Wearable/ Stretchable Ultrasound Transducers

Using Piezoelectric Material

by Melissa Nguyen

University of California, San Diego

Summer Research Conference

Ultrasound transducers

In 1880, Jacques and Pierre Curie discovered piezoelectricity.

➢ Used in applications, such as eye imaging, intravascular imaging, blood flow measurement…

➢ Applied many concepts: piezoelectric effect, magnetostriction and photoacoustic effect.

Piezoelectric Effect: Polarization charges are induced in response to an external mechanical stress

nec-tokin.com

Electronic pulse → Transducer → Ultrasound Pulse Ultrasound pulse is reflected by human tissues, bones

→ Echo Pulse → Electric signal → Image

www.sprawks.org

Problem with Current Ultrasound Devices:Rigid Transducer Probes

cdn2.kevinmd.com/www.news-medical.net amerisoundmedical.com

Goal: Develop a piezoelectric material based soft ultrasound transducers which can be integrated

with the human body

Wearable/ Stretchable devices

nanowerk.com

Challenges: Acoustic Impedance

- Backing layer: mechanical support and allows acoustic energy flowing into the sample to be absorbed.

- Front matching layer: improve the energy transmission between active layer and load medium.

ndk.com

Device Fabrication: ACF cable vs. Copper wire

Lin Zhang, “Fabrication steps for soft ultrasound devices” [Presentation slides], 2016

Active Layer

Backing Layer

EcoflexWire

Device cross sectional area

Test on Aluminum block

Pulser/Receiver T/R R Oscilloscope

Al block

Ch 1

Ch 2

Transmitter Receiver

Velocity of sound in aluminum= 6100 m/s

Test on Aluminum block

Top view: Sample ultrasound device was placed on Al block

Front view: The defect on Al block

Velocity of sound in aluminum= 6100 m/s

Fabrication of Copper Wire

Laser cut on Cu layer (5 µm thick) and PDMS 1:20

Peel off the outside layer to reveal the wire patterns

Fabrication of Copper Wire

PDMS part A : B Adhesion

1:10 Poor

1:20 Good

1:30 Too high

- Copper foil (5 µm thick) and PDMS layer were activated using UV ozone at for 2 mins.

- The adhesion between Cu foil and PDMS depending on PDMS adhesion.

Copper wire designs

❖ Considerations:➢ Stress➢ Strain

❖ Tests: ➢ In planar ➢ Bending/ stretching configuration

Stretchability Test

Break pointBefore stretching

Stretchability Test

Serpentine + Ecoflex

Serpentine

L 39 7

L’ 61.6 11.8

ΔL 22.6 4.8

Strain 57.9% 68.5%

Acceptable: 60% StrainGoal: 100% Strain

⇒ Test using different thicknesses of Cu wires (10, 15, 20 µm)

Unit: mm

Future Work

- Optimize a design for copper wire

- Stretchability test on different thicknesses of Cu wires

- Eliminate noise and interference for better signals

THANK YOU FOR LISTENING! QUESTIONS?

Thank you...Professor Xu Sheng

Post-graduate: Lin Zhang

AEP Advisor: Sophia Tsai

Academic Enrichment Program (AEP)

New Scholarship Donor

...for making this research opportunity possible!