Martin Dieter Liess

A miniaturized multidirectional optical motion sensor and input device based on laser self-mixing

Using the laser self-mixing effect, a miniaturized two-dimensional motion sensor has been developed that works on almost any light-scattering surface. By applying the sensor to the surface of a finger, for example, an input device (scroll, click) can be built for hand-held applications. A three-dimensional input device (x, y, click), which will be presented soon, is based on the principles explained in this paper. We also present the physical and technological challenges and the solutions required to build a practical, miniaturized and robust device.

A description of properties and errors of simple and stacked sensors

In this paper the physical sensing effect in a generic sensor is described as a transfer function from a measured input magnitude to the desired output magnitude. Parasitic effects such as the influence of non-constant environmental conditions, sensor ageing and, to a certain extent, also the effect of noise, quantization and hysteresis may be described by the use of additional input variables. Applying a second-order Taylor approximation in multiple variables, the generic sensor is approximated and a system of sensor parameters is generated. All steady-state sensor properties, among them sensitivity, parasitic and cross-sensitivity, drift, resolution, non-linearity, accuracy and the detection limit, are defined in one straightforward description. This system is used to mathematically analyse different cases of stacked sensors. In this way, the effects of well-known principles such as modulation or the use of a reference at different stages on the accuracy and the detection limit are analysed for generic sensor structures. As a result, the properties of a stacked sensor can be calculated if just some basic properties of the elementary sensors constituting the stack are known. For all designs, the behaviour of the stack follows a simple pattern.

Using the differential principle in chemical micro-sensors

Abstract Two new sensor principles are presented. Both are fabricated using a chemically sensitive In2O3 film. Other than classical gas-sensitive resistors based on metal oxide films such as In2O3, the sensors presented here do not suffer from offset drift due to re-crystallisation and ageing of the film. The improved behaviour can be explained by the fact that the new sensors function differentially so that the effect of an overall change of the film cancels out.

New operation principle for ultra-stable photo-ionization detectors

Photo-ionization detectors (PIDs) are suited ideally to be combined with gas chromatographs (GCs). Without a GC, a PID can be used as a cheap unspecific sensor for noxious substances in the air. In this case, the unpredictable slow offset drift of the device leads to a significantly worsened detection limit. The dependence of the sensitivity on ambient humidity further deteriorates the accuracy, so that the usability of a classical PID without GC in practice is highly limited. We present a new PID design that eliminates the offset and thus offset drift problems and reduces the cross-sensitivity to humidity. It is based on an additional grid that allows modulation of the ion flow in a part of the ionization chamber. This modified PID exhibits a 20 times improved detection limit and a reduction of the cross-sensitivity to humidity from 58% of the signal to 10% of the signal. Further reduction is possible.

50.5L: Late‐News Paper: A Compact, Laser‐based Optical Scrolling Device

In this paper, we describe a new input device that can be easily integrated into modern, compact equipment such as mobile telephones, laptops and PDAs, providing a solution for scrolling and/or click functionality. This laser-based device interacts with any light-scattering surface, including human skin. Apart from several application fields, this paper describes a simple solution for the detection of directional information using laser self-mixing.