Action potential propagation can be blocked in nerves by alternating current excitation, as is described for example in J. Tanner, “Reversible Blocking of Nerve Conduction by Alternating Current Excitation”, NATURE, Vol. 195, pp. 718-719, Aug. 18, 1962. Typically, a relatively large pair of neighboring cuff electrodes circumferentially surround the nerve with a small lateral distance between them. A high-frequency a.c. waveform, usually in the 1 kHz to 100 kHz frequency range creates an oscillatory current or voltage waveform between these electrodes. Due to the small impedance of the extracellular solution separating the two electrodes—for example, this impedance has a value of approximately 50Ω from a typical 5 V/100 mA measurement—these conventional stimulation systems dissipate a lot of energy as ohmic loss instead of directing the energy efficiently to induce nerve blocking. In fact, the energy consumption of current stimulation systems for nerve blocking is very high compared with those of even the most power-hungry FDA-approved stimulators for nerve excitation. Thus, for long-term clinical use in human beings, circuits and architectures for nerve-blocking a.c. stimulation with a much higher energy efficiency than that of the current systems are needed.
Prior patent-granted work as described in S. Arfin and R. Sarpeshkar, “An Electrode Stimulator with Energy Recycling and Current Regulation”, U.S. Pat. No. 8,700,144 B2, Issued Apr. 15, 2014, has used an inductor to recycle capacitive energy in an electrode impedance, shuttling this energy back and forth between a storage capacitance and electrode capacitance to lower power dissipation in nerve stimulation. This strategy enables the creation of a switching power supply that adaptively and adiabatically adjusts its compliance voltage to be just a little bit higher than that of the electrode voltage, thus minimizing ohmic losses. The differential value between the power supply and electrode voltage is regulated via a feedback loop to maintain constant-current stimulation into the electrode. The savings in power are near the fundamental limits of physics set by ohmic solution resistance. In most nerve stimulators that excite the nerve, electrode impedances are dominant such that this power scheme is as nearly optimal as it can be: one cannot dissipate less power than that caused by current flowing through an ohmic solution resistance. However, in blocking nerve stimulators, electrode impedances are typically not dominant such that it is the nerve impedance energy itself that needs to be recycled, not the electrode impedance energy. Furthermore, the waveform required for stimulation needs to be an oscillatory a.c. waveform such that the adiabatic switching power-supply techniques are not a power-efficient method for creating such a waveform.
The system described in Franke, Kilgore, and Bhadra, “Systems and Methods that Provide an Electrical Waveform for Neural Stimulation or Nerve Block” focuses on methods to achieve an oscillatory waveform with charge balancing but has little impact on energy: It creates an oscillatory waveform in one circuit component, ensuring that it is charge balanced in another circuit component, and then couples the final output of the second circuit component as an electrical waveform suitable for nerve stimulation or blocking. One embodiment described in Franke et al. uses an inductor. It is easy to create an oscillator with an inductor as is well known in elementary electrical engineering, physics, and in the public domain, for example, see R. Sarpeshkar, “Ultra Low Power Biolectronics: Fundamentals, Biomedical Applications, and Bio-inspired Systems”, Cambridge University Press, 2010. However, if the nerve and electrodes are separated from the waveform generators that create the oscillation, and not part of it, the nerve capacitive energy does not resonate with the inductor, just the capacitive energy of a circuit component in the oscillator. Thus, there is little energy benefit, and not surprisingly, none claimed.