The relationship between energy, phase charge, impedance, and perceived sensation in electrotactile stimulation

Abstract

Electrotactile stimulation is a common method of sensory substitution and haptic feedback. One problem with this method has been the large variability in perceived sensation that derives from changes in the impedance of the electrode-skin interface. One way to reduce this variability is to modulate stimulation parameters (current amplitude and pulse duration) in response to impedance changes, which are reflected in the time domain by changes in measured peak resistance, R p . To work well, this approach requires knowing precisely the relationship between stimulation parameters, peak resistance, and perceived sensation. In this paper, experimental results show that at a constant level of perceived sensation there are linear relationships between R p and both peak pulse energy, E p , and phase charge, Q, from which stimulation parameters are easily computed. These linear relationships held across different subjects, sessions, magnitudes of sensation, stimulation locations, and electrode sizes. The average R 2 values for these linear relationships were 0.957 for E p vs. R p and 0.960 for Q vs. R p , indicating a nearly perfect fit.

Parameterization of physical properties of layered body structure into equivalent circuit model

“…The applied source voltage was largely consumed at the skin surface. By shortening pulse width, the voltage drop at the skin surface can be mitigated, which is consistent with the reported experimental results [19,33,34]. These results validate the TPB-ECM method can model the layered body structure more accurately and efficiently than the current ECM and FEM methods.…”

“…Especially for the multifrequency components in TENS pulses, the ECM provides efficient computation to analyze the comprehensive responses to the frequency-dependent body impedances, and thus is better compared to the volume conductor approaches (ex. finite-element method (FEM)), where 3D Maxwell's equations are solved at each frequency separately and then integrated to see the final effect [15][16][17][18].Despite being very useful, the main limitation of conventional ECM is that it uses meta-parameters instead of the physically electrical and geometrical properties of each tissue layer [19,20]. Many researchers have performed in vitro and in vivo impedance experiments to optimize the metaparameters [14,16,21].…”

A portable, arbitrary waveform, multichannel constant current electrotactile stimulator

“…Because skin impedances can typically range from 10 kΩ to 100 kΩ on the forearm [4], electrotactile stimulators need to handle high voltages (typically between 150–300 V [6]). Conventional amplifier integrated circuits have limited supply voltages (≤ ±18 V), so a bootstrap network [8] was implemented, which linearly sweeps the supply rails of the operational amplifiers in the improved Howland current source as a function of the voltage drop across the load, and allows for a significant increase in compliance voltage.…”

“…It is useful as a method for delivering information via haptic feedback to a user, such as touch/pressure feedback in a virtual reality setting [2] or in a hand prosthesis [3]. To elicit the most expressive sensations to a user with the most consistency over time, it is important that the stimulator can produce arbitrary waveforms using constant current stimulation [1], [4]. In order to make this type of stimulation accessible to everyone, it is also important to keep stimulators low-cost.…”

An Epidermal Stimulation and Sensing Platform for Sensorimotor Prosthetic Control, Management of Lower Back Exertion, and Electrical Muscle Activation

“…In such cases, means for accommodating variations in stimulation parameters that occur with changes in the impedance of the electrode–skin interface over time will be important. [45] All such applications can exploit emerging capabilities in wireless power transfer and radio control in skin-like formats. [2,7,46] …”