Igor Paprotny

An untethered, electrostatic, globally controllable MEMS micro-robot

We present an untethered, electrostatic, MEMS micro-robot, with dimensions of 60 /spl mu/m by 250 /spl mu/m by 10 /spl mu/m. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator (USDA). These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace. These MEMS micro-robots demonstrate turning error of less than 3.7/spl deg//mm during forward motion, turn with radii as small as 176 /spl mu/m, and achieve speeds of over 200 /spl mu/m/sec with an average step size as small as 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths. The devices were fabricated through a multiuser surface micromachining process, and were postprocessed to add a patterned layer of tensile chromium, which curls the steering arms upward. After sacrificial release, the devices were transferred with a vacuum microprobe to the electrical grid for testing. This grid consists of a silicon substrate coated with 13-/spl mu/m microfabricated electrodes, arranged in an interdigitated fashion with 2-/spl mu/m spaces. The electrodes are insulated by a layer of electron-beam-evaporated zirconium dioxide, so that devices placed on top of the electrodes will experience an electrostatic force in response to an applied voltage. Control waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Hysteresis in the system allows on-board storage of n=2 bits of state information in response to these electrical signals. The presence of on-board state information within the device itself allows each of the two device subsystems (USDA and steering arm) to be individually addressed and controlled. We describe this communication and control strategy and show necessary and sufficient conditions for voltage-selective actuation of all 2/sup n/ system states, both for our devices (n=2), and for the more general case (where n is larger.).

Planar Microassembly by Parallel Actuation of MEMS Microrobots

We present designs, theory, and results of fabrication and testing for a novel parallel microrobotic assembly scheme using stress-engineered MEMS microrobots. The robots are 240-280 mum times 60 mum times 7-20 mum in size and can be controlled to dock compliantly together, forming planar structures several times this size. The devices are classified into species based on the design of their steering arm actuators, and the species are further classified as independent if they can be maneuvered independently using a single global control signal. In this paper, we show that microrobot species are independent if the two transition voltages of their steering arms, i.e., the voltages at which the arms are raised or lowered, form a unique pair. We present control algorithms that can be applied to groups of independent microrobot species to direct their motion from arbitrary nondead-lock configurations to desired planar microassemblies. We present designs and fabrication for four independent microrobot species, each with a unique transition voltage. The fabricated microrobots are used to demonstrate directed assembly of five types of planar structures from two classes of initial conditions. We demonstrate an average docking accuracy of 5 mum and use self-aligning compliant interaction between the microrobots to further align and stabilize the intermediate assemblies. The final assemblies match their target shapes on average 96%, by area.

Bistable springs for wideband microelectromechanical energy harvesters

This paper presents experimental results on a microelectromechanical energy harvester with curved springs that demonstrates an extremely wide bandwidth. The springs display an asymmetrical bistable behavior obtained purely through their geometrical design. The frequency down-sweep shows that the harvester 3-dB bandwidth is about 587 Hz at 0.208-g acceleration amplitude. For white noise excitation at 4×10−3 g2/Hz, we found that the bandwidth reaches 715 Hz, which is more than 250 times wider than in the linear-spring regime. By varying the bias voltage, an output power of 3.4 μW is obtained for frequency down-sweep at 1-g amplitude and 150-V bias.

Electromechanical Energy Scavenging From Current-Carrying Conductors

This paper describes a novel method for scavenging energy for electric power systems sensing applications by the use of permanent magnets that couple to the magnetic field generated by an alternating current flowing through a nearby conductor. The resulting mechanical energy is converted to electrical energy using piezoelectric transduction. This electromechanical AC energy scavenging method is an attractive alternative to coil-based AC energy scavengers in cases where the scavengers cannot encircle the conductor. In such cases, the electromechanical AC energy scavenger has the potential to produce significantly more power than comparable coil-based methods. The components of an electromechanical AC energy scavenger are described in detail, and experimental data from prototypes that are fabricated and tested in our laboratory are shown. The 20 cm3 prototypes generated up to 2.7 mW of power each from 20 A of nearby current. Theoretical power densities of electromechanical AC energy scavengers are compared to the power densities of representative coil-based methods, showing that in some cases the electromechanical AC scavengers can generate an order-of-magnitude more power than coil-based AC scavengers. This paper demonstrates that electromechanical AC energy scavenging is a potential method for powering small size low cost stick-on wireless sensor networks.

Review and Comparison of Spatial Localization Methods for Low-Power Wireless Sensor Networks

Spatial localization (colocation) of nodes in wireless sensor networks (WSNs) is an active area of research, with many applications in sensing from distributed systems, such as microaerial vehicles, smart dust sensors, and mobile robotics. This paper provides a comprehensive review and comparison of recent implementations (commercial and academic) of physical measurement techniques used in sensor localization, and of the localization algorithms that use these measurement techniques. Physical methods for measuring distances and angles between WSN nodes are reviewed, followed by a comprehensive comparison of localization accuracy, applicable ranges, node dimensions, and power consumption of the different implementations. A summary of advantages and disadvantages of each measurement technique is provided, along with a comparison of colocalization methods in WSNs across multiple algorithms and distance ranges. A discussion of possible improvements to accuracy, range, and power consumption of selected self-localization methods is included in the concluding discussion. Although the preferred implementation depends on the application, required accuracy, and range, passive optical triangulation is reported as the most energy efficient localization method for low-cost/low-power miniature sensor nodes. It is capable of providing micrometer-level resolution, however, the applicable range (internode distance) is limited to single centimeters.

Self-powered MEMS sensor module for measuring electrical quantities in residential, commercial, distribution and transmission power systems

Ongoing initiatives for energy conservation present the need for ubiquitous sensing of electrical power use in residential and commercial settings. Inexpensive and massively distributed electrical sensors installed in power distribution and transmission systems will enable collection of highly granular information regarding the operation of the power grid. Incorporated into the upcoming Smart Grid infrastructure, we envision this data-collecting capability to enhance the overall stability of the grid, as well as improve its diagnostic capabilities. In this paper, we present our ongoing work towards developing self-powered MEMS sensor modules that can be installed in both residential and commercial settings, as well as in power distribution and transmission systems. The sensor modules will measure electrical quantities such as voltage, current and instantaneous power using a suite of MEMS sensors, and will scavenge the energy needed for their operation from the current flowing in the energized conductor onto which they are attached.

Stick-On Piezoelectromagnetic AC Current Monitoring of Circuit Breaker Panels

We present a stick-on wireless electric current monitoring system that is designed to measure and report electricity usage from circuit breaker panels in residential and commercial settings. This monitoring system uses piezoelectromagnetic (PEM) AC current sensors to couple to the magnetic fields produced by the current-carrying conductors. The PEM sensors can be easily attached to the surfaces of common circuit breaker panels, facilitating the installation by non-technical individuals. This paper describes the sensing principles and provides an analytical model of the PEM AC sensors. It also presents the architecture for a wireless current monitoring system and describes its implementation for sub-metering a circuit breaker panel in a building at the University of California, Berkeley. The theory and experimental validation of a signal deconvolution and calibration method, essential for extracting signals from cross-coupled magnetic fields, are also included.

MEMS Particulate Matter (PM) monitor for cellular deployment

In this work, we present designs, modeling as well as initial results from ongoing fabrication of a novel, portable MEMS Particulate Matter (PM) monitor. The PM monitor uses an air-based microfluidic circuit to select the particles of interest based on their size, and then deposit them onto the surface of a temperature-compensated Film-Bulk Acoustic Resonator (FBAR). The relative change in the resonance frequency of the FBAR provides an indication of the mass of the particles that are deposited on its surface, and correspondingly of the PM concentration in the surrounding air. Our device measures 40 mm × 25 mm × 12 mm, and is 1 – 2 orders of magnitude smaller than commercially available PM monitors. The use of microfabricated components allowed us to reduce the size of the device by an order of magnitude from our previously developed prototype, while at the same time increasing its sensitivity. Combined with a location-aware cellphone, this technology will allow collection of personal PM exposure data.

Reducing model creation cycle time by automated conversion of a CAD AHMS layout design

Simulation is a popular tool for accurately estimating the performance of an automated material handling system (AMHS). Accuracy of the model is normally dependent on a detailed description of the AMHS physical system components and their coordinate positions. In this paper, a methodology is defined for automatically inputting the physical system components used to describe an AMHS within a simulation language. The method is based on data extraction from a CAD layout file of the system. Automatically generating the physical system components reduces simulation model building time and increases model accuracy.

Simultaneous Control of Multiple MEMS Microrobots

We present control algorithms that implement a novel planar microassembly scheme using groups of stress-engineered microrobots controlled through a single global control signal. The global control signal couples the motion of the devices, causing the system to be highly underactuated. Despite the high degree of underactuation, it is desirable that each robot be independently maneuverable. By exploiting differences in the designs and the resulting electromechanical interaction with the control signal, the behavior of the individual robots can be differentiated. We harness this differentiation by designing the control signal such that some devices remain confined in small circular orbits (limit cycles), while the non-orbiting robots perform work by making progress towards the goal. The control signal is designed to minimize the number of independent control voltage levels that are used for independent control, allowing us to maximize the number of simultaneously controllable devices.