This research explores distributed sensing techniques for mobile devices using synchronous gestures. These are patterns of activity, contributed by multiple users (or one user with multiple devices), which take on a new meaning when they occur together in time, or in a specific sequence in time. To explore this new area of inquiry, this work uses tablet computers augmented with touch sensors and twoaxis linear accelerometers (tilt sensors). The devices are connected via an 802.11 wireless network and synchronize their time-stamped sensor data. This paper describes a few practical examples of interaction techniques using synchronous gestures such as dynamically tiling together displays by physically bumping them together, discusses implementation issues, and speculates on further possibilities for synchronous gestures.

Building on Buxton’s foreground/background model, we discuss the importance of explicitly considering both foreground interaction and background interaction, as well as transitions between foreground and background, in the design and implementation of sensing techniques for sensor-enhanced mobile devices. Our view is that the foreground concerns deliberate user activity where the user is attending to the device, while the background is the realm of inattention or split attention, using naturally occurring user activity as an input that allows the device to infer or anticipate user needs. The five questions for sensing systems of Bellotti et al. [2002] proposed as a framework for this special issue, primarily address the foreground, but neglect critical issues with background sensing. To support our perspective, we discuss a variety of foreground and background sensing techniques that we have implemented for sensor-enhanced mobile devices, such as powering on the device when the user picks it up, sensing when the user is holding the device to his ear, automatically switching between portrait and landscape display orientations depending on how the user is holding the device, and scrolling the display using tilt. We also contribute system architecture issues, such as using the foreground/background model to handle cross-talk between multiple sensor-based interaction techniques, and theoretical perspectives, such as a classification of recognition

In this paper, we present a wireless sensor platform designed for processing multipoint human motion with low latency and high resolution. One application considered here is interactive dance, in which a choreographer wishes to translate the movements of multiple dancers into real-time audio or video content to accompany the performance. This can only be accomplished using a distributed measurement system capable of responding quickly with enough information to describe the expressive movements of multiple people. Similar requirements exist for biomechanical analysis, especially in the context of athletic training, where high resolution is demanded, and instant feedback is also desirable. Our approach to addressing such aggressive requirements involves a high-speed wireless network of compact inertial measurement units (IMUs) that can be worn at various locations on the body. Each device is equipped with its own 1Mbps radio link and a full six-axis IMU, as well as a capacitive node-to-node proximity sensor. Currently, the system supports real-time data collection and processing for up to 25 nodes with 100Hz full state updates, thereby handling much higher data rates than its predecessors. With locally buffered data, sample rates of up to 1kHz have been achieved successfully. Early results discussed here demonstrate the feasibility of our design through testing with both dancers and professional athletes.

Inertial measurement components, which sense either acceleration or angular rate, are being embedded into common user interface devices more frequently as their cost continues to drop dramatically. These devices hold a number of advantages over other sensing technologies: they measure relevant parameters for human interfaces and can easily be embedded into wireless, mobile platforms. The work in this dissertation demonstrates that inertial measurement can be used to acquire rich data about human gestures, that we can derive efficient algorithms for using this data in gesture recognition, and that the concept of a parameterized atomic gesture recognition has merit. Further we show that a framework combining these three levels of description can be easily used by designers to create robust applications.

an RFID sensor data logging platform that relies on a new, wirelessly-charged power model. A PDL has no battery yet (unlike a passive sensor tag) is able to collect data while away from an RFID reader. A PDL senses and logs data using energy stored in a capacitor; the capacitor can be wirelessly recharged (unlike active tags), and data can be uploaded whenever the PDL is near a reader. Standard EPC Generation 2 readers are used for WISP-PDL charging, ID-reading, and sensor data transfer. This allows WISP-PDLs to operate using commercial RFID readers as the only support infrastructure (for both data and power), and allows WISP-PDLs to co-exist with standard RFID tags. We describe the design and implementation of a prototype WISP-PDL, and report results from a short demonstration study that shows it can monitor the temperature and fullness of a milk carton as it is used over the course of a day. R

When subjected to alternating stresses, most materials degrade, e.g., suffer premature failure, due to a phenomenon known as fatigue. It is generally accepted that in brittle materials, such as ceramics, cyclic fatigue can only take place where there is some degree of toughening, implying that premature fatigue failure would not be expected in polycrystalline silicon where such toughening is absent. However, the fatigue failure of polysilicon is reported in the present work, based on tests on thirteen thin-film (2 µm thick) specimens cycled to failure in laboratory air (~25ºC, 30-50 % relative humidity), where damage accumulation and failure of the notched cantilever beams were monitored electrically during the test. Specimen lives ranged from about 10 seconds to 34 days (5 x 10 5 to 1 x 10 11 cycles) with the stress amplitude at failure being reduced to ~50 % of the low-cycle strength for lives in excess of 10 9 cycles.

When subjected to alternating stresses, most materials degrade, e.g., suffer premature failure, due to a phenomenon known as fatigue. It is generally accepted that in brittle materials, such as ceramics, fatigue can only take place in toughened solids, i.e., premature fatigue failure would not be expected in materials such as single crystal silicon. The results of this study, however, appear to be at odds with the current understanding of brittle material fatigue. Twelve thin-film ( 20 m thick) single crystal silicon specimens were tested to failure in a controlled air environment (30 0.1 C, 50 2% relative humidity). Damage accumulation and failure of the notched cantilever beams were monitored electrically during the "fatigue life" test. Specimen lives ranged from about 10 s to 48 days, or 1 10 6 to 1 10 11 cycles before failure over stress amplitudes ranging from approximately 4 to 10 GPa. A variety of mechanisms are discussed in light of the fatigue life data and fracture surface evaluation. [642] Index Terms---Fatigue failure, MEMS devices, single-crystal silicon, thin films.

incorporated in a traditional business suit. A key feature of the system is an array of input/output devices integrated into the garment. These devices are connected to a network bus incorporated into the suit jacket. The network connects the jackets sensors and I/0 with a Compaq iPAQ operating Windows CE. The iPAQ is connected to the users personal information systems via a wireless LAN. Demonstrated within is an application allowing the e-SUIT to control the factory installed Microsoft Pocket Outlook . Pocket Outlook is a functioning business class application that allows the proof of concept testing to be performed on an integrated product used in the marketplace 1

This article outlines the theory and hardware behind the different modes of electric field sensing. It then gives several application examples, including 3D hand sensors and track pads, proximitysensing computer monitors, and gesture-sensitive walls for interactive projected graphics

To evaluate the long-term durability properties of materials for microelectromechanical systems (MEMS), the stress-life (S/N) cyclic fatigue behavior of a 2-[tm thick polycrystalline silicon film was evaluated in laboratory air using an electrostatically actuated notched cantilever beam resonator. A total of 28 specimens were tested for failure under high frequency (40 kHz) cyclic loads with lives ranging from about 10 s to 34 days (3 x 105 to 1.2 x 1011 cycles) over fully reversed, sinusoidal stress amplitudes varying from 2.0 to 4.0 GPa. The thin-film polycrystalline silicon cantilever beams exhibited a time-delayed failure that was accompanied by a continuous increase in the compliance of the specimen. This apparent cyclic fatigue effect resulted in an endurance strength, at greater than 109 cycles, of 2 GPa, i.e. roughly one-half of the (single cycle) fracture strength. Based on experimental and numerical results, the fatigue process is attributed to a novel mechanism involving the environmentally-assisted cracking of the surface oxide film (termed reaction-layer fatigue). These results provide the most comprehensive, high-cycle, endurance data for designers of polysilicon micromechanical components available to date. 2001 Elsevier Science B.V. All rights reserved.