Chapter 8 Flashcards
Transducers
Any device that converts one form of energy into another
Transducer
Transmission
Reverse Piezoelectric Effect
Reception Piezoelectric
Piezoelectric Effect
Electrical energy from the system is converted into sound
Transmission, Reverse Piezoelectric effect
The reflected sound pulse is converted into electricity
Reception, Piezoelectric effect
Piezoelectric materials change shape when a voltage is applied to them, called
Reverse Piezoelectric effect
—– describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them.
Piezoelectric effect
Piezoelectric is also known as
Ferroelectric
Commonly used in clinical transducers
Lead zirconate titanate or PZT
Synonyms for PZT
Ceramic, Active element, Crystal
Positioned in front of the PZT at the face of the transducer
Matching layer
One half wavelength thick
PZT or active element
one quarter wavelength thick
Matching layer
Increase the efficiency of sound energy transfer between the active element and the body, and protects the PZT
Macthing Layer
Crystal damping enhances what
Axial resolution
Bonded to the back of the active element, which reduces the ringing of the PZT
Backing Material or Damping Material
Backing material is commonly made of what
Epoxy resin impregnated with tungsten filaments
What prevents vibrations in the case from inducing an electrical voltage in the PZT of the transducer
Acoustic insulator
Damping material do what to the SPL and Pulse duration
Shortens the SPL and Pulse duration
What are the characteristics of damping material
- High degree of sound absorption
- Acoustic impedance aimilar to PZT
3 consequences related to using a backing material
- decreased sensitivity
- Wide Bandwidth
- Low Quality Factor
The range of frequency in the pulse
Bandwidth
The difference between the highest and lowest frequency.
Bandwidth
Transport the voltage from the crystal of the transducer to the system for further processing
Wire
The use of gel eliminates the — layer and facilitates sound transmission into the body
Air
PZT-Matching layer-gel-skin
Increases the efficiency of the sound energy transfer between the active element and the body and protects the active element
Matching layer
The matching layer is —- wavelength thick
one quarter wavelength thick
Bonded to the back of the active element it reduces the ringing of the PZT
Backing Material
Damping material
Backing material is made of what
Epoxy resin impregnated with tungsten filaments
What restricts the extent of PZT deformation
Backing material
What will the damping material do?
- Shortens the spatial pulse length and pulse duration,
- Improves image quality
Short Pulses= higher image quality - Decreases the transducer sensitivity
What is the relation between Q-factor and bandwidth
Inversely related
Formula for Q-factor
Main Frequency / bandwidth
Shorter damped pulse has
Lower Q-factor
Longer Undamped pulse has
Higher Q-factor
A transducer produces a freq equal to its operating freq also called
Resonance Frequency
Expose the PZT to strong electrical field while being heated to a substantial temp the process is called
Polarization
The sound in PZT and the freq of the sound are
Directly related
