible ground plate bonded to the upper surface.

- Backing material pedestal with crystal and matching layers bonded to it.

- Cut into a row of individual elements leaving air kerfs.

- Cylindrical silicone rubber lens bonded on top.

17

## What is the ideal array geometry?

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- The pitch should be lambda/2 in tissue.

- The thickness should be lambda/2 in the crystal.

- w/d should be 0.7 for "width expanders".

18

## What are the properties of a mechanically scanned array?

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- Curved array with a silicone rubber lens in an oil bath.

- Used in private clinics for antenatal "bonding" scanning.

- 4D frame rate limited to about 4Hz due to sweep speed.

19

## What are the properties of a biplane transrectal transducer?

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- Two separate curved arrays for sagittal and transverse views.

- Used widely in urology clinics for prostate biopsies.

20

## What are the properties of a radial transrectal transducer?

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- Aperture size is limited by the array diameter (11mm).

- Used in some urology clinics to endoanal scanning.

21