Ultrasound Microscopy and High Frequency Coded Signals - PowerPoint Presentation

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