Chapter 9: Transducers
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
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Help!
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| What is a transducer? | Any device that converts one form of energy into another
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| What two functions do U/S transducers perform? | transmission: electrical energy from system is converted into sound
reception: sound pulse is converted into electrical energy
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| What is the Piezoelectric Effect? | property of certain materials to create voltage when they are mechanically deformed
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| What is reverse piezoelectric effect? | when materials deform (change shape) when voltage is applied
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| What are piezoelectric materials? | material capable of converting sound into electricity and vice versa
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| What is another name for piezoelectric materials? | ferroelectric materials
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| Name some natural and man-made piezoelectric materials. | Natural: quartz, tourmaline
Man-made: lead zirconate titanate (PZT)
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| What piezoelectric matterial is commonly used in clinical transducers? | PZT
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| PZT is also known as what? | ceramic, active element, crystal
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| What are the 7 components of a basic transducer? | active element (PZT)
case
electrical shield
acoustic insulator
wire
matching layer
damping element (backing material)
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| What is the case made of and what is its purpose? | constructed of metal or plastic;
protects the internal components from damage and insulates the patient from electricalshock
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| What is the electrical shield and what is its function? | thin metallic barrier lining the inside of the case;
prevents false electrical signals unrelated to diagnostic information from entering the transducer
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| What is the acoustic insulator and what is its function? | thin barrier of cork or rubber that isolates internal components of the TD from the case;
prevents case vibrations from inducing an electrical voltage in the PZT
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| What is the matching layer and what is its function? | positioned in front of the PZT at the face of the transducer;
has an impedance between that of the skin and the active element to increase percentage of transmission
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| What between the matching layer and skin also helps with transmission of the sound beam? | Gel
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| What is the backing material (damping element) and what is its funtion? | bonded to the active element to limit "ringing";
commonly composed of epoxy resin impregnated with tungsten
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| What are the advantages and disadvantages of the backing material? | Advantages: shortens SPL and pulse duration, increased bandwidth with decreased Q factor, increases axial resolution (picture quality)
Disadvantages: decreases sensitivity,
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| Greater differences in what result in more reflection at a boundary? | impedance
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| PZT impedance is about how much more than skin impedance? | 20 times
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| What impedance is between that of skin and PZT? | matching layer
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| The impedance of what is between that of the matching layer and skin? | gel
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| The thickness of the matching layer is what the wavelength of sound in the matching layer? | 1/4
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| The thickness of the active element (PZT) is what the wavelength of sound in the active element? | 1/2
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| What are some characteristics of backing material? | high degree of sound absorption;
acoustic impedance similar to PZT so sound energy moves away from patient into backing material
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| What does it mean when its said that backing material causes decreased sensitivity of the TD? | the TD is less able to convert low-level sound reflections into meaningful electrical signals (won't display on monitor);
reduces the vibration of the PZT during transmission and reception phases;
These make the transducer less responsive
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| What is resonant frequency and what are some other names for it? | a long pure tone of single frequency;
operating frequency, single, main, primary, pure frequency, TD frequency
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| What happens to the PZT when backing material is present? | PZT cannot vibrate freely so the pulse becomes short duration "click" instead of a long steady tone
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| The short click caused by the backing material contains what? | many frequencies above and below the resonant frequency
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| what is bandwidth? | the range between the highest and lowest frequencies emitted from the TD
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| What is the relationship between bandwidth and pulse duration? | long pulse = narrow bandwidth
short pulse = wide bandwidth
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| An imaging TD has what kind of pulse and bandwidth? CW probe? | Imaging TD: short pulse, wide bandwidth
CW probe: no backing: long pulse, narrow bandwidth
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| In CW transducers, the sound wave's frequency equals what? | the frequency of the voltage applied to the PZT
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| With CW transducers, electrical frequency equals what? | acoustic frequency
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| With PW transducers, the frequency produced depends on what? | characteristics of the PZT
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| What are the two characteristics of the PZT that determine the frequency of sound from pulsed wave transducer? | Speed of sound in the PZT
Thickness of the PZT
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| The speed of sound in the PZT means what? | the propagation speed of the PZT
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| With PW TDs, when sound's speed in PZT is faster, the frequency created is what? | higher
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| With PW TD's the speed of sound in the PZT is related how to frequency of sound? | directly related
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| How much greater is the speed of sound in the PZT of PW transducers than in soft tissue? Whats the range? | about4 times greater than soft tissue.
the range: 4-6mm/us
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| With pulsed wave transducers, thinner PZT crystals create what kind of frequency sound pulse? | higher frequency
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| With PW transducers, a thinner PZT crystal creates what kind of wavelength? | short wavelength pules
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| With PW transducers, the thickness of the PZT crystal is related how to frequency? | inversely related
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| What is the thickness range of PZT crystals in PW transducers? | thickness range: 0.2-1mm
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| What is the equation for frequency for pulsed wave transducers? | frequency(MHz)= speed of sound in PZT(mm/us)/(2 x thickness(mm))
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