Ian Horsfall

The mechanisms of skull impact loading may change following surgical interventions such as the removal of bone lesions, but little is known about the consequences in the event of subsequent head trauma. We, therefore, prepared acrylonitrile butadiene styrene human skull models based on clinical computed tomography skull data using a three-dimensional printer. Six replicate physical skull models were tested, three with bone excisions and three without. A drop tower was used to simulate the impact sustained by falling backwards onto the occipital lobe region. The impacts were recorded with a high-speed camera, and the occipital strain response was determined by digital image correlation. Although the hole affected neither the magnitude nor the sequence of the fracture pattern, the digital image correlation analysis highlighted an increase in strain around the excised area (0.45%–16.4% of the principal strain). Our approach provides a novel method that could improve the quality of life for patients on many fronts, including protection against trauma, surgical advice, post-operative care, advice in litigation cases, as well as facilitating general biomechanical research in the area of trauma injuries.

Introduction On military operations, ballistic impact damage is possible to lithium ion (Li-ion) batteries worn on the body by military personnel and the potential for exothermic reactions may result in injury. This paper investigated the effect of impact on batteries that might be worn in front or behind body armour. Methods Li-ion batteries were subjected to ballistic impact both without and in combination with body armour using 7.62×39 mm ammunition (mean velocity=769 m/s) at charge levels up to 40%. The effect of penetrating impacts on charged batteries was also investigated using an outdoor range. Results The backface signature due to ballistic impact was reduced by including a battery pack between fabric body armour and an armour plate, however the batteries were crushed and mechanically disrupted. Ballistic impacts on batteries mounted in front of an armour plate resulted in perforation of the batteries. Increases in temperature, fire and toxic gas emission were noted when batteries were penetrated by an impact. Conclusions Batteries provided limited ballistic protection disproving the hypothesis that batteries could replace or enhance existing body armour solutions. Ballistic impact of charged batteries could lead to injury due to heat/flame and toxic discharge. It is recommended that batteries need to be carried in a position from which they can be rapidly removed from contact with the body.

There is an interest within forensic science to understand the physical and mechanical properties of human skin and the natural and synthetic simulants used to represent it, particularly with reference to reconstruction studies that consider injury to humans, for example during sharp-weapon and ballistic impact assaults. This paper discusses literature in the broad area of (i) human skin, (ii) animal skin and products such as leather and (iii) synthetic polymeric skin simulants. The physical and mechanical properties of human skin appear to be reasonably well documented in the literature. Animal models discussed appear to be restricted primarily to pig and to a lesser extent goat, plus some data on different types of leather. All skin (human and animal) and derivatives such as leather (from various animal sources) are natural materials and therefore variable in their physical and mechanical properties. The variability of commonly used simulants for human skin such as various types of leather could impact on the confidence of any reconstruction study data obtained by using such simulants. While it is recognized that synthetic simulants (polymers such as silicone and polyurethane) do not have the structure of human skin, their physical and mechanical properties can be manipulated relatively easily to match those of skin and are typically of low variability, providing confidence in the repeatability and reproducibility of reconstruction studies.

This paper presents the design, fabrication and performance of fusion deposition modeled 3D printed X-band horn antennas. The WR90 waveguide feed and pyramidal horn flare are printed as one piece from Acrylonitrile Butadiene Styrene (ABS). Different metallisation techniques are assessed to provide a uniform 40 micron coat on the ABS surfaces. Uniquely, the coaxial waveguide launcher is integrated with the waveguide section in a single interference fit operation. The measured and simulated radiation patterns showed good correlation and the antenna return loss was -10dB over the 8.212.4GHz operating range. The measured and simulated antenna gain was in good agreement and increased monotonically from 10-17+ 1.0dBi across the operating frequency.

A novel near-field microwave imaging system was designed and fabricated using the three-dimensional (3D) printing technique to manufacture X-band Pyramidal horn antennas and planar graded-index (GRIN) lenses. The flat lens focusing profile is synthesised by varying the refractive index radially in incremental steps that adjust the air-dielectric mixture. The lens is designed for direct attachment to the antenna aperture and transforms spherical waves emanating from antenna phase center into plane radiating waves. Simulated and measurement results show the antenna lens system input impedance is -10 dB, radiation pattern gain is between 17-20dBi over the 8.2-12.4GHz frequency band and when arrayed for polarimetry sensing has a polarisation cross-talk of -50 dB. A ground penetrating radar system using the nearfield array was scanned over buried targets. The SAR results demonstrated high resolution and polarisation discrimination imagery capable of detecting subsurface objects.

Currently the certification of UK ballistic resistant police body armour is determined according to HOSDB Body Armour Standards (2007). The test round DM11A1B2 manufactured by Dynamit Nobel is used to assess handgun protection (levels HG1A, HG1 and HG2). This round has proven consistent performance; however, Dynamit Nobel has ceased manufacture of the DM11A1B2 and an alternative test round was required. It was identified that Metallwerk Elisenhütte GmbH (MEN)had manufactured a DM11 A1B2 9mm FMJ Luger which appeared to be the same as the one previously supplied by Dynamit Nobel. However, it became apparent after initial testing that the bullet performance against body armour compared to the current test round varied. This paper presents the work that has been carried out to date to investigate why this discrepancy in performance exists. The comparison included dimensional measurements, micro hardness testing, scanning electron microscopy analysis and elemental analysis.