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Design News, May 2013

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M E D I CA L DESIGN APPLICATIONS Safe, Portable Power Source VARTA Microbattery helps to insure that a surgical helmet's light and ventilation runs reliably in the operating theatre. BY JULIA PALU, VARTA MICROBATTERY (US) Challenging Combination of Design Requirements The portable power supply in a surgical helmet must balance a number of apparently opposing requirements. A complex medical operation can last for several hours. If the power in the helmet failed — which would cause the LED light to dim and the visor to become misted as the fan stopped working — the resulting interruption to the surgeon's activity could cause serious harm to the patient. The battery pack must therefore offer high energy capacity to sustain continuous operation over many hours, and predictable power delivery. The theatre crew must be able to read out the State of Charge (SoC) of the battery, and to estimate accurately the remaining run-time on the basis of the SoC value. [w ww. d e s i g n n e w s . c om] magenta cyan yellow black In general, the bigger the battery, the greater its energy capacity and the longer its run-time between charges. But at the same time, the helmet must be light and comfortable, since Battery pack. the surgeon will wear it for long periods. The battery pack must therefore be as small and light as possible. It must also be capable of tolerating the difficult conditions inside a protective suit: high humidity caused by vapor in the wearer's exhaled breath, as well as potential exposure to contaminants and high temperatures. Finally, compliance with FDA regulations governing end products requires that suppliers of key components such as power supplies verify or validate that their products perform as specified, to within precisely defined tolerances. Small and Light The choice of cell in a battery pack is of fundamental importance. VARTA implemented a design in this application using four 18650 lithium-ion cells. Lithium battery types typically offer higher energy density than any other chemistry. In the surgical helmet, VARTA has achieved a high capacity of 35Wh in a pack weighing just 225g and measuring 80 mm x 43.7 mm x 41.5 mm. Withstands Harsh Conditions The protective suit completely encloses the surgeon, protecting him or her from particulate matter from the outside. This means that, inside the suit, it is hot and humid. The VARTA Microbattery battery pack's sealed plastic enclosure protects it from all external materials — vapor, contaminants, and liquids. This enclosure must be highly robust, since surgical helmets must be able to withstand MAY 2013 T R E ND WAT CH : ME DICAL / A S UP P LE ME NT TO DE S IG N NEWS T17 ES245767_DNTW1305_T17.pgs 05.03.2013 02:01 UBM Source: Varta I In an operating theatre, much of the equipment exists to protect the health of the patient. Equally important, however, is protection of the health of the medical staff, but this barrier must not impair their vision or freedom of movement. A surgical protection suit is the doctor's first and most important line of defense. An important element of the suit is the helmet, as this provides clean, uncontaminated air for the surgeon to breathe, and a protective visor that offers a clear and unobstructed view of the patient without misting. Today's most advanced surgical helmets include a powerful LED light to illuminate the area of the patient's body that the surgeon is focused on, and a multi-speed fan to ventilate both the helmet and the body of the suit. Since the surgeon requires complete freedom of movement, the suit cannot be tethered to a main power supply. A hightech surgical protective suit will therefore include a battery power unit. The latest helmet includes a custom lithium-ion battery pack from VARTA Microbattery that balances the constraints of size, weight, run-time, and reliability.

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