Research ArticleENGINEERING

Stretchable ultrasonic transducer arrays for three-dimensional imaging on complex surfaces

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Science Advances  23 Mar 2018:
Vol. 4, no. 3, eaar3979
DOI: 10.1126/sciadv.aar3979
  • Fig. 1 Schematics and design of the stretchable ultrasonic transducer array.

    (A) Schematics showing the device structure. (B) Exploded view to illustrate each component in an element. (C) The optical image (bottom view) of four elements, showing the morphology of the piezoelectric material and bottom electrodes. (D) The tilted scanning electron microscopy image of a 1-3 piezoelectric composite. (E) The optical image (top view) of four elements, showing the morphology of the backing layer and top electrodes. (F to H) Optical images of this stretchable device when (F) bent around a developable surface, (G) wrapped on a nondevelopable surface, and (H) in a mixed mode of folding, stretching, and twisting, showing its mechanical robustness.

  • Fig. 2 Characterizations of piezoelectric and mechanical properties.

    (A) The impedance and phase angle spectra of the 1-3 composite before and after processing, showing good electromechanical coupling of the fabricated transducer (keff, ~0.60; θ, ~50°). (B) Pulse-echo response and frequency spectra, with a short spatial pulse length (~1.94 μs), a high SNR (~20.24 dB), and a wide bandwidth (~47.11%). (C) The resonance and antiresonance frequency variations of the 100 transducer elements. The mean values/SDs are 3.51 MHz/56.8 kHz (resonant) and 4.30 MHz/59.1 kHz (antiresonant), respectively. The 100% yield demonstrates fabrication robustness. (D) Average cross-talk levels between elements that are adjacent, two elements away, and three elements away, showing the outstanding anti-interference capacity of the device. (E) The optical image (left) and corresponding finite element analysis (FEA) simulation (right) of a 2 × 2 array under 50% biaxial tensile strain, showing its excellent stretchability. The local strain level (maximum principal strain) in the interconnects is indicated by the color scale. (F) The optical image after releasing the biaxial strain of 50%. The zoomed-in image highlights plastic deformation and local delamination of the interconnects upon loading/unloading. (G) Electrical impedances of the transducer under different strain levels, showing the mechanical stability of the device.

  • Fig. 3 Characterization of spatial resolution.

    (A) Schematics of spatial resolution measurement setup, with focal lengths of 20, 32, 37, and 52 mm, respectively. (B) Comparison of noise floors reconstructed by DMAS and DAS algorithms, revealing the benefits of the DMAS algorithm with only 0.01% energy ratio of noise to the reflector. (C) Images of wire phantom combining the four tests with different f numbers, showing the capability of focusing at different depths and obtaining high-resolution images. (D) Axial and (E) lateral line spread functions for the center wire at different focal lengths. Resolution is defined as the linespread function width at an intensity of −6 dB. (F) Experimental (Exp.) and simulation (Simu.) results of lateral and axial resolutions.

  • Fig. 4 Two-dimensional images of a linear defect under complex surfaces.

    Optical images of experimental setups with the stretchable ultrasonic device tested on (A) planar, (B) concave, and (C) convex surfaces showing the good conformability of the device on these surfaces (first column); simulation results showing the different wave fields and sensing modes (second column); pulse-echo signals from the defects and boundaries with high SNR (third column); and acquired 2D images using DMAS algorithms with accurate and artifact-free positions (fourth column). S wave, shear wave; L wave, longitudinal wave; SNRD, SNR of pulse-echo response from the defect.

  • Fig. 5 Three-dimensional image reconstruction of intricate defects under a convex surface.

    (A) Schematics of the experimental setup, illustrating the spatial location and relative orientation of the two defects in the test subject. (B) The reconstructed 3D image, showing complete geometries of the two defects. (C to E) The 3D image from different view angles, showing the relative positions and orientations of the two defects to the top surface, which match the design well.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaar3979/DC1

    section S1. Piezoelectric transducer design using the KLM model

    section S2. SAF imaging and DMAS algorithm

    fig. S1. Testing performance of a commercial rigid probe on curved surfaces.

    fig. S2. Schematic illustration of the device fabrication process.

    fig. S3. Ecoflex thickness as a function of spin coating speed on a glass slide.

    fig. S4. Acoustic damping effects of silicone substrates.

    fig. S5. The vibration mode comparison between PZT and 1-3 composites.

    fig. S6. Pulse-echo response and bandwidth differences of transducers with and without the backing layer (KLM simulation).

    fig. S7. Bottom electrode design.

    fig. S8. Top electrode design.

    fig. S9. Four-layer top electrode fabrication processes.

    fig. S10. Optical images of Cu serpentine interconnections under different laser parameters.

    fig. S11. Laser ablation resolution experiments.

    fig. S12. Photographs of the device seamlessly laminated on different curved surfaces.

    fig. S13. ACF cable bonding.

    fig. S14. Simulation results from the KLM model.

    fig. S15. Dielectric properties of the device.

    fig. S16. The phase angle change during the fabrication process and after repetitive testing.

    fig. S17. Experimental and simulation of a small array under biaxial tensile strain.

    fig. S18. Electric impedances under different bending curvatures.

    fig. S19. The real and imaginary parts of electrical impedance under different levels of bending and stretching.

    fig. S20. Relative resistance changes of Cu serpentine under stretching.

    fig. S21. Instruments for nondestructive evaluation.

    fig. S22. Switch circuit of the entire testing system.

    fig. S23. Reconstructed images based on simulation under flat, concave, and convex surfaces.

    fig. S24. The pulse-echo signal and 2D image of the two defects.

    fig. S25. Polarization conditions.

    fig. S26. The matching circuit of the ultrasound testing system.

    fig. S27. Ultrasound signal filtering.

    fig. S28. Simplified schematics of a transducer element.

    fig. S29. The electrical model of a transducer.

    fig. S30. General diagram showing the transmission line model of a two-port system.

    fig. S31. Schematics showing the basic concept of SAF.

    fig. S32. Block diagrams for the imaging algorithms.

    table S1. Parameters for the 1-3 composite, backing layer, and Ecoflex.

    movie S1. Simulation of wave field under a planar surface.

    movie S2. Simulation of wave field under a concave surface.

    movie S3. Simulation of wave field under a convex surface.

    Reference (59)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Piezoelectric transducer design using the KLM model
    • section S2. SAF imaging and DMAS algorithm
    • fig. S1. Testing performance of a commercial rigid probe on curved surfaces.
    • fig. S2. Schematic illustration of the device fabrication process.
    • fig. S3. Ecoflex thickness as a function of spin coating speed on a glass slide.
    • fig. S4. Acoustic damping effects of silicone substrates.
    • fig. S5. The vibration mode comparison between PZT and 1-3 composites.
    • fig. S6. Pulse-echo response and bandwidth differences of transducers with and without the backing layer (KLM simulation).
    • fig. S7. Bottom electrode design.
    • fig. S8. Top electrode design.
    • fig. S9. Four-layer top electrode fabrication processes.
    • fig. S10. Optical images of Cu serpentine interconnections under different laser parameters.
    • fig. S11. Laser ablation resolution experiments.
    • fig. S12. Photographs of the device seamlessly laminated on different curved surfaces.
    • fig. S13. ACF cable bonding.
    • fig. S14. Simulation results from the KLM model.
    • fig. S15. Dielectric properties of the device.
    • fig. S16. The phase angle change during the fabrication process and after repetitive testing.
    • fig. S17. Experimental and simulation of a small array under biaxial tensile strain.
    • fig. S18. Electric impedances under different bending curvatures.
    • fig. S19. The real and imaginary parts of electrical impedance under different levels of bending and stretching.
    • fig. S20. Relative resistance changes of Cu serpentine under stretching.
    • fig. S21. Instruments for nondestructive evaluation.
    • fig. S22. Switch circuit of the entire testing system.
    • fig. S23. Reconstructed images based on simulation under flat, concave, and convex surfaces.
    • fig. S24. The pulse-echo signal and 2D image of the two defects.
    • fig. S25. Polarization conditions.
    • fig. S26. The matching circuit of the ultrasound testing system.
    • fig. S27. Ultrasound signal filtering.
    • fig. S28. Simplified schematics of a transducer element.
    • fig. S29. The electrical model of a transducer.
    • fig. S30. General diagram showing the transmission line model of a two-port system.
    • fig. S31. Schematics showing the basic concept of SAF.
    • fig. S32. Block diagrams for the imaging algorithms.
    • table S1. Parameters for the 1-3 composite, backing layer, and Ecoflex.
    • Reference (59)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Simulation of wave field under a planar surface.
    • movie S2 (.mp4 format). Simulation of wave field under a concave surface.
    • movie S3 (.mp4 format). Simulation of wave field under a convex surface.

    Files in this Data Supplement:

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