Ultrasonic Instrumentation Flashcards
What is ultrasound?
Longitudinal waves at frequencies above 20kHz.
What happens when ultrasound reaches a boundary between two materials of different acoustic impedance?
Some of the ultrasound will be reflected back.
What does SONAR stand for?
SOund Navigation And Ranging.
When was SONAR developed and why?
Developed after the Titanic disaster in 1912.
as an aid in finding both submarines and icebergs
List some applications of ultrasound. (4)
- Detecting submarines during WWII
- Railway line flaw detection
- Gas bubble content in crude oil pipelines
- Medical: Skin depth measurement, Baby scanner, Blood flow measurement, Heart movement imaging
What generates and detects ultrasound?
Piezoelectric transducers.
What occurs when a voltage pulse is applied across a piezoelectric crystal?
It vibrates at its resonant frequency and produces ultrasound.
What is the resonant frequency of a piezoelectric crystal that emits ultrasound at 1MHz?
1MHz.
What are common piezoelectric materials used in ultrasonic transducers? (3)
- Quartz
- Barium titanate
- PZT (lead zirconate titanate)
What is the relationship between the resonant wavelength of a transducer and its thickness?
The resonant wavelength is equal to twice its thickness.
Calculate the thickness of a PZT crystal that resonates at a frequency of 1.5MHz, given the velocity of ultrasound in PZT is 3790m/s.
1.26mm.
What is the formula for acoustic impedance (Z) of a material?
Z = ρ . c
What do the symbols ρ and c represent in the acoustic impedance formula?
ρ = density, c = velocity of wave through the material.
True or False: The acoustic impedance of a material affects the attenuation of a wave passing through it.
True.
What is the Intensity Reflection Coefficient?
The ratio of the reflected intensity (Ir) and the incident intensity (Ii).
What is the formula for calculating the Intensity Reflection Coefficient?
Ir / Ii = [ (Z2 – Z1) / (Z2 + Z1) ]^2
Calculate the intensity of ultrasound transmitted through a muscle-fat interface with an incident intensity of 2.5W/m².
2.47W/m².
What is a pulse generator used for in ultrasound technology?
To generate pulsed ultrasound signals.
What is an A-scan in ultrasound technology?
A representation of the amplitude of the received ultrasound signal.
How is a B-scan created from an A-scan?
By enhancing the cathode-anode voltage instead of connecting to the Y plates of the CRO.
What does an M-scan represent in ultrasound technology?
A stream of lines down the screen of varying intensity.
What is the use of motion scans in ultrasound cardiography (UCG)?
To monitor the movement of an organ such as the heart wall or a heart valve.
How do modern ultrasound scanners build up each frame of the display?
Using an array of transducers to take a series of scans in rapid succession.
What is the relationship between pulse repetition rate and accuracy of internal organ movement display?
Higher pulse repetition rate results in more accurate display.
Calculate the depth at which reflection occurred if an ultrasound echo is received after 120µs in soft tissue.
92.5mm.
If the time between transmission of an ultrasound pulse and reception is 12µs, what is the maximum pulse transmission rate?
0.083 . 10^6 pulses/sec.
