Chapter 8

Question 1

Transducer

Answer 1

Any device that converts one form of energy into another

Question 2

2 functions of Transducers:

Answer 2

1. During transmission, electrical energy from the system is converted into sound
2. During reception, the reflected sound pulse is converted into electricity

Question 3

Piezoelectric Effect

Answer 3

describes the property of certain materials to create a voltage when they are mechanically deformed

Question 4

Reverse Piezoelectric Effect

Answer 4

these same materials change shape when a voltage is applied to them
Spark/voltage -> deform -> pressure oscillations

Question 5

Deformation

Answer 5

crystal goes thin/thick

Question 6

piezoelectric or ferroelectric

Answer 6

Materials that convert pressure waves (in our case sound waves) into electricity and vice versa

Question 7

Case (also known as housing)

Answer 7

-cylindrical plastic or metal tube
-Most outer layer
-Protects the components and insulates the patient from electrical shock

Question 8

Electrical shield

Answer 8

-thin metallic barrier
-lining under the case
-blocks unwanted outside electrical signals from entering probe and being sent to the system and processed = noise on our image

Question 9

Acoustic Insulator

Answer 9

-thin barrier of cork or rubber
-Layer under the electrical shield
-Insulates/anchors internal components preventing them from sending vibrations down the probe that could induce an electrical voltage from the PZT that is processed by the system

Question 10

PZT or active element

Answer 10

-Piezoelectric material (In a simple probe coin or disc shaped)
-Positioned in front of damping material and behind matching layer
-Generates sound waves on transmission; voltage on reception

Question 11

Wire

Answer 11

-metal drawn out into the form of a thin flexible thread
-Runs from system to crystal in probe
-Provides an electrical connection between the PZT and the US system

Question 12

Matching Layer

Answer 12

-It is a material engineered to have an impedance between the active element and the gel/skin.
-Positioned in front of the PZT at the face of the transducer
-increases the efficiency of sound transfer between the crystal and the body (also protects the active element)

Question 13

Backing Material or Damping Element (Material)

Answer 13

-typically made of epoxy resin impregnated with tungsten filaments (adhesive, sticky substance with metallic fibers)
-bonded to the back of the active element
-This material restricts the extent of PZT deformation limiting the ringing (# of cycles in the pulse)

Question 14

In decreasing order of impedance

Answer 14

PZT> matching layer> gel> skin

Question 15

Two characteristics of backing material

Answer 15

1. An impedance close to that of the crystal, allowing sound to move into it
2. Sound absorbing

Question 16

Additional consequences of backing material

Answer 16

Decreased sensitivity
Wide bandwidth
Low quality factor

Question 17

Polarization

Answer 17

material is exposed to a strong electrical field, while being heated to a substantial temperature

Question 18

Curie Temperature or Curie Point

Answer 18

The temperature at which PZT is polarized (~350)

Question 19

Endocavitary

Answer 19

probes designed to enter the body via the vagina, rectum, esophagus

Question 20

Catheter Probe (intracardiac or intravascular)

Answer 20

slice of PZT on end of catheter floated into blood vessel or heart

Question 21

Cardiac

Answer 21

transthoracic

Question 22

General

Answer 22

transabdominal; transpelvic, transvascular

Question 23

Sterilization

Answer 23

is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation

Question 24

Disinfection

Answer 24

is the application of a chemical agent to reduce or eliminate infectious organisms.

Question 25

Two crystal characteristics determine the operating frequencies that a probe will support

Answer 25

1. Propagation Speed of the crystal
2. Thickness of the crystal

Question 26

Propagation Speed and the frequency are directly related

Answer 26

PS ∝ frequency

Question 27

PZT thickness and the frequency are inversely related

Answer 27

PZT thickness increases, then frequency decreases