9 Questions
What is the main function of a transducer in ultrasound?
Convert electrical energy into acoustical energy
What is the term used to describe the phenomenon where crystals vibrate and send sound waves into the medium when an electrical signal is applied?
Piezoelectric effect
What material is commonly used as a backing material behind a transducer to absorb backward directed ultrasound energy?
Cork
What is the main purpose of the matching layer placed on the front surface of a transducer?
Improve energy transmission efficiency
What characteristic determines the spatial resolution of a transducer?
Frequency bandwidth
What property of Piezoelectric Transducers allows them to convert electrical energy to mechanical/ultrasonic energy?
Polarisation
What is the main reason for using a coupling gel in ultrasound imaging?
To eliminate air pockets
Which material has 20 times the acoustic impedance of soft tissue?
Lead Zirconate Titanate (PZT) ceramic elements
What determines the efficiency of a piezoelectric transducer at converting electrical energy to acoustical energy?
Resonant frequency
Study Notes
Transducers
- Convert electrical energy into acoustical energy and vice versa in US
- Act as both detectors and transmitters in ultrasound
Piezoelectric Transducers
- Convert electrical energy to mechanical/ultrasonic energy
- Piezoelectric effect: force applied to crystals stimulates an electrical signal
- When an electrical signal is applied to crystals, they vibrate and send a sound wave into the medium
- Ultrasound waves are generated by applying an AC voltage to piezoelectric material
Piezoelectric Materials
- Lead Zirconate Titanate (PZT) ceramic elements are commonly used
- Can be shaped to suit the transducer
- Mechanically brittle and composed of microscopic crystals
- Must be polarized to be useful in US
- Polarization gives piezoelectric crystals their unique properties
Transducer Construction
- Single element piezoelectrical element mounted coaxially in a cylindrical case
- Cork or rubber used as acoustic insulation
- Metal electrical shield prevents pick up of extraneous noise
- Backing material/damping block absorbs backward directed ultrasound energy
- Damping material must have similar acoustic impedance to the crystal
Transducer Frequency Characteristics
- Damping material shortens pulse produced by the crystal
- Improves axial resolution
- Frequency bandwidth of the transducer can be measured by spectral analysis
Matching Layer
- Material placed on front surface of transducer to improve efficiency of energy transmission
- Has acoustic properties intermediate to those of soft tissue and the transducer material
- Thickness is equal to ¼ of the wavelength of sound in the material
Resonant Frequency
- Piezoelectric transducer has a resonant frequency at which it is most efficient at converting electrical energy to acoustical energy
- Resonant frequency mainly determined by thickness
- Thin elements have a high resonant frequency, while thick elements have a lower resonant frequency
Bandwidth
- Ratio of the transducer centre frequency to its bandwidth
- US imaging uses wide bandwidth and low Q factor transducers
Transducers and Spatial Resolution
- Refers to how closely positioned two reflectors can be to one another and be distinguished
- Axial resolution and lateral resolution are affected by frequency
- Higher frequency results in better resolution, while lower frequency results in less resolution
Test your knowledge on transducers, devices that convert energy from one form to another, and the piezoelectric effect, where crystals generate an electrical signal when pressure is applied. Learn about how transducers are used as detectors and transmitters in ultrasound technology.
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