Transducers Edelmen Flashcards
Describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied to them
Piezoelectric effect
Pzt materials change shape when a voltage is applied to them
Reverse piezoelectric effect
Materials which convert sound into electricity and vise versa are called
Piezoelectric/ ferroelectric
Man made transducers
Pzt
Protects the internal components of the transducer from damage and insulated the patient from electrical shock
Case
Prevents spurious electrical signals in the air from entering the transducer. Prevents electrical noise from contaminating the clinicals important electrical signals
Electrical shield
Prevents vibrations in the case from inducing an electrical voltage in the Pzt of the transducer. Isolates or uncouples the internal components of the transducer from the case
Acoustic insulator
Shaped like a coin. Characteristics of the sound beam emitted by the transducer are related to the dimensions of the active element
Pzt or active element
Electrical connection between the Pzt and us system. Active element require electrical contact so during transmission the voltage can cause the crystal to vibrate and produce an ultrasonic wave
Wire
Positioned in front of the Pzt at the face of the transducer. Protects the active element and increases the efficiency of sound energy transfer between the active element and the body
Matching layer
Back of the active element and reduces the ringing of the Pzt. Made of epoxy resin with tungsten filaments. It enhances axial resolution
Backing material / damping element
Decreasing order of impendance
PZT > matching layer > gel > skin
Thickness of the matching layer
1/4 wavelength thick
Thickness of active element
1/2 wavelength thick
3 consequences of backing material
decreased sensitivity, wide bandwidth, low quality factor
Less able to convert low level sound reflections into meaningful electrical signals
Decreased sensitivity
Range of frequencies in a pulse. Difference between the highest and lowest frequencies
Bandwidth
Long duration events have what type of bandwidth
narrow
unitless number that is inversely related to bandwidth. main frequency divided by the bandwidth
Quality factor
A short, dampened pulse has a ___ Q factor
lower
Q factor and bandwidth are ____ related
inversely
Destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation
Sterilization
Application of a chemical agent to reduce or eliminate infectious organisms on an object.
Disinfection
Transducers should be disinfected with
Cidex or other cold germicides
Backing material ___ duty factor and _____ quality factor
decreases
Characteristics of high frequency PW imaging transducers
Thinner Pzt crystals & Pzt with higher speeds
Characteristics of low frequency PW transducers imaging transducers
Thicker PZT crystals and lower speeds
Terms describe the shape and regions of a sound beam
Focus
Near zone
Focal length / near zone length
Far zone
Focal zone
Location where the beam is the narrowest
Focus / focal point
Region from the transducer to the focus
Near field / fresnel zone
Distance from the transducer to the focus
Focal length / focal depth / near zone length
Region that starts at the focus and extends deeper
Far zone / far field / Fraunhofer zone
Region around the focus where the beam relatively narrow
Focal zone
At the transducer the beam diameter equals
Transducer diameter
At the focus the beam diameter is
1/2 transducer diameter
A 2 near zone lengths, the beam diameter
Equals transducer diameter
Deeper than 2 near zone lengths the beam diameter is
Wider than transducer diameter
What characteristics of a fixed focus transducer determine the focal depth
Tranducer diameter and frequency of sound
A smaller diameter Pzt and low frequency creates a ____ focus
Shallow
What transducers is steered by a motor or reflecting mirror
Mechanical and annular phased array transducer
4 transducers that focus the us beam electronically
Linear switched array, linear phased array, annular phased array, and convex/curvilinear array
The minimum number of active elements in a mechanical transducer is
1
Describe a linear phased array transducer
rectangular, 1/2 to 1/4 wavelength wide
How are the pzt crystals of a linear phased array fired
At almost exactly the same time
Describe a linear sequential array transducer
rectangular, 1 wavelength wide
What component of an ultrasound system is made of lead zirconate titanate
Transducers active element
How thick is an active element of a 3 mhz pw transdcuer
Half the wavelength of the sound wave in the pzt
What component of the transducer is made from a slab of epoxy embedded with tungsten particles
Damping material
Impedance from highest to lowest
PZT, matching layer, gel, skin
Impedance from lowest to highest
skin, gel, matching layer, pzt
How thick is the matching layer of a 2 mhz pw transducer
one quarter the wavelength of sound in the matching layer
The spatial pulse length ___ with backing material
decreases
To calculate bandwidth
highest frequency - lowest frequency
Damping material ____ sensitivity
decreases
What helps determine the frequency of the sound produced by the transducer of a cw us system
US system electronics. It has nothing to do with the crystals thickness and speed
2 characteristics to determine the frequency of sound in a pulse
Thickness and speed of the active element
Characteristics of a high emitted acoustic wave frequency
Thin element and high prop speed
the higher the frequency the length of the near zone will be
longer
____ diameter and ____ frequency will have a deep focus (long near zone)
large diameter and high frequency
3 terms to describe a shape of a sound created by a tiny fragment of pzt
Spherical, huygens wavelet, and V shaped
