Measurement of nonlinear optical refraction of composite material based on sapphire with silver by Kerr-lens autocorrelation method

Silver nanoparticles synthesized in a synthetic sapphire matrix were fabricated by ion implantation using the metal vapor vacuum arc ion source. The optical absorption spectrum of the Ag: Al2O3 composite material has been measured. The analysis of the supercontinuum spectrum displayed the nonlinear refractive property of this kind of sample. Nonlinear optical refraction index was identified at 800 nm excitation using the Kerr-lens autocorrelation (KLAC) technique. The spectrum showed that the material possessed self-defocusing property (n(2) = -1.1 × 10(-15) cm(2)W). The mechanism of nonlinear refraction has been discussed.

A new medical device to measure a stiffness of soft materials

An objective in vivo measurement technique for assessing the material properties of soft tissue would be a valuabe tool in diagnosing dermatological pathologies. In order to make advancements in this field, a new hand-held device was designed to measure the stiffness of soft materials. The device measures the reaction forces experienced by the soft tissue under constant indentation deformations at the time of stiffness measurement. Agarose gel samples were prepared in a range of molarities to mimic the stiffness variabilities found in vivo. The stiffness of each gel was evaluated using two different measurement techniques. The first method utilized an industry standard durometer, designed to measure the hardness of materials in shore type 00 scales of soft plastics. The second measurement was taken using an original custom-built soft tissue stiffness meter, designed specifically for the present study. These two devices were compared and a strong correlation was found between them (r²=1.00, Spearman rank test). Additionally, it was observed that gels of different stiffness could be distinguished by both devices. In conclusion, the soft tissue stiffness can be accurately evaluated using the proposed device. The new device should be evaluated on human subjects in future studies, before it can be used to assess soft tissue disorders.

Acoustic nonlinearity parameter B/A determined by means of thermodynamic method under elevated pressures for alkanediols

The so-called Beyer nonlinearity parameter B/A is calculated for 1,2- and 1,3-propanediol, 1,2-, 1,3-, and 1,4-butanediol, as well as 2-methyl-2,4-pentanediol by means of a thermodynamic method. The calculations are made for temperatures from (293.15 to 318.15) K and pressures up to 100 MPa. The decrease in B/A values with the increasing pressure is observed. In the case of 1,3-butanediol, the results are compared with corresponding literature data. The consistency is very satisfactory. A simple relationship between the internal pressure and B/A nonlinearity parameter has also been studied.

Release of metal ions from fixed orthodontic appliance: an in vitro study in continuous flow system

OBJECTIVE

To evaluate the release of metal ions from fixed orthodontic appliances.

MATERIALS AND METHODS

A new system for in vitro testing of dental materials was constructed and consisted of a thermostatic glass reactor that enabled immersion of the studied material. Experimental conditions reflected the human oral cavity, with a temperature of 37°C and a saliva flow rate of 0.5mL/min. The simulated fixed orthodontic appliance made of stainless steel was evaluated. Sampling was performed at several time points during the 28-day study, and the metal ion concentration was determined by inductively coupled plasma optical emission spectrometry.

RESULTS

The total mass of released metal ions from the appliance during 4 weeks of the experiment was as follows nickel 18.7 μg, chromium 5.47 μg, copper 31.3 μg.

CONCLUSIONS

The estimated doses of nickel, chromium, and copper determined by extrapolation of experimental data released during the treatment period were far below the toxic dose to humans. This shows that orthodontic treatment might not be a significant source of exposure to these metal ions.

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (100) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol-gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (100) silicon wafer was measured along various directions between [100] and [010] to represent the anisotropic features.

High resolution direct measurement of temperature distribution in silicon nanophotonics devices

Following the miniaturization of photonic devices and the increase in data rates, the issues of self heating and heat removal in active nanophotonic devices should be considered and studied in more details. In this paper we use the approach of Scanning Thermal Microscopy (SThM) to obtain an image of the temperature field of a silicon micro ring resonator with sub-micron spatial resolution. The temperature rise in the device is a result of self heating which is caused by free carrier absorption in the doped silicon. The temperature is measured locally and directly using a temperature sensitive AFM probe. We show that this local temperature measurement is feasible in the photonic device despite the perturbation that is introduced by the probe. Using the above method we observed a significant self heating of about 10 degrees within the device.

Using STED and ELSM confocal microscopy for a better knowledge of fused silica polished glass interface

Characteristics and nature of close surface defects existing in fused silica polished optical surfaces were explored. Samples were deliberately scratched using a modified polishing process in presence of different fluorescent dyes. Various techniques including Epi-fluorescence Laser Scanning Mode (ELSM) or STimulated Emission Depletion (STED) confocal microscopy were used to measure and quantify scratches that are sometimes embedded under the polished layer. We show using a non-destructive technique that depth of the modified region extends far below the surface. Moreover cracks of 120 nm width can be present ten micrometers below the surface.

Localized strain sensing with fiber Bragg-grating ring cavities

We report the theoretical description and the experimental demonstration of an optical resonator formed by inserting a Fiber Bragg Grating (FBG) in a closed fiber loop. The spectral characteristics of such a resonator strongly depend on the reflectivity of the FBG. In the wavelength region where the FBG reflectivity R is negligible, the system behaves like a conventional ring resonator. On the other hand, when R is not vanishing, a split-mode structure can be observed, associated to the degeneracy removal of two counterpropagating resonant modes. The magnitude of the mode splitting can be used to sense small variations of the FBG physical parameters, such as length, temperature or group index. An example of strain sensing with this setup is reported, showing that the mode splitting is sensitive to a mechanical strain applied to the FBG, while it is almost insensitive to a strain applied to any other point of the resonator. This peculiar feature allows to perform cavity-enhanced, local strain measurements with a reduced sensitivity to environmental perturbations, which represents an important improvement in the framework of the fiber-optic sensors.

Transmission ellipsometric method without an aperture for simple and reliable evaluation of electro-optic properties

A transmission ellipsometric method has been reformed without a spatial filtering aperture to characterize electro-optic (EO) performance of EO polymers. This method affords much simpler optical setup compared to the reflection method, and lets us easily perform detailed incident angle dependence measurements using a conventional glass substrate and an un-collimated beam. It is demonstrated that the reliable characterization with this method is possible in combination with a simple data analysis. By using the recently matured deposition technique of indium zinc oxide (IZO) on soft materials, it is possible to prepare the EO polymer sandwiched between two transparent electrodes. Thus the transmission method should be re-evaluated.

Demonstration of complex refractive index of graphene waveguide by microfiber-based Mach-Zehnder interferometer

The complex refractive index (CRI) of graphene waveguide (GW) is of great importance for modeling and developing graphene-based photonic or optoelectronic devices. In this paper, the CRI of the GW is investigated theoretically and experimentally, it is found that the CRI of the GW will modulate the intensity and phase of transmitting light. The phase alterations are obtained spectrally by a Microfiber-based Mach-Zehnder interferometer (MMZI), experimental results demonstrate that the CRIs of the GW vary from 2.91-i13.92 to 3.81-i14.64 for transmitting wavelengths ranging from 1510 to 1590 nm. This method cannot only be used to determine the CRI of the GW optically and provide one of the fundamental parameters for designing graphene-based optic devices for communication and sensing applications, but also is adoptable in graphene-based transformation optics for determination of the CRI of the GW at other wavelengths.

The development of a custom-built portable impact-testing device for assessing the cushioning properties of athletic socks

Despite manufacturer claims that athletic socks attenuate force during exercise, no device exists to assess this. Therefore, this study outlines the development of a custom-built impact-testing device for assessing the cushioning properties of socks. The device used a gravity-driven impact striker (8.5 kg), released from 0.05 m, which impacted a no-sock, sock or a basic shoe/sock condition in the vertical axis. A load cell (10,000 Hz) assessed peak impact force, time to peak impact force and loading rate. Reliability was investigated between day, between trial and within trial. Excellent reliability (coefficient of variation < 5% adjusted for 95% confidence limits) was reported for peak impact force in all conditions, with no evidence of systematic bias. Good reliability (coefficient of variation < 10% adjusted for 68% confidence limits) was reported for time to peak impact force and loading rate with some evidence of systematic bias. It was concluded that the custom-built impact-testing device was reliable and sensitive for the measurement of peak impact force on socks.

Resonant excited state absorption and relaxation mechanisms in Tb3+-doped calcium aluminosilicate glasses: an investigation by thermal mirror spectroscopy

Resonant excited state absorption (ESA) and relaxation processes in Tb(3+)-doped aluminosilicate glasses are quantitatively evaluated. A model describing the excitation steps and upconversion emission is developed and applied to interpret the results from laser-induced surface deformation using thermal mirror spectroscopy. The fluorescence quantum efficiency of level (5)D(4) was found to be close to unity and concentration independent while, for the level (5)D(3), it decreases with Tb(3+) concentration. Emission spectroscopy measurements supported these results. ESA cross sections are found to be more than three orders of magnitude higher than the ground state absorption cross section.

The "round trip" theory for reconstruction of Green's functions at passive locations

An expression for the Green's function at an arbitrary set of passive locations (no applied force) is derived and validated by experiment. Three sets of points are involved, the passive reconstruction points, c, which lie on a virtual boundary and two sets of auxiliary points, denoted a and b, located either side. The reconstruction is achieved using Green's functions forming a "round trip" from and to the reconstruction points via a and b. A two stage measurement procedure is described involving excitation at b and a but with no excitation required at the reconstruction points. A known "round trip" relationship is first introduced which is theoretically exact for points on a multi-point interface between two linear, time invariant subsystems. Experimental results for frequency response functions of a beam-plate structure show that this relationship gives good results in practice. It is then shown that the theory provides an Nth order approximation for the Green's function at arbitrary points, where N is the number of points at b. The expression is validated by reconstructing point and transfer frequency response functions at two passive points on an aluminum plate.

A low temperature Co-fired ceramic-based dielectrophoretic device for manipulating micro and nanostructure materials

A dielectophoretic (DEP) device fabricated by a conventional low temperature co-fired ceramic (LTCC) process, for manipulating micro and nanostructure materials, such as spherical polystyrene microspheres, titanium dioxide (TiO2) nanotubes, and silver (Ag) nanowires, is described. To generate a non-uniform electric field, a castellated electrode configuration was applied to the LTCC-based DEP device using a screen printing method. The actual motions of the micro and nanostructure materials under both a positive and a negative DEP force were observed in detail and the findings compared with numerical simulation data for the electric field distribution. The performance of the LTCC-based DEP device for separating and trapping was evaluated and potential applications are discussed.

A high-speed vertical optical trap for the mechanical testing of living cells at piconewton forces

Although atomic force microscopy is often the method of choice to probe the mechanical response of (sub)micrometer sized biomaterials, the lowest force that can be reliably controlled is limited to ≈0.1 nN. For soft biological samples, like cells, such forces can already lead to a strain large enough to enter the non-elastic deformation regime. To be able to investigate the response of single cells at lower forces we developed a vertical optical trap. The force can be controlled down to single piconewtons and most of the advantages of atomic force microscopy are maintained, such as the symmetrical application of forces at a wide range of loading rates. Typical consequences of moving the focus in the vertical direction, like the interferometric effect between the bead and the coverslip and a shift of focus, were quantified and found to have negligible effects on our measurements. With a fast responding force feedback loop we can achieve deformation rates as high as 50 μm/s, which allow the investigation of the elastic and viscous components of very soft samples. The potential of the vertical optical trap is demonstrated by measuring the linearity of the response of single cells at very low forces and a high bandwidth of deformation rates.

A new corrosion sensor to determine the start and development of embedded rebar corrosion process at coastal concrete

The corrosion of reinforcements induced by chloride has resulted to be one of the most frequent causes of their premature damage. Most corrosion sensors were designed to monitor corrosion state in concrete, such as Anode-Ladder-System and Corrowatch System, which are widely used to monitor chloride ingress in marine concrete. However, the monitoring principle of these corrosion sensors is based on the macro-cell test method, so erroneous information may be obtained, especially from concrete under drying or saturated conditions due to concrete resistance taking control in macro-cell corrosion. In this paper, a fast weak polarization method to test corrosion state of reinforcements based on electrochemical polarization dynamics was proposed. Furthermore, a new corrosion sensor for monitoring the corrosion state of concrete cover was developed based on the proposed test method. The sensor was tested in cement mortar, with dry-wet cycle tests to accelerate the chloride ingress rate. The results show that the corrosion sensor can effectively monitor chloride penetration into concrete with little influence of the relative humidity in the concrete. With a reasonable corrosion sensor electrode arrangement, it seems the Ohm-drop effect measured by EIS can be ignored, which makes the tested electrochemical parameters more accurate.

Using the quartz crystal microbalance with dissipation monitoring to evaluate the size of nanoparticles deposited on surfaces

A quartz crystal microbalance with dissipation (QCM-D) monitoring can be an alternative tool to characterize nanoparticle size by virtue of its acoustic principle to sense adsorbed mass. In this study, sizes obtained by QCM-D for polymer-coated metallic nanoparticles and polydisperse polystyrene latex particle suspensions were compared with those obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS). We describe the obtained "QCM-D mass", which is weighted over surface area, by a general particle height distribution equation that can be used to determine the average particle diameter of a distribution of particles deposited on the QCM-D surface. Because the particle height distribution equation can be used for any particle geometry and surface packing geometry, it is described how the QCM-D can also be used to study the orientation of deposited nonspherical particles. Herein, the mean nanoparticle sizes obtained by QCM-D were generally in closer agreement with the primary particle size determined by TEM than with the sizes obtained by DLS, suggesting that primarily smaller particles within the particle population deposited on the sensor surface. Overall, the results from this study demonstrate that QCM-D could serve as an alternative and/or complementary means to characterize the size of nanoparticles deposited on a surface from suspensions of varying complexity.

Crack orientation and depth estimation in a low-pressure turbine disc using a phased array ultrasonic transducer and an artificial neural network

Stress corrosion cracks (SCC) in low-pressure steam turbine discs are serious hidden dangers to production safety in the power plants, and knowing the orientation and depth of the initial cracks is essential for the evaluation of the crack growth rate, propagation direction and working life of the turbine disc. In this paper, a method based on phased array ultrasonic transducer and artificial neural network (ANN), is proposed to estimate both the depth and orientation of initial cracks in the turbine discs. Echo signals from cracks with different depths and orientations were collected by a phased array ultrasonic transducer, and the feature vectors were extracted by wavelet packet, fractal technology and peak amplitude methods. The radial basis function (RBF) neural network was investigated and used in this application. The final results demonstrated that the method presented was efficient in crack estimation tasks.

Adhesion failure at 180,000 frames per second: direct observation of the detachment process of a mushroom-shaped adhesive

Nature has successfully evolved the mushroom-shaped contact geometry in many organisms in order to solve the attachment problem. We studied the detachment process of individual bioinspired artificial mushroom-shaped adhesive microstructures (MSAMSs) resolving the failure dynamics at high spatiotemporal resolution. The experimental data provide strong evidence for a homogeneous stress distribution in MSAMS, which was recently proposed. Our results allow us to explain the advantage of such contact geometry and provide a suggestion for the widely observed mushroom-shaped contact geometry.

Continuous gradient scaffolds for rapid screening of cell-material interactions and interfacial tissue regeneration

In tissue engineering, the physical and chemical properties of the scaffold mediates cell behavior, including regeneration. Thus a strategy that permits rapid screening of cell-scaffold interactions is critical. Herein, we have prepared eight "hybrid" hydrogel scaffolds in the form of continuous gradients such that a single scaffold contains spatially varied properties. These scaffolds are based on combining an inorganic macromer (methacrylated star polydimethylsiloxane, PDMSstar-MA) and organic macromer (poly(ethylene glycol)diacrylate, PEG-DA) as well as both aqueous and organic fabrication solvents. Having previously demonstrated its bioactivity and osteoinductivity, PDMSstar-MA is a particularly powerful component to incorporate into instructive gradient scaffolds based on PEG-DA. The following parameters were varied to produce the different gradients or gradual transitions in: (1) the wt.% ratio of PDMSstar-MA to PEG-DA macromers, (2) the total wt.% macromer concentration, (3) the number average molecular weight (Mn) of PEG-DA and (4) the Mn of PDMSstar-MA. Upon dividing each scaffold into four "zones" perpendicular to the gradient, we were able to demonstrate the spatial variation in morphology, bioactivity, swelling and modulus. Among these gradient scaffolds are those in which swelling and modulus are conveniently decoupled. In addition to rapid screening of cell-material interactions, these scaffolds are well suited for regeneration of interfacial tissues (e.g. osteochondral tissues) that transition from one tissue type to another.

Polydimethylsiloxane thin film characterization using all-optical photoacoustic mechanism

This paper presents a nondestructive ultrasound testing method for characterization of the resonant frequencies of polydimethylsiloxane (PDMS) thin film by using a miniature fiber optic photoacoustic (PA) probe. The PA probe was fabricated with an optical fiber and a synthesized gold nanocomposite. During the experiment, a cured PDMS thin film with a thickness of 220 μm was immersed into a water medium using a custom-designed holder to clamp the film. An acoustic pulse was generated by the PA probe and propagated through the water media to excite the fixed film. A fiber optic pressure sensor based on the Fabry-Perot principle was used to collect the excited acoustic signals on the other side of the film. The acquired response of the acoustic pulse was used to compute the resonant frequencies of the PDMS thin film based on a deconvolution method.

A novel flow chamber for biodegradable alloy assessment in physiologically realistic environments

In order to better understand the in vivo corrosion of biodegradable alloys, it is necessary to replicate the physiological environment as closely as possible. In this study, a novel flow chamber system is developed that allows the investigation of biodegradable alloy corrosion in a simulated physiological environment. The system is designed to reproduce flow conditions encountered in coronary arteries using a parallel plate setup and to allow the culturing of cells. Computational fluid dynamics and analytical methods are used as part of the design process to ensure that suitable flow conditions are maintained in the test region. The system is used to investigate the corrosion behavior of AZ31 alloy foils of different thickness, in test media with and without proteins and in static and dynamic solutions. It is observed that pulsatile flows, similar to those in the coronary arteries, significantly increase corrosion rates and lead to a different corrosion surface morphologies relative to static immersion tests.

A practical data recovery technique for long-term strain monitoring of mega columns during construction

A practical data recovery method is proposed for the strain data lost during the safety monitoring of mega columns. The analytical relations among the measured strains are derived to recover the data lost due to unexpected errors in long-term measurement during construction. The proposed technique is applied to recovery of axial strain data of a mega column in an irregular building structure during construction. The axial strain monitoring using the wireless strain sensing system was carried out for one year and five months between 23 July 2010 and 22 February 2012. During the long-term strain sensing, three different types of measurement errors occurred. Using the recovery technique, the strain data that could not be measured at different intervals in the measurement were successfully recovered. It is confirmed that the problems that may occur during long-term wireless strain sensing of mega columns during construction could be resolved through the proposed recovery method.

On-line flatness measurement in the steelmaking industry

Shape is a key characteristic to determine the quality of outgoing flat-rolled products in the steel industry. It is greatly influenced by flatness, a feature to describe how the surface of a rolled product approaches a plane. Flatness is of the utmost importance in steelmaking, since it is used by most downstream processes and customers for the acceptance or rejection of rolled products. Flatness sensors compute flatness measurements based on comparing the length of several longitudinal fibers of the surface of the product under inspection. Two main different approaches are commonly used. On the one hand, most mechanical sensors measure the tensile stress across the width of the rolled product, while manufacturing and estimating the fiber lengths from this stress. On the other hand, optical sensors measure the length of the fibers by means of light patterns projected onto the product surface. In this paper, we review the techniques and the main sensors used in the steelmaking industry to measure and quantify flatness defects in steel plates, sheets and strips. Most of these techniques and sensors can be used in other industries involving rolling mills or continuous production lines, such as aluminum, copper and paper, to name a few. Encompassed in the special issue, State-of-the-Art Sensors Technology in Spain 2013, this paper also reviews the most important flatness sensors designed and developed for the steelmaking industry in Spain.

Photothermal analysis of individual nanoparticulate samples using micromechanical resonators

The ability to detect and analyze single sample entities such as single nanoparticles, viruses, spores, or molecules is of fundamental interest. This can provide insight into the individual specific properties which may differ from the statistical sample average. Here we introduce resonant photothermal spectroscopy, a novel method that enables the analysis of individual nanoparticulate samples. Absorption of light by an individual sample placed on a microstring resonator results in local heating of the string, which is reflected in its resonance frequency. The working principle of the spectrometer is demonstrated by analyzing the optical absorption of different micro- and nanoparticles on a microstring. We present the measurement of a simple absorption spectrum of multiple polystyrene microparticles illuminated with an unfocused LED light source. Using a diode laser, single 170 nm polystyrene nanoparticles are detected. With the current setup, nanoparticulate samples with a mass of ~40 ag are detectable. By using nanostrings, visible and infrared photothermal spectroscopy in the subattogram mass regime is possible and single molecule detection is within reach.