TECHNICAL FIELD

[001] The present invention concerns a system of components and processes whereby a human or animal heart rate (pulse) and other factors indicative of metabolism can be accurately and conveniently sensed and recorded during normal and vigorous exercise activity.

PRIOR ART

[002] Conventional heart rate monitors are used to detect a human or animal pulse by

sensing the electric field generated by the heart as it progresses through a cycle of contraction and relaxation. Conventionally the electrical potential at the skin surface is sensed via one or more "wet" conductive biosensor electrodes in intimate adhesive contact with the subject's skin. Electrical contact is generally achieved via a conductive gel. However, such systems suffer from a range of well-known problems including: a requirement for the skin to be prepared clean and free of hair, and variations in sensitivity caused by metabolic changes such as perspiration and, partial, or total displacement during activity.

[003] Dry contact sensors have also been used but are even more vulnerable to imprecise sensing due to the skin condition of the subject even when the skin is well prepared.

[004] Non-contact sensors have been researched as exemplified by the disclosure in

WO2015061282A.

[005] The electric field does propagate beyond the skin. As remarked in WO2015061282A development in "dry" biosensor electrodes has focused on non-contact capacitive sensors in which two capacitive sensors comprising capacitor plates generate signals on two separate channels. Different input load capacitances are provided at each channel. When disposed close to the skin of a subject the input coupling capacitance of each capacitor plate can in theory be determined from the different input load capacitances.

[006] An object of a non-contact sensor is to facilitate mounting the monitor for use close to the chest and heart without resorting to straps and adhesives. For example to clamp or pin the monitor to the an item of clothing such as a sports bra. However, mounting in this way inevitably means that the sensor will move relative to the subject users skin, both towards and away from the skin and parallel to the skin. Such movements will induce fluctuations in the output signal which obscure the fluctuations induced by the beating heart (the heart field or heart signal).

[007] In practice the electric field generated by the heart action is very weak and is liable to fluctuate in frequency and amplitude during exercise. The heart field is also weak by comparison with unwanted electric fields generated by other user muscular activity, in particular involuntary muscular activity caused by respiration and voluntary muscular activity caused by exercise. The sensors are also liable to pick up electrical noise from nearby extraneous machinery. The unwanted electric fields have hitherto proven difficult to eliminate reliably with a monitor system which is convenient and practical to use.

[008] In a medical environment it is desirable to collect a great deal of information about the changes to the electric field caused over time by the heart function, because these can indicate underlying disease conditions. In a non-medical environment the main interest in ECG sensing is to determine pulse as an indicator of metabolic rate and

performance during exercise. A relatively accurate estimate of energy expended (calories) during exercise can then be calculated from the record of pulse (heart rate) over time and other characteristics of the individual such as weight and age. The rate of change of a user's pulse and degree of change in reaction to activity is a further indicator of fitness.

[009] Non-medical or sports heart rate monitors commonly use a dry contact electrode

sensor package containing the bio-electrode strapped to the chest of a user via a band. Such electrodes are susceptible to poor connectivity depending on the condition and preparation of the subjects skin. Signals from the sensor package are fed to a processing and recording device, often a wrist borne device or smart phone.

Communication is via a wire or wirelessly via a protocol such as ZIGBEE®,

BLUETOOTH ® or WiFi. Where wireless communication is employed each of the sensor package and PRD must have separate power supplies, usually in the form of compact cells. The cells require frequent inconvenient and expensive replacement. Rechargeable cells require ports for charging plugs which may add to the weight and size of the package and may be vulnerable to fouling or damage.

[010] There is also an interest in monitoring general levels of activity and fitness, that is to say, non-exercise oriented activity throughout a user's day. Prior art monitors such that disclosed in US2014213858A1 disclose a system to estimate or calculate a user's heart rate based on motion activity sensed by an inertial accelerometer in a wearable device attached to the person based on empirical statistical data and a users characteristics such as height, weight, sex and age. However, the reliability of such motion detectors is highly dependent on the kind of activity. For example, a wrist borne motion sensor device may indicate minimal movement during vigorous activity such as static or track cycling where the heart and lungs (ie the chest) are working very vigorously but the wrist is relatively inactive.

[on] While conventional heart rate monitors are intended to measure heart rate

performance during vigorous sports or fitness activity sessions they are generally ill suited to monitoring activity the rest of the time if only because of the inconvenience of wearing a chest strap and issues relating to keeping the device charged. Recently there has been a trend to offer fitness monitors such as the Fitbit ® and Apple ® watch capable of monitoring activity from a wrist band mounted device. Because such devices are wrist mounted they are not particularly accurate during fitness sessions but are convenient devices to wear during other activities. Users wishing to capture accurate heart rate activity data during fitness sessions as well as to gain a more general impression of their activity during the day will need to switch between different devices, which is inconvenient and expensive.

[012] Known wrist-borne devices such as the Apple ® watch are notoriously power hungry and therefore require frequent battery replacement or recharging. This is not a significant problem for intermittently worn conventional heart rate monitors.

[013] One aim of the present invention is to provide a system which provides the

advantages of accurate heart rate capture during fitness sessions with a convenient wrist-borne device monitoring activity during normal (ie non-fitness) activity, and which alleviates the issues of maintaining power on the device.

[014] Wrist-borne wearable devices need to take account of aesthetic appearance as well as weight and bulk, especially, but certainly not exclusively, if the device is intended for use by women. It is therefore desirable to be able to provide a writs wearable device which is slim and light without being fragile. It is also desirable to be able to readily change the wristband, for repair, and more importantly for aesthetic reasons.

[015] Conventional wrist band fastenings require a structure, usually a pair of projecting lug parts extending from the casing. The casing will comprise a ring extending around the mechanism with a base plate or back which is commonly removable to service the wrist watch. In some prior art a single lug is provided integral with the ring. The lug will have a through hole to receive an expandable spring bar or a screw which is also received into a corresponding moulded recess into the wrist band. The mirror arrangement with two circumferentially spaced lugs formed integral with the casing and a single lug formation on the end of the wrist strap to receive a screw or spring bar is also common. US2014156916 (Fitbit Inc) discloses a wrist band formed of a single unitary moulding of a viscoelastic material including a chamber into which a correspondingly shaped fitness monitor is inserted and retained by cooperation between the shape of the monitor device and chamber and the elasticity of the watchband. Inserting the monitor device requires removal of the wristband from the wrist and is somewhat fiddly. The use of such unitary structures moulded from elastic materials necessarily limits the design opportunities and materials which can be used.

[016] The Apple ® watch addresses the problem of exchanging a wrist band by means of a substantial case of sufficient depth to have two cylindrical channels formed into it. A wristband has two cylindrical formations provided at an end intended for attachment to the watch. The cylindrical formation is adapted to be captured into the cylindrical channel so attaching the strap. While a strap can easily be exchanged and can be formed from a range of materials with many design freedoms for the designer, the case of the Apple © watch is necessarily thick to accommodate the cylindrical formations. The present invention aims to address at least one of the technical problems described above in a heart rate and activity monitoring system.

STATEMENTS OF INVENTION First Aspect

[on] According to a first aspect of the present invention the present invention there is

provided a wearable heart rate and activity monitor system comprising:

a heart rate monitor sensor package; and

a communications package;

wherein the heart rate monitor package contains, a non-contact sensor system capable of sensing changes in a bio-electric field indicative of heart activity, a rechargeable power supply, and a charge transfer module;

the communications package comprising a wireless communications module and a communications package rechargeable power supply; and

means to separably connect the wireless communication module to the heart rate monitor package whereby the charge transfer module will transfer charge to the communications package power supply to recharge the communications package power supply.

[018] The non-contact sensor system present in the heart rate monitor package will

advantageously be a pair of capacitance electrodes sensitive to the electric field generated by the heart activity of a user without requiring direct electrical contact with the user's skin.

[019] The heart rate monitor package power supply may include at least one storage cell, to power the systems in the heart rate monitor package such as the sensor electrodes, analogue and digital filters and communication of data, especially heart rate data to the communications package.

[020] The charge transfer module will include means to receive a charge from an external power supply and transfer the charge onto the heart rate monitor package power supply. An external power supply may be any source of electric charge and will preferably be transferred via an inductive charging external power supply to an inductive charging module having a charge storage cell within the heart rate monitor package power supply.

[021] Preferably the means to separable connect the heart rate monitor package and

communications package forms a clip to grip a fabric,. Preferably a surface of the heart rate monitor package provides one jaw of the clip while the surface of the communications package provides the opposing jaw. The connected heart rate monitor package and communications package can conveniently be clamped around the edge of a sports bra or the collar of a shirt close to the chest and underlying heart.

[022] The means to separably connect the heart rate monitor package to the

communications package power supply may comprise a permanent magnet arranged to attract a permanent magnet disposed within the communications package. The means to separably connect may further comprise a flexible strap or "U" shaped spring supporting conductors and connectors to electrically connect the heart rate monitor package to the communications package. Where a flexible strap is used the magnetic attraction between the heart rate monitor package and the communications package will be sufficient to enable a span of clothing to be firmly clamped between the heart rate monitor package and the communications package thus securing the combined heart rate monitor package and communications package to the user. [023] In an alternative embodiment of the heart rate monitor system the flexible strap may be replaced by a hinge spring biased to close the jaws of the clip. The hinge may or may not be assisted by a magnetic closure.

[024] Each capacitance electrode will preferably be protected from external interference by means of an active shield guard ring forming a faraday cage. The capacitance electrodes will receive electric field signals generated by all the subject's active muscles, not solely the heart. The most consistent activity will be from the subject breathing. Preferably analogue and/or digital filters will operate to isolate signals generated from the heart activity from other electrical signals generated by other muscle activity such as respiration and voluntary muscle activity. In particular the received signals may be amplified by differential amplifiers tuned to filter out noise signals outside the frequency range of the heart generated signals to eliminate motion generated noise. A Driven right Leg (DRL) and/or an active body ground to further reduce motion artefacts, and DC noise generated from the capacitive connection. A fast test signal outside the frequency range of interest to evaluate quality of body connection. An adaptive filter responsive to feedback from the fast test signal to further filter out noise. An adaptive filter based on amplitude to remove poor signals.

[025] Charging of the communications package is achieved from the heart rate monitor

package while connected.

[026] While connected the signals acquired by the heart rate monitor package are

transmitted to the communications package. The communications package then retransmits the signals to a processing and readout device such as an application equipped smartphone or any other computer to be recorded processed and stored.

[027] When the heart rate monitor package is not in use it may be stored connected to a charger, preferably an inductive charger.

[028] The communications package may contain additional sensors such as a temperature sensor or acceleration sensor. The communications package may be adapted to be coupled to a body fastening such as a wrist band, finger ring, brooch, thigh band, ankle band, belt, or headband whereby it can be secured to a subjects wrist, finger, leg, lower torso, neck or forehead to capture data from the movement and general activity of the user. As a consequence of the charging arrangement the communications package can be used substantially continuously to collect data and serve other functions such as a time keeping watch without the need to interrupt use for charging. Second aspect

[029] According to the present invention there is provided a heart rate and activity monitor system comprising:

a heart rate monitor package; and

a communications package;

wherein the heart rate monitor package contains;

a pair of contactless sensors capable of sensing changes in a bio-electric field indicative of heart activity,

means to connect the heart rate monitor package to the communications package;

wherein the signals from each contactless sensor are filtered through a motion differential amplifier disposed in one of the heart rate monitor package or the communication package and arranged to subtract signal changes caused by relative movement of the heart rate monitor sensor package and the user.

[030] The sensors are separated and will sense a difference in strength of the heart electric field. The difference will be amplified by the motion differential amplifier. Changes in field strength caused by movements common to each sensor will be suppressed.

Second aspect

[031] According to a second aspect of the present invention there is provided a heart rate and activity monitor system comprising:

a heart rate monitor sensor package;

a communications package;

wherein the heart rate monitor package has a subject skin facing side and an opposite clip facing side and contains a pair of contactless sensors capable of sensing changes in a bio electric field indicative of heart activity, and

means to separably connect the heart rate monitor package to the communications package;

a guard amplifier arranged to receive signals from the contactless sensor and disposed in one of the heart rate monitor package or the communication package; wherein a conductive layer is disposed to partially envelop each capacitive sensor on the clip facing side and is coupled to a guard amplifier stage to shield the contactless sensor from extraneous signals. [032] The conductive layer leaves the subject facing side of each capacitive sensor exposed. Preferably the conductive layer extends into one or more side walls forming a cup around the capacitive sensor. Preferably the conductive layer is electrically connected to the guard differential amplifier stage to provide an active guard ring which attenuates the capacitive sensor signals induced by random motion of the monitor.

Third aspect

[033] According to a third aspect of the present invention there is provided a heart rate and activity monitor system comprising:

a heart rate monitor sensor package; and

a communications package;

and a pair of contactless sensors capable of sensing changes in a bio electric field indicative of heart activity,

a fast signal generator to generate a signal with a predetermined frequency "fast" in comparison with the frequency of the heart and to project an oscillating electric field at a frequency corresponding to the fast frequency;

said contactless sensors arranged to communicate with a fast filter module tuned to the "fast" frequency and a processor module responsive to a signal passed by the fast frequency filter to confirm that the contactless sensors are sensing a signal from the subject's bio-electric field without interfering with the heart rate signal.

[034] The system will have at least one pair of contactless sensors and may have three or more contactless sensors any two of which may be paired or may have multiple pairs of contactless sensors.

[035] The fast signal generator will preferably generate a fast signal above 100 Hz and

preferably of 2kHz. The projected electric field will induce a fast response signal in the subject's bio electric field sympathetic to the fast signal which is stronger and otherwise easier to detect than the heart signal because the frequency is predetermined and three or four orders of magnitude higher. The fast frequency filter can therefore be narrowly tuned to filter out all signals other than the fast response signal. The heart signal has a very slow frequency in the range 0.7-6Hz. The received fast response signal may be passed to a quality assessment module adapted to assess

characteristics indicative of the quality of the fast response signal. Reception of the fast response signal will indicate the quality of connection to confirm the functionality of the monitor system. The system may respond to the absence of a received fast response signal to alert the user. This can allow the user to adjust the position of the clip or take other remedial action. The system may respond to the absence of a confirmation signal to power down the system processes such as digital filters in order to conserve power or the presence of the signal may initialise the other system filters.

[036] The system will preferably include an adaptive filter responsive to the quality of the fast response signal to alter the adaptive filter pass band and thereby eliminate unwanted signals and help isolate the heart signal. The adaptive filter may be an amplitude filter and a band-pass or a combination of a low-pass filter and a high-pass filter may be used. The pass band may be altered according to the quality of the fast response signal.

[037] The monitor may include any possible combination of the first second and third aspects of the invention and will preferably include each of the first second and third aspects and the preferred features mentioned above.

[038] The means to connect the heart rate monitor package to the communications package will preferably be means to separably connect including a plug and socket to facilitate deliberate connection and disconnection during normal use.

[039] The communications package will preferably include a rechargeable power supply, and a charge transfer module to receive charge from the heart rate monitor package.

[040] The communications package will preferably include a wireless communications

module to transmit data received from the sensors to a recording and readout device such as a smart phone or a tablet.

[041] The heart rate monitor package will include a power supply which may include at least one storage cell, to power the systems in the heart rate monitor package.

[042] The heart rate monitor package will preferably include a charge transfer module having means to receive a charge from an external power supply and transfer the charge onto the heart rate monitor package power supply. An external power supply may be any source of electric charge.

[043] The means to separably connect the heart rate monitor package to the

communications package power supply will advantageously comprise a heart rate monitor package magnet arranged to attract a communications package magnet disposed within the communications package. One of the means to separably connect may further comprise a flexible strap or "U" shaped spring supporting conductors and connectors to electrically connect the heart rate monitor package to the

communications package. Where a flexible strap is used the magnetic attraction between the heart rate monitor package and the communications package will be sufficient to enable a span of clothing to be firmly clamped between the heart rate monitor package and the communications package thus securing the combined heart rate monitor package and communications package to the user. Where a spring is used the magnet will assist the spring in a clamping action. The connected heart rate monitor package and communications package can conveniently be clamped around the edge of conventional clothing such as a sports bra or the collar of a shirt close to the chest and underlying heart.

[044] Charging of the communications package is achieved from the heart rate monitor package while connected.

[045] While connected the signals acquired by the heart rate monitor package are

transmitted to the communications package. The communications package then retransmits the signals to a processing and readout device such as an application equipped smartphone or any other computer to be recorded, processed and stored.

[046] When the heart rate monitor package is not in use it may be stored connected to a charger, preferably an inductive charger.

[047] The communications package may contain additional sensors such as a temperature sensor or acceleration sensor. The communications package may be adapted to be coupled to a body fastening such as a wrist band, finger ring, brooch, thigh band, ankle band, belt, or headband whereby it can be secured to a subjects wrist, finger, leg, lower torso, neck or forehead to capture data from the movement and general activity of the user.

Fourth aspect

[048] According to a fourth aspect of the present invention there is provided a heart rate and activity monitor system comprising:

a heart rate monitor sensor package having non-contact sensors capable of sensing changes in a bio electric field indicative of heart activity,

a communications package including a motion sensor; and

means to connect the communications package to the heart rate monitor package; wherein the system has at least one active motion sensor filter responsive to movements sensed by the motion sensor to alter the pass band of said motion sensor filter to filter out signals received from the non-contact sensors corresponding to the motion sensed by the motion sensors. [049] During activity such as running the movements induced by muscular activity generate electric field fluctuations with an approximately regular frequency cycle. The frequency may be quite close to the pulse frequency. By sensing the actual gross physical movements a movement sensor filter can be tuned to remove electric field fluctuations corresponding to such movements and facilitate revealing the actual pulse signal.

[050] The movements of large muscle groups involved in physical exercise result in electric field fluctuations with an amplitude large by comparison with the heart signal. The motion sensor may be used to identify which received signals correspond to such motions and set an active amplitude filter, responsive to the motion sensor signals, to eliminate such signals. Because the motions sensed may vary suddenly as the activity changes these filters will update frequently.

Fifth aspect

[051] According to a fifth aspect of the present invention there is provided:

an array of at least two non-contact sensors capable of detecting changes in a bio-electric field generated by a beating heart near to the array, wherein the array is disposed in the back of a seat to detect the pulse of a person seated in the seat.

Sixth aspect

[052] According to a sixth aspect of the present invention there is provided:

an array of at least two non-contact sensors capable of detecting changes in a bio electric field generated by a beating heart near to the array, wherein the array is disposed in a seat belt to detect the pulse of a person seated in the seat.

Seventh Aspect

[053] According to a seventh aspect of the present invention there is provided:

an array of at least two non-contact sensors capable of detecting changes in a bio electric field generated by a beating heart proximate the array, wherein the array is disposed in the mattress of a stretcher or bed to detect the pulse of a person lying in the stretcher or bed.

[054] It is perceived to be useful to determine the pulse of a driver, pilot, passenger or

patient for a number of purposes, including at least; to mitigate the risks of sudden illness causing a serious accident while seated in the control seat of a vehicle and as a means to monitor the level of alertness of a driver or pilot. Other applications may include monitoring the anxiety, comfort and health of a passenger, for example an airline passenger. It may also be useful in other situations where the seated person is controlling machinery or directing air traffic.

[055] It is also perceived to be useful to monitor the pulse of a person, usually a patient lying on a stretcher or bed. Conventional medical pulse monitors require the attachment of electrodes to the patient and therefore the deliberate intervention of a medical practitioner and cooperation of the patient not to remove the electrodes. In some situations this may not occur or may be delayed. Some patients may be uncooperative and remove the electrodes, for example those suffering from dementia, under the influence of drugs or children.

[056] These application present a particular problem to conventional non-contact sensors embedded in a seat or mattress because the dimensions of each of the range of individuals using the seat or mattress are likely to vary considerably. Therefore the optimum location of sensors disposed in the seat back or mattress to detect the individuals pulse will also vary. Furthermore, any particular individual is likely to move from time to time sufficiently that the optimum location of a pair of sensors to detect that individuals pulse will change.

Eighth aspect

[057] Accordingly the eight aspect of the present invention provides a heart rate monitor system having:

an array of at least three non-contact bio-electric field sensors disposed in a region of a seat back or mattress designed to receive the upper torso of a seated or lying person:

a fast signal generator arranged to generate an electric field having a frequency high in comparison with the bio-electric heart field,

a processor adapted to execute a process whereby the strength of the fast signal received by each of the array of sensors is detected and compared to each of the other received signals, said processor responsive to said comparison to select the pair of sensors receiving the two strongest high frequency signals to detect a heart rate signal.

[058] In this system the array of sensors will comprise at least three and in most cases many more sensors to cover the region of a seat back or mattress where the upper torso of a seated or lying person is expected to rest. One preferred example has an array of nine sensors. The system facilitates the selection of a pair of sensors receiving the best signal and therefore able to filter the most reliable pulse. In a car environment, additional functionality may be achieved by the fast signal. The system may self- adjust to allow different size persons, or different clothing (i.e. winter/Summer wear) - selecting the appropriate sensor automatically.

[059] Preferably the system repeats the process of selecting the best pair of sensors over a predetermined period. For example the period may be one second. This allows for the normal movement of the seated or lying person.

[060] The system may set a minimum threshold signal strength determined so that any

signal weaker than the threshold is rejected before comparison as too weak to provide a reliable result.

[061] An advantage of the systems of the fifth, sixth and seventh embodiments is

unobtrusive and continuous monitoring of a seated or reclining person.

[062] In the case of the fifth, sixth, seventh or eighth aspects of the invention the system may interface with a monitor system able to detect significant changes to the heart signal received. For example, if the heart rate escalates rapidly it may indicate anxiety. An erratic heart rate may indicate deteriorating health or other distress. Frequent or erratic changes to the pair of sensors detecting the heart rate may indicate other discomfort, for example increased levels of pain. The loss of the heart signal is likely to indicate that the subject has moved from the seat, stretcher or bed and may need attention. The monitor system may include means to periodically compare the heart rate received from the system with an earlier established record of the subjects heart rate in order to determine if the system should alert a supervisor, for example a nurse.

Ninth aspect

[063] According to a ninth aspect of the present invention there is provided a wrist band for use with heart rate and activity monitor system comprising a heart rate monitor package; and a communications package adapted to be separably attached to the heart rate monitor package wherein the communications package can be separably attached to a wrist band;

said wrist band comprising a ring into which the communications package can be received and removably secured and at least one strap part attached to the ring by an attachment assembly;

said attachment assembly comprising at least one aperture formed in the ring;

a resiliently deformable spring permanently fastened to the strap at an end region and adapted to press fit into the recess to attach the strap part to the ring.

The ring will preferably extend around a through hole into which the communications package fits. For aesthetic reasons and to save weight and material it is desirable to make the ring small in cross section. The ring is also preferably arcuate where the strap part attaches and two attachment assemblies will be required on opposing parts of the ring. The strap of the wrist band must be formed of a material different to the ring to comply with the requirement that the ring is stiff and compact while the strap must flex to bend around a wrist, and may need to be elastic if a single strap part is used as an alternative to male and female strap parts with a fastening.

[064] Preferably the ring is free of any projecting lugs. Preferably the spring is generally "U" shaped having two roughly parallel prongs connected by a cross bar. Where the strap part is formed of moulded plastics the cross bar part of the spring may conveniently be secured to the end of the strap by moulding the strap around the cross bar so that the prongs project from the end. The free ends of the prongs remote from the cross may be cemented into the recess or where materials are compatible, welded in place, for example if the spring is of plastics material. Preferably the free ends of the spring are provided with formations which locate in correspondingly shaped apertures in the recess to prevent the spring withdrawing from the recess. The formations may be configured to have a barb like action. The coupling end of the strap part where the strap part joins to the ring may be contoured to complement the external contours of the ring surrounding the recess and thus form a gapless join.

Brief Description of the Figures

[065] Embodiments of a heart rate and activity monitor system constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative figures, in which:

Figure 1 is an isometric view of an heart rate monitor package and communications package separated, to be brought into contact;

Figure 2 is an isometric view of the heart rate monitor package and communications package coupled together for use during exercise;

Figure 3A is an isometric view of the heart rate monitor package with the cover removed to show some internal details;

Figure 3B is a side elevation of the communications package;

Figure 3C is a bottom view of the communications package:

Figure 4 is a sketch of the connected heart rate monitor package and communications package clamped to a sports bra during use;

Figure 5A is an isometric view of a wrist band and mount for the communications package;

Figure 5B is an isometric view of a wrist band with the communications package mounted; and

Figure 6 is a block diagram of the system components.

Figure 7A is a sectional view through a circuit board incorporating a pair of contactless sensors;

Figure 7B is a isometric view of the skin facing side of the circuit board;

Figure 7C is a plan view of the circuit board;

Figure 8A is a circuit diagram of the guard amplifier stage and frequency band pass filter:

Figure 8B is a circuit diagram of an op amp stage,

Figure 9A is circuit diagram of a fast frequency generator;

Figure 9B is a circuit diagram of a fast frequency band pass filter;

Figure 10 is a flow chart illustrating the control process for an adaptive frequency band filter responsive to movement sensed by a motion sensor;

Figure 1 1A is a diagram illustrating the hardware implementation of a noise reduction system;

Figure 1 1 B is an image of an analogue circuit ;

Figure 1 1 C is an image of an electrode and shield;

Figure 12 is a diagram illustrating the filter stages of the noise reduction system illustrated in figure 1 1 and which may be implemented in any embodiment of the heart rate and activity monitor system;

Figure 13A is a diagram of a second embodiment of the heart rate monitor system implemented in a chair, seat, bed or stretcher;

Figure 13B is a perspective view of a car seat incorporating the second embodiment of the system;

Figure 13C is a partial side view of the back of the car seat of figure 13B;

Figure 14 is a process implemented in the second embodiment to select the best receiving sensors;

Figure 15 is a perspective view of a wrist band part of the first embodiment;

Figure 16 is an exploded perspective view of the wrist band of figure 15; and

Figure 17 is a partial view of a strap part end of the wrist band of figure 15

disassembled from the wrist band. Detailed Description

Figures 1-10

[066] The system of the embodiment shown comprises a heart rate monitor package 1

sometimes known as a Smartag™ a communications package 2 sometimes known as the Pill™ and a wrist band 3. The heart rate monitor package 1 comprises a rear or skin side housing part 4 intended to sit next to the skin of a user. A front housing part 5 is secured by screws to the rear housing part 4 to form a sealed hollow enclosure. A "U" shaped spring 6 extends from a base of the heart rate monitor package 1 to support a clasp 7 having two resiliently deformable arcuate horn shaped elements 8 adapted to engage in a groove 9 extending around the periphery of the

communications package 2. Conductors (not shown) run through the spring 6 from the electronics in the heart rate monitor package 1 to connectors 10 which couple with corresponding connectors 1 1 formed in the underside of the communications package 2. The connectors 10, 1 1 and spring 6 are adapted to facilitate deliberate connection and separation of the heart rate monitor package and the communications package 2.

[067] Figure 6 illustrates the electronics in the heart rate monitor package 1 and

communications package 2. The electronics in the heart rate monitor package 1 is powered by a heart rate monitor package power supply 29 comprising a rechargeable chemical cell and an inductive charging module In the heart rate monitor package 1 the electric field generated by a heart pulse is sensed by a pair of contactless sensors 12 provided by capacitance sensors. The sensors 12 are shielded from external electric fields by an active shield 13. Signals received from the contactless sensors 12 are filtered by a low and high pass differential amplifier 14 to isolate signals with the frequency appropriate to a heart pulse, ie approximately 0.6Hz to 3.3 Hz.

[068] A high frequency fast test signal is generated by the module 15 and emitted from the sensors 12. The response is sensed by the sensors 12 to confirm reliable sensor coupling with the body's electric field and to control a further active filter 16 responsive to the coupling from the fast test filter. Finally an amplitude band filter 17 removes signals with an amplitude exceeding or below the amplitude expected from a heart.

[069] The filtered signals are fed to a communications module and transmitted via

conductors in the spring 6 to the communications package 2.

[070] Communications package 2 includes an input module 18 to communicate signals

received from the heart rate monitor package 1 to wireless communications module 19 which transmits the data signals to a recording and processing device such as a smart phone (not shown). The communications package 2 includes a communications package power supply 20 including a power storage cell charged by charge received from the heart rate monitor package power supply 21 during connection over two or more of the conductors in the spring 6.

[071] In use the communications package 2 is mounted into the clasp 7 which is then

clamped around the edge of an item of clothing such as the bottom of the sports bra 22 as shown in figure 4. A magnet 23 is disposed in the heart rate monitor package 1 and works in concert with a magnet or ferromagnetic material (not shown) provided in the communications package 2 to close the gap between the front of the heart rate monitor package 1 and the back of the communications package 2. To further enhance the grip of the system on the fabric ribs 24 are formed on the front of the heart rate monitor package 1 .

[072] When the communications package 2 is charged and recordal of an accurate heart rate is not desired the communications package 2 can be separated from the clasp 7 and secured in a frame 25 attached to a wrist strap 26 as shown in figure 5A and 5B. In this condition sensors such as an accelerometer 27 and thermometer 28 are able to sense motion and temperature of the user and produce an indication of activity throughout the day.

[073] When not in use to determine heart rate the heart rate monitor package can be

charged using a substantially conventional inductive charger.

[074] The communications package 2 is retained in the frame 25 by means of a spring

loaded latch 26. Depressing the latch releases the communications package 2.

[075] Figures 7A to 7C illustrate the structure of a PCB 32 in which each of a pair of

contactless sensors 12 are embedded. Each sensor consists of a main plate 12a embedded in the skin facing surface 33 of the PCB 32. A shield plate 12b is annular and overlies the opposite clip facing side of the main plate 12a. Shield plate 12b is formed with a rim wall 12c which encircles the main plate. A hole 12d is formed through the shield plate 12b and provides an insulated passage for a conductor 12e communicating the main plate to a guard differential amplifier. A conductor 12f communicates electrically with the shield plate 12b and perforates the clip side of the PCB to communicate with and be grounded by the guard amplifier stage. Thus the contactless sensor 12 is effectively shielded from extraneous electric field signals by a faraday cage formed by the shield plate. The PCB 32 is embedded in the heart rate monitor package as shown in figure 3.

[076] As shown in figure 8 each contactless sensor is connected via the conductors to the inputs of a guard differential amplifier stage 34 as shown in figure 8A. The output from each guard differential amplifier stage is delivered to a frequency band pass filter 35 tuned to eliminate frequencies below 0.7 Hz and above 3.5 Hz before non-unity gain signal amplification at gain amplification stage 36.

[077] Fig 9A illustrates the high frequency fast test signal generator designed to generate a 2kHz sine wave in fluctuation in an electric field projected from a 2kHz pad (not shown) located on the skin side of the heart rate monitor package 1. The signal generator circuit may be built onto the PCB 32.

[078] Fig 9B illustrates the two fast frequency test channels connected to each of the two contactless sensors 12' and 12". To be concise only one of the two identical channels will be described. Signals received from the first contactless sensor electrode 12a are communicated to a high pass filter stage 37 tuned to pass frequencies received above 1590Hz. The remaining signal is then passed to a low pass filter stage 38 which eliminates signal with frequencies above 2340H The human body does not naturally generate electric fields with frequency fluctuations of this size so any signal emitted from the low pass filter stage 38 will have been induced by the fast test signal emitted by the generator of figure 9A.

[079] Apart from confirming that there is effective signal pickup from the contactless sensors

12, the quality of the fast test signal received through the low pass filter 38 can be used to adjust the settings of other analogue or digital filters of the system and thereby improve reception of the heart signal.

[080] Figure 10 illustrates the process of operation of a digital filter wherein the signals from the accelerometer 27 are read for a predetermined period and digitised at step 101. At step102 the accelerometer readout is analysed for regular cycles of movement and the movement frequencies are identified. The movement frequencies are then applied to a frequency bandwidth filter at step 103 to remove signals of corresponding frequency from the detected electric field signal to reveal the heart signal.

Figures 11-14

[081] Figure 1 1 diagrammatically illustrates the configuration of a pair of contactless sensor electrodes 12 each having a metal main plate12a and the shield plate 12b. As previously described the shield plate is electrically grounded to shield the main plate 12a from any electric field generated from a source other than the human body. Field signals captured by the main plate 12a are communicated to an analogue circuit layer 12i which is physically disposed overlying the electrode and shield 12b. The analogue circuit layer communicates with a digital processor layer 12j.

[082] The high frequency test signal is generated from a high frequency electrode 12k

disposed "outside" and behind the shield 12b, 12c so that the shielding lies between the position of the high frequency test signal electrode 12k and each main electrode. Thus the primary high frequency signal is not directly sensible to the main plate12a. However, the high frequency signal will have an effect on any heart signal generated by the subjects body. If the heart signal can be sensed by the main plate 12a this will be confirmed by filters tuned to the high frequency 2kHz signal.

[083] Figure 12 diagrammatically illustrates the layers of signal filtering applied to the signals received by the main plate. The high frequency signal received by a first main plate 12a' is passed to a first high frequency analogue band pass filter 12m'. Any resulting signal is then passed to an analogue to digital converter 12n'. If there is output from the ADC 12n' this is flagged by the system CPU. Substantially simultaneously any high frequency signal received from the second main electrode 12a" is passed through analogue filter 12m", ADC 12n" and confirmed to the system CPU where it is flagged.

[084] As previously described the combined signals from the main plates 12a are applied to a differential amplifier , subject to analogue filtering and the output digitised. The CPU is responsive to the presence of both high frequency signals detected by each main plate 12a' and 12a" being flagged as present to process the ECG sample signal from the differential amplifier. If either flag is missing at least one main plate has an inadequate heart signal pickup and the ECG sample signal is not processed by the CPU.

[085] Figures 13A to 13C illustrate a second embodiment of the system implemented in a car seat, in this embodiment an array 30 of nine electrodes 12 is disposed in the back of a vehicle seat 31. The nine electrodes are disposed on the nodes of a regular rectangular grid. The array is located in a region of the seat back above the lumber support 33 and below any head restraint 34 to be coincident with the upper torso of a person sitting in the seat and therefore probably coincident with the person's heart. It will be understood that a greater or lesser number of electrodes 12 may be deployed on the array and the array may be arranged in other patterns. The array may be hidden behind the back seat fabric 32 of the vehicle seat 31 so that none of the electrodes are naked eye visible. Included in the array is at least one high frequency test signal electrode 12k. There may be multiple test signal electrodes associated one each with each electrode or a single electrode dispersed over the region of the array.

[086] The system will include a test signal generator 33 to generate the test signal for

application to the test signal electrode 12k.

[087] The process and system of figures 13 and 14 are arranged to detect the heart signal of a person sitting in Figure 14 illustrates a process used to control the sensor array illustrated in figure 13. At step 201 the high frequency signal is applied. At step 202 the first of the n electrodes 12 is selected and a register count R is incremented by 1 at step 202.1. At step 203 any signal tn received from the n ^th sensor under test is subject to analogue filtering and digitisation in step 204 before comparison with a

predetermined threshold signal value "T" at step 205. If tn is less than or equal to the threshold at 205 the n ^th sensor is flagged at step 206. At step 207 the system checks for any remaining un-flagged sensors before the process returns to step 203. If the signal tn exceeds the threshold T the process goes to step 208 where the value of tn is saved and a register addressed by the sensor identity "n". The process then goes to step 206.

[088] The process goes from step 206 to step 207 where the system checks for any

un-flagged sensors. If there are un-flagged sensors the process returns to step 202.1.

[089] If all the sensors have been flagged the process checks for two or more values of tn being registered, that is that at least two sensors 12 are receiving high frequency signals above the threshold T. If there are two or more sensors 12 receiving above threshold signals the systems progresses to step 209 where each value of tn registered is compared to the other registered values of tn to determine which two sensors 12 are receiving the strongest signal. At step 210 the sensors 12 receiving the strongest signals are selected and applied to the differential amplifier and other filters to derive the heart rate.

[090] At step 212 the system counts a predetermined period, for example one second before resetting the register count to zero and clearing the recorded values of tn before returning to step 201 to repeat the process.

[091] As a result the system will select the sensors receiving the most reliable heart signal.

Furthermore as the person sitting in the seat moves the system will frequently update which pairs of sensors receive the most reliable heart signal. Figure 15-17

[092] Figures 15-17 illustrate an embodiment of a wrist band adapted to receive a

communications package 2 as shown in figures 5A and 5B. Unlike the embodiment of figures 5A and 5B the wrist strap is in two parts; male 3a and female 3b. Frame 25 is in the form of a ring having two elongate straight parallel side members 39 joined by two arcuate end parts 40.

[093] The arcuate end parts 40 are each formed with two circumferentially spaced blind recesses 41 which open into an outer wall surface of the arcuate end part at passage 42. Each recess 41 is elliptical in cross-section with the major axis of the ellipse extending at an acute angle relative to the long axis of the frame 25.

[094] A frame joining end of the female watch strap part 3b is shown in figures 16 and 17.

The corresponding male watch strap part end is identical. Each watch strap part 3a, 3b is moulded from plastics. During the moulding process a spring 43 is embedded in the frame joining end of the watch strap part 3a, 3b. The spring 43 is generally "U" shaped having two parallel prongs 44 extending from a cross bar 45. The ends of each prong 44 remote from the cross bar 45 are fabricated with formations 46. The formations 46 are of elliptical cross section and correspond in size and shape to the size and shape of each recess 41 . As with the recesses, the major axis of the elliptical formations 46 are inclined at an acute angle to the long axis of each prong 44.

[095] The joining end of the watch strap part is formed to an arcuate shape corresponding to the shape of the arcuate end 40. To attach the watch strap each formation 46 is pressed through passage 42 into one of the recesses 41 . The material and structure of the formations and spring prongs are such as to allow the formations to deform elastically to be received into the recesses and recover when located. Once recovered in location the formations act as barbs preventing withdrawal of the formation from the recess.

[096] In a variation of the embodiment the recesses 41 may open into the underside or

topside of the frame 25. In this case the formations and prongs are introduced from the open side of the recess and subsequently retained by adhesive, welding or a fitted cover (not shown).