Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.     

CMOS fully digital integrated pressure sensors

Most commercially available silicon pressure transducers are based on a Wheatstone bridge configuration and given an analogue output signal. These devices are generally very sensitive to noise and require complicated circuits (by using passive components) for temperature and non-linearity compensation. This limits the transducer accuracy and increases the calibration cost. To overcome these problems, a new generation of pressure transducers with digital output, based on MOSFET ring oscillators, has been developed. A fully digital integrated pressure sensor and data-acquisition procedures will be presented.     

Experimental study of the characteristics of top-loaded microstrip monopoles

The characteristics of microstrip monopoles fed at the center with antiphase currents are investigated experimentally. First the impedance is measured as a function of frequency. It is found that the radiation resistance at the resonance nearL simeq 05 lambda, is very low while the radiation resistance at the resonance nearL simeq lambdais very high. For a given physical length of the monopole, the resonant frequency is dependent on the strip width and the substrate thickness. The effect of substrate thickness and strip width on the input impedance and bandwidth has also been studied. Finally theE-plane radiation pattern is found to contain two maxima, occurring at approximatelypm 40degfrom broadside.     

Assessing the benefit and cost for a voluntary indoor air quality certification scheme in Hong Kong

A voluntary indoor air quality certification scheme has been proposed in Hong Kong for assessing and evaluating the indoor air quality level in a variety of public places like offices, restaurants and pubs. The scheme intends to promote the public well being, however, its technical and financial practicality has led to serious discussions among the government officials, practitioners and premises owners. Accordingly, this study intends to develop a protocol for examining its financial viability by linking the appropriate dose-response and economic data with the results from indoor micro-environment models. The financial viability of the scheme is evaluated by examining the cost and benefit associated with compliance on the different prescribed indoor particulate (PM10) levels. According to our analysis, the indoor action level of 180 microg/m3 as 8-h mean (with the objective of protecting the health of general public) does not require office owners to improve beyond the base setting. Nevertheless, owners should consider altering the base settings in their air conditioning systems so as to secure more benefit on every dollar they spent. On the contrary, the 20 microg/m3 level as 8-h mean (with the objective of providing comfort) is not considered to be financially viable for office owners as they will incur financial loss on compliance. Subsequent sensitivity analysis indicates that the total net benefit derived have a great dependency on the value-of-life estimates used. If conservative health estimates are adopted, the optimum level determined to be beneficial to both owners and the society will be 55 microg/m3, which can be obtained by operating the air conditioning system with a ventilation rate of 10 l/s, primary filters of 80-85% efficiency and secondary filters efficiency of 60-65% arrestance. This information should be extremely valuable for government officials and policy makers in assessing the financial viability of the voluntary indoor assessment scheme.     

Performance of a cylindrical tissue-equivalent proportional counter for use in neutron monitoring

Tissue-equivalent proportional counters (TEPC) allow the measurements of the absorbed dose and the ambient dose equivalent for neutron fields. A device based on this approach, called NAUSICAA((1,2)), has already been developed by IRSN to be used in high energy neutron fields for space applications. The response of this detector underestimates significantly the dose equivalent at low energies (several hundred keV) which represent the major component of neutron fields at workplaces in the nuclear industry. A counter with a similar geometry (cylindrical detector) and a lower gas pressure was studied in order to simulate a 1 microm biological site. In 2003, the performance of the device was further improved by adding a small amount of 3He to the tissue-equivalent gas (propane based) in order to increase the response for the lower energies of neutrons. Three amplification circuits were used to cover lineal energy range from 10(-1) to 10(4) keV microm(-1). Tests were performed in monoenergetic neutron and source fields. This paper presents the experimental results obtained with this change.     

Numerical and experimental results of the operational neutron dosemeter 'Saphydose-N'

Since 1993, the Institute for Radiological Protection and Nuclear Safety (IRSN) has lead, in association with Electricité de France (EDF), a R&D study of a neutron personal electronic dosemeter. This dosemeter, called 'Saphydose-N', is manufactured by the SAPHYMO company. This paper presents first the optimisation of some detector components using Monte Carlo calculations, and second the test of the manufactured Saphydose-N under radiation following the IEC 1323 standard's recommendations for active personal neutron dosemeters. The measurements with the manufactured dosemeter were performed on the one hand at PTB (Physikalisch-Technische Bundesanstalt) in mono-energetic neutron fields and, on the other hand at IRSN in neutron fields generated by a thermal facility (SIGMA), radionuclide ISO sources and a realistic spectrum (CANEL/T400). The manufactured dosemeter Saphydose-N was also tested during measurement campaigns of the European programme EVIDOS ('Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields') at different nuclear workplaces. The study showed that Saphydose-N complies with the recommendations of standard IEC 1323 and can be used at any workplace with no previous knowledge of the neutron field characteristics.     

Experimental Determination of Micromachined Discrete and Continuous Device Spring Constants Using Nanoindentation Method

A rapid and accurate static and quasi-static method for determining the out-of-plane spring constants of cantilevers and a micromachined vibratory sensor is presented. In the past much of the effort in nanoindentation application was to investigate the thin-film mechanical properties. In this paper, we have utilized the nanoindentation method to measure directly some micromachined device (e.g. microgyroscope) spring constants. The cantilevers and devices tested were fabricated using the MUMPS process and an SOI process (patent pending). Spring constants are determined using a commercial nanoindentation apparatus UMIS-2000 configured with both Berkovich and spherical indenter tip that can be placed onto the device with high accuracy. Typical load resolution is: 20 N to 0.5 N and a displacement resolution of 0.05 nm. Information was deduced from the penetration depth versus load curves during both loading and unloading.     

Falls and working individuals: role of extrinsic and intrinsic factors

Falls are frequent occupational accidents involving workers and lead to important social and economic consequences both for the individual and for the employer. Different factors can modify balance control and lead to falling, especially environment-related and individual factors. The literature would appear to indicate that there have been few studies on the intrinsic factors involving the mechanisms of generating falls. This review determines the main factors involved in the mechanisms of falling, whether related to the environment, work or the individual. Knowledge of the extrinsic and intrinsic factors contributing to the fall could allow securer environment planning and occupational conditions for employers, and the use of balance rehabilitation methods for individuals to reduce the risk of falls.     

Low complexity radix-4 butterfly design for the soft-decision Viterbi decoder

This study presents a new radix-4 butterfly design for Viterbi decoders. The branch symmetry of the proposed radix-4 butterfly is exploited to design a low-complexity radix-4 butterfly module to simplify the implementation of the soft-decision Viterbi decoder. By exploiting the branch symmetry, only a half of branch metrics need to be computed, while other metrics can be derived from the computed branches. Therefore, the branch metric computation of the radix-4 butterfly can be reduced by a factor of 2. Considering the convolutional code in the DAB system as an example, experimental results indicate that the proposed radix-4 butterfly design can reduce the number of FPGA slices of the radix-4 butterfly module by 24% over the conventional design.     

Influence of Boundary Conditions on the Dynamic Characteristics of Squeeze Films in MEMS Devices

Micromechanical structures that have squeeze-film damping as the dominant energy dissipation mechanism are of interest in this paper. For such structures with narrow air gap, the Reynolds equation is used for calculating squeeze-film damping, which is generally solved with trivial pressure boundary conditions on the side walls. This procedure, however, fails to give satisfactory results for structures under two important conditions: 1) for an air gap thickness comparable to the lateral dimensions of the microstructure and 2) for nontrivial pressure boundary conditions such as fully open boundaries on an extended substrate or partially blocked boundaries that provide side clearance to the fluid flow. Several formulas exist to account for simple boundary conditions. In practice, however, there are many micromechanical structures such as torsional microelectromechanical system (MEMS) structures that have nontrivial boundary conditions arising from partially blocked boundaries. Such boundaries usually have clearance parameters that can vary due to fabrication. These parameters, however, can also be used as design parameters if we understand their role on the dynamics of the structure. We take a MEMS torsion mirror as an example device that has large air gap and partially blocked boundaries due to static frames. We actuate the device and experimentally determine the quality factor Q from the response measurements. Next, we model the same structure in ANSYS and carry out computational fluid dynamics analysis to evaluate the stiffness constant K, the damping constant D, and the quality factor Q due to the squeeze film. We compare the computational results with experimental results and show that without taking care of the partially blocked boundaries properly in the computational model, we get unacceptably large errors.