Download - Ultrasonic Transducer Fundamentals
Rad225/Bioe225UltrasoundFall 2019Ultrasonic Transducer
Fundamentals
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019Piezo Effect
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Discovered by Pierre and Jacques Curie in 1880.
Direct Effect Reverse Effect
Rad225/Bioe225UltrasoundFall 2019PZT
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lead zirconate titinatecrystals oriented randomlyheating beyond Curie temperature (365°C for PZT) frees the microscopic crystals, allowing them to movehigh voltage produces partial alignment, or polarization, then cooled, called poling
Rad225/Bioe225UltrasoundFall 2019Bone
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bone exhibits some piezoelectric propertiescollagen exhibits the polar orientation of molecular dipolesbiological force sensorshown to stimulate resorption and growth
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019Transducer Anatomy
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Rad225/Bioe225UltrasoundFall 2019Transducer Anatomy
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Matching layer 2
Piezoelectric
Backing
Matching layer
Electrode
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019Resonant Frequency
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fo is determined by the transducer thickness
f0 =ncp2L
L = nλ2
n=odd integers
Wave going backwards experiences one round trip through crystal, then is back in phase with wave emanating from front of crystal.
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019Quarter Wave Matching Layer
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If Zm = ZstZtand thickness of matching layer = λ/4then, it appears that transducer has same impedance as soft tissue.This maximizes transmission for one frequency.Multiple matching layers can be used for multiple frequencies.
where st=soft tissue, t=transducer, m=matching layer
Rad225/Bioe225UltrasoundFall 2019Effects of Matching Layer
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Rad225/Bioe225UltrasoundFall 2019Backing Material
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Rad225/Bioe225UltrasoundFall 2019Effects of Backing
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Rad225/Bioe225UltrasoundFall 2019Quality Factor
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Q =f0BW
low Q
high Q
Imaging
Therapy
Rad225/Bioe225UltrasoundFall 2019Transducer Characterization
Experimental Bandwidth = 48.2%
Imaging Xducer, damped, low Q
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Rad225/Bioe225UltrasoundFall 2019Transducer Characterization
Sputtered Electrode
Wires
PZT
Brass Housing
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• HIFU - air backed, high Q
Rad225/Bioe225UltrasoundFall 2019Efficiency
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=Acoustic Power/Electrical Power
~ Eg. 50% for an air-backed therapy systempotential for heat for any transducer, CW system need cooling
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Rad225/Bioe225UltrasoundFall 2019Single Elements Diced into
Multiple Elements
21Duck
Rad225/Bioe225UltrasoundFall 2019
Outline
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piezo effecttransducer anatomyresonance frequencymatching layer, backing material, Qmultielements/dicingaxial resolutiondemo
Axial Resolution Lateral Resolution
Resolvable
NotResolvable
Resolvable
NotResolvable
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Axial Resolution
Pulses
Objects you want to resolve
Resolvable Not Resolvable Resolvable
How to get a smaller SPL? Higher frequency, low Q 24
Rad225/Bioe225UltrasoundFall 2019Quality Factor
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Q =f0BW
low Q
high Q
Imaging
Therapy
Resolution is determined by SPL
x
To resolve x, the spatial pulse length must be < 2x.nλ < 2x
Axial Resolution x = nλ/2
• Ex. n=3, f = 1.5 MHz, λ = 1 mm, resolution = 1.5 mm
SPL2x
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Higher FrequencyBetter Resolution
Body WallFat, muscle
Liver Capsule
Rad225/Bioe225UltrasoundFall 2019Outline
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piezo effecttransducer anatomyresonance frequencybacking material, matching layer, Qaxial resolutiondemo