Experimental Investigation of a Functionally Graded Composite Layer for Sound Absorption in Ultrasonic Transducers with an Approach to Fabrication and Characterization

Abstract

Conventional single-layer backing materials in ultrasonic transducers often show limited sound absorption and suffer from particle agglomeration, bubble formation, and uneven impedance distribution, reducing transducer efficiency. This study focuses on developing and characterizing epoxy-Al₂O₃functionally graded composites (FGMs) to overcome these limitations. FGMs were fabricated with alumina particle sizes of 50, 100, and 200 µm and varying volume percentages to optimize acoustic and mechanical properties. Mechanical testing showed that hardness and elastic modulus increased up to 19% and 15% alumina content, respectively, while higher contents caused bubbles and cavities that reduced performance. Acoustic analysis demonstrated that FGMs achieved up to 98% sound absorption, representing a 30% improvement in attenuation compared to single-layer composites, due to impedance gradients and enhanced wave energy dissipation. Scanning electron microscope confirmed uniform particle ispersion at optimal alumina concentrations, mitigating agglomeration and structural defects. These results highlight the potential of epoxy-Al₂O₃ FGMs as high-performance backing layers for ultrasonic transducers, with further studies recommended on frequency-dependent behavior andlong-term stability.

Received: 4 December 2025 | Revised: 24 February 2026 | Accepted: 28 May 2026

Conflicts of Interest

The author declares that he has no conflicts of interest to this work.

Data Availability Statement

Data are available from the corresponding author upon reasonable request.

Author Contribution Statement

Majid Mohammadi: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration.