Cristiano Riminesi

Microwave Reflectometric Tool for Non-Destructive Assessment of Decay on Timber Structures

Timber structures can be degraded during their life both by structural problems and, mainly, by biological degradation factors like fungi, and insects (Coleoptera and termites). The occurrence of these biodegradation agents leads, in the absence of appropriate maintenance interventions, to the loss of their structural integrity. Furthermore, if these biological agents decay old buildings, the loss of mechanical resistance of timber structures can be added to loss of cultural heritages. Just in these contexts an early evaluation of decay is crucial to design remedial treatments and a less invasive restoration intervention. This work presents a new microwave diagnostic system for the in situ evaluation of timber structures based on microwave reflectometry, i.e on the measurement of the microwave reflection coefficient as a function of frequency. The continuous-wave (CW) microwave signal is launched by a double-ridged antenna, which also measures the wave reflected by the material under investigation. The measurement system allows diagnosing the effects of biodegradation during a first quick survey in a non-destructive and non-invasive manner. Measurements on laboratory models demonstrated the feasibility of the method. Results obtained on timber beam sections, compared with the findings of traditional investigation methodologies, demonstrate the potentiality of microwave reflectometry, suggesting its usefulness for decay detection and as a support to invasive diagnostic tools.

Measuring the permittivity of thin samples in the X band: a thickness-independent technique

A new method is proposed for determining the permittivity of thin materials in the X band and estimating their thickness. The procedure consists of measuring two reflection coefficient values at the input of a waveguide modified to accommodate the material under measurement and then computing the unknown parameters by means of a numerical procedure employing a genetic algorithm. The method has been tested on certified dielectric materials and it can be successfully applied to materials whose thickness is not constant (i.e. leaves). Results concerning paper and thin cardboard are presented.

MOdihMA at Sforza Castle in Milano: Innovative Techniques for MOisture Detection in Historical Masonry

The research line MOdihMA (MOisture detection in historical MAsonry) proposes to improve the innovative techniques recently developed to measure different parameters related to water content in masonry, that has an important role in the damage of historical buildings. The first objective of this project is to compare the effectiveness of the different methods in understanding how the quantitative data obtained are directly related to water content. The second objective of the MOdhiMa project is to compare the ability of the different techniques to map water as a function of its location and depth within the masonry structure, both on macro and micro-scale. A selection of these innovative techniques recently had an application on the “Sala delle Asse” in the Sforza Castle in Milan. The hall is famous for the decoration of the vault and the monochrome on the northwest wall, attributed to Leonardo. Recently Milano Municipality defined the plan of diagnostics for detecting the causes of the increasing damage on the painting and the poor conditions of conservation of the vault. Unilateral NMR, SUSI, IR Thermography, gravimetric and chemical tests were applied for mapping the moisture distribution in the bottom of the northwest wall. The comparison with the results of the standardized techniques confirmed the low moisture content distributed in the masonry.

Microwave permittivity measurements through cross-shaped ring sensors

A microwave sensor designed to determine the complex permittivity of planar materials is proposed. The sensor is implemented using a full planar microstrip technology. The near fields of the ring resonator interact with the material under test (MUT) and the electrical characteristics of the resonator change. A scalar network analyzer is used to measure the resonant frequency and the corresponding amplitude of the transmission parameter for the fundamental mode. The complex permittivity is estimated by inverting the measured parameters using by an algorithm based on Artificial Neural Network (ANN). The proposed sensor is extremely compact and guarantees a good accuracy for low permittivity material. The design procedure is described and experimental results are reported validating the sensor performance.

Moisture and salt monitoring in concrete by evanescent field dielectrometry

Monitoring the water content and detecting the presence of soluble salts in concrete is a key issue for its maintenance. Evanescent field dielectrometry, originally developed for the diagnostics of frescoes and mural paintings, is proposed as a tool for monitoring the decay of cement-based materials. A measuring system, based on a scalar network analyzer and a resonant probe, has been realized and tested on concrete samples taken from historical buildings in France or purposely developed in the laboratory. Measurements on water-saturated and oven-dry samples provide the basis for calibrating the instrument for on site monitoring of concrete historical buildings, sculptures and cement-based artifacts.

A microwave scanner for sub-surface diagnostics of artefacts

A microwave scanner operating in the frequency band 1-10 GHz is described. The system is based on an evanescent-field resonant sensor, allowing to obtain maps of dielectric contrast through a measurement of resonance frequency (F maps) and quality factor (Q maps). Laboratory experiments are presented with results validating the measurement system.

First Trials for a Microwave Reflectometric Tool to Survey Decay in Historic Timber Structures

Timber structures can be degraded during their life both by structural problems and by biological degradation factors like fungi, and insects. The occurrence of those biodegradation agents could lead to a loss of their structural integrity, in the absence of appropriate maintenance. An early assessment of the decay is even more important when the wooden structures are part of historical buildings, in the interest of conservation of cultural heritage. This work presents an application of microwave reflectometry for the in situ evaluation of timber structures. The measurement system allows detecting anomalies inside the material in a non-destructive and non-invasive manner. The reflection coefficient is measured by means of a vector network analyzer (VNA) using a double-ridge antenna, which transmits the continuous-wave microwave signal and receives the signal reflected by the material under investigation. Measurements on laboratory models demonstrated the feasibility of the method. Results obtained on timber beam sections, compared with the findings of traditional investigation methodologies, demonstrate the potentiality of microwave reflectometry, suggesting its possible usefulness during the diagnostic phase as a non-invasive tool for preliminary screening.

Microwave system for moisture mapping by a linear array of slot sensors

A linear array of microwave sensors for moisture content mapping in thin or thick material sheets is introduced. The array building block is represented by a straight microstrip line electromagnetically coupled to a resonant slot structure properly loaded by two PIN diodes. Each array element constitutes a single slot sensor interacting with the material under test by means of the fields radiated through the slot. When the diodes are in the ON state, each sensor and, thus, the whole array, acts like a low loss transmission line. Otherwise, when the diodes are in the OFF state, the slots are allowed to resonate. Switching the array elements one at a time, the array electronically scans the specimen under test.

Environmental impact assessment on the stone decay in the archaeological site of Hierapolis (Denizli, Turkey)

The archaeological site of Hierapolis (Denizli province, Turkey) is unique in terms of the conservation of marbles and travertines. Environmental factors (i.e. interaction with thermal waters, high thermal stress, CO2 degassing) and geological aspects (presence of seismic faults, frequent earthquakes, formation of travertine) play a fundamental role in the durability and conservation state of the stone materials. This paper presents a multi-analytical approach aimed to identify the phenomena and causes of stone decay related to environmental conditions. The analyses of alteration and decay phenomena are discussed together with the monitoring of the main environmental parameters and with analyses of waters and gases present in the archaeological site. Finally, the need of a continuous monitoring of the environmental parameters affecting the archaeological site is stressed.

First Trials to Set Up a Microwave Reflectometric Tool for the Survey of Historic Timber Structures

ABSTRACT Timber structures can be degraded during their life both by structural problems and by biological degradation factors like fungi and insects. The occurrence of those biodegradation agents could lead to a loss of their structural integrity, in the absence of appropriate maintenance. An early assessment of the decay is even more important when the wooden structures are part of historical buildings, in the interest of conservation of cultural heritage. This article presents an application of microwave reflectometry for the in situ evaluation of timber structures. The measurement system allows detecting anomalies inside the material in a non-destructive and non-invasive manner. The reflection coefficient is measured by means of a vector network analyzer (VNA) using a double-ridge antenna which transmits the continuous-wave (CW) microwave signal and receives the signal reflected by the material under investigation. Measurements on laboratory models demonstrated the feasibility of the method. Results obtained on timber beam sections, compared with the findings of traditional investigation methodologies, demonstrate the potentiality of microwave reflectometry, suggesting its possible usefulness during the diagnostic phase as a non-invasive tool for preliminary screening.