We report current developments in biomimetic flow-sensors based on flow sensitive mechano-sensors of crickets.
Crickets have one form of acoustic sensing evolved in the form of mechanoreceptive sensory hairs. These filiform hairs
are highly perceptive to low-frequency sound with energy sensitivities close to thermal threshold. In this work we
describe hair-sensors fabricated by a combination of sacrificial poly-silicon technology, to form silicon-nitride suspended
membranes, and SU8 polymer processing for fabrication of hairs with diameters of about 50 &mgr;m and up to 1 mm length.
The membranes have thin chromium electrodes on top forming variable capacitors with the substrate that allow for
capacitive read-out. Previously these sensors have been shown to exhibit acoustic sensitivity. Like for the crickets, the
MEMS hair-sensors are positioned on elongated structures, resembling the cercus of crickets. In this work we present
optical measurements on acoustically and electrostatically excited hair-sensors. We present adaptive control of flow-sensitivity
and resonance frequency by electrostatic spring stiffness softening. Experimental data and simple analytical
models derived from transduction theory are shown to exhibit good correspondence, both confirming theory and the
applicability of the presented approach towards adaptation.
A comb-drive is a structure of interdigitated conductive fingers from which one part is able to move. Electrostatic forces allow the structure to function as an actuator whereas capacitance changes give way to use the structure as a sensor. Such structures became feasible on micrometer scale with the advent of surface micromachining in the late eighties. Since then there has been an overwhelming number of applications of comb-drives both in micro-actuation and sensing. This paper gives an overview of the basic operation of a comb-drive and its applications in sensing and actuation.
A 10kN silicon force sensor is realized in which the force is measured by compressing a meander shaped polysilicon strain gage. A second gage which is not loaded, is used for temperature compensation, for compensation of bending and stretching stresses in the chip and for common changes in zero load resistor values. It is shown that the output of the bridge is a linear function of the force and is independent of the force distribution on the chip. By measuring the resistance change along both gages, the force distribution on the chip can be determined so that it can be detected whether the sensor has an oblique load or not. The production process of the chip is simple and robust. A package is designed to apply the load. Hysteresis experiments are performed at four temperatures between 25 $DEGC and 49 $DEGC. Hysteresis measurements at room temperature are in close agreement with finite element calculations. The maximum hysteresis error is within +/- 0.14% of the fill-scale output (fso). Creep was tested by loading it five times. It follows that creep is smaller than 0.01% of the fso. The total error including interpolation error is within +/- 0.23%.
This paper describes the implementation and investigation of an all-optical amplified ring network with Phased Array based optical add/drop multiplexers (OADMs). From crosstalk analysis follows that an OADM with a foldback-structure and 1 X 2-switches has an outstanding crosstalk performance. From the investigation of the dynamic behavior of Erbium doped fiber amplifiers (EDFAs) in a ring configuration we found that EDFAs in a ring-configuration require a faster gain-control when compared to a cascade-configuration.
A method to construct modal fields for an arbitrary one- or two-dimensional intensity dependent refractive index structure is described. An arbitrary starting field is propagated along a complex axis using the slowly varying envelope approximation for the Finite Difference Beam Propagation Method. By suitably choosing the complex value of the propagation step, one mode is maximally increased in amplitude. The applicability of the method is discussed and illustrated by a one-dimensional cross section test example with Kerr- type nonlinearity.