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SPI Chapter 8
Tranducers
| Question | Answer |
|---|---|
| What is the transducer's role? | converting one form of energy into another |
| What 2 functions do transducer perform? | transmission and reception |
| What is transmission? | electrical energy converted to sound |
| What is reception? | reflected sound pulse converted into electricity |
| What is piezoelectric effect (PZT)? | create voltage when pressure is applied |
| What is reverse PZT? | change shape when a voltage is applied |
| What is PZT materials or ferroelectric? | materials that convert sound into electricity |
| What are synonyms for PZT? | ceramic, active element, or crystal |
| What is the case of a transducer? | cylindrical tube |
| What is the electrical shield of a transducer? | metallic barrier inside the case |
| What is the acoustic insulator of a transducer? | barrier of rubber inside the case |
| What is the PZT or active element of a transducer? | a crystal |
| What is the wire of a transducer? | provides electrical connection |
| What is the matching layer of a transducer? | face of transducer |
| What is the back material or damping element of a transducer? | reduces ringing of the PZT, behind active element |
| How many times is the impedance of PZT greater than the skin? | 20x |
| What is the thickness of the matching layer? | one-quarter of the wavelength |
| What is the thickness of the active element? | one-half of the wavelength |
| What role does backing material play? | optimizing the pulses created by imaging transducer |
| What happens when a damping crystal is attached to the PZT crystal? | vibration is substantially reduced |
| What are the 2 characteristics of damping material? | high degree of sound absorption and acoustic impedance similar to PZT |
| What are the three consequences of using backing material? | decreased sensitivity, wide bandwidth, and low quality factor |
| What is decreased sensitivity? | it means that during reception, transducers with damping material are less able to convert low-level sound reflections into meaningful electrical signals |
| What is resonant frequency? | when the string vibrates freely for a long time at a single frequency |
| What is bandwidth? | range of frequencies in the pulse |
| With long duration events, what kind of bandwidth is present? | a narrow bandwidth |
| With short duration events, what kind of bandwidth is present? | a wide bandwidth |
| What is quality factor (Q-factor)? | unitless number that is inversely related to bandwidth |
| What is the formula for quality factor (Q-factor)? | quality factor = main frequency/bandwidth |
| What kind of Q-factor does a wide bandwidth have? | a low bandwidth |
| What kind of Q-factor does a narrow bandwidth have? | a high bandwidth |
| Because imaging probes use backing material and have a wide bandwidth, they are often referred to as? | low-Q |
| How is PZT created by polarization? | by exposing the material to a strong electrical field while being heated to substantially temperature |
| What is Curie temperature or (Curie point) , and what is its importance? | named after the scientist who created the PZT effect |
| The loss of PZT properties is called? | depolarization |
| PZT is said to be... | depolarized |
| What is sterilization? | destruction of all microorganisms by exposure to extreme heat, chemical agents, or radiation |
| What is disinfection? | the application of a chemical agent to reduce or eliminate infectious organisms of an object |
| Ultrasound transducers rarely penetrate mucous membranes which means...? | they are less likely to transmit infection |
| What form of cleaning a transducer require? | disinfection |
| What disinfectant should transducers be cleaned with? | Cidex or other cold germicides |
| What should transducers not be exposed to? | extreme temperatures to prevent loss of PZT properties |
| What determines the frequency of sound produced by a transducer? | depends on whether the transducer produces continuous wave sound or pulses |
| what is electrical frequency equal to? | acoustic frequency |
| With pulsed wave transducer, what two characteristics of active elements combine to determine the frequency of sound? | speed of sound in the PZT and thickness of the PZT |
| What is the speed of sound in PZT directly related to? | frequency of sound |
| What does the speed of sound in most PZT material ranges from? | 4 to 6 mm/us |
| What is PZT thickness inversely related to? | frequency |
| What is the mathematical relationship to find frequency? | frequency (MHz) = sound's speed in PZT (mm/us)/ 2 x thickness (mm) |
Created by:
Lazacha
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