Wireless Electrode-Tissue Impedance Sensing for Neural Stimulation
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Solution Overview
Problem
Existing implantable stimulator devices face challenges in efficiently delivering electrical stimulation to excitable tissue due to poor power transfer efficiency and the need for complex medical imaging to locate the implant, while also dealing with limited RF power delivery and impedance mismatch issues.
Innovation Solution
A wireless stimulation system using RF energy to power an implantable stimulator device without cables or inductive coupling, incorporating a directional coupler and RF phase detector to adjust stimulus pulses based on electrode-tissue impedance, and a feedback mechanism to monitor and adjust power delivery for optimal therapy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wireless RF power delivery is used to power the implantable stimulator device, then the need for cables and inductive coupling is eliminated, but power transfer efficiency deteriorates
Solution Approach 1:
The system measures the impedance of the electrode-tissue interface and uses this information to adjust the RF power delivery parameters, optimizing power transfer efficiency while maintaining wireless operation. The feedback loop continuously monitors and adjusts the system to compensate for energy losses.
2Measurement precision
If complex medical imaging is used to locate the implant, then implant location can be precisely determined, but the procedure becomes more complex and time-consuming
Solution Approach 1:
The system uses the RF signals already present in the wireless power delivery system as an intermediary to determine implant location and impedance characteristics, eliminating the need for separate complex imaging systems. The RF signals serve dual purposes: power delivery and diagnostic information gathering.
3Ease of operation
If RF power delivery is used to power the implantable device, then cable connections are eliminated, but impedance mismatch issues arise
Solution Approach 1:
The system dynamically adjusts the RF power delivery parameters based on real-time measurements of the electrode-tissue interface impedance. This dynamic adaptation allows the system to maintain optimal impedance matching despite changes in tissue properties or electrode position, ensuring reliable wireless operation.
4Reliability
If stimulus parameters are adjusted in real-time based on impedance measurements, then therapy effectiveness is improved, but the system complexity increases
Solution Approach 1:
The RF power delivery system performs multiple functions: it provides wireless power to the implantable device, measures the electrode-tissue interface impedance, and adjusts stimulus parameters based on these measurements. This multi-functionality reduces the need for separate specialized components, managing system complexity while improving therapy effectiveness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and safe neural stimulation with minimal surgical incision, allowing for real-time adjustment of stimulus parameters and impedance compensation, ensuring effective therapy delivery without complex imaging techniques.
Implementation Method 1
a directional coupler coupled to the second non-inductive antenna and configured to detect a radio frequency (RF) signal reflected from the first non-inductive antenna
Implementation Method 2
a radio frequency (RF) phase detector coupled to the directional coupler and configured to detect phase differences between the RF signal reflected from the first non-inductive antenna and an RF signal transmitted from the second non-inductive antenna to the first non-inductive antenna
Implementation Method 3
an external pulse generator and an implantable wireless stimulator device. The external pulse generator is configured to: transmit a first set of radio-frequency (RF) pulses to the implantable wireless stimulator device via electric radiative coupling
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A method includes: transmitting a first set of radio-frequency (RF) pulses to an implantable wireless stimulator device such that electric currents are created from the first set of RF pulses and flown through a calibrated internal load on the implantable wireless stimulator device; in response to the electric currents flown through a calibrated internal load, recording a first set of RF reflection measurements; transmitting a second set of RF pulses to the implantable wireless stimulator device such that stimulation currents are created from the second set of RF pulses and flown through an electrode of the implantable wireless stimulator device to tissue surrounding the electrode; in response to the stimulation currents flown through the electrode to the surrounding tissue, recording a second set of RF reflection measurements; and characterizing an electrode-tissue impedance by comparing the second set and the first set of RF reflections measurements.