Patent Publication Number: US-2023152076-A1

Title: System and method for emf manipulation

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system and method for EMF (electromagnetic field) manipulation and in particular, to such a system and method for shaped wave patterning for EMF tracking. 
     BACKGROUND OF THE INVENTION 
     EMF (electromagnetic field) sensors may be used for detecting the position of any attached object and hence may be used for tracking. For example, such sensors may be used to detect the position of humans and/or specific human appendages when attached to a human, for example when worn as an item of clothing. Determining the position of humans and/or specific human appendages may be useful, for example, for virtual reality (VR) or augmented reality (AR) devices. 
     US Published Application No. 20170090568 to Ke-Yu Chen et al describes such an item of clothing, which is a glove that features multiple magnetic field generators at various locations on the glove, for example at the fingertips, and a single magnetic flux density sensor or magnetic field strength sensor at a predetermined position relative to the glove, for example at the wrist. As described, each magnetic field generator includes one or more electromagnets that can be independently driven to result in the creation of a three dimensional magnetic field with known wave-like characteristics and geometry. Furthermore, the magnetic fields generated by each of the electromagnets can be distinguished from magnetic fields generated by other electromagnets by controlling one or more of the wave-like characteristics of the field. For example, each electromagnet can be driven at a different frequency (e.g., frequency division multiplexing) for disambiguation from other electromagnets. Alternatively, each electromagnet can be driven at a different instance in time (e.g., time division multiplexing) for disambiguation from (and interoperability with) other electromagnets or undesired interference in the form of ambient or external magnetic flux. However, this application requires centralized control and synchronization of the signals to avoid interference. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention overcomes the drawbacks of the background art, by providing a system and method for shaped wave patterning for EMF tracking. The waves are shaped at the source, when generating the input signal. The waves may be shaped as square patterns or triangular patterns. 
     Implementation of the method and system of the present invention involves performing or completing certain selected tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and system of the present invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting. 
     An algorithm as described herein may refer to any series of functions, steps, one or more methods or one or more processes, for example for performing data analysis. 
     Implementation of the apparatuses, devices, methods and systems of the present disclosure involve performing or completing certain selected tasks or steps manually, automatically, or a combination thereof. Specifically, several selected steps can be implemented by hardware or by software on an operating system, of a firmware, and/or a combination thereof. For example, as hardware, selected steps of at least some embodiments of the disclosure can be implemented as a chip or circuit (e.g., ASIC). As software, selected steps of at least some embodiments of the disclosure can be implemented as a number of software instructions being executed by a computer (e.g., a processor of the computer) using an operating system. In any case, selected steps of methods of at least some embodiments of the disclosure can be described as being performed by a processor, such as a computing platform for executing a plurality of instructions. The processor is configured to execute a predefined set of operations in response to receiving a corresponding instruction selected from a predefined native instruction set of codes. 
     Software (e.g., an application, computer instructions) which is configured to perform (or cause to be performed) certain functionality may also be referred to as a “module” for performing that functionality, and also may be referred to a “processor” for performing such functionality. Thus, processor, according to some embodiments, may be a hardware component, or, according to some embodiments, a software component. 
     Further to this end, in some embodiments: a processor may also be referred to as a module; in some embodiments, a processor may comprise one or more modules; in some embodiments, a module may comprise computer instructions—which can be a set of instructions, an application, software—which are operable on a computational device (e.g., a processor) to cause the computational device to conduct and/or achieve one or more specific functionality. 
     Some embodiments are described with regard to a “computer,” a “computer network,” and/or a “computer operational on a computer network.” It is noted that any device featuring a processor (which may be referred to as “data processor”; “pre-processor” may also be referred to as “processor”) and the ability to execute one or more instructions may be described as a computer, a computational device, and a processor (e.g., see above), including but not limited to a personal computer (PC), a server, a cellular telephone, an IP telephone, a smart phone, a PDA (personal digital assistant), a thin client, a mobile communication device, a smart watch, head mounted display or other wearable that is able to communicate externally, a virtual or cloud based processor, a pager, and/or a similar device. Two or more of such devices in communication with each other may be a “computer network.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the drawings: 
         FIG.  1 A  shows a non-limiting, exemplary system for shaped wave patterning; 
         FIGS.  1 B and  1 C  show non-limiting, illustrative examples of various wave shapes; 
         FIG.  1 D  shows another non-limiting, exemplary system for shaped wave patterning; 
         FIG.  2    shows an exemplary, non-limiting method for operating a system according to  FIG.  1 A or  1 D ; 
         FIG.  3    shows a non-limiting, exemplary schematic of a glove that is to be worn by a user, for tracking the positions of the fingers; 
         FIG.  4    is a non-limiting, exemplary schematic diagram of the electronics and sensors used in the glove of  FIG.  3   ; 
         FIG.  5    shows an exemplary, non-limiting method for gauging RF (radiofrequency) interference) with a plurality of EMF sensors; 
         FIG.  6    shows an exemplary, non-limiting system incorporating a plurality of wearable devices as described herein; 
         FIG.  7    shows an exemplary, non-limiting method for operating a system incorporating a plurality of wearable devices as described herein; 
         FIG.  8    shows an exemplary, non-limiting method for operating a system according to  FIG.  1 A or  1 D , and  FIG.  6   ; and 
         FIGS.  9 A and  9 B  relate to non-limiting, exemplary methods for transmission of binary data through EMF transmission. 
     
    
    
     DESCRIPTION OF AT LEAST SOME EMBODIMENTS 
       FIG.  1 A  shows a non-limiting, exemplary system for shaped wave patterning. As shown in a system  100 A, an EMF generator  102  comprises a synthesizer  104  and a transmission coil  106 . Synthesizer  104  generates the electrical signals which are then passed to transmission coil  106  for transmission as EMF signals  112 . A processor  108 A executes instructions stored in a memory  110 A to determine when EMF signals  112  are to be emitted by transmission coil  106 . Such signals  112  are emitted intermittently, with a periodicity and duration of transmission that is determined according to the instructions stored in the memory  110 A and executed by the processor  108 A. In particular, the shape of the waves is determined according to these instructions, which in turn determine the electrical signals that are put into transmission coil  106 . 
     EMF signals  112  are received by a sensor  114 , through a sensor coil  116 . A processor  108 B executes instructions stored in a memory  110 B which enables the received signals from sensor coil  116  to be measured and optionally for further processing on these signals to be performed. 
     EMF signals  112  pass through sensor coil  116  and in turn induce a current in sensor coil  116  based on the rate of change of this magnetic field. The current and therefore also the voltage over sensor coil  116  takes the shape of the first derivative of the electrical signal that is put into transmission coil  106 . The optimal shape of the input electrical signals from synthesizer  104  may be determined so that EMF signals  112  may remain measurable as far away as possible. The optimal shape may comprise a square wave or a triangular wave. Instructions stored in memory  110 A and executed by processor  108 A determine the shape of the input electrical signals. 
     Although the optimal shape of the electrical signals may comprise a square wave, because such a shape may provide the largest measurable range for sensor  114 , the derivative of a square wave is a pulse on the rising edge and another one on the falling edge of each square. These pulses are extremely short and thus difficult to measure at sensor  114 . Shaping the electrical input signals as triangular signals makes EMF signals  112  easier to measure at sensor  114 , because the derivative is a square wave. In addition, such a triangular shape enables binary information to be embedded in the transferred signal.  FIG.  1 B  shows non-limiting, illustrative examples of various wave shapes according to the input signal and the resultant output signal at sensor  114 . 
     When shaping the electrical input signals as triangular signals, the steepness of the signal increases with the frequency of the signal. As the frequency of the input signals increases, the measurable range of EMF signals  112  for sensor  114  also increases. In addition, such a triangular wave results in a square wave when measured by sensor  114 , such that binary data may easily be embedded in this signal. Differentiating between signals from different EMF generators  102  and/or from a single EMF generator  102  but generated at different times, is easier. Optionally a start and end code may be embedded in EMF signals  112  for synchronization. Such differentiation may also enable a plurality of different sensors  114  to measure each other&#39;s signal and so to determine the distance between them. 
       FIG.  1 C  illustrates a plurality of signals in a square wave shape, showing how a square wave may be measured at sensor  114 . Such a square wave is preferably processed at sensor  114  with a very short pulse. Sensor  114  therefore needs to measure EMF signals  112  at the exact time of the pulse if a square wave is implemented. Such EMF signals  112  may be measured by employing a Fourier series and providing such signals at a plurality of different frequencies. For such an implementation, synthesizer  104  preferably comprises an analog low pass filter  118 A, to remove all high frequencies from the generated electrical signals and to therefore obtain the base frequency. The base frequency may then be used for further calculations. Such an implementation optimizes the signal for the magnetic field, and for amplitude and phase detection, without wishing to be limited by a closed list. 
       FIG.  1 D  shows a similar system as for  FIG.  1 A , except that low pass filter  118 B is now located at sensor  114 . That is, low pass filter  118 B is now located at the EMF receiver rather than the EMF transmitter. The other components in system  100 B operate in an identical or at least similar manner to the components of system  100 A. 
       FIG.  2    shows an exemplary, non-limiting method for operating a system according to  FIG.  1 A . As shown in a method  200 , the process begins at  202  with initialization of the EMF generator. At  204 , a wave shape is selected according to instructions executed by the processor at the EMF generator. The wave shape may be triangular or square shaped, as described with regard to  FIG.  1   , depending for example on the configuration of the EMF generator. 
     At  206 , instructions executed by the processor determine the input electrical signals to the transmission coil, which in turn determine the wave shape. These input electrical signals are then generated by a synthesizer according to the executed instructions at  208 . If a square wave is to be transmitted by the transmission coil, then optionally the signals are passed through an analog low pass filter at  210 . 
     However, if a triangular wave shape is to be transmitted, then at  212  optionally a start code is embedded in the transmitted EMF signals, to indicate the start of EMF signal transmission and/or a particular period of EMF signal transmission. At  214 , EMF signals are received by the sensor. Various measurements and/or other types of processing may then be performed as described herein. If a square wave is to be received by the sensor, but an analog low pass filter has not been applied at the transmission coil, then optionally the signals are passed through an analog low pass filter at  216 . 
     At  218 , stages  208 - 216  may be repeated. At  220 , if a triangular wave shape is being transmitted, optionally an end code is embedded in the transmitted EMF signals, to indicate the end of EMF signal transmission and/or a particular period of EMF signal transmission. 
       FIGS.  3  and  4    relate to exemplary, illustrative implementations of shaped wave patterning for tracking human appendages with magnetic fields. Without wishing to be limited in any way, the present invention may be used to track the position of arms, legs, head, torso, hands, feet joints and/or individual fingers. Sensors for such magnetic fields are attached to each such appendage that is to be separately tracked. For example, the sensors may be attached to an item of clothing that is worn by the user on the appropriate appendage. It is desirable to be able to track such appendages for more than one user at the same or similar time. For example, two or more users may have such sensors attached to items of clothing, and may then come into physical proximity. Differentiating between the systems that are attached to the different users is important for correct tracking of each such appendage. 
       FIG.  3    shows a non-limiting, exemplary schematic of a glove that is to be worn by a user, for tracking the positions of the fingers. A glove  300  is worn on a hand  304  of the user. Glove  300  may feature a single EMF source  301 , which may be placed at the palm or wrist of glove  300  as shown. A plurality of fingers is tracked with a plurality of sensors  302 , for sensing the EMF generated by EMF source  301 . EMF source  301  may generate triangular shaped waves, square shaped waves or a combination thereof. If square shaped waves are at least generated primarily, EMF source  301  may feature a lower power implementation than if sinusoidal waves are generated. Alternatively, sensors  302  may be correspondingly less sensitive. 
     In this non-limiting implementation, each finger of glove  300  features a sensor  302 , shown as a sensor  302 - 1  on the thumb, and as sensors  302 - 2  to  302 - 5  on the other fingers. A plurality of wires  303  optionally connect sensors  302  to EMF source  301 , to connect analog signals from sensors  302  to EMF source  301 . Alternatively, a wireless communication unit may provide a data communication channel from sensors  302  to EMF source  301 . Such a wireless communication unit is preferably implemented with triangular shaped waves, due to the lower power requirements. As described below in greater detail, EMF source  301  also comprises a processor and memory for storing instructions, for analyzing the incoming signals from sensors  302 . 
     Glove  300  may comprise any suitable fabric or material for placing each sensor  302  in a desired position on a finger or thumb of the user. For example and without limitation, each sensor  302  may be placed closer to a tip of the finger or thumb of the user as shown. Glove  300  may comprise continuous fabric or material, or may have such fabric or material at a plurality of locations, but not necessarily covering the entire hand. For example, fabric may encircle a location on each finger or thumb where sensor  302  is to be placed, and may further comprise straps or other connecting material between sensors  302  and source  301 . A wristband or other material may support source  301  in a desired location, such as on or near the palm or wrist of the user, or on the back of the hand of the user. Source  301  may be contained within a case (not shown; see  FIG.  2   ). 
     Sensors  302  may comprise a magnetic flux density sensor or magnetic field strength sensor, three Hall effect sensors or any other suitable magnetic sensor or combination thereof. It should be noted that for the combined application of such sensors to sample a set frequency to gauge RF interference, as well as for EMF signal reception, Hall effect sensors are not used. Such sensors preferably operate at a frequency of at least six times the sample frequency, more preferably at least eight times and most preferably at least 10 times. Each such sensor may comprise a magnetometer which is able to detect EMF from source  301 , but preferably comprises a sensor that is at least able to determine an amplitude of the EMF at the appropriate speeds. 
     As shown, preferably the location of each finger is tracked with a separate sensor  302 , while the location of all sensors  302 , and hence all fingers on one hand, is preferably tracked with one EMF source  301 . However, different gloves  300  may each use a separate source  301  to track their corresponding sensors  302  and hence their corresponding fingers. For example, if EMF source  301  emits triangular shaped waves, then a start code and end code may be embedded, such that sensors  302  for each glove  300  is more easily able to determine which EMF signals are relevant. Each such EMF source  301  creates an alternating magnetic field, which is preferably emitted periodically for a short period of time. The duration of this period of time is preferably determined according to the frequency of the sine wave that is sent out. 
       FIG.  4    is a non-limiting, exemplary schematic diagram of the electronics and sensors used in the glove of  FIG.  3   . As shown, a system  400  comprises a plurality of sensors  401 , which are preferably located at the fingers and thumb of the user as previously described with regard to  FIG.  3   . Sensors  401  may comprise the types of sensors described with regard to  FIG.  3   , for example. A case  420  may be attached to the wrist or hand of the user, for example at the palm or back of the hand. Case  420  contains a plurality of components as shown, including without limitation a transmission coil  407  which emits EMF  408  as shown, for detection by sensors  401 . 
     An amplification unit  402  receives signals from sensors  401  through a plurality of wires  422 , of which one is shown for simplification. Amplification unit  402  then amplifies the received signal and passes the amplified signal to a filtering unit  403 . Filtering unit  403  may comprise one or more cut-off filters and/or notch filters, to reduce noise and to boost the desired signal frequency, optionally comprising and/or in addition to the low pass filter if necessary. The signal is then passed to an ADC (analog-to-digital converter)  404 , to digitize the analog signals for further processing. The digitized signals may then by analyzed by a MCU (microcontroller unit)  405 , which comprises a processor unit, a memory, communication interfaces and peripherals (not shown). 
     MCU  405  also determines when EMF signals  408  are to be emitted by transmission coil  407 , as well as the required shape as described herein. Such signals  408  are emitted intermittently, with a periodicity and duration of transmission that is determined according to instructions stored in the memory and executed by the processor. The signals are generated by a synthesizer  406  and then passed to transmitter  407 . 
     Analyzed data may be transmitted by a radio  409 , which in this non-limiting example comprises a 2.4 GHz radio. 
     To determine when EMF signals  408  are to be emitted, MCU  405  features a clock (not shown) for timing this activity and other activities. Such clocks typically have an expected accuracy, which determines the precision of the timing. The clock may for example comprise an internal oscillator, such as an internal RC oscillator, featuring a linear oscillator circuit which uses an RC network, a combination of resistors and capacitors. Alternatively, the clock may preferably comprise a crystal clock. The precision of the clock may be defined in terms of tolerance, which is the extent (by time) to which the clock signal timing differs from the expected timing. The greater the tolerance, the lower the precision of the clock and hence the greater possible variability in timings between different clocks, such as those located at different gloves. This variability in turn means that EMF signals  408  will be emitted at different times for MCUs  405  located on different gloves. 
       FIG.  5    shows an exemplary, non-limiting method for gauging RF (radiofrequency) interference) with a plurality of EMF sensors. The EMF sensors when tuned properly can also act as an antenna. When not used for EMF tracking, they can be used to sample the 2.4 Ghz radio band and use this to determine the optimal channel to send its data over. Any suitable sensor may be used for this implementation, with the exception of Hall effect sensors. A non-limiting implementation of a sensor system featuring a generated 2.4 Ghz radio band is shown with regard to  FIG.  4   . Without wishing to be limited by a closed list, such an optimal channel selection improves both the range of the sensor system and power draw. 
     A method  500  starts at  502 , when the system is initialized. Such initialization may include initiating the functions of the EMF generator and of the sensors as described herein. At  504 , the sensor coil for the EMF sensors is adjusted so that it is able to act as an antenna for a set frequency. The adjustment comprises adjusting the sensor coil and its tuning, such that the output of the sensor coil would be switched to a different circuit, for example through a MUX, when receiving the set frequency. Also optionally, alternatively or additionally, a portion of the sensor coil would be of the correct size and shape to receive the set frequency. The set frequency may for example comprise the 2.4 Ghz radio band, but in any case, is different from the frequency used for EMF tracking. 
     At  506 , the sensors listen at this set frequency. Such listening preferably occurs according to instructions executed by a processor at each sensor, such that the sensor alternates between listening for the set frequency and listening for EMF signals used for EMF tracking. At  508 , each sensor samples the set frequency. At  510 , such samples are analyzed by the sensor to gauge RF interference, by measuring the incoming energy on each potential channel. The incoming energy may be used to determine potential RF interference, such that preferably a channel is selected that is less heavily used. According to such a preference, a channel is selected by the sensor at  512 . Now EMF signals are received by the sensors at the selected channel at  514 . The sensor data then received by a tracker at  516 , such that EMF tracking may be performed. At  518 , the sensor location is determined according to the sensor data. At  520 , optionally stages  506 - 518  are repeated at least once. 
       FIG.  6    shows an exemplary, non-limiting system incorporating a plurality of wearable devices as described herein. As shown, a system  600  features a plurality of wearable devices  604 , of which four are shown herein as wearable devices  604 A- 604 D for the purpose of illustration and without any intention of being limiting. Wearable devices  604  may comprise devices as described herein, such as the gloves described herein and/or a headset. System  600  also optionally and preferably features a central computational device  620 , which is in contact with wearable devices  604  through a computer network  610 . Network  610  may comprise any suitable wired or wireless communication network, including without limitation Wi-Fi, Bluetooth, radio frequencies and cellular network communication. 
     Central computational device  620  preferably comprises a processor  630  and a memory  631 . Memory  631  stores a plurality of instructions for execution by processor  630  to fulfill the functions of central computational device  620 , for example and without limitation to provide an engine  636 . For example and without limitation, engine  636  may support game play for an interactive electronic game. A plurality of users may wear wearable devices  604 , and may interact with the game according to game play supported by engine  636 . The relative location of the users may be determined through wearable devices  604 ; such a relative location may affect game play. The location may be provided to central computational device  620  by wearable devices  604 . In turn, central computational device  620  may send information and/or instructions, and/or may fulfill such functions as keeping score, according to the provided location. 
     Central computational device  620  may also comprise an electronic storage  522 , for example for storing user profile information, additional game data and/or other information for supporting the functions of central computational device  620  and/or of system  600  overall. 
     System  600  may also, additionally or alternatively, comprise a plurality of user computational devices  602 , shown as user computational devices  602 A and  602 B for the purpose of illustration only and without any intention of being limiting. Optionally one or more user computational device(s)  602  replace central computational device  620 . User computational devices  602 A and  602 B may be used for example to control game play, to receive information about game play and/or to participate in game play, in combination with wearable devices  604 . Other optional uses include but are not limited to motion capture (for example for film and/or animation), education, training, coaching (for example for sports or other activities), simulation and so forth. 
     Within system  600 , synchronization between wearable devices  604  may occur according to instructions from central computational device  620 , one or more user computational devices  602 A and  602 B, and/or in a peer to peer manner. If triangular shaped waves are transmitted by an EMF source, then synchronization may occur according to start and end codes. Optionally a single EMF source, or fewer EMF sources, may be implemented in system  600  due to such synchronization (not shown). Additionally or alternatively, triangular shaped waves may enable the distance between an EMF source and one or more sensors to be larger, the power of the EMF source to be lower and/or the sensors to be less sensitive. Such adjustments may decrease the cost, or otherwise increase the ease and simplicity of implementation of wearable devices  604 . 
       FIG.  7    shows an exemplary, non-limiting method for operating a system incorporating a plurality of wearable devices as described herein. As shown in a method  700 , the process begins by initializing a plurality of wearable devices at  702 . The wearable devices are assumed to comprise at least one, and preferably a plurality of, sensors. For example, for a wearable device comprising a glove, each of a plurality of fingers features a sensor, while the glove may feature a single EMF source, for example at the wrist, back of the hand or palm of the hand. Optionally a plurality of gloves may share a single EMF source as described herein, in which case the EMF source may be remote from the glove. If square shaped waves are used, optionally a single EMF source may transmit to a single glove, but may still be remote from the glove. 
     Such initialization may include calibration, for example. Initialization may also include functions to support initial communication between the plurality of sensors and the EMF source. The user may put on (wear) the wearable device during the initialization process or before it begins. Pairing may then occur with a data connection for each wearable device at  704 . The data connection may for example feature a connection to the previously described EMF generator, which may control EMF source, and/or to a central computational device as previously described. 
     At  706 , the wave shaped pattern is selected, preferably as square shaped waves, triangular shaped waves or a combination thereof; in which the combination is preferably implemented as a rapid sequence of alternating wave shapes, optionally in a pattern with a plurality of repeated waves of a particular shape. Optionally the wave shapes may be combined to create a distorted wave shape. At  710 , the sensors are tuned, for example as previously described. At  712 , the degree of RF interference is determined, for example as previously described. At  714 , the channel for receiving EMF signals by each sensor is selected according to the degree of RF interference, for example as previously described. At  716 , sensor data is received. 
       FIG.  8    shows an exemplary, non-limiting method for operating a system according to  FIG.  1 A or  1 D , and  FIG.  6   . The system is assumed to feature a plurality of wearable devices, although any potentially mobile device may be substituted for one or more wearable devices. Each wearable device preferably features the components of  FIG.  1 A or  1 D , although these components may be distributed across multiple locations, such that for example an EMF source may be located at one location and the corresponding sensor at a different location. The wearable devices may perform peer-to-peer tracking, to determine a relative location of one or more other wearable devices to each wearable device; tracking may be performed centrally; or a combination thereof. 
     In a method  800 , the method begins at  802  by initializing the system, including initializing each wearable device and any central device that receives information from one or more wearable devices. Initialization may be performed as described herein for the EMF source and sensor. 
     At  804 , a wave shape is selected according to instructions executed by the processor at the EMF generator. The wave shape may be triangular or square shaped, as described with regard to  FIG.  1   , depending for example on the configuration of the EMF generator. However, for an embedded identifier to be sent, preferably the wave shape is triangular for at least the time period during such the identifier is transmitted. 
     At  806 , instructions executed by the processor determine the input electrical signals to the transmission coil, which in turn determine the wave shape. These input electrical signals are then generated by a synthesizer according to the executed instructions at  808 . If a square wave is to be transmitted by the transmission coil, then optionally the signals are passed through an analog low pass filter at  810 . 
     However, if a triangular wave shape is to be transmitted, then at  812  preferably a start code is embedded in the transmitted EMF signals, to indicate the start of EMF signal transmission and/or a particular period of EMF signal transmission. The start code preferably comprises an identifier, to identify the transmitting EMF source, which is preferably a wearable device as described herein. At  814 , EMF signals are received by the sensor. Various measurements and/or other types of processing may then be performed as described herein. If a square wave is to be received by the sensor, but an analog low pass filter has not been applied at the transmission coil, then optionally the signals are passed through an analog low pass filter at  816 . 
     When a triangular wave shape has been transmitted, with the identifier, then a receiving device determines that an identifier has been transmitted at  818 . At  820 , the receiving device may match the identifier to a particular wearable device. For example, if the receiving device is another wearable device, then the receiving device may identify a specific wearable device as being within receiving range, for example for tracking purposes. Additionally or alternatively, such information may be determined by a central receiving device. 
     At  822 , the identification is fed into a tracking process for determining at least the relative location of at least two wearable devices, relative to each other. 
     At  824 , stages  808 - 822  may be repeated. At  826 , if a triangular wave shape is being transmitted, preferably an end code is embedded in the transmitted EMF signals, to indicate the end of EMF signal transmission and/or a particular period of EMF signal transmission. 
       FIGS.  9 A and  9 B  relate to non-limiting, exemplary methods for transmission of binary data through EMF transmission. The systems and methods as described herein may be used for transmission of binary data, and not only start/end codes and/or identity information. For example, the method of  FIG.  8    may be used to send binary data more generally, whether to wearable devices and/or mobile devices, or for other purposes. These methods assume that a triangular wave is used as the transmission shape when creating the EM field (EMF), as in this situation, the derivative thereof is a square wave when received on another coil, for example at a sensor as described herein. By using either frequency modulation or timed pulsing of the EMF, binary data may be transmitted over the EM field to the receiver. 
     When using frequency modulation, the transmission processor varies the frequency of the transmitted EMF wave. The variation in frequency enables a 0 or a 1 to be encoded in the field, depending on the time the derived square signal is high vs low, as shown with regard to  FIG.  9 A . For example, when the derived square signal is high for longer than a threshold period of time, the field may be read as “1”; when the derived square signal is high for shorter than the threshold period of time, the field may be read as “0”, as shown in the diagram. 
     Another method, shown with regard to  FIG.  9 B , maintains a steady frequency but selectively maintains the voltage at a high or low level in a timed pulse. A high voltage level timed pulse is read as “1”; a low level timed pulse is read as “0”. 
     These methods may increase the difficulty of accurately deriving the receiver&#39;s position and rotation at the same time. One method to overcome this difficulty is to avoid using FFT (Fast Fourier Transform) to determine the core frequency but this avoidance increases overhead in the signal processor. Another method to overcome this difficult is to attach the data either on the start or end of the transmission signal, for example with regard to the start or end codes as described above. This way the processor can later determine what to do with the data it gathered. 
     The frequency of information transmission then determines the amount of data that may be transmitted in a particular period of time. For example, if data transmission occurs on a higher frequency and includes the actual transmission frequency used for the positioning calculations, the receiver and the transmitter do not require an alternative data stream to communicate basic settings. This short information field can then be used to transmit either source identification information, relative positioning in a wider space, and other information that might be relevant to the receiver. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. 
     Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.