Transducers Ch 8 Flashcards
A device that converts one form of energy into another
Transducer
When is electrical energy from the system converted into sound?
During transmission
When is the reflected sound pulse converted into electricity?
Durning reception
The property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them.
The piezoelectric effect
Piezoelectic materials change shape when a voltage is applied to them.
Reverse piezoelectric effect
Materials which convert sound into electricity are called
piezoelectric or ferroelectric
Lead zirconate titanate
PZT
Ceramic, active element, or crystal are other names for
PZT
The cylindrical tube, constructed of metal or plastic that protects the internal components of the transducer from damage and insulates the patient form electrical shock.
Case
A thin metallic barrier lining the inside of the case. The shield prevents spurious electrical signals in the air from entering the transducer.
Electrical shield
A thin barrier of cork or rubber that isolates or uncoulples the internal components of the transducer from the case.
Acoustic insulator
The piezoelectric crystal itself, the active element is shaped like a coin and is one half wavelength thick
PZT or active element
Provides an electrical connection between the PZT and the ultrasound system. The active element requires electrical contact so that during transmission the voltage from the ultrasound system can cause the crystal to vibrate and produce an ultrasonic wave.
Wire or channel
Positioned in front of the PZT at the face of the transducer. Increases the efficiency of sound energy trasfer between the active element and the body and protects the active element is one quarter wavelength thick
Matching layer
Bonded to the back of the active element, it reduces the ringing of the PZT.commonly made of epoxy resin with tungsten fillaments. The emitted sound pulse is dampened thus its short in duration and length. It enhances axial resolution
Backing material or dampening element
1/2 wavelength
Active element
1/4 wavelength
Matching Layer
PZT>matching layer>gel>skin
Decreasing order of impedence
Characteristics of damping material
High degree of sound absorption and acoustic impedence similar to PZT
3 consequences of the use of backing material
Decreased sensitivity, wide bandwidth, and low quality factor.
Single frequency that vibrates for a long time
resonant frequency
The range of frequencies in the pulse. Its the difference between the highest and lowest frequencies.
Bandwidth
Long duration events have what size bandwidths?
Narrow
Short duration events have what size bandwidths?
Wide
