Aleksander S. Paterno

Benchmark for Peak Detection Algorithms in Fiber Bragg Grating Interrogation and a New Neural Network for its Performance Improvement

This paper presents a benchmark for peak detection algorithms employed in fiber Bragg grating spectrometric interrogation systems. The accuracy, precision, and computational performance of currently used algorithms and those of a new proposed artificial neural network algorithm are compared. Centroid and gaussian fitting algorithms are shown to have the highest precision but produce systematic errors that depend on the FBG refractive index modulation profile. The proposed neural network displays relatively good precision with reduced systematic errors and improved computational performance when compared to other networks. Additionally, suitable algorithms may be chosen with the general guidelines presented.

Multiplexed Fiber Bragg Grating Interrogation System Using a Modulated Fiber Bragg Grating and the Tunable-Filter Method

This paper describes the use of a mechanically modulated fiber Bragg grating (FBG) to address FBG sensors using the tunable-filter method. A demonstration of FBG sensors multiplexing using this interrogation method is also presented, where the tunable FBG is used to scan the spectral operating range of the sensors. All the FBG used in this paper do not need to match their center wavelengths

Determination of setting expansion of dental materials using fibre optical sensing

The use of fibre Bragg grating sensors to study dental materials like resin-based composite and gypsum products is reported. Two commercially available composite resins and three types of gypsum products were tested in order to determine polymerization contraction and setting expansion. Temperature and strain evolution during the hardening phase of the material were also obtained. The presented technique can be a good tool for dentists in order to better manipulate a material and predict how it will behave in vivo.

Stepwise fabrication of arbitrary fiber optic tapers

This work reports a modified flame-brush technique to fabricate fiber tapers with arbitrary waist profiles. The flame-brush approach is used to produce small step reductions in the fiber diameter, or step-tapers, with a constant speed flame brush sweep, while the fiber is uniformly stretched. Arbitrary waist profiles in tapers are fabricated by approximating the taper diameter function to any monotonic function of the fiber length while combining a superposition of step-tapers. This method to produce the arbitrary profiles is described and a set of tapers with dissimilar transition regions are fabricated for its validation.

Measurement of composite shrinkage using a fibre optic Bragg grating sensor

Fibre Bragg grating is used to determine resin-based composite shrinkage. Two composite resins (Freedom from SDI and Z100 from 3M) were tested to determine the polymerization contraction behaviour. Each sample of resin was prepared with an embedded fibre Bragg grating. A LED activation unit with wavelength from 430 nm to 470 nm (Dabi Atlante) was used for resin polymerization. The wavelength position of the peak in the optical reflection spectra of the sensor was measured. The wavelength shift was related to the shrinkage deformation of the samples. Temperature and strain evolution during the curing phase of the material was monitored. The shrinkage in the longitudinal direction was 0.15 ± 0.02% for resin Z100 (3M) and 0.06±0.01% for Freedom (SDI); two-thirds of shrinkage occurred after the first 50 s of illumination.

Fiber taper rig using a simplified heat source and the flame-brush technique

This paper presents the implementation of an automated fiber optic taper rig capable of manufacturing fiber optic tapers with diameters in the micron and sub-micron range. The implemented taper rig uses the flame-brush technique to taper the fiber optic with a heat source made by a low cost commercial air aspirated/butane/propane refillable and controllable micro-torch. Adiabatic tapers with exponential waist profiles, tapering excess loss of less than 1% and with diameters in the micron range are reported and the feasibility of such a simple heat source is demonstrated for the fabrication of fiber optic tapers. The taper rig has the dimensions and structure to manufacture tapers in the sub-micron range, but such tapers were not presented in this work.

Hybrid Wavelength-Time-Domain Interrogation System for Multiplexed Fiber Bragg Sensors Using a Strain-Tuned Erbium-Doped Fiber Laser

A system for the interrogation of fiber Bragg grating (FBG) sensors using a strain-tuned EDF laser with linear cavity is described. An optical switch is spliced to one end of the laser cavity and connects one of two high-strength draw-tower fiber Bragg gratings (DTGs). The gratings are simultaneously tuned by a stretching device and act as the end reflector of the laser cavity. By applying a ramp signal to the actuator synchronized to the optical switch, the laser signal sweeps over two different wavelength intervals, depending on the connected DTG. This approach represents a hybrid wavelength-time-domain interrogation for multiplexed sensors and doubles the number of sensors that may be addressed when compared with single DTG scanning. In addition, the use of the DTG allows a fivefold increase in the strain tuned wavelength interval over standard fiber Bragg gratings. An example application is demonstrated where temperature inside an electrical motor is measured during operation.

An approach to improve the spatial resolution of a force mapping sensing system

This paper proposes a smart sensor system capable of detecting sparse forces applied to different positions of a metal plate. The sensing is performed with strain transducers based on fiber Bragg gratings (FBG) distributed under the plate. Forces actuating in nine squared regions of the plate, resulting from up to three different loads applied simultaneously to the plate, were monitored with seven transducers. The system determines the magnitude of the force/pressure applied on each specific area, even in the absence of a dedicated transducer for that area. The set of strain transducers with coupled responses and a compressive sensing algorithm are employed to solve the underdetermined inverse problem which emerges from mapping the force. In this configuration, experimental results have shown that the system is capable of recovering the value of the load distributed on the plate with a signal-to-noise ratio better than 12 dB, when the plate is submitted to three simultaneous test loads. The proposed method is a practical illustration of compressive sensing algorithms for the reduction of the number of FBG-based transducers used in a quasi-distributed configuration.

Efficient Computational Techniques in Bioimpedance Spectroscopy

Electrical Bioimpedance Analysis (BIA) is an important tool in the characterization of organic and biological material. For instance, its use may be mainly observed in the characterization of biological tissues in medical diagnosis (Brown, 2003), in the evaluation of organic and biological material suspensions in biophysics (Cole, 1968; Grimnes & Martinsen, 2008), in the determination of fat-water content in the body (Kyle et al., 2004) and in in vivo identification of cancerous tissues (Aberg et al., 2004), to name a few important works. It is also natural to have different computational approaches to bioimpedance systems since more complex computational techniques are required to reconstruct images in electrical impedance tomography (Holder, 2004), and this would open a myriad of other computational and mathematical questions based on inverse reconstruction problems.

Sparse Force Mapping System Based on Compressive Sensing

This paper reports the development and application of a reconstruction method based on differential evolution (DE) to solve an underdetermined tactile sensing system with quasi-distributed fiber sensors. The reconstruction relies on the coupled responses from eight fiber Bragg grating-based transducers. The sensing system is capable of locating and quantifying up to three loads simultaneously applied to a metallic plate divided into 16 regions. The signal reconstruction is performed using compressive sensing methods to infer the spatial distribution of the applied forces. A comparison between the implemented method based on DE and traditional sparse signal recovery schemes (LASSO, OMP, Robust-SL0, and CoSaMP) showed the better performance of the proposed algorithm in the demonstrated application.