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A Level Physics OCR(A) 6.5.3 Ultrasound - Coggle Diagram
A Level Physics OCR(A) 6.5.3 Ultrasound
Ultrasound is a logitudinal wave with a frequency greater than 20kHz
The shorter the wavelength of ultrasound used the more detailed the scan is but the shallower the scan will go
Because the wavelength of the ultrasound used is the minimun resolution of the scan
Production and Reception of Ultrasound
Piezoelectric effect - When a pd is applied through a material it causes a compression or extension in the mateial
An alternating pd is applied accross a crystal
This causes a vibration in the crystal
Which produces ultrasound
Ultrasound is incident on a crystal
Which causes a vibration in the crystal
Which induces a pd across the crystal that can be measured
Ultrasound Scans
Consist of emitting ultrasound into the body then measuring the time for the reflection and the intensity of the reflection
A-Scan
Ultrasound is emitted into the body in one direction
This produces a trace with peaks where the ultrasound is reflected off the boundary between different tissues
Which can be used to measuere the depth of different pats of the body eg the thickness of skin
When taking data from a trace the distance worked out is twice the depth of that material
B-Scan
Ultrasound is emitted into the body in many directions
This can produce a 2d or 3d image
Used in prenatal scanning
Acoustic Impedance
The acaustic impedance of a material is the product of the density of the material and the speed of sound in that material
The greater the differance in acoustic impedances the greater the percentage of ultrasound is refleced at a boundary of materials
If there is air between the transducer and skin
There will be a big gap between the acoustic impedances of the air and skin
So lots of the ultrasound will be reflected by the skin and less will be transmitted into the body
Impedance Matched Gel
A gel with a similar acoustic impedance to the skin
It is applied to the skin
So there is no air between the transducer and skin
So less ultrasound is reflected at the boundary between the skin and gel
Blood Flow Rate
Dopler Effect - A change in frequency and wavelength due to realative motion between an emitter and observer
Ultrasound in emitted into the body at an angle to the blood vessel in question
The dopler effect happens twice (when reflected by the blood then when received by the transducer