Ultrasonic non-destructive evaluation of timber: Bibliometric mapping, engineering translation gaps and emerging pathways for submerged timber pile assessment

Reliable assessment of aging timber infrastructure requires methods that detect internal deterioration and translate material degradation into engineering-scale structural information. Ultrasonic non-destructive evaluation (NDE) is widely used for timber condition assessment and material characterization, yet its engineering application and translation towards structural assessment have not been systematically quantified. This study presents a bibliometric, science-mapping and critical analysis of ultrasonic timber NDE, focusing on its temporal evolution, thematic structure, methodological development and engineering translation. Bibliographic data were retrieved from Scopus (1988–2026) and analyzed using descriptive statistics and VOSviewer-based network visualization. Progressive screening reduced the literature from 7443 records in the broad timber degradation and structural-performance corpus to 177 ultrasonic timber NDE studies and 31 engineering-relevant studies. Within the 31-study corpus, 14 studies (45.2%) addressed defect, deterioration or condition assessment, 12 (38.7%) focused on mechanical-property estimation and 5 (16.1%) addressed member-, component- or structural-condition assessment; overall, 26 studies (83.9%) remained concentrated on diagnosis or material-property characterization. Temporal and thematic mapping shows methodological expansion towards tomography, guided waves, advanced signal processing, machine-learning-assisted interpretation and structural health monitoring, but limited validated translation into structural-performance assessment. Submerged timber pile assessment was examined as a focused engineering context within these gaps. Only 1 of 31 core studies (3.2%) directly addressed permanently waterlogged timber foundation piles, while evidence on ultrasonic pile assessment, moisture-dependent response, waterlogged deterioration and ultrasonic–mechanical-property relationships remains distributed across separate studies. No study integrates environmental exposure, ultrasonic response, deterioration, effective mechanical properties and structural performance (0/31). The findings identify an evidence-based translation gap rather than an absence of ultrasonic capability and establish a prospective pathway from environmental exposure and ultrasonic response to deterioration, effective properties, structural response/capacity and reliability-based assessment. Validation under representative submerged conditions is required to establish these interfaces.