Sandra Bellekom

Influence of mechanical stress on the offset voltage of Hall devices operated with spinning current method

The effect of mechanical stress on the offset voltage of a symmetrical CMOS Hall device was measured when operated by the continuous spinning current method. This method allows the expansion of the spatially periodic offset voltage into components of a Fourier series up to the fifteenth order. The influences of stress on these components are caused by piezoresistive effects changing the current distribution in the active region of the Hall sensor. Further influences are due to a stress-dependent thickness modulation of the insulating pn-junction that defines the device geometry. However, measuring the sensor response in four different directions for the bias current proved to be sufficient to eliminate ail stress-dependent contributions to the offset voltages of a CMOS Hall device.

Power to the people: local energy initiatives as seedbeds of innovation?

BackgroundTwo decades after the launch of Local Agenda 21 in Rio de Janeiro, we have witnessed the emergence and development of local initiatives in sustainable development. Local energy communities are a clear manifestation of this development. The questions the paper raises are as follows: can local energy initiatives be considered seedbeds of innovation? If so, how can such initiatives lead to innovations in the energy supply?MethodsWe applied desk research and reviewed secondary literature.ResultsThe questions are answered empirically and theoretically. Empirically, the paper analyses the causes and manifestations of local community initiatives throughout Europe and especially in the Netherlands, to discover the drivers and foci of the initiatives. Theoretically, the paper provides an institutionally oriented classification of local electricity initiatives, based on coordination, technology and performance. In a final step, the paper analyses the innovative capacity of the local energy initiatives.ConclusionsThe conclusion is that local electricity initiatives can be considered a seedbed of innovation but with no potential to develop dominance in the electricity supply. The local initiatives will develop as niches inside the dominant central generating station electricity system and will add to the hybridisation of its products and services.

Offset reduction of Hall plates in three different crystal planes

Silicon Hall plates show an offset of a few millitesla. A large portion of this offset is caused by mechanical stress in the device. The offset can be reduced by a factor 1000 to 10 000 when the spinning-current principle is applied. This paper presents a model for the influence of mechanical stress in (spinning-current) Hall plates, realized in different crystal planes. Devices realized in a (110) plane show a larger stress than devices fabricated in a (100) or (111) plane, as predicted by the model presented. However, independent of the original offset, the offset after spinning is reduced to only a few microtesla. This is in agreement with the model, which predicts only a periodic offset voltage as a result of the mechanical stress. Periodic offset voltages are removed by the spinning-current method.

Spatial aspects affecting acidification factors in European acidification modelling

Plain linear models have recently been used in methodologies to model fate and transport for assessing acidification in life cycle impact assessment (LCIA), or in support of air pollution abatement policies. These models originate from a statistical analysis of the relationship between inputs and outputs of physically-based models that reflect the mechanics of a system in detail. Linear models applied to assess acidification use an acidification factor (AF), which relates changes in the magnitude of emissions to changes in the total area that is protected against acidification in Europe. The changes in emission volume refer to changes of one substance, within one country and one sector or one grid cell. This paper evaluates the dependence of AFs on three spatial characteristics, i.e. the spatial emission and deposition resolution, the spatial emission distribution and the actual spatial location of emissions. The applied spatial resolutions of emission and deposition cause non-systematic variations in AFs of up to 60%, relative to the finest resolution. The manner in which the distribution of emissions is modelled, i.e. grid or sector-specific, is shown to affect AFs considerably, as well. We conclude that spatial characteristics of the physically-based acidification model can affect the assessment of acidification by means of plain linear models.

INFLUENCE OF SUBSTRATE VOLTAGE ON SENSITIVITY AND OFFSET OF (SPINNING-CURRENT) HALL PLATES

Hall sensors are used for the measurement of magnetic fields and for the indirect measurement of mechanical quantities. Traditional Hall plates show a large, unpredictable offset, making them less suited for applications involving small magnetic fields. To reduce the offset of Hall plates, Munter introduced the so-called spinning-current principle [1]. Using this principle he successfully reduced the offset of Hall plates. The research into these spinning-current Hall plates concentrates on the influence of important parameters like temperature, substrate voltage, mechanical stress, etc. on the properties of these Hall plates. In this paper the influence of the substrate voltage on the sensitivity and offset of spinning-current Hall plates is discussed.