SINGLE ELEMENT TRANSDUCERS: CONSTRUCTION AND OPERATION Flashcards
Transducer Design
First transducers employed a single-element circular ____ to both transmit and receive sound
Info obtained from scanning depends a large part on beam characteristics»_space;> influence transducer design
Design criteria
Proper frequency in ____ range
Capability of doing ____ wave operation
____ control
Uniform ____
Limited ____ extent
disk MHz pulsed directional intensity spatial
Transducer Design
What does an ultrasound transducer do?
____»_space; ultrasound ____»_space; ____ energy
____ energy»_space; ultrasound ____»_space; ____
So how does a transducer work?
electricity transducer mechanical mechanical transducer electricity
Piezoelectric Properties
Piezoelectric Principle
(Greek) ____ = to press,
____ = amber
“PRESSURE ELECTRICITY”
effect 1st described by
the Curies in 1880
piezo
elektron
Piezoelectric Properties
In certain materials, when sound is applied perpendicular to their surface, an ____ charge is created
-OR-
Some materials produce a ____ when deformed by applied pressure
electrical
voltage
Piezoelectric Properties
AND……………
Certain materials, when exposed to an electrical shock, will begin to ____ and transmit a sound wave
vibrate
Piezoelectric Properties
US probes contain elements that have this piezoelectric effect
These elements are called
Medical US ____ convert electricity to sound
transducers
Piezoelectric Properties
Transducers usually driven by 1 cycle of AC voltage for US imaging which produces a
____ – ____ cycles US pulse
Longer driving voltages (5-30 cycles) are used for ____ techniques
2
3
doppler
Piezoelectric Properties
MAN-MADE CERAMICS
____ ZIRCONATE TITANATE (PZT)
____ lead titanate
____ sulfate
polyvinylidine difloride (PVF2)
Those not naturally piezoelectric, are made so by placing the material in a strong electronic field while they are at a ____ temperature (poling)
lead
barium
lithium
high
Piezoelectric Materials
MAN-MADE CERAMICS
LEAD ZIRCONATE TITANATE (PZT)
Easy to ____
Effective at ____ wattage
____
shape
low
inexpensive
Piezoelectric Properties
If this critical temperature, the Curie point (Curie point for PZT of 3650 C = 6890 F) is subsequently exceeded, the element will lose its ____ properties
piezoelectric
Dipoles
There are regions of ____ and ____ charges on a molecule
Normally, randomly arranged and cannot migrate
positive
negative
Dipoles
Material is heated above Curie temperature (at which point the molecules are released and can move freely)
A pair of charged plates (one ____, one ____) is placed across the material
The negative ends point to the ____ plate, and the positive ends point to the ____ plate (opposites attract)
positive
negative
positive
negative
Dipoles
Material is then cooled ____ the Curie temperature with the electric plates still in place; the molecules then maintain their alignment
below
Dipoles
Material is then cooled ____ the Curie temperature with the electric plates still in place; the molecules then maintain their alignment
below
Dipoles
When the voltage is switched, the molecules twist the other way»_space; ____ the thickness
decreasing
Dipoles
Flipping back/forth cause expansion/contraction (about 10-6m, a few microns) of the crystal, which creates mechanical ____
When the expanding/____ crystal is placed on the body, sound waves are passed into the body
And vice versa
vibrations
contracting
CW Transducers
frequency of sound equals
frequency of driving voltage
(reasonably near operating frequency)
sound
voltage
CW Transducers
frequency of ____ equals
frequency of driving ____
(reasonably near operating frequency)
sound
voltage
Determinants of Frequency
PW Transducers
OPERATING FREQUENCY
a.k.a. ____ frequency is the transducers preferred frequency of operation
resonance
PW Transducers
Operating frequency is determined by:
propagating ____ of transducer material (4-6 mm/ms )
-and-
the ____ of the element (0.2-1mm)
speed
thickness
PW Transducers
f (MHz) = ct / 2 x thickness
Primarily:
the ____ of the element (0.2-1mm)
thickness
PW Transducers
THICKNESS CORRESPONDS TO ____ THE WAVELENGTH
WAVELENGTH DECREASES AS FREQUENCY ____
THINNER ELEMENTS ____ FREQUENCIES
half
increases
higher
Transducers Construction
____/Backing Material
____ Layer
____
____ Shield
Housing and ____
damping matching electrodes radiofrequency insulation
Damping/Backing Material
Immediately ____ the crystal
Composed of epoxy resin loaded with tungsten powder (medical US) or air (therapeutic US); acoustic ____ comparable to that of the crystal, absorbs sound energy
behind
impedance
