Fig. 9 presents three developments in the antenna design in mobile phones that may be of relevance in thyroid carcinogenesis. The second generation (2G) mobile phones appeared in the 1990s with the external retractable monopole or helical antennas. The 2G GSM band operated at a 800/900 MHz frequency band, later accompanied by a 1,800 MHz band. Around the turn of the millennium, the external antennas began to disappear, replaced with new phone models with internal planar or microstrip antennas. The first internal antenna was introduced in 1998 and the first dual-band mobile phone, with the internal antenna, was introduced on the market in 1999 (76). The internal antennas were positioned at the top of the telephone. With the emergence of the smartphones in the mid- and late 2000s, the internal antenna location started to shift from the top of the phone to the bottom. Currently, the majority of smartphone models have their antenna positioned at the bottom of the phone, thus closer to the thyroid gland (shown by grey color in Fig. 9). This would have a major impact on increasing radiation to the thyroid gland from smartphones.
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Source: STANDARD HANDBOOK OF MACHINE DESIGN CHAPTER 1 EVOLUTION OF A SUCCESSFUL DESIGN Thomas H. Brown, Jr., Ph.D., P.E. Faculty Associate Institute for Transportation Research and Education North Carolina State University Raleigh, North Carolina 1.1 EVOLUTION OF A DESIGN / 1.1 1.2 USING THE HANDBOOK / 1.2 1.3 SOME OPPORTUNITIES TO DISCOVER / 1.3 1.4 FINAL THOUGHTS / 1.8 1.1 EVOLUTION OF A DESIGN Most likely you have, right at this moment, at least one machine design project in progress. Maybe you were the originator of the design, but I suspect you inherited this design from others. I further suspect that you have already identified elements of the design you feel could be improved. You might be under pressure from customer service or marketing to respond to some need for change. In responding successfully, either to your own observations for change or to those of others, the design will evolve. Recognizing that the evolutionary design process is decidedly complex, with a seemingly random sequence of steps, the primary purpose of Standard Handbook of Machine Design is to make the information you need as readily accessible and usable as possible. As an example of how a design can evolve, and to provide perspective on how the information in this Handbook has traditionally been used, let me review for you a project I was given in my first job as a mechanical engineer. It involved the positioning of a microwave feed horn for a 30-ft-diameter antenna dish. The original design (not mine, by the way) called for a technician to climb up onto a platform, some 20 ft off the ground, near the backside of the feed horn. The technician had to loosen a half dozen bolts, rotate the feed horn manually, and then retighten the bolts. This design worked quite well until several systems were sold to a customer providing telecommunications along the Alaskan oil pipeline. Workers were not really safe going out in below 0F weather, with snow and ice on everything.As a result of their concerns for safety, this customer asked that we provide remote positioning of the feed horn from the nearby control room. The critical design requirement was that the positioning of the feed horn needed to be relatively precise. This meant that our design had to have as little backlash in the drive mechanism as possible. Being a young engineer, I was unaware of the wide variety of different drive systems, in particular their respective properties and capa- 1.1 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 2ff7e9595c
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