Midfield transmitter polarization techniques

Abstract

An implantable device can be configured to receive a wireless power signal from a midfield external transmitter. The midfield transmitter can include a plurality of excitation signal paths coupled to respective excitable sub-wavelength structures and a controller circuit configured to control a first phase adjustment circuit to change a first phase characteristic of a first signal in a first signal path of the plurality of excitation signal paths. A power signal transfer efficiency between the midfield transmitter and the implantable device can be a function of the first phase characteristic of the first signal. The controller circuit can be configured to change the first phase characteristic to optimize the power signal transfer efficiency.

Description

MIDFIELD TRANSMITTER POLARIZATION TECHNIQUESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority to United States Provisional Application No. 63 / 584,028, filed on September 20, 2023, and entitled “MIDFIELD TRANSMITTER POLARIZATION TECHNIQUES,” the entirety of which is incorporated herein by reference.BACKGROUND

[0002] Various wireless powering methods for implantable electronics are based on nearfield or farfield coupling. These and other methods suffer from several disadvantages. A power harvesting structure in an implanted device is typically large (e.g., typically on the order of a centimeter or larger). In nearfield communications, coils external to the body can similarly be large, bulky and oftentimes inflexible. Such constraints present difficulties regarding incorporation of an external device into a patient’s daily life. Furthermore, the intrinsic exponential decay of nearfield signals limits miniaturization of an implanted device beyond superficial depths, for example, at depths greater than 1 cm. On the other hand, the radiative nature of farfield signals can limit energy transfer efficiency.

[0003] Wireless midfield technology can be used to provide signals from an external source to an implanted sensor or therapy-delivery device. Midfield-based devices can have various advantages over conventional nearfield or farfield devices. For example, a midfield device may not require a relatively large implanted pulse generator and one or more leads that electrically connect the pulse generator to stimulation electrodes. A midfield device can have a relatively small receiver antenna and can therefore provide a simpler implant procedure, which can lead to a lower cost and a lower risk of infection or other complications related to implant or explant.

[0004] Another advantage of using midfield powering technology includes a battery or power source that can be provided externally to a patient, and thus the low power consumption and high efficiency circuit requirements of battery-powered implantable devices can be relaxed. Another advantage of using midfield powering technology can include an implanted device that can be physically smaller than a battery-powered device.Thus, midfield powering technology can help enable better patient tolerance and comfort along with potentially lower manufacturing and implantation costs.SUMMARY

[0005] Systems and methods are presented for optimizing power transfer between an external midfield transmitter and an implantable receiver device. The system comprises an implantable device configured to receive a wireless power signal and a midfield transmitter configured to provide the wireless power signal from outside a patient's body. The midfield transmitter includes multiple excitation signal paths coupled to respective excitable subwavelength structures and a controller circuit. The controller circuit is configured to control a phase adjustment circuit to change a phase characteristic of a signal in one or more of the excitation signal paths. The power signal transfer efficiency between the transmitter and implantable device is a function of this phase characteristic.

[0006] A method for optimizing power transfer includes determining an axial orientation of the implantable device in body tissue and selecting a first polarity of transmitter excitation signals based on this orientation. The external transmitter is then programmed to use the selected polarity and provides a midfield signal to the implantable device. Information about the magnitude of the received signal can be used to determine a signal transfer efficiency.

[0007] In an example, the implantable device includes a helical antenna configured as either a left-handed or right-handed circularly polarized receiver. The transmitter comprises multiple programmable phase shifters coupled to respective different antenna ports. In an example, one of the ports can be configured as a reference. By adjusting the relative phases between these ports, the "handedness" of the resulting fields can be modified to align the transmitted field components for constructive interference at the implanted device, to thereby maximize signal transfer efficiency.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0009] FIG. 1 illustrates generally an example of a system with an external midfield transmitter and an implantable receiver device.

[0010] FIG. 2A illustrates generally an example of a midfield source or transmitter device.

[0011] FIG. 2B illustrates generally an example of a midfield receiver or implantable device.

[0012] FIG. 3 illustrates generally an example of an antenna with multiple sub -wavelength structures.

[0013] FIG. 4 illustrates generally an example of a phase-adjusting network for an external midfield transmitter.

[0014] FIG. 5 illustrates generally an example of circuitry of an implantable device.

[0015] FIG. 6 illustrates generally a diagram of an example of an implantable device.

[0016] FIG. 7 illustrates generally an example of a proximal portion of an implantable device.

[0017] FIG. 8 illustrates generally a top view of an example of a layered first transmitter.

[0018] FIG. 9 illustrates generally a top view of a second layer superimposed over a first layer of a layered transmitter.

[0019] FIG. 10 illustrates generally a perspective view of an example of a layered transmitter.

[0020] FIG. 11 illustrates generally a side, cross-section view of an example of a layered transmitter.

[0021] FIG. 12 A illustrates generally an example that shows a first surface current pattern when a first transmitter is excited by a drive signal.

[0022] FIG. 12B illustrates generally an example that shows a second surface current pattern when a first transmitter is excited by a drive signal.

[0023] FIG. 13 illustrates generally an example of a chart that shows a relationship between coupling efficiency of orthogonal transmitter ports of a transmitter to an implanted receiver with respect to a changing angle or rotation of the implanted receiver.

[0024] FIG. 14 illustrates generally a top view of the second layer from the example of FIG. 9 superimposed over a different first layer of a layered transmitter.

[0025] FIG. 15 A illustrates generally a first representation of an oscillatory, optimal current distribution on a midfield transmitter.

[0026] FIG. 15B illustrates generally a second representation of an oscillatory, optimal current distribution on a midfield transmitter.

[0027] FIG. 16A illustrates generally an example of a bidirectional coupler that can comprise a portion of a midfield transmitter.

[0028] FIG. 16B illustrates generally an example of a bidirectional coupler with an adjustable load.

[0029] FIG. 17 illustrates generally an example of implantable devices placed through the left and right sacral foramen of a patient sacrum.

[0030] FIG. 18 illustrates generally an example of a chart showing a relationship between an axial angle of an implantable device and a power transfer characteristic.

[0031] FIG. 19 illustrates generally an example of a phase relationship diagram for a four- port transmitter.

[0032] FIG. 20 illustrates generally an example of a chart showing a relationship between a voltage ratio and phase.

[0033] FIG. 21 illustrates generally an example of a first method that includes optimizing a power transfer characteristic between an external midfield transmitter device and an implantable receiver device.

[0034] FIG. 22 illustrates generally an example of a second method that includes optimizing a power transfer characteristic between an external midfield transmitter device and an implantable receiver device.DETAILED DESCRIPTION

[0035] In the following description that includes examples of different nerve-electrode interfaces, reference is made to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. The present inventors contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein. Generally discussed herein are implantable devices and methods of assembling the implantable devices.

[0036] Midfield powering technology can provide power to a deeply implanted electrostimulation device from an external power source located on or near a tissue surface, such as at an external surface of a user’s skin. The user can be a clinical patient or other user. The midfield powering technology can have one or more advantages over implantablepulse generators. For example, a pulse generator can have one or more relatively large, implanted batteries and / or one or more lead systems. Midfield devices, in contrast, can include relatively small battery cells that can be configured to receive and store relatively small amounts of power. A midfield device can include one or more electrodes integrated in a unitary implantable package. Thus, in some examples, a midfield-powered device can provide a simpler implant procedure over other conventional devices, which can lead to a lower cost and a lower risk of infection or other implant complications. One or more of the advantages can be from an amount of power transferred to the implanted device. The ability to focus the energy from the midfield device can allow for an increase in the amount of power transferred to the implanted device.

[0037] An advantage of using midfield powering technology can include a main battery or power source being provided externally to the patient, and thus low power consumption and high efficiency circuitry requirements of conventional battery-powered implantable devices can be relaxed. Another advantage of using midfield powering technology can include an implanted device that can be physically smaller than a battery-powered device. Midfield powering technology can thus help enable better patient tolerance and comfort along with potentially lower costs to manufacture and / or to implant in patient tissue.

[0038] In one or more examples, multiple devices can be implanted in patient tissue and can be configured to deliver a therapy and / or sense physiologic information about a patient and / or about the therapy. The multiple implanted devices can be configured to communicate with one or more external devices. In one or more examples, the one or more external devices are configured to provide power and / or data signals to the multiple implanted devices, such as concurrently or in a time-multiplexed fashion. The provided power and / or data signals can be steered or directed by an external device to transfer the signals to an implant efficiently. Although the present disclosure may refer to a power signal or data signal specifically, such references are to be generally understood as optionally including one or both of power and data signals.

[0039] A system can include a signal generator system adapted to provide multiple different sets of signals (e.g., RF signals). Each set can include two or more separate signals in some embodiments. The system can also include a midfield transmitter including multiple excitation ports, the midfield transmitter coupled to the RF signal generator system, and the midfield transmitter being adapted to transmit the multiple different sets of RF signals concurrently or at respective different times via the excitation ports. The excitation ports can be adapted to receive respective ones of the separate signals from each set of RFsignals. Each of the transmitted sets of RF signals can include a non-negligible magnetic field (H-field) component that is substantially parallel to the external tissue surface. In one or more examples, each set of transmitted RF signals is adapted or selected to differently manipulate an evanescent field at or near the tissue surface to transmit a power and / or data signal to one or more target devices implanted in the tissue via a midfield signal instead of via inductive nearfield coupling or radiative far-field transmission.

[0040] In one or more examples, an implantable therapy delivery device (e.g., a device configured to provide neural stimulation) includes receiver circuitry including an antenna (e.g., an electric-field or magnetic field based antenna) configured to receive a midfield power signal from an external source device, such as when the receiver circuitry is implanted within tissue. The implantable therapy delivery device can include therapy delivery circuitry. The therapy delivery circuitry can be coupled to the receiver circuitry. The therapy delivery circuitry can be configured to provide signal pulses to one or more energy delivery members (e.g., electrostimulation electrodes), which may be integrally coupled to a body of the therapy delivery device or positioned separately from (e.g., not located on) the body of the therapy delivery device), such as by using a portion of the received midfield power signal from the external source device (e.g., sometimes referred to herein as an external device, an external source, an external midfield device, a midfield transmitter device, a midfield coupler, a midfield powering device, a powering device, or the like, depending on the configuration and / or usage context of the device). The signal pulses can include one or more electrostimulation therapy pulses and / or data pulses. An external transmitter and / or receiver (e.g., transceiver) device that includes an electrode pair configured to be disposed at an external tissue surface can be provided, and the electrode pair is configured to receive an electrical signal via the tissue. The electrical signal can correspond to an electrostimulation therapy delivered to the tissue by the therapy delivery device. Demodulator circuitry can be coupled to the electrode pair and can be configured to demodulate a portion of the received electrical signal, such as to recover a data signal originated by the therapy delivery device.

[0041] In one or more examples that include using a midfield wireless coupler, tissue can act as a dielectric to tunnel energy. Coherent interference of propagating modes can confine a field at a focal plane to less than a corresponding vacuum wavelength, for example, with a spot size subject to a diffraction limit in a high-index material. In one or more examples, a receiver (e.g., implanted in tissue) positioned at such a high energy density region, can be one or more orders of magnitude smaller than a conventional nearfield implantable receiver,or can be implanted more deeply in tissue (e.g., greater than 1 cm in depth). In one or more examples, a transmitter source described herein can be configured to provide electromagnetic energy to various target locations, including for example to one or more deeply implanted devices. In an example, the energy can be provided to a location with greater than about a few millimeters of positioning accuracy. That is, a transmitted power or energy signal can be directed or focused to a target location that is within about one wavelength of the signal in tissue. Such energy focusing is substantially more accurate than the focusing available via traditional inductive means and is sufficient to provide adequate power to a receiver. In other wireless powering approaches using nearfield coupling (inductive coupling and its resonant enhanced derivatives), evanescent components outside tissue (e.g., near the source) remain evanescent inside tissue, which does not allow for effective depth penetration. Unlike nearfield coupling, energy from a midfield source is primarily carried in propagating modes and, as a result, an energy transport depth is limited by environmental losses rather than by intrinsic decay of the nearfield. Energy transfer implemented with these characteristics can be at least two to three orders of magnitude more efficient than nearfield systems.

[0042] One or more of the systems, apparatuses, and methods discussed herein can be used to help treat a patient disorder. Disorders such as fecal or urinary incontinence (e.g., overactive bladder) can be treated for example by stimulating the tibial nerve or any branch of the tibial nerve, such as but not limited to the posterior tibial nerve, one or more nerves or nerve branches originating from the sacral plexus, including but not limited to S1-S4, the tibial nerve, and / or the pudendal nerve. Urinary incontinence may be treated by stimulating one or more of muscles of the pelvic floor, nerves innervating the muscles of the pelvic floor, internal urethral sphincter, external urethral sphincter, and the pudendal nerve or branches of the pudendal nerve.

[0043] One or more of the systems, apparatuses, and methods discussed herein can be used to help treat various disorders including, but not limited to, sleep apnea and / or snoring, vaginal dryness, migraines or other headaches, post-traumatic stress disorder, hot flashes, and / or complex regional pain syndrome, neuralgia (e.g., trigeminal neuralgia), dry mouth (e.g., caused by side effects from medications, chemotherapy or radiation therapy cancer treatments, Sjogren's disease, or by other cause of dry mouth), a transected nerve, cerebral palsy, erectile dysfunction, menstrual pain, hypertension, paroxysmal supraventricular tachycardia, vocal cord dysfunction, cancer, diabetes, neurological conditions, disorders or diseases (such as Parkinson’s disease (e.g., by stimulating an internus or nucleus of thebrain), Alzheimer’s disease, Huntington’s disease, dementia, Creutzfeldt-Jakob disease, epilepsy (e.g., by stimulating a left cervical vagus nerve or a trigeminal nerve), post- traumatic stress disorder (PTSD) (e.g., by stimulating a left cervical vagus nerve), or essential tremor, such as by stimulating a thalamus), neuralgia, depression, dystonia (e.g., by stimulating an internus or nucleus of the brain), phantom limb (e.g., by stimulating an amputated nerve, such an ending of an amputated nerve), dry eyes (e.g., by stimulating a lacrimal gland), arrhythmia (e.g., by stimulating the heart), a gastrointestinal disorder, such as obesity, gastroesophageal reflux, and / or gastroparesis. One or more of the systems, apparatuses, and methods discussed herein can be used to help repair tissue, such as by stimulating tissue to do one or more of enhancing microcirculation and protein synthesis to heal wounds and restoring integrity of connective and / or dermal tissues. One or more of the systems, apparatuses, and methods discussed herein can be used to help asthma or chronic obstructive pulmonary disease, such as by one or more of stimulating the vagus nerve or a branch thereof, blocking the release of norepinephrine and / or acetylcholine and / or interfering with receptors for norepinephrine and / or acetylcholine. One or more of the systems, apparatuses, and methods discussed herein can be used as an intrauterine device, such as by sensing one or more PH and blood flow or delivering current or drugs to aid in contraception, fertility, bleeding, or pain. One or more of the systems, apparatuses, and methods discussed herein can be used to incite human arousal, such as by stimulating female genitalia, including external and internal, including clitoris or other sensory active parts of the female, or by stimulating male genitalia. Using one or more examples discussed herein, stimulation can be provided continuously, on demand (e.g., as demanded by a physician, patient, or other user), or periodically.

[0044] In providing the stimulation, an implantable device can be situated five centimeters or more below a tissue interface, that is, below a surface of the skin. In one or more examples, an implantable device can be situated between about 2 centimeters and 4 centimeters, about 3 centimeters, between about 1 centimeter and five centimeters, less than 1 centimeter, about two centimeters, or other distance below the surface of the skin. The depth of implantation can depend on the use of the implanted device.

[0045] Although many embodiments included herein describe devices or methods for providing stimulation (e.g., electrostimulation), the embodiments may be adapted to provide other forms of modulation (e.g., denervation) in addition to or instead of stimulation. In addition, although many embodiments included herein refer to the use of electrodes to deliver therapy, other energy delivery members (e.g., ultrasound transducers or otherultrasound energy delivery members) or other therapeutic members or substances (e.g., fluid delivery devices or members to deliver chemicals, drugs, cryogenic fluid, hot fluid or steam, or other fluids) may be used or delivered in other embodiments.

[0046] FIG. 1 illustrates generally a schematic of an embodiment of a system 100 using wireless communication paths. The system 100 includes an example of an external source 102, such as a midfield transmitter source, sometimes referred to as a midfield coupler or external unit or external power unit, and the external source 102 can be located at or above an interface 105 between air 104 and a higher-index material 106, such as body tissue. The external source 102 can produce a source current (e.g., an in-plane source current). The source current can generate an electric field and a magnetic field. The magnetic field can include a non-negligible component that is parallel to the surface of the source 102 and / or to a surface of the higher-index material 106 (e.g., a surface of the higher-index material 106 that faces the external source 102). In accordance with several embodiments, the external source 102 may comprise structural features and functions described in connection with the midfield couplers and external sources included in WIPO Publication No. WO / 2015 / 179225 published on November 26, 2015 and titled “MIDFIELD COUPLER”, which is incorporated herein by reference in its entirety.

[0047] In an example, the external source 102 can include at least a pair of outwardly facing electrodes 121 and 122. The electrodes 121 and 122 can be configured to contact a tissue surface, for example, at the interface 105. In one or more examples, the external source 102 is configured for use with a sleeve, pocket, or other garment or accessory that maintains the external source 102 adjacent to the higher-index material 106, and that optionally maintains the electrodes 121 and 122 in physical contact with a tissue surface. In one or more examples, the sleeve, pocket, or other garment or accessory can include or use a conductive fiber or fabric, and the electrodes 121 and 122 can be in physical contact with the tissue surface via the conductive fiber or fabric.

[0048] In one or more examples, more than two outwardly facing electrodes can be used and processor circuitry on-board or auxiliary to the source 102 can be configured to select an optimal pair or group of electrodes to use to sense farfield signal information (e.g., signal information corresponding to a delivered therapy signal or to a nearfield signal). In such embodiments, the electrodes can operate as antennas. In one or more examples, the source 102 includes three outwardly facing electrodes arranged as a triangle, or four outwardly facing electrodes arranged as a rectangle, and any two or more of the electrodes can be selected for sensing and / or can be electrically grouped or coupled together for sensing ordiagnostics. In one or more examples, the processor circuitry can be configured to test multiple different electrode combination selections to identify an optimal configuration for sensing a farfield signal (an example of the processor circuitry is presented in FIG. 2A, among others).

[0049] FIG. 1 illustrates an embodiment of an implantable device 110, such as can include a multi-polar therapy delivery device configured to be implanted in the higher-index material 106 or in a blood vessel. In one or more examples, the implantable device 110 includes all or a portion of the circuitry 500 from FIG. 5, discussed in further detail below. In one or more examples, the implantable device 110 is implanted in tissue below the tissueair interface 105. In FIG. 1, the implantable device 110 includes an elongate body and an electrode array. The array can comprise multiple electrodes (e.g., E0, El, E2, and E3) that are axially spaced apart along a portion of the elongate body. The implantable device 110 includes receiver and / or transmitter circuitry (not shown in FIG. 1, see e.g., FIGS. 2A, 2B, and 4, among others) that can enable communication between the implantable device 110 and the external source 102.

[0050] The various electrodes E0-E3 can be configured to deliver electrostimulation therapy to patient tissue, such as at or near a neural or muscle target. In one or more examples, at least one electrode can be selected for use as an anode and at least one other electrode can be selected for use as a cathode to define an electrostimulation vector. In one or more examples, electrode El is selected for use as an anode and electrode E2 is selected for use as a cathode. Together, the E1-E2 combination defines an electrostimulation vector V12. Various vectors can be configured independently to provide a neural electrostimulation therapy to the same or different tissue target, such as concurrently or at different times.

[0051] In one or more examples, the source 102 includes an antenna (see, e.g., FIG. 3) and the implantable device 110 includes an antenna 108 (e.g., an electric field-based or magnetic field-based antenna). The antennas can be configured (e.g., in length, width, shape, material, etc.) to transmit and receive signals at substantially the same frequency. The implantable device 110 can be configured to transmit power and / or data signals through the antenna 108 to the external source 102 and can receive power and / or data signals transmitted by the external source 102. The external source 102 and implantable device 110 can be used for transmission and / or reception of RF signals. A transmit / receive (T / R) switch can be used to switch each RF port of the external source 102 from a transmit (transmit data or power) mode to a receive (receive data) mode. A T / R switch can similarly be used to switch theimplantable device 110 between transmit and receive modes. See FIG. 4, among others, for examples of T / R switches. In an example, the electrode array portion of the implantable device 110 comprises a portion of the antenna 108.

[0052] In one or more examples, a receive terminal on the external source 102 can be connected to one or more components that detect a phase and / or amplitude of a received signal from the implantable device 110. The phase and amplitude information can be used to program a phase of the transmit signal, such as to be substantially the same relative phase as a signal received from the implantable device 110. To help achieve this, the external source 102 can include or use a phase-matching and / or amplitude-matching network, such as shown in the embodiment of FIG. 4. The phase-matching and / or amplitude matching network can be configured for use with a midfield antenna that includes multiple ports, such as shown in the embodiment of FIG. 3.

[0053] Referring again to FIG. 1, in one or more examples, the implantable device 110 can be configured to receive a midfield signal 131 from the external source 102. The midfield signal 131 can include power and / or data signal components. In some embodiments, a power signal component can include one or more data components embedded therein. In one or more examples, the midfield signal 131 includes configuration data for use by the implantable device 110. The configuration data can define, among other things, therapy signal parameters, such as a therapy signal frequency, pulse width, amplitude, or other signal waveform parameters. In one or more examples, the implantable device 110 can be configured to deliver an electrostimulation therapy to a therapy target 190, such as can include a neural target (e.g., a nerve, or other tissue such as a vein, connective tissue, or other tissue that includes one or more neurons within or near the tissue), a muscle target, or other tissue target. An electrostimulation therapy delivered to the therapy target 190 can be provided using a portion of a power signal received from the external source 102. Examples of the therapy target 190 can include nerve tissue or neural targets, for example including nerve tissue or neural targets at or near cervical, thoracic, lumbar, or sacral regions of the spine, brain tissue, muscle tissue, abnormal tissue (e.g., tumor or cancerous tissue), targets corresponding to sympathetic or parasympathetic nerve systems, targets at or near peripheral nerve bundles or fibers, at or near other targets selected to treat incontinence, urinary urge, overactive bladder, fecal incontinence, constipation, pain, neuralgia, pelvic pain, movement disorders or other diseases or disorders, deep brain stimulation (DBS) therapy targets or any other condition, disease or disorder (such as those other conditions, diseases, or disorders identified herein).

[0054] Delivering the electrostimulation therapy can include using a portion of a power signal received via the midfield signal 131, and providing a current signal to an electrode or an electrode pair (e.g., two or more of E0-E3), coupled to the implantable device 110, to stimulate the therapy target 190. As a result of the current signal provided to the electrode(s), a nearfield signal 132 can be generated. An electric potential difference resulting from the nearfield signal 132 can be detected remotely from the therapy delivery location. Various factors can influence where and whether the potential difference can be detected, including, among other things, characteristics of the therapy signal, a type or arrangement of the therapy delivery electrodes, and characteristics of any surrounding biologic tissue. Such a remotely detected electric potential difference can be considered a farfield signal 133. The farfield signal 133 can represent an attenuated portion of the nearfield signal 132. That is, the nearfield signal 132 and the farfield signal 133 can originate from the same signal or field, such as with the nearfield signal 132 considered to be associated with a region at or near the implantable device 110 and the therapy target 190, and with the farfield signal 133 considered to be associated with other regions more distal from the implantable device 110 and the therapy target 190. In one or more examples, information about the implantable device 110, or about a previously-provided or future planned therapy provided by the implantable device 110, can be encoded in a therapy signal and detected and decoded by the external source 102 by way of the farfield signal 133.

[0055] In one or more examples, the device 110 can be configured to provide a series of electrostimulation pulses to a tissue target (e.g., neural target). For example, the device 110 can provide multiple electrostimulation pulses separated in time, such as using the same or different electrostimulation vectors, to provide a therapy. In one or more examples, a therapy comprising multiple signals can be provided to multiple different vectors in parallel, or can be provided in sequence such as to provide a series or sequence of electrostimulation pulses to the same neural target. Thus, even if one vector is more optimal than the others for eliciting a patient response, the therapy as a whole can be more effective than stimulating only the known-optimal vector because (1) the target may experience a rest period during periods of non-stimulation, and / or (2) stimulating the areas nearby and / or adjacent to the optimal target can elicit some patient benefit.

[0056] The system 100 can include a sensor 107 at or near the interface 105 between air 104 and the higher-index material 106. The sensor 107 can include, among other things, one or more electrodes, an optical sensor, an accelerometer, a temperature sensor, a force sensor, a pressure sensor, or a surface electromyography (EMG) device. The sensor 107may comprise multiple sensors (e.g., two, three, four or more than four sensors). Depending on the type of sensor(s) used, the sensor 107 can be configured to monitor electrical, muscle, or other activity near the device 110 and / or near the source 102. For example, the sensor 107 can be configured to monitor muscle activity at a tissue surface. If muscle activity greater than a specified threshold activity level is detected, then a power level of the source 102 and / or of the device 110 can be adjusted. In one or more examples, the sensor 107 can be coupled to or integrated with the source 102, and in other examples, the sensor 107 can be separate from, and in data communication with (e.g., using a wired or wireless electrical coupling or connection), the source 102 and / or the device 110.

[0057] The system 100 can include a farfield sensor device 130 that can be separate from, or communicatively coupled with, one or more of the source 102 and the sensor 107. The farfield sensor device 130 can include two or more electrodes and can be configured to sense a farfield signal, such as the farfield signal 133 corresponding to a therapy delivered by the device 110. The farfield sensor device 130 can include at least one pair of outwardly facing electrodes 123 and 124 configured to contact a tissue surface, for example, at the interface 105. In one or more examples, three or more electrodes can be used, and processor circuitry on-board or auxiliary to the farfield sensor device 130 can select various combinations of two or more of the electrodes for use in sensing the farfield signal 133. In one or more examples, the farfield sensor device 130 can be configured for use with a sleeve, pocket, or other garment or accessory that maintains the farfield sensor device 130 adjacent to the higher-index material 106, and that optionally maintains the electrodes 123 and 124 in physical contact with a tissue surface. In one or more examples, the sleeve, pocket, or other garment or accessory can include or use a conductive fiber or fabric, and the electrodes 123 and 124 can be in physical contact with the tissue surface via the conductive fiber or fabric. An example of at least a portion of a farfield sensor device 130 is further described herein in connection with FIG. 2B.

[0058] In one or more examples, the external source 102 provides a midfield signal 131 including power and / or data signals to the implantable device 110. The midfield signal 131 includes a signal (e.g., an RF signal) having various or adjustable amplitude, frequency, phase, and / or other signal characteristics. The implantable device 110 can include an antenna, such as described below, that can receive the midfield signal 131 and, based on characteristics of receiver circuitry in the implantable device 110, can modulate the received signal at the antenna to thereby generate a backscatter signal. In one or more examples, the implantable device 110 can encode information in the backscatter signal 112, such asinformation about a characteristic of the implantable device 110 itself, about a received portion of the midfield signal 131, about a therapy provided by the implantable device 110, and / or other information. The backscatter signal 112 can be received by an antenna at the external source 102 and / or the farfield sensor device 130, or can be received by another device. In one or more examples, a biological signal can be sensed by a sensor of the implantable device 110, such as a glucose sensor, an electropotential (e.g., an electromyography sensor, electrocardiograph (ECG) sensor, resistance, or other electrical sensor), a light sensor, a temperature, a pressure sensor, an oxygen sensor, a motion sensor, or the like. A signal representative of the detected biological signal can be modulated onto the backscatter signal 112.

[0059] FIG. 2A illustrates, by way of example, a block diagram of and embodiment of a midfield source device, such as the external source 102. The external source 102 can include various components, circuitry, or functional elements that are in data communication with one another. In the example of FIG. 2 A, the external source 102 includes components, such as processor circuitry 210, one or more sensing electrodes 220 (e.g., including the electrodes 121 and 122), a demodulator circuitry 230, a phase-matching or amplitude-matching network 400, a midfield antenna 300, and / or one or more feedback devices, such as can include or use an audio speaker 251, a display interface 252, and / or a haptic feedback device 253. The midfield antenna 300 is further described below in the embodiment of FIG. 3, and the network 400 is further described below in the embodiment of FIG. 4. The processor circuitry 210 can be configured to coordinate the various functions and activities of the components, circuitry, and / or functional elements of the external source 102.

[0060] The midfield antenna 300 can be configured to provide a midfield excitation signal, such as can include RF signals having a non-negligible H-field component that is substantially parallel to an external tissue surface. In one or more examples, the RF signals can be adapted or selected to manipulate an evanescent field at or near a tissue surface, such as to transmit a power and / or data signal to respective different target devices (e.g., the implantable device 110, or any one or more other implantable devices discussed herein) implanted in tissue. The midfield antenna 300 can be further configured to receive backscatter or other wireless signal information that can be demodulated by the demodulator circuitry 230. The demodulated signals can be interpreted by the processor circuitry 210.

[0061] The midfield antenna 300 can include a dipole antenna, a loop antenna, a coil antenna, a slot or strip antenna, or other antenna. The antenna 300 can be shaped and sized to receive signals in a range of between about 400 MHz and about 4 GHz (e.g., between 400MHz and 1 GHz, between 400 MHz and 3 GHz, between 500 MHz and 2 GHz, between 1 GHz and 3 GHz, between 500 MHz and 1.5 GHz, between 1 GHz and 2 GHz, between 2 GHz and 3 GHz, overlapping ranges thereof, or any value within the recited ranges). For embodiments incorporating a dipole antenna, the midfield antenna 300 may comprise a straight dipole with two substantially straight conductors, a folded dipole, a short dipole, a cage dipole, a bow-tie dipole or batwing dipole.

[0062] The demodulator circuitry 230 can be coupled to the sensing electrodes 220. In one or more examples, the sensing electrodes 220 can be configured to receive the farfield signal 133, such as based on a therapy provided by the implantable device 110, such as can be delivered to the therapy target 190. The therapy can include an embedded or intermittent data signal component that can be extracted from the farfield signal 133 by the demodulator circuitry 230. For example, the data signal component can include an amplitude-modulated or phase-modulated signal component that can be discerned from background noise or other signals and processed by the demodulator circuitry 230 to yield an information signal that can be interpreted by the processor circuitry 210. Based on the content of the information signal, the processor circuitry 210 can instruct one of the feedback devices to alert a patient, caregiver, or other system or individual. For example, in response to the information signal indicating successful delivery of a specified therapy, the processor circuitry 210 can instruct the audio speaker 251 to provide audible feedback to a patient, can instruct the display interface 252 to provide visual or graphical information to a patient, and / or can instruct the haptic feedback device 253 to provide a haptic stimulus to a patient. In one or more examples, the haptic feedback device 253 includes a transducer configured to vibrate or to provide another mechanical signal.

[0063] FIG. 2B illustrates generally a block diagram of a portion of a system configured to receive a farfield signal. The system can include the sensing electrodes 220, such as can include the electrodes 121 and 122 of the source 102, or the electrodes 123 and 124 of the farfield sensor device 130. In the example of FIG. 2B, there are four sensing electrodes represented collectively as the sensing electrodes 220, and individually as SEO, SEI, SE2, and SE3; however, other numbers of sensing electrodes 220 may be used. The sensing electrodes can be communicatively coupled to multiplexer circuitry 261. The multiplexer circuitry 261 can select pairs of the electrodes, or electrode groups, for use in sensing farfield signal information. In one or more examples, the multiplexer circuitry 261 selects an electrode pair or grouping based on a detected highest signal to noise ratio of a receivedsignal, or based on another relative indicator of signal quality, such as amplitude, frequency content, and / or other signal characteristic.

[0064] Sensed electrical signals from the multiplexer circuitry 261 can undergo various processing to extract information from the signals. For example, analog signals from the multiplexer circuitry 261 can be filtered by a band pass filter 262. The band pass filter 262 can be centered on a known or expected modulation frequency of a sensed signal of interest. A band pass filtered signal can then be amplified by a low-noise amplifier 263. The amplified signal can be converted to a digital signal by an analog-to-digital converter circuit (ADC) 264. The digital signal can be further processed by various digital signal processors 265, as further described herein, such as to retrieve or extract an information signal communicated by the implantable device 110.

[0065] FIG. 3 illustrates generally a schematic view of an embodiment of a midfield antenna 300 with multiple excitable structures, including sub -wavelength structures 301, 302, 303, and 304. The midfield antenna 300 can include a midfield plate structure with a substantially planar surface. The one or more sub -wavelength structures 301-304 can be formed in the plate structure. In the example of FIG. 3, the antenna 300 includes a first subwavelength structure 301, a second sub -wavelength structure 302, a third sub -wavelength structure 303, and a fourth sub -wavelength structure 304. Fewer or additional subwavelength structures can be used. The sub -wavelength structures can be excited individually or selectively by one or more RF ports (e.g., first through fourth RF ports 311, 312, 313, and 314) respectively coupled thereto.

[0066] A “sub -wavelength structure” can include a hardware structure with dimensions defined relative to a wavelength of a field that is rendered and / or received by the external source 102. For example, for a given ko corresponding to a signal wavelength in air, a source structure that includes one or more dimensions less than ko can be considered to be a sub -wavelength structure. Various designs or configurations of sub -wavelength structures can be used. Some examples of a sub -wavelength structure can include a slot in a planar structure, or a strip or patch of a conductive sheet of substantially planar material. Various examples of midfield antenna and excitable structures are discussed elsewhere herein. In some examples, the excitable structures include or use striplines or microstrips.

[0067] In an example, the midfield antenna 300 and its associated drive circuitry (discussed elsewhere herein) are configured to provide signals to manipulate or influence an evanescent field at or adjacent to tissue, where tissue serves as a medium with a relatively high dielectric constant (e.g., tissue is a high-K medium). That is, energy from the antenna300 can be directed through the tissue or other high-K medium rather than through air. An efficiency of transmission from the midfield antenna 300 can be greatest when the antenna 300 is properly loaded by tissue, and the efficiency can be intentionally low when unloaded by tissue.

[0068] FIG. 4 illustrates generally a phase-adjusting / matching or amplitude- adjusting / matching network 400. In an example, the network 400 can include the antenna 300, and the antenna 300 can be electrically coupled to a plurality of switches 404A, 404B, 404C, and 404D, for example, via the first through fourth RF ports 311, 312, 313, and 314 illustrated in FIG. 3. The switches 404A-D are each electrically coupled to a respective phase and / or amplitude detector 406A, 406B, 406C, and 406D, and a respective variable gain amplifier 408A, 408B, 408C, and 408D. Each amplifier 408A-D is electrically coupled to a respective phase shifter 410A, 410B, 410C, and 410D, and each phase shifter 410A-D is electrically coupled to a source, such as can include a power divider 412 that receives an input signal 414 to be transmitted using the external source 102. In an example, the phase shifters 410A-D are digitally-configurable devices configured to adjust a phase response in specified intervals. For example, the phase shifters 410A-D can comprise 4-bit phase control devices that can be configured to adjust phase in increments of 22.5 degrees.

[0069] In one or more examples, the switches 404A-D can be configured to select either a receive line (“R”) or a transmit line (“T”). A number of switches 404A-D of the network 400 can be equal to a number of ports of a midfield source such as the antenna 300. In the example of the network 400, the midfield source includes four ports (e.g., corresponding to the four sub -wavelength structures in the antenna 300 of the example of FIG. 3), however any number of ports (and switches), such as one, two, three, four, five, six, seven, eight or more, can be used.

[0070] The phase and / or amplitude detectors 406 A-D are configured to detect a phase (1, 2, 3, 04) and / or power (Pl, P2, P3, P4) of a signal received at each respective port of the midfield source. In one or more examples, the phase and / or amplitude detectors 406A-D can be implemented in one or more modules (hardware modules that can include electric or electronic components arranged to perform an operation, such as determining a phase or amplitude of a signal), such as including a phase detector module and / or an amplitude detector module. The detectors 406A-D can include analog and / or digital components arranged to produce one or more signals representative of a phase and / or amplitude of a signal received at the external source 102.

[0071] The amplifiers 408 A-D can receive respective inputs from the phase shifters 410A- D (e.g., Pk phase shifted by k, <b l + k, 02 + Ok, 03 + Ok, or 04 + Ok). The output of the amplifier, O, is generally the output of the power divider, M, when the input signal 414 has an amplitude of 4*M (in the embodiment of FIG. 4), multiplied by the gain of the amplifier Pi*Pk. Pk can be set dynamically as the values for Pl, P2, P3, and / or P4 change. k can optionally be a constant or a variable.

[0072] In one or more examples, the phase shifters 410A-D can dynamically or responsively configure the relative phases of the signals provided to the ports. That is, a polarization of the external transmitter or external source 102 can be adjusted to optimize power communication to an implanted device, such as by optimizing constructive interference of electric field and magnetic field components at their respective receivers, and by minimizing destructive interference of the same. In an example, one or more of the phase shifters 410A-410D can be adjusted based on information received from the implantable device or from a patient, as further discussed below. In an example, one or more of the phase shifters 410A-D can be adjusted based on amplitude or phase information received from the detectors 406 A-D.

[0073] In an example, excitation signal paths in the network 400 can be configured to operate in pairs. A first pair of signal paths can include, for example, the signal path corresponding to the first phase shifter 410A and the signal path corresponding to the third phase shifter 4 IOC. Similarly, a second pair of signal paths can include, for example, the signal path corresponding to the second phase shifter 41 OB and the signal path corresponding to the fourth phase shifter 410D. In an example, each of the phase shifters drives a respective transmitter antenna port, as further discussed elsewhere herein. By way of example, each of the phase shifters can provide a signal to a respective excitable structure (e.g., a stripline) that corresponds to a respective portion or quadrant of an emitter, and the pairs of phase shifters can correspond to oppositely-oriented excitable structures on the emitter. Referring ahead to FIG. 9, for example, the first and third phase shifters 41 OA and 4 IOC can correspond to the first and third striplines 1131 A and 1131C, respectively, and the second and fourth phase shifters 41 OB and 410D can correspond to the second and fourth striplines 113 IB and 113 ID.

[0074] In an example, the fourth phase shifter 410D can be set to a reference phase shift value, such as zero degrees. In this example, the second phase shifter 410B can be set to 180 degrees, since each pair of signals is offset by 180 degrees. The third phase shifter 410C can be adjusted to maximize power transfer efficiency to an implanted device. The first phaseshifter 410A can be configured to maintain a 180 degree offset relative to that imposed by the third phase shifter 410C. Accordingly, when the third phase shifter 410C is set to 90 degrees, the first phase shifter 410A can be set to 270 degrees, and so forth. A phase relationship among or between the four ports or signal paths can therefore be fully defined by the setting of the third phase shifter 410C. Stated differently, the value of the third phase shifter 410C can define a relative phase difference between the pairs of opposing ports in the external source 102.

[0075] In one or more examples, a transmit power requirement from the midfield source is Ptt. The signal provided to the power divider 412 has a power of 4*M. The output of the amplifier 408 A is about M*Pl*Pk. Thus, the power transmitted from the midfield coupler is M*(Pl*Pk + P2*Pk + P3*Pk + P4*Pk) = Ptt. Solving for Pk yields Pk = Ptt / (M*(P1 + P2 + P3 + P4)).

[0076] The amplitude of a signal at each RF port can be transmitted with the same relative (scaled) amplitude as the signal received at the respective port of the midfield coupler coupled thereto. The gain of the amplifiers 408A-D can be further refined to account for any losses between the transmission and reception of the signal from the midfield coupler. Consider a reception efficiency of q = Pir / Ptt, where Pir is the power received at the implanted receiver. An efficiency (e.g., a maximum efficiency), given a specified phase and amplitude tuning, can be estimated from an amplitude received at the external midfield source from the implantable source. This estimation can be given as q ~ (Pl+P2+P3+P4) / Pit, where Pit is an original power of a signal from the implanted source. Information about a magnitude of the power transmitted from the implantable device 110 can be communicated as a data signal to the external source 102. In one or more examples, an amplitude of a signal received at an amplifier 408A-D can be scaled according to the determined efficiency, such as to ensure that the implantable device receives sufficient power to perform one or more programmed operation(s) or to delivery a specified therapy using the received power. Given the estimated link efficiency, q, and an implant power (e.g., amplitude) requirement of Pir’, Pk can be scaled as Pk=Pir7[q(Pl+P2+P3+P4)], such as to help ensure that the implant receives adequate power to perform the programmed functions.

[0077] Control signals for the phase shifters 410A-D and the amplifiers 408 A-D, such as the phase input and gain input, respectively, can be provided by processing circuitry that is not shown in FIG. 4. The circuitry is omitted to not overly complicate or obscure the view provided in FIG. 4. The same or different processing circuitry can be used to update a statusof one or more of the switches 404A-D between receive and transmit configurations. A processor circuitry example is discussed herein at processor circuitry 210 of FIG. 2A.

[0078] FIG. 5 illustrates generally a diagram of an embodiment of circuitry 500 of the implantable device 110, or target device, such as can include an elongate device and such as can optionally be deployed inside a blood vessel, according to one or more of the embodiments discussed herein. The circuitry 500 includes one or more pad(s) 536, such as can be electrically connected to the antenna 108. The circuitry 500 can include a tunable matching network 538 to set an impedance of the antenna 108 based on an input impedance of the circuitry 500. The impedance of the antenna 108 can change, for example, due to environmental changes. The tunable matching network 538 can adjust the input impedance of the circuitry 500 based on the varying impedance of the antenna 108. In one or more examples, the impedance of the tunable matching network 538 can be matched to the impedance of the antenna 108. In one or more examples, the impedance of the tunable matching network 538 can be set to cause a portion of a signal incident on the antenna 108 reflect back from the antenna 108, thus creating a backscatter signal.

[0079] A transmit-receive (T / R) switch 541 can be used to switch the circuitry 500 from a receive mode (e.g., in which power and / or data signals can be received) to a transmit mode (e.g., in which signals can be transmitted to another device, implanted or external). An active transmitter can operate at an Industrial, Scientific, and Medical (ISM) band of 2.45 GHZ or 915 MHz, or the 402 MHz Medical Implant Communication Service (MICS) band for transferring data from the implant. Alternatively, data can be transmitted using a Surface Acoustic Wave (SAW) device that backscatters incident radio frequency (RF) energy to the external device.

[0080] The circuitry 500 can include a power meter 542 for detecting an amount of received power at the implanted device. A signal that indicates power from the power meter 542 can be used by a digital controller 548 to determine whether received power is adequate (e.g., above a specified threshold) for the circuitry to perform some specified function. A relative value of a signal produced by the power meter 542 can be used to indicate to a user or machine whether an external device (e.g., the source 102) used to power the circuitry 500 is in a suitable location for transferring power and / or data to the target device.

[0081] In one or more examples, the circuitry 500 can include a demodulator 544 for demodulating received data signals. Demodulation can include extracting an original information-bearing signal from a modulated carrier signal. In one or more examples, the circuitry 500 can include a rectifier 546 for rectifying a received AC power signal.

[0082] Circuitry (e.g., state logic, Boolean logic, or the like) can be integrated into the digital controller 548. The digital controller 548 can be configured to control various functions of the receiver device, such as based on the input(s) from one or more of the power meter 542, demodulator 544, and / or the clock 550. In one or more examples, the digital controller 548 can control which electrode(s) (e.g., E0-E3) are configured as a current sink (anode) and which electrode(s) are configured as a current source (cathode). In one or more examples, the digital controller 548 can control a magnitude of a stimulation pulse produced through the electrode(s).

[0083] A charge pump 552 can be used to increase the rectified voltage to a higher voltage level, such as can be suitable for stimulation of the nervous system. The charge pump 552 can use one or more discrete components to store charge for increasing the rectified voltage. In one or more examples, the discrete components include one or more capacitors, such as can be coupled to pad(s) 554. In one or more examples, these capacitors can be used for charge balancing during stimulation, such as to help avoid tissue damage.

[0084] A stimulation driver circuitry 556 can include a neurostimulation signal generator circuit configured to provide programmable stimulation through various outputs 534, such as to an electrode array. The stimulation driver circuitry 556 can include an impedance measurement circuitry, such as can be used to test for correct positioning of the electrode(s) of the array. The stimulation driver circuitry 556 can be programmed by the digital controller to make an electrode a current source, a current sink, or a shorted signal path. The stimulation driver circuitry 556 can be a voltage or a current driver. The stimulation driver circuitry 556 can include or use a therapy delivery circuitry that is configured to provide electrostimulation signal pulses to one or more electrodes, such as using at least a portion of a received midfield power signal from the external source 102. In one or more examples, the stimulation driver circuitry 556 can provide pulses at frequencies up to about 100 kHz. Pulses at frequencies around 100 kHz can be useful for nerve blocking.

[0085] The circuitry 500 can further include a memory circuitry 558, such as can include a non-volatile memory circuitry. The memory circuitry 558 can include storage of a device identification, neural recordings, and / or programming parameters, among other implant related data.

[0086] The circuitry 500 can include an amplifier 555 and analog digital converter (ADC) 557 to receive signals from the electrode(s). The electrode(s) can sense electricity from nerve signals within the body. The nerve signals can be amplified by the amplifier 555. These amplified signals can be converted to digital signals by the ADC 557. These digitalsignals can be communicated to an external device. The amplifier 555, in one or more examples, can be a trans-impedance amplifier.

[0087] The digital controller 548 can provide data to a modulator / power amplifier 562. The modulator / power amplifier 562 modulates the data onto a carrier wave. The power amplifier 562 increases the magnitude of the modulated waveform to be transmitted.

[0088] The modulator / power amplifier 562 can be driven by an oscillator / phase locked loop (PLL) 560. The PLL disciplines the oscillator so that it remains more precise. The oscillator can optionally use a different clock from the clock 550. The oscillator can be configured to generate an RF signal used to transmit data to an external device. A typical frequency range for the oscillator is about 10 kHz to about 2600 MHz (e.g., from 10 kHz to 1000 MHz, from 500 kHz to 1500 kHz, from 10 kHz to 100 kHz, from 50 kHz to 200 kHz, from 100 kHz to 500 kHz, from 100 kHz to 1000 kHz, from 500 kHz to 2 MHz, from 1 MHz to 2 MHz, from 1 MHz to 10 MHz, from 100 MHz to 1000 MHz, from 500 MHz to 800 MHz, overlapping ranges thereof, or any value within the recited ranges). Other frequencies can be used, such as can be dependent on the application. The clock 550 is used for timing of the digital controller 548. A typical frequency of the clock 550 is between about one kilohertz and about one megahertz (e.g., between 1 kHz and 100 kHz, between 10 kHz and 150 kHz, between 100 kHz and 500 kHz, between 400 kHz and 800 kHz, between 500 kHz and 1 MHz, between 750 kHz and 1 MHz, overlapping ranges thereof, or any value within the recited ranges). Other frequencies can be used depending on the application. A faster clock generally uses more power than a slower clock.

[0089] A return path for a signal sensed from a nerve is optional. Such a path can include the amplifier 555, the ADC 557, the oscillator / PLL 560, and the modulator / power amplifier 562. Each of these items and connections thereto can optionally be removed.

[0090] In one or more examples, the digital controller 548, the amplifier 555, and / or the stimulation driver circuitry 556, among other components of the circuitry 500, can comprise portions of a state machine device. The state machine device can be configured to wirelessly receive power and data signals via the pad(s) 536 and, in response, release or provide an electrostimulation signal via one or more of the outputs 534. In one or more examples, such a state machine device needs not retain information about available electrostimulation settings or vectors, and instead the state machine device can carry out or provide electrostimulation events after, and / or in response to, receipt of instructions from the source 102.

[0091] For example, the state machine device can be configured to receive an instruction to deliver a neural electrostimulation therapy signal, such as at a specified time or having some specified signal characteristic (e.g., amplitude, duration, etc.), and the state machine device can respond by initiating or delivering the therapy signal at the specified time and / or with the specified signal characteristic(s). At a subsequent time, the device can receive a subsequent instruction to terminate the therapy, to change a signal characteristic, or to perform some other task. Thus, the device can optionally be configured to be substantially passive, or can be configured to be responsive to received instructions (e.g., contemporaneously received instructions).

[0092] FIG. 6 illustrates generally a diagram of an embodiment of a first implantable device 600. The first implantable device 600 can comprise an example of the implantable device 110 from the system 100 of FIG. 1. The device 600 includes a body portion 602, multiple electrodes 604, a circuitry housing 606, and an antenna housing 608. The antenna housing 608 encapsulates an antenna 610. The implantable device 600 can be configured to sense electrical (or other) activity information from a patient, or to deliver an electrostimulation therapy to the patient such as using one or more of the electrodes 604.

[0093] The body portion 602 can be made of a flexible or rigid material. In one or more examples, the body portion 602 can include a bio-compatible material. The body portion 602 can include, among other materials, platinum, iridium, titanium, ceramic, zirconia, alumina, glass, polyurethane, silicone, epoxy, and / or a combination thereof. The body portion 602 includes one or more electrodes 604 thereon or at least partially therein. The electrodes 604, as illustrated in the example of FIG. 6, are ring electrodes. In the example of FIG. 6, the electrodes 604 are substantially evenly distributed along the body portion, that is, a substantially equal space is provided between adjacent electrodes. Other electrode configurations can additionally or alternatively be used.

[0094] The body portion 602 can include, or can be coupled to, a circuitry housing 606. In an example, the circuitry housing 606 is coupled to the body portion 602 at a first end 601 of the body portion 602. In the example of FIG. 6, the first end 601 of the body portion 602 is opposite a second end 603 of the body portion 602.

[0095] The circuitry housing 606 can provide a hermetic seal for electric and / or electronic components and / or interconnects housed therein. The electrodes 604 can be respectively electrically connected to circuitry in the circuitry housing 606 using one or more feedthroughs and one or more conductors, such as is illustrated and described herein. Thatis, the circuitry housing 606 can provide a hermetic enclosure for the electronic components.

[0096] In an example, the antenna housing 608 is attached to the circuitry housing 606 at a first side end of the circuitry housing 606. An antenna 610 can be provided inside the antenna housing 608. In an example, the antenna 610 is used for receiving at and / or transmitting from the first implantable device 600 power and / or data signals. The first side end is opposite a second side end of the circuitry housing 606. In an example, the second side end is an end to which an electrode assembly, such as including the electrodes 604, or other assembly, can be electrically connected.

[0097] The antenna housing 608 can be coupled to the circuitry housing 606 in various ways or using various connective means. For example, the antenna housing 608 can be brazed (e.g., using gold or other conductive or non-conductive material) to the circuitry housing 606. The antenna housing 608 can include an epoxy, tecothane, or other substantially radio frequency (RF) transparent (e.g., at a frequency used to communicate to / from the device) and protective material.

[0098] In one or more examples, the antenna housing 608 can include a ceramic material such as zirconia or alumina. The dielectric constant of zirconia is similar to a dielectric constant of typical body muscle tissue. Using a material with a dielectric constant similar to that of muscle tissue can help stabilize the circuit impedance of the antenna 610 and can decrease a change in impedance when the antenna 610 is surrounded by different tissue types.

[0099] A power transfer efficiency such as from an external transmitter to the first implantable device 600 can be influenced by the selection of antenna or housing materials. For example, a power transfer efficiency of the first implantable device 600 can be increased when the antenna 610 is surrounded or encapsulated by a lower permittivity tissue, such as when the antenna housing 608 comprises a ceramic material. In an example, the antenna 610 can be composed as a single ceramic structure with the feedthrough.

[0100] FIG. 7 illustrates generally, by way of example, a perspective view diagram of a proximal portion of an embodiment of the implantable device 110 of FIG. 1 or the first implantable device 600 of FIG. 6. The illustrated proximal portion includes an example of an antenna housing 704 coupled to a circuitry housing 712 via a ceramic cap 706. One or more antenna structures can be provided in the antenna housing 704, in the circuitry housing 712, or both, or elsewhere in or along the implantable device 110.

[0101] The example of FIG. 6 includes a first antenna 708 disposed inside the antenna housing 704. The first antenna 708 can comprise a helical antenna, such as including a conductor that is wound or formed in a helical path. A normal vector of the first antenna 708 can be generally parallel to a magnetic field induced by the first antenna 708. The first antenna 708 can include a helical traveling wave antenna configured to receive a signal its normal vector generally parallel with a pointing vector of an incident wave.

[0102] In an example, the first antenna 708 comprises a helical-shaped conductor that is coupled to circuitry inside the circuitry housing 712. The helical-shaped conductor can have multiple taps such that a feed port for the conductor can be coupled to a top or bottom portion of the conductor. By changing the feed location, the polarity of the antenna can be adjusted to optimize power reception from the external transmitter. For example, connecting the feed port to the top portion of the helical conductor can result in one circular polarization (e.g., right-handed), while connecting to the bottom portion can result in the opposite circular polarization (e.g., left-handed). This allows the implanted device's antenna to be customized to match the polarization of the incoming magnetic fields to maximize received signal strength. By selecting the optimal feed location, constructive interference between the electric and magnetic field components can be maximized at the receiver, thereby improving overall power transfer efficiency between the external transmitter and the implanted device.

[0103] In an example, the first antenna 708 can be an asymmetric dipole antenna with the hermetic package of the device serving as part of the dipole. In an example, the antenna can be a dielectric rod antenna.

[0104] In an example, power can be transferred from the first antenna 708 to a structure (e.g., other circuitry or another antenna) within the circuitry housing 712. The energy transfer can occur or can be effected through the ceramic cap 706, such as can comprise an electric feedthrough for one or more conductors. The ceramic cap 706 can be used to hermetically seal one end of the circuitry housing 712, at the antenna housing 704.

[0105] In an example, the first antenna 708 includes a loop or helix structure encapsulated in the antenna housing 704. Electromagnetic energy from outside the patient body is transferred to the first antenna 708, which in turn transfers the energy to receiver circuitry inside the circuitry housing 712 or transfers the energy to a second antenna 710 within the circuitry housing 712, or both. In some examples, the first antenna 708 is configured to act as a relay to the second antenna 710. The second antenna 710 can be connected to the other circuitry of the implantable device.

[0106] In other examples, the second antenna 710 comprises a portion of the electrode array of the implantable device 110. The first antenna 708 can be configured to receive a magnetic field component of a propagating signal inside body tissue and the second antenna 710 can be configured to receive an electric field component of the same propagating signal.

[0107] In an example, a midfield transmitter device, such as corresponding to the external source 102 of the example of FIG. 1, can include a layered structure with one or multiple tuning elements. The midfield transmitter can be a dynamically configurable, active transceiver that is configured to provide RF signals to modulate an evanescent field at a tissue surface and thereby generate a propagating field within tissue, such as to transmit power and / or data signals to an implanted target device.

[0108] In an example, a midfield transmitter device includes a combination of transmitter and antenna features. The device can include a slot or patch antenna with a back plane or ground plane, and can include one or more striplines or microstrips or other features that can be excited by an electrical signal. In an example, the device includes one or more conductive plates that can be excited and thereby caused to generate a signal, such as in response to excitation of one or more corresponding striplines or microstrips. In an example, the external source 102 includes a layered structure with excitable features that comprise the antenna 300, and the antenna is coupled to the network 400 illustrated in FIG. 4. In an example, one or more layers of the various transmitters discussed herein can include one or more flexible substrates or flexible layers to provide a flexible transmitter device.

[0109] FIG. 8 illustrates generally a top view of an example of a layered first transmitter 1000, including a first layer 1001A. Various features of the first transmitter 1000 are illustrated as being circular, however other shapes or profiles for the transmitter and its various elements or layers can be similarly used. The first layer 1001 A includes a conductive plate that can be etched or cut to provide various layer features as shown in the drawing and / or as described herein.

[0110] In the example of FIG. 8, the first layer 1001A includes a copper substrate that is etched with a circular slot 1010 to separate a conductive outer region 1005 from a conductive inner region 1015. In this example, the outer region 1005 includes a ring or annular feature that is separated by the circular slot 1010 from a substantially disc-shaped feature comprising the inner region 1015. That is, in the example of FIG. 8, the conductive inner region 1015 is electrically isolated from the conductive annulus comprising the outer region 1005. When the first transmitter 1000 is excited using one or more stripline features, such as can be provided on a different device layer than is illustrated in FIG. 8, theconductive inner region 1015 produces a tuned field, and the outer annulus or outer region 1005 can be coupled to a reference voltage or ground. That is, the conductive inner region 1015 comprises at least a portion of an emitter provided on a surface of the first layer 1001 A or substrate.[OHl] The example of FIG. 8 includes tuning features with various physical dimensions and locations with respect to the first layer 1001 A to influence a field transmitted by the first transmitter 1000. In addition to the etched circular slot 1010, the example includes four radial slots, or arms 1021A, 1021B, 1021C, and 1021D, that extend from the circular slot 1010 toward the center of the first layer 1001 A. Fewer or additional tuning features, such as having the same shape as illustrated or another shape, can similarly be used to influence a resonant frequency of the device. That is, although linear radial slots are shown, one or more differently shaped slots can be used.

[0112] A diameter of the first layer 1001A and the slot 1010 dimensions can be adjusted to tune or select a resonant frequency of the device. In the example of FIG. 8, as the length of one or more of the arms 1021A-1021D increases, a resonance or center operating frequency correspondingly decreases. Dielectric characteristics of one or more layers adjacent or near to the first layer 1001A can also be used to tune or influence a resonance or transmission characteristic.

[0113] In the example of FIG. 8, the arms 1021A-1021D are substantially the same length. In an example, the arms can have different lengths. Orthogonal pairs of the arms can have substantially the same or different length characteristics. In an example, the first and third arms 1021A and 1021C have a first length characteristic, and the second and fourth arms 102 IB and 102 ID can have a different second length characteristic. Designers can adjust the arm lengths to tune a device resonance. Changing an arm length, a slot width, or other characteristic of the first layer 1001A can also lead to corresponding changes in a current distribution pattern about the layer when the layer is excited.

[0114] In an example, one or more capacitive elements can be provided to bridge the slot 1010 in one or more places, such as to further tune an operating frequency of the transmitter. That is, respective plates of a capacitor can be electrically coupled to the outer region 1005 and the inner region 1015 to tune the first transmitter 1000, as further discussed below.

[0115] Dimensions of the first layer 1001A can vary. In an example, an optimal radius is determined by a desired operating frequency, characteristics of nearby or adjacent dielectric materials, and excitation signal characteristics. In an example, a nominal radius of the firstlayer 1001A is about 25 to 45 mm, and a nominal radius of the slot 1010 is about 20 to 40 mm. In an example, a transmitter device comprising the first layer 1001 A can be made smaller at a cost of device efficiency, such as by decreasing the slot radius and / or increasing the length of the arms.

[0116] FIG. 9 illustrates generally a top view of a second layer 1101 superimposed over the first layer 1001 A of the layered first transmitter 1000. The second layer 1101 is spaced apart from the first layer 1001 A, such as using a dielectric material interposed therebetween. In an example, the second layer 1101 includes multiple striplines configured to excite the first transmitter 1000. The example of FIG. 9 includes first through fourth striplines 1131 A, 113 IB, 1131C, and 113 ID, corresponding respectively to the four regions of the conductive inner region 1015 of the first layer 1001 A. In the example of FIG. 9, the striplines 1131A- 113 ID are oriented at about 45 degrees relative to respective ones of the arms 1021 A- 102 ID. Different orientations or offset angles can be used. Although the example of FIG. 9 shows the striplines 1131A-1131D spaced at equal intervals about the circular device, other non-equal spacings can be used. In an example, the device can include additional striplines or as few as one stripline.

[0117] The first through fourth striplines 1131A-1131D provided on the second layer 1101 can be electrically isolated from the first layer 1001A. That is, the striplines can be physically spaced apart from the conductive annular outer region 1005 and from the discshaped conductive inner region 1015, and a dielectric material can be interposed between the first and second layers 1001 A and 1101 of the first transmitter 1000.

[0118] In the example of FIG. 9, the first through fourth striplines 1131 A-l 13 ID are coupled to respective first through fourth vias 1132A-1132D. The first through fourth vias 1132A-1132D can be electrically isolated from the first layer 1001 A, however, in some examples the first through fourth vias 1132A-1132D can extend through the first layer 1001 A. In an example, the vias can include or can be coupled to respective ones of the RF ports 311, 312, 313, and 314 illustrated in the examples of FIG. 3.

[0119] In an example, one or more of the first through fourth striplines 1131 A-l 13 ID can be electrically coupled to the conductive inner region 1015 of the first layer 1001 A, such as using respective other vias that are not illustrated in the example of FIG. 9. Such electrical connections are unnecessary to generate midfield signals using the device, however, the connections may be useful for further tuning or performance enhancement of the device.

[0120] Various benefits are conferred by providing excitation microstrips and / or striplines, such as the first through fourth striplines 1131 A-l 13 ID, on a layer that is adjacent to andextends over the conductive inner region 1015 of the first layer 1001 A. For example, an overall size of the first transmitter 1000 can be reduced. Various different dielectric materials can be used between the first and second layers 1001 A and 1101 to additionally reduce a size or thickness of the first transmitter 1000.

[0121] FIG. 10 illustrates generally a perspective view of an example of the layered first transmitter 1000. FIG. 11 illustrates generally a side, cross-section view of the layered first transmitter 1000. The examples include, at the bottom side of each of FIGS. 10 and 11, the first layer 1001 A of the first transmitter 1000. At the top of the figures, the first transmitter 1000 includes a third layer 1201. The third layer 1201 can be a conductive layer that provides a shield or backplane for the first transmitter 1000. The second layer 1101, such as comprising one or more striplines, can be interposed between the first and third layers 1001 A and 1201. One or more dielectric layers (not illustrated) can be interposed between the first and second layers 1001 A and 1101, and one or more other dielectric layers can be interposed between the second and third layers 1101 and 1201.

[0122] The examples of FIG. 10 and FIG. 11 include vias that electrically couple the outer region 1005 on the first layer 1001 A with the third layer 1201. That is, ground vias 1241 A- 1241H can be provided to couple a ground plane (e.g., the third layer 1201) with one or more features or regions on the first layer 1001 A. In the example, and as described above, each of the first through fourth striplines 1131 A-l 13 ID is coupled to a respective signal excitation source via 1132A-1132D. The signal excitation source vias 1132A-1132D can be electrically isolated from the first and third layers 1001 A and 1201.

[0123] In the examples of FIG. 10 and FIG. 11, the transmitting side of the illustrated device is downward. That is, when the first transmitter 1000 is used and positioned against or adjacent to a tissue surface, the tissue-facing side of the device is the downward direction in the figures as illustrated.

[0124] Providing the third layer 1201 as a ground plane confers various benefits. For example, other electronic devices or circuitry can be provided on top of the third layer 1201 and can be operated substantially without interfering with the transmitter. In an example, other radio circuitry (e.g., operating outside of the range of the midfield transmitter) can be provided over the third layer 1201, such as for radio communication with an implanted or other device (e.g., the implantable device 110, or other implantable device as described herein). In an example, a second transmitter can be provided, such as in a back-to-back relationship with the first transmitter 1000, and can be separated from the first transmitter 1000 using the ground plane of the third layer 1201.

[0125] FIG. 12 A illustrates generally an example that shows a surface current pattern 1400A that results when the first transmitter 1000 is excited by a drive signal, or by a plurality of drive signals provided respectively to the first through fourth striplines 1131A- 113 ID. The various drive signals can be adjusted in phase and / or amplitude relative to one another to produce various surface currents at the first transmitter 1000. In the example of FIG. 12A, the surface current pattern closely mimics an oscillatory, optimal distribution that, when provided using the transmitter placed near a tissue interface, influences an evanescent field that will give rise to propagating or non- stationary fields inside of tissue.

[0126] An example of an optimal current distribution for a transmitter is illustrated generally by the pattern 1400B in FIG. 12B. That is, when the first transmitter 1000 is excited with signals that induce or provide a particular current pattern that corresponds to the pattern 1400B, one representative instance of which is illustrated in the surface current pattern 1400 A, then a corresponding optimal evanescent field can be provided, such as at or near a tissue interface.

[0127] In an example, the excitation signals (e.g., provided to the first through fourth striplines 1131 A-l 13 ID) that provide an optimal or target current pattern include oscillating signals provided to oppositely-oriented striplines (e.g., second and fourth striplines 113 IB and 113 ID in the example of FIG. 9). In an example, the excitation signals further include signals provided to one or more other pairs of striplines (e.g., first and third striplines 1131 A and 1131C in the example of FIG. 9). This type or mode of excitation can be used to generate the optimal current pattern and efficiently transfer signals to a deeply implanted receiver. In an example, an implanted receiver such as the implantable device 110 includes a loop receiver oriented in parallel with the current signal direction 1401. That is, the loop receiver can be installed in tissue in parallel with a prominent direction of the oscillating current distribution, as illustrated by the arrow indicating the signal direction 1401. Stated differently, a normal of the loop receiver can be oriented orthogonally to the current signal direction 1401.

[0128] FIG. 13 illustrates generally an example of a first chart 1300 that shows a relationship between coupling efficiency of orthogonal transmitter ports of the first transmitter to an implanted receiver with respect to a changing angle or rotation of the implanted receiver. The example illustrates that weighting the input or excitation signals provided to the orthogonal ports (e.g., to the first through fourth striplines 1131 A-l 13 ID) can be used to compensate for a changing location or rotation of the implanted receiver. When the transmitter can compensate for such variations in target device location,consistent power can be delivered to the target device even when the target device moves away from an initially-configured position.

[0129] In the example of FIG. 13, a first curve 1302 shows an S-parameter, or voltage ratio of signal at the transmitter and the receiver, when a first pair of oppositely-oriented (e.g., top / bottom, or left / right) striplines are excited by an oscillating signal. A second curve 1304 shows an S-parameter when a second pair of the oppositely-oriented striplines are excited by an oscillating signal. In the example of FIG. 13, the first and second pairs of striplines are orthogonal pairs. The example illustrates that signals provided to the orthogonal pairs can be optimally weighted to achieve consistent powering with different implant angles, such as through constructive interference.

[0130] The example of FIG. 13 further illustrates that the transmitters discussed herein and their equivalents can be used to effectively steer or orient a propagating field such as without moving the transmitter or external source 102 itself. For example, rotational changes in a position of the implantable device 110 can be compensated by weighting the signals provided to the various striplines with different phases, such as to ensure a consistent signal is delivered to the implantable device 110. In an example, the weighting can be adjusted based on a sensed or measured signal transfer efficiency, such as can be obtained using feedback from the implantable device 110 itself. Adjusting the excitation signal weighting can change a direction of the transmitter current distribution, which in turn can change characteristics of the evanescent field outside of the body tissue and thereby affect a propagation direction or magnitude of a field in tissue.

[0131] FIG. 14 illustrates generally a top view of the second layer 1101 from the example of FIG. 9 superimposed over a different first layer 100 IB of a layered transmitter. That is, relative to FIG. 9, the example of FIG. 14 includes the different first layer 1001B instead of the first layer 1001 A that includes the arms 1021 A-1021D. The different first layer 1001B includes a substrate that is etched with a circular slot 1810 to separate a conductive outer region from a conductive inner region. In addition to the etched circular slot 1810, the example includes a pair of linear slots 1811 arranged in an “X” pattern and configured to cross at a central axis of the device. In the example of FIG. 14, the pair of linear slots 1811 extends to opposite side edges of the substrate or layer. The example thus includes, on the different first layer 100 IB, eight regions that are electrically decoupled, including four equally-sized sectors, or pie-piece shaped regions, and four equally-sized regions of an annulus. Differently-sized, rather than equally-sized, regions can similarly be used, such as when the linear slots 1811 are not arranged exactly orthogonally to each other.

[0132] When a device with the different first layer 1001B is excited (e.g., using the striplines on the second layer 1101), a resulting current density across or over the different first layer 100 IB can be relatively more concentrated at the outer annulus portions of the layer than at the inner sector portions of the layer. FIG. 15A and FIG. 15B illustrate generally examples showing different surface current patterns 1900 A and 1900B, respectively, for an excited device that includes or uses the different first layer 1001B. Drive signals providing excitation of the device can be tuned or adjusted in phase and / or amplitude relative to each other to produce the different surface currents.

[0133] In the example of FIG. 15 A, the surface current pattern closely mimics an oscillatory, optimal distribution to adjust an evanescent field that will give rise to propagating fields inside of tissue. As indicated by the illustrated arrow density, a current density can be more concentrated at the outer annulus portion than at the inner sector portion of the different first layer 1001B. When the device in the example of FIG. 15A is excited by a first excitation signal or signal pattern, the device can have an oscillatory current distribution that approximates a pair of adjacent, vertically-oriented lobes, indicated by dashed line segments 1901 and 1902 and corresponding to the directions indicated by the bolded arrows 1903 and 1904, at the different first layer 1001B. A receiver, such as the implantable device 110, can be most strongly coupled with the transmitter comprising the different first layer 100 IB excited in the manner illustrated in FIG. 15A when the implantable device 110 includes a receiver antenna normal that is oriented orthogonally to a direction of the lobes as illustrated by a first receiver orientation arrow 1909.

[0134] A direction or orientation of the current paths induced on the different first layer 100 IB can change in correspondence with changes in excitation signals. In the example of FIG. 15B, a second surface current pattern closely mimics an oscillatory, optimal distribution to adjust an evanescent field that will give rise to propagating fields inside of tissue. As indicated by the illustrated arrow density, a current density can be more concentrated at the outer annulus portion than at the inner sector portion of the different first layer 1001B. When the device in the example of FIG. 15B is excited by a second excitation signal or signal pattern, the device can have an oscillatory current distribution that approximates a pair of adjacent, horizontally-oriented lobes, indicated by dashed line segments 1911 and 1912 and corresponding to the directions indicated by the bolded arrows 1913 and 1914, at the different first layer 1001B. A receiver, such as the implantable device 110, can be most strongly coupled with the transmitter comprising the different first layer 100 IB excited in the manner illustrated in FIG. 15B when the implantable device 110includes a receiver antenna normal that is oriented orthogonally to a direction of the lobes as illustrated by a first receiver orientation arrow 1919.

[0135] A device that includes or uses the different first layer 100 IB can have its operating frequency or resonance determined based in part on an area characteristic of the outer annulus, such as rather than being based on the length of the arms 1021 A-1021D from the example of FIG. 9. Total signal transfer efficiency from a transmitter using the embodiment of FIG. 14 to an implanted midfield receiver is similar to the efficiency from a transmitter using the embodiment of FIG. 9, however, greater current density at the outer annulus portion of the embodiment of FIG. 14 can allow for greater steerability (that is, transmitted field steering) and thus potentially better access and transmission characteristics for communication with the implantable device 110, including when the receiver is off-axis relative to the transmitter. Furthermore, the specific absorption rate (SAR) can be reduced when the embodiment of FIG. 14 is used, and unwanted coupling between ports can be reduced. Other transmitter configurations and geometries for an external source 102 can similarly be used to achieve the same current distribution and steerable fields contemplated herein for the illustrated embodiments.

[0136] The external source 102, such as including a midfield transmitter, can be tuned or adjusted to enhance signal transfer efficiency to the implantable device 110 or other midfield receiver. Signal transfer characteristics can be monitored, such as using a bidirectional coupler or circulator, and transmitter power or drive signal characteristics can be intermittently or periodically updated to enhance transfer efficiency. In an example, midfield transmitter tuning includes adjusting a value of a capacitive tuning element based on a reflected power measurement, such as can be used to determine a coupling efficiency between a transmitter and a receiver antenna. In an example, midfield transmitter tuning includes adjusting a value of a capacitive tuning element based on a data signal received from the implanted or other midfield receiver, and the data signal includes information about a quality or quantity of signal received at the receiver.

[0137] FIG. 16A illustrates a diagram that includes a bidirectional coupler 2601 that can comprise a portion of a midfield transmitter. The bidirectional coupler 2601 includes multiple ports, including an input port Pl, a transmitted port P2, a coupled port P3, and an isolated port P4. The input port Pl receives a signal, such as a test signal or power signal, from a signal generator 2611 (e.g., a signal generator component of a midfield transmitter device or external source 102). In an example, the signal generator 2611 is configured to provide an AC signal having a frequency between about 300 MHz and 3 GHz.

[0138] The coupled port P3 receives a portion of the signal that is received by the input port Pl from the signal generator 2611. In the example of FIG. 16A, the coupled port P3 is terminated with a load 2631. In an example, the load 2631 includes a reference load with a specified matching impedance, such as a fixed-value resistor (e.g., a 50 ohm resistor). The transmitted port P2 transmits another portion of the signal that is received by the input port Pl from the signal generator 2611. In other words, the transmitted port P2 transmits a signal that corresponds to the signal received at the input port Pl less any signal provided at the coupled port P3 and less any other losses. In an example, the transmitted port P2 is coupled with an antenna port 2621 or other excitation port of a midfield transmitter, such as one of the first through fourth RF ports 311, 312, 313, and 314 from the example of FIG. 3.

[0139] The isolated port P4 can be coupled to a receiver circuit 2641. The receiver circuit 2641 can include monitoring or analysis circuitry. In an example, the receiver circuit 2641 is configured to monitor signals received from the isolated port P4 and provide information about a reflected power, such as can be used to determine an efficiency of a transmitted power signal from the transmitted port P2. In an example, the isolated port P4 is coupled to an RF diode detector circuit or a switch. The switch can be configured to switch between the RF diode detector and a mixer circuit, such as for receiving backscatter communications from the implantable device 110.

[0140] In the example of FIG. 16 A, the input port Pl receives an amplified test signal from the signal generator 2611 or other transceiver circuit portion of a midfield transmitter device. When signal characteristics on the transmitter side are well-matched to a receiver device, then a relatively large portion of the energy from the test signal is provided through the bidirectional coupler 2601 to the transmitted port P2, and a relatively small portion of the energy from the test signal is provided at the isolated port P4. If, however, the transmitter and receiver devices are not well-matched, then a relatively larger portion of the energy from the test signal is provided at the isolated port P4. Therefore, signal characteristics at the isolated port P4 can be monitored and used to assess a transmission quality or a power transfer efficiency, or to detect a fault condition. In an example, characteristics of a test signal provided to the input port Pl, such as a signal frequency, can be changed to enhance the signal transmission efficiency.

[0141] FIG. 16B illustrates a diagram that includes an example of the bidirectional coupler 2601 with an adjustable load 2602. The example of FIG. 16B can comprise a portion of a midfield transmitter that is configured to receive or use a backscatter signal such as for communication with an implanted midfield receiver device. Due at least in part to achanging position of an external transmitter relative to its target receiver, there can be interference, or changes in interference, between an external transmitter source and a receiver. Such interference can compromise an effectiveness of backscatter communications. In an example, a cancelation signal can be introduced to help mitigate or process such interference. For example, an external transmitter can be configured to generate a tuned, self-interference cancellation signal to help separate a carrier signal from self-interference or leakage signals from the transmitter to receiver sides of the bidirectional coupler 2601.

[0142] In the example of FIG. 16B, the bidirectional coupler 2601 can receive an RF source signal at the input port Pl (e.g., from the signal generator 2611), and can provide a corresponding signal to the transmitted port P2 (e.g., to be provided to an output port of a midfield transmitter or to the antenna port 2621) and to the coupled port P3. The coupled port P3 can feed the adjustable load 2602, and the adjustable load 2602 can be tuned to a specified nominal impedance.

[0143] In the example of FIG. 16B, the adjustable load 2602 is nominally tuned to about 50 ohms at various different frequencies, and a particular operating frequency can be selected by adjusting a capacitance of one or more of the capacitors Cl, C2, and C3. Other nominal impedance set points can similarly be used. In an example, the capacitors can be adjusted such that the adjustable load 2602 is mismatched to the coupled port P3, and a reflection can be generated and added to a received signal (e.g., a backscatter signal) from the transmitted port P2.

[0144] In an example, a leakage signal can be present at the isolated port P4 (e.g., based on an input signal provided at the input port Pl). An iterative algorithm can be used to minimize a power of a signal received at the receiver circuit 2641 (e.g., an IQ receiver circuit) via the isolated port P4 to mitigate the leakage signal and improve an efficacy of backscatter communication. For example, capacitances provided by the capacitors Cl, C2, and / or C3, can be adjusted during use to provide a cancellation signal that is substantially opposite in phase and equal in magnitude to the leakage signal. The adjustable load 2602 and the bidirectional coupler 2601 can thus be used by the external source 102 to generate a dynamic, controlled reflection or cancellation signal that can be used to help minimize noise and extract information from a backscatter signal, such as under changing use or interference conditions.

[0145] The examples of FIG. 16A and FIG. 16B include the bidirectional coupler 2601, however, other examples can similarly include or use other elements to determineinformation about a coupling efficiency between a midfield transmitter and midfield receiver. For example, a circulator can be used to couple an RF port of a midfield transmitter to both an excitation source and to a receiver circuit, such as can be configured to receive a backscatter or other signal that can include information about a received power signal at a midfield receiver.

[0146] FIG. 17 illustrates generally an example of implantable devices placed through the left and right sacral foramen of a patient sacrum 1702, respectively. For example, a leftsided implantable device 1704 is implanted in a left sacral foramen and its electrode array portion can be curved toward the patient's left side, and a right-sided implantable device 1706 is implanted in a right sacral foramen and its electrode array portion can be curved toward the patient's right side. Each of the left-sided implantable device 1704 and the rightsided implantable device 1706 can comprise a respective instance of the implantable device 110, or the implantable device 600, or a variation thereof.

[0147] As explained above, the implantable devices discussed herein are configured to receive power and / or data signals wirelessly, from a body-external transmitter such as the external source 102, when the implantable devices are implanted in tissue. In an example, an implantable device is configured to be implanted adjacent to the sacral nerve (among other nerve targets), either on the left or right side of the patient.

[0148] The present inventors have recognized that a problem to be solved includes mitigating a difference in power transfer efficiency from the external transmitter to each of the left-sided implantable device 1704 and to the right-sided implantable device 1706. For example, the present inventors observed that a power transfer efficiency from the external transmitter to implanted devices on a first body side may be different than a power transfer efficiency from the external transmitter to implanted devices on a second body side, where the first and second body sides are opposite sides of a body midline.

[0149] The power transfer efficiency problem is illustrated in the chart 1802 in FIG. 18. The chart 1802 shows a relationship between the axial angle (in degrees) of an implanted device (x-axis) and a maximum depth (in millimeters) at which the implanted device can receive a sufficient power signal from the external transmitter to provide therapeutic electrostimulation. In the example of the chart 1802, 0 degrees corresponds to no tilt or rotation of an implanted device inside the body. The chart 1802 includes several traces corresponding to respective different implanted devices. As the axial angle of each implanted device moves away from 0 degrees to one side (e.g., toward -90 degrees or the left side) the maximum implanted depth decreases. As the axial angle of each implanteddevice moves to an opposite side (e.g., toward +90 degrees or the right side) the maximum implanted depth remains reasonably stable. Under ideal circumstances, the maximum implanted depth would be constant at any axial angle of an implanted device.

[0150] The present inventors have recognized that the power transfer efficiency problem is caused in part by constructive and destructive interference of electric field and magnetic field components of the transmitted signal that is received at the implanted device. As similarly explained above, the external transmitter (e.g., comprising the external source 102) can be located at or above an interface 105 between air 104 and a higher-index material 106, such as body tissue. The external source 102 can produce a source current (e.g., an in-plane source current), and the source current can generate an electric field and a magnetic field. The magnetic field can include a non-negligible component that is parallel to the surface of the source 102 and / or to a surface of the higher-index material 106. That is, the magnetic field includes a non-negligible component at a surface of the higher-index material 106 that faces the external source 102. The interference between these fields can depend on factors such as transmitter placement or positioning, power settings, and tissue type, among others, and gives rise to the power transfer efficiency and propagation differences observed at the left-sided implantable device 1704 and the right-sided implantable device 1706.

[0151] The present inventors have recognized that a solution to the power transfer efficiency problem includes adjusting a tuning of the external source 102 or transmitter to optimize characteristics of the evanescent and propagating fields created by the transmitter when the transmitter is excited. In an example, tuning the transmitter includes adjusting a phase and / or amplitude of one or more of the signals that are fed to the ports of the antenna 300. In other words, the power transfer efficiency problem can be addressed in part by controlling the magnetic field and electric field components produced by the external transmitter.

[0152] The power transfer efficiency difference between left-sided and right-sided devices can be explained in part by the different rotation or orientation of the implanted devices, and the interference between the magnetic field and electric field components of the transmitted signal. For example, constructive and destructive interference at the receiver element(s) of the implanted device can be sensitive to device polarization. Accordingly, differently-angled implanted devices can have different phase delay characteristics for receiving the magnetic field and the electric field, for example, such that an implanted device on the right side (e.g., with an electrode array portion of the device that curves to the right) can act as a LeftHanded Circularly Polarized (LHCP) receiver and an implanted device on the left side (e.g.,with an electrode array portion of the device that curves to the left) can act as a Right Handed Circularly Polarized (RHCP) receiver. FIG. 17 illustrates generally that the axial rotation of the left-sided implantable device 1704 and right-sided implantable device 1706 changes the phase delay of the fields experienced by the receivers of the respective devices.

[0153] The curved orientations of the left-sided implantable device 1704 and right-sided implantable device 1706 in opposite directions visually demonstrate, in the example of FIG. 17, how the devices are angled differently relative to the incoming electromagnetic fields. The lower portion of FIG. 17 depicts the magnetic and electric field components for each device. For the left-sided device 1704, the magnetic field is shown entering the page (represented by a circle with an X), while the electric field is depicted by an arrow pointing to the left. Conversely, for the right-sided device 1706, the magnetic field is shown exiting the page (represented by a circle with a dot), and the electric field is depicted by an arrow pointing to the right. Above each implanted device, a representation of the propagating electromagnetic field is illustrated. The orientation of the field representations relative to the devices visually depicts how the axial rotation of the devices affects their interaction with the incoming fields.

[0154] The inventors have recognized that an RHCP transmitter may not effectively transmit energy to a LHCP receiver, and vice versa. For transmitter and receiver pairs that can be configured to transmit in multiple directions, generally, the polarity of the transmitter and receiver can be flipped or changed from LHCP to RHCP by flipping the transmitter (or excitation of the transmitter) orthogonally to the direction of transmission or reception. The solution can thus include or use an external transmitter device, such as the antenna 300 driven by the network 400 of FIG. 4, with programmable phase shifters.

[0155] In an example, the transmitter or external source 102 comprises at least three programmable (e.g., 4-bit) phase shifters (e.g., PSI, PS2, PS3) coupled to respective different antenna ports, and a fourth port or reference port. The value of the phase shifters can be changed (e.g., automatically or manually through calibration) to adjust the relative phases between the ports. In an example, the ports are grouped such that signals received by ports 1 and 3 are 180 degrees offset, and the signals received by ports 2 and 4 are 180 degrees offset. Thus, by adjusting the relative phase between opposing ports, a “handedness” of the resulting fields or propagating wave can be adjusted and updated to achieve and maintain maximum power transfer from the external source 102 to one or more implantable devices, whether implanted on the left side or the right side, and at different axial rotations of such devices.

[0156] In an example, the problem of power transfer efficiency differences between leftsided and right-sided implanted devices can be addressed by modifying the receiver (i.e., the implanted device) itself. This approach focuses on optimizing the helical antenna structure of the implanted device to maximize constructive interference with the incoming fields.

[0157] Referring to FIG. 7, the implantable device includes a first antenna 708 disposed inside the antenna housing 704. This first antenna 708 comprises a helical antenna with a conductor wound in a helical path. The direction of the helical winding can be either clockwise or counterclockwise. In some examples, multiple helical windings can be provided in the same antenna housing 704, and each of the windings can be oppositely- oriented. In this example, circuitry inside the circuitry housing 712 can be used to select one or the other of the helical windings for use as a receiver.

[0158] The polarity of the antenna can correspond to the winding direction, and thus can be adjusted or selected to better align with the incoming electromagnetic fields from the external transmitter. This selection of winding direction can help ensure that the electric and magnetic field components constructively interfere at the receiver, thereby improving power transfer efficiency.

[0159] In an example, the polarity of the connection between the helical antenna winding and the receiver circuitry can be selected to optimize power reception. This can include choosing the appropriate connection point on the helical antenna (i.e., choosing the signal flow direction) to match the expected field orientations based on the implant position on the patient's left side or right side. Accordingly, the implanted device can be configured to act as either a Left Handed Circularly Polarized (LHCP) or Right Handed Circularly Polarized (RHCP) receiver, depending on its implantation site. This customization allows for improved alignment with the transmitted fields, resulting in more efficient power transfer.

[0160] FIG. 19 illustrates generally an example of a phase relationship diagram 1900. The labels RF1-RF4 refer to the phases of the respective signals driving the ports of a 4-port antenna, such as the antenna 300. The phases RF2 and RF4 are, in an example, fixed to provide a reference. For example, RF4 can correspond to the fourth port having a 0 degree phase shift, and RF2 can correspond to the second port having a 180 degree phase shift relative to RF4. This phase relationship between RF2 and RF4 (e.g., 180 degrees out of phase) can be fixed or static.

[0161] In an example, a relationship between the phases of the signals provided to the first and third ports can also be fixed at 180 degrees apart, but can be variable relative to the signals provided to the second and fourth ports. In an example where the phase shifters(e.g., the phase shifters 410A-410D from the example of FIG. 4) provide 16 different phase shift amounts, the phases of the signals provided to the first and third ports can be changed in fixed increments, such as 22.5 degrees.

[0162] In an example where the third phase shifter corresponding to the third port applies a phase shift of +22.5 degrees relative to the reference provided by the phase at the fourth port (e.g., 0 degrees), the first phase shifter corresponding to the first port applies a phase shift of +22.5 + 180 = 202.5 degrees relative to the reference provided by the phase of the signal at the fourth port. A stepped phase relationship between the RF2 / RF4 pair and the RF1 / RF3 pair is illustrated graphically in FIG. 19. The size of the phase increments can depend on the resolution of the phase shifters and, in some examples, can provide continuous adjustment rather than fixed increments.

[0163] In an example that includes configuring a transmitter or external source 102 to efficiently communicate power to an implanted device, the phase of signals corresponding to the first and third ports (i.e., RF1 and RF3) can be stepped to find an optimal configuration such that the electric field and magnetic field components of the resulting propagating wave in body tissue interfere constructively at the implanted device.

[0164] FIG. 20 illustrates generally a voltage ratio versus relative phase chart 2000. The chart shows the voltage ratio between the transmitter and receiver (S21) as a function of the phase configuration of the transmitter (P3), or the relative phase of the signal provided to the third port of the antenna. In other words, the x-axis of the chart represents the phase shift applied to the input signal by the third phase shifter (e.g., the phase shifter 410C), and such phase information defines the respective phases of the four signals provided to the transmitter, as described above (e.g., due to the fixed phase relationship between the port pairs). The y-axis of the chart represents the magnitude of the power received by the implantable device or receiver. The several traces correspond to different orientations of the receiver, in 30 degree increments, from -90 degrees (e.g., corresponding to a left-sided implantable device pointed to the left) to +90 degrees (e.g., corresponding to a right-sided implantable device pointed to the right).

[0165] The example of the voltage ratio versus relative phase chart 2000 shows that different implantable device orientations can be accommodated by adjusting the value of P3 that is used by the transmitter. For example, in the case of the +60 degree device orientation, a P3 value of +22.5 degrees provides a signal with electric field and magnetic field components that destructively interfere at the implantable device receiver, and accordingly a minimum amount of power is received. However, at a P3 value of -157.5degrees, the electric field and magnetic field components constructively interfere (or do not destructively interfere) and a maximum power transfer efficiency can be achieved.

[0166] FIG. 21 illustrates generally an example of a first method 2100 that includes optimizing a power transfer characteristic between an external midfield transmitter device and an implantable receiver device. The first method 2100 can be used to calibrate components of the system 100.

[0167] At operation 2102, the first method 2100 includes exciting the transmitter (e.g., the midfield transmitter or external source 102) using a particular excitation configuration. At initiation of the first method 2100, the excitation configuration can include a default configuration. The default configuration can include using a first pair of signal ports to provide a first pair of first antenna excitation signal components that are 180 degrees out of phase. The first pair of signal components can be provided to respective sub -wav elength structures of the transmitter. The default configuration can include using a second pair of signal ports to provide a second pair of second antenna excitation signal components that are 180 degrees out of phase, and the second pair can be phase-offset relative to the first pair of antenna excitation signal components. The second pair of signal components can be provided to respective other sub -wavelength structures of the transmitter.

[0168] At operation 2104, the first method 2100 includes receiving power wirelessly, from the transmitter, at the implantable receiver device (e.g., at the implantable device 110). In an example, operation 2104 includes receiving the power via a wireless signal that propagates through body tissue and comprises electric field and magnetic field components. The field components can constructively and destructively interfere at different depths and locations in the tissue.

[0169] At decision operation 2106, the first method 2100 can include determining whether, and to what extent, the wireless power signal is received at the implantable receiver device. In an example, decision operation 2106 includes using circuitry of the implantable receiver device to measure an amount of the wireless power that is received from the transmitter, and can include using other circuitry of the implantable receiver device to communicate information about the amount of received power back to the transmitter or to another controller. In an example, decision operation 2106 includes using patient feedback about an electrostimulation or other sensation provided by the implantable receiver device to the patient. For example, decision operation 2106 can include or use patient-reported information about a strength or presence of an electrostimulation signal provided in response to the transmission from the external transmitter. In an example, decision operation2106 includes using circuitry of the transmitter to measure an amount of power transferred to the sub -wavelength structures. The measured amount of transferred power can be used to determine an indication of an amount of power that was received, or likely received, by the implantable receiver device.

[0170] If inadequate power is received by the implantable receiver device, then the first method 2100 continues at operation 2108 and / or operation 2110. Operation 2108 can include adjusting one or more of the phase shifters of the transmitter device to update or adjust a characteristic of the electric field and the magnetic field at the implantable receiver device. Operation 2108 can include exciting the transmitter using the adjusted phase shifter(s). The first method 2100 can then return to operation 2104 for another iteration of receiving power at the implantable receiver device and then to decision operation 2106 for another iteration of determining whether an adequate amount of power was received.

[0171] Operation 2108 can include changing the phase characteristics of the signals provided to the antenna ports of the external transmitter. In an example, the transmitter comprises at least three programmable (e.g., 4-bit) phase shifters coupled to respective different antenna ports, with a fourth port serving as a reference. By adjusting the relative phases between these ports, the "handed-ness" of the resulting fields or propagating wave can be modified. The adjustment process is configured to align the electric and magnetic field components of the traveling wave in tissue such that they constructively interfere at the receiver components of the implantable device. The alignment can be optimized to accommodate differently-angled implanted devices, which in turn exhibit different phase delay characteristics for receiving the magnetic and electric field components of the transmitted signal.

[0172] In an example, additionally or alternatively to operation 2108, the first method 2100 can include changing a polarity of a helical antenna of the implantable receiver device. By changing a polarity of the helical antenna, the phase at which the helical antenna intersects with the magnetic field component of the signals transmitted by the external transmitter also changes. Accordingly, operation 2110 can be used to optimize power transfer efficiency to the implantable receiver device.

[0173] If, at decision operation 2106, it is determined that adequate power is received at the implantable receiver device, then the first method 2100 can continue at operation 2112 with other device operations, such as delivering neurostimulation therapy.

[0174] In an example, the first method 2100 can be used iteratively to determine which phase setting(s) can be used to communicate an adequate amount of power to theimplantable receiver device while consuming the least amount of power at the transmitter. That is, the first method 2100 can be configured to determine which phase shifter settings use the least amount of power at the transmitter to communicate a power signal to the implantable receiver device that is sufficient to provide a neurostimulation therapy to the patient with a sufficient amplitude for a therapeutic effect. In an example, an optimal setting for the phase shifters can be determined by having the patient report the threshold at which stimulation is perceived by the patient. If no sensation is reported, then an insufficient amount of power is communicated to the implantable receiver device and a different phase shifter setting can be used. In an example, each of multiple (e.g., 16) phase shifter settings can be tested to identify a most efficient power transfer setting for each patient.

[0175] FIG. 22 illustrates generally an example of a second method 2200 that includes optimizing a power transfer characteristic between an external midfield transmitter device and an implantable receiver device. The second method 2200 can be used to calibrate components of the system 100.

[0176] At operation 2202, the second method 2200 can include determining an axial orientation of an elongated implantable device in body tissue. Operation 2202 can include using imaging techniques or other sensing methods to ascertain the position and angle of the implanted device within the patient's body. For example, the axial orientation could be determined relative to anatomical landmarks or using external sensors to detect the device's orientation. In an example, operation 2202 can be based on information from the implanting physician about the orientation or placement of the implantable device in a patient body.

[0177] At operation 2204, the second method 2200 can include using information about the determined axial orientation of the implantable device to select a first polarity of one or more excitation signals for use by the external transmitter. Based on whether the implant is oriented more towards the left or right side, or at a particular angle, the appropriate transmitter signal polarity (e.g., corresponding to a RHCP or LHCP receiver) can be selected to optimize power transfer. The selection can help to match the transmitter's excitation signal characteristics to the implant's orientation.

[0178] At operation 2206, the second method 2200 can include programming the external transmitter to use the selected first polarity of the one or more excitation signals. Operation 2206 can include adjusting the phase shifters and other components of the transmitter, such as the antenna 300 driven by the network 400, to generate the appropriate signal. In an example, the relative phases between the signals provided to the antenna ports may be adjusted to achieve the desired transmitter signal polarity.

[0179] At operation 2208, the second method 2200 can include using the programmed transmitter and providing a midfield signal to the implantable device. At operation 2208, the transmitter, configured with the selected polarity, can send a power and / or data signal through the tissue to the implanted device.

[0180] At operation 2210, the second method 2200 can include receiving information about a magnitude of the midfield signal received by the implantable device. Operation 2210 can include using the implanted device to measure or quantify the wirelessly-received power and communicate this information back to the external system or transmitter. For example, the implantable device can use its power meter 542 to detect the amount of received power and transmit this information back to the external source 102.

[0181] At operation 2212, the second method 2200 can include, in response to the information about the magnitude of the wireless power signal received, programming the transmitter to use a second polarity of the one or more excitation signals. If the received power magnitude is below a specified threshold, then the transmitter can be reprogrammed with a different polarity setting. If the received power magnitude meets or exceeds the specified threshold, then the implantable device can be used to deliver therapy or carry out other operations.

[0182] The following Examples provide a non-limiting overview of, among other things, the power transfer optimization systems, methods, and other techniques and features discussed herein.

[0183] Example l is a system, comprising: an implantable device configured to receive a wireless power signal; and a midfield transmitter configured to provide the wireless power signal to the implantable device from outside of a patient body, the midfield transmitter comprising: a plurality of excitation signal paths coupled to respective excitable subwavelength structures; and a controller circuit configured to control a first phase adjustment circuit to change a first phase characteristic of a first signal in a first signal path of the plurality of excitation signal paths; wherein a power signal transfer efficiency between the midfield transmitter and the implantable device is a function of the first phase characteristic of the first signal.

[0184] In Example 2, the subject matter of Example 1 optionally includes the plurality of excitation signal paths comprises first, second, third, and fourth signal paths coupled to respective first, second, third, and fourth sub -wavelength structures.

[0185] In Example 3, the subject matter of Example 2 optionally includes, first, second, third, and fourth phase adjustment circuits configured to selectively adjust the respective phase characteristics of signals on the first, second, third, and fourth signal paths.

[0186] In Example 4, the subject matter of any one or more of Examples 2-3 optionally includes a phase relationship between first and second signals on the first and second signal paths is fixed.

[0187] In Example 5, the subject matter of Example 4 optionally includes a phase relationship between third and fourth signals on the third and fourth signal paths is fixed.

[0188] In Example 6, the subject matter of Example 5 optionally includes a phase relationship between the signals on the first and second signal paths is variable relative to the signals on the third and fourth signal paths according to the first phase characteristic.

[0189] In Example 7, the subject matter of any one or more of Examples 1-6 optionally includes the implantable device comprises a helical antenna configured as a left handed circularly polarized (LHCP) receiver.

[0190] In Example 8, the subject matter of any one or more of Examples 1-7 optionally includes the implantable device comprises a helical antenna configured as a right handed circularly polarized (RHCP) receiver.

[0191] In Example 9, the subject matter of any one or more of Examples 1-8 optionally includes the implantable device comprises a helical antenna, a neurostimulation signal generator circuit, and an electrode array, and wherein the electrode array is configured to provide a neurostimulation therapy to a nerve target using signals from the neurostimulation signal generator circuit.

[0192] Example 10 is an external midfield transmitter comprising: a plurality of excitation signal paths coupled to excitable sub -wavelength structures; and a controller circuit configured to control a first phase adjustment circuit to change a phase characteristic of a first signal in a first signal path of the plurality of excitation signal paths, wherein the first signal path is coupled to a first one of the excitable sub -wavelength structures; wherein a power signal transfer efficiency between the transmitter and an implantable device is adjusted in response to the change of the phase characteristic of the first signal.

[0193] In Example 11, the subject matter of Example 10 optionally includes the plurality of excitation signal paths comprise first and second pairs of respective signal paths coupled to respective pairs of excitable sub -wavelength structures; wherein the first pair of signal paths includes the first signal path and a second signal path of the plurality of excitationsignal paths; wherein a first phase relationship of signals on the first pair of signal paths is fixed.

[0194] In Example 12, the subject matter of Example 11 optionally includes the first phase relationship includes signals on the first and second signal paths being 180 degrees out of phase.

[0195] In Example 13, the subject matter of any one or more of Examples 11-12 optionally includes a second phase relationship of signals on the second pair of signal paths is fixed.

[0196] In Example 14, the subject matter of Example 13 optionally includes the first phase relationship includes signals on the first pair of signal paths being 180 degrees out of phase with each other, and the second phase relationship includes signals on the second pair of signal paths being 180 degrees out of phase with each other.

[0197] In Example 15, the subject matter of any one or more of Examples 11-14 optionally includes a reference phase characteristic for signals on the first pair of signal paths is variable relative to a fixed reference phase characteristic for signals on the second pair of signal paths.

[0198] Example 16 is a method comprising: determining an axial orientation of an elongated implantable device in body tissue; based on the determined axial orientation of the implantable device, selecting a first polarity of one or more excitation signals; programming a midfield external transmitter to use the selected first polarity of the one or more excitation signals; and using the programmed transmitter, providing a midfield signal to the implantable device.

[0199] In Example 17, the subject matter of Example 16 optionally includes, receiving information about a magnitude of the midfield signal received by the implantable device; and in response to the information about the magnitude of the midfield signal received, programming the transmitter to use a second polarity of the one or more excitation signals.

[0200] In Example 18, the subject matter of Example 17 optionally includes receiving information about the magnitude of the midfield signal received by the implantable device comprises receiving data from the implantable device via backscatter communication.

[0201] In Example 19, the subject matter of any one or more of Examples 16-18 optionally includes selecting the first polarity of the one or more excitation signals comprises choosing between a Right Handed Circularly Polarized (RHCP) signal and a Left Handed Circularly Polarized (LHCP) signal based on whether the implantable device is oriented more towards a left side or a right side of the patient's body.

[0202] In Example 20, the subject matter of any one or more of Examples 16-19 optionally includes programming the midfield external transmitter comprises adjusting phase shifters coupled to antenna ports of the transmitter to generate the selected first polarity.

[0203] In Example 21, the subject matter of any one or more of Examples 16-20 optionally includes iteratively adjusting the polarity of the one or more excitation signals to optimize power transfer efficiency between the midfield external transmitter and the implantable device to accommodate changes in the axial orientation of the implantable device over time.

[0204] In Example 22, the subject matter of any one or more of Examples 16-21 optionally includes receiving the midfield signal at the implantable device; and using a neurostimulation generator circuit of the implantable device, generating a neurostimulation signal using power from the midfield signal.

[0205] Example 23 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement of any of Examples 1-22.

[0206] Example 24 is an apparatus comprising means to implement of any of Examples 1- 22.

[0207] Example 25 is a system to implement of any of Examples 1-22.

[0208] Example 26 is a method to implement of any of Examples 1-15.

[0209] Each of these non-limiting examples or embodiments can stand on its own or can be combined in various permutations or combinations with one or more of the other examples or embodiments.

[0210] Although various general and specific embodiments are described herein, it will be evident that various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the present disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part of this application show, by way of illustration, and not of limitation, specific embodiments in which the subject matter can be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments can be used or derived therefrom, such that structural and logical substitutions and changes can be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims areentitled. Specific embodiments or examples are illustrated and described herein, however, it should be appreciated that any arrangement calculated to achieve the same purpose can be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

[0211] In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0212] The ranges disclosed herein also encompass any and all overlap, sub-ranges, and combinations thereof. Language such as “up to,” “at least,” “greater than,” “less than,” “between,” and the like includes the number recited. Numbers preceded by a term such as “about” or “approximately” include the recited numbers. For example, “about 10 kHz” includes “10 kHz.” Terms or phrases preceded by a term such as “substantially” or “generally” include the recited term or phrase. For example, “substantially parallel” includes “parallel” and “generally cylindrical” includes cylindrical.

[0213] In the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0214] Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a non-transitory, computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronicdevice to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Such instructions can be read and executed by one or more processors to enable performance of operations comprising a method, for example. The instructions are in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like.

[0215] Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0216] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention(s) and embodiments should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

CLAIMSWhat is claimed is:

1. A system, comprising: an implantable device configured to receive a wireless power signal; and a midfield transmitter configured to provide the wireless power signal to the implantable device from outside of a patient body, the midfield transmitter comprising: a plurality of excitation signal paths coupled to respective excitable subwavelength structures; and a controller circuit configured to control a first phase adjustment circuit to change a first phase characteristic of a first signal in a first signal path of the plurality of excitation signal paths; wherein a power signal transfer efficiency between the midfield transmitter and the implantable device is a function of the first phase characteristic of the first signal.

2. The system of claim 1, wherein the plurality of excitation signal paths comprises first, second, third, and fourth signal paths coupled to respective first, second, third, and fourth sub -wavelength structures.

3. The system of claim 2, comprising first, second, third, and fourth phase adjustment circuits configured to selectively adjust the respective phase characteristics of signals on the first, second, third, and fourth signal paths.

4. The system of claim 2, wherein a phase relationship between first and second signals on the first and second signal paths is fixed.

5. The system of claim 4, wherein a phase relationship between third and fourth signals on the third and fourth signal paths is fixed.

6. The system of claim 5, wherein a phase relationship between the signals on the first and second signal paths is variable relative to the signals on the third and fourth signal paths according to the first phase characteristic.

7. The system of claim 1, wherein the implantable device comprises a helical antenna configured as a left handed circularly polarized (LHCP) receiver.

8. The system of claim 1, wherein the implantable device comprises a helical antenna configured as a right handed circularly polarized (RHCP) receiver.

9. The system of claim 1, wherein the implantable device comprises a helical antenna, a neurostimulation signal generator circuit, and an electrode array, and wherein the electrode array is configured to provide a neurostimulation therapy to a nerve target using signals from the neurostimulation signal generator circuit.

10. An external midfield transmitter comprising: a plurality of excitation signal paths coupled to excitable sub -wavelength structures; and a controller circuit configured to control a first phase adjustment circuit to change a phase characteristic of a first signal in a first signal path of the plurality of excitation signal paths, wherein the first signal path is coupled to a first one of the excitable sub -wavelength structures; wherein a power signal transfer efficiency between the transmitter and an implantable device is adjusted in response to the change of the phase characteristic of the first signal.

11. The external midfield transmitter of claim 10, wherein the plurality of excitation signal paths comprise first and second pairs of respective signal paths coupled to respective pairs of excitable sub -wavelength structures; wherein the first pair of signal paths includes the first signal path and a second signal path of the plurality of excitation signal paths; wherein a first phase relationship of signals on the first pair of signal paths is fixed.

12. The external midfield transmitter of claim 11, wherein the first phase relationship includes signals on the first and second signal paths being 180 degrees out of phase.

13. The external midfield transmitter of claim 11, wherein a second phase relationship of signals on the second pair of signal paths is fixed.

14. The external midfield transmitter of claim 13, wherein the first phase relationship includes signals on the first pair of signal paths being 180 degrees out of phase with each other, and the second phase relationship includes signals on the second pair of signal paths being 180 degrees out of phase with each other.

15. The external midfield transmitter of claim 11, wherein a reference phase characteristic for signals on the first pair of signal paths is variable relative to a fixed reference phase characteristic for signals on the second pair of signal paths.

16. A method comprising: determining an axial orientation of an elongated implantable device in body tissue; based on the determined axial orientation of the implantable device, selecting a first polarity of one or more excitation signals; programming a midfield external transmitter to use the selected first polarity of the one or more excitation signals; and using the programmed transmitter, providing a midfield signal to the implantable device.

17. The method of claim 16, comprising: receiving information about a magnitude of the midfield signal received by the implantable device; and in response to the information about the magnitude of the midfield signal received, programming the transmitter to use a second polarity of the one or more excitation signals.

18. The method of claim 17, wherein receiving information about the magnitude of the midfield signal received by the implantable device comprises receiving data from the implantable device via backscatter communication.

19. The method of claim 16, wherein selecting the first polarity of the one or more excitation signals comprises choosing between a Right Handed Circularly Polarized (RHCP) signal and a Left Handed Circularly Polarized (LHCP) signal based on whether the implantable device is oriented more towards a left side or a right side of a patient's body.

20. The method of claim 16, wherein programming the midfield external transmitter comprises adjusting phase shifters coupled to antenna ports of the transmitter to generate the selected first polarity.

21. The method of claim 16, comprising iteratively adjusting the polarity of the one or more excitation signals to optimize power transfer efficiency between the midfield external transmitter and the implantable device to accommodate changes in the axial orientation of the implantable device over time.

22. The method of claim 16, comprising: receiving the midfield signal at the implantable device; and using a neurostimulation generator circuit of the implantable device, generating a neurostimulation signal using power from the midfield signal.

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