Coded data generation or conversion – Bodily actuated code generator – Including keyboard or keypad
Reexamination Certificate
1997-11-06
2001-04-03
Horabik, Michael (Department: 2635)
Coded data generation or conversion
Bodily actuated code generator
Including keyboard or keypad
C340S010510, C340S870370, C345S156000, C455S100000
Reexamination Certificate
active
06211799
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic communication, and in particular to the propagation of electrical signals across a user's body through electrostatic coupling.
BACKGROUND OF THE INVENTION
The goal of truly integrating computational capacity with the everyday lives of individuals has consumed substantial research effort, and from a variety of perspectives. Through component miniaturization, wearable items (such as wristwatches, jewelry, and clothing accessories) can now offer computer processing power to perform a variety of tasks while remaining casually and continuously available. Recent advances in fabric design permit clothing itself to carry electrical signals, while electrodes distributed around a an individual's environment can silently and unobtrusively monitor position, orientation and movements. In these ways, processing capacity can be dispersed over various worn components, and the user can, without conscious effort, interact computationally with the surrounding environment.
An important principle of design for wearable devices is adaptation to users' existing habits and preferences, rather than forcing the user to adapt to accommodate new appliances. The concept of “personal area networks” (PANs), which utilize the user's body as an electronic communication channel, represents a significant step in this direction. As described in U.S. Pat. No. 5,914,701, electrostatic coupling among worn or carried electronic devices allows these items to intercommunicate via the user's body, sharing data or control signals among themselves, or transferring data to an external recipient (such as another person or a wall-mounted receiver) by close proximity or touching.
Electrostatic coupling represents a departure from traditional forms of electronic communication, which involve radiated energy. For example, radio-frequency identification (RFID) devices have been employed for some time to remotely sense parameters of interest in people or objects. An RFID device receives a wireless signal from an externally located “reader,” which determines the parameter of interest based on the response of the RFID device to the transmitted signal. A simple application of this technology is security: an individual wears an RFID “tag” or badge, and a controlled-entry system unlocks a door only if the wearer's tag is recognized as s/he approaches.
Radiative systems can be configured for a relatively large (i.e., far field) read range. But this capability can actually represent a disadvantage if the environment contains multiple, independent RFID devices, since the reader will excite all devices within the read range simultaneously. Proximately located devices, in other words, cannot share the same frequency channel; separate addressing requires separate frequencies or cumbersome efforts to focus the electromagnetic field from the reader.
Magnetostatic and electrostatic RFID systems, by contrast, operate through near-field interaction, and thereby facilitate selective coupling or “channel sharing”; that is, so long as the tagged items are not immediately adjacent (i.e., within a few centimeters of each other), they can be individually addressed. In terms of selectivity, electrostatic systems offer practical advantages in terms of the ease of focusing an electric field as compared with a magnetic field. Electrostatic systems also offer manufacturing and cost advantages, since the induction coil required for magnetostatic systems is eliminated and electrodes can be conveniently and inexpensively deposited on substrates of widely varying shapes and materials. For example, the tag in a magnetostatic system may have a coil with 100-1000 turns and a radius of 1-5 cm, while a typical reader has a 20-cm coil.
On the other hand, a person's body can act as a shield in electrostatic systems, compromising the coupling between reader and RFID device. The PAN approach, which uses the entire body as a signal carrier, not only overcomes this limitation, but also substantially extends the read range. For example, a computer housed in a user's shoe can readily communicate electrostatically with the user's wristwatch, personal digital assistant, and/or notebook computer.
One limitation of the PAN concept has been the need for autonomously powered devices. Again, components such as batteries or power supplies add significantly to the weight and cost of PAN devices, and contradict the goal of seamless integration of computational capacity into the user's lifestyle and habits.
DESCRIPTION OF THE INVENTION
BRIEF SUMMARY OF THE INVENTION
The present invention capacitively transmits not only data but power through a user's body. In one implementation, a transmitter carried by the user transmits power and data to a receiver, which is also carried on the user's body; the return path for the current is provided by environmental ground. The signal that the transmitter applies to the user's body not only contains a data component, but also powers the receiver and enables it to detect and decode the data.
Various strategies for simultaneous transmission of power and data may be employed. In one approach, power and data are simply transmitted at different frequencies. In another approach, the data is transmitted by modulating a carrier from which power is derived. Virtually any modulation scheme can be adapted to the present invention. For example, data may be encoded by frequency modulation of a carrier; the receiver recovers the data by detecting carrier modulations, and derives power from the frequency-varying carrier itself. Alternatively, the data may be encoded by amplitude modulation or phase modulation of a carrier. In still another approach, the data is modulated using, for example, a pseudorandom code to provide spread-spectrum encoding within a broadband carrier, with the carrier again supplying power. And in yet another approach, the data is not actually “transmitted” at all, but is instead imparted to the transmitter by the receiver in the form of loading variations. In the time domain, the temporal pattern of these variations can encode a sequence of bits. In the frequency domain, multiple receivers resonating at different frequencies can impart information merely by their presence or absence, or can instead impart a continuous range of information through variation of resonant frequency (or frequencies).
Furthermore, the coupling of resonators to a transmitter (i.e., a reader) can impart information about their proximity to the transmitter. The coupling strength is inversely proportional to the square of the distance between transmitter and receiver. Receivers having different resonant frequencies can be individually addressed and the coupling strengths separately assessed to obtain distance measurements. Increasing the number of resonators increases the resolution of the measurement (if they lie in a straight line) and the dimensionality of the measurement (if they are not collinear).
In other implementations, the transmitter or the receiver is physically displaced from the user's body (although both receiver and transmitter are coupled to environmental ground), and data and power are transmitted when the transmitter and receiver become sufficiently proximate—via the user's body—to permit capacitive coupling. For example, the transmitter may refrain from sending the data component until alerted (e.g., via a loading measurement) of the coupling to a receiver. In still other implementations, the user may wear more than one receiver. The receivers may also be capable of transmitting data to other receivers. Modulation schemes such as spread-spectrum FM, time-division multiplexing or frequency-division multiplexing facilitate simultaneous operation of multiple transmitters, each using a different modulation parameter.
The invention is amenable to a wide variety of applications, ranging from “interbody” exchange of digital information between individuals through physical contact (e.g., a handshake) to “intrabody
Gershenfeld Neil
Nivi Babak
Post E. Rehmi
Edwards, Jr. Timothy
Horabik Michael
Massachusetts Institute of Technology
Testa Hurwitz & Thibeault LLP
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