Helmholtz Coils Based WPT Coupling Analysis of Temporal Interference Electrical Stimulation System

Abstract

Electrical nerve stimulation (ENS) is clinically important in treating neurological diseases. This paper proposes a novel temporally interfering wireless power transfer (WPT) system, based on Helmholtz coils, to address energy depletion and the miniaturization of wireless power transfer systems for implantable devices. Compared to conventional WPT systems, this paper uses Helmholtz coils with a centrosymmetric structure as the transmitting coils. A more uniform and stable magnetic field was obtained through structural improvements. It also improves the problem that changes in the receiving coil’s position affect the transmission power’s stability. Based on the principle of temporal interference (TI), two transmitting coils with a slight frequency difference generate a superposition of magnetic fields on the receiving coil and then induce a low-frequency electrical signal on it. The electrical stimulation system applies stimulation parameters of a specific intensity and frequency directly to the target nerve with electrodes connected to it. This eliminates the need for the conventional high-frequency signal to low-frequency signal processing circuitry and reduces the device’s size. In this paper, numerical calculations and an experimental verification of the proposed system are carried out. The magnetic field distribution and the receiving coil current waveform of the system were tested to verify the effectiveness and stability of the proposed design. The experimental results showed that the proposed wireless power transfer system can generate electrical signals of the desired waveform in the receiving coil. Its frequency of 10 Hz and amplitude of 42.4 mA meet the requirements for the electrical stimulation of the sciatic nerve.

Electromagnetic Interaction Model between an Electric Motor and a Magnetorheological Brake

“…This configuration aims to achieve a consistent flow across the entire brake and its components. Despite the field's uniformity, the values are higher at the bottom of the brake compared to most of its surface, echoing findings from similar cases [22]. Like previous configurations, the magnetic field exhibits greater intensity at the bottom of the fluid and lower values on the top, creating a more blended distribution throughout.…”

“…]. In summary, as has also been shown by [22,26], only defining a specific geometry for the motor allows implementation of the kind of arrangement of a Halbach array style. The Helmholtz coil arrangement was determined to be the optimum choice for mimicking the motor's magnetic field in various setup configurations due to the array's smaller and shorter magnetic field.…”

“…This specialized source was crafted to assess the impact of varying magnetic flux densities on the brake. Helmholtz coils, comprising a pair of identical thin coils positioned apart to optimize the uniformity of the magnetic field in the central volume, were employed for this purpose [22]. While alternatives like square, rectangular, or polygonal coils exist, the common configuration entails two circular coils separated by a distance equal to the radius.…”

“…This constant assumes substantial values, ranging from 1 to 10 8 , so k = 1 ∼ 10 8 , allowing flexibility in adjusting magnetic flux diversity in calculations and simulations while keeping other parameters at a more natural level. The corresponding data for this modified geometry can be found in Table 1, coming from multiple previous analyses [22,23]. Having established the data parameters, the focus shifted to determining an optimal geometric configuration representative of the magnetic flux emitted by a motor.…”