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24 The PCB Magazine • January 2015 which, interestingly, is no stranger to 3D print- ing having been using it in production for well over a decade. For example, NASA developed open coil arrays as aircraft vehicle sensor arrays that double as lightning conductors on com- posite airframes that otherwise lack the ability to conduct lightning (Figure 1). However, wide area circuit boards are not the only way to solve this problem. EADS Inno- vation Works and Vienna University of Tech- nology used a wireless sensor network with power obtained via energy harvesting, a solu- tion that would not benefit from 3D printed electronics. Severe, unpredicted corrosion of reinforced steel concrete in bridges, tunnels and buildings calls for strengthening retrofit with embedded sensors. In Japan they spin carbon fiber around the support structure and embed in polymer with sensors as a smart skin. Printed electron- ics may well prove to be a competitive way to manufacture these wide area circuit boards in the future. Another application of structural electronics is building integrated photovoltaics (BIPV). This refers to products designed either to substitute for conventional building materials or to be in- stalled flush on a building surface with minimal disruption of the underlying and surrounding building architecture. BIPV is one of the mostly watched segments of the photovoltaic industry, but it is far from mainstream. The BIPV mar- ket development is impeded by the existence of standardised solar panels that have become a commodity having decreased in price drasti- cally. So far BIPV products are produced on a smaller scale. Sales are growing as architects and building specifiers look for more aesthetic ways to use solar energy and sales propositions are starting to take such forms as solar tiles and walkable PV roofing. Over the last few years, there has been a proliferation in the market of rigid BIPV panels designed to function as roof- ing tiles and, in some cases, exterior wall clad- ding. These include large, interlocking, weath- er-tight BIPV tiles that mount directly onto the OPPORTuNITIES FOR 3D PRINTED STRuCTuRAL ELECTRONICS continues Figure 1: nasa sans eC open coil arrays (a) placed on aircraft (b) as array of laminar open circuit coils and (c) the shape of a typical coil used. (source: nasa) FEaturE