ultrasound microscopy and high frequency coded signals
DESCRIPTION
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 PresentationTRANSCRIPT
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Ultrasound Microscopy and High Frequency Coded Signals
Antti Meriläinen, Edward Hæggström
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• 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