Radio frequency waves (RF) are generated when an alternating current goes through a conductive material.當交流電通過導電材料時會產生射頻波（RF）。 Waves are characterized by their frequency and length.波的特徵在於其頻率和長度。 Frequency is measured in hertz (or cycles per second) and wavelength is measured in meters (or centimeters).Radio waves are electromagnetic waves and they travel at the speed of light in free space.The equation that join frequency and length is the following:頻率以赫茲（或每秒週期）為單位，波長以米（或厘米）為單位。

光速（c）=頻率x波長。

In the equation you can see that, if the RF frequency increases, its wavelength decreases.The RFID technology uses four frequency bands: low, high, ultra high, and microwaves .在等式中，您可以看到，如果RF頻率增加，則波長減小。RFID技術使用四個頻帶：低，高，超高和微波。 Low frequency uses the band of 120-140 kilohertz.低頻使用13,56-860赫茲的頻帶。 High frequency uses RFID technology in 960 MHz.高頻使用2,45 MHz的RFID技術。 Ultra high frequency RFID uses the frequency range XNUMX to XNUMX mega hertz.超高頻RFID使用XNUMX至XNUMX兆赫茲的頻率範圍。 Microwave RFID generally uses XNUMX Giga Hertz and superior.微波RFID通常使用XNUMX Giga Hertz和更高的頻率。 For the four frequency bands used in RFID, microwave frequencies have the shorter wavelength.對於RFID中使用的四個頻段，微波頻率具有較短的波長。

Electromagnetic waves consist of two different (but related) fields: an electric field (known as “E” field), and a magnetic field (known as “H” field).電磁波由兩個不同（但相關）的場組成：電場（稱為“ E”場）和磁場（稱為“ H”場）。 The electronic field is generated by voltage differences.電場是由電壓差產生的。 Since a radio frequency signal is an alternation, constant tension change creates an electric field that increases and decreases them with the frequency of radio frequency signals.由於射頻信號是一種交替信號，因此恆定的張力變化會產生電場，該電場會隨著射頻信號的頻率而增大和減小它們。 The electronic field irradiates from an area of increased tension to one of less voltage.電場從張力增加的區域輻射到電壓較小的區域。

在RFID中

LF和HF頻帶中的RFID標籤使用磁場，而RFID UHF和微波標籤使用電場。

When a reader emits radiofrequency signals , it causes variations in the electric and magnetic fields.當閱讀器發出射頻信號時，會引起電場和磁場的變化。 When a conductive material, as a tag´s antenna, is inside the same variable field, a current is produced in its antenna.當導電材料（如標籤的天線）位於同一可變場內時，其天線中會產生電流。When a tag is near a reader´s field, the coupling of the tag´s antenna with a reader´s magnetic field creates a current.當標籤靠近閱讀器的磁場時，標籤天線與閱讀器磁場的耦合會產生電流。 This coupling is known as inductive coupling.這種耦合稱為感應耦合。 Inductive coupling is the communication process used by LF and HF passive tags.電感耦合是LF和HF無源標籤使用的通信過程。

In the case of UHF and microwave tags, tags modulate and reflect the reader´s sign to communicate with the reader.對於UHF和微波標籤，標籤會調製並反映閱讀器的標誌，以與閱讀器進行通信。 This is called backscatter passive communication (or backscatter modulation.).這稱為反向散射無源通信（或反向散射調製）。
001兆瓦= XNUMX瓦。

Performing calculations using the decimal form of milliwatts can be tedious, so the standard is to calculate in decibels, or in powers of ten.使用毫瓦的十進制形式進行計算可能很乏味，因此標準是以分貝或1的冪為單位進行計算。 The abbreviation “dB” is used when decibels are used.使用分貝時使用縮寫“ dB”。 In the case of RF calculations, energy levels are generally mentioned as XNUMXmW decibels, and the abbreviation "dBm" is used.在進行RF計算時，能量水平通常以XNUMXmW分貝為單位，並使用縮寫“ dBm”。

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