Phantom model of transcutaneous electrical stimulation with kilohertz signals

Transcutaneous electrical stimulation (TES) of nerve fibers may be optimized by overcoming the impedance of the skin using high-frequency (HF) stimulation signals. The excitation properties of nerve fibers depend on the spatiotemporal distribution of the extracellular field, and therefore quantifying the potentials during HF-TES is warranted. We present a physical phantom of TES that includes elements representing the skin and underlying tissue, and incorporates dispersion of the electrical conductivity as required during HF stimulation. We used both agar-based gels and biological materials, and doped the gels with graphite to add dispersion. We measured the dielectric properties of the materials, which we modified by adjusting the concentration of sodium chloride and graphite. We assembled up to three layers of material, and quantified the impedance as a function of frequency and depth. The impedance at any depth decayed with frequency, which suggests that HF signal may reach deeper structures in TES.