MXPA97008271A - System for detection without direct contact and signal sending, using the human body as a means of signal transmission - Google Patents

Abstract

The present invention relates to a wireless system includes a transmitter (14) and a receiver (22) that are coupled through a user (10) and the site earth (11). The transmitter produces signals of low frequency, low power that, through the capacitive coupling, pass as displacement current (13) to and from the body of the user. The land of the shared site provides the path back to the current. The transmitter includes an internal electrode (18) and an external electrode and a signal generator (16) that produces modulated signals that vary the voltage between the electrodes. The internal electrode is tightly coupled in a capacitive manner with the body of the user in such a way that the "nearly electrostatic" field resulting from the potential of the electrode causes a displacement current to pass to the body of the user. The external electrode is oriented so that its coupling with the earth of the site is more intense than that of the internal electrode, such that the earth of the site acts as a return path for the current from the receiver. The receiver similarly includes a pair of electrodes (24, 26) and also a detector / demodulator (28) that acquires and directs the transmitted signal. One of the electrodes of the receiver (24) is coupled capacitively narrowing with the user's body in such a way that the displacement current that passes from the body passes to that electrode. The current then flows through the detector circuit to the other electrode (26) which is symmetrically coupled in capacitive manner with the site earth to complete the path for the current. The detector circuit detects the current and operates in a conventional manner to recover the transmitted information. One or more receivers may be carried by other users or may be placed in a fixed position around a room, and the return path may be a combination of air and ground. Therefore, the user does not need to physically contact the receivers to pass the information to them. Alternatively, receivers can be mounted as a formation on a computer screen, with the transmitter being placed on the key

Description

"SYSTEM FOR DETECTION WITHOUT DIRECT CONTACT AND SENDING OF SIGNALS, USING THE HUMAN BODY AS A MEANS OF TRANSMISSION OF SIGNALS" 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 with systems that can be used for wireless communication between nearby devices and to detect a person's position for use in tasks of control.

BACKGROUND OF THE INVENTION There is a need for personal communication systems that allow portable devices such as radiolocation devices, telephones, computer terminals and so on in person to communicate with each other and with fixed location devices. For example, a user may wish to store on a personal computer a message received over the air via a radiolocation terminal. The communication systems Previously known personal features typically require these two devices to be interconnected by wire, which makes it difficult to fix them to users and / or interconnect them with one another and therefore, inconvenient to use. In medical environments, systems for collecting information, such as blood pressure, EKG readings and so on, typically require instruments that take a patient's readings to connect, via wire, to a component of the system worn by the patient that supervises or stores the information. These systems are also cumbersome to fix on a user. In other applications, wireless systems are currently used to transmit information between the system components by for example radio waves, microwaves, infrared signals and so on. These systems may not be suitable for sending information between the components of the user-mounted system discussed above due to problems with interference in the immediate environment or between the signals transmitted from the different devices. For example, devices in systems that use infrared signals must communicate optimally with visual line transmissions, which are not always possible between devices carried by a user. In addition, infrared systems suffer from interference with ambient light, which can not always be controlled by the user. And for systems that transmit signals at high frequencies, the bodies of the vessels absorb the radiation energy and therefore, degrade the signals. In addition, these systems are subject to government regulations, since their signals radiate significantly. Also, these systems allow other people to furtively listen to the transmissions. Wireless transmission systems have also been used to determine the relative position. These systems determine the position of a transmitter based on the synchronization or intensity of the signals received by the different receivers. These systems are not well suited and can be unreliable to determine position and orientation at close distances.

COMPENDIUM OF THE INVENTION The invention is a wireless system in which a transmitter and a receiver are coupled through a user and the site earth instead of wires or through optical or high-frequency transmitted signals. The transmitter produces signals of low power, low frequency that, through the capacitive coupling, pass as displacement currents to and from the body of the user. The body of the user acts as a conducting node and a receiver that is capacitively coupled to the body of the user that responds to the displacement currents passed thereto from the body, to detect the low frequency signals. The user's body, therefore, it becomes part of the system instead of an impediment to the propagation of signals. Also, since the transmitter and the receiver do not mesh with each other directly, the shared site earth provides the return path for the stream. The transmitter includes a signal generator and a pair of electrodes, which will be referred to below as internal and external electrodes. The signal generator produces modulated signals that vary the voltage between the electrodes. The internal electrode is tightly capacitively coupled to the user's body in such a way that an "almost-electrostatic" field resulting from the electrode potential causes a current of displacement to pass to the body of the electrode. user. The external lectrode is oriented so that its coupling with the earth of the site is more intense than that of the internal electrode, in such a way that the earth of the site acts as a return path for the current from the receiver. The signal generator can modulate the information to be transmitted using, for example, a pseudorandom code, to produce scattered spectrum signals. This increases the immunity to noise 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 requires and follows the signal of the scattered spectrum. One of the electrodes is tightly coupled capacitively with the user's body in such a way that the displacement current that passes from the body passes to that electrode. The current then flows through the detector circuit to the other electrode which is capacitively asymmetrically coupled to the site ground to complete the path for the current. The current varies according to the current passed to the body from the transmitter and, therefore, in accordance with the signals produced by the signal generator.

The detector circuit 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 to both "intra-body" and "inter-body" receivers that are capacitively coupled with the user. The system can also be used as a position sensor, with a formation of multiple receivers that determine the appearance of the person based on the relative intensities of the signals received coupled outside the person. Since signals are not transmitted as irradiated energy, small (compared to a wavelength) and essentially flat electrodes can be used in transmitters and receivers. These electrodes are efficiently coupled to the user due to their surface area and, for example, can be easily incorporated into a watch, a credit card size component, a shoe and so on. These electrodes are in contrast to the antennas required to efficiently transmit and receive the radiated energy. In addition, since there is negligible radiation of electromagnetic energy from the electrodes, the system is not under government regulations directed to the transmission systems. In addition, the system does not have the problem that the Flat capacitive detection system with transmission through a ground plane of intervention. In one configuration, the system passes the information between the carried or used components of, for example, a radiolocation system. In this configuration, a user carries in his pocket a radiolocation terminal that includes a transmitter. The user also uses a watch that includes a presentation device and a receiver. Both the transmitter and the receiver are capacitively coupled to the user and to the site ground, such that the signals from the transmitter pass to the receiver as displacement currents to and from the user, respectively. When the radiolocation terminal receives a radiolocation message over the air, the transmitter passes the message to the receiver for presentation. 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 used and carried by a user, the information of the medical instruments that are monitoring the physiological condition of the user. In this configuration, each medical instrument is connected directly to an associated transmitter that is used by the user. Each of these transmitters is capacitively coupled to the user and to the site ground in such a way that the signals are passed as displacement currents to the user and from the user to the receiver. In an alternative modality, a transmitter carried by the user passes the signals to one or more of the nearby receivers carried by other users or placed in fixed positions. In the quasi-electrostatic field produced by the transmitter, the user is capacitively coupled to the receivers through the atmosphere. Therefore, the user does not need to physically contact the receivers to pass information to them. For example, two users who shake hands can transfer information between the transmitters and receivers that each of them carries. The proximity of the hands provide a conductive path for the signal current. The return path can be a combination of air and ground. Any of the materials in the vicinity of the transmitter and receiver, such as metal cabinets, short reinforcing pins and so on, also contribute to the return path.

An alternative system can be incorporated into a computer for general purposes and provide the user with a multidimensional input device. This system includes a formation of receivers and one or more transmitters. Receiver formation is mounted around the periphery of the computer screen and the transmitter can be carried by the user or mounted, for example, on the side of a keyboard. The user returns to place the object on the screen in two-dimensional space or in the virtual three-dimensional space presented on the screen, making contact with the transmitter with one hand, for example, his left hand and, moving his right forward from the screen. A processor connected to the receivers in the formation determines, based on the relative intensities of the received signals, the relative position of the user's right hand and moves the object to the position in the corresponding screen. To allow a user to select, or "connect" to, an object on the specific screen, one or more auxiliary receivers can be mounted on the keyboard, for example, below the slash bar. The user directs the object to a desired location by moving his right hand forward of the screen and connects that location by moving the thumb of his left hand closer to the auxiliary receiver on the board. Since the user does not need to make contact with the auxiliary receiver, the receiver can be combined with or incorporated directly into the slash bar or one or more of the keyboard keys. When the system is going to be used to move three-dimensional objects or the user, that is, moves the visual point of the user in the three-dimensional virtual space, the receiver formation detects the relative position of the user's hand in front of the screen and based on that position, determines whether the user wants to move through the virtual space forward, backward, upward, downward, leftward or rightward, and also how quickly the user wants to move, as will be discussed in more detail continuation. In addition, a pedal can be used as an accelerator to further control the "granularity" of the user's movement through the virtual space, as will be discussed below. The system may include a portable, scalable receiver device consisting of three orthogonal electrodes that respectively connect with three receivers. A processor connected to the three receivers determines, based on the signals received by the individual receivers, the relative position of the receiver. 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 virtual three-dimensional space presented in an associated display.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned and other advantages of the invention can be better understood by reference to the following description together with the accompanying drawings, in which: Figure 1 is a functional block diagram of a system constructed in accordance with the invention; Figure 2 is a simplified schematic view of the system of Figure 1, showing the typical numbers for capacitance; Figure 3 is a functional block diagram of a transmitter and a receiver of Figure 1; Figure 4 illustrates an exemplary use of the system with a plurality of transmitters; Figure 5 illustrates an alternative use of the system; Figure 6 illustrates an alternative configuration of the system; Figure 7 illustrates a use of the system as part of a personal computer; Figure 8 illustrates a use of the system as part of the laptop by battery; Figure 9 illustrates a scalable receiver; and Figure 10 illustrates an alternative system.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE MODALITIES Figure 1 illustrates a user 10 having attached to an arm 12 a transmitter 14 consisting of a signal generator 16 connected between a pair of electrodes 18 and 20, which is referred to individually as an internal electrode 18 and an electrode 18 external. As will be discussed in more detail below, the internal and external electrodes 18 and 20 are capacitively and asymmetrically coupled respectively to the user 10 and to the site ground represented in the drawing by the number 11. The signal generator 16 produces between these electrodes 18 and a voltage that results in an almost-electrostatic field illustrated in the drawing by solid lines. A resulting displacement current passes between the internal electrode 18 and the user 10. A portion of this current flows through the user in a path 13, illustrated in the drawing by a dotted line and passes as a displacement current to a receiver 22 which is fixed to the other arm 12 of the user. The receiver 22 includes a detector 28 and a pair of electrodes 24 and 26, which are referred to individually as an internal electrode and an external electrode. The internal electrode 24 is tightly coupled in a capacitive manner to the user 10 and the electrode 26 is capacitively coupled to the site ground in such a way that a displacement current passes from the user 10 to the electrode 24. The current then flows through the detector 28 to ground and in this way back to transistor 14. Detector 28 detects the current and extracts the transmitted information from it. The current also flows along other trajectories (not illustrated) through the user. Most notably, the current flows from the user to the site earth. This results in an attenuation of the current that passes to the receiver 22. Therefore, the receiver must be able to detect or measure relatively small currents. The transmitter 14 can modulate the signals using, for example, dispersion spectrum modulation of direct sequence. This increases the immunity of the system to noise. It also allows multiple transmitters each using a different modulation code, to transmit the information at the same time, as discussed in more detail below. Alternatively, the modulation may instead be simply connected-disconnected binary modulation and if multiple transmitters are used, each transmits at a different frequency. A simplified electrical model of the wireless system is shown in Figure 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 driver node. The signal generator 16 is connected between two nodes 30 and 31 representing, respectively, the internal and external electrodes 18 and 20. The signals produced by the signal generator 16 result in a current passing from the nodule 30 to a nodule. 40 to which is coupled by a capacitance 36. The current passes from the nodule 40 of the user to a nodule 43 representing the internal electrode 24 of the receiver 22. A capacitance 46 represents the coupling between these two nodes. The current then flows through the receiver 22, i.e., through a detector 47 and the nodule 44, the ground through a coupling represented by a capacitance 48. The nodule 31 of the transmitter provides the return path for the current , as represented by a capacitance 34. Direct capacitive coupling is present between the electrodes 18 and 20 of the transmitter 14, as represented by a capacitance 35 between the nodes 30 and 31. The nodule 30 is also capacitively coupled to the receiver 22 through of the air, by means of a capacitance 38. This coupling is relatively weak, however, due to the distance between the transmitter and the receiver. The nodule 31 is coupled to the nodule 40 of the usuaur via air, as represented by a capacitance 32. This coupling provides additional current paths for the transmitted signal traveling through the nodule 40 of the user. The user's node 40 is coupled to ground, as represented by a capacitance 42. This coupling short-circuits a relatively large portion of the current to ground, and therefore therefore, it significantly attenuates the current that has passed from the user to the receiver. The coupling from the internal electrode 24 to the external electrode 26 of the receiver is represented by a capacitance 45. If the detector 47 is detecting the current, this coupling has little effect since the current measuring resistance, represented by R in the drawing of FIG. amplifier 47, is typically smaller than the impedance of capacitance 45. Detector 47 is detecting a potential, the coupling between the nodes creates a current leakage path through receiver 22 to ground. Referring now to Figure 3, the transmitter preferably includes a signal generator 16 and a direct sequence spread spectrum modulator 29. The modulator modulates the signals produced by the signal generator in accordance with the pseudorandom code, and supplies the modulated signal through a tank resonator 50 to the electrodes 18 and 20. The tank resonator 50 converts the square waves into sine waves. at the frequency of interest, without radiating energy in the higher frequency components of the square wave.

The receiver 22 includes an amplifier 47, which amplifies a signal corresponding to the displacement current that passes from the user to the internal electrode 24 through a synchronous detector 52 towards the external electrode 26. A synchronous detector 52, which operates in a conventional manner, demodulates the signal and produces the transmitted information. As discussed, multiple transmitters 14 can 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 the different transmitters based on the codes. Alternatively, the transmitters may transmit at different or different times at different times, in which case the receiver distinguishes between the different signals based on these frequencies or transmission times. Figure 4 illustrates an application for the system. In this configuration, the system is incorporated into the different components of a radiolocation system that the user uses or carries. The user carries, for example, in his pocket a radiolocation terminal 60 receives the radiolocation messaging via the air in a conventional manner. The terminal - lí Radiolocation includes the transmitter 14, which is capacitively coupled with the user and with ground. The transmitter produces signals that include information of the received messages and passes the signals to the user as displacement currents. A display device 62 that is incorporated, for example, in the user's clock 64, includes a receiver 22 that is capacitively coupled to the user. The receiver 22 reproduces the signals of the displacement current based thereon, and the presentation device then presents the information included in the same user. The clock 64 may also include one or more buttons (not shown) that a user may use to select, for example, storage options for the radiolocation messages. The various components of the system can instead be incorporated into the user's glasses 66, the shoes 68, the buckle of the belt 70 and so on. There is no wire connection between the receiver and the transmitter, since they are capacitively coupled with the user and the site ground and therefore, communicate through the body of the user. Therefore, the system does not interfere with the user's clothing or restrict his movements.

Another application for the wireless system is to pass the information representing the physiological condition of the user between a plurality of transmitters and a receiver that each is capacitively coupled with the user. Referring now to Figure 5, a plurality of transmitters 14] _, 142, 143- ..., respectively, are connected to the instruments 74] _, 742, 7¿ ^ 3 '•••. which measures the blood pressure, takes the ECG readings and so on. Each transmitter receives the data of the associated instrument and produces modulated signals that include the data. These signals result in the displacement currents that pass between the transmitters and the user 10 and from the user 10 to the receiver 22, which is connected to a recording apparatus 76 that records the data. Referring now to Figure 6, the system can also be used to pass inter-body signals to a receiver that is close to but not mounted or carried in the user's body. As discussed above, the return path for the current is through the earth of space and connection wires are not required. A user uses the transmitter 14 for example as part of his watch 64 and the receiver 22 is mounted on a door, (not shown) or inside a door handle 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 holds or arrives sufficiently close to the door handle. The receiver 22 determines whether it recognizes the number and if so, closes or disengages the door, as appropriate. Similarly, two users who shake hands can exchange information between the receivers and the transmitters they may be carrying to exchange, for example, electronic business cards. Other applications of the system are discussed below with reference to Figures 7 and 8. In these applications, a receiver array 102 is in a fixed location. The receivers 22 determine the relative position of the transmitter carried by the user from the relative intensities of the received signals. Figure 7 illustrates the wireless system incorporated into a personal computer 100. The system provides the user with a multidimensional input device that allows a user, with hand gestures, to move an object on the screen in two dimensions, such as a cursor, or in three dimensions a object on the three-dimensional screen or likewise, that is, its point of view through a virtual space that is presented on the screen. The system includes the formation 102 of the receivers 22 which is mounted in close proximity to a screen 104 of a monitor 106. The transmitter 14 is incorporated in a pedal 108 with which the user makes contact when he wishes to move an object on the screen or , your virtual point of view. The user places his foot 110 on the pedal 108 and moves one of his hands 112 forward of the screen 104. As discussed above, the transmitter 14 is capacitively coupled to the user 10 and ground. The signals produced by the transmitter 14 are passed as streams through the user and from the user's hand 112 to the formation 102 of the receivers 22. A processor (not shown) connected to receive signals from the array 102 determines the position reltative of one or both of the user's hands, based on the relative intensities of the signals received by the different receivers. The processor then moves, for example, the object on the screen to a corresponding location on the screen. When the system is used to move the user or an object or in the three-dimensional virtual space that is presented in the screen, the system determines whether the user's hand is relative to a predetermined "neutral" position corresponding to an intermediate point in the movement scale to which the receiver responds. If for example, the receiver responds to the movements of the user's hand when the hand is at a distance of a meter from the screen, 10 centimeters to the left, right, above or below the screen, the neutral position is the center of the screen in the distance between the screen and a meter that corresponds to the middle part of the scale of operation of the receivers. If the user moves one of his 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 his hands to the left of the neutral position, the system moves the user to a corresponding angle to the left in space, and so on. As the user moves one or both of his hands farther and farther from the neutral position, the system brings the user nine more and more rapidly through the virtual broadsword 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 in the keyboard 116 or in a chair cushion 114, instead of the pedal 108. In this arrangement, the pedal can optionally be used to control the "granularity" of the movement of the pedal. user in the virtual space, that is, to control the scale of movements through space. The user presses the pedal to accelerate the user's total movement in the virtual space and then releases it to slow down that movement. If, for example, the user is moving between the buildings in the virtual space press the pedal to accelerate its advance through space and return to place your hand to regulate and direct the movements. When the user enters a room in the building, he releases the pedal to slow down his movements and again uses his hand to regulate and direct the miscellaneous movements. The wireless system easily translates the three-dimensional movements of a user's hand to user movements through the virtual three-dimensional space. This is in contrast to the input devices that work in two dimensions and can not easily transport the movements simultaneously backwards or forwards, upwards, downwards and to the left or right of the objects on the screen.

In addition, the user can direct the movements using one or both of their hands as appropriate. Referring now to Figure 8, the portable computer 120 per battery incorporates the wireless system to replace the mouse and / or control the movement of the user through the virtual three-dimensional space. The array 102 of receivers 22 is mounted adjacent to the screen 104 on the cover 121 of the portable laptop. The transmitter 14 is incorporated into the base 122 of the battery laptop on one side of or adjacent the keyboard 116. The user touches the transmitter 14 with one hand, for example, his left hand and controls the movements of the objects presented in the screens by placing their right hand in front of the screen as discussed above with reference to Figure 7. One or more receivers 22a or signals may be mounted on the keypad 116 to allow a user to select, or "connect" an object on the specific screen. The user makes his selection by moving the thumb of his left hand, next to the appropriate auxiliary receiver 22a. Figure 9 illustrates a portable step adjustment input device 200 consisting of a formation 201 of receivers 22. The training includes three orthogonal, electrically insulated 202-204 electrodes that are part of three receivers 22. Each electrode is capacitively coupled, through the air and through the site site with a user (not shown) that is a short distance away. A processor (not shown) connected to process the signals received by the electrodes determines the relative position of the user based on the intensities of the signals received by each of the electrodes. This formation can be used instead of the formation 102 illustrated in Figures 7 and 8. The electrodes 202-204 can be extended or collapsed across the scale of several centimeters to 610 meters as necessary to graduate the expected movement scale of the user or users up to the scale of movements in the objects on the screen, for example, in the three-dimensional virtual space. The electrodes can be extended and collapsed selectively to fully accommodate the scale of expected movement. The device 200, when it collapses fits into a pocket for easy transport. Figure 10 illustrates an alternative wireless system that includes multiple receivers 22 that are connected to lines 204. The lines are placed on a grid 206 and can be included in a rug or floor.

A user wears a transmitter 14, preferably in his shoes. The wireless system determines the position of the user by determining which receivers receive the most intense signals from the transmitter. The receivers distinguish the individual users based on the modulation codes associated with their transmitters associated with their respective transmitters. Again, the return path for the current is through the ground of the site and in this way, the electrodes of the transmitter and receiver pass the signals capacitively instead of as radiated energy. The foregoing description has been limited to a specific embodiment of the invention. It will be evident, however, that variations and modifications can be made to the invention with the achievement of some or all of its advantages. Therefore, an object of the appended claims is to cover all those variations and modifications that remain within the true spirit and scope of the invention.

Claims (13)

R E I V I N D I C A C I O N E S:

1. A wireless system that includes: A. a transmitter to produce low frequency signals that include data, the transmitter being capacitively coupled to a user, and ground, the transmitter passes the user through a current that is associated with the low frequency signals; and B. a receiver that is capacitively coupled to the user and to the ground to receive from the user a current that is associated with the signals produced by the transmitter, the receiver produces the transmitted signals and retrieves the data.

The wireless 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 generates 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; Y ii. a signal detector connected between the electrodes, the signal detector reproduces 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: i. a plurality of receivers; and ii. a processor for determining the signals reproduced by the receivers the relative position of the user.

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 relative position of the user.

The wireless communication system of claim 2, wherein the transmitter further includes a signal modulator for the spread spectrum that modulates the signals with a predetermined pseudorandom code.

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 receivers use the codes to distinguish between the signals based from each of the transmitters in the plurality of transmitters.

The wireless communication system of claim 7, wherein each of the transmitters in the plurality of transmitters is capacitively coupled to a different user.

9. The wireless system system of claim 8, wherein the system further includes: a. a plurality of receivers; and b. a processor to determine the signals reproduced by the receivers, the relative position of the users.

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 relative positions of one or more of the users.

11. A system that includes: A. a screen to present objects on the screen; B. a keyboard for entering data into the system; C. a transmitter for producing low frequency signals, the transmitter being capacitively coupled with 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, determining the receptors the relative position of the closest extremity of the user's body; and E. a processor for controlling the presentation of the screen, the processor directs the screen to present the objects in positions corresponding to the position of the end of the user as determined by the receivers.

The computer system of claim 11, wherein the transmitter is incorporated into the keyboard.

13. The computer system of claim 11, which further includes a receiver that is mounted on the keyboard, the receiver determines, based on the intensity of the received signals, if the user is selected the information that is presented below the cursor, determining the system that the user is selecting the information if the intensity of the signals received by the receiver mounted on the keyboard, is above a predetermined threshold. SUMMARY OF THE INVENTION A wireless system includes a transmitter (14) and a receiver (22) that are coupled through a user (10) and the site earth (11). The transmitter produces signals of low frequency, low power that, through the capacitive coupling, pass as displacement current (13) to and from the body of the user. The land of the shared site provides the path back to the current. The transmitter includes an internal electrode (18) and an external electrode and a signal generator (16) that produces modulated signals that vary the voltage between the electrodes. The internal electrode is tightly coupled capacitively with the user's body in such a way that the "quasi-electrostatic" field resulting from the potential of the electrode causes a displacement current to pass to the user's body. The external electrode is oriented so that its coupling with the earth of the site is more intense than that of the internal electrode, such that the earth of the site acts as a return path for the current from the receiver. The receiver similarly includes a pair of electrodes (24, 26) and also a detector / demodulator (28) that acquires and directs the transmitted signal. One of the receiver's electrodes (24) it is closely coupled capacitively to the user's body in such a way that the displacement current that passes from the body passes to that electrode. The current then flows through the detector circuit to the other electrode (26) which is symmetrically coupled in capacitive manner with the site earth to complete the path for the current. The detector circuit detects the current and operates in a conventional manner to recover the transmitted information. One or more receivers may be carried by other users or may be placed in a fixed position around a room, and the return trajectory may be a combination of air and ground. Therefore, the user does not need to physically contact the receivers to pass the information to them. Alternatively, the receivers can be mounted as a formation on a computer screen, with the transmitter being placed on the keyboard.