Chapter 8 Flashcards
Transducer
Any device that converts one form of energy into another
2 functions of Transducers:
- During transmission, electrical energy from the system is converted into sound
- During reception, the reflected sound pulse is converted into electricity
Piezoelectric Effect
describes the property of certain materials to create a voltage when they are mechanically deformed
Reverse Piezoelectric Effect
these same materials change shape when a voltage is applied to them
Spark/voltage -> deform -> pressure oscillations
Deformation
crystal goes thin/thick
piezoelectric or ferroelectric
Materials that convert pressure waves (in our case sound waves) into electricity and vice versa
Case (also known as housing)
-cylindrical plastic or metal tube
-Most outer layer
-Protects the components and insulates the patient from electrical shock
Electrical shield
-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
Acoustic Insulator
-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
PZT or active element
-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
Wire
-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
Matching Layer
-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)
Backing Material or Damping Element (Material)
-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)
In decreasing order of impedance
PZT> matching layer> gel> skin
Two characteristics of backing material
- An impedance close to that of the crystal, allowing sound to move into it
- Sound absorbing
Additional consequences of backing material
Decreased sensitivity
Wide bandwidth
Low quality factor
Polarization
material is exposed to a strong electrical field, while being heated to a substantial temperature
Curie Temperature or Curie Point
The temperature at which PZT is polarized (~350)
Endocavitary
probes designed to enter the body via the vagina, rectum, esophagus
Catheter Probe (intracardiac or intravascular)
slice of PZT on end of catheter floated into blood vessel or heart
Cardiac
transthoracic
General
transabdominal; transpelvic, transvascular
Sterilization
is the destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation
Disinfection
is the application of a chemical agent to reduce or eliminate infectious organisms.
Two crystal characteristics determine the operating frequencies that a probe will support
- Propagation Speed of the crystal
- Thickness of the crystal
Propagation Speed and the frequency are directly related
PS ∝ frequency
PZT thickness and the frequency are inversely related
PZT thickness increases, then frequency decreases
