Session: 03-11-02: Laser-Based Advanced Manufacturing and Materials Processing II

Paper Number: 166601

Scalable Fabrication of Wearable Ultrasound Transducers Using Laser-Induced Graphene and 3d-Printed Piezopolymer 

Ultrasound imaging is a widely used and non-invasive technique that provides real-time visualization of internal tissues, organ structures, and blood flow dynamics. Its ability to capture high-resolution images without exposing patients to ionizing radiation has made it indispensable in medical diagnostics and therapeutic applications. In musculoskeletal health, ultrasound plays a crucial role in assessing soft tissue injuries by offering quantitative insights into structural changes and functional recovery, particularly during physical activity. The fundamental principle of ultrasound imaging relies on transmitting high-frequency sound waves and detecting their reflections from tissue boundaries. This process depends on an ultrasound transducer (UST), which utilizes piezoelectric materials to convert electrical signals into mechanical waves and reciprocally transform returning acoustic signals into electrical output.

Conventional ultrasound transducers are typically handheld and composed of rigid piezoelectric ceramics. While effective for diagnostic procedures, these designs are impractical for continuous monitoring or use during movement. Wearable ultrasound patches have been explored as an alternative, aiming to provide long-term imaging solutions without the need for constant operator positioning. However, many of these designs rely on assembling individual transducer elements onto flexible substrates, a process that often results in low active transducer coverage, reduced imaging resolution, and complex fabrication requirements. Additionally, common materials such as lead-based piezoelectrics introduce environmental and regulatory concerns. To overcome these limitations, a new approach is needed that enables scalable, high-performance, and adaptable ultrasound imaging.

We employ a rapid and scalable laser graphitization technique to create conductive electrode patterns and synthesize graphene from polyimide film. A far-infrared laser generates localized photothermal energy, elevating the temperature within the laser's focal area. This thermal effect disrupts covalent bonds between carbon atoms in the polyimide precursor, leading to the release of gaseous byproducts and the development of a porous structure. The resulting 3D porous graphene is then combined with polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) via 3D printing PVDF-TrFE ink to form a graphene-piezopolymer composite. Deposition and infiltration of PVDF into graphene pores increased surface area interaction and create a strong bond between PVDF and graphene. To enhance its piezoelectric response, the transducer undergoes a poling treatment, which aligns the piezoelectric domains within the PVDF-TrFE matrix. The final fabrication steps include gold sputter-coating for grounding and depositing a 5 µm-thick parylene layer for passivation.

We characterized the dielectric, piezoelectric, and acoustic properties of the graphene-based USTs. Deposition of PVDF could be tuned to achieve a center frequency ranging from 10 MHz to 28 MHz. Graphene-based ultrasound transducer demonstrates a high signal amplitude of 6.59 V and a signal-to-noise ratio (SNR) of 433, along with a −6 dB bandwidth of 8.86 MHz (37%). A high-quality two-dimensional ultrasound image, including a B-mode image of a cyst phantom, was produced with graphene-based UST, which is comparable to one obtained by the clinical system. To demonstrate the versatility of our approach, we fabricated graphene-based USTs of different geometries and configurations, which included a single circular element 3.5 mm in diameter, an M-shaped UST 7-mm across, a dual-element doppler transducer, and a 32-element array with 400-μm pitch. Patterning of graphene-based electrodes produced the desired sensor configuration with uniform PVDF deposition across the entire device. Hydrophone scans of the M-shaped and doppler devices reveal that the acoustic fields are well-matched to the geometry of the underlying graphene pattern, which illustrates the suitability of our novel technique for applications requiring special ultrasound geometries. The method is also amenable for producing transducer arrays for B-mode imaging. The production cost of our UST is estimated to be under $5 per unit, making them a low-cost solution for flexible USTs.

Presenting Author: Shirin Movaghgharnezhad George Mason University

Presenting Author Biography: Shirin Movaghgharnezhad is a Research Assistant Professor in the Department of Bioengineering and affiliate faculty in the Department of Mechanical Engineering at George Mason University. She obtained her Ph.D. in Mechanical Engineering at George Mason University. She then did her postdoctoral research in the Department of Bioengineering at GMU. Her research focuses on the advanced manufacturing of multifunctional materials with enhanced electrical, electrochemical, and piezoelectric properties, designed for seamless integration into wearable and flexible devices for medical applications. Her research aims to develop high-performance flexible sensors by employing surface engineering techniques and nanostructuring of 2D materials into 3D structures. Dr. Movaghgharnezhad's key interests include nanomaterials, advanced manufacturing, graphene, sensors, and electrochemistry.

Authors:

Shirin Movaghgharnezhad George Mason University
Ehsan Ansari George Mason University
Clayton Baker George Mason University
Dulcce Valenzuela George Mason University
Ahmed Bashatah George Mason University
Pilgyu Kang George Mason University
Parag Chitnis George Mason University