[11] As a Ph.D. student,[12] Declercq published 30 peer-reviewed articles in reputed scientific journals, including Annalen der Physik, and made 42 presentations (with papers in proceedings) at international congresses in his field.

[33] Beyond his primary academic responsibilities, he advises PhD students at the Doctoral Schools of École Nationale Supérieure des Arts et Métiers[34] and Université de Lorraine in France.

[52] He conducted a study and documented the history of the Portuguese along the Kalu Ganga river in Sri Lanka, specifically focusing on the village of Uduwara and the town of Kalutara.

Declercq’s theoretical models, published in the Journal of the Acoustical Society of America and Nature, discuss the pyramid’s design suggested a potential influence on cognition.

Bilsen (2006) expanded on Declercq’s findings, proposing new theoretical frameworks for acoustic phenomena in ancient monuments, suggesting intentional sound manipulation in Mesoamerican and Mediterranean structures.

His focus on piezoelectric crystals, which generate electric charges under mechanical deformation, has broad applications in acousto-optic devices, non-destructive evaluation (NDE), and sonar systems.

His theoretical and experimental contributions have enabled more precise control of sound waves, with significant applications in structural health monitoring and advanced signal processing.

[89] He has made advancements in non-destructive evaluation (NDE) techniques, particularly for detecting internal damage in fiber-reinforced polymers (FRPs) and composites used in the aerospace and automotive industries.

He has enabled real-time damage detection by employing techniques like Lamb waves, infrared thermography, and X-ray tomography, offering solutions for operational monitoring in industries reliant on these materials.

[90][91] His ultrasonic-guided wave techniques have demonstrated efficient in detecting delamination, of importance in aerospace engineering, where real-time, noninvasive integrity monitoring of components under extreme stress is essential.

[92] His advancements in Scanning Acoustic Microscopy (SAM) have enabled subsurface analysis of composite and biological materials, extending its utility to evaluating microscale periodic structures, notably in semiconductors and microelectronics.

SAM’s precision in measuring surface and subsurface properties is now pivotal in determining the viscoelastic characteristics of materials, a key aspect for both scientific inquiry and industrial applications.

[95] His incorporation of machine learning with ultrasonic NDE techniques improves damage detection in noisy environments, important for industries like aerospace, where real-time accuracy is essential.

His work on THz wave interactions with carbon fiber orientation enables precise differentiation between intra-laminar and inter-laminar damage, an essential advancement for aerospace applications.

[100] His research has made strides in ophthalmology, employing GHz Scanning Acoustic Microscopy (GHz-SAM) to examine the biomechanical properties of corneal tissues, particularly the Descemet's membrane.

This indicator offers reliable damage estimation that aligns with X-ray analysis, providing essential non-destructive evaluation (NDE) techniques applicable in both production and maintenance phases.

The importance of this work is highlighted in the 2020 report by the French Committee of Automobile Constructors (CCFA), which cites the successful reduction of 100 kg in average car mass as one of the developments contributing to reduced carbon dioxide emissions in France.

[104] Prior to his contributions to the automotive sector, his work involved the development of Polar Scan systems for the inspection of lightweight composite structures composed of carbon fibers embedded in polypropylene thermoplastic (PPT), as seen in applications such as the Airbus A380.

By fine-tuning these structures, materials can be designed to redirect, focus, or block sound, benefiting industries like automotive noise control and defense stealth technologies.

His studies on the Goos-Hänchen effect in acoustic waves have informed the design of metamaterials for sonar and ultrasound imaging, enabling more precise sound control in these technologies.

His work integrates Lamb waves-based sensors into robotic platforms in collaboration with other teams, enabling long-range, non-destructive evaluations (NDE) with minimal human intervention, improving safety and efficiency in hazardous or labor-intensive environments.

[111] An essential contribution is his integration of SLAM (Simultaneous Localization and Mapping) algorithms into robotic inspection systems, enabling autonomous navigation in complex, noisy, or visually obstructed environments like underwater or industrial settings.

[112] His enhancements in SLAM systems enable autonomous inspection robots to more effectively navigate and map large-scale metal structures, even in traditionally challenging environments.

By advancing pose-graph SLAM models, his work allows for more accurate mapping, even in the structural complexities of ship hulls and natural gas storage tanks.

Additionally, he uncovered previously unknown details about the family's land acquisitions following the Fall of Granada and their contributions to regional urban development and repopulation efforts.

Furthering his examination of military history, his work on the Eighty Years' War uncovered new details about the Spanish Army's efforts to retain control over the Low Countries.

Through the study of previously unpublished military records, he highlighted the significant roles that members of the Desclergues family played in critical battles, such as the 1604 Siege of Ostend, as commanders and logistical organizers.

His findings shed light on how these soldiers' lives intersected with the broader historical forces at play, offering a human perspective on the vast and complex wars that shaped Europe.

[126] Declercq is a patrilineal descendant of Don Pere Desclergue (I),[127] who was born early in the 15th century AD [128] [129] at Montblanc in the Conca de Barberà in Catalunya, Spain.

[3][147] The Desclergues of Montblanc originate from Bertrand du Guesclin,[148][139]: 97–130  who was a military commander from Brittany and who supported Henry of Trastámara, the first King of Castile and León in the period 1365-1370.