David J. Nagel

Noise in MEMS

This review provides a comprehensive survey of noise research in MEMS. Some background on noise and on MEMS is provided. We review noise production mechanisms, and highlight work on the theory and modeling of noise in MEMS. Then noise measurements in the specific types of MEMS are reviewed. Inertial MEMS (accelerometers and angular rate sensors), pressure and acoustic sensors, optical MEMS, RF MEMS, surface acoustic wave devices, flow sensors, and chemical and biological MEMS, as well as data storage devices and magnetic MEMS, are reviewed. We indicate opportunities for additional experimental and computational research on noise in MEMS.

Measurement of Energy Costs of Security in Wireless Sensor Nodes

Both correct transmission using hashing and protection of messages using encryption in sensor nodes require additional energy. This paper describes our measurement results for energy consumption in CrossBow and Ember sensor nodes for the process of exchanging data messages between nodes both in the clear and in a protected form. Full strength algorithms were loaded into and executed in nodes. It was found that the CPU operates for substantially longer times for both hashing and encryption operations compared to the time for handling messages without any security. The longer radio transmission times due to hashing were especially costly. Hence, security algorithms have great impacts on energy consumption in sensor nodes. For the full operational mode, with CPU processing and also radio transmission of messages, our results indicate that the lifetime of a transmitting node in a security regime is only about one-half of the lifetime without security.

Measurement of noise characteristics of MEMS accelerometers

Microelectromechanical systems (MEMS) are devices that have static or movable components with dimensions on the scale of a micrometer. One particular device that is widely used commercially is the MEMS accelerometer. Such accelerometers typically contain some movable micro beams that measure acceleration in one or two orthogonal directions. Major markets for MEMS accelerometers are automobile airbag triggers, earthquake detection circuits and health care. MEMS accelerometers have advantages over conventional accelerometers because they are smaller, lighter and cheaper. Since MEMS accelerometers are used in many systems, the noise characteristics of these devices are very important. The noise characteristics will influence the performance of the accelerometers especially when operating at lower g conditions. In this work, we report on the noise characteristics and special measurement techniques for Analog Devices ADXL202, ADXL 105 and ADXL 190 accelerometers.

Assessment of Energy Consumption in Wireless Sensor Networks: A Case Study for Security Algorithms

WSN nodes are usually powered by batteries. Energy consumption during node operation determines battery life. Power consumption depends on the different hardware and software components in a WSN node and their various activities. In order to determine the life of the battery, we must measure the energy consumption of a node that is active in a network. That is, we must know the power consumption and time duration for node activities including computations, and RF transmission and reception. In this paper, we introduce an easy and accurate method for dynamic energy measurements without disturbing the node or network. The method consists of an oscilloscope, which can stream digitized voltages into a PC, which calculates the profile of energy consumption. We employed this capability to determine energy consumption for different security algorithms in CrossBow MICA2 nodes.

Balancing security and energy consumption in wireless sensor networks

Appling security to messages traveling over wireless links in sensor nodes requires additional energy. This paper describes our suggestions on balancing the level of security and energy consumption based on our measurements using CrossBow and Ember sensor nodes. It was found that the node microcontrollers CPU operates for substantially longer times for both hashing and encryption operations compared to the time for handling messages without any security. However, this has little overall impact on energy consumption. The longer high-power radio transmission times due to hashing were especially costly. For the full operational mode, with CPU processing and also radio transmission of messages, our results indicate that the lifetime of a transmitting node in a security regime is only about one-half of the lifetime without security. Hence, we provided design guidelines to apply security with energy consideration for WSN. They include 2 to 8 bytes MACs for integrity and authentication instead of SHA-1, and the size of messages should match the steps of encryption algorithms.

Design of MEMS and microsystems

Facile, integrated and comprehensive software is needed for the design of processes, models and simulation, which are required for effective production of MEMS and microsystems. The characteristics of computer-aided design software now available from seven companies are reviewed. Three of the firms have roots in microelectronics, and three were formed specifically for MEMS design. Electronic, mechanical, thermal and fluidic mechanisms are commonly included. One company is especially strong in microfluidics. Two of the design suites permit computational coupling between a MEMS device and its package. High spatial- and temporal- resolution optical diagnostics are now producing detailed data that will challenge design and simulation software for MEMS and microsystems. Near and far term prospects for the CAD of MEMS and microsystems are projected.

Go with the (micro) flow

The integration of electronics and optics with miniature fluidic systems has produced remarkable capabilities that have spawned a new industry, primarily in the past decade. Devices made by several companies, most of them start-ups, enable point-of-care analyses for clinical samples and on-site field studies, as well as providing instruments for research and development. The companies, the materials and processes they use to make devices, and the markets that are served, are the subjects of this overview of the microfluidics industry. Microfluidic chips are part of the field of microelectromechanical systems (MEMS). This is the case since they are made by the micromachining processes developed in the field of MEMS, whether or not they have moving parts. Instruments based on microfluidic chips are likely to become smaller and more widely used in the coming years. The chips themselves are candidates for even greater technical integration.

Technologies for Micrometer and Nanometer Pattern and Material Transfer

This chapter illustrates a framework for relating and comparing technologies for the transfer of patterns and materials with micrometer and nanometer resolution. It discusses the basic concepts for each technology by providing some references and examples. Methods for the production and assembly of parts vary widely. The micrometer scale involves parallel production of objects, using pattern transfer and other methods, with layering or bonding being primary methods of assembly. In the nanometer regime, a different approach to the production of objects is followed. The bottom-up approach of chemistry and biology dominates nanometer technology. Molecular synthesis and self-assembly are used as primary approaches for making functional systems on the nanometer scale. The chapter provides an overview of self assembly, in which both the material and pattern are effectively transferred at once. The material essentially contains its own patterning information, which may or may not be expressed, depending on conditions at the time of transfer and subsequently.

Energetics Of Defects And Strains In Palladium

Pd employed as cathodes in cold fusion experiments contains various defects, each of which has an associated energy. In principle, some of the energy in Pd due to defects that exist before a cold fusion experiment could be released as apparent excess heat during the experiment. Energy densities were computed for high concentrations of vacancies, impurities (both substitutional and interstitial atoms), dislocations and grain boundaries, as well as for strains. It is concluded that pre-existing defects and strains cannot account for the energies released during cold fusion experiments. Nonetheless, defects may play other supporting or central roles in cold fusion.

Digital noise spectroscopy system and its application to solar cells

A creative combination of hardware and software has produced a new digital noise spectroscopy system. It provides a low cost, user-friendly, rapid, non-destructive and non-invasive capability to acquire noise spectra. Thorough testing showed that the system has a very low noise floor (3×10-17 V2/Hz), as well as a broad frequency range (1 to 105 Hz). The system has been applied to survey solar cells with a variety of materials and geometries. In particular, we acquired noise spectra from (a) single junction Si and GaAs solar cells and (b) triple-junction solar cells that were heavily irradiated with 3 MeV protons. The results should make it possible to determine characteristics of solar cells, for example, trap densities, from the spectra. Later work will compare noise spectroscopy with normal means of characterizing solar cells.