Investigation on experimental method of low-impedance materials using modified Hopkinson pressure bar

To increase the detectability of split Hopkinson pressure bar （SHPB） of low-impedance materials, modifications were conducted on traditional SHPB apparatus with a PMMA tube to output transmitted signal, and weak signals were further amplified by semiconductor strain gauges. Experiments on soft rubbers and cushioning foam materials were carried out. In order to analyze the accuracy of the experimental results, the stress equilibrium issues involved in the assumptions of SHPB were investigated. First, by way of re-constructing loading process of incident wave, the stress- strain curve was obtained, along with the stress equilibrium ratio of specimen. Secondly, the influences on the accuracy of stress-strain curves were investigated through the elastic modulus comparisons. And the results illustrate that the bilinear incident wave from experiments can ensure the stress equilibrium deformation of specimen after 2 normalized times, much sooner than ramp incident waves. Moreover, it even facilitates specimen deformation with a constant strain rate. The results confirm that the detectability of the modified SHPB can be down to tens kPa with enough accuracy level.

Claw-shaped flexible and low-impedance conductive polymer electrodes for EEG recordings: Anemone dry electrode

Electroencephalogram(EEG) signals provide important brain information in healthcare settings. Wet electrodes have several limitations, including their time-consuming preparation and no long-term acquisition, and dry electrodes have become a promising candidate. However, dry electrodes face several challenges related to signal quality, comfort, conductivity and cost.This study aims to develop and evaluate a novel dry electrode for EEG recordings. The electrode material properties are characterized by electrochemical, mechanical force, and skin measurements. The electrode performance is evaluated by comparing the impedance, signal-to-noise ratio(SNR), and EEG signal features of the proposed electrode with those of a wet electrode and two commercial dry electrodes. The dry electrode design is based on the biological structure of the sea anemone and demonstrates an improved scalp fit and reduced signal noise and motion artifacts. The electrode materials include advanced conducting polymers combined with thermoplastic elastomers(TPEs) and carbon nanotubes(CNTs), which exhibit good electrical conductivity, mechanical properties, and safety. A low-cost injection molding fabrication method is proposed. The dry electrodes show a scalp contact impedance of 7 kΩ at 20 Hz, which is lower than that of wet and commercial dry electrodes.Resting-state EEG and event-related potential signals collected by the anemone dry electrode achieved more than 90% similarity with signals acquired by wet electrodes. Thus, a low-cost, comfortable anemone dry electrode that exhibits excellent EEG recording performance is presented. The anemone dry electrode represents an important technological advance in material and structural design for EEG recording sensors.

High‑Performance Flexible Microneedle Array as a Low‑Impedance Surface Biopotential Dry Electrode for Wearable Electrophysiological Recording and Polysomnography

Microneedle array(MNA)electrodes are an effective solution to achieve high-quality surface biopotential recording without the coordination of conductive gel and are thus very suitable for long-term wearable applications.Existing schemes are limited by flexibility,biosafety,and manufacturing costs,which create large barriers for wider applications.Here,we present a novel flexible MNA electrode that can simultaneously achieve flexibility of the substrate to fit a curved body surface,robustness of microneedles to penetrate the skin without fracture,and a simplified process to allow mass production.The compatibility with wearable wireless systems and the short preparation time of the electrodes significantly improves the comfort and convenience of electrophysiological recording.The normalized electrode–skin contact impedance reaches 0.98 kΩcm^(2)at 1 kHz and 1.50 kΩcm^(2)at 10 Hz,a record low value compared to previous reports and approximately 1/250 of the standard electrodes.The morphology,biosafety,and electrical/mechanical properties are fully characterized,and wearable recordings with a high signal-to-noise ratio and low motion artifacts are realized.The first reported clinical study of microneedle electrodes for surface electrophysiological monitoring was conducted in tens of healthy and sleep-disordered subjects with 44 nights of recording(over 8 h per night),providing substantial evidence that the electrodes can be leveraged to substitute for clinical standard electrodes.