Erich D. Bain

Developing an Alternative to Roma Plastilina #1 as a Ballistic Backing Material for the Ballistic Testing of Body Armor

Ballistic clay (Roma Plastilina #1; RP1) is currently used as a backing material that is meant to simulate the penetration resistance of the human body during the ballistic testing of body armor. RP1 is a modeling clay with a primary market in the artistic community. Over time, RP1’s formulation and performance have changed to meet the demands of the artistic community. As a result, RP1 must now be heated to 100 °F to obtain the desired response and exhibits a strong temperature-dependent performance such that the backing material is considered out of calibration after 45 min. This presentation will focus on our efforts to develop a replacement for RP1 that exhibits the desired backing material response at room temperature with minimal temperature-dependence. Specifically, the challenges of designing a viscoplastic material with a controlled response that exhibits dimensional stability while providing minimal elastic recovery from deformation even at high strain rates and linking the quasistatic mechanical response with the ballistic performance.

Carbon nanofiber-filled conductive silicone elastomers as soft, dry bioelectronic interfaces

Soft and pliable conductive polymer composites hold promise for application as bioelectronic interfaces such as for electroencephalography (EEG). In clinical, laboratory, and real-world EEG there is a desire for dry, soft, and comfortable interfaces to the scalp that are capable of relaying the μV-level scalp potentials to signal processing electronics. A key challenge is that most material approaches are sensitive to deformation-induced shifts in electrical impedance associated with decreased signal-to-noise ratio. This is a particular concern in real-world environments where human motion is present. The entire set of brain information outside of tightly controlled laboratory or clinical settings are currently unobtainable due to this challenge. Here we explore the performance of an elastomeric material solution purposefully designed for dry, soft, comfortable scalp contact electrodes for EEG that is specifically targeted to have flat electrical impedance response to deformation to enable utilization in real world environments. A conductive carbon nanofiber filled polydimethylsiloxane (CNF-PDMS) elastomer was evaluated at three fill ratios (3, 4 and 7 volume percent). Electromechanical testing data is presented showing the influence of large compressive deformations on electrical impedance as well as the impact of filler loading on the elastomer stiffness. To evaluate usability for EEG, pre-recorded human EEG signals were replayed through the contact electrodes subjected to quasi-static compressive strains between zero and 35%. These tests show that conductive filler ratios well above the electrical percolation threshold are desirable in order to maximize signal-to-noise ratio and signal correlation with an ideal baseline. Increasing fill ratios yield increasingly flat electrical impedance response to large applied compressive deformations with a trade in increased material stiffness, and with nominal electrical impedance tunable over greater than 4 orders of magnitude. EEG performance was independent of filler loading above 4 vol % CNF (< 103 ohms).