Midfield power source for wireless implanted devices
Systems, devices, and methods discussed herein include wireless midfield transmitters and implantable receiver devices. A midfield transmitter can be configured to provide signals outside of tissue that give rise to propagating signals inside of tissue. The present subject matter includes a protection circuit for a transmitter device, a layered transmitter device, an implantable receiver device, implantation and extraction methods, test and assembly methods, and the like. In an example, a protection circuit includes a first control circuit to receive an RF drive signal and conditionally provide an output signal to an antenna. A second control circuit can generate a control signal based on the antenna output signal and/or information about the RF drive signal. A gain circuit can provide the RF drive signal to the first control circuit. The gain circuit can change an amplitude of the RF drive signal based on the control signal from the second control circuit.
1. A tunable transmitter comprising:
an excitation structure configured to receive an excitation signal;
a first substrate;
a first emitter comprising first and second conductive regions excitable by the excitation structure in response to the excitation structure receiving the excitation signal, wherein the first and second conductive regions are provided on a first surface of the first substrate and the first and second conductive regions are spaced apart from the excitation structure and the first and second conductive regions are electrically decoupled from each other on the first surface of the first substrate and from the excitation structure, and wherein an insulator electrically separates the first and second conductive regions; and
a variable capacitor coupling the first and second conductive regions of the first emitter, the variable capacitor being configured to adjust a capacitance characteristic of the first emitter to tune a resonant frequency of the tunable transmitter based on at least one of a reflection coefficient or feedback information from a receiver device.
2. The tunable transmitter of claim 1 , further comprising a control circuit configured to provide an indication about whether the tunable transmitter is or is likely to be near body tissue based on information about the reflection coefficient.
3. The tunable transmitter of claim 1 , wherein the excitation structure comprises a stripline provided on a second surface adjacent and parallel to the first substrate, the stripline extending at least partially over the first emitter.
4. The tunable transmitter of claim 3 , wherein the first conductive region of the first emitter comprises an inner disc region and the second conductive region of the first emitter comprises an outer annular region, and wherein the stripline extends at least partially over the inner disc region of the first emitter.
5. The tunable transmitter of claim 4 , wherein the inner disc region and the outer annular region have substantially the same surface area.
6. The tunable transmitter of claim 1 , further comprising:
a ground plane; and
a second substrate, wherein the second substrate is provided between the ground plane and the excitation structure.
7. The tunable transmitter of claim 1 , wherein the tunable transmitter is configured to generate an adaptive steering field in tissue, wherein the adaptive steering field has a frequency between about 300 MHz and 3000 MHz.
8. The tunable transmitter of claim 1 , further comprising an excitation circuit configured to provide the excitation signal to the excitation structure, the excitation signal having a frequency between about 300 MHz and 3000 MHz.
9. The tunable transmitter of claim 1 , wherein a capacitance value of the variable capacitor is configured to be updated based on the reflection coefficient or based on the feedback from the receiver device.
10. The tunable transmitter of claim 1 , further comprising:
a signal generator coupled to the excitation structure; and
processing circuitry configured to:
cause the signal generator to energize the excitation structure with a first drive signal having a first frequency; and
sweep parameter values of the variable capacitor to change a capacitive coupling between the first and second conductive regions of the first emitter to thereby tune the first emitter to multiple different resonant frequencies at respective multiple instances.
11. The tunable transmitter of claim 10 , wherein the processing circuitry is further configured to:
for each of the multiple different resonant frequencies, detect respective amounts of power reflected by the first emitter when the first emitter is energized by the first drive signal;
identify a particular parameter value, among the swept parameter values, of the variable capacitor corresponding to a detected minimum amount of power reflected by the first emitter; and
programming the variable capacitor to the particular parameter value to communicate power and/or data to an implanted device using a wireless propagating wave inside body tissue.
12. The tunable transmitter of claim 11 , wherein the processing circuitry is further configured to:
based on information about capacitance value states of the variable capacitor and the identified particular parameter value, provide a likelihood indication that the tunable transmitter is positioned within a specified distance range of a body tissue interface.
13. The tunable transmitter of claim 12 , wherein the processing circuitry is further configured to:
when the likelihood indication indicates the tunable transmitter is within the specified distance range of the body tissue interface, communicate power and/or data with an implantable device using the excitation structure and the variable capacitor tuned to the particular parameter value.
14. The tunable transmitter of claim 11 , wherein the excitation structure is configured to energize a first one of the first and second conductive regions distributed about the first emitter; and
wherein the detecting the respective amounts of power reflected by the first emitter includes receiving a reflected signal using a second one of the first and second conductive regions.
15. The tunable transmitter of claim 10 , wherein the first drive signal includes a frequency between about 850 MHz and 950 MHz.
16. The tunable transmitter of claim 10 , wherein the first emitter is substantially symmetrical about an axis extending through the first and second conductive regions.
17. The tunable transmitter of claim 1 , wherein the excitation structure is a subwavelength conductive member.
18. A transmitter comprising:
an excitation structure configured to receive an excitation signal;
a signal generator coupled to the excitation structure;
a first substrate;
a first emitter comprising first and second conductive regions provided on a first surface of the first substrate and spaced apart from the excitation structure;
a variable capacitor coupling the first and second conductive regions of the first emitter, the variable capacitor configured to tune a resonant frequency of the transmitter; and
processing circuitry configured to:
cause the signal generator to energize the excitation structure with a first drive signal having a first frequency; and
sweep capacitance values of the variable capacitor to change a capacitive coupling between the first and second conductive regions of the first emitter to tune the first emitter to multiple different resonant frequencies at respective multiple instances;
wherein the processing circuitry is further configured to:
for each of the multiple different resonant frequencies, detect respective amounts of power reflected by the first emitter when the first emitter is energized by the first drive signal;
identify a particular capacitance value, of the swept capacitance values, corresponding to a detected minimum amount of power reflected by the first emitter; and
adjusting the variable capacitor to the particular capacitance value.
19. The transmitter of claim 18 , wherein the processing circuitry is further configured to:
based on both capacitance value states of the variable capacitor and the identified particular capacitance value, provide a likelihood indication that the transmitter is positioned within a specified distance range of a body tissue interface; and
communicate power and/or data with an implantable device using the excitation structure and the variable capacitor tuned to the particular capacitance value when the likelihood indication indicates the transmitter is within the specified distance range of the body tissue interface.
20. The transmitter of claim 18 , wherein the first conductive region of the first emitter comprises an inner disc region and the second conductive region of the first emitter comprises an outer annular region, and wherein the excitation structure extends at least partially over the inner disc region.
21. The transmitter of claim 18 , wherein the first drive signal has a frequency between 850 MHz and 950 MHz.