U.S. patent number 5,914,701 [Application Number 08/907,062] was granted by the patent office on 1999-06-22 for non-contact system for sensing and signalling by externally induced intra-body currents.
This patent grant is currently assigned to Massachusetts Institute of Technology. Invention is credited to David Allport, Neil Gersheneld, Thomas Zimmerman.
United States Patent |
5,914,701 |
Gersheneld , et al. |
June 22, 1999 |
Non-contact system for sensing and signalling by externally induced
intra-body currents
Abstract
A wireless system includes one or more transmitters and one or
more remote receivers that are respectively coupled through one or
more users and room ground. The transmitters each produce
low-frequency, low power signals that, through capacitive coupling,
pass as displacement currents into and from the body of the user,
which acts as a conductive node. A receiver that couples
capacitively to the user responds to the displacement currents and
reproduces the signals. The transmitter includes a signal generator
and a pair of electrodes. The signal generator produces modulated
signals that vary the voltage between the electrodes, a first one
of which is closely coupled capacitively to the user's body such
that the "quasi-electrostatic" field resulting from the electrode
potential causes a displacement current to pass to the user's body.
The second electrode is oriented so that its coupling to the room
ground is stronger than that of the first electrode, such that room
ground acts as a return path for the current from the receiver. The
signal generator may modulate the information to be transmitted
using, for example, a pseudorandom code, to produce spread spectrum
signals. This increases noise immunity and allows multiple
transmitters, each using a different modulation code, to operate at
the same time. The receivers each include a detector/demodulator
that acquires and tracks the signals from the one or more
transmitters.
Inventors: |
Gersheneld; Neil (Somerville,
MA), Zimmerman; Thomas (Flushing, NY), Allport; David
(Boston, MA) |
Assignee: |
Massachusetts Institute of
Technology (Cambridge, MA)
|
Family
ID: |
23734590 |
Appl.
No.: |
08/907,062 |
Filed: |
August 6, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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436982 |
May 8, 1995 |
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Current U.S.
Class: |
345/156; 455/100;
340/870.37; 345/158; 345/157; 455/41.1; 340/539.12; 340/539.21;
340/573.1; 340/567; 340/539.23; 340/13.31 |
Current CPC
Class: |
H04B
5/0012 (20130101); G06F 3/0346 (20130101); G06K
19/07758 (20130101); G06K 7/10326 (20130101); H04B
5/04 (20130101); G06F 3/017 (20130101); G06F
3/044 (20130101); H04B 13/005 (20130101); G06F
3/04162 (20190501); G06K 19/07749 (20130101); G06K
19/041 (20130101); H04B 5/02 (20130101); G06K
19/07788 (20130101); G06F 3/046 (20130101); Y02D
30/70 (20200801) |
Current International
Class: |
H04B
13/00 (20060101); G06K 7/08 (20060101); H04B
5/00 (20060101); G06K 19/077 (20060101); G06K
19/04 (20060101); H04B 005/00 (); G09G
005/00 () |
Field of
Search: |
;345/156,158,157,174
;340/562,561,407.1,870.37,563,564,825.71 ;341/21,31,32,33 ;434/12
;455/41,100 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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60-250731 |
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May 1986 |
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JP |
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61-046639 |
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Jul 1986 |
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JP |
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2 129 176 |
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May 1984 |
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GB |
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Primary Examiner: Peng; John K.
Assistant Examiner: Lo; Linus M.
Attorney, Agent or Firm: Cesari and McKenna, LLP
Parent Case Text
This application is a continuation of Ser. No. 08/436,982 filed on
May 08, 1995 now is abandoned.
Claims
What is claimed is:
1. A wireless communication system including:
A. a transmitter for producing low frequency signals that include
data, the transmitter being capacitively coupled to a user and to
ground, the transmitter passing to the user a current that is
associated with the low frequency signals; and
B. a receiver that is displaced from the user and is coupled to
ground for receiving when capacitively coupled to the user a
current that is associated with the signals produced by the
transmitter, the receiver reproducing the transmitted signals and
recovering the data.
2. The wireless communication system of claim 1, wherein the
transmitter includes:
i. a pair of electrodes; and
ii. a signal generator connected between the electrodes, the signal
generator generating the low frequency signals that result in an
associated displacement current between the electrodes and the
user.
3. The wireless communication system of claim 2, wherein the
receiver includes:
i. a pair of electrodes; and
ii. a signal detector connected between the electrodes, the signal
detector reproducing the low frequency signals from a displacement
current developed between the electrodes and the user.
4. The wireless communication system of claim 1 wherein the system
further includes
a. a plurality of receivers; and
b. a processor for determining from the signals reproduced by the
receivers the position of the user relative to one or more of the
receivers.
5. The wireless communication system of claim 4 wherein:
the receivers are mounted on the periphery of a computer screen;
and
the processor moves a cursor to a position on the screen that is
associated with the position of the user relative to one or more of
the receivers.
6. The wireless communication system of claim 2 wherein the
transmitter further includes a signal modulator for spread spectrum
modulating the signals with a predetermined pseudorandom code.
7. The wireless communication system of claim 6 wherein the system
further includes a plurality of transmitters, each of the
transmitters being associated with a predetermined code that
differs from the codes associated with the other transmitters in
the system, the receiver using the codes to distinguish between the
signals passed from each of the transmitters in the plurality of
transmitters.
8. The wireless communication system of claim 7 wherein each of the
transmitters in the plurality of transmitters is capacitively
coupled to a different user, and the receiver receives signals
respectively from the individual transmitters when the receiver is
capacitively coupled to the individual transmitters.
9. The wireless communication system of claim 8 wherein the system
further includes:
a. a plurality of receivers; and
b. a processor for determining from the signals reproduced by the
receivers the relative positions of the users.
10. The wireless communication system of claim 9 wherein:
the receivers are mounted on the periphery of a computer screen;
and
the processor moves one or more objects to positions on the screen
that are associated with the positions of one or more of the users
relative to one or more of the receivers.
11. A computer system including:
A. a screen for displaying on-screen objects;
B. a keyboard for data entry to the system;
C. a transmitter for producing low frequency signals, the
transmitter being capacitively coupled to a user to pass to the
user a current that is associated with the low frequency
signals;
D. a plurality of receivers mounted on the periphery of the screen,
each of the receivers in the plurality receiving from the user,
through capacitive coupling to the user, a current that is
associated with the signals produced by the transmitter, the
receivers determining the position of the closest extremity of the
user's body relative to one or more of the receivers; and
E. a processor for controlling the screen display, the processor
directing the screen to display the objects in positions that
correspond to the position of the user's extremity as determined by
the receivers.
12. The computer system of claim 11 wherein the transmitter is
incorporated into the keyboard.
13. The computer system of claim 11 further including a receiver
that is mounted on the keyboard, the receiver determining, based on
the strength of the received signals if the user is selecting the
information that is displayed below the cursor, the system
determining that the user is selecting the information if the
strength of the signals received by the receiver mounted on the
keyboard is above a predetermined threshold.
14. A wireless communication system including:
A. a plurality of transmitters for producing low frequency signals,
the transmitters being capacitively coupled to one or more users
and to ground and, respectively, including a pair of electrodes and
connected between the electrodes a signal generator that generates
low frequency signals, each transmitter passing to the associated
user a current that is associated with the low frequency signals;
and
B. a plurality of receivers coupled to ground for receiving,
respectively, from the one or more users to which they capacitively
couple one or more currents associated with the signals produced by
the transmitters, the receivers reproducing the transmitted
signals; and
C. a processor for determining from the signals reproduced by the
receivers the respective positions of the users relative to one or
more of the receivers.
15. The wireless communication system of claim 14 wherein:
i. the transmitters each, respectively, transmit signals associated
with a different predetermined code; and
ii. the receivers distinguish between the signals produced by the
individual transmitters based on the codes.
16. The wireless communication system of claim 14 wherein the
receivers distinguish between the signals produced by the
individual transmitters based on the times the signals are
transmitted.
17. The wireless communication system of claim 14 wherein:
i. the transmitters each, respectively, transmit signals at
different predetermined frequencies; and
ii. the receivers distinguish between the signals produced by the
individual transmitters based on the frequencies.
18. A system including:
A. a screen for displaying one or more on-screen objects including
a cursor;
B. a keyboard for data entry to the system;
C. a transmitter for producing low frequency signals, the
transmitter being capacitively coupled to a user to pass to the
user a current that is associated with the low frequency
signals;
D. a plurality of receivers mounted on the periphery of the screen,
each of the receivers in the plurality receiving from the user,
through capacitive coupling to the user, a current that is
associated with the signals produced by the transmitter, the
receivers determining the position of the closest extremity of the
user's body relative to one or more of the receivers;
E. a selection receiver mounted on the system for determining,
based on the strength of the received signals, if the user is
selecting the information that is displayed below the cursor, the
system determining that the user is selecting the information if
the strength of the signals received by the selection receiver is
above a predetermined threshold; and
F. a processor for controlling the screen display, the processor
directing the screen to display one or more of the objects in
positions that correspond to the position of the user's extremity
as determined by one or more of the plurality of the receivers.
19. The system of claim 18 wherein the selection receiver is
mounted on the keyboard.
20. The system of claim 19 wherein the system further includes a
plurality of selection receivers.
21. The wireless communication system of claim 1 wherein the
receiver is mounted on an object.
22. The wireless communication system of claim 1 wherein the
receiver is coupled to another user.
23. The wireless communication system of claim 1 wherein the system
further includes:
a. a plurality of transmitters that are capacitively coupled to one
or more users;
b. a plurality of receivers that are displaced from the users;
and
c. a processor for determining from the signals reproduced by the
receivers the positions of the one or more users relative to one or
more of the receivers.
24. The wireless communication system of claim 23 wherein:
i. the transmitters also receive signals; and
ii. the receivers also transmit signals.
25. The wireless communication system of claim 1 wherein:
i. the transmitter also receives signals; and
ii. the receiver also transmits signals.
Description
FIELD OF THE INVENTION
This invention relates generally to the use of small currents
externally induced in people by electrostatic field coupling, and
more particularly, to systems that can be used for wireless
communication among proximate devices, and for sensing a person's
position for use in control tasks.
BACKGROUND OF THE INVENTION
There is a need for personal communication systems that allow
portable devices, such as pagers, telephones, computer terminals,
and so forth, carried on the person to communicate with each other
and with fixed location devices. For example, a user may want to
store in a personal computer a message received over the air by a
paging terminal. Known prior personal communication systems
typically require that these two devices be interconnected by wire,
which makes it cumbersome to affix them to users and/or
interconnect them to each other, and thus, inconvenient to use.
In medical environments, systems for gathering information such as
blood pressure, EKG readings, and so forth typically require that
instruments taking the readings from a patient be connected, by
wire, to a patient-carried system component that monitors or stores
the information. These system are also cumbersome to affix to a
user.
In other applications, wireless systems are currently used to
transmit information between system components by, for example,
radio waves, microwaves, infra-red signals and so forth. These
systems may not be suitable for sending information between the
user-mounted system components discussed above because of problems
with interference in the immediate environment or between the
signals transmitted from the various devices.
For example, devices in systems that use infra-red signals should
optimally communicate with line-of-sight transmissions, which are
not always possible between devices carried by a user. Further, the
infra-red systems suffer from interference with ambient light,
which can not always be controlled by the user. And, for systems
transmitting signals at high frequencies, the users' bodies absorb
the radiating energy, and thus, degrade the signals.
Further, such systems are subject to government regulation, since
their signals radiate significantly. Also, these systems allow
others to eavesdrop on the transmissions.
Wireless transmission systems have also been used to determine
relative position. Such systems determine the position of a
transmitter based on the timing or strength of signals received by
various receivers. These systems are not well suited for and can be
unreliable for determining position and orientation at close
distances.
SUMMARY OF THE INVENTION
The invention is a wireless system in which a transmitter and a
receiver are coupled through a user and room ground, rather than by
wire or by optical or high frequency transmitted signals. The
transmitter produces low-frequency, low power signals that, through
capacitive coupling, pass as displacement currents into and from
the body of the user. The user's body acts as a conductive node and
a receiver that is capacitively coupled to the user's body responds
to the displacement currents passed to it from the body, to detect
the low frequency signals. The user's body thus becomes part of the
system rather than an impediment to signal propagation. Also, since
the transmitter and receiver do not couple with one another
directly, the shared room ground provides the return path for the
current.
The transmitter includes a signal generator and a pair of
electrodes, referred to hereinafter as inner and outer electrodes.
The signal generator produces modulated signals that vary the
voltage between the electrodes. The inner electrode is closely
coupled capacitively to the user's body such that the
"quasi-electrostatic" field resulting from the electrode potential
causes a displacement current to pass to the user's body. The outer
electrode is oriented so that its coupling to the room ground is
stronger than that of the inner electrode, such that room ground
acts as a return path for the current from the receiver.
The signal generator may modulate the information to be transmitted
using, for example, a pseudorandom code, to produce spread spectrum
signals. This increases noise immunity and allows multiple
transmitters, each using a different modulation code, to operate at
the same time.
The receiver includes a pair of electrodes and a
detector/demodulator that acquires and tracks the spread spectrum
signal. One of the electrodes is closely coupled capacitively to
the user's body such that displacement current that passes from the
body passes to that electrode. The current then flows through
detector circuitry to the other electrode, which is asymmetrically
coupled capacitively to room ground, to complete the path for the
current. The current varies in accordance with the current passed
to the body from the transmitter, and thus, in accordance with the
signals produced by the signal generator.
The detector circuitry detects the current and operates in a
conventional manner to recover the transmitted information
therefrom.
There are a number of uses for the system--to communicate
information both "intra-body" and "inter-body," to receivers that
are capacitively coupled to the user. The system may also be used
as a position-sensor, with an array of multiple receivers
determining the position of the person based on the relative
strengths of the received signals coupled out of the person. Since
the signals are not transmitted as radiated energy, small (compared
to a wavelength) and essentially flat electrodes may be used in the
transmitters and receivers. These electrodes efficiently couple to
the user by virtue of their surface area and can, for example, be
readily incorporated into a watch, a credit card sized component, a
shoe, and so forth. These electrodes are in contrast to the
antennas required to efficiently transmit and receive radiated
energy. Moreover, since there is negligible radiation of the
electromagnetic energy from the electrodes, the system does not
fall under government regulations directed to transmitting systems.
Further, the system does not have the problem that planar
capacitive sensing system have with transmitting over an
intervening ground plane.
In one configuration the system passes information between carried
or worn components of, for example, a paging system. In this
configuration a users carries in his pocket a paging terminal that
includes a transmitter. The user also wears a watch that includes a
display and a receiver. Both the transmitter and the receiver are
capacitively coupled to the user and to room ground, such that
signals from the transmitter pass to the receiver as displacement
currents to and from the user, respectively. When the paging
terminal receives a paging message over the air, the transmitter
passes the message to the receiver for display. The transmitter
passes the message to the user as a displacement current, and the
receiver receives the message from the user as a displacement
current.
In an alternative configuration the system passes to a receiver
that is worn or carried by a user, information from medical
instruments that are monitoring the physiological condition of the
user. In this configuration, each of the medical instruments is
connected directly to an associated transmitter that is worn by the
user. Each of these transmitters is capacitively coupled to the
user and to room ground, such that the signals are passed as
displacement currents to the user and from the user to the
receiver.
In an alternative embodiment, a transmitter carried by the user
passes signals to one or more nearby receivers carried by other
users or located in fixed positions. In the quasi-electrostatic
field produced by the transmitter the user is capacitively coupled
to the receivers through the atmosphere. Accordingly, the user need
not physically contact the receivers to pass information to them.
For example, two users shaking hands may transfer information
between transmitters and receivers they each carry. The proximity
of the hands provides a conductive path for the signal current. The
return path can be a combination of air and earth ground. Any
materials in the vicinity of the transmitter and receiver, such as
metal cabinets, reinforcement studs, and so forth, also contribute
to the return path.
An alternative system may be incorporated into a general-purpose
computer and provide the user with a multi-dimensional input
device. Such a system includes an array of receivers and one or
more transmitters. The array of receivers are mounted around the
periphery of the computer screen and the transmitter may be carried
by the user or mounted on, for example, the side of a keyboard.
The user repositions an on-screen object in two-dimensional space
or three-dimensional virtual space displayed on the screen by
making contact with the transmitter with one hand, for example, his
left hand, and moving his right in front of the screen. A processor
connected to the receivers in the array determines, based on the
relative strengths of the received signals, the relative position
of the user's right hand and moves the object to the corresponding
on-screen position.
To allow a user to select, or "click on," a particular on-screen
object, one or more auxiliary receivers may be mounted on the key
board, for example, below the space bar. The user directs the
object to a desired location by moving his right hand in front of
the screen and clicks on that location by moving the thumb of this
left hand closer to the auxiliary receiver in the keyboard. Since
the user need not make contact with the auxiliary receiver, the
receiver can be combined with, or incorporated directly into, the
spacebar or one or more keys of the keyboard.
When the system is be used to move three-dimensional objects or the
user, that is, move the user's viewpoint, in three-dimensional
virtual space, the array of receivers senses the relative position
of the user's hand in front of the screen and based on that
position determines if the user desires to move through the virtual
space forward, backward, up, down, left or right, and also how fast
the user desires to move, as discussed in more detail below. In
addition, a foot pedal may be used as an accelerator to further
control the "granularity" of the movement of the user through the
virtual space, as discussed below.
The system may include a portable, scalable receiving device that
consists of an array of three orthogonal electrodes that are,
respectively, connected to three receivers. A processor connected
to the three receivers determines, based on the signals received by
the individual receivers, the relative position of the user. The
electrodes are extended or collapsed, as necessary, to accommodate
the relative scale of the user's physical movements to the
movements of the user within, for example, the three-dimensional
virtual space displayed on an associated screen.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and further advantages of the invention may be better
understood by referring to the following description in conjunction
with the accompanying drawings, in which:
FIG. 1 is a functional block diagram of a system constructed in
accordance with the invention;
FIG. 2 is a simplified schematic of the system of FIG. 1 showing
typical numbers for capacitances;
FIG. 3 is a functional block diagram of a transmitter and receiver
of FIG. 1;
FIG. 4 illustrates an exemplary use of the system with a plurality
of transmitters;
FIG. 5 illustrates an alternative use of the system;
FIG. 6 illustrates an alternative configuration of the system;
FIG. 7 illustrates a use of the system as part of a personal
computer;
FIG. 8 illustrates a use of the system as part of laptop
computer;
FIG. 9 depicts a scalable receiver; and
FIG. 10 depicts an alternative system.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
FIG. 1 depicts a user 10 who has attached to one arm 12 a
transmitter 14 that consists of a signal generator 16 connected
between a pair of electrodes 18 and 20, referred to individually as
an inner electrode 18 and an outer electrode 20. As discussed in
more detail below, the inner and the outer electrodes 18 and 20 are
capacitively and assymetrically coupled, respectively, to the user
10 and to room ground denoted in the drawing by the numeral 11. The
signal generator 16 produces between these electrodes 18 and 20 a
voltage that gives rise to a quasi-electrostatic field depicted in
the drawing by solid lines 15. A resulting displacement current
passes between the inner electrode 18 and the user 10. A portion of
this current flows through the user in a path 13, depicted in the
drawing by a dotted line, and passes as a displacement current to a
receiver 22 that is attached to the user's other arm 12.
The receiver 22 includes a detector 28 and a pair of electrodes 24
and 26, referred to individually as an inner electrode and an outer
electrode. The inner electrode 24 is closely coupled capacitively
to the user 10 and the outer electrode 26 is coupled capacitively
to room ground, such that a displacement current passes from the
user 10 to the inner electrode 24. The current then flows through
the detector 28 to ground, and thus, back to the transmitter 14.
The detector 28 detects the current and extracts therefrom the
transmitted information.
Current flows also along other paths (not shown) through the user.
Most notably, the current flows from the user to room ground. This
results in an attenuation of the current that passes to the
receiver 22. Accordingly, the receiver must be capable of
detecting, or measuring, relatively small currents.
The transmitter 14 may modulate the signals by using, for example,
direct-sequence spread spectrum modulation. This increases the
system's immunity to noise. Also, it allows multiple transmitters,
each using a different modulation code, to transmit information at
the same time, as discussed in more detail below. Alternatively,
the modulation may instead be simply binary on/off modulation, and
if multiple transmitters are used each transmits at a different
frequency.
A simplified electrical model of the wireless system is shown in
FIG. 2. The signal generator 16 produces low frequency signals,
preferably between 100 and 1000 kilohertz. At these frequencies and
with the relative impedances involved in the circuit, the user can
be considered as a conductive node 40.
The signal generator 16 is connected between two nodes 30 and 31
that represent, respectively, the inner and outer electrodes 18 and
20. The signals produced by the signal generator 16 result in a
current passing from node 30 to a node 40, to which it is coupled
by a capacitance 36. The current passes from the user-node 40 to a
node 43 that represents the inner electrode 24 of the receiver 22.
A capacitance 46 represents the coupling between these two nodes.
The current then flows through the receiver 22, that is, through a
detector 47 and node 44, to ground through a coupling represented
by a capacitance 48. The node 31 of the transmitter provides the
return path for the current, as represented by a capacitance
34.
There is direct capacitive coupling between the electrodes 18 and
20 of the transmitter 14, as represented by a capacitance 35
between the nodes 30 and 31. The node 30 is also capacitively
coupled to the receiver 22, through the air, by a capacitance 38.
This coupling is relatively weak, however, because of the distance
between the transmitter and the receiver.
The node 31 is coupled to the user-node 40, through the air, as
represented by a capacitance 32. This coupling provides additional
current paths for the transmitted signal traveling through the
user-node 40.
The user-node 40 is coupled to ground, as represented by a
capacitance 42. This coupling shorts a relatively large portion of
the current to ground, and thus, significantly attenuates the
current passed from the user to the receiver.
The coupling from the inner electrode 24 to the outer electrode 26
of the receiver is represented by a capacitance 45. If the detector
47 is detecting current, this coupling has little affect since the
current measuring resistance, denoted by R in the drawing, of the
amplifier 47 is typically smaller than the impedance of the
capacitance 45. If the detector 47 is detecting a potential, the
coupling between the nodes creates a current leakage path through
the receiver 22 to ground.
Referring now to FIG. 3, the transmitter preferably includes the
signal generator 16 and a direct-sequence spread spectrum modulator
29. The modulator modulates the signals produced by the signal
generator in accordance with a pseudorandom code, and supplies the
modulated signal through a tank resonator 50 to the electrodes 18
and 20. The tank resonator 50 converts square waves to sine waves
at the frequency of interest, without radiating energy at the
higher-frequency components of the square wave.
The receiver 22 includes the amplifier 47, which amplifies a signal
that corresponds to the displacement current that passes from the
user to the inner electrode 24, though a synchronous detector 52 to
the outer electrode 26. A synchronous detector 52, operating in a
conventional manner, demodulates the signal and reproduces the
transmitted information.
As discussed, multiple transmitters 14 may be included in the
system. Each transmitter uses a different pseudorandom code in its
modulator 29. This allows the receiver to distinguish the signals
transmitted simultaneously by various transmitters, based on the
codes. Alternatively, the transmitters may transmit at different
carrier frequencies or at different times, in which case the
receiver distinguishes between the various signals based on these
frequencies or times of transmission.
FIG. 4 depicts one application for the system. In this
configuration the system is incorporated into various components of
a paging system that the user wears or carries. The user carries,
for example, in his pocket, a paging terminal 60 that receives
paging messages over the air in a conventional manner. The paging
terminal includes the transmitter 14, which is capacitively coupled
to the user and to ground. The transmitter produces signals that
include information from the received messages and passes the
signals to the user as displacement currents.
A display device 62 that is incorporated in, for example, the
user's watch 64, includes a receiver 22 that is capacitively
coupled to the user. The receiver 22 reproduces the signals from
the displacement current passed to it, and the display then
presents the information included therein to the user. The watch 64
may also include one or more buttons (not shown) that a user may
use to select, for example, storage options for the paging
messages. The various system components may instead be incorporated
into the user's glasses 66, shoes 68, belt buckle 70, and so
forth.
There is no wire connection between the receiver and the
transmitter, since they are each capacitively coupled to the user
and to room ground, and thus, communicate through the user's body.
Accordingly, the system does not interfere with the user's clothing
or restrict his movements.
Another application for the wireless system is to pass information
that represents the user's physiological condition between a
plurality of transmitters and a receiver that are each capacitively
coupled to the user. Referring now to FIG. 5, a plurality of
transmitters 14.sub.1,14.sub.2,14.sub.3 . . . are connected,
respectively, to instruments 74.sub.1,74.sub.2,74.sub.3 . . . that
measure blood pressure, take EKG readings, and so forth. Each
transmitter receives data from the associated instrument and
produces modulated signals that include the data. These signals
result in displacement currents passing between the transmitters
and the user 10 and from the user 10 to the receiver 22, which is
connected to a recorder 76 that records the data.
Referring now to FIG. 6, the system may also be used to pass
signals inter-body to a receiver that is proximate to but not
mounted or carried on the user's body. As discussed above, the
return path for the current is through room ground, and no
connecting wires are required. A user wears the transmitter 14, for
example, as part of his watch 64, and the receiver 22 is mounted on
a door (not shown) or within a doorknob 80 that controls the
opening of the door. The transmitter 14 produces a modulated signal
that includes a personal identification number. This signal is
capacitively coupled to the receiver 22 when the user grasps or
comes sufficiently close to the doorknob. The receiver 22
determines if it recognizes the number, and if so locks or unlocks
the door, as appropriate.
Similarly, two users shaking hands can each exchange information
between receivers and transmitters that they are carrying, to
exchange, for example, electronic business cards.
Other applications of the system are discussed below, with
reference to FIGS. 7 and 8. In these applications an array 102 of
receivers 22 is at a fixed location. The receivers 22 determine the
relative position of a user-carried transmitter from the relative
strengths of the received signals.
FIG. 7 depicts the wireless system incorporated into a personal
computer 100. The system provides to the user a multi-dimensional
input device that allows a user, with hand gestures, to move in two
dimensions an on-screen object such as a cursor, or in three
dimensions a three-dimensional on-screen object or herself, that
is, her viewpoint, through a virtual space that is displayed on the
screen.
The system includes the array 102 of receivers 22, which are
mounted in close proximity to a screen 104 of a monitor 106. The
transmitter 14 is incorporated into a foot pedal 108 that the user
contacts when she desires to move an on-screen object or, her
virtual space viewpoint.
The user places her foot 110 on the foot pedal 108 and moves one of
her hands 112 in front of the screen 104. As discussed above, the
transmitter 14 is capacitively coupled to the user 10 and to
ground. The signals produced by the transmitter 14 are passed as
currents through the user and from the user's hand 112 to the array
102 of receivers 22. A processor 111a, which is housed in the
computer drive 111, connected to receive signals from the array 102
determines the relative position of one or both of the user's
hands, based on the relative strengths of the signals received by
the various receivers. The processor then moves, for example, the
on-screen object to a corresponding location on the screen.
When the system is used to move the user or an object in a
three-dimensional virtual space that is displayed on the screen,
the system determines where the user's hand is relative to a
predetermined "neutral" position that corresponds to a mid-point in
the range of movement to which the receiver responds. If, for
example, the receiver responds to movements of the user's hand when
the hand is at most one meter from the screen and ten centimeters
to the left, right, above or below the screen, the neutral position
is the center of the screen at the distance between the screen and
one meter that corresponds to the middle of the operational range
of the receivers.
If the user moves one of her hands between the neutral position and
the screen the system moves the user forward through the virtual
space. If the user also moves one of her hands to the left of the
neutral position, the system moves the user at a corresponding
angle to the left in the space, and so forth. As the user moves one
or both of her hands farther and farther from the neutral position,
the system moves the user faster and faster through the virtual
space in the direction that corresponds to the relative position of
the user's hand.
In an alternative arrangement of this system, the transmitter 14 is
included on the keyboard 116 or in a chair cushion 114, instead of
in the foot pedal 108. In this arrangement, the foot pedal may
optionally be used to control the "granularity" of the user's
movement in the virtual space, that is, to control the scale of the
movements through the space. The user depresses the foot pedal to
speed the user's overall movement in the virtual space and released
to slow that movement. If, for example, the user is moving between
buildings in the virtual space she depresses the foot pedal to
accelerate her progress through the space and repositions her hand
to regulate and direct the accelerated movements. When the user
enters a room in the building, she releases the foot pedal to slow
her movements, and again uses her hand to regulate and direct the
decelerated movements.
The wireless system readily translates the three-dimensional
movements of a user's hand to movements of the user through
three-dimensional virtual space. This is in contrast to input
devices that operate in two-dimensions and cannot readily convey
simultaneously backward or forward, up or down, and left or right
movements to the on-screen objects. Further, the user may direct
the movement using one or both of her hands, as appropriate.
Referring now to FIG. 8, a laptop computer 120 incorporates the
wireless system to replace the mouse and/or control the movement of
the user through three-dimensional virtual space. The array 102 of
receivers 22 is mounted adjacent to the screen 104 in the lid 121
of the laptop. The transmitter 14 is incorporated into the base 122
of the laptop, on one side of or next to the keyboard 116. A user
touches the transmitter 14 with one hand, for example, her left
hand, and controls the movements of objects displayed on the screen
by positioning her right hand in front of the screen, as discussed
above with reference to FIG. 7
One or more auxiliary receivers 22a may be mounted on the keyboard
116, to allow a user to select, or "click on," a particular
on-screen object. The user makes her selection by moving the thumb
of her left hand proximate to the appropriate auxiliary receiver
22a.
FIG. 9 depicts a portable, scalable input device 200 that consists
of an array 201 of receivers 22. The array includes three
orthogonal, electrically isolated electrodes 201-203 that are part
of three receivers 22. Each electrode is capacitively coupled,
through the air and through room ground, to a user (not shown) who
is nearby. A processor 205 connected to process the signals
received by the electrodes determines the relative position of the
user based on the strengths of the signals received by each of the
electrodes. This array may be used instead of the array 102
depicted in FIGS. 7 and 8.
The electrodes 201-203 can be extended or collapsed over a range of
several inches to two feet, as necessary, to scale the expected
range of movement of the user or users to the range of movements of
on-screen objects in, for example, three-dimensional virtual space.
The electrodes can be selectively extended and collapsed to
accommodate fully the expected range of movement. The device 200,
when collapsed fits into a pocket for easy transport.
FIG. 10 illustrates an alternative wireless system that includes
multiple receivers 22 that are connected to lines 204. The lines
are arranged in a grid 206 and may be included in a rug or floor. A
user carries a transmitter 14, preferably in his or her shoes. The
wireless system determines the position of the user by determining
which receivers receive the strongest signals from the transmitter.
The receivers distinguish individual users based on the modulation
codes associated with their respective transmitters. Again, the
return path for current is through room ground, and thus, the
transmitter and receiver electrodes pass the signals capacitively
instead of as radiated energy.
The foregoing description has been limited to a specific embodiment
of this invention. It will be apparent, however, that variations
and modifications may be made to the invention, with the attainment
of some or all of its advantages. Therefore, it is the object of
the appended claims to cover all such variations and modifications
as come within the true spirit and scope of the invention.
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