Transducers Flashcards
A property of certain materials to create a voltage when pressure is applied or when the material is mechanically deformed is known as __________?
Piezoelectric effect
___________ is any device that converts one form of energy into another.
A transducer
PZT, ceramic, active element, and crystal are all other names for what?
Piezoelectric material
What happens when piezoelectric material is heated above 360°C?
It loses its piezoelectric properties, it is depolarized.
Complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation?
Sterilization
This term refers to the application of a chemical agent to reduce or eliminate infectious organisms on an object, such as a transducer.
Disinfection
Should a transducer be disinfected or sterilized?
As a rule, transducers should be disinfected using Cydex or other cold germicide’s, such as Glutaraldehyde. Transducer should never be sterilized using either dry heat, moist heat, or chemicals because this could damage the transducer. Do not use alcohol as a disinfectant.
How thick is the active element of the transducer?
1/2 wavelength
What component of a transducer protects the internal components from damage and insulates the patient from electrical shock?
The case
This component is how the active element in a transducer obtains the electrical connection so that the voltage from the system can excite the crystal thereby producing sound during transmission.
The wire
This component of the transducer has an impedance between those of the skin and the active element to increase the percentage of transmitted ultrasound between the active element and the skin.
Matching layer
The impedance of ________ is in between those of the matching layer and the skin to further increase the efficiency of sound transmission.
Gel
How thick is the matching layer?
The matching layer is 1/4 wavelength thick.
Because short pulses create better images, a material is bonded to the active element to reduce it’s ringing. This material is known as what?
Damping element or backing material
These types of transducers do not require backing material…
Continuous wave transducers do not require damping material.
The range of frequencies between the highest and lowest frequency emitted from the transducer is known as what?
Bandwidth
Do imaging transducers have a wider or narrower bandwidth than therapeutic transducers?
Imaging transducers have a wide bandwidth or broadband, compared to therapeutic transducers.
The main frequency emitted by the transducer is called…
The main frequency emitted by the transducer is called the center, resonant, primary, or natural frequency.
A unitless number representing the extent of damping.
Quality factor
When compared to therapeutic transducers, imaging transducers have _____ and a wider _____.
Low-Q and a higher bandwidth
The main or center frequency of sound from a pulsed transducer is determined by what 2 characteristics of the crystal?
- the thickness
2. The propagation speed of the piezoelectric material.
What is the propagation speed for PZT?
4 to 6 mm/microsecond
A thin crystal and a fast PZT equates to what?
Higher frequency
A thick crystal and a slow PZT equates to what?
Lower frequency
The thinner the active element…
…the higher the transducer’s resonant or natural frequency.
(Think of a crystal wine glass.)
When a PZT crystal is half as thick…
…the sound’s frequency is twice as high.
True or false? If the frequency of the electrical excitation voltage of a pulsed-wave transducer is 6 MHz, the main or center frequency of the transducer is 6 MHz.
False
True or false? If the pulse repetition frequency of a transducer is increased, the frequency of ultrasound produced by the transducer remains the same.
True
True or false? The diameter of the active element of a transducer helps to determine the frequency of the ultrasound produced by the transducer.
False
True or false? If the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz, the main or center frequency of the transducer is 6 MHz.
True
True or false? Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with a higher frequency.
False
True or false? For a pulsed wave transducer, if the PZT crystal thickness is doubled, then the frequency of sound is halved.
True
True or false? The normal propagation speed for piezoelectric material is approximately 3 to 5 times greater than soft tissue.
True
True or false? The acoustic impedance of the matching layer equals the acoustic impedance of skin.
False
True or false? A broadband transducer is more characteristic than a narrow bandwidth for imaging transducers.
True
True or false? A very high Q factor transducer is more common than low-Q factor for diagnostic imaging.
False
The impedance of a transducer active element is 1,900,000 rayls and for the skin is 1,400,000 rayls. What is an acceptable impedance for the matching layer? 1 million, 500,000, 2.3 million, or 1,700,000?
1,700,000
Which of the following does not fit with the others?
Broadband, backing material, short pulse, good lateral resolution, low-Q
Good lateral resolution
