Science and Engineering Forum

D igital cameras give a whole new meaning to the idea of painting by numbers. Unlike old-style  film cameras , they capture and record images of the world around us using digital technology. In other words, they store photographs not as patterns of darkness and light but as long strings of numbers. This has many advantages: it gives us instant photographs, allows us to edit our pictures, and makes it easier for us to share photographs using  cell phones  (mobile phones), e-mail, and  web sites . Photo: A typical low-cost digital camera. The circle is the lens; the rectangle above it is a  xenon flash lamp . You can see what this camera looks like inside in the photo lower down this page. How ordinary film cameras work Photo: An old-style film camera from the late 1980s. The film loads in a spool on the right and winds across to another spool on the left, passing in front of the lens on the way. When you take a photo, the shutter lets  light  enter from the lens and expose th

The following is excerpted from Chapter 3: Radio Basics for UHF RFID from the Book,  The RF in RFID: Passive UHF RFID in Practice  by Daniel M. Dobkin. Order a copy of  The RF in RFID: Passive UHF RFID in Practice  before December 31, 2007 to receive an additional 20% off! Visit  www.newnespress.com  or call 1-800-545-2522 and use code 91090. While this book excerpt from The RF in RFID:Passive UHF RFID in Practice, focuses on RFID applications, it is an excellent primer for RF basics.  Part 1  covers electromagnetic waves, signal voltage, and power.  Part 2  covers modulation and multiplexing. Part 4  reveals how to determine the link budget. Part 5  focuses on the effect of antenna gain on range. Part 6  covers antenna polarization. Part 7  covers antenna propagation. This Part covers backscatter radio links and introduces link budgets. Backscatter Radio Links Passive and semipassive RFID tags do not use a radio transmitter; instead, they use modulation of the reflected power