Implantable wireless sensor system

Abstract

A wireless implant system has an external device and an implant device; the implant device includes a hermetically sealed housing containing an implant resonant circuit, an implant control circuit and a pressure sensor; the external device includes a primary resonant circuit and a primary control circuit configured to transmit a digitally encoded amplitude shift keyed power signal of a selected duration to the implant device; the implant device is solely energised by the power signal, and the control circuit is configured to receive power from the power signal and to simultaneously demodulate the power signal to decode instructions from the external device; the implant device control circuit is configured to detect when the selected duration has elapsed, determine a pressure from the pressure sensor and to transmit a digitally encoded phase shift keyed information signal representing the determined pressure to the primary resonant circuit.

Description

[0001] IMPLANTABLE WIRELESS SENSOR SYSTEM

[0002] Field

[0003] The present disclosure relates generally to wireless implantable sensors and similar Active Implantable Medical Devices (AIMDs). The disclosure has particular relevance to pressure sensing within the body of a human or other animal to monitor pressure within the body.

[0004] Background

[0005] Implantable sensors that use wireless technologies for powering the sensor are useful for medical applications. Such sensors may include a pressure sensor and are known for use in measuring the pressure in the heart's pulmonary artery for treatment of congestive heart failure. However, these sensors present many technical challenges.

[0006] The implant carrying the sensor may need to be present and functioning within the body for decades. Therefore, the implant housing needs to be biocompatible and resistant to ingress and attack from bodily substances. The implant needs to have a form factor which allows it to be implanted easily so that trauma to a recipient is minimised. The pressure sensor must have sufficient accuracy and have low drift in vivo. The sensor may be very deeply implanted in the body, which presents a technical problem in delivery of power wirelessly to the sensor and in communicating data from the sensor.

[0007] Summary

[0008] It is an object of this disclosure to provide an improved implant or implant system, or to at least provide methods, apparatus or systems which provide a useful alternative to those that are presently known.

[0009] The disclosure provides a wireless implant or sensor, a primary or wand apparatus for use with the sensor, a wireless implant or sensor system, and methods therefor.

[0010] In an aspect the disclosure provides a wireless implant comprising: an enclosed rigid housing structure having a length, a width and a height, wherein the length is greater than the width and height and wherein the housing structure defines a first chamber; the first chamber containing a wireless power and control circuit; a pressure sensor chamber provided on a rigid wall of the rigid housing structure, wherein the pressure sensor chamber has a pressure flexing wall provided along a length of the rigid wall of the housing structure; and wherein the pressure sensing wall is configured to deform relative to the rigid wall dependent on pressure exerted on the pressure sensing wall.

[0011] In another aspect the disclosure provides a wireless implant system comprising: an external device and an implant device; the implant device comprising a hermetically sealed housing containing an implant resonant circuit, an implant control circuit and a pressure sensor; the external device comprising a primary resonant circuit and a primary control circuit configured to transmit a digitally encoded amplitude shift keyed power signal of a selected duration to the implant device; wherein the implant device is solely energised by the power signal, and the control circuit is configured to receive power from the power signal and to simultaneously demodulate the power signal to decode instructions from the external device; and wherein the implant device control circuit is configured to detect when the selected duration has elapsed, determine a pressure from the pressure sensor and to transmit a digitally encoded phase shift keyed information signal representing the determined pressure to the primary resonant circuit.

[0012] Other aspects of the invention are set forth and described in the clauses at the end of the description and in the appended claims.

[0013] The invention consists in the foregoing, but further aspects will become apparent from the description below which envisages embodiments and constructions of which the following gives examples only. Drawing Description

[0014] One or more examples or embodiments will be described with reference to the accompanying drawings in which:

[0015] Figure 1 is a system diagram;

[0016] Figure 2 is a further system diagram showing data flows;

[0017] Figure 3 is an isometric view of an implantable sensor;

[0018] Figure 4 is a plan view of the sensor;

[0019] Figure 5 is a view from below of the sensor;

[0020] Figure 6 is a side view of the sensor;

[0021] Figure 7 is a cross section across the width of the sensor;

[0022] Figure 8 is a cross section along the length of the sensor;

[0023] Figure 9 is another view of Figure 7 without electronic components in the sensor;

[0024] Figures 9A-9C are diagrammatic cross section views of some embodiments of the sensor;

[0025] Figures 10 and 11 are plan views of capacitor electrodes in the sensor;

[0026] Figure 12 is an isometric view showing capacitor electrodes and vias in the sensor;

[0027] Figure 13 is a further plan view of capacitor electrodes in the sensor with expanded portions to show further detail;

[0028] Figure 14 is a further view of Figure 9;

[0029] Figures 14A-14D are diagrammatic cross sections across the width of the sensor showing different embodiments of a sensor chamber;

[0030] Figure 15 is an isometric view of a sensor and locator;

[0031] Figures 16A-16C are diagrams showing placement of the sensor according to one example of use of the sensor;

[0032] Figure 17 is a side view of a placement or introducer apparatus;

[0033] Figures 17A-17D are isometric, side, end and sectional views of a tip of the apparatus of

[0034] Figure 17;

[0035] Figures 17E-17H are isometric, side, end and sectional views of a tip plunger of the apparatus of Figure 17;

[0036] Figure 18 is an isometric view of a wand or wireless primary apparatus for use with the sensor;

[0037] Figure 19 shows side and rear views of the wand of Figure 18;

[0038] Figure 20 is a block diagram showing functional aspects of the wand; Figure 21 shows part of a circuit in wand and signals relating thereto;

[0039] Figure 22 shows a diagram of a memory or part of a memory of the sensor;

[0040] Figure 22A shows an example of a digital data communication packet transmitted by the sensor;

[0041] Figure 23 is a diagram of an example of a capacitive sense circuit of the sensor;

[0042] Figures 24 and 25 are block diagrams of circuits of the sensor;

[0043] Figures 26 to 29 are diagrams showing waveforms during use of the sensor;

[0044] Figure 30 is a block diagram of a clock extraction and frequency divider circuit for use in the sensor;

[0045] Figure 31 shows a plot amplitude against frequency for signals relating to the circuit of Figure 30.

[0046] Detailed Description

[0047] This disclosure teaches the use of digital wireless technology along with unique transduction and hermetic housing designs for medical implantable devices which enable health monitoring and treatments. General impacts of this technology include reduced health costs, reduced health impact from use (smaller, less reactive devices), enabling remote monitoring, and improving health confidence (reduced anxiety) in patients. Specific to the device in this disclosure, at-home monitoring of intracranial pressure is not currently available, hence one or more embodiments disclosed herein will allow caregivers and patients to make decisions about potential life-saving treatments without incurring the high costs associated with in- hospital diagnostics that are currently required.

[0048] Turning to Figure 1 , a diagram showing an example of an overall wireless implant system 100 is shown. In the examples and embodiments discussed herein reference will frequently be made to a system for monitoring intracranial pressure (ICP), however it will be understood that the system can be used to monitor pressure in any anatomical region, for example other organs, regions or parts of the body. The implantable sensor 100 is also referred to as an implant or a sensor in this disclosure.

[0049] ICP monitoring is particularly useful for detecting or monitoring hydrocephalus. Therefore, in an embodiment the implant or implant system disclosed herein may be used for the long- term measurement of intracranial pressure for patients diagnosed with hydrocephalus (either acquired or congenital), or chronic disturbance of cerebrospinal fluid, and treated with a shunt. The sensor can be surgically placed by neurosurgeons and subsequently used at home to make ICP measurements by patients and carers, or be used in the hospital or in the doctor's office. Therefore, in an embodiment, the sensor is configured to be inserted into the cortex of the brain thus it may be in contact with parenchymal tissue, CSF and meninges.

[0050] Still referring to Figure 1 , the sensor 100 is configured to wirelessly communicate with, and receive power from, a primary device 200, which will be referred to herein as a wand and is described further below. In an embodiment, communication may occur using a method and apparatus substantially in accordance with patent publication W02020050728A1 , the disclosure of which is incorporated herein by reference. The implant 100 may be physically implanted in the body using an implantation device 300, referred to herein as an introducer.

[0051] The wand 200 is configured to provide data to another device, such as a personal mobile communications device, for example a mobile phone running an App 400 from which the received data can be uploaded to a clinical portal for use as necessary by users 600.

[0052] In Figure 2, the data flow for the system 10 is shown. A first wireless link 102 is used to transfer data between the sensor 100 and the wand 200. In an embodiment, data transfer between the wand 200 and the App 400 running on device 402 is via Bluetooth or a similar protocol. In another embodiment a wired data transfer connection can be used. Data can be stored in a memory of device 402 if required. Data can also be uploaded to portal 500 by internet connection 404. A remote database 502 can be used to store data accumulated via the portal 500.

[0053] Various components or parts of the system broadly disclosed above will now be described.

[0054] Figures 3-14 show views of the implant or sensor device 100, or parts thereof. The device 100 has a housing 104 which has a locator connection 106 that in this embodiment comprises an aperture provided at one end of the housing 104. In an embodiment the aperture is 0.5mm diameter and is provided at one end for attachment of a locator, which may comprise a flexible element such as a locator thread, as will be described further below.

[0055] The housing 104 may be made from glass, for example in an embodiment all external surfaces are borosilicate glass. In an embodiment the material for the housing or parts thereof includes one or more of sapphire, quartz, fused silica, silicon, diamond. As can be seen from Figure 3, the rigid housing comprising the first chamber has a length dimension 104a, a height dimension 104b and a width dimension 104c. The implant 100 has a length dimension which is greater than either the width or height dimensions. In an embodiment the length dimension is greater than a combination of the width and height dimensions. In an embodiment the ratio of the length dimension to the height or width dimension is in the range of 4 to 15, or more preferably 5 to 10.

[0056] In an embodiment the housing has overall external dimensions of 20.1 mm x 3.6mm x 2.0mm. In an embodiment the housing is fabricated from a plurality of pieces of glass material that are joined together by laser or ultrafast welding to provide a hermetically sealed interior. There is a chamfer 108 on the top and bottom edges. Chamfer 108 has the same dimension on both the top and bottom edges. Having a chamfer avoids sharp edges which can damage surrounding tissue during the insertion process. Having a consistent chamfer on top and bottom edges (i.e. opposing edges at either end of the height and / or width dimension of the body) encourages linear or uniform insertion, that is to say the housing is unbiased during insertion so will tend to travel in a straight line when inserted (for example by being pushed from one end), into tissue of relatively uniform density. As can be seen from Figure 14, in an embodiment, the chamfer 108 is formed by elimination the edge illustrated by the triangle having sides 108a and 108b. In some embodiments the sides 108a and 108b are in the range of 0.05 to 0.2 of the dimension of the width or height of the housing. In an embodiment having width and height dimensions of 3.6mm x 2.0mm the length of sides 108a and 108b may be selected to be 0.25 mm. In an embodiment the density of the implant is configured to be substantially the same as, or within a range close to, or have a density of the same order as the density of the tissue it is implanted within to facilitate 'discrete' implantation so that a fixation structure is not required to fix the implant in place. The housing 104 is configured with a first chamber 1 10 and a second chamber 150. In an embodiment the first chamber is formed as a rigid structure that is constructed from a central piece of glass 120 which defines two opposed side walls 122 and two opposed end walls 124. A base layer 126 is welded to the base of the walls 122 and 124, the components 1 12-1 16 are placed inside the open space formed by the base 125 and walls 122 and 124. A top layer 128 is then bonded, for example by being welded or adhered, to the top of the walls 122 and 124 to form hermetically sealed first chamber 1 10. In one or more other embodiments the order of these steps can be changed e.g. the top layer is attached, then the components are added and the bottom layer is attached.

[0057] First chamber 110 houses a coil 1 12 and electronic circuits and their components 1 14 mounted on circuit board 1 16 which are configured to receive power wirelessly and to communicate with wand 200. Electronic components 1 14 include ASICs, patterned thin metal films, capacitors, and epoxies. In an embodiment, the at least one of the components within one or both chambers are selected to be radio-opaque and / or provide contrast for x-rays and / or fluoroscopy.

[0058] The second chamber 150 is formed on an exterior of the rigid structure that forms first chamber 1 10. The second chamber is formed on upper or top layer 128 of the first chamber, extending along at least part of the length and across at least part of the width of the top layer. It will be understood that the second chamber could alternatively be provided on bottom layer 126.

[0059] In an embodiment, second chamber 150 is configured with a pressure sensing wall member 132.

[0060] The cross-sectional views shown in Figures 7 and 8 indicate the relative size of the first and second chambers according to an embodiment. Figures 9A-9C show diagrammatic crosssections across a width of the sensor 100 which provide a clearer view of various embodiments. In an embodiment, second chamber 150 is formed by providing an upstand 130 which may be a separate part, or an integral part of components 128 or 132. In an embodiment shown in Figure 9A, the pressure sensing wall member 132 comprises side walls and end walls and is integrally formed with the upstand 130 to thereby define a closed cavity to provide second chamber 150. In an embodiment as shown in Figure 9B, upper wall 128 of the first chamber comprises side walls and end walls and is integrally formed with the upstand 130 to thereby define a closed cavity once it has been joined to member 132 to thus provide second chamber 150. In an embodiment as shown in Figure 9C, the upstand 130 is configured as a separate component having side walls and end walls, and is joined to both component 128 and pressure sensing wall 132 to define a closed cavity that comprises second chamber 150.

[0061] Figures 9A-9C also show vias 148 which provide conductive paths through wall 128 while maintaining the first and second chambers as separate hermetic compartments. In an embodiment, the height of wall 128 is selected to provide a via length (or height) that is sufficient to provide a hermetic seal between the first and second chambers

[0062] Wall 132 may comprise a diaphragm and is configured to flex in a direction toward the first chamber as external pressure (i.e. the pressure on the outer walls of the sensor 100) increases, and return (i.e. flex in the opposite direction) as the external pressure decreases. In an embodiment wall 132 is configured with a flex region which is formed to a thickness which is thinner than other parts of housing 104, for example wall 132 has a flex region which is thinner than upper wall 128. The flex region may be created by etching for example. In an embodiment flex region of wall 132 extends substantially 75% to 95% of the length of the first chamber and extends across the width of the first chamber. In an embodiment the flex region extends 75% to 95% of the width of the first chamber. Providing the wall 132 with a flex region that extends along a length of the housing 104 allows the flex region to flex more significantly for a given change in pressure. In an embodiment the wall 132 including the flex region presents a uniform or flat surface. Thus, there are no recesses or ridges or crevices that can disrupt surrounding tissue during placement for example. Moreover, in an embodiment the housing including the first and second chambers is hermetic. In an embodiment the housing including the first and second chambers fully encloses the chambers in an electrical insulative material so that there are no external exposed conductive regions. Having wall 132 extend across the length and width of the implant maximises response for area. Because the area determines the capacitance this can improve digitisation resolution. This also reduces the relative negative impact of unavoidable parasitic capacitances in the transducer and transduction circuitry. Having a wall 132 with a length that is a multiple of its width (i.e. having a high aspect ratio) allows the flexing region or portion of the wall to be selectively stiffened or flattened along the minor (width) aspect - this avoids allowing flexure of the wall at this scale (that is present due to manufacturing limitations) that may lead to faults / defects. This is opposed to having a circular or large square flex region (low aspect).

[0063] Second chamber 150 comprises a transduction cavity which houses components which form a transducer to allow measurement of pressure in a space in which the implant 100 is located by detecting changes in flexure of wall 132. The hermetically sealed interior of the second chamber 150 houses capacitive electrodes 136-140 used for capacitive transduction of external pressure.

[0064] The transducer includes one or more capacitive sense electrodes 136a and 136b and one or more reference electrodes 134a and 134b provided on the base of second chamber 150. The base of chamber 150 may comprise for example an upper surface of upper wall 128 or an inner upper surface of upstand 130. The transducer also includes at least one sense electrode 140 and at least one reference electrode 138 provided on an inner surface of wall 132. The electrodes can be provided on the respective surfaces by patterning methods, for example etching one or more conductive coatings.

[0065] As external pressure increases, wall 132 and thus electrode 140 moves progressively further toward electrode 136, which increases the capacitance between the electrodes, and vice versa.

[0066] The sense electrodes are provided a selected distance from the inner periphery of the second chamber. In an embodiment the sense electrodes are nearer a centre of the respective walls wall 132 or 128 than the reference electrodes. It has been found that placing the sense electrodes in a central or middle wall area which corresponds to a region in which the maximum changes in distance of flexure occurs allows a maximum capacitive response to be achieved for more accurate pressure transduction.

[0067] The reference electrodes are provided nearer to the periphery of the chamber in order to minimise response as there is minimal flexure of wall 132 in those regions. The reference electrodes therefore provide a reference capacitance in the second chamber. The reference electrodes are used in an embodiment to create optimal compensation using C-V measurement methods, e.g. for reduction in common-mode noise.

[0068] Providing sense electrodes and reference electrodes in the same shared chamber 150 has the advantage of allowing compensation for shared offsets and noise, e.g. dielectric changes

[0069] In the embodiment illustrated electrode patterning permits '2 in parallel' design with 4 total capacitors (2 sense in series and 2 reference in series). As the transducer is hermetically isolated from first chamber 1 10 which houses the electronics, four internal vias 148 are provided through wall 128 to allow electrical connection of the electrodes to the electronic circuitry. In an embodiment vias 148 comprise 'hermetic vias' with the advantage being that the transduction chamber and electronics chamber are hermetically isolated. This reduces the impact of outgassing that results from the inclusion of polymeric materials in the electronics cavity on the transducer performance. Corresponding connector regions 146 are provided at the other end of the vias in the first chamber for connection with the electronic circuits in the first chamber. In an embodiment, the vias 148 are located on the projecting connection regions comprising 'tabs' 142a, b and 144a, b which are part of, or at least electrically connected to, the sense and reference electrodes. These tabs are outside of capacitor electrode overlap regions. This has the advantage of avoiding faults, for example the non-overlap avoids bridging-type shorting defects leading to faults that may result from via fabrication limitations.

[0070] In an embodiment the reference electrode 140 can comprise a plurality of electrodes, for example being "broken" through small insulating regions into a plurality of smaller electrodes 140a,b,c,...n as shown in Figure 13. Providing a plurality of reference electrodes on the flex wall (diaphragm) 132 can reduce coupling of electronic fields with the transducer and thus improve performance of the reference capacitor in chamber 150. Providing a plurality of reference electrodes also has the advantage of reducing the impact of top-bottom bridging / shorting faults that can be a result of manufacturing limitations and which can affect capacitor performance.

[0071] Figure 14A shows a diagrammatic cross section along the length i.e. parallel to the longitudinal axis of the sensor, illustrating the flex wall 132 when the pressure on either side of the wall 132 is approximately the same. The flex wall 132 in this embodiment is bonded at cavity edges 133 to wall 128. For simplicity, the sense electrodes 136 and 140 are shown, but the reference electrodes are omitted. The substantially balanced pressures on either side of the wall 132 result in the wall 132 lying in a flat, non-flexed rest position.

[0072] In Figure 14B the effect of an increase in external pressure is shown represented by force F, resulting in flexure of wall 132. As described above, as a flexure region of the wall 132 flexes into chamber 150, electrode 140 gets closer to electrode 136, which can be detected as an increase in capacitance that the circuit within the first chamber can use to measure the external pressure. If the external pressure becomes sufficient to make electrodes 140 and 136 contact each other (i.e. if the pressure reaches or exceeds the transduction range), resulting in a malfunction. Therefore, in an embodiment, as shown in Figure 14B, a dielectric is provided on at least one of the sense electrodes (and / or on one or more reference electrodes) to prevent an electrical short from occurring. In an embodiment, the physical contact that occurs will prevent further change in capacitance, and in this way the physical state of the wall 132 can be determined. In an embodiment an electrical property of the dielectric can be selected to provide a characteristic or known change in capacitance which can alternatively or additionally be detected to determine the physical state of the wall 132. Knowing the physical state of wall 132 for a given pressure or change in pressure can be used to check, and if desired or necessary, modify calibration of the sensor.

[0073] A further embodiment of a switch is seen in Figure 14C. In this embodiment an upstand 139 is provided. The upstand can be non-conductive, or have a known conductivity or other electrical property to assist in detection once the wall 132 deflects to a position in which it contacts the upstand, as disclosed above.

[0074] In Figure 14D an embodiment is shown in which the range or extent of a flex region of the wall 132 is altered by changing the position of one or more of the bonding points 133. In Figure 14D both bonding points are moved to add to the length of the flexure region. This allows the flexure region of wall 132 to change physical behaviour if the external pressure is less than the pressure in chamber 150. As shown in Figure 14D, the upward flexure under force F results in a larger flexure region flexing upwardly away from the chamber so that regions 139 of wall 128 no longer support the adjacent regions of the wall 132. The change in capacitance as the wall 132 separates from the wall 128 is markedly different from the change in capacitance as the wall 132 flexes outwardly while still supported by regions 139.

[0075] Turning to Figures 15-16, the implant 100 is shown with a locator 152 connected to locator connection 106. In an embodiment the locator comprises a length of flexible material which is secured to locator connection 106. In an embodiment the locator comprises a surgical thread. The locator can be looped through the locator aperture 106 and tied to complete the loop as shown in Figure 15.

[0076] Placement of the implant 100 is shown in Figure 16 in an example in which the implant is used to sense intracranial pressure. In Figure 16A, the implant 100 is shown introduced into the brain parenchyma through burr hole 156 in skull 154. In Figure 16A a ventricular shunt catheter 160 is also introduced through the same burr hole. Figure 16B shows an example in which catheter 160 is introduced through a hole 156b, and the implant 100 is introduced through a separate hole 156a. Figure 16C shows a plan view of placement. Locator 152 can be disposed so that an end on the locator is remote from the implant and sits outside the skull i.e., under the skin. This locator may be tied to nearby tissue or a surgical plate. In the example described in Figure 16, the locator allows the sensor to be subsequently located for example for retrieval if that is required.

[0077] Figures 17-17H show apparatus 300 for introducing the sensor 100 into an anatomical region, the apparatus being referred to generally as an introducer 300. In an embodiment, as shown in Figure 17, the introducer can comprise in part a syringe assembly having a plunger 302 that is slideably axially guided within a barrel 304. For example, the syringe barrel and plunger may comprise a 3ml OEM luer-lock syringe. The introducer tip 308 is configured to receive the sensor 100, and has a portion carrying a connector such as flange 310 which is configured to engage with the hub or luer lock portion of the syringe barrel. The tip 308 has one or more internal retention formations that are configured to support or contact or engage with the sensor 100. In an embodiment, the internal retention formations comprise corner, and / or partial side wall and / or top or bottom wall contact formations 311, as shown in Figures 17c and 17D. These may be provided at any location within the tip 308. In an embodiment the retention formations may include one or more restrictions or bumps 312 which may be located at a distal end. The bump(s) serve to retain the sensor 100 when inserted in the tip (to avoid falling out prior to use) and give an amount of resistance to the insertion of the sensor to aid in 'feel'. The interference distance of the bumps are tuned - and ideally remove 50um from the total tight-fit of the entrance (e.g. 3.500 mm entrance - 0.05mm bumps, with each providing 0.025mm) but can be between 0.01 and 0.2mm depending on the materials used for the tip device.

[0078] In an embodiment the formations 311 (but which may not include the bumps) that contact the sensor 100 do not contact flex wall 132. Clearance 313 is provided between the flex wall and the tip body. Therefore, the assembly 308 receives, retains, and allows for verification measurements by allowing the flex wall to move freely.

[0079] As can be seen in Figure 17A, B and D, the tip assembly 308 has an open channel or window 312 which allows locator 152 to slide therealong as the sensor 100 is expelled from the tip. Window 312 also allows a user to check that the sensor 100 is in the correct orientation in the device.

[0080] A tip plunger 306 is provided having a distal end 313 which can extend into the proximal end of the tip 308, and a proximal end 315 which is can be provided in the barrel 304. When the plunger is pressed into the barrel 304, the end of plunger 302 bears on end 315 of tip plunger 306 which in turn causes end 313 to bear on the distal end 34 of sensor 100 which is nearest the proximal end of the tip 308. Therefore, as plunger 302 is pressed into the barrel, the sensor is ejected from end 314 of the tip 308 into the required placement position. In the example of Figure 16, the distal end 314 of assembly 308 is positioned at the entrance, or within, a burr hole and once the end 314 is in a required position, the plunger is pressed to deliver the sensor and expel the sensor from the introducer.

[0081] It will be understood that in an embodiment the introducer may comprise the tip 308, which may or may not include tip plunger 306. In this way the introducer may be packaged ready to be used with an existing syringe. In another embodiment, the implant or sensor 100 may be provided already packaged into the introducer, and the implant 100 may also be provided ready with locator 152. In another embodiment the syringe, tip plunger and tip 308 are provided ready to receive a sensor 100.

[0082] In an embodiment, the tip plunger 306 is assembled into the barrel of the syringe, with the smaller diameter portion oriented to be able to protrude out of the syringe nozzle. The syringe is them reassembled with the tip plunger inside, and the tip 308 is threaded onto the luer-lock of the syringe.

[0083] The implant is inserted into the Introducer tip with a preferred orientation with the diaphragm facing the window of the tip 308. This aids in surgical placement and enables orientation of the Implant with respect to features nearby (for example a shunt catheter). In an embodiment, the tip plunger 306 is sized to push the sensor 100 2mm past the end 314 of the tip, which for intracranial implantation is a suitable insertion depth into the brain tissue given the surgeon places the tip on the brain tissue. This insertion depth can be from 0 to 20 mm in range but is preferably about 1 -5 mm.

[0084] An embodiment of wand 200 is shown in Figures 18 and 19. The wand 200 as shown in Figures 18-19 has a halo portion 202 that is configured to accommodate a coil as will be explained further below. Halo portion 202 is dimensioned and configured to allow the coil to transmit and receive a sufficient field for energisation and communication with the implant 100. A handle portion 204 is provided which may contain a power source such as one or more batteries and may also carry a user interface which may comprise a display 206 and one or more buttons or keys 208. A charging and / or communications port 210 is also provided. As can be seen from Figures 19A and 19B, the handle 204 has a longitudinal axis that extends from an end of the handle that is connected the halo to a distal end remote from the halo. The longitudinal axis is at an angle relative to a plane of the halo. This configuration allows the wand to be easily picked up from a flat surface. It can also be seen that a lower distal end or extremity 212 of handle 204 is in the same plane as the lower side of halo portion 202. This configuration allows the wand 200 to sit stably on a flat surface such as a desk or shelf.

[0085] The wand 200 can function as a wireless power primary circuit to provide wireless power via a coil to the implant 100 for a fixed period of time in order to energise the implant so that the implant can conduct sensing and communication tasks. Once the wand has provided power wirelessly to the implant 100, the wand transitions to a data reception mode. This is explained further with reference to Figures 20 and 21.

[0086] A block diagram illustrating components or modules and operation of wand 200 is shown in Figure 20. A measurement cycle begins with the wand generating an alternating magnetic field to energise the implant 100 so that the implant can measure the pressure and store energy for data transmission back to the wand. The operating frequency is preferably 6.78Mhz which is an Industrial, Scientific and Medical band (ISM band) where higher electromagnetic emissions are allowed but other frequencies near or in the range of 100kHz to 30Mhz would work equally well.

[0087] The wand has an inductive coil 500 which is driven by a resonant inverter. Coil 500 may be varied in size or geometry as required by the implant or the implant orientation. This could for example be a pancake coil, figure 8 coil, an array of coils or a coil including shielding. The resonant inverter may comprise a series, parallel or combination resonant circuit to give a required impedance and / or voltage transformation property. In an embodiment, it is a series tuned tank comprising coil 500 and a reactance comprising tuning capacitor 501 . The resonant circuit may have a series tuned tank as part of the circuit, or one with a boost up capability to make a large voltage on the coil and a large magnetic field from a low voltage provided by a battery. This may be implemented by using a high Q coil in the range of 100 to 500, which Q is the quality factor Q = omega*L / R, where omega is the frequency of the power transfer, L is the inductance and R is the loss in the resonant circuit. But other Q values are considered suitable and are equivalent from a functional point of view.

[0088] The resonant tank is driven by an inverter 502 which applies AC to the tank. In an embodiment the inverter is a Class D, Class E, Class F or other high efficiency switching converter and may have zero voltage, zero current or zero derivative of the current, or other switching and reverse recovery loss reduction features so that the system efficiency is high. In an embodiment, the inverter is a half bridge or full bridge inverter. It is preferred to drive the inverter frequency from a high tolerance oscillator such as a crystal or MEMs oscillator with tolerance appropriate to ensure the system operates inside the approved band. In some embodiments the oscillator is of a variable frequency and may be modulated so that the EMI is reduced when detected by a quasi-peak detector, or may have a variable frequency to allow operation with multiple devices within the body, which operate at different frequencies, or where the frequency in changed to reduce the noise on the sensed signal from the implant 100.

[0089] The power regulator 503 provides DC to the resonant inverter 502 and uses feedback of the coil current in 500 or 501, or other circuit element, to control the strength of the magnetic field for power transfer. In one embodiment, this current is determined by safety regulations on the Specific Absorption Rate and is regulated to maximize power and implantation depth whilst meeting a safety limit described by ICNIRP, IEEE C95 or other safety standard. In another it is set to maximise the current to also meet a electromagnetic compatibility requirement, such as maximum magnetic field at a known distance. The power regulator is preferably a switching or DC / DC converter with high efficiency such as a buck, boost, buckboost or other equivalent type which can boost or reduce the output voltage relative to the battery voltage. The feedback sensor for the power regulator is preferably a low loss type such as a capacitive divider, a transformer or a sense resistor, where the sensor system losses are low so that the Q is not significantly affected by it.

[0090] The coil 500 and reactance 501 are preferably matched in frequency to the inverter to maximise the efficiency and to allow a high current in the coil to be generated but with a fixed frequency, so the system operates in the approved radio spectrum band such as 6.78MHz. Thus, a tuning system is required to maintain tank resonance near the operating frequency, and this is created by a combination of a tuning bank 505, a control system and a detector 506. This is preferably a switch bank of capacitors, but could equivalently be a variable capacitor or inductor implemented by other means. Preferably the switching elements are AC switches 507 created from pairs of source connected MOSFETs, such as wide bandwidth MOSFETs with low output capacitance or other low output capacitance types, as output capacitance can reduce the switches performance by allowing current to flow in the off state. These are preferably optically isolated from the circuit so that the source floats with respect to other circuits in the wand.

[0091] The phase detector 506 could be many types, but is preferably configured to compare the voltage and current on the resonant elements which gives a signal proportional to the tank phase angle. But it could also be a measure of the circuit voltage or current or impedance which indicates the tuning of the tank such as a hill climbing algorithm which maximises current in the coil for a given input voltage. The phase measurement is used by a control system to adjust parameters of the tuning bank such as reducing capacitance by disabling AC switches, or varying a voltage on a voltage control capacitor or equivalent parameter in a tuning inductor.

[0092] The tuning system and power regulator operate together to control the coil current with the tuning bank coarsely tuning the tank and the power regulator using feedback to precisely control the power and current.

[0093] The wand provides wireless power via the coil 220 shown as "Power Enable" high in Figure 21. During this period the implant 100 measures the pressure and stores the data in a buffer. During this period, the voltage on the resonant tank comprising coil 5000 and capacitor 501 as shown in Figure 20 can be high and may be several hundred volts. This voltage would damage the Low Noise Amplifier of the Automatic Gain Control (AGC) 515 of the receiver 5138 which may only accept a few mV before saturation and may be damaged by more than 3V to 5V. The circuit 230 provides a switching function to allow the primary or wand to switch from power transmission to data reception. Therefore, the switch effectively disconnects the AGC from the resonant voltage. With reference to Figure 21 , node C is connected to a data receiver which could be a Low Noise Amplifier, a filter, an ADC, or other sensitive data receiver that would be damaged by the high voltages experienced during wireless power transmit. L1 is the wireless power transmit, and wireless data receive coil, i.e. coil 220 in the system diagram of Figure 20. Q2 and Q4 are high voltage MOSFETs and have higher VDS rating than the AGC. They also have low output capacitance so that when turned off they don't provide a large capacitive path to the receiver which would cause losses and also potentially damage the receiver AGC. In an embodiment, Q2 and Q4 are preferably high voltage wide band gap devices such as GAN or silicon MOSFETs or equivalent. R7 and R8 are resistors with approximately the same impedance as the coil at the signal frequency. In the case of ideal matching, they are twice the impedance of L1 but values between 1 / 10thand 10 times the impedance of L1 have been found to be effective. Q5 is a low capacitance low voltage MOSFET such as a GAN or Silicon MOSFET with RDS on< < R8. R9 is a resistor which enables impedance matching to following filters of the input of the AGC. It could be series connected to NODE C, or parallel connected with Q5.

[0094] The circuit 230 operates as follows:

[0095] The wireless power system operates when Power Enable is high to transfer power to the implant via the coil L1. Q2 and Q4 are off and prevent large currents flowing through to ground via R7 which could generate a large voltage into the receiver. However, some voltage may appear on R7 due to the leakage current through the output capacitance of Q2 and Q4. Q5 is on, which clamps the voltage at Node C to near zero with a magnitude attenuated by a factor of RDS on / R8.

[0096] At T1 wireless power is disabled, and NODE A goes high relative to Q4's source terminal. This turns on Q2 and Q4 and current flows into R7 and R8 and to ground. Because these are similar impedances to L1 , the resonant current is quickly damped to close to zero volts. At T2, Q5 turns off and the receiver input is no longer clamped. T2 can occur as soon as the voltage is below the operating common voltage of the AGC, or could be held on for longer in another embodiment. After T2 the receiver, which is connected to NODE C, can operate to amplify and decode the wireless transmission. Between T2 and T3, data is received from the implant 100 or wireless transition system. There is a gap between T3 and T4 (new wireless power cycle) to enable the implant 100 to reset. Node B goes high at the same time or before T4 to protect the AGC from damage when wireless power is enabled and the voltages on L1 become high.

[0097] The data that is received from the implant 100 is provided in a digital format. Measurements are converted to digital form within the implant, and data is transmitted in a separate step using digital communication methods. One advantage of transferring data digitally is that data packets containing additional data can be included and sent from the implant to the wand (external reader unit) 200. For example, in an embodiment, packets are transmitted from the implant that include system data, calibration data and measurement data in each packet. An example is shown in Figure 22 in which a memory or section of memory 702 of the implant is shown diagrammatically in which system data, calibration data and measurement data are stored. Upon the implant being energised by wand 200, the implant can transmit packets which comprise some or all of the data in memory 702. An example of a packet 708 is shown in Figure 22A. In an embodiment calibration data packets, system data packets and measurement data packets can be requested individually.

[0098] Regarding calibration data itself, the following can be used in examples or embodiments: 2nd order polynomial fit data for pressure measurements; 2nd order polynomial fit coefficients for temperature measurements; 2nd order coefficients for pressure temperature fit. These may be used individually or in combination using multivariable polynomials to allow accurate calibration across pressure and temperature. 2nd order polynomials are used in some examples, but other calibration equations could be applied to generate calibration data.

[0099] Transmission of calibration data and measurement data has the advantage that all data for an accurate measurement, e.g. calibration coefficients, are included in the transmitted packet and the external measurement devices (such as the wand 200) does not need to store them. This means that other measurement devices may be used. It also has the advantage that cost can be removed from the measurement unit through making it simpler. Transmission of implant identifier (ID) can improve security and privacy, for example each wand 200 can be programmed to only operate with implants having the correct ID. For example, one patient's wand would not report data from other patients' implants. This also allows the implant ID to be tracked.

[0100] In an embodiment the implant 100 can use two different measurement modes to measure the capacitance of the capacitive pressure sensor. These are the difference and the ratio, as seen in Figure 22.

[0101] Referring to Figure 23, the sense electrode capacitance Cs and the reference electrode capacitance CR are shown as inputs to a converter 704 which provides a digital output corresponding to the capacitance measurements to micro controller 706 in the implant 100.

[0102] The difference measurement is proportional to Cs - C i.e. the sense electrode capacitance minus the reference electrode capacitance, and the ratio mode is proportional to CS / CR. Capacitance is equal to C = £Q£RA / (1 where E0is the vacuum permittivity, and EBis the relative permittivity, A is the capacitance area and d is the capacitance plate separation. Changes in the transducer which lead to changes in relative permittivity can be detected as a divergence between the expected relationship between capacitance difference measurements which are proportional to EBand ratio measurements which are independent of £R-

[0103] At calibration, capacitance difference and ratio measurements can be taken at set pressures and temperatures. In an embodiment a look up table is be constructed so that for a given measurement e.g. difference, the corresponding ratio measurement will be known. In another embodiment, a polynomial or other calibration is constructed to calculate the ratio measurement based on the difference measurement. After implantation, the measured ratio measurement can be compared to the expected ratio measurement based on the look up table or calibration data. If these values diverge, drift can be predicted and compensated.

[0104] In at least some embodiments, the implant 100 can be operated for over 10 years within a patient. Certain failure modes such as tin-whisker growth, capacitor failure or other circuit failures could result in short circuit conditions or high-load conditions within the implant leading to significant implant heating. The implant heating depends on the magnetic field strength of the wand 200 and the length of time the implant is powered.

[0105] In an embodiment, a "Search Mode" is implemented as a safety feature whereby the wand 200 applies power for a minimal duration allowing the implant 100 to power-up and transmit a search signal for detection by the wand 200. The search signal duration can be significantly shorter than a typical power cycle as the implant does not need to take measurements or construct data packets. For example, in an embodiment the search signal duration is 1 / 20th of the typical power signal duration. In an embodiment the search signal duration is configured to be of a sufficient time to receive an unmodulated transmission from the implant 100. An unmodulated transmission from the implant allows the wand 200 to detect the implant's presence. It can also allow the wand to detect correct function of the implant. On detecting the correct function, the wand can shift to the typical power cycle. This ensures that an unresponsive implant would experience heating 20 times less than using a typical power cycle.

[0106] As mentioned above, the wand 200 provides a power signal that is used to energise the implant. Figure 25 shows a circuit diagram for the implant 100 when receiving a power signal from wand 200. The coil 1 12 is tuned by a capacitor 113 and the induced resonant alternating voltage and current is rectified to DC and provided to energy storage capacitor 1 19, the voltage on which is regulated by voltage regulator 1 17. The energy in capacitor 1 19 is used to energise the implant circuits and perform sensing and transmission functions. Figure 24 shows a circuit diagram of the implant 100 when in a transmission mode. Once controller 125 detects that the power signal from the wand 200 has stopped (which may occur for example by detecting when the voltage induced across coil 112 or present on the rectifier 115 has diminished or ceased for a required period), then a transmission mode is entered. As is described in detail in patent publication W02020050728A1 , in an embodiment a driver 121 energises the resonant circuit and a phase modulator 123 activates or deactivates switch S1 to short capacitor 113 at zero voltage for at least part of a resonant cycle. Wand 200 is at this time in a receiver mode to detect the phase shifts. In an embodiment, wand 200 modulates the power signal it transmits. In an embodiment the modulation is amplitude modulation, for example ASK. An example of amplitude-shift- keying (ASK) is shown in Figure 26. Typically, ASK is demodulated in RFID and IPT systems by looking at the output of a rectifier and measuring the voltage increase or decrease due to ASK. Using smaller modulation indexes results in longer times for a detectable change to occur. Using larger modulation indexes results in sub-optimal power delivery.

[0107] In wireless-power-transfer (WPT) or inductive-power-transfer (IPT) systems the supply after the rectifier will ideally be stable and have a long time constant to avoid sudden changes due to shifts in load or field strength. This results in long modulation lengths for ASK to detect data and hence low data transfer rates. Alternately, a second rectifier and envelope detector can be used solely for data transfer.

[0108] For any one load at the wireless power secondary, there is an optimum secondary open circuit voltage. Using ASK will result in the open circuit voltage varying below and above the optimum required voltage. Therefore, ASK with a minimum modulation index is desired.

[0109] In a wireless power link, ideally variations in the open circuit voltage from ASK modulation will not affect the DC supply voltage generated after the rectifier. The supply should be filtered at a frequency well below the modulation frequency if it is not to add ripple to the supply. If the supply voltage does not vary, the rectifier will clip the resonant voltage in the secondary pickup to the supply voltage, as seen in Figure 27. This presents an issue for detecting ASK modulation even with a secondary, data only, rectifier and envelope detector. The amplitude on a parallel tuned secondary (e.g. the resonant circuit in implant 100) is:

[0110] V2= QlVoc where Q2is the unloaded secondary pickup quality factor. When loaded by the rectifier and load, the loaded Q is Q2Land:

[0111] ^2L=Q2lVoc=jul

[0112] Because the effective load depends on the output voltage and hence the open circuit voltage, it is not constant. As Vocdrops, so does the effective load from the rectifier resulting in Q2Lincreasing until it meets Q2. The point Voc modat which Vocis low enough for y2to fall below the output voltage Voutis:

[0113] Substituting the nominal open circuit voltage required under full load conditions and rearranging gives:

[0114] When designed for maximum power transfer or =2O and:

[0115] For ASK to be visible on a parallel tuned secondary pickup set up for maximum power transfer, the modulation index must be greater than 50%. This may not occur at low modulation indexes.

[0116] Therefore, in an embodiment, implant 100 uses a method of demodulation amplitude-shift- keying (ASK) data from the wand (primary side) to the implant (secondary side) of an inductive power transfer link. As amplitude at the primary changes, the amount of power delivered to the secondary changes. If an active rectifier 1 15 is used for AC-DC conversion at the secondary, the amount of time the rectifier switches are on will increase if amplitude increases and decrease if amplitude decreases. The change in on time of the rectifier switches can be monitored and used to demodulated ASK signals as shown in Figure 27A.

[0117] The advantage of using the rectifier switch times (i.e. clip-length-detection) is that the on- time of the rectifier switches changes at low modulation indexes which do not result in an amplitude change at the secondary. As less power is being delivered to the load, the switches are on for a shorter time and this can be detected by filtering the rectifier control voltages.

[0118] In one embodiment, the control signal for the rectifier switches could also be used to activate and deactivate a current source driving an RC lowpass filter. When the primary voltage is larger, the rectifier switches would be activated for longer and hence the average voltage on the RC filter would be larger. With a lower primary voltage, the switches would be active for a shorter period of time and the voltage on the RC filter would decrease. A comparator could be used to detect if the voltage on the RC filter is higher or lower than a set threshold.

[0119] Alternately, A differential comparator could be used with one input connected to the RC filter voltage and one input connected to a second RC filter in series with the first RC filter to allow the threshold to track the average wireless power strength.

[0120] In an embodiment another method of demodulation amplitude-shift-keying (ASK) data from the primary side wand 200 to the secondary side implant of the inductive power transfer link is used. Shorting-control is a power-flow-control method used to limit the power received by the implant and prevent excess heating or voltages occurring. With reference to Figure 28, if excess power is received from the secondary, the supply voltage within the implant VDD increases. This may lead to voltages occurring that are above the implant component ratings. Shorting control operates by using switches to short-circuit the implant coil when the supply voltage reaches a predetermined upper threshold VMAX. Provided the shorting switches have a low resistance relative to the impedance of the implant coil and resonant capacitor, very little power is dissipated and shorting-control results in power-flow-control with minimal additional implant heating. When shorting-control is active, no power is delivered to the implant supply and the supply voltage drops as the implant draws power. When the supply voltage falls below a set threshold VMIN, the shorting switches are opened and power transfer to the implant resumes. Other control methods of controlling the shorting switches include pulse-width-modulation, pulse-density-modulation and pulse-frequency-modulation. Typically, ASK is demodulated in RFID and IPT systems by looking at the output of a rectifier and seeing the voltage increase or decrease due to ASK. When shorting-control is used as a power-flow-control method, it intermittently clamps the secondary voltage to zero when the voltage in the storage element reaches a maximum as shown in Figure 28. This has the disadvantage of masking or corrupting the amplitude changes from ASK at the primary.

[0121] As amplitude at the primary changes, the amount of power delivered to the secondary changes. The frequency of shorting-control activating and the duty cycle both increase with the received power. The shorting control frequency or number of shorting-control activations can be monitored and used to demodulate the ASK power signal. A threshold can be set to determine if a bit 1 or bit 0 has been transmitted as shown in Figure 27B.

[0122] Using the number of times shorting-control is active, or the active and inactive durations allows detection of ASK without any additional demodulator. This method has advantages that include a lower probability of corrupted data when shorting-control is used as a power- flow-control method. It is also sensitive to moderate modulation indexes, as opposed to many other methods which require large modulation indexes leading to non-optimal power transfer.

[0123] In an embodiment, the implant 100 also uses another power flow control method which allows control of power flow from the primary (for example wand 200 or a similar device) to the secondary (implant 100). This resonant power flow reversal power flow control method allows the power flow to be controlled from the implant, as the device receiving wireless power, rather than being controlled by control of the wand which is the device delivering the power. As shown in Figures 24 and 25, in an embodiment the implant has a parallel tuned resonant circuit which can be used for receiving power (and information), and for transmitting information in digital format back to the wand 200.

[0124] Although Figure 24 shows the implant circuit as used for transmission, the switch S1 may be used when in power receiving mode to implement this method. Thus, when the implant is receiving power wirelessly from wand 200, the resonant voltage in the parallel tuned coil 1 12 is short circuited with switch S1 at the zero-voltage / maximum-current crossing and kept shorted for half of the resonant cycle. The switch is then opened allowing resonance to continue with a 180 degree phase shift introduced. The resonant voltage in the secondary coil destructively interferes with the voltage induced from the primary preventing power being delivered to the secondary. This is used to control power delivery to the implant, and is illustrated in Figure 29.

[0125] This method could also be used in a series tuned implant coil and could be implemented by open circuiting the pickup at maximum-voltage / zero-current.

[0126] This method has the advantage that it allows power to be controlled from the secondary without feedback to the primary side. This reduces complexity and cannot fail due to disruption / noise in the feedback path to the primary. It also works in the case that the secondary is placed in a magnetic field produced by a primary with an incompatible RF feedback system. Compared with other secondary based power-flow-control methods resonant-phase-reversal (RPR) does not require any of the passive components i.e. resistors, capacitors or inductors used in alternative methods allowing for a smaller physical implementation. RPR uses the power already in the secondary coil to destructively interfere with the voltage induced by the primary. Therefore, power in the secondary is temporarily returned to the primary rather than dissipated in the secondary. This allows lossless power flow to be controlled i.e. no additional heating at the implant. Practically, the only losses are the power lost in the switches during the phase shift and the power lost in the equivalent series resistance (ESR) of the implant pickup. The power lost in the shorting switches is minimal and the losses in the implant coil ESR are lower than during power transfer. RPR could provide substantially lower loss power- flow-control than any other secondary based method.

[0127] Advantageously, RPR uses the same or similar circuitry as resonant-phase-shift-keying (RPSK) disclosed in W02020050728A1 making it an appropriate fit to combine with RPSK. RPSK is sequential, meaning there is a power phase and a communication phase. During the powering phase no communication can be sent from the secondary to the primary. During these times RPR could effectively control power-flow.

[0128] In an embodiment, the implant has a clock extraction circuit to extract a measurement clock from the AC magnetic field for use in the measurement circuitry to avoid noise or aliasing of EMI due to the AC magnetic field. The AC magnetic field can cause electromagnetic interference (EMI) on the transducer and electronics which can be sampled by the measurement circuit and appear as noise. This is exacerbated when sampling at an integer division of the AC magnetic field frequency as the EMI is aliased into a low frequency or DC signal close to the measurement frequencies of interest herein referred to as the signal band. A clock extraction circuit such as a comparator can extract a clock at the frequency of the AC magnetic field such as using a comparator across the resonant circuit. In an embodiment the extracted clock is tied to the AC magnetic field frequency and hence EMI frequency. The extracted clock can be multiplied by N and divided by M to ensure the aliased EMI is outside of the signal band. When the sampling frequency is lower than the signal frequency or EMI frequency in this case, the aliased frequency is described by the equation:

[0129] Where fais the aliased frequency, fwpis the wireless power frequency, fsis the sampling frequency | | is the absolute value and roundQ expression rounds to the nearest integer. If the sampling frequency is tied to the wireless power frequency such that fs= (N / M)fwp, s M / N approaches an integer, faapproaches DC and moves towards the signal band. When M / N approaches a number with a remainder of 0.5, faapproaches fs / 2 and can be removed using a digital filter. It is also noted that a sampling frequency resulting in an aliased EMI frequency other than 0.5fsmay be selected in cases where significant harmonics are expected in the EMI. As an example, an EMI source with frequency fwphaving harmonics at 2fwpand 3fwpsampled at fs= fwp / 50.5 such that fa= 0.5fsfor the first harmonic would result in the second harmonic occurring at 0fswhich is DC and would not be filtered with a low pass filter. However, choosing fs=fwp / 50.167 would result in the first, second and third harmonics being aliased to 0.167fs, 0.333fsand 0.5fsrespectively. Provided the sampling frequency is high relative to the signal frequency, all harmonics could be filtered while retaining the signal.

[0130] As shown in Figure 30, a clock divider 800 such as an integer-N PLL or a fractional-N PLL can be used to generate a measurement clock that is at a fractional division of the EMI frequency ensuring that the EMI is aliased to a frequency away from the measurement frequencies of interest. As shown in Figure 31 , a low pass filter with a cut-off frequency between the measurement band and aliased noise frequency can be used to remove the aliased noise. Furthermore, the measurement clock can be set to a frequency that is a division with remainder 0.5 for any harmonics of the AC magnetic field frequency thereby ensuring aliased noise from the AC magnetic field and any of its' harmonics are aliased to a frequency away from the measurement frequencies of interest.

[0131] This method is especially suited to applications where the sampling frequency is significantly higher than the signal frequency, for example in oversampling converters such as delta-sigma ADCs. The highest frequency hat can be accurately represented by sampling without aliasing is known as the Nyquist frequency and is half the sampling rate. In the case of oversampling converters, the sampling frequency, and hence Nyquist frequency, are significantly higher than the signal frequency. Oversampling rates of 64, 128, 256, and higher are not uncommon. In such cases, the sampling frequency can be derived from the EMI frequency to ensure the EMI is aliased to fs / 2 which is an order of magnitude or more higher than the signal frequency and allowing a digital filter to be used to remove the aliased EMI. This is particularly advantageous in integrated circuit technology where a digital filter is easier and less costly to implement than an analogue filter. In addition, in a small, space constrained implanted device, there is often limited space to implement an analogue filter using discrete components such as resistors and capacitors. Further benefits of deriving the sampling frequency from the EMI frequency include tracking changes in the EMI frequency. As an example, in the case if a wirelessly powered implant, small shifts in the wireless power frequency due to use of different wireless power primaries or aging of components in the primary relative to the sampling frequency will shift the aliased EMI frequency. Driving the sampling frequency from the wireless power frequency ensures the EMI is filtered correctly regardless of the primary used.

[0132] In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

[0133] As used herein the term "and / or" means "and" or "or", or both. As used herein "(s)" following a noun means the plural and / or singular forms of the noun. The term "comprising" as used in this specification means "consisting at least in part of". When interpreting statements in this specification which include that term, the features prefaced by that term in each statement all need to be present, but the other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner. The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference.

[0134] Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine-readable medium such as a storage medium or other storage(s). A processor may perform the necessary tasks. A code segment may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc.

[0135] In the foregoing, a storage medium may represent one or more devices for storing data, including read-only memory (ROM), random access memory (RAM), magnetic disk storage mediums, optical storage mediums, flash memory devices and / or other machine readable mediums for storing information. The terms "machine readable medium" and "computer readable medium" include, but are not limited to portable or fixed storage devices, optical storage devices, and / or various other mediums capable of storing, containing or carrying instruction(s) and / or data.

[0136] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1 , 1 .1 , 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0137] Some aspects of the disclosure are set forth in the clauses below and the appended claims.

[0138] Clauses

[0139] 1. A wireless implant comprising: an enclosed rigid housing structure having a length, a width and a height, wherein the length is greater than the width and height and wherein the housing structure defines a first chamber; the first chamber containing a wireless power and control circuit; a pressure sensor chamber provided on the rigid housing structure, wherein the pressure sensor chamber has a pressure flexing wall provided along a length of the rigid housing structure; and wherein the pressure sensing wall is configured to deform dependent on pressure exerted thereon.

[0140] 2. A wireless implant comprising: a housing having a first chamber containing a wireless power transfer circuit and a rectifier, and a second chamber containing a pressure sensor; and a locator connection at one end of the housing.

[0141] 3. A wireless implant comprising: a housing having a first chamber containing a wireless power transfer circuit and a second chamber containing a pressure sensor; and a capacitive reference electrode in the second chamber.

[0142] 4. A wireless implant comprising: a housing having a first chamber containing a wireless power transfer circuit and a second chamber containing a pressure sensor; and wherein the wireless power transfer circuit is configured to transmit pressure measurement data and one or more of: reference data; calibration data; system data.

[0143] 5. A wireless implant comprising: a housing having a first chamber containing a wireless power transfer resonant circuit comprising a coil and a capacitor, and a second chamber containing a pressure sensor; and wherein the wireless power transfer resonant circuit further comprises a switch and a controller configured to active or deactivate the switch to either short circuit the coil at maximum current or open circuit the capacitor at maximum voltage for at least part of a resonant cycle; whereby in a power receiving mode in which the implant is receiving wireless power from a remote device the controller activates the switch to control power received by the resonant circuit, and in a communication mode in which the implant is communicating data to a remote device the controller activates the switch to encode data.

[0144] 6. The implant of clause 4 or 5 wherein the data is transmitted in one or more packets.

[0145] 7. A wireless implant comprising: a resonant circuit configured to receive an amplitude modulated power signal; a control circuit configured to control power supplied to a load in the implant by a control signal to control the connection between the resonant circuit and the load, or control a phase of the resonant circuit or to control rectification of an alternating current from the resonant circuit; wherein the control circuit is further configured to demodulate the power signal dependent on the control signal. 8. A wireless implant according to clause 7 wherein a duration or frequency or number of activations of the control signal is used to demodulate the power signal.

[0146] 9. A wireless implant comprising : a resonant circuit configured to receive an amplitude modulated power signal; a rectifier for converting alternating current from the resonant circuit to direct current for supply of power to a load; an amplitude shift keying demodulator configured to demodulate data from the power signal by detecting changes in power delivered to the load due to the amplitude modulated power signal.

[0147] 10. A wireless implant according to clause 9 wherein power delivered to the load is detected by measuring the duration over which the resonant voltage is greater than or equal to the rectified voltage.

[0148] 11. A wireless implant according to clause 9 or 10 wherein the rectifier is an active rectifier.

[0149] 12. A wireless implant according to any of clauses 9-11 wherein the rectifier is an active rectifier and the duration over which the resonant voltage is greater than or equal to the rectified voltage is detected from the on time of one or more switches active rectifier.

[0150] 13. A wireless implant comprising: a resonant circuit configured to receive an amplitude modulated power signal; an active rectifier for converting alternating current from the resonant circuit to direct current for supply of power to a load; an amplitude shift keying demodulator configured to demodulate data from the power signal by detecting an on time of one of more switches of the active rectifier.

[0151] 14. A wireless implant comprising: a resonant circuit configured to receive a wireless power signal for provision of power to a load, the resonant circuit comprising a coil tuned with a capacitor; a control circuit configured to control power delivered to the load by selectively phase shifting the current in the resonant circuit by 180 degrees.

[0152] 15. A wireless implant according to clause 14 wherein the phase shift comprises either short circuiting the coil at maximum current or open circuiting the capacitor at maximum voltage for half of a resonant cycle while power is being received wirelessly by the resonant circuit.

[0153] 16. The wireless implant of clause 14 or 15 wherein the wireless power signal is amplitude modulated, and control circuit is further configured to demodulate the power signal dependent on the phase shifts.

[0154] 17. A wireless implant comprising two chambers wherein the sensor capacitance in first said chamber varies with applied pressure and the second chamber encompasses an oscillator who properties determine the transmit frequency of the wireless communication from the implant to the receiver, where the oscillator frequency, amplitude or phase are independent of the pressure on the implant.

[0155] 18. A wireless implant comprising two chambers wherein the sensor capacitance in first said chamber varies with applied pressure and the second chamber encompasses an analog to digital converter which converts the capacitance property of the first chamber into a digital data stream and combines it with calibration values to enable the body pressure to be calculated from the capacitance.

[0156] 19. A wireless implant, comprising: a measurement circuit to measure and digitize a physiological signal; a receiver circuit configured to receive energy from an AC magnetic field; wherein a clock is derived from the AC magnetic field to supply to the measurement circuit ensuring measurements are sampled at a frequency avoiding aliasing with EMI from the AC magnetic field.

[0157] 20. The wireless implant of clause 19 wherein the clock derived from the AC magnetic field is divided by a non-integer number. 21. The wireless implant of clause 19 or 20 wherein the clock is divided using an integer-N

[0158] PLL

[0159] 22. The wireless implant of clause 19 or 20 wherein the clock is divided using a fractional-N PLL.

[0160] 23. A wireless implant, comprising: a measurement circuit to measure and digitize a physiological signal; a receiver circuit configured to receive energy from an AC magnetic field; a clock extraction circuit used to derive a clock from the AC magnetic field to supply to the measurement circuit; a frequency divider circuit used to derive a measurement frequency that is not an integer division of the fundamental AC magnetic field frequency or an integer division of a harmonic of the AC magnetic field frequency; wherein the measurement clock is supplied to the measurement circuit whereby measurements are sampled at a non-integer division of the AC magnetic field frequency and a non-integer division of any harmonics of the AC magnetic field frequency.

[0161] 24. The wireless implant of clause 23 wherein the clock derived from the AC magnetic field is divided by a non-integer number.

[0162] 25. The wireless implant of clause 23 or 24 wherein the clock is divided using a fractional-N PLL.

[0163] 26. The wireless implant of any preceding clause, wherein the pressure sensor is configured to sense pressure in an anatomical region.

[0164] 27. The wireless implant of any preceding clause wherein the implant is configured to detect or monitor a brain related condition, or a cardiac condition. 28. The wireless implant of any preceding clause wherein the pressure flexing wall extends substantially 75% to 95% of the length and / or width of the first chamber.

[0165] 29. The wireless implant of any preceding clause wherein the pressure flexing wall has a length greater than its width.

[0166] 30. The wireless implant of any preceding clause wherein at least one of the pressure flexing wall or the rigid housing have one or more upstands to limit movement of the pressure flexing wall relative to the rigid housing in at least one direction.

[0167] 31. The wireless implant of clause 30 wherein the upstand is dependent from the rigid housing.

[0168] 32. The wireless implant of any preceding clause wherein the pressure sensor comprises a first conductive region provided on the rigid housing and a second conductive region provided on the pressure flexing wall.

[0169] 33. The wireless implant of any preceding clause wherein the pressure sensor comprises a reference electrode.

[0170] 34. The wireless implant of clause 33 wherein the pressure sensor comprises a sense electrode configured to provide a capacitive sensor.

[0171] 35. The wireless implant of clause 33 or claim 34 wherein the sense electrode and the reference electrode are provided in the same chamber.

[0172] 36. The wireless implant of clause 35 wherein the chamber is hermetically sealed.

[0173] 37. The wireless implant of any preceding clause wherein the pressure sensor and control circuit are configured to detect pressure and temperature. 38. The wireless implant of any preceding clause wherein the pressure sensor is configured to detect absolute pressure.

[0174] 39. The wireless implant of any preceding clause wherein the implant has a plurality of chamfered edges.

[0175] 40. The wireless implant of any preceding clause wherein the control circuit is configured to determine a pressure from the pressure sensor and to transmit a digitally encoded phase shift keyed information signal representing the determined pressure.

[0176] 41. The wireless implant of clause 40 wherein the control circuit is configured to detect when power is not being received by the resonant circuit and to use the resonant circuit to transmit the digitally encoded phase shift keyed information signal.

[0177] 42. Apparatus for delivering a wireless implant into an anatomical region, comprising: a tip housing configured to receive the implant and having an outlet; a plunger configured to expel the implant from the tip housing through the outlet, and wherein the tip housing comprises an open channel configured to expose a wall of the implant in use.

[0178] 43. Apparatus for delivering a wireless implant into an anatomical region, comprising: a hollow tip housing configured to receive the implant and comprising one or more retention formations configured to contact one or more walls of the implant; a plunger configured to expel the implant from the tip housing, wherein the retention formations support the implant without inhibiting flexure of a pressure sensing wall region of the implant.

[0179] 44. Apparatus for transmitting power wirelessly to a wireless implant, comprising: a tuned coil; an inverter configured to energise the tuned coil to transmit a power signal; a switch circuit configured to switch the coil to a data reception mode; a phase detector configured to detect data received wirelessly from the implant. 45. The apparatus of clause 44 wherein the switch circuit comprises an impedance which is substantially matched to the impedance of the coil.

[0180] 46. The apparatus of clause 44 or 45 wherein the data is received as one or more packets.

[0181] 47. A wireless implant system comprising: an external device and an implant device; the implant device comprising a hermetically sealed housing containing an implant resonant circuit, an implant control circuit and a pressure sensor; the external device comprising a primary resonant circuit and a primary control circuit configured to transmit a digitally encoded amplitude shift keyed power signal of a selected duration to the implant device; wherein the implant device is solely energised by the power signal, and the control circuit is configured to receive power from the power signal and to simultaneously demodulate the power signal to decode instructions from the external device; and wherein the implant device control circuit is configured to detect when the selected duration has elapsed, determine a pressure from the pressure sensor and to transmit a digitally encoded phase shift keyed information signal representing the determined pressure to the primary resonant circuit.

[0182] 48. The wireless implant system of clause 38 wherein the implant device comprises the wireless implant according to any one of clauses 1 -41 .

[0183] 49. The wireless implant system of clause 47 or 48 wherein the external device comprises the apparatus of any one of clauses 44-46.

[0184] 50. A method of implanting an implantable wireless sensor comprising; placing the sensor in a hollow housing; positioning the housing in a placement location; using a plunger to expel the sensor from the housing. 51. The method of clause 50 further comprising attaching a locator to the sensor.

[0185] 52. The method of any one of clauses 50- 51 further comprising placing the sensor in the housing such that the housing supports the implant without inhibiting flexure of a pressure sensing wall region of the implant.

[0186] 53. A method for transmitting data from a wireless implant having a pressure sensor, the method comprising: transmitting pressure measurement data and one or more of: reference data; calibration data; system data.

[0187] 54. A method of operating a wireless implant containing a wireless power transfer resonant circuit comprising a coil and a capacitor, and a second chamber containing a pressure sensor, the method comprising: activating or deactivating a switch to either short circuit the coil at maximum current or open circuit the capacitor at maximum voltage for at least part of a resonant cycle; whereby in a power receiving mode in which the implant is receiving wireless power from a remote device the controller activates the switch to control power received by the resonant circuit, and in a communication mode in which the implant is communicating data to a remote device the controller activates the switch to encode data.

[0188] 55. The method of clause 53 or 54 wherein the data is transmitted in one or more packets.

[0189] 56. A method of controlling a wireless implant comprising: controlling power from a wireless power signal to a load in the implant by a control signal to control the connection between a resonant circuit and the load, or control a phase of the resonant circuit or to control rectification of an alternating current from the resonant circuit; and demodulating the power signal dependent on the control signal.

[0190] 57. A method as claimed in clause 56 wherein a duration or frequency or number of activations of the control signal is used to demodulate the power signal. 58. A method for controlling a wireless implant comprising: receiving an amplitude modulated power signal at a resonant circuit of the implant; rectifying to an alternating current from the resonant circuit to provide a direct current for supply of power to a load of the implant; demodulating data from the power signal by detecting changes in power delivered to the load due to the amplitude modulated power signal.

[0191] 59. A method as claimed in clause 58 wherein power delivered to the load is detected by measuring the duration over which the resonant voltage is greater than or equal to the rectified voltage.

[0192] 60. A method as claimed in clause 58 or 59 wherein the rectifier is an active rectifier.

[0193] 61. A method as claimed in any of clauses 58-60 wherein the rectifier is an active rectifier and the duration over which the resonant voltage is greater than or equal to the rectified voltage is detected from the on time of one or more switches of the active rectifier.

[0194] 62. A method of controlling a wireless implant, the method comprising: receiving an amplitude modulated power signal; actively rectifying the power signal to provide a direct current for supply of power to a load; demodulating data from the power signal by detecting an on time of one of more switches of the active rectifier.

[0195] 63. A method of controlling a wireless implant, the method comprising: receiving a wireless power signal for provision of power to a load; controlling power delivered to the load by selectively phase shifting the current in the resonant circuit by 180 degrees.

[0196] 64. The method as claimed in clause 63 wherein the phase shift comprises either short circuiting the coil at maximum current or open circuiting the capacitor at maximum voltage for half of a resonant cycle while power is being received wirelessly by the resonant circuit. 65. The method of clause 63 or 64 wherein the wireless power signal is amplitude modulated, and control circuit is further configured to demodulate the power signal dependent on the phase shifts.

[0197] 66. A method of controlling a wireless implant, comprising: measuring and digitizing a physiological signal; receiving energy from an AC magnetic field; deriving a clock from the AC magnetic field to supply to allow measurements to be sampled at a frequency avoiding aliasing with EMI from the AC magnetic field.

[0198] 67. The method of clause 66 wherein the clock derived from the AC magnetic field is divided by a non-integer number.

[0199] 68. The method of clause 66 or 67 wherein the clock is divided using an integer-N PLL

[0200] 69. The method of clause 66 or 67 wherein the clock is divided using a fractional-N PLL.

[0201] 70. A method of controlling a wireless implant, comprising: measuring and digitizing a physiological signal; receiving energy from an AC magnetic field; deriving a clock from the AC magnetic field to a measurement circuit; deriving a measurement frequency that is not an integer division of the fundamental AC magnetic field frequency or an integer division of a harmonic of the AC magnetic field frequency; wherein the clock supplied to the measurement circuit allows measurements to be sampled at a non-integer division of the AC magnetic field frequency and a non-integer division of any harmonics of the AC magnetic field frequency.

[0202] 71 . The method of clause 70 wherein the clock derived from the AC magnetic field is divided by a non-integer number.

[0203] 72. The method of clause 70 or 71 wherein the clock is divided using a fractional-N PLL.

Claims

Claims1 . A wireless implant comprising: an enclosed rigid housing structure having a length, a width and a height, wherein the length is greater than the width and height and wherein the housing structure defines a first chamber; the first chamber containing a wireless power and control circuit; a pressure sensor chamber provided on a rigid wall of the rigid housing structure, wherein the pressure sensor chamber has a pressure flexing wall provided along a length of the rigid wall of the housing structure; and wherein the pressure sensing wall is configured to deform relative to the rigid wall dependent on pressure exerted on the pressure sensing wall.

2. The wireless implant of claim 1 further comprising a locator connection at one end of the housing structure.

3. The wireless implant of claim 1 or claim 2 wherein the pressure flexing wall extends substantially 75% to 95% of the length and / or width of the first chamber.

4. The wireless implant of any one of the preceding claims wherein wherein the wireless power circuit is configured to transmit pressure measurement data and one or more of: reference data; calibration data; system data.

5. The wireless implant of any one of the preceding claims wherein the wireless power circuit comprises a resonant circuit comprising a coil and a capacitor, and a second chamber contains a pressure sensor; and wherein the wireless power circuit further comprises a switch and a controller configured to active or deactivate the switch to either short circuit the coil at maximum current or open circuit the capacitor at maximum voltage for at least part of a resonant cycle; whereby in a power receiving mode in which the implant is receiving wireless power from a remote device the controller activates the switch to control power received by the resonantcircuit, and in a communication mode in which the implant is communicating data to a remote device the controller activates the switch to encode data.

6. The wireless implant of claim 5 wherein the resonant circuit is configured to receive an amplitude modulated power signal; the control circuit is configured to control power supplied to a load in the implant by a control signal to control the connection between the resonant circuit and the load, or control a phase of the resonant circuit or to control rectification of an alternating current from the resonant circuit; and / or wherein the control circuit is further configured to demodulate the power signal dependent on the control signal.

7. The wireless implant of claim 5 wherein the control circuit is configured to control power delivered to the load by selectively phase shifting the current in the resonant circuit by 180 degrees.

8. The wireless implant of any one of the preceding claims wherein a sensor capacitor is provided in the pressure sensing chamber and a circuit provided in the second chamber converts a capacitance of the sensor capacitor into a digital data stream and combines it with a calibration value.

9. The wireless implant of claim 8 wherein the sensor capacitor comprises a first conductive region provided on an outer surface of the rigid wall and a second conductive region provided on an inner surface of the pressure flexing wall.

10. The wireless implant of claim 9 wherein the sensor capacitor further comprises a reference electrode.

11. The wireless implant of any one of the preceding claims wherein the wireless power circuit is configured to receive energy from an AC magnetic field;the control circuit is configured to derive a clock signal from the AC magnetic field whereby sensor measurements are sampled at a frequency to avoid aliasing with EMI from the AC magnetic field.

12. The wireless implant of claim 1 1 wherein the clock signal derived from the AC magnetic field is divided by a non-integer number.

13. The wireless implant claimed in claim 1 1 or 120 wherein the clock is divided using a fractional-N PLL14. The wireless implant of any preceding claim wherein the pressure sensor is configured to detect absolute pressure.

15. The wireless implant of any preceding claim wherein the implant has a plurality of chamfered edges.

16. The wireless implant of any one of the preceding claims wherein the control circuit is configured to detect the cessation of wireless power delivery to the wireless power circuit.

17. A wireless implant system comprising: an external device and an implant device; the implant device comprising a hermetically sealed housing containing an implant resonant circuit, an implant control circuit and a pressure sensor; the external device comprising a primary resonant circuit and a primary control circuit configured to transmit a digitally encoded amplitude shift keyed power signal of a selected duration to the implant device; wherein the implant device is solely energised by the power signal, and the control circuit is configured to receive power from the power signal and to simultaneously demodulate the power signal to decode instructions from the external device; and wherein the implant device control circuit is configured to detect when the selected duration has elapsed, determine a pressure from the pressure sensor and to transmit adigitally encoded phase shift keyed information signal representing the determined pressure to the primary resonant circuit.

18. The wireless implant system of claim 17 wherein the implant device comprises the wireless implant according to any one of claims 1 -16.

19. The wireless implant system of claim 17 or 18 wherein the external device comprises: a tuned coil; an inverter configured to energise the tuned coil to transmit a power signal; a switch circuit configured to switch the coil to a data reception mode; a phase detector configured to detect data received wirelessly from the implant.

20. The wireless implant system of any one of claims 17 to 19 wherein the external device decodes pressure measurement data and calibration data received wirelessly from the implant device.

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