Alessandro Massaro

Design and Characterization of a Nanocomposite Pressure Sensor Implemented in a Tactile Robotic System

In this paper, we present the implementation of a new class of optical pressure sensors in a robotic tactile-sensing system based on polydimethylsiloxane (PDMS). The sensor consists of a tapered optical fiber, where an optical signal goes across, embedded into a PDMS-gold nanocomposite material (GNM). By applying different pressure forces onto the PDMS-based nanocomposite, changes in the optical transmittivity of the fiber can be detected in real time due to the coupling between the GNM and the tapered fiber region. The intensity reduction of a transmitted light is correlated to the pressure force magnitude. Light intensity is converted into an electric signal by a system suitable for robotic implementation. High sensitivity using forces by applying weights of a few grams is proved. Sensitivity on the order of 5 g is checked. A detailed algorithm for the detection of roughness and shapes by means of a robotic finger is proposed.

3-D FEM Modeling and Fabrication of Circular Photonic Crystal Microcavity

In this paper, we study an unconventional kind of quasi-three-dimensional (3-D) photonic crystal (PhC) with circular lattice pattern: it consists of air holes in a GaAs material (n=3.408) along circular concentric lines. This particular PhC geometry has peculiar behavior if compared with the traditional square and triangular lattices, but it is difficult to model by using conventional numerical approaches such as wave expansion method. The resonance and the radiation aspects are analyzed by the 3-D finite-element method (FEM). The model, based on a scattering matrix approach, considers the cavity resonance frequency and evaluates the input-output relationship by enclosing the photonic crystal slab (PhCS) in a black box in order to define the responses at different input-output ports. The scattering matrix method gives important information about the frequency responses of the passive 3-D crystal in the 3-D spatial domain. A high sensitivity of the scattering parameters to the variation of the geometrical imperfection is also observed. The model is completed by the quality factor (Q-factor) estimation. We fabricated the designed circular photonic crystal over a slab membrane waveguide embedding InAs/GaAs quantum dots emitting around 1.28 mum. Good agreement between numerical and experimental results was found, thus validating the 3-D FEM full-wave investigation.

Accurate Time-Domain Modeling of Reconfigurable Antenna Sensors for Non-Invasive Melanoma Skin Cancer Detection

The full-wave electromagnetic characterization of reconfigurable antenna sensors for non-invasive detection of melanoma-related anomalies of the skin is presented. To this end, an enhanced locally conformal finite-difference time-domain procedure, based on the definition of effective material parameters and a suitable normalization of the electromagnetic field-related quantities, is adopted. In this way, an insightful understanding of the physical processes responsible for the performance of considered class of devices is achieved. This in turn is important in order to enhance the structure reliability, optimizing the design cycle. A suitable microelectromechanical-system-based sensor layout is finally discussed in details.

Freestanding piezoelectric rings for high efficiency energy harvesting at low frequency

Energy harvesting at low frequency is a challenge for microelectromechanical systems. In this work we present a piezoelectric vibration energy harvester based on freestanding molybdenum (Mo) and aluminum nitride (AlN) ring-microelectromechanical-system (RMEMS) resonators. The freestanding ring layout has high energy efficiency due to the additional torsional modes which are absent in planar cantilevers systems. The realized RMEMS prototypes show very low resonance frequencies without adding proof masses, providing the record high power density of 30.20u2002μWu2009mm−3 at 64 Hz with an acceleration of 2g. The power density refers to the volume of the vibrating RMEMS layout.

Experimental Optical Characterization and Polymeric Layouts of Gold PDMS Nanocomposite Sensor for Liquid Detection

We present a new concept of liquid sensing based on gold nanocomposite material showing enhancement of optical radiation and coupling. In particular, we experimentally characterize the optical transmittivity response of a millimeter pillar-type sensor made of gold micro/nanoparticles in PDMS material. The choice of the millimeter pillar-type layout is studied in order to collect better the light in a multimode receiver optical fiber. After a first three-dimensional (3D) finite-element method (FEM) modeling which analyzes the physical aspects of the proposed sensor, we experimentally characterize the PDMS/PDMS-Au pillar-type layout, and we measure the variation of the transmittivity response comparing different liquids, such as ethanol and oil, placed on the PDMS-Au sensor. Concerning the reusable process of the sensor, we study the dynamics of the sensing by measuring the transmittivity response during the time by applying ethanol as target liquid. Finally, we propose an implementation of the proposed sensor in robotics finger.

Diffusion Tensor Imaging measurements for neuro-detection

The interest of scientific community on brain activities and issues are well-known, especially for neuro-detection of variety of impairments that affect cerebral areas. Various techniques and methods have been using to characterize and to try to understand brain activities for many purposes. Epilepsy, one of them, is a topic of great impact in brain research as well as in Alzheimer issues. Thanks to the development of new biomedical instrumentation it is possible to use appropriate techniques to diagnose the specific pathology. DTI (Diffusion Tensor Imaging) is one of the ultimate technique to have a comprehensive approach to brain activities. This interdisciplinary research highlights the use of DTI to determine preliminarily the ROI (Region Of Interest) for patients with suspected cases of epilepsy. A specific algorithm has been developed to trace out the ROI and the fibers.

Optical Performance Evaluation of Oil Spill Detection Methods: Thickness and Extent

The release of petroleum liquids in water, such as marine, riverine, and lacustrine basins, is a matter of concern that shoves authorities and experts to adopt technical approaches for preventing damages, monitoring oil content in water and cleaning up environmental aqueous matrices. In this paper, a dedicated system for oil spill detection is presented. The proposed system consists of an optical fiber sensor and an image processing unit useful to steer and optimize the measurement process. An optical fiber-based antenna sensor is used to detect the oil concentration in water. The sensor consists of two slanted optical probes acting as transmitter and receiver, respectively. Both probes are completely immersed into water being analyzed. The sensing approach is based on the measurement of the light coupling level affected by the reflectivity of the oil layer floating on the water surface. The experimental measurement of different types of oil is performed to assess the sensitivity of the developed system. Special attention is put on the image postelaboration useful to derive the characteristics of the oil distribution on the water surface. In this respect, two different image processing techniques are considered: the first one is based on a suitable energy-minimizing spline fitting procedure subject to external constraint forces, whereas a judicious use of the Hough transform is made in the second one.

Detection Analysis of Small Notches Damages Using a New Tactile Optical Device

In this paper, the experimental application of a new class of optical pressure sensors based on polydimethylsiloxane (PDMS)-Au aimed at detecting and classifying millimetric surface damages of mechanical components is developed. The device consists of a tapered bended optical fiber, where an optical signal goes across, embedded into a PDMS-gold nanocomposite material (GNM). The sensor is automatically moved for the optical scanning of surfaces by means of a high-accuracy servo motor. After moving and positioning the detector, the sensor output data are acquired and processed in such a way as to pinpoint small notches on a beam. Notches of different lengths to within a few millimeters were scanned to test the realized device capability in recognizing and characterizing very small defects. The experimental results are very encouraging; they exhibit high sensitivity and inspire the use of the sensor in multifarious applications of robotics.

Flexible nanocomposites with all-optical tactile sensing capability

Plasmonic resonators have generated much interest in recent years due to their ability to localize optical energy into thin continuous metallic regions. We present the integration of such resonators into flexible polydimethylsiloxane–gold nanocomposite materials that couple light efficiently, in order to prepare a totally optical layout for tactile sensors, able to detect low applied pressure forces. The development of plasmonic nanostructured resonators of thin gold layers onto polydimethylsiloxane is achieved using light texturing. In particular, this technique creates uniform patterns of gold nanoparticles forming quasi continuous gold thin layers behaving as plasmonic resonators. The excitation of the resonators and the detection of the signal after the application of the pressure are done through optical fibers avoiding electrical connections or circuits embedded into the elastomer. The proposed totally optical tactile sensor is easily processable and ideal for upscaling oriented towards humanoid robotics and biocompatible elastomeric human interface skin prostheses.

Design and Full-Wave Analysis of Piezoelectric Micro-Needle Antenna Sensors for Enhanced Near-Field Detection of Skin Cancer

The design and full-wave analysis of piezoelectric microneedle antenna sensors for minimally invasive near-field detection of cancer-related anomalies of the skin is presented. To this end, an accurate locally conformal finite-difference time-domain procedure is adopted. In this way, an insightful understanding of the physical processes affecting the characteristics of the considered class of devices is achieved. This is important to improve the structure reliability, so optimizing the design cycle. In this regard, a suitable sensor layout is described, and discussed in detail. The major benefit of the proposed system stems from the potential for obtaining a superior performance in terms of input impedance matching and efficiency, in combination with an electronically tunable steering property of the near-field radiation intensity which can be profitably used to enhance the illumination and, hence, the localization of possible malignant lesions in the host medium. By using the detailed modeling approach, an extensive parametric study is carried out to analyze the effect produced on the sensor response by variations of the complex permittivity of the skin due to the presence of anomalous cells, and thus useful heuristic discrimination formulas for the evaluation of the exposure level to cancer risk are derived. Received 12 October 2011, Accepted 9 November 2011, Scheduled 6 March 2012 * Corresponding author: Diego Caratelli (d.caratelli@tudelft.nl). 392 Caratelli et al.