Corneliu Rablau

Fabrication and characterization of microstructures with optical quality surfaces in fused silica glass using femtosecond laser pulses and chemical etching

We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.

Providing haptic feedback in robot-assisted minimally invasive surgery: A direct optical force-sensing solution for haptic rendering of deformable bodies

Abstract This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system with the optical force sensor, and (b) study human haptic perception during the identification of remote object deformability. The first experiment was carried out to discriminate deformability of objects when human subjects were in direct contact with deformable objects by means of a laparoscopic tool. The control parameters were then tuned based on the results of this experiment using a gain-scheduling method. The second experiment was conducted to study the effectiveness of the force feedback provided through the enhanced teleoperation system. The results show that the force feedback increased the ability of subjects to correctly identify materials of different deformable types. In addition, the virtual force feedback provided by the teleoperation system comes close to the real force feedback experienced in direct MIS. The experimental results provide design guidelines for choosing and validating the control architecture and the optical force sensor.

Nanoparticle aggregation and relaxation effects in ferrofluids: studied through anisotropic light scattering

We have investigated the aggregation and dissociation dynamics of 6-nm size Fe3O4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size γ-Fe2O3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns. For the Fe3O4 ferrofluid, a strong anisotropy in light scattering was observed for light propagating perpendicular to the magnetic field. This behavior is attributed to the aggregation of the nanoparticles into chain-like and column-like structures oriented parallel to the magnetic field. A significantly different behavior is observed for the aqueous suspension of γ-Fe2O3 nanoparticles precipitated in alginate hydrogel, for which the application of the dc magnetic field produced little to no change in the light scattering patterns. We attribute this difference to the constrained random distribution of γ-Fe2O3 nanoparticles precipitated in the alginate matrix. Correlating the results from this investigation with our previous study of magneto-thermal measurements in ac fields [Vaishnava et al., J. Appl. Phys. 102, 063914 (2007)], we conclude that for a ferrofluid to exhibit significant thermal effects under an ac magnetic field, it should exhibit optical anisotropy by developing a chain like structure under the influence of a dc magnetic field.

A method for measuring the Néel relaxation time in a frozen ferrofluid

We report a novel method of determining the average Neel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude ( H0=20 kA/m) driven at frequencies of 171 kHz, 232 kHz, and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Neel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of ...

Design and mathematical modeling of a fiber-optic displacement and force sensor

We report on the design, mathematical modeling and preliminary development work for a novel fiber optic force sensor for applications of force sensing and force-feedback in robotic surgery and in other systems where a small passive sensor immune to electromagnetic interference (EMI) may be needed. The proposed sensor uses a novel (patent pending) approach, not reported in the existing literature, based on a fiber collimator and a four-quadrant dichroic mirror. The sensor is small enough to fit at the distal end of typical surgical devices for laparoscopic surgery (d<;10 mm), can be assembled from glass/dielectric materials (EMI immune) and does not require active local powering and conditioning (filtering, amplification) of the signal it produces in response to an applied external force.

Magneto-optic effects in ferrofluids

Ferrofluids are stable colloidal suspensions of superparamagnetic nanoparticles in a carrier liquid. The ordering and phase transitions of these polarizable media under the effect of an externally applied dc magnetic field are accompanied by a number of magneto-optic effects. Light scattering, in particular, has been used in studies investigating the kinematics of the field-induced self-assembly of nanoparticles in chain-like structures. In previous reports we discussed the correlation between the time-dependent light-scattering patterns and the creation of such field-induced ordered structures of nanoparticles in the ferrofluid. This present work is the first reported systematic study of the morphing of the light scattering patterns with the thickness of the ferrofluid layer (0.1 mm to 10 mm) and with temperature, in ferrofluids consisting of water suspensions of dextran-coated iron oxide nanoparticles. In particular we discuss the origin and angular dependence of an elliptical pattern produced by light scattered through thin layers (<;1 mm) of ferrofluids and contrast it with the patterns produced by longer light paths (10 mm) through the ferrofluid.