The purpose of this research was the diagnosis of the detachments and the analysis of the subsequent stabilization intervention of antique roman plaster in Room 38 of the Domus Aurea. We carefully assessed the extent of the detachments in the fresco-decorated plaster before initiating the stabilization intervention. Two methods were implemented: manual auscultation and automatic scanning using the PICUS system. Both produced a map representing the defects prior and after the intervention. The comparison between the map obtained by the auscultation method and the PICUS map shows that they can be superimposed. The map obtained with the PICUS system highlights the most severe defects using a colorimetric scale, which is normally not used in a manual scan. The PICUS system has proven to be a valid support to the classical manual auscultation to prepare the map of the defects of antique, damaged cultural heritage.

The present study proposes a simple and low-cost indirect method for estimating the thickness of plates by measuring the contact time (TC) generated by the impact of a free-falling sphere. The theoretical model has been developed on Tsai approximation of Zener’s theory, which describes the dynamic interaction between the sphere and the plate taking in account the propagation of flexural waves. The methodology was validated through FEM simulations and through an extensive experimental campaign, where the contact times were measured using a simple electrical circuit. The results show excellent agreements between predicted and actual thicknesses, with relative errors below 3% for λ < 1.5 (where λ is the inelasticity parameter). For very thin plates and highly deformable materials, the above accuracy decreases due to flexibility and plastic deformation. We believe the proposed approach to be particularly promising in non-destructive testing applications within several scenarios, where speed, cost-effectiveness, and safety are essential requirements.

Debonding, especially in plastic materials, refers to the separation occurring at the interfacewithin a bonded structure composed of two or more polymeric layers. Due to the greatheterogeneity of materials and layering configurations, highly specialized expertise isoften required to detect the presence and extent of such defects. This study presentsa novel approach that leverages transfer learning techniques to improve the detectionof debonding defects across different surface types using PICUS, an acoustic diagnosticdevice developed at Roma Tre University for the assessment of defects in heritage wallpaintings. Our method leverages a pre-trained deep learning model, adapting it to newmaterial conditions. We designed a planar test object embedded with controlled subsurfacecavities to simulate the presence of defects of adhesion and air among the layers. This wasrigorously evaluated using non-destructive testing using PICUS, augmented by artificialintelligence (AI). A convolutional neural network (CNN), initially trained on this mock-up,was then fine-tuned via transfer learning on a second test object with distinct geometryand material characteristics. This strategic adaptation to varying physical and acousticproperties led to a significant improvement in classification precision of defect class, from88% to 95%, demonstrating the effectiveness of transfer learning for robust cross-domaindefect detection in challenging diagnostic applications.

This paper aims is to show an automated intelligent measurement system for the detection of adhesion defects between architectural antique plaster layers. The method emulates the traditional conservators' procedure based on acoustical perturbations, auscultation, detection and classification. The system makes use of a hardware device, known in literature as PICUS, for the generation and acquisition of acoustic signals, while the processing of the acquired signals is handled by a deep learning (DL) architecture designed ad hoc. After a brief description of the PICUS system and the acoustic data acquisition procedure, the whole architecture of the DL system is carefully described. The proposed method has been validated by a significant case study. The system shows an accuracy of up to 82% ( +/- 2%) in multi-class classification and up to 99% ( +/- 1%) in binary classification. In particular, the obtained results suggest a satisfactory precision in the detection of areas where stabilization is necessary. (c) 2024 The Author(s). Published by Elsevier Masson SAS on behalf of Consiglio Nazionale delle Ricerche (CNR). This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Acoustic characteristics and defects of adhesion of ancient construction materials using the PICUS system

The technique of panel painting played a particularly significant role in Italian art, especially between the thirteenth and sixteenth centuries, before canvas came into general use. The conservation of panel paintings, however, is complex and largely depends on the original materials and techniques used to create the support and the many layers of preparation for painting. The state of conservation is influenced also by the history of stress/deformation that the painting has undergone and the microclimatic conditions in which it is exposed. The large thermo-hygrometric variation induces changes in the structure of the wood and can create cracks even for the gypsum which is more rigid than the wood and can develop dangerous detachments. Recently, a low-cost, portable test system for the measurement of detachments between layers of architectural coatings, called PICUS, inspired by the method used by restorers during diagnosis and conservation interventions, has been successfully developed. The same system was then tested to acquire information about the execution technique, the state of conservation and previous interventions of stratified structures such as paintings on wood.

The Non-Destructive investigations used until now to detect the presence of detachments in wall coverings are hardly executable in situ. For these motivations, we designed an automatic system, similar to a “mouse”, portable, battery powered, and with a clear, fast, and accurate read-out. It use the technique of detection based on the “stiffness measure” of the cover: the surface is hit with a small “hammer” to measure the impact time. The aim of this work was to develop a system that, starting from the basic concepts known in literature, and making use of a powerful but economical 32 bit Arduino-like board, allows to obtain a pocket tester easily usable by any maintenance technician, with a cost of the device very low, while maintaining an efficient measurement methodology.

An innovative, robust method has been developed, based on the use of a simple, compact, expressly designed device, named PICUS (the ‘woodpecker’ in ancient Latin), and inspired by the auscultation method carried out by the experts in the field of conservation of cultural heritage. This method entails gently knocking the surface, controlling and measuring the impact time of the stroke’s force, recording the generated sound, comparing the acquired sound with a reference sound by calculating the cross-correlation function, and its maximum, as a measure of the detachment. In a nutshell, it performs an analysis similar to that carried out by a professional who performs a routine examination on the detachments by hand. The experimental apparatus consists of a probe made of an electromechanical percussion element that gently taps the surface producing a sound, a force sensor purposely developed to measure the impact force, and a microphone, all connected with an Arduino-like low cost board, to record and elaborate the sounds and the force sensor signal. The probe XY position on the scene is recognized using an infra-red (IR) system with a low-cost IR camera and an IR light-emitting diode (IR-LED) positioned on the probe. The “tapper” and the microphone replace the hand and the ear of a conservator carrying out a detachment investigation, while the comparison with a reference is the typical mind process of a professional restorer. The result is the fusion of the microphone data and the force sensor data.

Detecting the presence, the position and the extension of the detachments in architectural coverings is at the base of the analysis of the state of conservation of ancient structures. Many non-destructive investigation methodologies have been used, and the ultrasound technique applied through the use of parametric transducers appears be very promising. The use of parametric transducers to detect structural defects has been widely proven, but normally the systems "off the shelf" are not focused: these systems have beams with dimensions of the order of tens of cm. Recently, the introduction of a parametric transducer driven by an Arduino board, called Ultraino, has allowed to have available a focused parametric transducer at very low cost. The use of "Ultraino" permits to obtain beams with focal areas of the order of millimeters, at very small distances from the radiating device. This advantage, combined with the possibility of driving the device by a Matlab script, permits to implement the well-known technique of the measurement of the impulsive response in the audio range, and extract the acoustic reflectivity of the superficial point under test. Finally, the entire instrumentation has a very low price and it is easily portable and usable in situ.

Electrostatically actuated MEMS ultrasonic transducers, also known as Capacitive Micromachined Ultrasonic Transducers (CMUTs), offer better performance with respect to conventional piezoelectric transducers in terms of bandwidth and efficiency. The enhanced compatibility between MEMS and standard integrated circuit technologies enables the integration of the transducer and the front-end electronics, and is currently leveraged in the development of new-generation diagnostic systems for clinical, emergency and point-of-care uses. This paper reports on the development of an integrated 2-D CMUT array designed for volumetric ultrasound imaging. An acoustically optimized 3-D packaging technology has been applied to the design, fabrication and characterization of a Multi-Chip Module (MCM) obtained by 3-D interconnection of a 256-element CMUT spiral array and a 256-channel analog front-end Application Specific Integrated Circuit (ASIC) with integrated pulsers, low-noise receivers and a programmable TX beamformer.

Detecting the presence, the position and the extension of architectural coverings separations, both on horizontal and vertical layers – such as mosaics, plasters, slabs or other functional and decorative layers – is at the base of the analysis of the state of conservation of ancient structures. Non-destructive investigations used to find detachments, like Laser Doppler Vibrometry (LDV), are hardly executable in situ. They are also influenced by the boundary conditions and often need the intervention of onerous technical consultations. For this reason, traditionally, conservators rely on the technique of auscultation, which entails gently knocking with the hand, listening to the sound produced by the surface and perceiving the vibration of it. Together with the thermographic analysis, the results of these examinations are translated into the graphic documentation of the discontinuities of the structural elements, detachments and cracks between layers, in order to achieve the conservative diagnosis and outline a project of intervention. Analysis carried out with such method is accurate, but introduces a strong subjective conservator's connotation, which makes it not repeatable. In this contribution, after having briefly examined the state of the art of in situ technologies, an innovative acoustic-vibrational technique for the detection of detachment phenomena between layers and discontinuity is introduced. The proposed technique also allows tracing an accurate map, using an image correlation method between an acoustic “snap” of the point of interest and a “reference snap”. The analysis of the entire surface produces a graphics map of the detachments. This graphic documentation represents the “acoustic signature” of the structure, i.e. the “status quo” of the surface during the analysis. This representation can be used to monitor the state of conservation of the structure over time. In this paper, the method is developed and tested in laboratory using a personal computer and a hardware device specifically designed and fabricated, with the aim of providing a qualitative yet repeatable assessment of the state of conservation of a covering. The proposed method could be implemented in an easy-to-use and inexpensive portable version of the system using a smartphone, to which the developed hardware device would be connected through the audio jack to acquire the acoustic information, making the new system suitable for “in situ” operation. It can be also used for monitoring the evolution of the conservative scenario. The first results achieved on a test object are showed.

Biplane modality is frequently used in medical ultrasound imaging applications. Crossed array configurations, in which two orthogonal 1-D arrays co-exist on the same area, are particularly suitable for biplane imaging. However, the imaging performance is limited by the absence of focusing capability in the arrays respective elevation directions. In this paper, we present a novel 120+120-element 7 MHz crisscross Capacitive Micromachined Ultrasonic Transducer (CMUT) probe in which the orthogonal arrays are both provided with Fresnel elevation focusing capability. The CMUT probe includes low-noise amplifiers and high-voltage switches, which allow fast switching (<;200 μs) of the CMUT bias voltage of each array element between 0 V and high voltages up to +300 V. The bias polarity selection enables the elevation aperture Fresnel focusing, while the switching capability allows to alternately apply the elevation bias pattern to the two orthogonal arrays in realtime during biplane scan. A crisscross CMUT array was fabricated, packed and electrically characterized. The focusing capabilities were tested by interfacing the probe to the ULA-OP 256 scanner. C-scans of radiated pressure fields were acquired at the focal depth, and side lobe levels were evaluated.

The monitoring of concrete buildings is important to assess their solidity and promptly intervene in case of damage. Concrete structures suffer the formation of micro-cracks and the propagation of macro-cracks, due to ageing or to mechanical stresses. These cracks are sources of acoustic emission, and can be distinguished according to the frequency and intensity of the acoustic wave they generate; thus, transducers with high sensitivity and wide bandwidth are needed. Flextensional piezoelectric transducers are known for these characteristics, which make them suitable for acoustic emission applications. For this reason, we designed a flextensional transducer optimized for acoustic emission techniques applied to concrete structures. The performance of the device in receive mode in concrete-coupled operation was investigated by running harmonic analyses on a finite element model. The geometrical parameters of the device were designed in order to obtain a broadband receive sensitivity.

MEMS-based Capacitive Micromachined Ultrasonic Transducer (CMUT) technology enables the development of advanced transducer-electronics integrated multi-chip modules (MCM) for medical imaging applications. In this paper, we present the design, fabrication and characterization of a 256-element CMUT spiral array integrated with a 256-channel analog front end (AFE) ASIC featuring highvoltage unipolar pulsers, low-noise amplifiers and a programmable transmit beamformer. The spiral array, designed to perform volumetric beam steering at 7 MHz, is characterized by a density-tapered layout of 220μm -wide hexagonal elements distributed over a quasi-circular area of 10 mm diameter. The CMUT and the AFE were co-designed, fabricated and interconnected through an acoustically optimized 3-D packaging method. The resulting MCM was electromechanically and acoustically characterized, demonstrating the potential of the proposed approach for integrated 2-D CMUT array fabrication.

Electrical impedance characterization represents a practical way to evaluate the electro-mechanical parameters of Capacitive Micromachined Ultrasonic Transducers (CMUTs). This paper describes an accurate CMUT characterization method able to evaluate the electro-mechanical and parasitic parameters by fitting electrical impedance measurements at several bias voltages with an improved equivalent circuit model, which accounts for different parasitic phenomena including resistive and inductive behavior of electrical interconnections, stray capacitance, and dielectric loss of the insulating materials used in CMUT microfabrication. The method was analytically formalized, numerically implemented, and tested on air-coupled and water-coupled CMUTs. Experimental results showed excellent match between the experimental data achieved with a CMUT array element and the fitted impedance.

The electromechanical conversion efficiency and the long-term reliability of Capacitive Micromachined Ultrasonic Transducers (CMUT) are mainly limited by the parasitic capacitance and by charge injection phenomena, which are generated the first, by the portions of the CMUT electrodes used for interconnection, and the second, by the low dielectric strength of the in-cavity passivation materials. Reverse Fabrication Process (RFP) [doi: 10.1088/0960-1317/25/1/015012] is a sacrificial-release low-temperature CMUT technology that employs ultra-low-stress Silicon Nitride (Si x N y ) dielectrics and Titanium-Aluminum-Titanium metals. In this paper, we investigated the possibility of reducing both the parasitic capacitance, by acting on the electrodes layout, and the charge injection phenomena, by introducing Silicon Oxide (SiO 2 ) buffer layers between the electrodes and the in-cavity passivation layers.

As compared to piezoelectric technology, MEMS technology employed for Capacitive Micromachined Ultrasonic Transducer (CMUT) fabrication provides increased compatibility with 3D packaging methods, enabling the possible development of advanced transducer-electronics multi-chip modules (MCM) for medical imaging applications. In this paper, an acoustically optimized 3D packaging method for the interconnection of Reverse-Fabricated 2D CMUT arrays and front end ICs using a wafer-level compatible process is presented. The developed packaging method uses Cu pillars and Sn-Ag solder reflow for electrical interconnection, and patterned Benzocy-clobutene (BCB) for mechanical bonding. Process parameters were optimized by analyzing the acoustic behavior of a CMUT supported by a BCB film laying on a silicon substrate using Finite Element Modeling (FEM). Dummy CMUT and ASIC wafers were processed and MCMs were assembled following a chip-to-chip bonding approach using the optimized process parameters. Electrical characterization of the MCMs demonstrated successful contact across the entire fabricated devices. Probe head prototypes were assembled and pulse-echo experiments were carried out using the MCM surface as a reflector to verify the effectiveness of the optimization on the acoustic behavior of the device.