The determination of the state of conservation of historical masonries by non-destructive and non-invasive techniques must still gain its due widespread use, and this is clearly reflected in national norms that often refuse them as not being reliable enough to be used without the support of destructive ones (see for example the Italian OPCM 3274/2003 and subsequent modifications). Anyhow, the clear advantages of such techniques, and especially laser based ones like the Scanning Laser Doppler Vibrometry - SLDV here employed, drive the research towards this direction. In this work we will illustrate a case study done in the south of the Marche region, namely the investigations conducted inside and outside the Lanciano castle, near Castelraimondo (MC). A series of SLDV measurements have been made that have lead to the discovery of many hidden structural defects, such as delaminations of superficial layers, minor and also important cracks. To validate our findings a well reputed and consolidated technique has been employed, a Ground Penetrating Radar - GPR, along with manual beating of suspected areas. Also a brief session using an infrared camera has been conducted to check the results relative to superficial delaminations, where the GPR could fail due to insufficient spatial resolution.
Several experiments have been carried out to investigate the mechanical vibrations generated by an organ pipe. Measurements were made by using Laser Doppler Vibrometry. It is a not-invasive optical measurement technique which allows to detect pipe-wall vibrations. The mechanical vibration field is compared with the acoustic field. Namely, we study the behaviour of these fields when they are excited by different levels of pressure. Strong analogies have been evidenced by using techniques in time e frequency domain supporting the assumption that the pipe is not a passive resonator. The challenge is to understand the complex mechanism of coupling between modes of air and eigen-modes of pipe that produces the sound. Here, we present, in first approximation, a low dimensional dynamical system which describes the main characteristics of pipe-wall vibrations. What is interesting is that the same low dimensional dynamical system is able to reproduce also the recorded acoustic field, implying that wall vibrations and acoustic pressure field are strictly related one to each other.
In this work laser Doppler vibrometry has been used for damage detection in frescoes. Results were compared with the ones obtained through infrared thermography, and, for both techniques, mathematical models were implemented to simulate the physical domains and conditions of the employed test sample. The limitations of each methodology are also discussed. The numerical model of the vibrometric investigations has been constructed using Finite Elements Method modeling. A new procedure based on the observation of Rayleigh waves propagation velocities allowed to acquire sample mechanical parameters. Comparison of experimental and simulated data and independent defect diameter measurement by echographic equipment, allowed to establish the confidence level and the discrepancies in the developed model. Also operational limits of the vibrometric technique have been studied by acquisition of Signal-to-Noise ratio on different areas of a sample. The Fourier equation has been used for the mathematical model employed for the numerical simulation of the thermographic investigations. Numerical technique with formularization in finite volumes has been employed and a FORTRAN code has been developed to solve the thermal problem.
A large-scale survey (~700 m2) of frescos and wall paintings was undertaken in the U.S. Capitol Building in Washington, D.C. to identify regions that may need structural repair due to detachment, delamination, or other defects. The survey encompassed eight pre-selected spaces including: Brumidi's first work at the Capitol building in the House Appropriations Committee room; the Parliamentarian's office; the House Speaker's office; the Senate Reception room; the President's Room; and three areas of the Brumidi Corridors. Roughly 60% of the area surveyed was domed or vaulted ceilings, the rest being walls. Approximately 250 scans were done ranging in size from 1 to 4 m2. The typical mesh density was 400 scan points per square meter. A common approach for post-processing time series called Proper Orthogonal Decomposition, or POD, was adapted to frequency-domain data in order to extract the essential features of the structure. We present a POD analysis for one of these panels, pinpointing regions that have experienced severe substructural degradation.
Electric guitars have received far less attention than acoustical/classical ones from research teams, mainly for the reason that they are essentially considered as mere electro-mechanical transducers and little attention has been paid to their vibrational behavior. However, every guitarist knows from his/her experience how important are typical vibrational parameters such as resonances, damping, construction materials but usually lack the technical knowledge to express it in scientific terms. Also lute-makers usually work only by experience and tacit knowledge and even big companies do not use scientific research to improve their instruments. Following a research line devoted to modem music instruments, in this article we will present some experimental results derived from a series of measurement sessions on two electric guitars, aimed at identifying typical resonance frequencies, modal shapes, and sound characteristics. Experimental set ups have been implemented trying to simulate as much as possible real life situations, in particular excitation has been obtained mainly by acoustical sources and a mechanical device resembling a plastic plectrum. Moreover, in order to better correlate vibrational results with musical properties of electric guitars and traditional making experience, examined guitars have been played in an anechoic chamber and acoustical signals acquired.
KEYWORDS: Acoustics, Standards development, Systems modeling, Neodymium, Data modeling, Finite element methods, Interference (communication), Laser Doppler velocimetry, Signal generators, Amplifiers
Nowadays there are several direct or indirect measurement methods for the determination of the surface velocity in vibrating structures, but two of them seem to be the most promising and interesting, in particular for vibro-acoustic problems: Laser Doppler Vibrometry (LDV) and Near-field Acoustic Holography (NAH). While LDV is a direct laserbased vibration measurement technique, NAH allows the determination of the particle surface velocity starting from simultaneous microphone measurements performed on a plane array positioned near the vibrating object, although with some limitations. In this work a comparison between the two techniques is performed on a simple laboratory case, in order to carefully and quantitatively asses the measurement uncertainty in the indirect NAH method used to estimate the vibration velocity. Also advantages and disadvantages of the two methods are briefly discussed. This study was conducted within the European Growth Project "ACES" (Optimal Acoustic Equivalent Source Descriptors for Automotive Noise Problems) GRD1-1999-11202.
At present the standard procedure of loudspeaker design involves a time consuming path consisting of the production of a limited series of prototypes that are then tested and evaluated in order to check their conformity to prescribed features. If significant discrepancies are found between designated and actual behavior, this procedure is iteratively repeated till an optimal result is reached. Doing so design time may become unacceptably long and makes difficult a systematic approach to loudspeaker development. For these reasons loudspeaker companies are implementing software packages that simulate loudspeaker response and completely eliminate the need of going through the above mentioned methodology. The approach agreed by FAITAL and the Dept. of Mechanics to model loudspeakers diaphragms is based on the simultaneous use of Finite Element Modeling (FEM) software packages and validation measurements by Scanning Laser Doppler Vibrometry (SLDV). Due to the structural complexity of loudspeakers, FEM models may require an excessive number of nodes and calculation time would rise to unpractical limits. To ease simulation requirements, it has been decided to eliminate air contribution from computer simulations. In this work we will experimentally determine which is the contribution of air on a loudspeaker cone vibrations, defming the percentage deviation from the normal functioning situation.
Laser diagnostic systems based on shearography, vibrometry, and holography principles were employed to investigate the potential implementation of laser techniques in art conservation structural diagnostic field. The employed techniques offered the required measuring variability to allow a first discrimination on complex diagnostic uncertainties encountered often in art conservation. The systems were tested and used to assess the structural condition of well-documented Byzantine icons with known structural problems. Defects and mechanical deformations were identified in various distances from the artworks by alternative employment of techniques. In this way simultaneous eligibility classification of the used systems was also obtained. Results of the on-field application on the XVII century Byzantine icons are herein presented with discussion on the prospects of the techniques in the diagnostic field of art conservation.
During the last years the growing importance of the correct determination of the state of conservation of artworks has been stated by all personalities in care of Cultural Heritage. There exist many analytical methodologies and techniques to individuate the physical and chemical characteristics of artworks, but at present their structural diagnostics mainly rely on the expertise of the restorer and the typical diagnostic process is accomplished mainly through manual and visual inspection of the object surface. The basic idea behind the proposed technique is to substitute human senses with measurement instruments: surfaces are very slightly vibrated by mechanical actuators, while a laser Doppler vibrometer scans the objects measuring surface velocity and producing 2D or 3D maps. Where a defect occurs velocity is higher than neighboring areas so defects can be easily spotted. Laser vibrometers also identify structural resonance frequencies thus leading to a complete characterization of defects. This work will present the most recent results coming out of the application of Scanning Laser Doppler Vibrometers (SLDV) to different types of artworks: mosaics, ceramics, inlaid wood and easel painting. Real artworks and samples realized on purpose have been studied using the proposed technique and different measuring issues resulting from each artwork category will be described.
Almost forty years ago the electric bass was invented and after some years it established itself as the most important source of low frequency sounds in modern music. This work will aim at studying the vibrational behavior of this instrument using, as much as possible, exciting sources related to its normal use, namely acoustical waves and short pulses applied on the strings. A characterization of the forces applied while playing will also be briefly performed along with a description of the basic features of different musical signals.
Sequential double exposure holographic interferometry is employed for examining the mechanical effects induced in the UV ablation of polymers. Deformations, evidenced by changes in the refractive index of the substrate, are observed to develop at unexpectedly long distances (approximately equals 2 - 5 cm) from the irradiation area. The morphology of the induced effects depends on the substrate properties, with the major types observed being tentatively ascribed to delaminations and local fractures. For accounting for the highly delocalized spatial spread of the effects, laser doppler vibrometry was used for monitoring the propagation of the stresses generated by the ablation process. The examination confirms the development of intense vibrations far from the ablation point. The present results suggest that in UV laser processing of molecular substrates, the photomechanical effects can be significant and special attention should be paid in their characterization and their minimization.
A scanning laser doppler vibrometer employs Doppler frequency shift of a probe laser beam and interferometric mixing with a reference beam to measure target velocity. This technique offers high sensitivity, high spatial resolution and very low if any intrusivity.
In ceramic tile industry, delamination is one of the more important and difficult problems to detect. Among all the general non-destructive evaluation methods, optical inspection technique seem to be particularly suitable. A method based on acquisition and processing of IR thermal images is proposed. Measurements have been performed by artificial heating by an IR quartz lamp. The performance of the technique has been evaluated experimentally and results show that the examine defects in the measured samples have been correctly detected. Another proposed technique for detection of delaminations and voids in structures is vibration monitoring by a scanning laser doppler vibrometer (SLDV). The basic idea is that a defected area will show as a higher velocity one. Structure excitation may be performed by acoustic means, thus allowing for a remote contactless measurement system. Our tests put in evidence that IR thermal images provide a very fast defect detection method appropriate for on line applications, while SLDV results show a better geometrical definition of defects shapes.
Frescoes, icons and composite materials show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; past experiences demonstrated that the study of surface vibrations could be used to locate defects position and size. At present a non- invasive diagnostic system is under development and the aim of this work is to propose and compare different kinds of structural exciters. After initial measurement set-ups based on accelerometers and impact hammers, a novel system based on laser vibrometers and acoustic stimulation has been assembled; full remote and contactless investigation of detachments and delaminations is thus possible with a very high accuracy. At present three different types of acoustic sources are employed: unbaffled standard loudspeakers, horn loudspeakers and an elliptic mirror sound focuser. The last source has been developed to concentrate sound power in a very small area so to excite only localized defects of the structures and void annoying noises to be propagated around them. A new kind of exciter, namely a piezo actuator, has also been introduced in the measurement chain and its effectiveness in finding defects in icons will be demonstrated. This paper will present experimental result gathered from sample showing differences in data due to different exciting sources. A comparison with results furnished by traditional techniques will be shown.
An important research theme in today's dentistry is the selection of the appropriate resin to be used for the filling of drilled cavities. Some resins in fact may cause high sensitivity or pain in the patient also few days after their application. This phenomenon of high sensitivity seems to be used by the creation of likeages at the interface between dentin and resin.
Frescoes and icons show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; the aim of this work is to develop a diagnostic system for the measurement of the defects position and size. After initial measurement set-ups based on accelerometers and impact hammers a novel system based on laser vibrometers and acoustic stimulation of structures to allow full remote and contactless investigation of detachments and delaminations has been developed. This paper presents a measurement procedure based on two subsequent scans of the work of art is employed; the first scan aims at finding defects positions the second one to characterize their resonant response. A new kind of exciters, namely piezo actuators, has been introduced in the measurement chain and its effectiveness in finding defects in icons will be demonstrated. Also an on field measurement session on large sample walls will be described along with the result obtained that show how efficient this technique has become.
Frescoes and icons show analogies in terms of defects, both present layer-to-layer detachments and delaminations and surface cracks; our aim is to develop a diagnostic system for the measurement of the defects position and size. We employ laser vibrometers and acoustic simulation of structures to allow full remote and contactless investigation of detachments and delaminations. The use of advanced measuring devices combined with computer data backup systems allow the restorers to follow damage evolution during time and to verify the effectiveness of their work. A full working experimental measurement set-up is described along with the results obtained. Extensive measurement sessions were performed with on purpose built frescoes and icons samples, presenting a wide range of defects positions and dimensions and different surface finishes and colors; results were then compared with those obtained by professional restorers by manual techniques. Further to this, we demonstrate that the simultaneous use of a complementary technique, IR thermography, allows also the measurement of complex defect structures, especially of superimposed defects at different layers interfaces.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.