Single-mask thermal displacement sensor in MEMS

In this work we describe a one degree-of-freedom microelectromechanical thermal\ud displacement sensor integrated with an actuated stage. The system was fabricated in the device layer of a silicon-on-insulator wafer using a single-mask process. The sensor is based on the temperature dependent electrical resistivity of silicon and the heat transfer by conduction through a thin layer of air. On a measurement range of 50 μm and using a measurement bandwidth of 30 Hz, the 1-sigma noise corresponds to 3.47 nm. The power consumption of the sensor is 209 mW, almost completely independent of stage position. The drift of the sensor over a measurement period of 32 hours was 32 nm

A single-mask thermal displacement sensor in MEMS

Position sensing in MEMS is often based on the principle of varying capacitance [1]. Alternative position sensing principles include using integrated optical waveguides [2] or varying thermal conductance [3]. Lantz et al demonstrated a thermal displacement sensor achieving nanometre resolution on a 100mm range. However a multi-mask production process and manual assembly were needed to fabricate this displacement sensor. In this work we present a 1-DOF thermal displacement sensor integrated with an actuated stage, and its experimental characterization. The system was fabricated in the device layer of a silicon-on-\ud insulator (SOI) wafer using a single-mask process.\ud \u

A single-mask thermal displacement sensor in MEMS

This work presents a MEMS displacement sensor based on the conductive heat transfer of a resistively heated silicon structure towards an actuated stage parallel to the structure. This differential sensor can be easily incorporated into a silicon-on-insulator-based process, and fabricated within the same mask as electrostatic actuators and flexure-based stages. We discuss a lumped capacitance model to optimize the sensor sensitivity as a function of the doping concentration, the operating temperature, the heater length and width. We demonstrate various sensor designs. The typical sensor resolution is 2 nm within a bandwidth of 25 Hz at a full scale range of 110 μm

Subclinical Thyroid Dysfunction and the Risk of Cognitive Decline: a Meta-Analysis of Prospective Cohort Studies.

Although both overt hyper- and hypothyroidism are known to lead to cognitive impairment, data on the association between subclinical thyroid dysfunction and cognitive function are conflicting. This study sought to determine the risk of dementia and cognitive decline associated with subclinical thyroid dysfunction among prospective cohorts. We searched in MEDLINE and EMBASE from inception until November 2014. Two physicians identified prospective cohorts that assessed thyroid function and cognitive outcomes (dementia; Mini-Mental State Examination [MMSE]). Data were extracted by one reviewer following standardized protocols and verified by a second reviewer. The primary outcome was dementia and decline in cognitive function was the secondary outcome. Eleven prospective cohorts followed 16,805 participants during a median followup of 44.4 months. Five studies analyzed the risk of dementia in subclinical hyperthyroidism (SHyper) (n = 6410), six in subclinical hypothyroidism (SHypo) (n = 7401). Five studies analyzed MMSE decline in SHyper (n = 7895), seven in SHypo (n = 8960). In random-effects models, the pooled adjusted risk ratio for dementia in SHyper was 1.67 (95% confidence interval, 1.04; 2.69) and 1.14 (95% confidence interval, 0.84; 1.55) in SHypo vs euthyroidism, both without evidence of significant heterogeneity (I(2) = 0.0%). The pooled mean MMSE decline from baseline to followup (mean 32 mo) did not significantly differ between SHyper or SHypo vs euthyroidism. SHyper might be associated with an elevated risk for dementia, whereas SHypo is not, and both conditions are not associated with faster decline in MMSE over time. Available data are limited, and additional large, high-quality studies are needed

Design, Fabrication and Characterization of a MEMS Thermal Displacement Sensor

This thesis is a part of the CLEMPS (Closed Loop Embedded MEMS-based Precision Stage) project. Within this project a MEMS-stage should be positioned using a feedback (displacement) signal with 10-nm accuracy over a 100 ?m range. This thesis investigates if thermal sensing can be used as a reliable sensing mechanism within the CLEMPS project. Lantz et al demonstrated a promising thermal displacement sensor that achieves nanometre resolution on a 100 ?m range [1]. Using this sensor as a basis, five conceptual designs for thermal displacement sensors are introduced, of which one concept operates in vacuum and four concepts operate in a normal environment. Basic analysis showed that each conceptual design is feasible, except for thermal sensing in vacuum. The designs have large variety in fabrication complexity and estimated performance. The behaviour of the sensors is strongly nonlinear due to dependencies of the material properties on temperature. Different thermo electrical models are introduced that quantify the performance of the designs. Those models are used to gain extensive insight in the behaviour of the sensors and to provide comparison between the performances of the different sensor designs. The models are also applied as design tool for investigating the influence of geometric variations on the sensing performance. Only two of the designs are compatible with the available SOI-wafer based processing. These sensor designs were actually fabricated and integrated within an actuated MEMS stage. For experimental evaluation of the general feasibility of thermal displacement sensing, the thesis focuses on the simplest design. An electronic measurement circuit is designed and fabricated that provides the actuator voltages and performs the differential current-to-voltage amplification for the measurement signal. The mechanical behaviour of the stage is experimentally characterized to determine the relation between the actuator voltage and stage displacement. Now, the (quasi-) static measurement performance of the fabricated sensor can be experimentally characterized by actuating the stage at a low frequency, while recording the applied actuator voltage, the resulting individual heater currents and the differential measurement current in xPC. This data is analysed to obtain the sensor performance in terms of offset, sensitivity, nonlinearity, noise and power consumption. The static measurements are repeated on many sensors to investigate the repeatability and influence of geometric variations. The influence of varying conditions in terms of heater supply voltage, environmental temperature and humidity is determined by performing many characterizations on one device using controlled measurement conditions. Also, the dynamic performance is evaluated in terms of sensor drift, frequency behaviour and hysteresis of the device by using supplementary measurements The feasibility of thermal displacement sensing within the CLEMPS is evaluated using the results on the sensor performance for design IV. Using acquired insight, the performance limiting effects are identified and recommendations for improvements are presented.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

First lidar observations of mesospheric hydroxyl

Ground-based lidars have been used to detect and identify ground-state (v" =0) hydroxyl radicals (OH) in the mesosphere between about 75 and 85 km altitude. These lidars operate near 308 nm and OH is observed through laser-induced-fluorescence on the A 2∑ + -X 2II(0, 0) band. The results expose a valuable global set of nighttime OH observations, since existing long-term lidar data at several NDSC sites contain the (serendipitous) OH information. Results of lidar observations are presented from two mid-latitude sites, one in each hemisphere: Table Mountain (34°N), California, and Lauder (45°S), New Zealand. They show observations of a geometrically thin (∼3 km) nocturnal layer of OH near 80 km. For the Table Mountain observations, the derived values for the OH density at 80 km typically are 2 - 4 × 10 5 cm -3 which is in accordance with model predictions [Dodd et al., 1994]. The temporal behavior of the mesospheric OH signal, following sunset, that was found, supports previous model predictions [Allen et al., 1984] in a qualitative fashion

THYROID DYSFUNCTION AND THE RISK OF DEMENTIA AND COGNITIVE DECLINE: SYSTEMATIC REVIEW, META-ANALYSIS AND CLINICAL IMPLICATIONS

Pathophysiology, epidemiology and therapy of agein