Antti Meriläinen Edward Hæggström Using high frequency acoustic waves for mmµmscale imaging Method is nondestructive It Sees inside the sample Ultrasound images differences of acoustic impedances ID: 371037
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Slide1
Ultrasound Microscopy and High Frequency Coded Signals
Antti Meriläinen, Edward
HæggströmSlide2
Using high frequency acoustic waves for mm-/µm-scale imaging
Method is non-destructive
It “Sees” inside the sample
Ultrasound images differences of acoustic impedances
Ultrasound MicroscopyWhat it is?Slide3
Ultrasound Imaging
TOF
image
Amplitude
imageSlide4
Ultrasound MicroscopyBasic techniques
Phase Arrays
Single transducer pulse-echo
http://en.wikipedia.org/wiki/Ultrasonic_testing
http://www.nde.com/phased_array_technology.htmSlide5
Focused Ultrasound Transducer
[Yu, Scanning acoustic microscopy and its applications to material
characterization
, 1995]Slide6
TXPulser
, delta spike excitation
Gated sinus wave
For high frequencies ~1 GHzRXProtection circuit & Pre-amplifier(Envelope detector / pulse shaper)Oscilloscope
Tx
/Rx for USM
Camacho
, J.,
Fritsch
, C.: ‘
Protection
circuits
for ultrasound applications’
Ultrasonics, Ferroelectrics and Frequency Control, IEEE
Transactions, 2008, 55, (5), pp.1160-1164Slide7
Delta spike excitationStress for transducer and sampleEnergy/amplitude variation with high PRF
Gated sinus
Stress for transducer and sample
Uncertainty of Time-of-Fly (TOF)Depth resolution
Challenges with current techniquesSlide8
Coded USM
Coded signals
Electronics
Signal generation
Switch and timing
Preamplifier
Signal Synthesis
Ultrasound measurements
RF-design
Components
PCB layoutSlide9
Tx signal is wave packed
Frequency can be programmed
Phase can be programmed
Envelope (amplitude over time) can be programmedExample linear frequency modulation (LFM)/chirp
Coded SignalsSlide10
Cross Correlation
dt
descript depth resolution
dt
depends on bandwidth
dtSlide11
Coded Signal and SNR
SNR =10
SNR =1Slide12
Arbitrary waveform generatorsDigital to Analog converter (DAC)
Bandwidth up to 120 MHz (2 GS/s)
If you have money: 5.6 GHz (24 GS/s)
High frequency signal generatorsOutput: continuous sine waveFrequency range up to 4+ GHzNarrow modulation bandwidth (less than 1 kHz)
Signal generationNumerical vector to Electric signalSlide13
Modulation = change carrier wave by signalAmplitude modulation (AM)
Quadrature amplitude modulation (QAM)
Frequency modulation (FM)
Phase Modulation (PM)Many other ….
Modulation techniques
ModulationSlide14
AM:QAM:
QAM / IQ-modulation
Slide15
TRF370417 Modulator
Arbitrary/modulation bandwidth is 2*120 MHz
dt
= 4.2nsCenter output frequency is set by Local oscillatorOutput Bandwidth is NOT maximum output frequencySlide16
Modulator outputs
1 cm
Lo
Q
I
RF OutSlide17
Carrier Feedthrough and Sideband SuppressionSlide18
PreamplifierSlide19
AmplificationCascade design
Voltage range
Max/Min signal input strenght
Impedance machingInput impedanceOutput impedanceDC-blocksCapacitors and inductos for high frequencies
Same component can be tunet for different band
Preamplifier Design
Modulator -> Attenuator(-60 dB) -> Preamplifier(+55 dB)Slide20
Receiving during transmission is impossibleTransducer delay line gives time limit for coded signal
Typically 0.3 – 5 µs
Signal generator limits coded length 8 µs
Maximize signal time and minimize switching timeSwitch and TimingSlide21
Switch CircuitSlide22
Power handlingBandwidth Attenuation
Insertion loss (Smaller is better)
Isolation (Higher is better)
Switching timeGlitchAC/DC coupling Control voltages
Switch designingSlide23
Circuit based on AVR µControllerProgrammable
Predictable
Timing resolution is 62.5 ns
AVR trigs AWG and oscilloscope and controls the switchesTimingSlide24
Timing CircuitSlide25
Coded USM
Coded signals
Electronics
Signal generation
Switch and timing
Preamplifier
Signal Synthesis
Ultrasound measurements
RF-design
Components
PCB layoutSlide26
I and Q are numerical signals that can be generated by Matlab
Signal generation
How to generate I and Q
RF
LO sin
LO cos
X
X
Q
I
LP
LP
Matlab
RF
LO sin
LO cos
X
X
Q
I
+
Modulator
AWG
I & QSlide27
Results with 100 – 300 MHz
27
/15
Transmitted signal
Received A-line
B-scan imageSlide28
Signal-to-noise ratios (SNR) of surface echoes were estimated to compare coded excitation and delta spike excitation
Preliminary results showed that coded chirp signal excitation increased mean SNR (16±3) dB for 75 MHz transducer
Results from 2010: 30 – 70 MHz Coded signal
Pulse-echo measurement using a coded 5
V
pp
chirp signal excitation at 30-70 MHz (left) and a 33
V
pp
delta spike excitation (right).
The coded excitation increased mean SNR (16±3) dB
.Slide29
Higher frequency and coded signals
Higher frequency gives resolution
Modulator shift arbitrary band (Not increase bandwidth)
Coded signals may improve SNR/CNRCross correlation is sensitive for noise which has same band than signalBad modulator can generated ”noise” (Feedthrough
)Effective bandwidth can be tuned by arbitrary codeTransducer bandwidth Attenuation in immersion liquid
Arbitrary codes able multitone transmissionSlide30
RF design
Impedance matching
Single-end vs. Differential signals
Available IC components:AmplifiersAttenuatorsSwitches
Modulators / DemodulatorsPower detectorClock generator (PLL/VCO)All components are SMDSlide31
Single-End vs. Differential signals
Differential signals:
Single supply
No ground loopsLonger signal path
Reduces common-mode noise (noise from ground)Paired signal is requiredSingleSimpler design
(Dual supply)
There is amplifiers for conversionSlide32
Available IC components Amplifiers
Low noise (Pre. Amp.)
Noise figure <1dB
Gain ~20dBGain blocks50 Ω line driver
Power amplifier (Linear amplifier)Differential amplifierVariable gain amplifier (VGA)Slide33
Available IC components ModulatorsSlide34
Available IC components Modulators