Thermal effects on the photoelastic coefficient of polymer optical fibers

We measure the radial profile of the photoelastic coefficient C(r) in single-mode polymer optical fibers (POFs), and we determine the evolution of C(r) after annealing the fibers at temperatures from 40°C to 80°C. We demonstrate that C(r) in the fibers drawn from a preform without specific thermal pre-treatment changes and converges to values between 1.2 and 1.6×10-12 Pa-1 following annealing at 80°C. The annealed fibers display a smoothened radial profile of C(r) and a lowered residual birefringence. In contrast, the mean value of C(r) of the fiber drawn from a preform that has been pre-annealed remains constant after our annealing process and is significantly higher, i.e., 4×10-12 Pa-1. The annealing process decreases the residual birefringence to a lower extent as well. These measurements indicate the impact of annealing on the thermal stability of the photoelastic coefficient of POFs, which is an essential characteristic in view of developing POF-based thermomechanical sensors

Cold performance tests of blocked-impurity-band Si:As detectors developed for DARWIN

We report first results of laboratory tests of Si:As blocked-impurity-band (BIB) mid-infrared (4 to 28 um) detectors developed by IMEC. These prototypes feature 88 pixels hybridized on an integrated cryogenic readout electronics (CRE). They were developed as part of a technology demonstration program for the future DARWIN mission. In order to be able to separate detector and readout effects, a custom build TIA circuitry was used to characterize additional single pixel detectors. We used a newly designed test setup at the MPIA to determine the relative spectral response, the quantum efficiency, and the dark current. All these properties were measured as a function of operating temperature and detector bias. In addition the effects of ionizing radiation on the detector were studied. For determining the relative spectral response we used a dual-grating monochromator and a bolometer with known response that was operated in parallel to the Si:As detectors. The quantum efficiency was measured by using a custom-build high-precision vacuum black body together with cold (T ~ 4 K) filters of known (measured) transmission.Comment: 11 pages, 8 figures, to appear in "High Energy, Optical, and Infrared Detectors for Astronomy" SPIE conference Proc. 7021, Marseille, 23-28 June 200

On the guidance function in micromechanics

1) Modelling the stiffness of a circular notch hinge subjected to flexure, torsion or shear : asymptotic values for a vanishing thickness and correction factors for the general case. 2) Flexible membrane : stiffness for vanishing radius ratio and correction factor for the general case. 3) Conclusion. 4) Appendices, including a summary of useful formulae

Using circular notch hinges as flexible articulations.

Nous présentons un modèle permettant de déterminer les dimensions du col, R et ho, en fonction du matériau, de l'angle de rotation désiré et du nombre de cycles envisagé. Dans le cas du col circulaire, les équations de base de la résistance des matériaux appliquées aux poutres à section variable admettent une solution analytique grâce à un changement de variable judicieux inspiré de la théorie de la lubrification. Pour un rapport entre l'épaisseur de col et son rayon tendant vers zéro, nous pouvons également dériver des formes asymptotiques des équations obtenues. Dans le cas de rapports ho/R moyens, ces résultats doivent être affectés de coefficients correcteurs qui dépendent eux-mêmes du rapport ho/R et que l'on détermine à partir des résultats numériques obtenus par la théorie complète. Ainsi, toutes les propriétés du col peuvent déduites grâce aux équations aux limites et à ces coefficients simples

Mechanical based circular notch hinge design

At the microscale, classical bearings such as ball bearings, sliding bearings and other pivots may be difficult to manufacture. Among all possible solutions to replace them, the notch hinge seems to be very attractive through its many advantages. The major limitation is on the rotation angle. This paper presents a new simplified analytical model for the prediction of the maximum angular displacement and the angular stiffness of a notch hinge. To validate our model, an experimental set-up has been developed. Finally, the results are compared to other theories.4M-µpompe

Conception et test d'une articulation à col circulaire

peer reviewedAt the microscale, classical bearings such as ball bearings, sliding bearings and other pivots may be difficult to manufacture. Among all possible solutions to replace them, the notch hing seems to be very attractive through its many advantages. The major limitation is on the rotation angle. This paper presents a new simplified analytical model for the prediction of the maximum angular displacement and the angular stiffness of a notch hinge. To validate our model, an experimental set-up has been developed.4M-µpompe

Manufacturing of a circular notch hinge as guiding system by electrical discharge machining

Presentation of the notch hinge as a guiding system. Its manufacturing by wire electro-discharge machining. Notch design parameters. Future work.4M-micropompe

A 60 mu W 60 nV/root Hz readout front-end for portable biopotential acquisition systems

There is a growing demand for low-power, small-size and ambulatory biopotential acquisition systems. A crucial and important block of this acquisition system is the analog readout front-end. We have implemented a low-power and low-noise readout front-end with configurable characteristics for Electroencephalogram (EEG), Electrocardiogram (ECG), and Electromyogram (EMG) signals. Key to its performance is the new AC-coupled chopped instrumentation amplifier (ACCIA), which uses a low power current feedback instrumentation amplifier (U). Thus, while chopping filters the 1/f noise of CMOS transistors and increases the CMRR, AC coupling is capable of rejecting differential electrode offset (DEO) up to +/- 50 mV from conventional Ag/AgCl electrodes. The ACCIA achieves 120 dB CMRR and 57 nV/root Hz input-referred voltage noise density, while consuming 11.1 mu A from a 3 V supply. The chopping spike filter (CSF) stage filters the chopping spikes generated by the input chopper of ACCIA and the digitally controllable variable gain stage is used to set the gain and the bandwidth of the front-end. The front-end is implemented in a 0.5 mu m CMOS process. Total current consumption is 20 mu A from 3V.status: publishe