Radio-frequency (rf) tissue fusion involves the sealing of tissue between two electrodes delivering rf currents. Applications include small bowel fusion following anastomosis. The mechanism of adhesion is poorly understood, but one hypothesis is that rf modification is correlated to thermal damage and dehydration. A multimodal monitoring system capable of acquiring tissue temperature, electrical impedance, and optical transmittance at 1325-nm wavelength during rf delivery by a modified LigasureTM fusion tool is presented. Measurements carried out on single layers of ex vivo porcine small bowel tissue heated at 500-kHz frequency are correlated with observation of water evaporation and histological studies on full seals. It is shown that the induced current generates a rapid quasilinear rise of temperature until the boiling point of water, that changes in tissue transmittance occur before impedance control is possible, and that a decrease in transmission occurs at typical denaturation temperatures. Experimental results are compared with a biophysical model for tissue temperature and a rate equation model for thermal damage.
Radiofrequency tissue fusion consists in heating apposed tissue faces, which results in their sealing. Tissue
transformations must be controlled to obtain reliable reproducible seal. In this paper we demonstrate how to
extract information on the two main tissue transformations, thermal damage and dehydration, from continuous
wave transmission spectra.
A fibre based near infrared transmission spectroscopy system is presented and described theoretically. Show
demonstrate that such system can be fully modeled using ray optics considerations for the coupling of the
light into optical fibers, and MC simulations of light propagation in tissue. We then develop an algorithm
based on the absolute measurement of attenuation and the modified Beer Lambert Law that enables the
extraction of absolute tissue hydration and information on the degree of thermal damage, via scattering losses.
We also discuss the basis and limit of absolute measurement during broadband submicronic tissue
Radio-frequency (RF) tissue fusion is a novel method of tissue approximation that can seal tissue without the need for sutures or staples, based on the combined effects of heat and pressure on the apposed tissue surfaces. RF delivery must be controlled and optimized to obtain a reproducible, reliable seal. We use real-time optical measurements to improve understanding of the tissue modifications induced by RF fusion. The main macroscopic transformations are thermal denaturation and dehydration. Light propagation in tissue is a function of both and therefore should provide interesting insight into the dynamic of occurring phenomena. Quantification by continuous wave technique has proven challenging. We proposed an algorithm based on the measurement of the absolute transmittance of the tissue, making use of the modified Beer-Lambert law. The experimental method and the data algorithm are demonstrated by RF fusion of porcine small bowel. The proposed optical measurement modality is well adapted to modern surgical instrumentation used for minimally invasive procedures.
Electrothermal actuation provides the long displacement required by an increasing number ofMEMS applications. However, its high power consumption is a limiting factor, especially for applications in which multiple actuators are required. An iris type variable optical attenuator (VOA),5 which was recently introduced by our group, is an example of such an application. In this paper we introduce an improved single sided electrothermal design, which
reduces the power consumption by a factor of 70%, while at the same time removing an undesired mechanical resonance. The optical performance is also improved by the introduction of a novel aperture shape which provides higher extinction, independent of the process technology.
Micro-opto-electro-mechanical systems (MOEMS) typically require optical surfaces with high flatness and low roughness to be combined with high quality mechanical parts and low power, high force microactuators. In the past, attention has concentrated overwhelmingly on polysilicon surface micromachining, which allows an extremely flexible approach to the design of complex optical systems. However, polysilicon components typically suffer from poor surface flatness and high roughness, and lack the strength and rigidity to support and manipulate macroscopic optical components, which often have weights in the milligram range. Bonded silicon-on-insulator (BSOI) material provides an excellent alternative, allowing high optical quality to be combined with high mechanical strength. This paper will review a number of different approaches to BSOI MEMS, including deep reactive ion etching (for in-plane devices), double-sided processing (for through-wafer devices) and surface tension self-assembly (for 3D MOEMS). Applications ranging from variable optical attenuators to tunable laser systems will be described. Methods of mounting, aligning and fixing hybrid-integrated components will also be considered, together with appropriate high-force micro-actuators.
Focused laser micromachining in an optical microscope system is used to prototype packages for optoelectronic devices and to investigate new materials with potential applications in packaging. Micromachined thin fims are proposed as mechanical components to locate fibers and other optical and electrical components on opto-assemblies. This paper reports prototype structures which are micromachined in silicon carbide to produce beams 5 μm thick by (1) laser cutting a track in a SiC coated Si wafer, (2) undercutting by anisotropic silicon etching using KOH in water, and (3) trimming if necessary with the laser system. This approach has the advantage of fast turn around and proof of concept. Mechanical test data are obtained from the prototype SiC beam package structures by testing with a stylus profilometer. The Youngs modulus obtained for chemical vapor deposited silicon carbide is 360 +/- 50 GPa indicating that it is a promising material for packaging applications.
Optoelectronic subsystems are becoming increasingly important to reduce the costs of assembly and packaging. The mechanical properties of vapor-deposited thin films can be used to advantage; for example three-micrometer thick silicon nitride microclips to hold single mode optic fibers in place in silicon V-shaped grooves. This paper describes the proposed use of pairs of thin film microcantilevers to precisely locate an optic component such as a filter or a mirror in an optical bench. In this configuration the precision of the lithographic process for the cantilevers determines the exact location of the component in the package, and to first order the etched shape in the substrate is unimportant. Simulation software based on variational principles has been developed to examine the behavior of structures undergoing large-scale elastic deflections. The design software consists of spreadsheet front end to enter parameters, and then Visual Basic (VBA) code and Frontline 'solver' software to run simulations. The fabrication process is described for 5 micrometers thick silicon carbide beams which are then tested by bending them using a surface profiler (such as a Dektak) to deflect the fifty micrometer wide silicon nitride cantilevers through large angles. The possible consequences for more efficient optoelectronic packaging are briefly assessed.
Imaging the transverse vibrations of a resonating fibre cantilever is shown to be an effective method for generating 1D and 2D laser line scans. The resonant bending modes were excited by mounting a short length of 0.633(mu) m single mode optical fibre on to a commercially available piezo-electric transducer. For an applied sinusoidal driving voltage of 20V pk-pk, the maximum displacement at the free end of an 11mm long fibre cantilever exceeded +/- 1.0mm at resonance. The motion at the free end of the fibre was imagined and magnified using a 2mm diameter graded index lens and the resulting flying spot line scan was found to subtend a maximum arc of +/- 10 degree(s). Two distinct signal detection schemes were implemented and evaluated using standard bar code targets printed on plain paper. 2D Lissajous scans were demonstrated by exciting the orthogonal transverse bending modes of optical fibres with non-circular cross sectional areas. Both D-shaped fibres and circular fibres modified by reactive ion etching were investigated. The principles underlying the design of this Fibre Optic Resonant Scanner (FORS) are directly applicable to the design of an integrated optoelectronic micro-electro-mechanical scanning device.
An experimental study has been carried out using a Miniature Quadrupole Mass Spectrometer (MicroQuad) for gas analysis. Conventional quadrupole rods have been replaced with a micromachined mass filter made from silicon with Au metallized specially drawn glass fibers of length 30 mm and diameter 0.5 mm. A standard hot filament ion source and both Faraday detection and a channel electron multiplier have been used. The effect of ion focus voltage has also been modeled by SIMION simulation. Conventional electronics were adapted to run at 6 to 8 MHz and mass spectra in the range 0 - 50 a.m.u. The results indicate a good valley separation between O, OH, H2O and Ar2+ and a best resolution at 10% peak height of 0.9 a.m.u. at mass 40 with the multiplier. Application of a static magnetic field transversely to the body of the mass filter is shown to improve resolution howbeit at the expense of ion transmission through the filter.