Current touch devices are adept at tracking finger touches, but cannot distinguish if multiple touches are caused by different fingers on a single hand, by fingers from both hands of a single user, or by different users. This limitation significantly reduces the possibilities for interaction techniques in touch interfaces. We present GhostID, a capacitive sensor that can differentiate the origins of multiple simultaneous touches. Our approach analyzes the signal ghosting, already present as an artifact in a frequency-division touch controller, to differentiate touches from the same hand or different hands of a single user (77% reliability at 60 fps) or from two different users (95% reliability at 60 fps). In addition to GhostID, we also develop a framework of user-differentiation capabilities for touch input devices, and illustrate a set of interaction techniques enabled by GhostID.

We report on the Latency Hammer, a low-cost yet highaccuracy and high-precision automated tool that measures the interface latency of touchscreen devices. The Hammer directly measures latency by triggering a capacitive touch event on a device using an electrically actuated touch simulator, and a photo sensor to monitor the screen for a visual response. This allows us to measure the full end-toend latency of a touchscreen system exactly as it would be experienced by a user. The Hammer does not require human interaction to perform a measurement, enabling the acquisition of large datasets. We present the operating principles of the Hammer, and discuss its design and construction; full design documents are available online. We also present a series of tools and equipment that were built to assess and validate the performance of the Hammer, and demonstrate that it provides reliable latency measurements.

We present "Fast Multi-Touch" (FMT), an extremely high frame rate and low-latency multi-touch sensor based on a novel projected capacitive architecture that employs simultaneous orthogonal signals. The sensor has a frame rate of 4000 Hz and a touch-to-data output latency of only 40 microseconds, providing unprecedented responsiveness. FMT is demonstrated with a high-speed DLP projector yielding a touch-to-light latency of 110 microseconds.

This paper describes a long-term project exploring advanced visual interfaces for antenna design. MERL developed three successive prototypes that embodied an evolution towards larger scales and more concrete semantics for visualization of large sets of candidate designs and then winnowing them down. We experimented with multidimensional scaling and then collective line graphs before settling on linked scatterplots to visualize performance in a design space of up to 10 million antennas at a time. In the end, the scatterplot solution was most successful at balancing intelligibility with visualization of the space as a whole. The design allows for adding more 1D or 2D linked feature visualizations if needed, and it smoothly transitions to other "details on demand" views for final tweaking.

Backscatter radio is proposed for sensor networks. In that way, the transmitter for each sensor is simplified to a transistor connected to an antenna and therefore, the cost for each sensor's communicator becomes negligible, while energy used for wireless communication per sensor is minimized. A software-defined transceiver is built to transmit a carrier, receive the reflections from various sensors and extract their transmitted messages. This work presents a thorough model of the backscatter radio link, the system architecture and a set of data extraction techniques for each sensor's information, testing in practice a sensor communicating through backscatter at a range of approximately 15 meters indoors, with 5 milliwatt transmission power at 10 bits per second. This work highlights the idiosyncrasies of the backscatter channel and provides a new communication perspective in the fertile area of scalable sensor networks, especially when low bit-rate, ultra-low cost sensors are required.

We provide an overview of our experimental system, testing in practice a sensor communicating through backscatter at a range of approximately 15 meters indoors, with 5 mW transmission power at 10 bits per second. Our system is designed for simultaneous reception of signals continuously radio-backscattered from several ultra low-cost sensors. This work highlights the idiosyncracies of the backscatter channel and presents a proof- of-concept demonstration of backscatter radio for wireless sensor networks, especially when low bit-rate, ultra low-cost sensors are required.

We explore the design space of a two-sided interactive touch table, designed to receive touch input from both the top and bottom surfaces of the table. By combining two registered touch surfaces, we are able to offer a new dimension of input for co-located collaborative groupware. This design accomplishes the goal of increasing the relative size of the input area of a touch table while maintaining its direct-touch input paradigm. We describe the interaction properties of this two-sided touch table, report the results of a controlled experiment examining the precision of user touches to the underside of the table, and a series of application scenarios we developed for use on inverted and two-sided tables. Finally, we present a list of design recommendations based on our experiences and observations with inverted and two-sided tables.

Networks consisting of low-cost wireless sensors have been the subject of extensive research, with applications ranging from environmental monitoring to building control systems, to name a few. In this paper we consider networks intended to provide wide area coverage of one or more physical, chemical or biological parameters. We envision a target average data rate per sensor of 1-5 bps and transmission ranges of up to 100 m. Unlike conventional networks, the goal of wide-area parameter characterization can be achieved even with less than 100% node reliability, a feature that allows us to propose a novel ultra-low-cost architecture based on redundant sensors. To achieve the low-cost goal, sensor nodes include no receivers, and they transmit their information to a central reader using radio backscatter. This communication modality makes it possible to achieve a few years of battery life with small and inexpensive batteries. Performance impact due to absence of individual reception acknowledgement in this unidirectional communication channel is offset mainly by transmitter spatial diversity achieved through deployment of additional nodes. We describe the design of the system and its components, and analyze its performance characteristics.

In this paper, we show how traditional physical interface components such as switches, levers, knobs and touch screens can be easily modified to identify who is activating each control. This allows us to change the function per-formed by the control, and the sensory feedback provided by the control itself, dependent upon the user. An auditing function is also available that logs each user's actions. We describe a number of example usage scenarios for our tech-nique, and present two sample implementations.

Toolkits and other tools have dramatically reduced the time and technical expertise needed to design and implement graphical user interfaces (GUIs) allowing high-quality, iterative, user-centered design to become a common practice. Unfortunately the generation of functioning prototypes for physical interactive devices as not had similar support -- it still requires substantial time and effort by individuals with highly specialized skills and tools. This creates a divide between a designers' ability to explore form and interactivity of product designs and the ability to iterate on the basis of high fidelity interactive experiences with a functioning prototype. To help overcome this difficulty we have developed the Calder hardware toolkit. Calder is a development environment for rapidly exploring and prototyping functional physical interactive devices. Calder provides a set of reusable small input and output components, and integration into existing interface prototyping environments. These components communicate with a computer using wired and wireless connections. Calder is a tool targeted toward product and interaction designers to aid them in their early design process. In this paper we describe the process of gaining an understanding of the needs and workflow habits of our target users to generate a collection of requirements for such a toolkit. We describe technical challenges imposed by these needs, and the specifics of design and implementation of the toolkit to meet these challenges.

In this paper we present a system for providing tactile feedback for stylus-based touch-screen displays. The Haptic Pen is a simple low-cost device that provides individualized tactile feedback for multiple simultaneous users and can operate on large touch screens as well as ordinary surfaces. A pressure-sensitive stylus is combined with a small solenoid to generate a wide range of tactile sensations. The physical sensations generated by the Haptic pen can be used to enhance our existing interaction with graphical user interfaces as well as to help make modern computing systems more accessible to those with visual or motor impairments.

This paper describes how to instrument the physical world so that objects become self-describing, communicating their identity, geometry, and other information such as history or user annotation. The enabling technology is a wireless tag which acts as a radio frequency identity and geometry (RFIG) transponder. We show how addition of a photo-sensor to a wireless tag significantly extends its functionality to allow geometric operations - such as finding the 3D position of a tag, or detecting change in the shape of a tagged object. Tag data is presented to the user by direct projection using a handheld locale-aware mobile projector. We introduce a novel technique that we call interactive projection to allow a user to interact with projected information e.g. to navigate or update the projected information.The ideas are demonstrated using objects with active radio frequency (RF) tags. But the work was motivated by the advent of unpowered passive-RFID, a technology that promises to have significant impact in real-world applications. We discuss how our current prototypes could evolve to passive-RFID in the future.

A technique for creating a touch-sensitive input device is proposed which allows multiple, simultaneous users to interact in an intuitive fashion. Touch location information is determined independently for each user, allowing each touch on a common surface to be associated with a particular user. The surface generates location dependent, modulated electric fields which are capacitively coupled through the users to receivers installed in the work environment. We describe the design of these systems and their applications. Finally, we present results we have obtained with a small prototype device.

Construction toys are a superb medium for geometric models. We argue that such toys, suitably instrumented or sensed, could be the inspiration for a new generation of easy-to-use, tangible modeling systems—especially if the tangible modeling is combined with graphical-interpretation techniques for enhancing nascent models automatically. The three key technologies needed to realize this idea are embedded computation, vision-based acquisition, and graphical interpretation. We sample these technologies in the context of two novel modeling systems: physical building blocks that self-describe, interpret, and decorate the structures into which they are assembled; and a system for scanning, interpreting, and animating clay figures.

We describe a tangible interface for building virtual structures using physical building blocks. We demonstrate two applications of our system. In one version, the blocks are used to construct geometric models of objects and structures for a popular game, Quake II™. In another version, buildings created with our blocks are rendered in different styles, using intelligent decoration of the building model.