Surveillance system

Abstract

A monitoring system according to a first aspect of the present invention includes an implantable sensor device shaped and sized for implantation within a human body to measure conditions within the body and generate sensor data, the implantable sensor device having a single-axis antenna, and a wearable receiving device for wirelessly receiving the sensor data generated by the implantable sensor device, the receiving device including a Helmholtz coil arranged to communicate with the single-axis antenna to wirelessly charge the sensor device and receive the sensor data.

Description

[Technical Field]

[0001] The present invention relates to a monitoring system that includes an implantable device and a receiving device for communicating with and wirelessly charging the implantable device. [Background technology]

[0002] Implantable devices typically rely on wireless communication with external devices and recharging capabilities, which can be challenging to achieve, especially when the implantable device (and its antenna) is oriented in vivo based on the body cavity in which it is implanted.

[0003] The present invention is intended to address some of these limitations. Summary of the Invention

[0004] A monitoring system according to a first aspect of the present invention includes an implantable sensor device shaped and sized to be implanted within a human body to measure conditions within the human body and generate sensor data, the implantable sensor device having a single-axis antenna; and a wearable receiving device for wirelessly receiving the sensor data generated by the implantable sensor device, the receiving device including a Helmholtz coil arranged to communicate with the single-axis antenna to wirelessly charge the sensor device and receive the sensor data.

[0005] The sensor data may be physiological data, such as one or more of pH, temperature, and dissolved oxygen concentration. The sensor data may additionally or alternatively be glucose concentration, lactate concentration, pressure, and hormone levels.

[0006] The single-axis antenna may be configured to operate in a frequency range of 119 kHz to 140 kHz. Preferably, the single-axis antenna may be configured to operate in a frequency range of 130 kHz to 140 kHz. More preferably, the single-axis antenna may be configured to operate at a frequency of 139.6 kHz. The single-axis antenna may be configured to operate at a frequency of 134.2 kHz during charging of the implantable sensor device. The single-axis antenna may be configured to operate at a frequency of 123.3 kHz or 134.2 kHz to transmit or receive data.

[0007] A first Helmholtz coil may be located on a first side of the single axis antenna, and a second Helmholtz coil may be located on a second side of the single axis antenna.

[0008] The distance between the first Helmholtz coil and the second Helmholtz coil may be approximately 250 mm to 500 mm, preferably 350 mm to 450 mm, and more preferably approximately 400 mm.

[0009] The Helmholtz coil may have a radius selected to optimize both the coupling efficiency with the single-axis antenna and the peak magnetic field on the axis of the coil.

[0010] The sensor device may be implantable in a human uterus.

[0011] The implantable sensor device may include a body and one or more arms that project laterally from the body to anchor the sensor within the uterus.

[0012] The wearable receiving device may be a wearable garment.

[0013] The wearable garment may be underwear.

[0014] A first Helmholtz coil may be located on a first side of the garment and a second Helmholtz coil may be located on a second side of the garment, such that when the garment is worn by a user, the first Helmholtz coil is located on an opposite side of the user from the second Helmholtz coil.

[0015] Each Helmholtz coil may include a major axis, the major axis of the Helmholtz coil configured to be substantially aligned with the single-axis antenna of the implantable device when the implantable device is implanted in a user and the garment is worn by the user.

[0016] The Helmholtz coils may be positioned to follow the contours of the human body when the garment is worn by a user.

[0017] The receiving device may include two Helmholtz coils.

[0018] The receiving device may include four Helmholtz coils.

[0019] The Helmholtz coil may be a planar winding.

[0020] The Helmholtz coil may be disposed between two moisture-tight layers.

[0021] The Helmholtz coil may include copper tracks mounted on a polyimide film.

[0022] A second aspect of the present invention provides a method for monitoring a human body, comprising the steps of generating sensor data using an implantable sensor implanted in the human body, transmitting the sensor data to a wearable receiving device via a single-axis antenna, and wirelessly charging the sensor device using a Helmholtz coil of the receiving device, wherein the single-axis antenna communicates with the Helmholtz coil to transmit the sensor data.

[0023] The single-axis antenna may be configured to operate at a frequency in the range of 119 kHz to 140 kHz, preferably in the range of 130 kHz to 140 kHz, preferably 139.6 kHz. The single-axis antenna may be configured to operate at a frequency of 134.2 kHz while the implantable sensor device is charging. The single-axis antenna may be configured to operate at a frequency of 123.3 kHz or 134.2 kHz to transmit or receive data. [Brief explanation of the drawings]

[0024] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which like parts have corresponding reference numerals and in which:

[0025] [Figure 1] 1 illustrates a schematic diagram of an intrauterine monitoring system according to an embodiment of the present invention. [Figure 2] 1 illustrates a schematic diagram of an implantable sensor device according to one embodiment. [Figure 3] 10 illustrates a schematic diagram of an implantable sensor device according to another embodiment. [Figure 4A] 1A and 1B are schematic illustrations of a front view of a wearable garment according to one embodiment; [Figure 4B] 4B is a schematic diagram illustrating a rear view of the wearable garment according to the embodiment of FIG. 4A. [Figure 5] 4B shows a schematic diagram of the wearable garment according to the embodiment of FIG. 4A in use. [Figure 6] 10 is a schematic illustration of a wearable garment according to another embodiment; [Figure 7] FIG. 1 is a schematic block diagram of an implantable sensor device. [Figure 8] FIG. 2 is a more detailed schematic block diagram of the implantable sensor device. [Figure 9] FIG. 1 is a schematic block diagram of a wearable receiving device. [Figure 10(1)] 1 is a schematic flow diagram of the operation of the implantable sensor device. [Figure 10(2)]1 is a schematic flow diagram of the operation of the implantable sensor device. [Figure 11] 10 is a schematic flow diagram of the operation of multiple charging bases of the monitoring system. [Figure 12(1)] 1 is a schematic flow diagram of a multi-antenna procedure. [Figure 12(2)] 1 is a schematic flow diagram of a multi-antenna procedure. [Figure 12(3)] 1 is a schematic flow diagram of a multi-antenna procedure. [Figure 13] 1 is a comparison table of Helmholtz coil parameters and conventional system parameters. DETAILED DESCRIPTION OF THE INVENTION

[0026] Referring to Figure 1, a three-module, multiparameter in vivo sensing platform for intrauterine environmental monitoring is shown. The platform includes a smart sensor 1, shaped and sized for implantation within the human uterus, an external, typically wearable, receiver 2, and monitoring software installed on appropriate data processing hardware, such as a computer 3a or portable electronic device 3b. The smart sensor 1 is a fully implantable sensor device (within the uterus 5 of a human female body 6) incorporating multiple sensors for monitoring physiological parameters, including temperature, pressure, electrical stimulation, dissolved oxygen concentration (DOC), pH, glucose, lactate, other metabolomes, hormones, and other physiological markers for which suitable sensors may exist. Temperature, DOC, and pH are considered the three most important parameters to measure within the uterus to maintain the homeostatic control balance of gases and acid-bases essential for human life and reproduction. These may determine the receptivity of the intrauterine environment to an implanted embryo.

[0027] The smart sensor 1 can wirelessly receive power from and transmit data to a wearable receiver 2 located outside the user's body and worn by the user. As a result, the smart sensor 1 is battery- and cable-free and has a size comparable to that of an intrauterine device (IUD), which is widely used for contraception. This is important because, because it is implanted within the uterus, the device must meet strict size restrictions. Compared to intrauterine devices (IUDs), which are widely used for contraception, battery-based sensors have been found to be too large for use within the uterus. Furthermore, battery-based designs are typically limited by the physical size of the battery and the short lifespan it has before it can no longer continue operating. Furthermore, there are potential risks due to the toxic substances in the battery.

[0028] The receiver 2 serves as an intermediary between the implantable sensor device 1 and an external data processing device running appropriate software (thus acting as a data analysis device). Specifically, the receiver 2 supplies energy to the sensor device and collects real-time information. The antenna 4 of the receiver 2 may be embedded in clothing and wired to the receiver 2. A software module is developed to simultaneously upload in-vivo data to a smart terminal or PC server for subsequent data processing and analysis. The software module consists of a set of monitoring software running on a PC or smart terminal and is designed to provide an easy-to-use user interface for data processing and system configuration. The location of the smart sensor 1 in the uterus is shown in FIG. 1. In particular, the smart sensor 1 may typically have a generally elongated structure and is positioned substantially upright (vertical) in the uterus. As a result, the longitudinal axis of the smart sensor 1 is substantially vertical when the user is standing.

[0029] In this three-module system, the effectiveness of wireless energy and data transfer between the smart sensor 1 and the receiver 2 directly impacts the usability of the system. An optimal design not only improves performance, reduces size, power consumption, and costs, but also improves end-user experience and clinical practice.

[0030] Referring to FIG. 2, an exemplary structure of the smart sensor 1 is shown. As can be seen in FIG. 2(a), the upper portion of the T-shaped smart sensor includes an intermediate connector 20, a first arm 21, and a second arm 22 having a connector 23. In FIG. 2(b), it is illustrated that the intermediate connector 20 is formed of a different material having a different hardness from the first arm 21 and the joint of the second arm 22. In particular, a relatively hard material is used for the body and connector 23, while a relatively soft material is used to form the joint of the first arm 21 and the second arm 22. FIG. 2(c) illustrates how the first arm 21 and the second arm 22 bend together during delivery and removal into the uterus to facilitate insertion / removal. Once inserted, the first arm 21 and the second arm 22 help to hold the smart sensor 1 in place within the uterus. It should be understood that in this embodiment, two arms are used, while in other embodiments, a single arm or more than two arms may be used. In Figure 2(d) it can be seen that the main circuit board 24 is connected to the intermediate connector 20 and the antenna is fixed to the second arm 22 via connector 23. The main circuit board 24 carries the sensors and circuitry described in detail below. In this arrangement, one of the arms not only serves to hold the smart sensor 1 in place within the uterus, but also serves as an antenna for communicating with (receiving power from) the receiver 2. In the smart sensor of Figure 2, the antenna is generally positioned horizontally within the uterus, and is therefore suitable for use with a receiver having an antenna embedded in the tunica. In alternative embodiments, the antenna need not form part of the arm, but may be located elsewhere.

[0031] Referring to FIG. 3, a simplified structure of smart sensor 1 is shown. The left side of FIG. 3 shows a cross section of intermediate connector 32, while the right side of FIG. 3 shows the complete smart sensor 30, including the internal connections of intermediate connector 32. Intermediate connector 32 has two sockets, here a rectangular slot 38 that connects to main circuit board 36 (on which the sensor and circuitry reside) and a circular slot 39 that connects to tube antenna 34. The orientation of the sensor device in FIG. 3 is vertical within the uterus, making it suitable for use with a receiver having a belt antenna or an antenna embedded in underwear (or a disposable sanitary napkin). It will be understood that the sensor device in FIG. 3 may be provided with one or more arms to help stabilize its position within the uterus, if necessary. Compared to other antenna types, tube antennas are relatively small because they do not require a coil frame and can be tightly wrapped around a ferrite core. Considering the complexity of manufacturing and the need to keep the sensor as small as possible, tube antennas with ferrite cores are considered to be particularly suitable for implantable sensor devices. Antenna 34 is a single axis antenna, a coil antenna wound around a core, meaning that the wire is arranged circumferentially around only one axis of the core.

[0032] FIG. 4A shows a receiver 2 in the form of a wearable garment (in this case, underwear 40) equipped with Helmholtz coils. A front view is shown. The underwear 40 includes a first Helmholtz coil 42a located on the front of the underwear 40. The first Helmholtz coil 42a is located such that when worn, it substantially follows the contours of the wearer's body, for example, along the groove where the user's legs join the pelvis. FIG. 4B shows a back view of the underwear 40. The underwear 40 includes a second Helmholtz coil 42b located on the back of the underwear 40.

[0033] Each Helmholtz coil is a planar winding protected from moisture ingress by a moisture-tight barrier, for example by sandwiching the wire between two moisture-tight layers. Typically, a Helmholtz coil comprises copper tracks mounted on a polyimide film.

[0034] As shown, the Helmholtz coils 42a, 42b are substantially triangular in shape. However, the Helmholtz coils 42a, 42b may be any other suitable shape, such as circular. In this example, the first Helmholtz coil 42a has substantially the same size as the second Helmholtz coil 42b. In other examples, the first Helmholtz coil 42a and the second Helmholtz coil 42b may have different sizes. For example, the first Helmholtz coil 42a may be larger (in cross-sectional area) than the second Helmholtz coil 42b, or vice versa. The sizes of the Helmholtz coils 42a, 42b may be varied to fit the contours of the wearer. Preferably, the first Helmholtz coil 42a located on the front of the undergarment 40 is smaller than the Helmholtz coil 42b located on the back of the undergarment.

[0035] FIG. 5 shows underwear 40 being worn by a user. The user also has the smart sensor device 1 implanted in their uterus, as described above. The smart sensor device 1 has a single-axis antenna. As described above, underwear 40 includes a first Helmholtz coil 42a and a second Helmholtz coil 42b located on the front and back of underwear 40, respectively. Coils 42a, 42b are positioned such that first Helmholtz coil 42a is located on a first side of single-axis antenna 34, and second Helmholtz coil 42b is located on a second side of single-axis antenna 34. Because first Helmholtz coil 42a is located on a first side of the garment and second Helmholtz coil 42b is located on a second side of the garment, it can be seen that when the garment is worn by a user, first Helmholtz coil 42a is located on the opposite side of the user from second Helmholtz coil 42b.

[0036] Each Helmholtz coil 42a, 42b defines a respective major axis 44a, 44b that passes through the center of the coil and extends perpendicular to the plane of the coil. As can be seen, the major axes 44a, 44b of the two Helmholtz coils 42a, 42b substantially intersect at the location of the implantable sensor device 1. Thus, the major axes 44a, 44b of the two Helmholtz coils 42a, 42b and the implantable sensor device 1 are substantially aligned, i.e., the major axes 44a, 44b of the Helmholtz coils 42a, 42b and the implantable sensor device 1 are substantially aligned. Thus, when a current is passed through the Helmholtz coils, a highly uniform magnetic field is generated between them, within which the smart sensor 1 is located. Therefore, the smart sensor 1 can be wirelessly charged from this magnetic field using its single-axis antenna.

[0037] The direction of current in each of the coils can be applied in the same direction (clockwise or counterclockwise) through both the front and back coils, as viewed from the front of the body, to generate a magnetic field that is essentially aligned with the sensor's single-axis antenna, which is located between the transverse planes of the body and is close to, but not aligned with, the coronal plane of the body. Alternatively, the direction of current in each of the coils can be applied in a different direction through the front coil relative to the back coil, to generate a magnetic field that is essentially aligned with the sensor's single-axis antenna, which is aligned with the coronal plane of the body. This allows for the generation of a magnetic field with an appropriate direction depending on the orientation of the single-axis antenna. This direction will likely be determined by the orientation of the uterus in which the device is implanted, and typically, this in vivo orientation cannot be changed. Therefore, it is important to be able to control the direction of the applied magnetic field in the described manner.

[0038] FIG. 6 illustrates a wearable garment in the form of underwear 40 having Helmholtz coils 42a-d. In addition to two coils located on the front and back of underwear 40, there is an additional coil located on each side of underwear 40. The four coils 42a-d are provided in two pairs, with two Helmholtz coils 42a and 42c located on the front of underwear 40 and two Helmholtz coils 42b and 42d located on the back of underwear 40. Although not shown in this figure, as noted above, the Helmholtz coils each have major axes that substantially intersect at the location of implantable smart sensor device 1. Helmholtz coils 40a-d are provided in two pairs. For example, Helmholtz coil 42a is paired with Helmholtz coil 42b, and Helmholtz coil 42c is paired with Helmholtz coil 42d. In this example, each pair is positioned substantially opposite one another. In this example, Helmholtz coil pairs 42a-d may be positioned diagonally from one another (e.g., Helmholtz coil 42c may be connected to Helmholtz coil 42b, and Helmholtz coil 42a may be connected to Helmholtz coil 42d). Using four coils instead of two coils has the advantage of providing greater control over the direction of the magnetic field.

[0039] A similar embodiment is a wearable garment in the form of underwear 40 having four Helmholtz coils. In this embodiment, two coils are located on the front of the garment, arranged so that one coil is on top of the other when worn. Two coils are located on the back of the garment, arranged so that one coil is on top of the other when worn. By alternating between supplying current to which coils on the front of the garment and which coils on the back of the garment, a wider range of magnetic field location and alignment with the implant can be achieved.

[0040] Referring to FIG. 7, a block diagram of a suitable microsystem architecture for a smart sensor is shown. To achieve data capture, signal processing, and wireless communication, the microsystem includes an integrated sensor or multi-sensor array 51, analog signal conditioning circuitry 52, an analog-to-digital converter (ADC) 53, optionally including a multiplexer (MUX), a digital signal processor 54 or microprogrammed control unit (MCU), a wireless transmitter 55, and a power manager 56. In operation, the sensor 51 converts a physical parameter into an electronic signal. The sensor can be fabricated on a small silicon chip based on microfabrication technology suitable for microsystems. The conditioning circuitry 52 is used to improve the quality of the analog signal from the sensor 51. Generally, higher-end conditioning performance requires more complex circuitry. Simpler conditioning circuits result in limited performance, requiring additional data processing after analog-to-digital conversion. Therefore, the implementation of the system must balance signal conditioning performance with circuit complexity. A multiplexer (MUX) may be used to share circuit hardware, which has the advantage of reducing the size and power consumption of the device. The processor 54 performs logic control and digital signal processing. A microprogrammed control unit (MCU) is a widely used component due to its flexible functions and excellent scalability. At the same time, compared to a powerful processor, the MCU can reduce power consumption. A radio transmitter 55 and a power manager 56 are provided for data transmission and power control, respectively. The integration of these different units can facilitate the miniaturization of the device.

[0041] Referring to FIG. 8 , the main structure of the sensor device is shown in more detail, including sensors 61 a, 61 b, and 61 c (in this case, temperature, DOC, and pH), respective analog signal conditioning units 62 a, 62 b, and 62 c (for conditioning the respective outputs of the sensors 61 a, 61 b, and 61 c), a multiplexer 63 a (interfacing the array of sensors with an ADC), an analog-to-digital converter 63 b, an MCU 64, and a transmitter 65. Bidirectional communication with the MCU from outside the body is also possible, for example, to wake the device from a power-saving sleep state. Furthermore, the antenna can be used for wireless power transfer via inductive coupling. Here, the transmitter 65 includes a passive RF control unit 65 a for communicating with the MCU 64 and controlling an antenna driver circuit 65 b and a charging circuit 65 c. The antenna driver circuit can perform bidirectional data communication with an external receiver (antenna, ANTa) via an antenna (in this case, a Helmholtz coil antenna) 68, and can also receive power (charging voltage, VCL) via the antenna 68. It can thus be seen that the system utilizes wireless power transfer via inductive coupling, transmitting data and receiving power via the user's abdomen using low-frequency RFID signals. The charging circuit 65c can use power received via the antenna 68 and the driving circuit 65b to charge the capacitor 67 and also power the control unit 65a. All power is managed through the power management block 66. The flow of power around the circuits in FIG. 8 is indicated by solid directional arrows. Analog data signal flow is indicated by a first type of dashed directional arrow. Control signal flow is indicated by a second type of dashed directional arrow. Data flow is indicated by solid block arrows. It can be seen that the charging capacitor 67 powers the power manager 66 (which in turn manages the power supply to the multiplexer 63a, the ADC 63b, and the MCU 64) and the signal conditioning units 62a, 62b, and 62c. The capacitor 67 is preferably a ceramic capacitor. This type of capacitor is particularly suitable for this purpose for safety reasons, as it does not use any toxic materials and there is little or no risk of leakage.

[0042] Referring to Figure 9, an overview of the receiver structure is shown. A microcontroller 71 links and controls different peripheral devices. A low-level radio unit 72 provides wireless energy transfer and data communication to the implantable sensor device via a Helmholtz coil antenna 73. The radio unit 72 includes a radio base station integrated circuit 72a, which implements an RF analog front-end to generate antenna drive signals and modulate and demodulate digital signals, and a full-bridge antenna driver 72b, which provides output power and drives the antenna. A user interface 74, including an LCD display 74a and a keyboard 74b, displays received sensor data and system information provided by the microcontroller 71, as well as providing the user with the convenience of operating the device via the microcontroller 71. A Bluetooth module 75 provides advanced communication with a server or smart terminal that can perform data analysis. A real-time clock 76 provides time information, for example, to timestamp each data item or achieve continuous measurement, and a microSD card interface 77 provides local data storage. A power manager 78 converts power from a rechargeable battery 79 to match the different voltage requirements of peripheral devices. The flow of power around the circuit in Figure 6 is shown by solid directional arrows. Analog data signal flow is shown by a first type of dashed directional arrow. Control signal flow is shown by a second type of dashed directional arrow. Data flow is shown by solid block arrows.

[0043] Referring to FIG. 10, a flow diagram of the operational procedures for single sampling (a) and continuous sampling (b) is shown. For single sampling, the system is powered on in step S1 and then booted in step S2, initializing the various circuits shown in FIG. 9. The system then enters an idle or low-power mode in step S3 and remains in this mode until it receives a single data request (e.g., in response to a user activating a wearable receiver or wirelessly connected control device). In response to such a trigger, a sampling / measurement cycle is initiated in step S4. In step S5, the receiver attempts to detect the smart sensor device and obtain its identifier. This procedure is described in more detail in FIG. 10(c). If, in step S6, it is determined that the sensor device is not within range and cannot be detected, the process returns to the idle / low-power state S3. If, in step S6, it is determined that the sensor device is within range, a first charging operation is performed in step S7. This first charging operation is described in more detail in FIG. 10(d). The first charging operation is intended to provide the sensor device with enough power to perform a boot procedure, which powers up and initializes the circuitry of FIG. 8 . More specifically, the boot procedure may include hardware initialization, MCU state initialization, operational parameter initialization (firmware), and transitioning to a low-power mode immediately after booting, waiting for an instruction to start operation, etc. It will be understood that the boot procedure uses some or all of the power provided by the first charging operation. After step S7, after a short delay (during which the sensor device boots), a second charging operation is performed in step S8 to replenish the charge in the sensor device's capacitor, after which the sensor device can begin sensing (but not transmitting) in step S9. In step S10, a third charging operation is used to transfer enough energy to the sensor device to read data from the sensor in step S11 and perform wireless data transmission of the sensor data in step S12. After data transmission, the system returns to idle mode in step S3 and waits for the next sampling cycle.The continuous sampling procedure (b) is similar to a single sampling cycle, with corresponding steps being represented by the same step number. The difference here is that the sampling cycle is automatically executed at predetermined time intervals controlled by step S13, which can keep the system in idle mode or low-power mode, cancel a task, or trigger the start of operation by returning the process to step S4. In practice, after data transmission in step S12, the system enters sleep mode, and a timer counts down to trigger the next sampling cycle. When the "Cancel" button is triggered, the system returns to idle mode. This procedure helps transfer energy efficiently, limit crosstalk noise between energy transfer over the shared link and data transmission, and shorten the sampling cycle. The sensor device employs multi-stage charging instead of single charging, which ensures sufficient energy for each operation step and shortens the overall charging time compared to single charging.

[0044] Referring to FIG. 10(c), the device detection and ID acquisition procedure (step S5) will be described in more detail. In particular, step S5a performs a primary charging operation for sensor device detection. This only requires charging a part of the sensor device, e.g., the wireless unit 65, and is sufficient to read the sensor ID in step S5b shortly after performing the charging step S5a. Step S5c determines whether the read ID is accurate. If not (e.g., the ID is not recognized or is corrupted due to a poor wireless connection), step S5g generates a signal indicating the sensor device is not in range (used in step S6). However, if step S5c determines that the ID was read accurately, step S5d writes a test byte to the sensor device. Next, step S5e determines whether the test byte was successfully written. If not, step S5g generates a not-in-range signal again. However, if it is determined that the test byte was successfully written, step S5f generates a signal indicating the sensor device is in range (used in step S6). The test write procedure of steps s5d and S5e is an optional procedure for verifying the reliability of the wireless connection between the sensor device and the receiver.

[0045] Referring to FIG. 10(d), the first charging procedure of step S7 will be described in more detail. In particular, step S7a performs the first main charging phase. This is a single continuous charging phase that supplies power to the sensor device to charge the capacitor. The main charging phase can relatively quickly charge the capacitor, for example, to 50% of its capacity. However, continuous charging beyond this range may cause overheating of the sensor device or its components. Therefore, step S7a is followed by multiple iterations of steps S7b (transferring a small amount of power to the sensor device) and S7c (returning to step S7b until the cycle has been performed N times). The combination of steps S7a, S7b, and S7c fully charges the capacitor. The use of multiple short-term charging controls the heating effect by limiting continuous heating in the coil and power driver circuit (located on the wearable receiver), thereby preventing coil overheating for implantable sensors.

[0046] A low power state may be a "sleep" state in which the device is essentially powered down to conserve power, but can be woken up to operate. In contrast, an idle state may be an operating state in which the device is simply waiting for instructions. A device may respond faster in an idle state than in a low power (sleep) state.

[0047] Referring to FIG. 11, a flow diagram of the operation of an implantable sensor device is shown. In FIG. 11, the operation of the sensor device is configured according to the sensor device detection in steps S5 and S6 of FIG. 10. In step R1, as described above, energy is collected by the sensor device in step S7 (first charging procedure), which is used to power on the sensor device and perform system boot in step R2. In step R3, the sensor device enters a low-power mode and remains in that mode unless an event occurs. When the sensor device receives a command from the receiving device to begin measurements, in step R4, the sensor device enables the voltage reference and analog-to-digital conversion circuitry and begins measurements using the sensor. Step R4 is performed using the power supplied to the sensor device in the second charging procedure in S8 of FIG. 10. Once measurements are taken and stored locally, the sensor device re-enters the low-power mode in step R5 and remains in this mode until interrupted by a command (data request) from the receiving device, at which point the process proceeds to step R6, where the RF unit of the sensor device is enabled and transmission of sensor data from the sensor device to the receiving device occurs. Step R6 is performed using the power supplied to the sensor device in the third charging procedure, step S10 of Figure 10. After step R6, in step R7, the sensor device remains in active mode until the capacitor is depleted, at which point the sensor device is powered down in step R8. The reason for actively depleting the capacitor is so that the sensor device is fully reinitialized each time it is used, allowing the capacitor to be continually energized from an empty state to a fully charged state using the charging steps shown in Figure 10.

[0048] Referring to FIG. 12, a flow diagram of the operation procedure of a multi-antenna receiver system is shown. Multiple antennas may be present in a single device, such as a wearable receiver or a receiver using antennas embedded in furniture, or one or more antennas may be provided in a wearable form and another one or more antennas embedded in furniture. As will be understood from the following description, the multiple antennas work in concert to improve overall performance. Compared to a single receiver system, the challenge of a multi-antenna receiver system is how to coordinate different antennas and perform sampling quickly and efficiently, regardless of the position and orientation of the sensor device relative to the various antennas. FIG. 12(a) illustrates the operation procedure of a multi-antenna receiver system. In step A1, the system is powered on. In step A2, the system boots in a manner similar to step S2 of FIG. 10. Next, in step A3, the system enters idle mode or low-power mode and waits for an event trigger, such as a button press, or a timer event in the case of continuous sampling. When triggered, it begins a sampling (measurement) cycle. To achieve this in a multi-array configuration, step A4 enables the first antenna, and step A5 attempts to detect the sensor device and obtain its identifier. This process is shown in FIG. 12(b) and corresponds closely to FIG. 10(b). In particular, steps A5a-A5g in FIG. 12(b) are similar to steps S5a-S5g and will not be described again. If step A6 determines that the sensor device is not within range of this antenna, step A7 disables the first antenna. If step A6 determines that the sensor device is within range of the first antenna, step A8 adds this antenna to the "OK" list (list of available antennas). Next, step A9 determines whether all antennas have been checked. If not, step A10 enables the next antenna, and the process returns to step A5, where steps A5-A8 are repeated for the next antenna. This process continues until all antennas have been considered and either added to the "OK" list or disabled.After cycling through all antennas, step A11 determines whether the "OK" list is empty. If so, step A21 determines that no device is detected. If not, the process proceeds to step A12, where the first antenna in the "OK" list is enabled. In particular, step A13 performs a first and second charging procedure with the first antenna (described in FIG. 12(c)). Step A14 determines whether all antennas in the list have performed a charging procedure. If not, step A15 enables the next antenna in the list, and steps A13 and A14 are repeated. If step A14 determines that all antennas in the list have performed a charging procedure, step A16 selects the first antenna in the "OK" list, and step A17 triggers the data sensing procedure described above in connection with FIG. 10 (see also FIG. 12(d)). Step A18 disables this antenna. Next, step A19 determines whether the sensor data reading was successful. If so, there is no need to use any other antennas in the "OK" list, and the list can be emptied in step A20. Otherwise, if the sensor data reading was successful, then in step A21 it is determined whether all antennas have attempted to acquire sensor data from the sensor device. If so, the process proceeds to step A22, where it is determined that no device has been detected (or at least the device cannot be read). If not, in step A22, the next antenna device in the "OK" list is selected, and steps A17 to A22 are repeated for the next antenna device. After step A22, it is determined in step A23 whether continuous sampling mode is active. If not, the process returns to the idle state in step A3. If continuous sampling mode is active, a timer is set in step A24, and then the process returns to the idle mode or low power mode in step A3. After the timer expires, step A4 is initiated. In this way, it is known that the charging phase of all available antennas entered in the "OK" list has been performed.Charging with all available antennas (one at a time) ensures that the device is supplied with enough energy even if the position and orientation of each antenna on the receiver is not optimal. Then, after the charging phase, the available antennas read data continuously. This sampling cycle ends when data is successfully acquired. If all available antennas do not acquire accurate data, a failure message may be sent back to the software.

[0049] Referring to Figure 12(c), a multiple charging procedure is shown to include a first charging step A13a followed by multiple charging operations performed N times represented by steps A13b and A13c followed by a second charging step A13d. Referring to Figure 12(d), a data sensing procedure is shown in which the sensor device is instructed to start sensing in step A17a, and then the sensor device is charged (by the receiving device) in step A17b to provide enough power for step A17c of reading sensor data and step A17d of transmitting the read sensor data to the receiving device.

[0050] As described above, electromagnetic induction wireless transmission technology is used for near-field energy transfer by using two coupled coils (primary and secondary coils) in the receiving device and the implantable sensor, respectively. Current flowing through the primary coil generates a magnetic field that acts on the secondary coil, generating an induced current in the secondary coil. Tight coupling is required to achieve high energy collection efficiency and a long operating distance. Increasing the distance between the coils causes the magnetic field to extend beyond the receiving area of ​​the secondary coil, resulting in loss of transmitted energy. For its intended application, the implantable sensor device requires small size, low power consumption, and a relatively short operating distance of approximately 10 cm. Energy loss due to tissue absorption of the wireless signal (electromagnetic energy is converted into other forms of energy (e.g., heat) by substances within the tissue medium) depends on the signal frequency. Lower-frequency signals have better propagation characteristics and therefore less tissue absorption. Therefore, wireless energy transfer based on low-frequency electromagnetic induction is used in implantable sensor devices. The circuitry for wireless energy transfer can also function as a low-frequency RFID link for wireless data communication, reducing the need for additional circuitry or board space for data communication. In the intended application, the in-vivo information and system configuration do not require high data rate transmission, and the LF RFID link can provide sufficient data bandwidth to meet the demand. The data communication range is usually longer than the energy transfer distance, meaning it is not a bottleneck for the effective operating range.

[0051] Figure 13 shows a table showing the percentage improvement in induced voltage of Helmholtz coils compared to conventional techniques used for wireless charging of implantable sensors. The table displays data for normal, intermediate, and retrograde cavities within the body, as well as the location of the implant within the cavity itself.

[0052] Although the various technologies and implantable sensor devices and external receivers have been described in terms of intrauterine monitoring, it will be appreciated that these technologies and structures may also be applied to monitoring other body cavities in the human or animal body, such as within the vagina, bladder or gastrointestinal tract.

[0053] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications can be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. an implantable sensor device having a single-axis antenna and shaped and sized to be implanted within a human body to measure conditions within the human body and generate sensor data; a wearable receiving device for wirelessly receiving the sensor data generated by the implantable sensor device; The receiving device includes a Helmholtz coil, the Helmholtz coil positioned in communication with the single-axis antenna to wirelessly charge the sensor device and receive the sensor data.

2. The monitoring system of claim 1 , wherein the sensor data is one or more of pH, temperature, and dissolved oxygen concentration.

3. A surveillance system according to claim 1 or 2, wherein the single axis antenna is configured to operate at a frequency in the range 119kHz to 140kHz, preferably in the range 130kHz to 140kHz, preferably 139.6kHz.

4. a first Helmholtz coil located on a first side of the single axis antenna and a second Helmholtz coil located on a second side of the single axis antenna; and optionally 4. The monitoring system according to claim 1, wherein a distance between the first Helmholtz coil and the second Helmholtz coil is between about 250 mm and 500 mm, preferably between 350 mm and 450 mm, preferably about 400 mm.

5. 5. A monitoring system according to claim 1, wherein the Helmholtz coil has a radius selected to optimise both coupling efficiency with the single-axis antenna and peak magnetic field on the axis of the coil.

6. The sensor device is implantable in a human uterus, and optionally includes:

6. The monitoring system of claim 1, wherein the implantable sensor device includes a body and one or more arms, the arms projecting laterally from the body for securing the sensor within the uterus.

7. The wearable receiving device is a wearable garment, and optionally The monitoring system according to any one of claims 1 to 6, wherein the wearable garment is underwear.

8. 8. The monitoring system of claim 7, wherein a first Helmholtz coil is located on a first side of the garment and a second Helmholtz coil is located on a second side of the garment, such that when the garment is worn by a user, the first Helmholtz coil is located on an opposite side of the user from the second Helmholtz coil.

9. 9. The monitoring system of claim 7 or 8, wherein each Helmholtz coil includes a major axis, the major axis of the Helmholtz coil being configured to be substantially aligned with the single-axis antenna of the implantable device when the implantable device is implanted in a user and the garment is worn by the user.

10. A monitoring system according to any one of claims 7 to 9, wherein the Helmholtz coils are positioned to follow the contours of a human body when the garment is worn by a user.

11. A monitoring system according to any preceding claim, wherein the receiving device comprises two Helmholtz coils.

12. 12. The monitoring system of claim 11, wherein, when viewed from a first perspective, a first current is driven in a first direction around a first one of the Helmholtz coils, and, when viewed from the first perspective, a second current is driven in the first direction around a second one of the Helmholtz coils.

13. 12. The monitoring system of claim 11, wherein, when viewed from a first perspective, a first current is driven in a first direction around a first one of the Helmholtz coils, and when viewed from the first perspective, a second current is driven in a second direction different from the first direction around a second one of the Helmholtz coils.

14. 12. The monitoring system of claim 11, wherein the receiving device includes four Helmholtz coils.

15. 16. The monitoring system of claim 15, wherein the four Helmholtz coils are provided as two pairs of coils, one coil of the pair and the other coil of the pair being positioned on opposite sides of the implantable sensor device.

16. A monitoring system according to any preceding claim, wherein the Helmholtz coil comprises a planar winding.

17. 17. The monitoring system of claim 16, wherein the Helmholtz coil is disposed between two moisture-tight layers.

18. A monitoring system according to any preceding claim, wherein the Helmholtz coil comprises a copper track provided on a polyimide film.

19. generating sensor data using an implantable sensor implanted within a human body; and transmitting the sensor data via a single-axis antenna to a wearable receiving device; and wirelessly charging the sensor device using a Helmholtz coil of the receiving device, wherein the single-axis antenna is in communication with the Helmholtz coil to transmit the sensor data.

20. A monitoring system according to claim 19, wherein the single axis antenna is configured to operate at a frequency in the range 119kHz to 140kHz, preferably in the range 130kHz to 140kHz, preferably 139.6kHz.

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