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Ultrasound Microscopy and High Frequency Coded Signals. Antti Meriläinen, Edward Hæggström. Ultrasound Microscopy What it is?. Using high frequency acoustic waves for mm-/µm-scale imaging Method is non-destructive It “Sees” inside the sample - PowerPoint PPT Presentation
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www.helsinki.fi/yliopisto
Ultrasound Microscopy and High Frequency Coded Signals
Antti Meriläinen, Edward Hæggström
www.helsinki.fi/yliopisto
• 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?
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Ultrasound Imaging
TOF image
Amplitude image
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Ultrasound MicroscopyBasic techniques
Phase Arrays Single transducer pulse-echo
http://en.wikipedia.org/wiki/Ultrasonic_testinghttp://www.nde.com/phased_array_technology.htm
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Focused Ultrasound Transducer
[Yu, Scanning acoustic microscopy and its applications to material characterization, 1995]
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• TX• Pulser, delta spike excitation• Gated sinus wave
‒ For high frequencies ~1 GHz
• RX• Protection 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.1160-1164
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• Delta spike excitation• Stress for transducer and sample• Energy/amplitude variation with high PRF
• Gated sinus• Stress for transducer and sample• Uncertainty of Time-of-Fly (TOF)
‒ Depth resolution
Challenges with current techniques
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Coded USM
•Coded signals
•Electronics• Signal generation• Switch and timing• Preamplifier
•Signal Synthesis
•Ultrasound measurements
•RF-design• Components• PCB layout
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• Tx signal is wave packed• Frequency can be programmed• Phase can be programmed• Envelope (amplitude over time)
can be programmed
• Example linear frequency modulation (LFM)/chirp
Coded Signals
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Cross Correlation
dt descript depth resolutiondt depends on bandwidth
dt
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Coded Signal and SNR
SNR =10SNR =1
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• Arbitrary waveform generators• Digital 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 generators• Output: continuous sine wave• Frequency range up to 4+ GHz• Narrow modulation bandwidth (less than 1
kHz)
Signal generationNumerical vector to Electric signal
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• Modulation = change carrier wave by signal• Amplitude modulation (AM)
‒ Quadrature amplitude modulation (QAM)
• Frequency modulation (FM)• Phase Modulation (PM)• Many other ….
Modulation techniques
Modulation
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• AM:
• QAM: •
QAM / IQ-modulation
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TRF370417 Modulator
• Arbitrary/modulation bandwidth is 2*120 MHz
‒ dt = 4.2ns
• Center output frequency is set by Local oscillator
• Output Bandwidth is NOT maximum output frequency
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Modulator outputs
1 cm
LoQ I
RF Out
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Carrier Feedthrough and Sideband Suppression
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Preamplifier
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• Amplification• Cascade design
• Voltage range• Max/Min signal input strenght
• Impedance maching• Input impedance• Output impedance
• DC-blocks• Capacitors and inductos for high frequencies• Same component can be tunet for different band
Preamplifier Design
Modulator -> Attenuator(-60 dB) -> Preamplifier(+55 dB)
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• Receiving during transmission is impossible
• Transducer 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 time
Switch and Timing
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Switch Circuit
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• Power handling• Bandwidth • Attenuation
• Insertion loss (Smaller is better)• Isolation (Higher is better)
• Switching time• Glitch• AC/DC coupling • Control voltages
Switch designing
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• Circuit based on AVR µController• Programmable• Predictable• Timing resolution is
62.5 ns
• AVR trigs AWG and oscilloscope and controls the switches
Timing
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Timing Circuit
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Coded USM
•Coded signals
•Electronics• Signal generation• Switch and timing• Preamplifier
•Signal Synthesis
•Ultrasound measurements
•RF-design• Components• PCB layout
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• I and Q are numerical signals that can be generated by Matlab
Signal generationHow to generate I and Q
RF LO sin
LO cos
X X
Q I
LPLP
Matlab
RF
LO sin
LO cos
X X
Q I
+
Modulator
AWG
I & Q
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Results with 100 – 300 MHz
27/15
Transmitted signal
Received A-line
B-scan image
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• 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 Vpp chirp signal excitation at 30-70 MHz (left) and a 33 Vpp delta spike excitation (right). The coded excitation increased mean SNR (16±3) dB.
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Higher frequency and coded signals• Higher frequency gives resolution
• Modulator shift arbitrary band (Not increase bandwidth)
• Coded signals may improve SNR/CNR• Cross correlation is sensitive for noise which has same
band than signal• Bad modulator can generated ”noise” (Feedthrough)
• Effective bandwidth can be tuned by arbitrary code• Transducer bandwidth• Attenuation in immersion liquid
• Arbitrary codes able multitone transmission
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RF design
• Impedance matching• Single-end vs. Differential signals• Available IC components:
• Amplifiers• Attenuators• Switches• Modulators / Demodulators• Power detector• Clock generator (PLL/VCO)All components are SMD
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Single-End vs. Differential signals
• Differential signals:• Single supply• No ground loops• Longer signal path• Reduces common-mode noise (noise
from ground)• Paired signal is required
• Single• Simpler design• (Dual supply)
There is amplifiers for conversion
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Available IC components Amplifiers
• Low noise (Pre. Amp.)• Noise figure <1dB• Gain ~20dB
• Gain blocks• 50 Ω line driver
• Power amplifier (Linear amplifier)• Differential amplifier• Variable gain amplifier (VGA)
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Available IC components Modulators
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Available IC components Modulators