Silicon carbide MEMS for harsh environments

Silicon carbide (SiC) is a promising material for the development of high-temperature solid-state electronics and transducers, owing to its excellent electrical, mechanical, and chemical properties. This paper is a review of silicon carbide for microelectromechanical systems (SiC MEMS). Current efforts in developing SiC MEMS to extend the silicon-based MEMS technology to applications in harsh environments are discussed. A summary is presented of the material properties that make SiC an attractive material for use in such environments. Challenges faced in the development of processing techniques are also outlined. Last, a review of the current stare of SiC MEMS devices and issues facing future progress are presented     

Packaging of microsystems for harsh environments

Micromachined devices have great potential but using these fragile structures in aggressive environments can pose a challenge. Mechanical shock, chemical exposure, and temperature extremes can damage delicate microsystems. Also, substantial effort is often put forth to develop a device concept only to find later that the device is difficult or expensive to package suitably in a consumer or automotive environment. The cost of materials, processing, and manufacturing make the sensor or actuator device impractical for some applications. A successful MEMS device manages the proper balance for its application between the high device performance and low unit cost. The packaging of MEMS begins with a consideration of the microsystem's environment. An aerospace, automotive, or industrial component could be subjected to temperatures ranging from -40°C to over 150°C. Mechanical shocks in the 10 g to +500 g range can be experienced which can fracture poorly designed silicon beams. Chemical exposure, which can corrode silicon, or the metal interconnection lines on silicon, and shift electrical parameters, are challenges that must be overcome in these applications     

GaN HFET digital circuit technology for harsh environments

The first demonstration of GaN digital circuits is reported. First-generation GaN digital technology has already shown high yields for circuits of considerable complexity. Specifically, a 31-stage ring oscillator was implemented using 217 transistors. Properties of the AlGaN/GaN material system that enable outstanding power handling capabilities of GaN heterojunction field effect transistors (HFETs), i.e. large bandgap, high breakdown field and high saturation velocity, also make it attractive for digital applications in harsh environments. Because of these unique material characteristics, GaN digital control circuits have the potential to operate in high radiation environments, at elevated temperatures, and directly from high voltage rails. Successful operation of GaN 31-stage ring oscillators at the highest base-plate temperature attainable by the test setup of 265/spl deg/C, indicates that these circuits can operate at significantly higher temperatures.     

Thermo-mechanical reliability tradeoffs for deployment of area array packages in harsh environments

Fine-pitch ball grid arrays (BGAs) and underfills have been used in benign office environments and wireless applications for a number of years, however their reliability in harsh environments is not well understood. In this work, the design guidelines development effort for deployment of fine-pitch ball-grid array packages in the harsh environments have been presented. Guidelines are targeted toward government contractors, OEMs, and third party contract manufacturers who intend to select part architectures and board designs based on specified mission requirements. The guidelines are intended as an aid for understanding the sensitivity of component reliability to geometry, package architecture, material properties and board attributes in different thermal environments in order to quantitatively evaluate the impact of these parameters on the component reliability. The intent is to develop a tool for doing tradeoffs between geometry, materials and quantitatively evaluating the impact on reliability. Sensitivity relations for geometry, materials, and architectures based on statistical models and failure mechanics based closed form models have been developed. Convergence between statistical model sensitivities and failure mechanics based sensitivities has been demonstrated. Predictions of sensitivities have been validated against experimental test data.     

Differentiated service strategies for ad-hoc wireless sensor networks in harsh communication environments

In some wireless sensor network applications, sensor nodes will be deployed in harsh communication environments. In such environments, the deployment may not be adequately controlled, and nodes may have to communicate with a single destination node. For nodes to alert the destination on critical data that has been sensed, in addition to the harsh communication environment, contention resulting from both the deployment and network density must be appropriately overcome. In this paper, we create theoretical models for the behavior of Timeout-MAC (T-MAC) protocol, and evaluate five possible solutions, each designed to be easy to implement on a device by simply tuning T-MAC parameters, so as to overcome these environment-specific issues and effectively alert the destination to critical data. Our results indicate that slight changes to the behavior of the network can improve the awareness of the destination to critical regions in the environment, and that these changes have different levels of effectiveness at different network densities.     

Visual tracking of robots in uncalibrated environments

This paper presents a new adaptive controller for visual tracking control of a robot manipulator in 3D general motion with a fixed camera whose intrinsic and extrinsic parameters are uncalibrated. In addition to camera parameters, the feature positions are also assumed unknown. Based on the fact that the unknown parameters appears linearly in the closed-loop dynamics of the system if the depth-independent interaction matrix is adopted to map the image errors onto the joint space of the manipulator, a new adaptive algorithm was developed to estimated the unknown parameters on-line. With a full consideration of dynamic responses of the robot manipulator, the Lyapunov method is employed to prove asymptotic convergence of the image errors. Simulation and experiment results are used to demonstrate the performance of the proposed approach.     

一种提高恶劣环境中电台话音质量的方法

针对恶劣环境中电台话音质量差这一难题,提出了一种有效的解决方法。首先在最小值控制的递归平均Ⅱ型（MCRA-2）算法基础上,提出了一种改进的MCRA-2算法。该算法采用自适应平滑参数和双检测门限,能有效减小音乐噪声,提高噪声估计准确性;然后将该噪声估计算法与对数最小均方误差估计器相结合,实现话音降噪,提高恶劣环境下电台话音质量;最后利用噪声估计结果和降噪后的话音信号,采用信噪比判决算法,自适应估计静噪门限,实现自适应静噪,进一步提高话音舒适度。实验表明,采用该方法的电台在大噪声、强干扰等恶劣环境中使用时,能明显改善话音质量,有效减轻收听者听觉疲劳。     

A new adaptive MAC layer protocol for broadband packet wirelessnetworks in harsh fading and interference environments

A new medium-access protocol is proposed for sharing a high-speed radio channel among a number of small wireless packet-access units, some of which may be stationary and some of which may be within moving vehicles. Such a system could provide fixed-point pedestrian and remote users with wireless access to CPU and database resources of an underlying asynchronous transfer mode (ATM) wireline network, essentially extending the ATM bandwidth-upon-demand interface directly to the wireless units and enabling delivery of multimedia services (albeit at the lower peak rate afforded by the radio channel). A primary goal of the proposed medium-access protocol is the pre-delivery of a signal from each packet-access unit as needed to rapidly compute the weights needed by a base station's adaptive array processor or a space-time processor, thereby protecting the packet flow in each direction from the effects of both multipath propagation and adjacent channel interference arising in neighboring radio cells. An impairment-robust direct sequence spread-spectrum-based polling signal is invoked to stimulate a pilot tone from a given remote immediately prior to packet transfer in either direction, thereby permitting the base station to determine a good set of antenna element combining or power splitting weights to be used for that packet. Reasonable approximations are invoked to study the performance of the proposed protocol and the link utilization efficiency and average message delay are found. By proper choice of protocol parameters, a radio resource utilization efficiency of about 95% is readily achieved. The accuracy of the approximations is confirmed by extensive computer simulations     

Virtual environments for Internet-based robots. II. Path planning

For pt.I. see ibid., p.383-8. This paper addresses the issue of path planning in a virtual environment (VE) for the control of an Internet-based robot manipulator. A hybrid method is proposed in which the dimension of the path-planning problem is reduced by separating the problem of planning the position of the gripper from that of planning the pose of the gripper. A global configuration-space technique is used for the former and a local operational-space technique is used for the latter. Particular attention is paid to fundamental issues such as mapping the graphical model into configuration space, on-line collision detection and obstacle avoidance in the VE.     

Virtual environments for Internet-based robots. I. Modeling a dynamic environment

In the context of using virtual environments (VEs) in Internet-based teleoperation, this paper addresses the issue of parameter acquisition for single-image-based modeling of VEs. By studying the properties of basic three-dimensional features such as point sets and edge corners, a parameter-searching method was developed that employs virtual objects as feature-matching templates. This approach is particularly valuable if the environment is subject to unpredictable change.     

An end-to-end transmission architecture for the remote control of robots over IP networks

Teleoperation via the Internet is attracting more and more attention from both academia and industry. Physical interaction with remote environments over IP networks, however, poses many technical challenges that are still outstanding, such as time delay, limited bandwidth, and unreliable transmission. To deal with these problems, the majority of current work is concentrated on developing advanced remote control algorithms or interface techniques whereas data transmission between the human operator and the remote robot through the Internet is often treated as a given condition. This paper describes a novel data transmission architecture, for which the core is the trinomial transport protocol, to facilitate the remote control of Internet robots. The trinomial protocol is analyzed theoretically and its advantages over other existing protocols are verified by simulation and experimental studies.     

A framework for Internet-based interaction of humans, robots, and responsive environments using agent technology

In this paper, a systematic framework for Internet-based interaction of humans, robots, and environments is proposed by using agent technology. The framework is validated by proposing the concept of slave agents, a virtual directory facilitator (VDF) to control the slave agents, and a responsive multiagent environment. It creates a robot control system in which humans, robots, and environments can interact without much prior knowledge. Finally, a number of experiments have been conducted successfully by adopting JadeLeap middleware and Foundation for Intelligent Physical Agents (FIPA) standard under the environment composed of a personal digital assistant (PDA), a home service robot-intelligent, sweeping security assistant companion (ISSAC), and a video camera network. Experimental results show that the proposed framework increases the availability of whole system, decreases the time for Internet connection of robots and user devices such as PDAs, and provides the responsiveness of environments.     

Secure multi‐factor remote user authentication scheme for Internet of Things environments

Because of the exponential growth of Internet of Things (IoT), several services are being developed. These services can be accessed through smart gadgets by the user at any place, every time and anywhere. This makes security and privacy central to IoT environments. In this paper, we propose a lightweight, robust, and multi‐factor remote user authentication and key agreement scheme for IoT environments. Using this protocol, any authorized user can access and gather real‐time sensor data from the IoT nodes. Before gaining access to any IoT node, the user must first get authenticated by the gateway node as well as the IoT node. The proposed protocol is based on XOR and hash operations, and includes: (i) a 3‐factor authentication (ie, password, biometrics, and smart device); (ii) mutual authentication ; (iii) shared session key ; and (iv) key freshness . It satisfies desirable security attributes and maintains acceptable efficiency in terms of the computational overheads for resource constrained IoT environment. Further, the informal and formal security analysis using AVISPA proves security strength of the protocol and its robustness against all possible security threats. Simulation results also prove that the scheme is secure against attacks.     

用于压电和电容微麦克风的体硅腐蚀相关研究

用溶胶-凝胶法制备的锆钛酸铅压电薄膜的微麦克风和纹膜电容式微麦克风都是基于微电子机械系统技术的硅基单片微麦克风。在其工艺制作过程中,在表面硅微加工之后进行体硅的湿法腐蚀,由此产生了硅片的正面保护和体硅腐蚀的控制等新的工艺问题。从各种正面保护方法和体硅腐蚀自停止技术两方面对这一问题进行了研究和解决。保持了微麦克风具有20~40 mV/Pa的开路灵敏度,并且使圆片级成品率达到70%以上。     

Connectors for self-reconfiguring robots

Connectors for self-reconfiguring robots are difficult to design because of the wide range of requirements. We describe the DRAGON connector, whose most distinctive features are its ability to self-align and its strength-to-weight ratio. It weighs 170 g, but holds over 70-kg load. It is able to self-align /spl plusmn/15 mm (O/5) lateral offsets and /spl plusmn/45/spl deg/ directional and rotational offsets. It allows autonomous docking and reconfiguration in a fraction of a second, without any complex control.     

Characteristics of SiCN microstructures for harsh environment and high-power MEMS applications

This paper describes a novel processing technique for the fabrication of polymer-derived silicone carbonitride (SiCN) microstructures for extreme microelectromechanical system (MEMS) applications. A polydimethylsiloxane (PDMS) mold was formed on an SU-8 pattern using a standard UV photolithographic process. Next, the liquid precursor, polysilazane, was injected into the PDMS mold to fabricate free-standing SiCN microstructures. Finally, the solid polymer SiCN microstructure was crosslinked using hot isostatic pressure at 400 °C and 205 bar. The optimal pyrolysis and annealing conditions to form a ceramic microstructure capable of withstanding temperatures over 1400 °C were determined. Using the optimal process conditions, the fabricated SiCN ceramic microstructure possessed excellent characteristics including shear strength (15.2 N), insulation resistance (2.163×10¹⁴ Ω cm), and BDV (1.2 kV, minimum). Since the fabricated ceramic SiCN microstructure has improved electrical and physical characteristics compared to bulk Si wafers, it may be applied to harsh environments and high-power MEMS applications such as heat exchangers and combustion chambers.     

Motion stereo for mobile robots

A method allowing a mobile robot to measure accurately its distance from external objects is introduced. It only requires a single uncalibrated camera and a dynamic vision system. The method was evaluated in an optical laboratory and also in outdoor-experiments. Even in outdoor-experiments with a vehicle moving at a speed of 30 km/h, errors of less than 1% of the true distance were achieved in real time. The accuracy achievable with the method depends on the nature of the image features used as a basis for the measurement. Laboratory experiments have been performed to investigate quantitatively the characteristics of the feature detectors under conditions of reduced lighting and, consequentially, reduced SNR, and with image features not matching the feature detectors perfectly. The best results can be achieved by using edge-like features. Point-like features do have certain desirable characteristics, but point detectors are more sensitive to noise than edge detectors. Hence, the accuracy achieved with corner detectors was less than the one achieved with edge detectors. Nevertheless, even with corner detectors the resulting error was less than 1%, despite the fact that the image of the target object did not contain good corners     

Self-replicating robots for lunar development

In this paper, the concept of self-replicating robots (SRRs) is reviewed, and the feasibility of a particular kind of minimalistic SRR is analyzed in the context of lunar resource development. The key issue that will determine the feasibility of this approach is whether or not an autonomous robotic factory can be devised such that it is light enough to be transported to the moon, yet complete in its ability to self-replicate with no other inputs than those resources available on the lunar surface. Self-replication leads to exponential growth, and would allow as few as one initial factory to spawn lunar production of materials and energy on a massive scale. Such capacity would dramatically impact man's ability to explore and colonize space and collect solar energy for terrestrial applications. Our concept of a self-replicating robotic factory consists of four subsystems: 1) multifunctional robots for digging and transportation of materials, and assembly of components during the replication process; 2) materials refining and casting facility; 3) solar energy conversion, storage and transmission; and 4) electromagnetic rail guns for long-distance transportation (for example, for sending materials to low-earth orbit (LEO), or transporting replicated factories to distal points on the moon). Each of these subsystems is described in the context of current technologies, with an emphasis on 1). We build on previous concepts for self-replicating systems, present a simple prototype that demonstrates active mechanical replication, and develop an analytical model of how the proliferation of such systems on the lunar surface would occur.