Milos Tomic

A fibre-optic displacement sensor for a cyclotron environment based on a modified triangulation method

Due to the very high magnetic and radio frequency fields and generally hostile environment inside cyclotrons, electronic devices are hindered from functioning. By implementing a modified triangulation method we developed a purely dielectric PC interfaced sensor head, which will be placed inside the cyclotron for electrode-position measurement. This represents a completely new cyclotron diagnostic tool designed to cope with cyclotron alignment problems. In this paper we present the motivations for developing such a sensor, the theoretical analysis, overall sensor design for two-coordinate simultaneous measurement and measurement results. A resolution of 10 μm within a 5 mm range was achieved independently of laser diode power variation, target reflectance variation and induced attenuation in optical fibres.

Synergistic anti-biofouling effect of Ag-exchanged zeolite and D-Tyrosine on PVC composite against the clinical isolate of Acinetobacter baumannii.

Due to their susceptibility to bacterial biofilm formation, commercial tubes for medical use are one of the main sources of hospital infections with Acinetobacter baumannii. The anti-biofouling activity of novel composites against the clinical isolate of the multi-drug resistant A. baumannii is reported here. The composites were prepared by addition of micronised silver-exchanged natural zeolite (Ag-NZ) into poly(vinyl chloride) (PVC), followed by coating of the composites with D-Tyrosine (D-Tyr). The Ag-NZ composites (containing 1–15 wt% of Ag-NZ) coated with D-Tyr (Ag-NZ-Tyr) showed a bactericidal effect (100% or a 6.9 log CFU reduction) towards immobilised bacterial cells. The uncoated Ag-NZ composites showed a reduction of up to 70% (4.4 log CFU) of immobilised bacteria in comparison with the original PVC. Rheological testing of the composites revealed that the addition of Ag-NZ slightly affected processability and formability of the PVC and increased the elasticity of the polymer matrix.

In-vitro and in-vivo measurement of the animal's middle ear acoustical response by partially implantable fiber-optic sensing system

The main obstacle in realization of a totally implantable hearing aid is a lack of reliable implantable microphone. In this paper we have described a potentially miniature fiber-optic vibrometer based on a modified Michelson interferometer, designed to serve as a middle-ear microphone for totally implantable cochlear- or middle-ear hearing aids. A model of the sensing system was used for in-vitro and in-vivo investigation of acoustical response of sheeps middle-ear ossicles. Surgical and implantation procedure of introducing the sensing optical fiber into the middle-ear and its aiming at the incus was investigated and described here in detail. The frequency responses of the incus was measured while a cadaver and living sheep was exposed to the sinusoidal acoustical excitation of 40-90dB SPL, in the frequency range from 100Hz to 10kHz. The amplitude of the incus vibration was found to be in the range between 10pm to 100nm, strongly depending on the frequency, with a lot of resonant peaks, corresponding mainly to the natural outer ear canal gain. The noise floor in the experiments was about 2pm/Hz1/2, but recently we have decreased it to < 0.5pm/Hz1/2, which corresponds to a minimal detectable sound level of 31-35dB(A) SPL for humans. The histological examination of temporal bones of cadaver animals and the intensity of in-vivo optical signal demonstrated that the aiming of the sensing fiber to the target has been preserved for five months after the implantation.

Impact damage detection of composite materials by fiber Bragg gratings

Usage of fiber-optic Bragg gratings (FBG) for strain measurement is well-known technique in structural health monitoring (SHM). However, this technique based on shift of spectral peak, suffers from different spurious signals, particularly caused by thermal effect. We present here a method for impact damage detection of composite materials based on FBG without thermal disturbance. This method is based on the broadening of the spectral peak in dependence on the FBG separation from the impact damage. We used a sensing configuration where an Optical Spectrum Analyzer was interrogated with an array of 10 FBGs with central wavelength between 812 and 817nm that were bonded on a CFRP composite plate with 8 plies. We performed two groups of impact experiments: by impact energy of about 10J and 20J. We found there was no any significant shift of the spectral peak after the impact. Contrary, we confirmed in the last experiments the spectral peak broadening caused by impact load. The spectrum broadening primarily depends on the strain gradient generated into the FBGs, i.e. into the damaged area. We made a correlation between the peak width and FBG-impact damage separation. There are three characteristic regions; near to impact, abrupt region and almost even region.

Response surface methodology for optimisation of edible coatings based on dextran from Leuconostoc mesenteroides T3

The aim of this study was to develop dextran-based edible films plasticized by sorbitol. In order to optimise the film-forming formulation, response surface methodology was used. The influence of dextran and sorbitol concentration on the mechanical and water vapour barrier properties of obtained films was investigated. The results showed that both parameters exhibited significant effect on the water vapour permeability of a film. Both dextran and sorbitol concentration had significant influence on tensile strength and elongation at break, whereas only sorbitol concentration had significant effect on Youngs modulus. After optimisation by desirability approach, it was found that a film made of 3.40 wt% of dextran and 20.43 wt% of sorbitol showed the lowest water vapour permeability and the highest tensile strength and elasticity.

Detection of failures of axle-bearings of railway vehicles

The failure of axle-bearing is one of the most common causes of derailments of railway vehicles which are usually accompanied by huge material damage and human casualties. Modern railways are working intensively on the development and implementation of appropriate systems for early detection of axlebearing malfunctions, which are typically manifested by increasing of its temperature. The most common approach is based on the use of wayside systems or checkpoints located in certain places along the track. There is also an innovative approach that involves using the system for continuous measuring and online monitoring of axle-boxes temperature. The main aim is to provide early detection of malfunctions of the axle-bearing and prevention of the potential derailment. This paper analyses the existing solutions for the detection of axle-bearings malfunctions with special emphasis on the working principle and the main advantages and disadvantages. The paper presents the basics of the one newly developed wireless measuring system for on-line monitoring of axle-boxes temperature. The measuring system was tested in real conditions and can be successfully applied to the commercial railway vehicles. The main conclusion is that systems for on-line monitoring of axle-bearings temperatures are far more efficient than wayside systems. Obtained results may be important for those who deal with these and similar problems, problems of development, exploitation and maintenance of railway vehicles, strategies, regulations, etc.

Characterization of small particles in liquid suspension by fiber-optofluidic platform

A method for characterization of small particles in downstream regime of water suspension is presented. Lowcoherence interferometric technique, based on fiber-optic Mach–Zehnder interferometer (MZI) integrated into the optofluidic platform, is applied for measuring refraction index and size, i.e. diameter of glass particles. Water suspension of glass balls and cylinders of different size (from 50-230μm in diameter) has been involved into the microchannels of the optofluidic platform under laminar flow. Two complementary algorithms have been applied for calculation of index of refraction and diameter of spherical glass parts out of raw interference signals. The accuracy of index of refraction measurement is about 1% that is predominantly determined by the accuracy of reading the position of mechanical scanner.

A comparative analysis of FBG and low-coherence fiber-optic sensors for SHM of composite structures

SHM of composite structures is an emerging technology due to several benefits in terms of higher safety and security of human life, better material understanding, save money. Fiber-optic sensing technologies (FOS) are already proved to be reliable in the family of non-destructive testing (NDT) methods. The most frequently used are fiber-optic Bragg grating (FBG) sensors. However, several drawbacks of FBG cause a permanent improvement in the field of FOS. Within this paper the authors will confront the fiber-optic low-coherence interferometric (LCI) against FBG sensor taking into account experimental results simultaneously obtained by investigation of polyetheretherketon (PEEK) probe on stress by applying the three-point loading test.

Non-contact measurement of thickness uniformity of chemically etched Si membranes by fiber-optic low-coherence interferometry

In this paper we present a contactless technique for thickness measurement of chemically etched Si membranes. This technique is based on low-coherence interferometry performed by single-mode fiber-optic sensing configuration. We are able to measure the thickness of Si membranes with accuracy of about 40 nm. We used the proposed technique for the fast measurement of thickness uniformity of central position of Si membranes with overall dimensions of 2times2 mm2 all around one 3 inch {100} Si wafer with starting thickness of 380 mum. Additionally, we measured the thickness uniformity of several membranes with central boss by scanning. The accuracy of the technique is about 100 nm.

In-Line Concentration Measurement of Nanoliter Liquid Sample Using Low-Coherence Spectral Interferometry

A method for in-line measurement of the refraction index and the concentration of binary liquid mixture in a nanoliter volume is presented. Low-coherence spectral interferometric technique, based on fiber optic Mach-Zehnder interferometer, is applied for measuring the liquid refraction index, from which its volume fractions are found. The accuracy of volume fractions measurement, of about plusmn0.2%, was predominantly determined by the accuracy and resolution of reading the light spectrum. The data rate has been limited to 40 Hz by the time of the light spectrum capturing