FIGURE 310 in Software

Painting QR Code JIS X 0510 in Software FIGURE 310

You should know that an HF tag has an antenna with three to seven turns of coil, while an LF tag antenna has several hundred turns of coil

The ultra high frequency range includes frequencies from 300 to 1000 MHz, but only two frequency ranges, 433 MHz and 860 960 MHz, are used for RFID applications The 433 MHz frequency is used for active tags, while the 860 960 MHz range is used mostly for passive tags and some semi-passive tags The frequency range of 860 960 MHz is often referred to by a single frequency of 900 or 915 MHz Tags and interrogators in this range are called UHF tags and UHF interrogators The passive and the semi-passive tags in this frequency range use far-field radiative coupling, or backscatter coupling The UHF tags have a read range of about 15 to 20 feet All the protocols in the UHF range have some type of anti-collision capability, allowing multiple tags to be read simultaneously in the IZ The new Gen 2 protocol for UHF tags is designed for reading several hundred tags per second UHF interrogators are usually costlier than HF interrogators, but UHF tags are becoming more economical Figure 3-11 shows some UHF tags

The UHF tag antennas are usually made of a copper, aluminum, or silver deposited on the substrate Their effective length is approximately 65 inches, which is approximately equal to one-half the wavelength of 900 MHz radio waves The optimum length of an UHF antenna is equal to one-half the wavelength of the carrier wave, though with proper design, the length can be reduced The UHF antennas are thin and easy to manufacture, allowing tags to be very thin, less than 100 M, almost two-dimensional The UHF tags cannot be easily read while attached to objects containing water and animal tissues because water absorbs UHF waves as well as detunes the tag The UHF tags also get detuned when they are attached to metal objects Separating UHF tags from the metal objects or objects with liquid improves their performance UHF tags cannot be read if water or any conductive material is placed between the interrogator antenna and the tags Radiative coupling used by the UHF interrogators uses radio waves to power and communicate with the tags Reflection, diffraction, and refraction of radio waves gives rise to a multipath effect, where radio signals arrive at the receiver using multiple paths Some of the signals from multipath attenuate the original signal This creates an IZ with varying signal strength The tags may not be readable in low signal spots, causing random tag readability problems The UHF antennas are directional, which helps create an IZ with well-defined boundaries, though the zone may have holes in it UHF tags are getting a big boost from the mandates by large organizations for their use in the supply chain This and the creation of the Gen 2 protocol have created a tremendous momentum in RFID industry to manufacture low-cost UHF tags in high volume UHF frequency regulations are not as uniform as HF frequency regulations Governments in various parts of the world had assigned the UHF frequencies at around 900 MHz, long before RFID, for uses other than for RFID Therefore, there is no common frequency range around 900 MHz available for RFID use Different countries have different bands available with varying allowable maximum power levels and duty cycles To overcome this problem, the Gen 2 protocol was designed to work with any frequency band within the 860 960 MHz range and with different maximum power levels The government regulations divide the allocated frequency range into a number of narrower frequency bands These narrower bands are called channels Different countries have different numbers of channels available within their allocated bandwidths The regulations also require that the interrogators do not use a single channel all the time but pseudorandomly hop among the available channels