Andrea Mencaglia

Fiber optic vibration sensor for remote monitoring in high power electric machines

A novel fiber optic vibration sensor is presented, based on the motion detection of an elastic cantilever by means of the optical triangulation technique. The sensor was designed to work at a fixed frequency of 100 Hz for applications in high power electrical plants where insulation and EM immunity requirements make fiber optic sensing the most suitable choice. The working linear range reaches a peak amplitude of 0.25 mm; resolution is 0.1 microm; accuracy is better than +/-3%; and sensitivity is 10 mV/microm. Design details and experimental results are reported.

Optical sensor for interstitial pH measurements

An optical fiber sensor for measuring the pH in interstitial fluid is described. Microdialysis is the approach followed for extracting the sample from the subcutaneous adipose tissue. The interstitial fluid drawn flows through a microfluidic circuit formed by a microdialysis catheter in series with a pH glass capillary. The pH indicator (phenol red) is covalently immobilized on the internal wall of the glass capillary. An optoelectronic unit that makes use of LEDs and photodetectors is connected to the sensing capillary by means of optical fibers. Optical fibers are used to connect the interrogating unit to the sensing capillary. A resolution of 0.03 pH units and an accuracy of 0.07 pH units are obtained. Preliminary in vivo tests are carried out in pigs with altered respiratory function.

Direct and chemically-mediated absorption spectroscopy using optical fiber instrumentation

This paper shows various applications of optical fiber sensors to absorption spectroscopy. Sensors for the monitoring of chromium in sewage water and for the colorimetry of gasoline samples are presented together with sensors for radiation dosimetry in radiotherapy and for lighting control in museum environments. In all these sensors, a combination of broadband and multi-band spectral measurements are collected using the same custom instrumentation unit consisting of LED light sources and an optical fiber microspectrometer. Extensions of the unit to implement other sensors making use of visible spectral range are discussed. The custom instrumentation implemented to address these sensors is their key unifying feature. It opens the possibility of addressing other sensors making use of absorption-based optrodes which present an analyte-modulated absorption spectrum in the visible spectral range.

Fiber-optic thermometric probe utilizing GRIN lenses

A multimode optical fiber thermometer is described, which makes use of a single fiber for light guiding and a thermochromic solution as a differential absorption temperature transducer. The probe has a novel design and utilizes graded-index microlenses to achieve high coupling efficiency between fiber and transducer. Technical data of the electrooptic unit, along with the working principle of the probe are presented, and calibration tests of the thermometer are given.

Array of opto-chemical sensors based on fiber-optic spectroscopy

A compact, flexible platform for reading out the variation of the optical absorption spectra in the visible range in a number of sensing materials is illustrated in this paper. This apparatus is based on an integrated spectrophotometer, an array of suitably controlled LEDs, optical fibers to carry and collect light, and a mechanical arrangement that makes possible the measurement, in sequence, of up to 15 different sensing layers. The unit was tested with a number of metalloporphyrins, known for their outstanding sensorial and optical properties. Data were analyzed using a multiway chemometrics approach. In this regard, a methodology to investigate the properties of an array of chemical sensors is introduced. This approach allowed an evaluation of the role played in the array by each sensing material in each spectral region to be performed. The analysis revealed interesting insight into the classification properties of the sensor array and the interaction mechanisms of porphyrins. The set of metalloporphyrins showed a variety of interaction mechanisms, and the relation of these mechanisms to the structure of the metalloporphyrins was evidenced by an accurate interpretation of the loadings of the multiway analysis.

Calibration and Use of Photosensitive Materials for Light Monitoring in Museums

Abstract Methodological aspects of the use of photosensitive materials as light dosimeters in museum monitoring are investigated. As a case study, a spectroscopic investigation in the 400–700 nm range is developed for Blue Wool Standard No. 1 (BWS1), a colorimetric indicator traditionally used by conservators to obtain a qualitative indication of the risk associated with lighting. Experiments using both artificial and natural light-aging were performed on BWS1 samples and a set of reflectance spectra was non-invasively collected during the aging process at increasing light-doses. A portable device based on fibre-optics technology, operating in real time, was used for the spectral acquisition. The problem of calibrating the BWS1 response to the light was investigated using the data-set of artificially light-aged samples, and different calibration models were compared. The calibration curves were then used to estimate the alteration, due to the possible synergistic action of light and other factors, which occurred in BWS1 samples naturally aged by exposure in situ. A method to account semi-quantitatively for the cumulative action of light and other environmental agents is proposed, by introducing the concept of ‘equivalent light-dose’, in terms of which the overall risk factor can be evaluated.

Time-resolved absorption as optical method for herbicide detection

A new sensing system for the detection of photosynthetic herbicides in water has been developed, based on the use of a trans-membrane protein complex, the reaction centre (RC) isolated from Rhodobacter sphaeroides. The stationary and excited state of this protein are characterised by different absorption properties. The path followed by the protein to return to the stationary state is influenced by the presence of photosynthetic herbicides. Therefore the concentration of herbicides could be measured by monitoring the temporal changes of absorption following optical excitation. For this purpose, an optoelectronic system has been realised. It makes use of a 860 nm light emitting diode and a hybrid photodetector and is coupled to a 5 cm-long optical cell containing the RC solution through optical fibres. The system was tested with atrazine and a limit of detection of 10 nM was obtained.

Array of opto-chemical sensors based on a fiber-optic spectroscopy

Thin films of metalloporphyrins have been used as sensing materials for the development of optical sensors devoted to the detection of different volatile organic compounds (VOC). Absorption spectra of thin films showed remarkable changes after interactions with analytes. The development of a measurement set-up is discussed and the results obtained in the context of VOCs detection are reported.

Equivalent light dosimetry in museums with blue wool standards and optical fibers

A novel optical-fiber instrument is presented for the monitoring of lighting in a museum environment. It makes use of blue wool standard dosimeters, the light-induced color-fading of which is continuously monitored by means of a miniaturized optical-fiber spectrophotometer. Field tests performed at the Uffizi Gallery of Florence are presented.

Dispersive Raman Spectroscopy for the Nondestructive and Rapid Assessment of the Quality of Southern Italian Honey Types

Raman spectroscopy performed using optical fibers, with excitation at 1064 nm and a dispersive detection scheme, was utilized to measure a selection of unifloral honeys produced in the Italian region of Calabria. The honey samples had three different botanical origins: chestnut, citrus, and acacia. A multivariate processing of the spectroscopic data enabled us to distinguish their botanical origin, and to build predictive models for quantifying important nutraceutic indicators, such as the main sugars and potassium. Furthermore, the Raman spectra of chestnut honeys were compared with the taste profile measured by an electronic tongue: A good correlation to a bitter-savory taste was obtained. This experiment indicates the excellent potential of Raman spectroscopy as a modern analytical tool for the nondestructive and rapid multi-component analysis of food quality indicators.