Fabrication and Dielectric Validation of an Arm Phantom for Electromyostimulation

Abstract

Electromyostimulation (EMS) is an up-and-coming training method that demands further fundamental research regarding its safety and efficacy. To investigate the influence of different stimulation parameters, electrode positions and electrode sizes on the resulting voltage in the tissue, a tissue mimicking phantom is needed. Therefore, this study describes the fabrication of a hydrogel arm phantom for EMS applications with the tissue layers of skin, fat, blood and muscle. The phantom was dielectrically validated in the frequency range of 20 Hz to 100 Hz. We also conducted electromyography (EMG) recordings during EMS on the phantom and compared them with the same measurements on a human arm. The phantom reproduces the dielectric properties of the tissues with deviations ranging from 0.8% to more than 100%. Although we found it difficult to find a compromise between mimicking the permittivity and electrical conductivity at the same time, the EMS-EMG measurements showed similar waveforms (1.9-9.5% deviation) in the phantom and human. Our research contributes to the field of dielectric tissue phantoms, as it proposes a multilayer arm phantom for EMS applications. Consequently, the phantom can be used for initial EMS investigations, but future research should focus on further improving the dielectric properties.

Keywords: dielectric validation; electrical muscle stimulation; electromyography; electromyostimulation; tissue phantom.

Figure 1

Schematic representation of the layered gelatin phantom.

Figure 2

Measuring setup for dielectric validations of the samples. (a) Placing the phantom sample on the copper plate; (b) parallel plate setup with sandwiched sample; (c) measurement setup with parallel plate method and LCR meter.

Figure 3

Possible equivalent circuits of the sample during dielectric measurement. (a) Parallel circuit and (b) series circuit of capacitance and resistance.

Figure 4

Measurement setup for electromyography (EMG) recordings during electromyostimulation (EMS) on the arm phantom.

Figure 5

Comparison of the measured dielectric properties of a 25% gelatin sample with reference data from the study of Kalra et al. [21]: (a) relative permittivity, (b) electrical conductivity.

Figure 6

Dielectric properties of different tissue phantoms compared to reference values of biological tissue from IT’IS database [23].

Figure 7

Relative deviations in conductivity and permittivity of the selected phantom samples over the course of frequency.

Figure 8

EMG signal section during electrical stimulation on the arm phantom vs. on a human arm: (a) phantom, 50 Hz, intensity level 15; (b) human, 50 Hz, intensity level 15; (c) phantom, 100 Hz, intensity level 23; (d) human, 100 Hz, intensity level 23. Pulse width: 300 µs, sampling rate: 4 kHz.