Kiyo Fujimoto

Passive monitoring techniques have been used for peak temperature measurements during irradiation tests by exploiting the melting point of well-characterized materials. Recent efforts to expand the capabilities of such peak temperature detection instrumentation include the development and testing of additively manufactured (AM) melt wires. In an effort to demonstrate and benchmark the performance and reliability of AM melt wires, we conducted a study to compare prototypical standard melt wires to an AM melt wire capsule, composed of printed aluminum, zinc, and tin melt wires. The lowest melting-point material used was Sn, with a melting point of approximately 230 °C, Zn melts at approximately 420 °C, and the high melting-point material was aluminum, with an approximate melting point of 660 °C. Through differential scanning calorimetry and furnace testing we show that the performance of our AM melt wire capsule was consistent with that of the standard melt-wire capsule, highlighting a path towards miniaturized peak-temperature sensors for in-pile sensor applications.

Soft structural textiles, or softgoods, are used within the space industry for inflatable habitats, parachutes and decelerator systems. Evaluating the safety and structural integrity of these systems occurs through structural health monitoring systems (SHM), which integrate non-invasive/non-destructive testing methods to detect, diagnose, and locate damage. Strain/load monitoring of these systems is limited while utilizing traditional strain gauges as these gauges are typically stiff, operate at low temperatures, and fail when subjected to high strain that is a result of high loading classifying them as unsuitable for SHM of soft structural textiles. For this work, a capacitance based strain gauge (CSG) was fabricated via aerosol jet printing (AJP) using silver nanoparticle ink on a flexible polymer substrate. Printed strain gauges were then compared to a commercially available high elongation resistance-based strain gauge (HE-RSG) for their ability to monitor strained Kevlar straps having a 26.7 kN (6 klbf) load. Dynamic, static and cyclic loads were used to characterize both types of strain monitoring devices. Printed CSGs demonstrated superior performance for high elongation strain measurements when compared to commonly used HE-RSGs, and were observed to operate with a gauge factor of 5.2 when the electrode arrangement was perpendicular to the direction of strain.

A fully inkjet printed and flexible multilayer graphene based three electrode device showed electrochemical reversibility.

This work aims to investigate the influence of various electrode materials on the signal‐to‐noise ratio (SNR) of passive microelectrode arrays (MEAs) intended for use in neural interfaces. Noise reduction substantially improves the performance of systems which electrically interface with extracellular solutions. The MEAs are fabricated using gold, indium tin oxide (ITO), inkjet printed (IJP) graphene, and chemical vapor deposited (CVD) graphene. 3D‐printed Nylon reservoirs are adhered to glass substrates with identical MEA patterns and filled with neuronal cell culture media. To precisely control the electrode area and minimize the parasitic coupling of metal interconnects and solution, SU‐8 photoresist is patterned to expose only the area of the electrode to solution and cap the remainder of the sample. Voltage signals with varying amplitude and frequencies are applied to the solution using glass micropipettes, and the response is measured on an oscilloscope from a microprobe placed on the contact pad external to the reservoir. The time domain response signal is transformed into a frequency spectrum, and SNR is calculated. As the magnitude or the frequency of the input signal gets larger, a significantly increased signal‐to‐noise ratio was observed in CVD graphene MEAs compared to others. This result indicates that 2‐dimensional nanomaterials such as graphene can provide better signal integrity and potentially lead to improved performance in hybrid neural interface systems.

This paper reports the first known investigation of power dissipation and electrical breakdown in aerosol-jet-printed (AJP) graphene interconnects. The electrical performance of aerosol-jet printed (AJP) graphene was characterized using the Transmission Line Method (TLM). The electrical resistance decreased with increasing printing pass number (n); the lowest sheet resistance measured was 1.5 kΩ/sq. for n = 50. The role of thermal resistance (R_TH) in power dissipation was studied using a combination of electrical breakdown thermometry and infrared (IR) imaging. A simple lumped thermal model ($${\boldsymbol{\Delta }}{\bf{T}}={\bf{P}}{\boldsymbol{\times }}{{\bf{R}}}_{{\bf{TH}}}$$ Δ T = P × R TH ) and COMSOL Multiphysics was used to extract the total R_TH, including interfaces. The R_TH of AJP graphene on Kapton is ~27 times greater than that of AJP graphene on Al₂O₃ with a corresponding breakdown current density 10 times less on Kapton versus Al₂O₃.