Presentation is loading. Please wait.

Presentation is loading. Please wait.

Www.helsinki.fi/yliopisto Ultrasound Microscopy and High Frequency Coded Signals Antti Meriläinen, Edward Hæggström.

Similar presentations


Presentation on theme: "Www.helsinki.fi/yliopisto Ultrasound Microscopy and High Frequency Coded Signals Antti Meriläinen, Edward Hæggström."— Presentation transcript:

1 Ultrasound Microscopy and High Frequency Coded Signals Antti Meriläinen, Edward Hæggström

2 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 Microscopy What it is?

3 Ultrasound Imaging TOF image Amplitude image

4 Ultrasound Microscopy Basic techniques Phase Arrays Single transducer pulse-echo

5 Focused Ultrasound Transducer [Yu, Scanning acoustic microscopy and its applications to material characterization, 1995]

6 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

7 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

8 Coded USM Coded signals Electronics Signal generation Switch and timing Preamplifier Signal Synthesis Ultrasound measurements RF-design Components PCB layout

9 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

10 Cross Correlation dt descript depth resolution dt depends on bandwidth dt

11 Coded Signal and SNR SNR =10SNR =1

12 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 generation Numerical vector to Electric signal

13 Modulation = change carrier wave by signal Amplitude modulation (AM) ‒ Quadrature amplitude modulation (QAM) Frequency modulation (FM) Phase Modulation (PM) Many other …. Modulation techniques Modulation

14 AM: QAM: QAM / IQ-modulation

15 TRF 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

16 Modulator outputs 1 cm LoQI RF Out

17 Carrier Feedthrough and Sideband Suppression

18 Preamplifier

19 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)

20 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

21 Switch Circuit

22 Power handling Bandwidth Attenuation Insertion loss (Smaller is better) Isolation (Higher is better) Switching time Glitch AC/DC coupling Control voltages Switch designing

23 Circuit based on AVR µController Programmable Predictable Timing resolution is 62.5 ns AVR trigs AWG and oscilloscope and controls the switches Timing

24 Timing Circuit

25 Coded USM Coded signals Electronics Signal generation Switch and timing Preamplifier Signal Synthesis Ultrasound measurements RF-design Components PCB layout

26 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 XX QI LP Matlab RF LO sin LO cos XX QI + Modulator AWG I & Q

27 Results with 100 – 300 MHz 27/15 Transmitted signal Received A- line B-scan image

28 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 MHz (left) and a 33 V pp delta spike excitation (right). The coded excitation increased mean SNR (16±3) dB.

29 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

30 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

31 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

32 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)

33 Available IC components Modulators

34 Available IC components Modulators


Download ppt "Www.helsinki.fi/yliopisto Ultrasound Microscopy and High Frequency Coded Signals Antti Meriläinen, Edward Hæggström."

Similar presentations


Ads by Google