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Modern polymer bonded explosives (PBX) are often characterized by a sensitive response to external thermomechanical insult that in some cases lead to accidental detonation. Current strategies for desensitizing PBXs come at the expense of a significant reduction in performance. A possible method for desensitizing PBX without adverse performance effects is the multifunctional tailoring of mechanical properties through strategic incorporation of multi-walled carbon nanotubes (MWCNTs) directly into the binder phase. In this work, a fabrication method is presented that produces polymer bonded simulants (PBS) of PBX that incorporate MWCNTs into the binder phase, hydroxyl-terminated polybutadiene (HTPB). These materials were characterized via microscopy and unconfined quasi-static compression testing to determine the effects of MWCNTs. Quasi-static compression showed evidence of a MWCNT induced structural skeleton effect that provided the binder with an increased strength, load transfer, and a greater ability to resist strain localizations prior to failure. These enhancements demonstrate the potential of using MWCNTs to enhance energetic materials.

Syngeneic models provide a robust platform to test new and cutting edge immune-oncology therapies. CT26 is a popular syngeneic colon carcinoma model that is known to respond to immune checkpoint inhibitors when engrafted into Balb/c mice as a subcutaneous flank tumor. The subcutaneous flank implant location provides a robust model, that is easy to set up, and allows for continuous measurement of the tumor growth by calipering. However, the location of tumor implant has been shown to impact tumor microenvironment and immune response for a number of cancer cell lines (Zhao 2017, Brand 2021, Oliver 2018). In addition to subcutaneous flank tumors, CT26 can be implanted to generate a lung metastasis or peritoneal metastasis model. We were interested to see if the lung metastasis or peritoneal metastasis CT26 model responded differently to immune checkpoint inhibition compared with the subcutaneous model and whether the different implant locations resulted in changes to the tumor infiltrating lymphocytes. CT26 cells were either injected intravenously to induce a lung metastasis model, intraperitoneally to produce a peritoneal metastasis model, or subcutaneously to generate a solid flank tumor model. Immune checkpoint inhibitor (ICI) therapy began on Day 5 following implant in each model, and tumor progression or survival provided the endpoint for analysis. In addition, tumor infiltrating leukocytes were assessed by flow cytometry to determine differences in the overall tumor microenvironment for each model. The response to both anti-PD-1 and anti-CTLA-4 monotherapies were strongest in the subcutaneous flank model, followed by moderate responses in the lung metastasis model, and no significant response to either ICI in the peritoneal metastasis model. This provides researchers with an opportunity to assess the ability of novel immune-oncology therapies to provoke an immunogenic response in models with identical antigenicity, but different tumor microenvironments based on the tumor location. Citation Format: Fei Zhao, Caitlin Thompson, Nicole Barnes, José Roques, Terrence Coleman, Tyler Rowe, Joseph Kolb, Chassidy Hall, Patrick Fadden. Site specific tumor microenvironments modulate the immune checkpoint inhibitors response in models of CT26 colon carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2872.

Non-Foster networks can be used to match the impedances of highly reactive loads to resistive loads over very broad bandwidths. They are used to design ultrawideband, electrically small antennas (ESAs) in which negative impedance converters (NICs) eliminate the very large input reactances of the antennas over wide bandwidths. NICs, however, use active elements that put upper bounds on their power-handling capability. We examine the limitations of the power-handling capabilities of non-Foster impedance-matching networks that use gridded vacuum tubes and compare them with those of the networks using power transistors. Specifically, we examine the requirements for transmitting 5 W of power from a 5.18-m monopole antenna and from an ideal, minimum-quality factor (Q) dipole antenna over the 3n30-MHz band. We describe the situations in which tubes outperform transistors and examine the efficiency levels that can be realistically achieved. The results provide important guidelines for determining the suitability, or lack thereof, of using non-Foster matching networks for ultrawideband transmitting ESAs. Moreover, we offer a method for selecting an active device and the antenna type that can deliver the required power level given the bandwidth and efficiency constraints.

Metal-based epsilon negative metamaterials (MTMs) have been investigated for use as a waveguide liner to allow for an electromagnetic passband below the cutoff frequency of the empty waveguide. In this paper, we investigate both the theory and a practical implementation of an MTM lined waveguide. Specifically, we have investigated the use of inductive meander lines as the elements of a vacuum-electronics-compatible MTM structure to line one side of a rectangular waveguide. The MTM implementation creates an effective medium with a Drude–Lorentz dispersion response. The transmission of the waveguide and dispersion were both simulated and measured experimentally and demonstrate good agreement.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) has been shown to be capable of producing large gains over wide bandwidths. Previous theoretical investigation of the ME-RWA focused on an idealized case using a homogenous dielectric with Drude dispersion to provide the negative permittivity required to achieve high gains. This paper reports the results of investigating practical metamaterial implementations with approximate Drude-type responses that enable the realization of a ME-RWA. Using these metamaterials, an architecture for a ME-RWA using periodically spaced inductive meandered lines is proposed. Our theoretical analyses and particle in cell simulations of this device predict that the proposed technique provides a practical method of implementing ME-RWAs, capable of providing a large gain over a substantial bandwidth.

The resistive wall amplifier (RWA), a vacuum electron device, has been theoretically predicted to provide extremely high gain. However, the properties of practical, naturally available bulk materials for the resistive wall support structure significantly reduce achievable gain. This paper investigates the capabilities of a metamaterial-enhanced RWA (ME-RWA). We predict that using epsilon-negative metamaterials can yield high gains that closely approach the idealized performance limit. ME-RWAs may exhibit bandwidths and gains much higher than many commercially available vacuum electron devices.

Resistive wall amplifiers are wideband vacuum electron devices that suffer from low gain due to available resistive materials 1. Metamaterial-enhanced resistive wall amplifiers (MERWAs) have been demonstrated, theoretically, to be a candidate for wideband, high gain, and high power microwave amplification 2. Implementation of a MERWA requires the use of an epsilon-negative (ENG) liner in a waveguide structure. A periodic array of inductively meandered wires have been demonstrated as one possible implementation of the ENG liner 3. In this work, we investigated how the choice of material for the periodic elements affects the device's performance. In particular, we have constructed metamaterial (MTM) structures using meander elements constructed from metals with very different conductivity values, copper and stainless steel. Modification of the element's conductivity drastically changes the performance of both the electromagnetic waves that propagate in the structure as well as the resistive wall mechanism.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) has been demonstrated, through theory, to be a high gain wideband amplifier. This work presents the design and preliminary cold test results of a constructed ME-RWA. In this ME-RWA design, the metamaterial consists of a periodic arrangement of inductive meandered lines. To verify the properties of the metamaterial, the structure's dispersion was measured and found to be in good agreement with simulation and theory.

Electron hop funnels have been simulated using the new version of the particle trajectory simulation software, Lorentz-2E. Simulations were conducted to determine the validity of the version 9.2 results and the consistency of the results with a previous version of the software, version 8. In addition, a new method of injecting a uniform current with all rays of equal charge is discussed, and the results of the method are presented. Version 9.2 of the software was successfully implemented and a new emission model was tested. The transition of the software version will allow for faster simulation times of the electron hop funnel simulations to increase the understanding of the device.

Insulating funnels, called electron hop funnels, use secondary electron emission and an electric field created by an electrode to transport current through the device. The surface charge along the funnel wall self-adjusts to get unity-gain transmission. Electron hop funnels allow increased control over the spatial and energy uniformity of the transmitted beam from a field emitter array. Measurements performed on the relationship between transmission through the device and the electrode voltage has shown hysteresis. To better understand the origin of the hysteresis, simulations have been performed using the particle trajectory code Lorentz 2E. The simulations reveal two very important mechanisms that define the transmission through the funnel. The simulations also show that hysteresis is a fundamental characteristic of hop funnels.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) is a wideband, high power, vacuum electron device1. In the ME-RWA, the resistive liner of the traditional resistive wall amplifier has been replaced with a lossy epsilon negative (ENG) metamaterial. This work investigated a relativistic, high power microwave (HPM) ME-RWA. Specifically, we examined the feasibility of a 50 MW, L-Band ME-RWA. The investigation of the relativistic HPM ME-RWA includes a theoretical investigation and particle-in-cell (PIC) simulations. In our theoretical analysis, we have modified the traditional resistive wall theory, presented by Birdsall and Whinnery2, to include relativistic effects. To simulate the ME-RWA's performance, we have used the CST Particle Studio software and used homogenous dielectrics with a Drude dispersion response, with the plasma frequency higher than the operating frequency, to emulate materials with negative permittivity. The results of our relativistic ME-RWA theory as well as the results of our PIC simulation will be presented to demonstrate the superior performance of the ME-RWA.

Non-foster impedance matching circuits are one method to achieve ultra-wideband matching to electrically small antennas (ESAs). In this work, we examine the requirements of an active element that can accommodate the high voltage and current swings required to drive an ESA. We have examined the requirements necessary to transmit 5 W of power from an electrically small dipole and loop antenna, each with a maximum linear dimension of 1 m, across the entire high frequency (HF) band. In addition, we evaluated the use of gridded vacuum tubes as the active elements of the non-foster matching circuit.

The metamaterial-enhanced resistive wall amplifier (ME-RWA) has been shown to theoretically have higher wideband gain than many commercially available high power microwave amplifiers. Previous work has idealized the situation by assuming the metamaterial of the structure to be a homogenous dielectric with a Drude dispersion model. This work investigates a practical meander line implementation of the metamaterial liner for the ME-RWA.

Non-foster matching networks can provide significantly larger bandwidth over passive matching networks. However, when a non-foster matching network, which contains active devices, is used to match electrically small antennas (ESAs), which have high Q impedances, very high currents and voltages are necessary to drive the antenna in transmit applications. This work demonstrates that the selected active element in the non-foster circuit has a large effect on the maximum power that can be radiated from an ESA. High power transistors and triode vacuum tubes are investigated as the active element of the non-foster circuit to improve maximum radiated power.

Summary form only given. A microplasma in a slit structure has been generated using an Inductively Coupled Plasma (ICP) source as a plasma reservoir. This unique configuration uses a slit structure fabricated in a Low Temperature Co-Fired Ceramic (LTCC) substrate. At the top of the substrate, a spiral ICP antenna [1] is fabricated 35 μm below the surface of the LTCC. This antenna is used to generate plasma above the substrate and over a slit that has been milled through the substrate at the center of the antenna spiral. The operating frequency is 800-1000 MHz with power levels from 0.5 to 50 W. Slits have been tested with diameters ranging from 0.4 to 1.2 mm. Embedded in the slits are two electrodes placed directly opposite each other. These electrodes are exposed to the slit vacuum space to act as electrodes for a DC glow discharge. When the ICP source is operated at pressures from 0.1 to 40 Torr in argon, a DC glow discharge can be initiated from the exposed electrodes. One of the electrodes is biased positive with respect to the antenna and the second electrode, both held at ground. This bias pulls electrons into the slit or channel and initiates the DC discharge between the two electrodes or between the electrode and the plasma reservoir. In this second case, the reservoir acts a virtual cathode. The goal of the project is to create transistor functionality by using an additional gate electrode. Experimental results of the device operation over a range of pressures and ICP powers will be presented. Simulation of the device structure using OOPIC will also be presented.

Summary form only given. Electron hop funnels have been constructed of Low Temperature Co-fired Ceramic (LTCC) to enhance the performance of gated field emitter arrays (FEAs). Electrons are emitted into the wide end of the funnel, transmitted through the funnel, and exit through the narrow opening. An electrode, referred to here as the hop electrode, is placed around the narrow end of the funnel to create the electric field necessary to sustain electron transport through the funnel.

This Poster Session discusses the following: PMOS Device Performance Improvement using Buried Contact Implants; Deep Trench Patterning and Lift-off Resist in Micro-fluidic Devices; and Nano-ionic Conductive Bridge Memristors based on Chalcogenide Glasses: Electrical Performance Characterization and Modeling.

Summary form only given. Traditionally, the cathodes used in Microwave Vacuum Electron Devices (MVEDs) have been thermionic cathodes. While thermionic cathodes are extremely reliable and well developed, they do have their disadvantages. Thermionic cathodes require heater power and do not allow for spatial or temporal control. The advances of processing techniques have enabled Field Emitter Arrays (FEAs) to emit the electrons with nearly the same current as thermionic cathodes and with gate voltages on the order of 100 Volts. FEAs are more efficient and allow spatial control. While the use of thermionic cathodes in MVEDs is well explored, the use of FEAs is not. Our study focuses on the use of FEAs in a linear Cross-Field Amplifier (CFA) configuration. To inject the electrons into this configuration, a plate with slits is used to protect the FEAs. The plate is fabricated from Low Temperature Co-fired Ceramic (LTCC). The sloped wall slits form hop funnels. These hop funnels use the secondary electron emission properties of a dielectric surface to concentrate electron emission from a FEA and enhance uniformity and spatial distribution. The injected electrons will cycloid down the tube with the E×B velocity and will interact with the RF wave on a slow wave circuit. In this work we will look at the effects of using hop structures with slit geometries as well as standard hop funnel holes using different wall slopes. Two different hop funnels will be tested each with a different wall slope. Measurements will include the funnel IV characteristics and the electron energy distribution at the funnel exit. We will also look at the electron trajectories down the length of the CFA tube. We will monitor the emitter current and will measure the currents into the anode, collector, FEA gate, and hop electrode in order to track the electron movement. These structures will be modeled using the particle trajectory simulation Lorentz2E2 and compared to the experimental results.

Electron hop funnels provide a method to integrate field emission arrays into microwave vacuum electron devices, to protect the arrays, and to provide a method to study the secondary electron characteristics of dielectrics. A hop funnel is a dielectric material with an electrode, known as the hop electrode, placed around the narrow end (exit) of the funnel to control the current transmitted through the device. Current is transmitted through the funnel via electron-hopping transport. This work investigates a hysteresis observed in the current–voltage characteristic of the device. The experimental results showing the observed hysteresis will be presented. This work will demonstrate that charging on the bottom of the hop funnel is not the fundamental cause of the hysteresis.