On-body sensor systems and methods

Abstract

An on-body sensor system (30) comprises means for determining the position of a skin interface unit (34) based on the transmission and reception of electrical signals transmitted from a known transmitter (32) position to the unit via an electrical channel of the body. By comparing sensed signal characteristics of the received signals with a plurality of sets of predetermined signal characteristics, each set being associated with one of a plurality of different reference positions and / or orientations of the on-body receiver (34), it is possible to derive an indication of the position of the on-body receiver unit.

Description

Technical Field

[0001] Various embodiments described herein relate to an on-body or handheld sensor system having one or more on-body or handheld sensor elements, and methods for configuring the on-body or handheld sensor system. Background Art

[0002] On-body sensing systems allow for accurate long-term monitoring of physiological parameters of a subject. On-body systems are based on the use of wearable devices or units (including, for example, patches) that are attached to or mountable on the body and maintain a relatively stable position over time. As another example, a handheld device is positioned relative to the body and can require a relatively stable position over time. By electrically interfacing with the skin or body, vital signs or other parameters can be monitored.

[0003] The on-body system can generally be used in less urgent environments (e.g., general wards) and in the subject's home. There is a need to improve the reliability of monitoring physiological parameters in general wards, thereby reducing mortality by enabling detection of any deterioration of the condition as early as possible. The ability to reliably monitor in the subject's home also allows the patient to be discharged earlier without the risk of undetected deterioration. For example, monitoring will generally continue for up to 30 days from discharge.

[0004] In the case of patches, due to battery charge depletion, adhesion degradation and / or skin irritation, patches need to be changed every 2-3 days in many cases. As a result, the patient himself and / or informal caregiver (e.g., relative) cannot successfully replace and reattach the patch. In some cases, the patch must be moved to other alternative positions and orientations. It is very important to accurately place the patch after changing the patch to ensure that the physiological parameters are correctly determined.

[0005] Similarly, accurate placement of handheld devices (e.g., handheld imaging sensors and / or devices) that are in contact with the body is important. For example, accurate placement of a handheld ultrasound device that may include a capacitive micromachined ultrasound transducer (cMUT) array for image acquisition is essential for registration of correct physiological images. Therefore, systems, methods, and / or devices for ensuring proper placement (orientation and positioning) of any sensor-related device are desired.

[0006] The electric field model of the human body has been previously described in academic works. This model can be used to determine the frequency response of the human body as a signal transmission medium. The frequency response is measured by generating and capacitively coupling an electrical signal of known frequency and amplitude at one point on the body. The coupled signal can be sensed and measured by sensors at different remote points on the body. The received signal can be analyzed and various signal properties derived. This process can be repeated for multiple different signals with different transmitter frequencies and for various distances and body positions of the sensing element on the body relative to the transmitting location.

[0007] An example model is presented in "The Human Body Characteristics as a Signal Transmission Medium for Intrabody Communication" by Namjum Cho et al. (IEEE Transactions on Microwave Theory and Techniques, 2007). In this article, the authors present a human near-field coupling model based on modeling the human body according to three cylinders (two cylinders for the arms and one cylinder for the human torso). This is illustrated in Figure 1.

[0008] As shown in Figure 1(a), the arms and human torso are segmented using 10 cm long unit blocks, each with a resistor and a capacitor. The arms and torso are modeled together as a distributed RC network as shown in Figure 1(b). In a similar manner, the human legs can be modeled using corresponding resistors and impedances. The arm model has resistors and capacitors with subscripts "A", while the torso has resistors and capacitors with subscripts "T".

[0009] A practical implementation of the signal transmission and sensing method is proposed in Zhang, Y. et al., “Skintrack: Using the body as an electrical waveguide for continuous finger tracking on the skin” (In Proceedings of the 2016 CHI Conference on Human Factors in Computing Systems, pp. 1491-1503, May 2016).

[0010] The article presents a continuous finger tracking technology called SkinTrack. SkinTrack is a wearable system that enables continuous touch tracking across the skin. The system includes a ring that emits a continuous high-frequency AC signal and a sensing wristband that implements multiple sensor electrodes. Due to the inherent phase delay in propagating high-frequency AC signals through the body, phase differences can be observed between electrode pairs. The SkinTrack system measures these phase differences to calculate the 2D coordinate position of the finger of an object touching on the object's skin. The resolution (i.e., accuracy) of the SkinTrack method is approximately 7mm.

[0011] The same article also describes a method in which the phase angle difference between signals sensed at two different locations on the human body is used as a measure of the positioning of the signal transmitter relative to the sensor. Figure 2 The technique is schematically illustrated where the transmitter is in the form of a ring 12. This technique is used to identify the position of the transmitter relative to two sensor electrodes 14a, 14b on the smart watch.

[0012] When using an 80MHz RF signal, the wavelength of the electromagnetic waves propagating through the human body is approximately 91cm. For one single cycle of the wave, this causes a phase angle difference of approximately 4° / cm. If positioning is performed within one wavelength of the RF signal (i.e., within approximately 91cm), then an indication of the position of the transmitter relative to the two sensors can be derived by measuring the phase angle difference between the two received signals.

[0013] When monitoring physiological parameters, accurately placing the patch is essential for correct operation. And when using various other sensing devices (for example, the handheld imaging sensor device described in this article), the placement of the device is essential for correct results. However, in family-based monitoring and / or other schemes described above, it is necessary for patients, non-clinical physician caregivers and / or medical professionals to replace the patch themselves. This can be challenging, even in the case of medical training, and especially so in the case of no medical training, and for patients with, for example, poor vision, dexterity or with reduced cognitive function. Therefore, promoting the solution of reliably placing the patch and / or other sensing devices as described in this article in the correct position will be valuable for improving the reliability of monitoring, sensing and / or imaging. Summary of the invention

[0014] Known methods and models for the placement of auxiliary sensor elements remain very limited in the extent to which they allow the position of the transmitter to be uniquely identified. Crucially, although it has been shown how to derive an indication of the relative distance between the transmitter and the receiver, this does not allow the position of either element on the body to be uniquely identified. Therefore, accurate position determination is not yet possible. This makes the known methods unsuitable for situations in which precise and unique positioning of elements on the body is required. Furthermore, even the known methods for determining relative distance are only achievable if the transmitter and receiver remain within a limited separation range of one wavelength (one period), which is very limiting.

[0015] According to an example of aspects of the embodiments described herein, there is provided an on-body or handheld sensor system comprising:

[0016] at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit for placement against a known area of ​​the subject's skin for coupling signals into the body, and at least one receiver unit for placement at a remote location for sensing the coupled signals;

[0017] a controller coupleable to the skin interface unit and adapted to control the transmission of signals between the at least one transmitter unit and the at least one receiver unit and to derive a set of signal characteristics associated with each signal received at the receiver, the characteristics being dependent on the position and / or orientation of the receiver unit;

[0018] the controller having access to a data set comprising a plurality of predetermined signal characteristic groups, each group being associated with one of a plurality of different reference positions and / or orientations of the receiver on the body;

[0019] Wherein the controller is configured to derive an indication of the position and orientation of the at least one receiver based on comparing the derived set of signal characteristics for the received signal with the predetermined set of signal characteristics, and to generate output information based on the derived indication of the position and orientation.

[0020] The embodiments described herein utilize at least two skin coupling elements, at least one of which is configured as a signal transmitter and at least the second of which is configured to receive the transmitted signal. The embodiments described herein are based on using the receiver to derive a set of multiple different signal characteristics associated with the sensed signal. These can be measured directly from the signal or they can be derived by processing or calculation based on the signal measurement results. This set of characteristics forms a unique "body channel fingerprint" for the receiver unit location, which uniquely characterizes the specific position and orientation of the receiver. By providing a predetermined set of similar signal characteristic groups for multiple different possible reference positions and orientations (i.e., reference fingerprints), it is possible to derive an indication of the current unique position and orientation of the receiver by comparison.

[0021] Thus, the basic methods of body passage sensing discussed in the prior art have been developed by the inventors to allow unique positioning of receiver elements (eg, sensor patches) to be achieved.

[0022] The embodiments described herein utilize a controller. The controller may be a separate (dedicated) controller, or the control functions may be performed by one or more of the skin interface units themselves. Thus, in the latter case, the controller may be a distributed controller. Thus, in some examples, one or more of the skin interface units may include the controller, i.e., the control functions may be distributed among the skin interface units of the system itself. In some examples, each of the skin interface units may include a local control module for performing at least part of the control functions of the overall system. For example, each may control at least its own transmit or receive functions. One of the units may be designated to perform a processing or determination step (i.e., determining an indication of a location). A configuration step may be performed in which the skin interface units communicate and one of the units is designated as being responsible for the determination step.

[0023] In all explanations and descriptions above and below, reference to a controller may be taken as a reference to a dedicated control unit or to one or more of the system's skin interface units performing the relevant control functions.

[0024] The electrical signal is an electrical stimulus applied to the skin or body. It is carried or transported by the body through electrical body channels. It can be an AC signal. The signal can be capacitively coupled into the body, or inductively coupled into the body. The same or different coupling mechanisms can be used to couple the signal out of the body for sensing.

[0025] The system comprises skin interface units for electrically coupling signals into and from the skin or body. Each may comprise one or more electrodes for electrically interacting or coupling with the skin. Each unit may preferably be arranged to be in contact with the skin or mounted or applied very close to it on the skin, possibly separated by a small gap or space.

[0026] One or both skin interface units may include or comprise a pad (eg, patch) for mounting on the skin. The skin interface unit(s) may also include a handheld device, such as a handheld imaging device as described herein.

[0027] Optionally, the controller may generate signals and the transmitter unit is controlled to apply these signals to the body. Alternatively, the transmitter unit itself comprises means (eg circuitry) to generate the signals.

[0028] The signal is sensed at a location remote (i.e. separate) from the first skin interface unit. This means a remote location on the body or skin. Preferably, the signal generated for coupling into the body is in the RF frequency range 10 MHz to 150 MHz, since in this frequency range the body acts as a waveguide for signal transmission.

[0029] One or both of the skin interface units may comprise a plurality of skin interface electrodes, eg skin contact electrodes.

[0030] The system has at least two skin interface units, at least one skin interface unit for generating and transmitting signals (transmitter), and the other skin interface unit for sensing signals at a remote location (receiver). The first and second interface units can be functionally interchangeable, that is, either interface unit can be selectively configured to act as either a signal transmitter or a signal receiver. In some examples, the two can be structurally identical.

[0031] The position of the receiver unit may refer to a location on the body or the skin. Position may refer to an absolute position (i.e., a position on the body), or may refer to a relative position (i.e., relative to the transmitter), for example, away from or separated from the transmitter. Orientation may refer to an orientation relative to the skin or an absolute orientation (e.g., measured using a gravity sensor and / or a compass).

[0032] The derived indication of position may be a direct or indirect indication of position. It may be, for example, a quantitative coordinate position. Alternatively, it may be based on the reference position, for example, it may be an indication of a reference position to which the current position corresponds or to which it is close.

[0033] The data set may be stored locally, for example in a memory comprised by the system (eg, by the controller). Alternatively, the data set may be stored remotely, for example in the cloud, or on a remote computer with which the controller can communicate.

[0034] In an advantageous embodiment, the controller may be configured to compare the derived indication of position and orientation with a defined target position and orientation and to generate guidance information based on the comparison for guiding a user in positioning the receiver unit at the target position and orientation. The guidance information may form the output information or the output information may comprise, for example, the guidance information.

[0035] This can be based on comparing the derived signal characteristics with the signal characteristics associated with the target position and orientation. The target position and orientation can be pre-programmed in the controller, or can be configurable, for example, based on user input. The target position and orientation can be one of a plurality of reference positions and orientations in the data set. In this way, a predetermined signal characteristic associated with the target position can be accessed from the data set, which can be used for the comparison in an example.

[0036] Guidance towards a target position and towards a target orientation may be performed or instructed in separate steps or stages, eg starting with the position and then moving to the orientation once the position has been correctly achieved.

[0037] The controller may be adapted to derive an indication of a distance between the derived position and the target position based on the comparison, the output information being based on the derived distance. The distance may be a true distance, i.e. in SI units of metres, or may be a locally defined distance in locally defined or relative units. The derived distance allows guidance information to be generated, which indicates how far the receiver needs to move to reach the target position.

[0038] The controller may be further adapted to determine whether the derived distance is within a defined acceptable proximity threshold of the target distance, and only generate guidance information for positioning the receiver closer to the target location if the distance is outside the acceptable threshold.

[0039] This improves efficiency by providing a wider allowed range of positions to which the receiver may be moved, thereby avoiding a large number of unnecessary fine adjustments of position (which may be difficult for patients with dexterity or vision problems). The proximity threshold may be predefined (e.g., preprogrammed), or may be configurable (e.g., by user input).

[0040] The controller may be adapted to determine a direction of displacement between the derived indication of position and the target position, and wherein the output information includes an indication of that direction. This helps guide the user to move the receiver closer to the target position. When optionally combined with the derived distance information, this allows fully translated instructions to be generated and provided to the user, indicating both the distance and direction for moving the receiver in order to reach the target position.

[0041] Thus, the controller may be adapted to generate guidance information for moving the receiver unit based on the derived distance and direction to the target location, the receiver unit being configured to minimize the distance between the receiver and the target location.

[0042] In this case, the guidance information comprises a distance and a direction for moving the receiver unit.

[0043] According to an advantageous embodiment, the at least one receiver unit comprises at least two pairs of skin coupling electrodes. The two pairs of electrodes are spatially separated. By providing at least two pairs of electrodes, additional (differential) signal characteristics can be measured, such as a phase angle difference between the two electrode pairs or a difference in measured signal attenuation and / or flight time of the signal at each electrode pair. Furthermore, a greater number of electrode pairs provides a greater number of degrees of freedom in sensing the signal characteristics.

[0044] In particular, the derived set of signal characteristics may preferably include a separate subset of derived signal characteristics for each of the electrode pairs. Due to their slightly different positions relative to the transmitter, the signal transmission time and attenuation will be different for each electrode pair. Thus, the body signal fingerprint for a given receiver unit can be made more comprehensive by sensing a separate subset of signal characteristics for each of the multiple electrode pairs.

[0045] In some examples, more than one transmitter unit may be provided. According to one or more embodiments, the controller may be configured to identify the total number of transmitter units, and in turn control the transmission of signals by each transmitter unit if more than one is present, and derive a separate set of signal characteristics associated with signals received from one transmitter unit.

[0046] Thus, the transmitter unit is controlled to sequentially generate and transmit signals with separate sets of signal characteristics derived for each one in turn. These separate sets can be combined into a composite set of signal characteristics that together form a complete body signal fingerprint corresponding to the receiver position. By using two transmitters, a more comprehensive fingerprint is created, which means that a more precise characterization of the unique position and orientation can be achieved. This allows for more accurate or precise receiver positioning.

[0047] According to an example, the at least one receiver unit may take the form of an on-body sensor patch.The at least one receiver unit may take the form of a handheld device.

[0048] In an example, the at least one transmitter unit may take the form of a wearable device for mounting to a specific part of the body, such as a wrist-worn wearable device. Thus, it may be adapted to be mounted on a predetermined area of ​​the skin. This helps ensure that the position of the transmitter on the body is stable and known, which improves the reliability of position determinations that rely on consistent and reliable transmitter positions.

[0049] Hence, the transmitter unit may be a unit adapted to fit to a specific part of the body, such as a wearable unit such as for example a watch, a ring, an arm or ankle band or an ear hook.

[0050] Alternatively, the at least one transmitter unit may take the form of an extra-body device for temporary placement on the skin of a specific part of the body. This should be a unit configured for placement on a known and consistent skin location. For example, the transmitter unit may take the form of (or be incorporated into) a weight scale on which a user stands.

[0051] The system may advantageously be used for monitoring one or more physiological parameters of a subject, and wherein the receiver unit may be used for use in sensing the one or more physiological parameters.

[0052] According to an example, the signal characteristics include one or more of the following: signal transmission time (between transmission and reception), signal attenuation between transmitter and receiver, and a phase angle difference between at least two electrodes comprised by the receiver unit. Another possible characteristic may simply include the signal amplitude (in volts).

[0053] According to an example, the signal characteristics may include one or more differential signal characteristics, which means the difference in the value of the signal characteristics between two pairs of skin coupling electrodes comprised by the receiver unit. These differential signal characteristics may include, for example, at least one of the following: phase angle difference, flight time (signal transmission time) difference, signal attenuation (path loss) difference between transmission and reception, and signal amplitude difference.

[0054] Since the difference in the measured signal characteristics at two spatially separated electrode pairs will vary in a consistent manner depending on the orientation, the differential signal characteristics are particularly useful in characterizing the orientation state of the receiver device. This will be described in more detail below.

[0055] Thus, the signal characteristics may be measured directly from the signal, or may be derived based on measured signal properties and other information. For example, the transmission time (i.e., duration) may be based on the arrival time and the time of transmission. Signal attenuation may be based on the initial signal strength and the sensed signal strength. Thus, the signal characteristics may be based on the signal characteristics at the transmission and reception.

[0056] Embodiments described herein may be based on comparing a measured set of signal characteristics with a plurality of predetermined sets of signal characteristics, each set being associated with one of a plurality of different reference positions and / or orientations of receivers on the body. These form a data set.

[0057] A method may be provided for generating and storing these predetermined sets of reference signal characteristics for use in subsequent configurations of skin interface unit locations.

[0058] Thus, examples according to embodiments described herein may include methods of training an on-body or handheld sensing system for configuring placement of a skin interface unit of the system.

[0059] The system comprises:

[0060] at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit for placement against a known area of ​​the subject's skin for coupling signals into the body, and at least one receiver unit for placement at a remote location for sensing the coupled signals, and

[0061] The method comprises:

[0062] sequentially placing the at least one receiver unit in each of a plurality of different reference positions and / or orientations on the body and controlling transmission of signals between the at least one transmitter unit and the at least one receiver unit for each position and / or orientation and deriving a set of signal characteristics associated with signals received at the receiver for that position and / or orientation; and

[0063] A plurality of sets of signal characteristics for the plurality of different reference positions are stored to thereby derive a data set of predetermined signal characteristics for use in subsequently deriving an indication of the position and / or orientation of the receiver unit based on comparing the sensed signal characteristics with the stored predetermined characteristics.

[0064] A method may provide for placement of a skin interface unit configuring an on-body or handheld sensing system, the system comprising:

[0065] at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit for placement against a known area of ​​the subject's skin for coupling signals into the body, and at least one receiver unit for placement at a remote location for sensing the coupled signals,

[0066] The method comprises:

[0067] controlling transmission of signals between the at least one transmitter unit and the at least one receiver unit to derive a set of signal characteristics associated with each signal received at the receiver, the characteristics being dependent on the position and / or orientation of the receiver unit;

[0068] accessing a data set comprising a plurality of predetermined signal characteristic groups, each group being associated with one of a plurality of different reference positions and / or orientations of said receiver on said body;

[0069] deriving an indication of the position and orientation of the at least one receiver based on comparing the derived set of signal characteristics for the received signal with the predetermined set of signal characteristics; and

[0070] Output information is generated based on the derived indication of position and orientation.

[0071] The variations, options and examples described with respect to the on-body sensor system outlined above may each be equally applicable to the above method.

[0072] According to one set of embodiments, the above configuration method may further comprise performing an initial system training procedure according to the training method defined above, so as to determine a predetermined set of signal characteristics for subsequent use in any of one or more iterations of the steps of the configuration method.

[0073] According to one set of embodiments, the configuration method may further comprise a recalibration procedure for recalibrating the data set of predetermined signal characteristics based on a known initial position of the receiver unit, for a procedure optionally performed before the steps for deriving the indication of position and orientation outlined above. Optionally, it may be performed after the initial training procedure mentioned above and before position determination.

[0074] The recalibration procedure may include, for a known initial position of the receiver unit:

[0075] controlling transmission of signals between the at least one transmitter unit and a receiver unit and deriving a set of signal characteristics associated with signals received at the receiver,

[0076] comparing the derived set of signal characteristics to a predetermined set of signal characteristics in a data set corresponding to the known initial position of the receiver unit; and

[0077] The predetermined signal characteristic of the data set is corrected based on any difference between the derived characteristic and the predetermined characteristic.

[0078] Preferably, based on any derived differences, a correction factor may be derived and this applied to each of the predetermined set of signals of characteristics in said data set, thereby updating said data set.

[0079] These and other advantages will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] For a better understanding of the invention and in order to more clearly show how the invention may be put into practice, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0081] FIG. 1( a ) and FIG. 1( b ) schematically depict a near-field coupling model of a human body according to the prior art;

[0082] Figure 2 Schematically depicting prior art for determining a position on a body based on an AC signal transmitted by the body;

[0083] Figure 3 An example system according to one or more embodiments is shown in block diagram form;

[0084] Figure 4 schematically illustrates an example system according to an embodiment;

[0085] Figure 5 An example signal transceiver as may be used in an example system according to one or more embodiments is shown in block diagram form;

[0086] Figure 6 schematically depicts an example on-body sensor system according to an embodiment;

[0087] Figure 7 and 8 schematically illustrates a system training process for establishing a data set of predetermined signal characteristics for different reference positions of a receiver unit of the system;

[0088] Fig. 9 An example method for configuring the position of a receiver unit of an on-body sensor system according to an embodiment is shown in block diagram form;

[0089] Fig.10An example method for configuring the orientation of a receiver unit of an on-body sensor system according to an embodiment is shown in block diagram form;

[0090] Fig.11 An example system training method for establishing a data set of predetermined signal characteristics for different reference positions of a receiver unit of the system is shown in block diagram form; and

[0091] Fig.12 An example recalibration method for correcting signal characteristics of a predetermined data set is shown in block diagram form. DETAILED DESCRIPTION

[0092] It should be understood that the detailed description and specific examples, although indicating exemplary embodiments of the apparatus, system and method, are intended for illustration purposes only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the apparatus, system and method described herein are better understood from the following description, claims and drawings. It should be understood that the drawings are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar components.

[0093] An on-body or handheld sensor system may be provided having means for determining the position of a skin interface unit based on the transmission and reception of electrical signals transmitted from a known transmitter location to the unit via an electrical channel of the body. By correlating the sensed signal characteristics of the received signals with a plurality of sets of predetermined signal characteristics, each set being associated with one of a plurality of different reference positions and / or orientations of a receiver on the body, it may be possible to derive an indication of the position of the receiver unit on the body. Advantageously, this may then be used to provide guidance instructions to the user in moving the receiver unit closer to a defined target location on the body.

[0094] The embodiments described herein are intended to allow an on-body or handheld sensor unit, e.g., for monitoring one or more physiological parameters, to continue to be used by a patient at home for an extended period after discharge from a hospital. The sensor patch of the system will often need to be replaced periodically. When the patient positions a new patch, it may not accurately position it. The system can determine an indication of the location of the patch, and optionally placement can be guided by the patient based thereon.

[0095] Embodiments described herein may be based on deriving a body signal fingerprint for a receiver, which includes a set of multiple signal characteristics associated with the received signal. The set of characteristics may uniquely characterize or identify the receiver location. By comparing this with multiple sets of predetermined characteristics for known locations, the location may be derived.

[0096] Figure 3An example on-body sensing system 30 is schematically depicted in block diagram form, in accordance with one or more embodiments.

[0097] The system may include two skin interface units 32, 34 for coupling electrical signals into and / or out of a subject's body. The skin interface units may include a transmitter unit 32 for coupling the signal into the body, and at least one receiver unit 34 for sensing the coupled signal. In use, the transmitter unit may be placed or mounted on a known area of ​​the subject's skin, and the receiver unit may be placed or mounted at a different location on the body that is remote (separate) from the location of the transmitter. It should be noted that although Figure 3 The transmitter and receiver units are shown adjacent to each other, but this is schematic only. In use, with the system positioned in situ on the subject's body, the transmitter and receiver units are preferably positioned remotely from each other on the body.

[0098] The system further comprises a controller 36 operatively coupled to the skin interface units 32, 34. The controller may be adapted to control the transmission of signals between the at least one transmitter unit and the receiver unit.

[0099] exist Figure 3 , the controller 36 is shown as a separate dedicated control unit. However, as described above, in other examples, the control functions may be performed by one or more of the skin interface units 32, 34 themselves. Thus, in the latter case, the controller may be a distributed controller, or its control functions may be distributed. Thus, in some examples, one or more of the skin interface units may include a controller, i.e., the control functions may be distributed among the skin interface units of the system.

[0100] In some examples, each of the skin interface units may include a local control module for performing at least part of the control functions of the overall system. For example, each may control at least its own transmit or receive functions. One of the units may be designated to perform a processing or determination step (for determining an indication of a location or generating, for example, guidance information). A configuration step may be performed in which the skin interface unit communicates and designates one of the units as being responsible for the determination step.

[0101] In the following description, references to controller 36 may be understood as references to a dedicated control unit or to one or more of the system's skin interface units that perform the relevant control functions.

[0102] As will be explained in more detail below, the circuitry for generating the signals and for processing the received signals may be distributed in different ways between the components of the system. In some examples, the circuitry may be entirely included by the central controller 36. In other examples, the transmitter unit 32 may include local circuitry for generating the electrical signals. In other examples, the signals may be generated externally, for example, by the central controller.

[0103] The controller 36 may also be adapted to derive a set of signal characteristics associated with each signal received at the receiver, the characteristics depending on the position and / or orientation of the receiver unit. The signal characteristics may be measured directly from the properties of the received signal, or may alternatively be derived or calculated from the properties of the signal. By way of example, it may include one or more of the following: signal transmission time ("flight time" between signal transmission and reception), signal attenuation (path loss) between the transmitter and the receiver, a phase angle difference between at least two electrodes included by the receiver unit 34.

[0104] A set of derived signal characteristics may define a body fingerprint (BFP) corresponding to the current placement location of the receiver unit 34 .

[0105] The system 30 may be a physiological parameter monitoring system. In particular, one or both of the skin interface units 32, 34 may be used to sense one or more physiological signals (such as, for example, electrocardiogram (ECG) or electromyogram (EMG) signals). In this case, accurate positioning of the (one or more) skin interface units (in particular, the receiver units) may be important so that the monitoring of these physiological parameters is accurate.

[0106] To assist in this, the controller 36 may be configured to derive an indication of the position and orientation of the receiver unit.

[0107] The controller 36 may have access to a data set including a plurality of predetermined signal characteristic groups, each group being associated with one of a plurality of different reference locations and / or orientations of a receiver on the body. An indication of the location and orientation of the receiver 34 may be derived based on comparing a derived set of signal characteristics for the received signal with the predetermined signal characteristic groups in the data set. The data set may be stored locally, such as in a memory included by the system, or remotely, such as in a cloud or a remote computer with which the controller may communicate.

[0108] Output information may be generated by controller 36 based on the derived indication of position and orientation.

[0109] Despite Figure 3In the example of only two skin interface units are shown, but in other examples, a greater number of interface units may be provided. In a particular example, a plurality of transmitter units 32 may be provided. In other examples, a plurality of receiver units may be provided additionally or alternatively.

[0110] Where multiple transmitter units 32 are provided, the controller may be adapted to sequentially control the multiple signal transmitter units, each of which in turn is configured to transmit signals as a transmitter. The signal may be sensed at the receiver 34 for each transmitter, and for each, a separate set of signal characteristics corresponding to the received signal from that transmitter may be derived or measured. The entire set of signal characteristics from all transmitters may be grouped to form a single overall set of signal characteristics (single body fingerprint (BFP)) for a given receiver location.

[0111] The controller 36 may be configured to identify the total number of transmitter units connected to the system 30 .

[0112] The skin interface units 32, 34 may take different forms.

[0113] The transmitter unit 32 may be an on-body unit for mounting on a predetermined area of ​​the subject's skin, or an off-body unit for temporarily placing on a predetermined area of ​​the subject's skin.

[0114] For example, the transmitter unit 32 may be a wearable unit configured for mounting to a specific part of the body. In an advantageous example, the transmitter unit may take the form of a wrist-worn device. This carries the advantage that in this case the position of the transmitter unit may be stable and reliably known. However, the effect may also be achieved with other body-mounted devices that may be immovably fixed to a part of the body, such as, by way of example, a chest strap, an ankle strap or an ear hook.

[0115] In an example, the transmitter unit 32 may take the form of a smart watch device. The smart watch device may include a controller 36 according to an example.

[0116] The transmitter unit 32 may alternatively take the form of an external body unit, such as a weighing scale.

[0117] The receiver unit 34 may take the form of a sensor patch or pad for mounting on the skin of a subject. The sensor patch may include a flexible electrode or one or more flexible electrode pairs for sensing electrical signals from the skin or body. The patch may have an adhesive layer for coupling the patch to the skin. The receiver unit 34 may also be included in a handheld device. For example, a handheld ultrasound device may include a capacitive micromechanical transducer (cMUT) array for image acquisition.

[0118] The receiver unit 34 may be used to also monitor one or more physiological parameters as part of the physiological parameter monitoring functionality of the system 30. For example, the physiological parameter may be a vital sign.

[0119] The output information generated by the controller 36 may be guidance information for guiding the user in positioning the receiver unit 34 at a defined target location. The output information may simply include, for example, a representation or indication of a derived position and / or orientation indication. The output information may be communicated from the controller to a user output device, such as a sensory output device, for communication to the user. The sensory output device may be, for example, a display and / or a speaker.

[0120] Where the output information is guidance information, the controller 36 may be configured to compare the derived indication of position and orientation with a defined target position and orientation and, based on the comparison, generate guidance information for guiding the user in positioning the receiver unit at the target position and orientation.

[0121] The target location may be preprogrammed. For example, it may be one of a predetermined set of locations known to provide accurate monitoring of the physiological parameter of interest using the receiver unit 34. The target location may be at least partially user defined, such as via a user input device. For example, the target location may be input by a clinician before the patient leaves the hospital, or one of a set of predefined target locations may be selected. The target location may be one of the reference locations to which each set of predetermined signal characteristics in the data set corresponds.

[0122] The provision of output information in the form of guidance information (based on the determined receiver position) can assist a user (e.g., a patient) in correctly positioning a sensor element (e.g., a sensor patch, a handheld device) in a target location. As described above, this may be necessary because sensor patches typically need to be replaced every few days when a patient returns home.

[0123] An example process for guiding the correct placement of the device described herein (e.g., patch, handheld device, etc.) will now be described by way of illustration only. Although a patch is used by way of example, various other devices (such as a handheld device as described herein) can be positioned using similar components and / or methods.

[0124] According to this example, the process of guided placement of the patch can be performed in two stages. In the first stage, the correct position placement can be achieved. In the second stage, the correct orientation placement can be achieved.

[0125] According to the first stage, a user performing placement of the receiver unit 34 may place the unit at an initial position P. With the receiver at position P, the transmission of signals from the transmitter unit 32 to the receiver unit may be controlled, and a set of signal characteristics for the signals are derived, thereby deriving a body fingerprint (BFP) for position P.

[0126] The BFP can be compared with various BFPs included in the data set of the predetermined signal characteristic group. Based on the comparison, the proximity of P to each of the reference positions corresponding to each of the predetermined signal characteristic (predetermined BFP) group can be determined. Various algorithms for implementing such proximity determination can be adopted. An example can be found, for example, in the paper Belay, A. et al. (May 2017). Indoor localization at 5GHz using Dynamic machine learning approach (DMLA). In Applied System Innovation (ICASI), 2017 International Conference on (pages 1763-1766). IEEE.

[0127] A distance metric may then be calculated given an indication of the distance between the current receiver position and the defined target position.For example, the defined target position may be one of the positions represented within the data set of predetermined signal characteristics.

[0128] It may then be determined whether the receiver 34 is within a defined acceptable proximity threshold of the target location. If the target location is outside the set boundaries, the controller 36 may generate output information for guiding the user to reposition the receiver unit 34 at a new location closer to the target location. The guidance information may minimize the remaining distance metric to the target location. The controller may output an indication of the distance the receiver must move to reach the target location, for example, an indication of the distance metric itself. The controller may also determine an indication of the direction of displacement between the receiver location and the target location, and include this information in the output guidance information.

[0129] Once the user has moved the receiver unit 34 to a position where the distance metric may be within the defined proximity threshold, output information may be generated for indicating to the user that the receiver should be secured at the corresponding body position.

[0130] Following the correct position placement, in the second stage, guidance information can be generated to guide the user when the receiver device is correctly oriented. Using the receiver unit at the correct position on the body, the user can begin to orient the receiver unit 34 (i.e., rotate it relative to the skin). For each orientation, the controller can determine a new set of signal characteristics. These can be compared with a corresponding set of signal characteristics stored in a predetermined data set for defining the target orientation. Based on this comparison, an error metric can be calculated, which provides an indication of the angular difference between the current orientation and the target orientation.

[0131] If the derived error metric is outside the defined tolerance threshold, the controller can generate output information for guiding the user to reorient the receiver unit 34 at a new orientation that is closer to the target orientation. The guidance information can minimize the remaining error metric. Once the user correctly orients the mobile wearable device so that the error metric is within the set boundaries (i.e., within the tolerance threshold), output information can be generated to indicate to the user to stop orienting the receiver unit 34.

[0132] Thereby a correct position and orientation of the receiver unit can be achieved.

[0133] As discussed, the process performed by the controller may involve determining one or more signal characteristics associated with the signal receiver at the receiver unit 34. This will be explained in greater detail.

[0134] By way of example, one or more derived signal characteristics may include phase angle, signal transmission time, and signal attenuation between transmission and reception. Transmission time may refer to signal flight time: the duration of propagation between initial transmission and reception. Signal attenuation may refer to signal path loss: the change in signal strength between initial transmission and reception. Other signal characteristics may be derived additionally or alternatively.

[0135] The derived signal flight time (transmission time) can be achieved simply by recording the time of the emission of the signal and the time of the reception of the signal and calculating the difference. To perform this, at least one transmitter unit 32 and at least one receiver unit can each include an internal clock, and the clocks can be synchronized. The central controller 36 can track the emission of the signal and the time of the reception of the same signal at the receiver unit. Direct sequential emission and reception events can be assumed to be associated with the same signal.

[0136] Deriving the path loss (signal attenuation) can be accomplished simply by recording the signal strength when transmitting (or generating a signal for transmitting at a known strength), measuring the strength of the same signal when receiving, and then calculating the change. The strength of the signal can, for example, refer to the signal amplitude, for example in volts, such as peak-to-peak amplitude. The receiver unit 34 and the transmitter unit 32 can each include a signal processing device that allows measurement results of the signal strength (e.g., signal amplitude). In this case, each of the units can include a clock, and the clocks can be synchronized, thereby allowing the transmission and reception of a given signal to match each other. In particular, direct sequential transmission and reception events can be assumed to be associated with the same signal. However, alternatively, the central controller can include a signal processing device for measuring the signal strength (e.g., amplitude) of the signal received at the receiver unit, and can be configured to calculate the signal attenuation between transmission and reception.

[0137] At least one receiver unit 34 may comprise two or more electrode pairs. In this case, advantageously, one or more differential signal characteristics corresponding to the difference in the value of a given signal characteristic between two pairs of electrodes of the receiver unit 34 may be derived.

[0138] For example, the differential signal characteristic can be one or more of the following: phase angle difference, signal transmission time (flight time) difference, and signal attenuation (path loss) difference. In each case, the difference can be between the values ​​measured at each of the two electrode pairs of the receiver unit 34. The value of the differential signal characteristic for the receiver unit can be determined by, for example, the controller 36, or can be determined locally by the receiver unit 34. Optionally, the differential value can be derived for one or more signal characteristics for each combination of electrode pairs included by the receiver unit (where there are more than two).

[0139] Since the difference of the measured values ​​at two spatially separated electrode pairs varies consistently depending on the orientation state, the differential signal characteristic provides a particularly precise characterization of the positioning and in particular the orientation.

[0140] For illustration purposes, Figure 4 An example receiver unit 34 is shown comprising four pairs of electrodes 521, 522, 523, 524. The receiver unit may be shown in situ on the body together with a transmitter unit 32 in the form of a wrist-worn device. All possible phase angle differences between signals that may be received at at least two electrode pairs of the receiver unit may be described as follows:

[0141]

[0142] They are respectively indicated on the electrode pair 52 i and 52 j The phase angle difference between the signals received at Therefore, the electrode pair 52 i All phase angle differences with itself (where i=1, 2, 3, 4) is zero. Electrode pair 52 i With 52 j The phase angle difference between Respectively with the electrode pair 52 j and 52 i The phase angle difference between them is the same but of opposite sign, that is, Among them, i=1, 2, 3, 4 and j=1, 2, 3, 4 and when i≠j.

[0143] For example, indicates the phase angle difference between the signals received at electrode pair 521 and 522, etc. Thus, in the case where receiver unit 34 is oriented such that Figure 4 As shown, the phase angle difference between the signals received at the electrode pairs 521 and 523, respectively, is will be negative, and the phase angle difference between the signals received at electrode pairs 523 and 521, respectively will be positive, indicating that electrode pair 521 is closer to transmitter unit 32 than electrode pair 523.

[0144] Due to the equal (or nearly equal) distances between the electrode pairs 1022 and 1024 and the transmitter unit 32, the phase angle difference between the signals received at the electrode pairs 522 and 524 is and the phase angle difference between the signals received at electrode pair 524 and 522 will be zero (or almost zero). The phase angle difference between the signals received at electrode pair 521 and 522 and the phase angle difference between the signals received at the electrode pair 521 and 524 will be small but negative, and the phase angle difference between the signals received at electrode pairs 523 and 522 is and the phase angle difference between the signals received at the electrode pair 523 and 524 will be small but positive. These phase angle differences can characterize in a precise manner the orientation of the receiver unit 34 relative to the transmitter unit 32. A body fingerprint comprising such a differential signal characteristic is advantageous for enabling the orientation of the receiver unit to be derived based on a data set also comprising this characteristic associated with a known corresponding orientation.

[0145] As discussed, another possible differential signal characteristic that may be additionally or alternatively derived may be the time of flight (ToF) of a signal received at one of the at least two electrode pairs 521, 522, 523, 524 of the receiver unit 34 relative to the time of flight of a signal received at at least one other of the at least two electrode pairs 521, 522, 523, 524 of the receiver unit 34. The relative time of flight of the signal may also indicate the orientation of the receiver unit relative to the transmitter unit 32. More specifically, the longer the time of flight of the signal received at the electrode pair 521, 522, 523, 524, the farther the electrode pair is from the transmitter unit. Similarly, the shorter the time of flight of the signal received at the electrode pair, the closer the electrode pair is to the transmitter unit.

[0146] For example, where the receiver unit 34 is oriented such that Figure 4 As shown, the flight time t1 from the transmitter unit 32 to the electrode pair 521 can be the lowest compared to the flight times t2, t3 and t4 from the transmitter unit 32 to the electrode pairs 522, 523 and 524, respectively. The flight time t3 from the transmitter unit 32 to the electrode pair 523 has the highest value, while the flight times t2 and t4 from the transmitter unit 32 to the electrode pairs 522 and 524, respectively, will be equal (or almost equal) and less than the flight time t3 from the transmitter unit 32 to the electrode pair 523 but greater than the flight time t1 from the transmitter unit 32 to the electrode pair 521.

[0147] Thus, with the receiver unit 34 oriented as Figure 4 As shown, the relative flight time of the signals can be described as follows:

[0148] t1≤t2,t4≤t3.

[0149] This may provide information, in particular, about the orientation of the receiver unit 34 relative to the transmitter unit 32. In the case where the characteristic is time of flight (ToF), the receiver unit 34 may be time synchronized with the transmitter unit 32 prior to transmission of the signal from the transmitter unit 32 (e.g., in the manner previously described). The receiver unit 34 may generate a reference signal using an internal synchronization clock of the receiver unit 34. The reference signal may provide a reference to the signal transmitted from the transmitter unit 32. The central controller 36 may track the times of transmission and reception.

[0150] As discussed, a signal characteristic that may be additionally or alternatively derived may be an amplitude of a signal received at one of the at least two electrode pairs 521, 522, 523, 524 relative to an amplitude of a signal received at at least one other of the at least two electrode pairs 521, 522, 523, 524. In these examples, the relative amplitudes of the signals may specifically indicate an orientation of the receiver unit 34 relative to the transmitter unit 32.

[0151] Due to the impedance of the body, the signal transmitted from the transmitter unit 32 may experience attenuation as it passes through the body. Therefore, the amplitude of the signal transmitted from the transmitter unit 32 may decrease as it passes through the body. Attenuation of the signal occurs. The longer the signal passes through the body, the more the signal may attenuate (or the more the amplitude of the signal decreases). Therefore, the amplitude of the signal received at the electrode pairs 521, 522, 523, 524 of the receiver unit 34 is lower, the farther the electrode pairs 521, 522, 523, 524 are from the transmitter unit 32. Similarly, the amplitude of the signal received at the electrode pairs of the receiver unit 34 is higher, the closer the electrode pairs are to the transmitter unit 32.

[0152] For example, in the case where the receiver unit 34 is oriented such as Figure 4 As shown, the amplitude of the signal received at electrode pair 523 may be the lowest compared to the amplitudes of the signals received at the other electrode pairs 521, 522, and 524. Similarly, the amplitude of the signal received at electrode pair 521 may be the highest compared to the amplitudes of the signals received at the other electrode pairs 522, 523, and 524. The amplitudes of the signals received at electrode pairs 522 and 524 are equal (or nearly equal) and are smaller than the amplitude of the signal received at electrode pair 521 but larger than the amplitude of the signal received at electrode pair 523.

[0153] In some embodiments, the signal attenuation G may be derived as follows:

[0154] G=20log 10 (V 接收 / V 发送 ),

[0155] Among them, V 接收 is the amplitude of the signal received at at least two electrode pairs 521, 522, 523, 524 of the transmitter unit 34, and V 发送 is the amplitude of the signal transmitted from the transmitter unit 32.

[0156] The signal attenuation of the signal received at the electrode pair 521, 522, 523, 524 of the receiver unit 34 is greater the farther the electrode pair is from the transmitter unit 32. Similarly, the attenuation of the signal received at the electrode pair of the receiver unit 34 is smaller the closer the electrode pair 521, 522, 523, 524 is to the transmitter unit 32. Therefore, in the case of the orientation of the receiver unit 34, as Figure 4 As shown, the attenuation of the signal received at the electrode pair 521 is greater than the attenuation of the signal received at the electrode pair 522 , and the attenuation of the signal received at the electrode pair 524 may be less than the attenuation of the signal received at the electrode pair 523 .

[0157] The above explanations represent examples of signal characteristics that can be derived and do not limit the invention. Advantageously, in addition to the absolute value of the same signal characteristic, the two differential signal characteristics (differences in the signal characteristic values ​​between the two electrode pairs of the receiver unit) can be calculated. The latter can be particularly useful for inclusion in a body fingerprint for characterizing and thus deriving the position of the receiver unit. The former can be particularly useful for characterizing the orientation.

[0158] As mentioned above, the manipulation of signal generation and processing functions may be distributed in different ways between the components of the system 300. In one set of examples, signal generation and processing of received signals may be performed centrally by a (central) controller 36, with the first and second skin interface units simply serving to electrically couple the generated and received signals into and out of the body. For example, they may each simply include one or more electrodes for facilitating this.

[0159] Signal generation and processing of received signals may be distributed between the skin interface units. For example, a first skin interface unit 32 (transmitter unit 32) may include circuitry for generating signals for application to the body, and a second skin interface unit (receiver unit 34) may include circuitry for processing sensed signals.

[0160] Moreover, both the nominal transmitter 32 and receiver 34 units can be selectively configurable as a signal generator (i.e., a transmitter) or a signal sensor (i.e., a receiver). Therefore, the functions of the two can be interchangeable. Each can include a circuit for generating a signal for coupling into the body and for processing a signal coupled out of the body and returned. Therefore, each skin interface unit can be switchable between two modes or functions, thereby increasing the flexibility of the system. Such a skin interface unit can be referred to as a multifunctional interface unit.

[0161] Figure 5 Circuitry that may be included by such a multifunctional skin interface unit to allow both signal generation (transmission) and processing of received signals is shown in block diagram form.

[0162] The circuits may together form a transceiver unit 42 for controlling the generation and transmission of signals through the body via a given skin interface unit and also for the reception of signals at a remote location via a second skin interface unit. The transceiver unit may be referred to as an RF unit.

[0163] The transceiver unit 42 in this example includes a set of components (transmitter circuit portion 44) for controlling signal generation and transmission and a second set of components (receiver circuit portion 46) for controlling the reception of signals. These two parts are operatively connected to a microcontroller unit (MCU) that controls the transmitter portion 44 and the receiver portion 46. Both the transmitter portion and the receiver portion can be connected to a switch 50, which is interfaced with two skin contact electrodes 51a, 51b (labeled as electrodes A1 and A2). In other examples, more than one pair of electrodes may be included. The switch 50 can be used to switch a given interface unit 32, 34 between a signal transmission mode (which connects the electrodes to the transmitter circuit portion 44) and a signal reception mode (which connects the electrodes to the receiver circuit portion 46).

[0164] The signal transmitting part 44 comprises a signal generator 56 adapted to generate an electrical signal for coupling into the skin by the electrode 51. The signal generator advantageously generates an alternating current signal at a radio frequency. Preferably, a signal in the frequency range of 10 MHz to 150 MHz can be generated, because in this frequency range the human body behaves as a waveguide for signal transmission.

[0165] The transmitter portion 44 may also include a voltage booster and driver 54 adapted to receive the generated raw signals, amplify them (ie, boost them), and drive the application of the signals to the body via the switches and electrodes 51 .

[0166] The signal receiver portion 46 may include an analog front end element 60 for receiving the raw signal sensed by the electrode 51 in analog form via the switch 50. The front end element may communicate the received signal to an analog-to-digital converter 62, which processes the signal and outputs the signal to the microcontroller unit 48 in digital form.

[0167] In other examples, each of the skin interface units 32, 34 may be configured to perform only one of signal generation or signal sensing. In this case, they may each include only Figure 5 44 or the receiver circuit portion 46 shown in the figure, and the switch can be omitted. For example, the nominal transmitter unit 32 can include only the transmitter circuit portion 44, and the nominal receiver unit 34 can include only the receiver circuit portion 46.

[0168] In another example, the central controller 36 may include Figure 5 4. Both the transmitter circuit portion 44 and the receiver circuit portion 46 of the transceiver unit 42 are shown in FIG. 4, wherein the controller 36 is configured to electrically communicate signals to and from the skin interface units 32, 34.

[0169] Figure 5 The illustrated transceiver unit 42 is representative of circuitry that may be used to generate and process signals according to an embodiment. Other suitable circuit implementations capable of achieving similar functionality will be apparent to the skilled person.

[0170] To illustrate these concepts, embodiments will now be described in detail by way of example only.

[0171] Figure 6 The layout of the system 30 according to this embodiment is schematically illustrated. Although patches are used by example, various other devices (such as handheld devices as described herein) can be positioned using similar components and / or methods. The system is illustrated in situ with components attached to or mounted on the body of the subject 70. The system may include a transmitter unit 32 in the form of a smart watch or other related device. The transmitter unit may constitute a first skin interface unit for coupling the generated signal into the body. The system may include a receiver unit in the form of a sensor patch 34. The sensor patch may constitute a second skin interface unit for sensing a signal coupled into the body by a smart watch device. Although a single transmitter unit is provided in this example, multiple transmitter units may alternatively be provided.

[0172] Although a smartwatch may be used, other examples according to this embodiment may use a different wearable device. Also, an off-body device such as a smart weight scale or a handheld device may be used. This provides the same advantage: the location of the on-body device is reliably known because it is configured for application to a specific location on the subject's skin (i.e., in this case, the foot).

[0173] The wearable device 32 and the sensor patch 34 may each include a plurality of electrodes for directly interacting with the skin. Preferably, the wearable device may include one or more electrode pairs configured as transmitter electrodes. Preferably, the sensor patch may include at least one pair of electrodes configured as receiver electrodes.

[0174] The wearable device 32 and the sensor patch 34 may each include Figure 5Transceiver circuit 42 is shown and described above. For a sensor patch, the circuit can be configured for reception (Body Channel Signal (BCS) receiver circuit 46 is active), while for a wearable device transmitter, the circuit can be configured for transmission (Body Channel Signal (BCS) transmitter circuit 44 is active). Alternatively, the patch can include only the receiver circuit portion 46, and the wearable device can include only the transmitter circuit portion 44.

[0175] The system may also include a dedicated controller (not shown). Alternatively, the control functions may be performed by one or more of the skin interface units 32, 34. For example, the controller may be included by the wearable device 32, or the wearable device may form or constitute the controller, i.e. may perform the functions of the controller. References to the controller may be taken as references to either option.

[0176] Communication between the patch 34 and the wearable device 32 may be facilitated either wired or wirelessly via any suitable communication medium or channel. Wireless communication may be preferred for reasons of comfort and flexibility. In this case, both the wearable device 32 and the patch 34 may include wireless communication modules that facilitate this. These may include standard communication technologies such as, for example, Bluetooth, Wi-Fi, ultra-wideband (UWB), or body-coupled communication.

[0177] In use, the wearable device 32 can be mounted on Figure 6 A known location on the body is shown (ie, in this case, the wrist).

[0178] The controller 36 may be configured to determine an indication of the position and orientation of the sensor patch 34. To accomplish this, a set of signal characteristics corresponding to signals transmitted between the wearable device 32 and the patch 34 may be determined.

[0179] For example, each electrode pair included by the transmitter unit 32 can be controlled to couple an electrical signal to the skin of the body (body channel signal (BCS)) for transmission via the body's electrical body channel. The electrode pairs can be controlled to couple the signals one at a time in a sequential manner. For each of these transmitted BCS signals, each electrode pair included by the patch 34 (receiver unit) can receive a signal.

[0180] For each received signal, a set of multiple signal characteristics may be derived. These may be based on directly measured properties of the signal or may be derived or calculated from measured signal properties.

[0181] Example procedures for deriving various signal characteristics at a receiver unit have been described above in detail.

[0182] In the case where the receiver patch 34 has only one pair of electrodes, it may be possible to measure signal characteristics including signal attenuation (path loss (PL)) and signal transmission time (time of flight (ToF)) of the received signal. If the receiver patch has more than one pair of electrodes, it may be possible to measure differential signals, such as phase angle difference, ToF difference, PL difference between two receiver electrode pairs. Optionally, multiple sets of measurements may be performed for different signal transmission frequencies. As discussed above, in the case where the system 30 includes multiple transmitter units, each transmitter may be controlled to transmit a signal through the body in turn and separate sets of signal characteristics derived for the signals received from each. When two or more transmitter units are present, optionally, one may be configured to operate as a master transmitter to coordinate the process of sequentially configuring each transmitter unit to transmit a signal. A separate central controller 36 may perform this function.

[0183] Thus, there are multiple degrees of freedom available for establishing a body fingerprint. Multiple sets of signal characteristics can be derived for each of multiple possible electrode pairs on each receiver and transmitter and for multiple transmitters. This allows for very comprehensive body fingerprint generation, allowing for detailed characterization of specific body locations, and therefore more accurate receiver localization.

[0184] As an example, for a given position and orientation of a receiver unit 34 on the body, there may be M receiving electrodes comprised by the receiver unit 34, N transmitting electrodes comprised by the transmitter unit 32, a total of P transmitter units, and a set of Q different signal characteristics that can be derived in each case. In this case, it may be possible to obtain a set of M*Q signal characteristic measurements for each electrode pair of each respective transmitter unit. Thus, for a single transmitter unit, it may be possible to obtain N*M*Q signal characteristic measurements. For the entire group of transmitter units, it may be possible to obtain a set of P*N*M*Q signal characteristic measurements.

[0185] Furthermore, this (P*N*( M C2)*Q) combinations are also possible, i.e., the differences in derived signal characteristics between different pairs of electrodes of receiver unit 34. Thus, in this example, the total number of signal characteristic measurements that can be obtained is (P*N*M*Q)+(P*N*( M C2)*Q) measurement results.

[0186] Furthermore, each of the measurements may be repeated for F different signal frequencies. In this case, a set of (F*P*N*Q)(M+*( M C2)) Different signal characteristics may be possible.

[0187] As described above, the complete set of signal characteristics for a given body position of a receiver unit 34 may be referred to as a body fingerprint of the receiver unit relative to the transmitter unit(s) 32 for a given position and orientation on the body.

[0188] A given body fingerprint can be expressed as a BPF i,j , where i indexes a complete set (i.e., i={1, 2, 3, …(F*P*N*Q)(M+*(MC2))}) of specific body channel characteristics, and j={1, 2, 3, …J} for J different possible positions and / or orientations (also known as positioning) of the receiver unit 34 on the body.

[0189] It may be noted that the above example is one of many possible ways by which a comprehensive body fingerprint (BFP) may be established. In other examples, other or additional signal characteristics may be derived for each signal, and other options and variations will be apparent to the skilled person.

[0190] It may be noted that certain measured or calculated signal characteristics may vary with the position of the receiver unit 34, whereas other parameters may vary with the orientation. It is therefore possible to derive indications of position and orientation independently by considering only an appropriate subset of the signal characteristics in each case and comparing these only with a corresponding appropriate subset of predetermined signal characteristics.

[0191] Embodiments are based on comparing a set of sensed signal characteristics with a data set of predetermined signal characteristics, each set being associated with one of a plurality of different reference positions and / or orientations of a receiver on the body. In this way, an indication of the position and orientation for the receiver unit 34 can be derived.

[0192] To facilitate this, there may be a system training method for initially establishing a data set for a plurality of predetermined signal characteristic groups. This may be performed once as an initial set-up process, and the derived data set then used by the system for each subsequent iteration of the location determination process. It may be performed, for example, by a nurse or other hospital personnel during the initial application of the patch to a patient in a hospital or other care facility. It may also be performed by a medical professional or technician during an imaging application as described with reference to a handheld imaging device. Although a patch is used by example, various other devices (such as a handheld device as described herein) may be positioned using similar components and / or methods.

[0193] To perform the system training process, a nurse or other personnel first installs one or more transmitter units 32 on or against the patient's body. For example, the transmitter unit can be a wearable device, such as a wrist-worn device, or can be one or more external body devices, such as a smart weight scale. The transmitter unit is configured to perform as a transmitter (e.g., in the case where the unit includes a general transceiver unit 42, such as the above Figure 5 A receiver unit 34 (such as a sensor patch) may also be prepared for mounting to the body, and this may be configured as a receiver.

[0194] The receiver unit 34 may be placed at a first specific position and orientation on the body. A specific control mode may be triggered on the controller 36 to activate a training process, for example, a specific app may be launched. The transmission of signals between the transmitter and the receiver unit may be controlled by the controller 36, and a first set of signal characteristics (i.e., a first body fingerprint (BFP)) corresponding to the received signal for the first position may be derived. This may be stored locally in a memory or in a controller or transmitter unit 34 (e.g., a wearable device), or remotely, for example, in the cloud.

[0195] Then, the nurse or other personnel then sequentially places the receiver unit 34 at multiple other locations (positions and orientations) on the body, and for each location and orientation, a corresponding set of signal characteristics (corresponding BFPs) can be derived and stored. The complete data set of signal characteristics for multiple different receiver positions thus formed can be compiled and stored either locally or remotely. It can be stored at the controller and / or the receiver unit. It can be stored in the cloud additionally or alternatively.

[0196] The nurse or other personnel then designates one of the trial positions and orientations as the target position and orientation where the patient should be guided by the system to place the patch or device when they begin replacing and / or reinstalling it. This designation can again be stored locally and / or remotely.

[0197] Process About Figure 7 and 8 Two example on-body sensor systems are schematically illustrated in FIG. Figure 7 Shows Figure 6 , including a single sensor patch 34 as a receiver unit and a single wrist-worn transmitter unit 32. Multiple dashed circles indicate various reference positions and orientations 72 to which the patch can be sequentially moved throughout the training method. The solid circle illustrates a single assigned target position and orientation 74 at which the user will be guided to place the patch by the system when replacing the patch at home. Again, although a patch is used by example, various other devices (such as a handheld device as described herein) can be positioned using similar components and / or methods.

[0198] Figure 8 A process is illustrated for a second example on-body sensor system comprising two transmitter units 32a, 32b, each in the form of a wrist-worn device. Again, the dashed circles indicate various reference positions and orientations 72 to which the patch can be sequentially moved, and the solid circles illustrate the assigned target positions and orientations 74 for later positioning of the patch. However, in this case, for each position and orientation 72, each of the transmitter units 32a, 32b can then be activated to generate and transmit a signal and a signal characteristic group derived for the signal of each transmitter. The signal characteristics for the two transmitter units are combined to form a single integrated signal characteristic group for each position and orientation (i.e., to form a single body fingerprint (BFP) for each position).

[0199] Aspects may include methods for configuring placement of a skin interface unit of an on-body sensing system. This includes determining an indication of a placement location for a skin interface unit (receiver unit), and (in a preferred embodiment) providing guidance information to a user for guiding the user in repositioning the unit closer toward a defined target location. As discussed above, such methods particularly find beneficial applications in which a system can be used for at-home monitoring of one or more physiological parameters over a period of time after a patient has been discharged from a hospital, and in which the receiver unit can be used for use in measuring those parameters. Receiver units (e.g., sensor patches) often need to be replaced frequently, which requires the patient to reposition them on their body after they are replaced. Accurate positioning is important to ensure reliable and accurate parameter monitoring, but can be difficult without medical training.

[0200] By way of illustration, reference will now be made to Fig. 9 and Fig.10

[0013] An example method for configuring placement of receiver units of a sensor system is outlined. The described examples are for illustration only and are not intended to be limiting.

[0201] The placement method can be divided into two sequential phases: a first phase 82 for placing the receiver unit at the target location (shown in block diagram form in Fig. 9 and a second stage 108 for orienting the receiver in a target orientation (shown in block diagram form in Fig.10 ).

[0202] refer to Fig. 9 In a first step 88, the user may remove the current receiver unit (e.g., sensor patch) for replacement by a new unit. Optionally, a data set of predetermined signal characteristics for different reference positions may need to be transferred to the new patch. This data may also be stored in the central controller 36.

[0203] A target position and orientation for placing the new device on the body may be acquired 90. This may be pre-assigned by the nurse, in which case the step includes retrieving the stored assigned target position and orientation. The user may also set or select the target position and orientation. This may be selected from the set of reference positions and orientations to which the predetermined signal characteristics of the data set correspond.

[0204] The user may then trigger a device placement process on the system, for example by triggering a specific control mode on the controller 36, or launching a specific app, and place 94 a new device (e.g., a patch or handheld device) in an initial first position. The transmitter unit 32 may be controlled to transmit a signal and signal characteristics are derived for the signal received at the receiver patch, thereby forming a body fingerprint (BFP) for the initial position. This may be compared to a predetermined set of signal characteristics (predetermined BFP) in a data set for an assigned target position.

[0205] An indication of the current location can be derived based on calculating 96 a distance metric between the measured BFP and a predetermined BFP in a data set for the target location. The paper Belay, A. et al. (May 2017). Indoor localization at 5 GHz using Dynamic machine learning approach (DMLA). In Applied System Innovation (ICASI), 2017 International Conference on (pp. 1763-1766). IEEE describes various algorithms that can be used to calculate this.

[0206] Based on the distance metric, the current position of the device relative to the target position can be determined. It can be determined 100 whether the distance metric between the current position and the target position is small enough that the device is within a defined acceptable proximity threshold. The proximity threshold can be configurable (e.g., input by a user), or can be predefined. It can be defined based on a required accuracy or precision of device placement.

[0207] If the device is not within the allowed proximity threshold ("No"), guidance information may be generated and output 102 to the user for guiding the user in repositioning the device closer to the target location. The guidance preferably includes an indication of the direction and distance that the device should move in order to minimize the distance metric. The distance metric calculation 96 and check 100 steps may then be repeated.

[0208] If and when the device is found to be within a proximity threshold of the target location, output information may be generated 104 for indicating to the user that the device is in the correct location and should be installed, attached, or left in place at the current location.

[0209] Following proper positioning, the second phase of the placement process involves placing the device in the correct orientation. Fig.10 The steps of this phase are shown in block diagram form.

[0210] Once the correct position is reached, if desired, the user orients the device 110 in a first initial orientation 110. As described above, a set of signal characteristics (BFPs) may be derived for the initial orientation. An error metric may be calculated 112 by comparing the current orientation BFPs with the BFPs in a predetermined data set corresponding to the target position.

[0211] It may be determined 114 whether the error metric is small enough to place the device within a defined angular proximity threshold of the target orientation. If the orientation is outside the defined bounds ("No"), guidance information may be generated and output 116 to the user for guiding the user in reorienting the device closer to the target orientation. The guidance information preferably includes an indication of the angular distance and direction in which the device should be moved to minimize the error metric. The error metric calculation 112 and check 114 steps may be repeated.

[0212] If and when the device is found to be within a proximity threshold of the target orientation, output information may be generated 118 for indicating to the user that the device is in the correct position and orientation and should be installed, attached, or remain in place at the current position and orientation.

[0213] The skin interface unit placement method can be complete.

[0214] As discussed above, embodiments may utilize a data set of predetermined sets of signal characteristics (BFPs) for different reference positions and orientations.

[0215] Now refer to Fig.11 An example system training method 130 for establishing a data set of predetermined signal characteristics for different reference locations is outlined in more detail. This may be performed prior to placement of a receiver unit, e.g., based on Fig. 9 and 10 Therefore, the process can be Fig. 9 The method is performed once before step 88. Fig. 9 and 10 The steps of the method may be repeated as many times as required in subsequent iterations without repeating Fig.11 Systematic training method.

[0216] refer to Fig.11In a first step 132 of the example training method 130, a nurse or clinician may instruct the controller 36 that system training is to be performed by triggering a particular control mode on the controller or, for example, initiating an app. The nurse or other user may then place 134 a receiver unit (e.g., a patch for this example) on the patient's body in a plurality of different positions and orientations, and for each, a set of signal characteristics (BFP) may be derived 136 according to the methods described in the previous examples. This may be repeated for N positions to derive what may be referred to as a BFP j N groups of signal characteristics (BFP), where j = {1, 2, 3…N}.

[0217] The entire set of BFPs may be stored 138 as a data set in local memory and / or remotely, such as in the cloud. It may be stored locally at the transmitter unit and / or at the central controller 36.

[0218] The user can attach 140 the patch at one of the reference locations and preferably store locally or remotely on the system an indication that the patch is fixed at that location. Preferably, the nurse also stores the specified target location where the patient will be guided in placing the patch during a subsequent placement procedure.

[0219] Due to changing skin properties (such as moisture level), the signal characteristics that make up the body fingerprint (BFP) corresponding to a specific receiver position and orientation may change over time. Therefore, the predetermined set of signal characteristics in the data set may become inaccurate over time. If the predetermined signal characteristics are not updated or corrected, this can lead to inaccurate position and orientation determination. Therefore, according to one or more advantageous embodiments, the system configuration method may further include a calibration step in which the predetermined set of signal characteristics is corrected.

[0220] The calibration method may assume a known initial position of the receiver unit 34, for example based on a known position where the receiver is placed by a nurse or clinician (e.g. stored by them during an initial training or calibration procedure), or based on a previously determined position. The method may include: controlling the transmission of electrical signals between the transmitter unit 32 and the receiver unit 34; and deriving a set of signal characteristics associated with the received signals. These form a body fingerprint corresponding to the current position of the receiver. The derived set of signal characteristics may be compared to a predetermined set of characteristics corresponding to the same current known position of the patch. The predetermined signal characteristics may be corrected based on any differences between the newly calculated characteristics and the previous characteristics.

[0221] Preferably, based on any derived differences, a correction factor may be derived and this applied to each of the predetermined set of signal characteristics in the data set, thereby updating the data set.

[0222] Although a patch is used by way of example, various other devices, such as a handheld device as described herein, may be positioned using similar components and / or methods.

[0223] Fig.12 An example calibration method, which will now be outlined in more detail, is shown in block diagram form. The calibration method may be used, if desired, to be performed after an initial training method for establishing a data set for a predetermined set of signal characteristics (e.g., based on Fig.11 However, calibration methods (if required) can be Fig. 9 and 10 The receiver unit placement method of the embodiment of the present invention is performed before. It can be used to be performed between these two processes. Again, although patches are used by example, various other devices (such as handheld devices as described herein) can be positioned using similar components and / or methods.

[0224] refer to Fig.12 In a first step 144 of a calibration process 142, the patient or other user may trigger a patch recalibration process on the central controller 36. The transmitter unit 32 may be controlled to transmit a signal through the body and derive 146 a set of signal characteristics of the signal received at the receiver patch 34 in its initial position and orientation.

[0225] It may be determined 148 whether the derived signal characteristics for the current (initially known) position are different from the predetermined signal characteristics for the same position stored in the data set. If not ("No"), recalibration may not be required. If there is a difference, a correction factor may be determined 152 between the measured signal characteristics (or BFP) for the correct position and the pre-stored signal characteristics for the same position. The correction factor should be suitable for mapping or transforming a set of pre-stored characteristics to the newly derived characteristics. The predetermined characteristics for the known position may be updated based on the newly derived characteristics.

[0226] The correction factors may be applied 154 to each of the predetermined sets of signal characteristics (BFPs) stored in the data sets for the various different reference positions and orientations to thereby correct the data sets to compensate for the changing skin conditions.

[0227] An updated data set of predetermined signal characteristics (BFP) sets may replace the previous data set locally (e.g., at a controller and / or patch and / or transmitter unit) and / or stored remotely 156, such as in the cloud or a remote computer with which the controller or system can communicate.

[0228] Output information may be generated 156 for indicating to the user that the recalibration procedure may be complete.

[0229] Once recalibration is complete, the user can remove the patch from their body in order to replace it.

[0230] The above outlines and Figure 9-12 The various methods and processes illustrated can be combined in a sequential order according to certain examples to provide a fully integrated on-body sensor system configuration method.

[0231] Therefore, in summary, according to the most comprehensive embodiment, the on-body sensor system configuration method can be understood as a four-step process:

[0232] Step 1: Establish a systematic training process for a data set of predetermined signal characteristics for different reference positions (e.g., based on Fig.11 method).

[0233] Step 2: Recalibration process of the established dataset to correct for any changes in skin properties (e.g., Fig.12 method).

[0234] Step 3: Receiver unit location placement process (e.g., based on Fig. 9 method).

[0235] Step 4: Receiver unit orientation placement process (e.g., according to Fig.10 method).

[0236] Although the above embodiments of the present invention are described in the form of a patch, it is apparent that the above embodiments can be advantageously applied to handheld devices that are in contact with the body, such as the handheld devices in contact with the body described throughout this disclosure. An example of this type of device is a handheld imaging sensor and in particular a handheld ultrasound device that may include a cMUT array for image acquisition.

[0237] As discussed above, embodiments may utilize a dedicated controller 36. The controller may be implemented in a variety of ways using software and / or hardware to perform the various functions required. A processor may be an example of a controller that employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the desired functions. However, the controller may also be implemented with or without a processor, and may also be implemented as a combination of dedicated hardware for performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuits) for performing other functions.

[0238] Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0239] In various embodiments, a processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memory, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that perform the desired functions when run on one or more processors and / or controllers. The various storage media may be fixed within a processor or controller, or may be transferable so that one or more programs stored thereon may be loaded into a processor or controller.

[0240] Those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed invention by studying the drawings, the disclosure and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the words "one" or "an" do not exclude multiple. A single processor or other unit can implement the functions of several items recorded in the claims. Although certain measures are recorded in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference numerals in the claims should not be interpreted as limiting the scope.

Claims

1. A body sensor system comprising: at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit and at least one receiver unit, the at least one transmitter unit being arranged to be placed against a known area of ​​the subject's skin for coupling signals into the body, and the at least one receiver unit being arranged to be placed at a remote location for sensing the coupled signals; a controller coupleable to the skin interface unit and adapted to control transmission of signals between the at least one transmitter unit and the at least one receiver unit and to derive a set of signal characteristics associated with each signal received at the at least one receiver unit, the set of signal characteristics being dependent on a position and an orientation of the at least one receiver unit, and the set of signal characteristics comprising at least one signal characteristic dependent on the position of the at least one receiver unit and at least one signal characteristic dependent on the orientation of the at least one receiver unit; the controller having access to a data set comprising a plurality of predetermined signal characteristic groups, each group being associated with one of a plurality of different reference positions and orientations of the at least one receiver unit on the body; Wherein the controller is configured to derive an indication of the position and orientation of the at least one receiver unit based on comparing the derived set of signal characteristics for the received signal with the predetermined set of signal characteristics, and to generate output information based on the derived indication of the position and orientation of the at least one receiver unit.

2. The on-body sensor system of claim 1, wherein: The controller is configured to compare the derived indication of the position and orientation of the at least one receiver unit with a defined target position and orientation, and to generate guidance information based on the comparison for guiding a user to position the at least one receiver unit at the target position and orientation.

3. The on-body sensor system of claim 2, wherein: The controller is adapted to derive an indication of a distance between the derived position and the target position based on the comparison, the output information being based on the derived distance.

4. The on-body sensor system of claim 3, wherein: The controller is adapted to determine whether the derived distance is within a defined acceptable proximity threshold of the target location and to generate guidance information for positioning the at least one receiver unit closer to the target location only if the distance is outside the acceptable proximity threshold.

5. The on-body sensor system of claim 3, wherein: The controller is adapted to determine a direction of displacement between the derived position and the target position, and wherein the output information includes an indication of the direction.

6. The on-body sensor system of claim 5, wherein: The controller is adapted to generate guidance information for moving the at least one receiver unit based on the derived distance and direction to the target location, the at least one receiver unit being configured to minimize the distance between the at least one receiver unit and the target location.

7. An on-body sensor system according to any one of claims 1 to 6, wherein: The at least one receiver unit comprises at least two pairs of skin coupling electrodes.

8. The on-body sensor system of claim 7, wherein: The set of derived signal characteristics comprises a separate subset of derived signal characteristics for each of the electrodes.

9. The on-body sensor system according to any one of claims 1 to 6, wherein: The controller is configured to identify the total number of transmitter units and then control transmission of signals by each transmitter unit if more than one transmitter unit is present and derive a separate set of signal characteristics associated with the signals received from each transmitter unit.

10. The on-body sensor system according to any one of claims 1 to 6, wherein: The at least one receiver unit takes the form of an on-body sensor patch.

11. The on-body sensor system according to any one of claims 1 to 6, wherein: The at least one transmitter unit takes the form of a wearable device for mounting to a specific part of the body, or The at least one transmitter unit takes the form of an extra-body device for temporary placement against the skin of a specific part of the body.

12. The on-body sensor system of claim 11, wherein: The wearable device is a wrist-worn wearable device.

13. An on-body sensor system according to any one of claims 1 to 6, wherein: The on-body sensor system is for monitoring one or more physiological parameters of a subject, and wherein the at least one receiver unit is for sensing the one or more physiological parameters.

14. An on-body sensor system according to any one of claims 1 to 6, wherein: The signal characteristics include one or more of: signal transmission time, signal attenuation between a transmitter and a receiver, and a phase angle difference between at least two electrodes included by the at least one receiver unit.

15. A method of training an on-body sensing system to configure placement of a skin interface unit of said on-body sensing system, The on-body sensing system comprises: at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit for placement against a known area of ​​the subject's skin for coupling signals into the body, and at least one receiver unit for placement at a remote location for sensing the coupled signals, and The method comprises: sequentially placing the at least one receiver unit in each of a plurality of different reference positions and orientations on the body, and controlling transmission of signals between the at least one transmitter unit and the at least one receiver unit for each position and orientation, and deriving a set of signal characteristics associated with signals received at the at least one receiver unit for that position and orientation, and the set of signal characteristics comprising at least one signal characteristic that depends on the position of the at least one receiver unit and at least one signal characteristic that depends on the orientation of the at least one receiver unit; and Storing multiple sets of signal characteristics for the multiple different reference positions and orientations of the at least one receiver unit to derive a data set of predetermined signal characteristics, the data set being used to subsequently derive an indication of the position and orientation of the at least one receiver unit based on comparing the sensed signal characteristics with the stored predetermined characteristics.

16. A method of configuring placement of a skin interface unit of an on-body sensing system, the on-body sensing system comprising: at least two skin interface units for coupling electrical signals into and / or out of a subject's body, the at least two skin interface units comprising at least one transmitter unit for placement against a known area of ​​the subject's skin for coupling signals into the body, and at least one receiver unit for placement at a remote location for sensing the coupled signals, The method comprises: controlling transmission of signals between the at least one transmitter unit and the at least one receiver unit to derive a set of signal characteristics associated with each signal received at the at least one receiver unit, the set of signal characteristics being dependent on a position and an orientation of the at least one receiver unit, and the set of signal characteristics comprising at least one signal characteristic dependent on the position of the at least one receiver unit and at least one signal characteristic dependent on the orientation of the at least one receiver unit; accessing a data set comprising a plurality of predetermined signal characteristic groups, each group being associated with one of a plurality of different reference positions and orientations of the at least one receiver unit on the body; deriving an indication of the position and orientation of the at least one receiver unit based on comparing the derived set of signal characteristics for the received signal with the predetermined set of signal characteristics; and Output information is generated based on the derived indication of the position and orientation of the at least one receiver unit.

17. The method according to claim 16, further comprising: The method according to claim 15 performs an initial system training procedure in order to determine the predetermined set of signal characteristics for subsequent use in any of one or more iterations of the steps of the method according to claim 16 .

Images