Tech Briefs

Fluid Helmet Liner for Protection Against Blast-Induced Traumatic Brain Injury

An Advanced Combat Helmet liner design uses the novel idea of including filler materials inside channels in the liner. An energy-absorbing foam was selected for the main liner structure, and several filler material candidates of widely varying properties are being considered. To date, material has been evaluated both experimentally and numerically. Numerical studies will include coupled simulations with a detailed finite element head model, providing insight into the effect of the new liner on the brain’s response to a blast wave impact.

Posted in: Briefs, Physical Sciences, Finite element analysis, Foams, Head injuries, Protective equipment, Military vehicles and equipment

Performance of Steel Stud Walls Subjected to Blast Loads

Construction trends have brought about an increase in the use of cold-formed steel studs in Air Force facilities. These steel stud walls have significant potential for mitigating large blast events. The current state of steel stud research, however, has not addressed all the variables that can influence the behavior of typical wall systems. As a result, there is a research gap that exists in the blast-resistant design of conventional steel stud wall systems.

Posted in: Briefs, Physical Sciences, Materials properties, Steel, Protective structures, Construction vehicles and equipment

Through-the-Wall Small Weapon Detection Based on Polarimetric Radar Techniques

Detecting concealed small weapons carried by people has received significant interest from law enforcement agencies as well as the military, most frequently for application in controlling checkpoints (in airports, border crossings, public spaces, etc.). Imaging systems for concealed weapons based on radar or other sensor technologies have been recently developed and tested. Most of the existing electromagnetic (EM) sensors suitable for this application operate at very high frequencies, usually in the millimeter or terahertz frequency bands and produce high-resolution images. Although these EM waves can penetrate through clothing (textile materials), they have very poor penetration properties through many common construction materials (such as brick or concrete). Most through-the-wall radars must operate at much lower frequencies, usually below 4 GHz, in order to “see” targets behind walls. However, at those low frequencies, the image resolution is degraded, so small weapons carried by humans may be difficult to detect directly in the image domain.

Posted in: Briefs, Physical Sciences, Imaging, Radar, Security systems, Sensors and actuators

Designing a Sensorless Torque Estimator for Direct Torque Control of an Induction Motor

Induction motors often are the preferred choice among industrial motors due to the modern power electronics that improve their speed control. Vitally important for the speed control of a motor is the accurate estimation of the magnetic flux and the electromagnetic torque. Knowing the electromagnetic torque of a motor, one is able to control it and thus monitor the speed faster and more stably.

Posted in: Briefs, Mechanical Components, Measurements, Power electronics, Industrial vehicles and equipment

A Bistable Microelectronic Circuit for Sensing an Extremely Low Electric Field

Bistable systems are prevalently found in many sensor systems. It is well established that a well-designed coupling scheme, together with an appropriate choice of initial conditions, can induce oscillations (i.e. periodic switching between stable fixed points) in over-damped bistable dynamical systems when a control parameter exceeds a threshold value. This behavior was demonstrated in a specific prototype system comprised of three unidirectionally coupled ferromagnetic cores, the basis of a coupled core fluxgate magnetometer. Another prototypical (quartic potential based) system of coupled over-damped Duffing elements has been applied to describe the dynamics of the polarization inside a ferroelectric material, the basis of an electric-field sensor currently under development.

Posted in: Briefs, Electronics & Computers, Architecture, Microelectricmechanical device, Sensors and actuators, Electric power, Product development

Fiber-Optic Seismic Sensor for Unattended Ground Sensing

Seismic military sensors are required to be robust, reliable, compact, and easy to install and operate to be effective in the battlefield environment. Three types of sensor technologies were addressed that provide improved design and novel signal processing techniques: (a) a wavelength scanning, pulsed-laser-based demodulation system; (b) digital lock-in amplifier and field-programmable gate array (techniques) for weak signal detection and processing; and (c) improved seismic sensitivity based on carbon fiber optic composite cantilever and fiber-Bragg-grating (FBG).

Posted in: Briefs, Physical Sciences, Fiber optics, Sensors and actuators, Defense industry

Reflected Signal Analysis

Forensic characterization of a wireless device is useful in many applications. An example of this is in the testing of Federal Communications Commission (FCC) Part 15 devices that must adhere to strict guidelines with regard to RF interference; one reason being problems with Portable Electronic Devices (PEDs) carried onboard aircraft. The operation of PEDs aboard U.S.-registered civil aircraft is limited. These rules also permit the use of specific PEDs after the aircraft operator has determined that the PED will not interfere with the operations of the aircraft. However, how can the aircraft operator know which PEDs are approved, or if the approved devices are being operated at inappropriate times? Compliance can be verified by detecting the operation of transmitting PEDs (T-PEDs) using an onboard monitoring system, or it could be verified by characterizing the device at a gate entry point, whether powered on or off, using specially designed probe signals and forensic techniques to classify the returned signal. In a more general setting, forensic characterization allows determination of the type of device, make, model, configuration, and other characteristics based on observation of the data that the device produces. The unique characteristics of the device are known as device signatures or device fingerprints.

Posted in: Briefs, Electronics & Computers, Electromagnetic compatibility, Wireless communication systems, Aircraft operations, Regulations, Identification