Ultrasound Microscopy and High Frequency Coded Signals

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Ultrasound Microscopy and High Frequency Coded Signals

Antti Meriläinen, Edward Hæggström


• 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?


Ultrasound Imaging

TOF image

Amplitude image


Ultrasound MicroscopyBasic techniques

Phase Arrays Single transducer pulse-echo

http://en.wikipedia.org/wiki/Ultrasonic_testinghttp://www.nde.com/phased_array_technology.htm


Focused Ultrasound Transducer

[Yu, Scanning acoustic microscopy and its applications to material characterization, 1995]


• 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


• 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


Coded USM

•Coded signals

•Electronics• Signal generation• Switch and timing• Preamplifier

•Signal Synthesis

•Ultrasound measurements

•RF-design• Components• PCB layout


• 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


Cross Correlation

dt descript depth resolutiondt depends on bandwidth

dt


Coded Signal and SNR

SNR =10SNR =1


• 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


• Modulation = change carrier wave by signal• Amplitude modulation (AM)

‒ Quadrature amplitude modulation (QAM)

• Frequency modulation (FM)• Phase Modulation (PM)• Many other ….

Modulation techniques

Modulation


• AM:

• QAM: •

QAM / IQ-modulation


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


Modulator outputs

1 cm

LoQ I

RF Out


Carrier Feedthrough and Sideband Suppression


Preamplifier


• 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)


• 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


Switch Circuit


• Power handling• Bandwidth • Attenuation

• Insertion loss (Smaller is better)• Isolation (Higher is better)

• Switching time• Glitch• AC/DC coupling • Control voltages

Switch designing


• Circuit based on AVR µController• Programmable• Predictable• Timing resolution is

62.5 ns

• AVR trigs AWG and oscilloscope and controls the switches

Timing


Timing Circuit


Coded USM

•Coded signals

•Electronics• Signal generation• Switch and timing• Preamplifier

•Signal Synthesis

•Ultrasound measurements

•RF-design• Components• PCB layout


• 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


Results with 100 – 300 MHz

27/15

Transmitted signal

Received A-line

B-scan image


• 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.


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


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


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


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)


Available IC components Modulators

Ultrasound Microscopy and High Frequency Coded Signals

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