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Radio Waves and RFID Types

Radio Waves

The electromagnetic spectrum is composed of various frequencies of waves that are produced using electromagnetic energy.

A radio wave is essentially a disturbance through space that carries energy from one place to another.

Oscillation Rate

  • Radio waves oscillate, in that, while traveling the energy continuously rises and falls in intensity.

  • This oscillation is what is typically depicted as a wave pattern consisting of peaks (highs) and troughs (lows).

  • The path from trough to trough, or peak to peak, is considered a full wave cycle.

  • The number of cycles that take place in one second is known as the wave’s rate of oscillation.

Frequency

Radio waves are characterized by frequency and wavelength.

Frequency is measured in Hertz (Hz), * One Hertz is equal to one full wave cycle per second; so, frequency is dependent upon the wave’s oscillation rate.

Equation for a wave's oscillation rate

Frequency = 865 MHz
Constant: 1 Megahertz = 10^6 Hertz (1 million Hertz)

865 * 10^6 = 865,000,000 Hz (865 million Hertz)

865 MHz is equal to 865,000,000 Hz, which means the oscillation rate is 865,000,000 cycles per second.

Equation for a wave's wavelength

Wavelength is measured in meters and is found using the formula: 

Frequency = 865 MHz
Constant: 1 Megahertz = 10^6 Hertz (1 million Hertz)
Speed of Light: 299,792,458 Meters/second

Wavelength = Speed of Light (m/s) / Frequency in Hertz (Hz)
299,792,458 / 865,000,000 = .3468 meters = 34.68 centimeters

For quick calculations, you can simplify:
300 / 865 = .3468 meters = 34.68 centimeters

Wavelength

Within the radio wave subset of the RF spectrum, there are eight designated frequency bands.

  • Very low frequency
  • Low frequency
  • Medium frequency
  • High frequency
  • Very high frequency
  • Ultra-high frequency
  • Super high frequency
  • Extremely high frequency

Starting at the left side of the spectrum and moving right, the wavelength gradually decreases.

Very low frequency (VLF), the first frequency range on the left side of the spectrum, has an average wavelength of around 55,000 meters.

That means that a VLF wave, from one peak to another (or one trough to another), has an average distance of 55,000 meters, or around 500 U.S. football fields stacked together.

Because radio wavelengths correlate with the speed of data transmission (i.e., the longer the wavelength, the slower the data transmission and vice-versa), VLF waves result in very low read rates.

Therefore, VLF is not used commonly for RFID applications.

Of the eight frequencies on the radio wave band, there are three that are typically used for RFID applications:

  • Low frequency (LF)
  • High frequency (HF)
  • Ultra-high frequency (UHF)

Low Frequency (LF)

About the LF Band

The Low Frequency, or LF band, is between 30 kHz and 300 kHz with long wavelengths of around 2,400 meters

Because there are multiple types of signals communicating on this band, LF RFID systems are only allowed to use the small range between 125 - 134 kHz.

The large wave size allows LF waves to penetrate metal and water which is unique to this frequency band.

Although LF RFID has a long wavelength, the read range is shorter than both HF and UHF RFID – only extending from a couple centimeters, up to about 50 centimeters in ideal conditions.
The short read range is due to dependence on magnetic coupling.

Things to consider: * LF tags are generally more expensive than HF and UHF RFID tags. * These are powered solely via magnetic coupling. * They cost between $0.70-$20.00 per tag. * They vary in cost depending on type and application.

Unlike other RFID tags, LF tags do not have security standards, so they are not recommended for applications where encrypted communication is a requirement.

LF RFID Applications

LF RFID systems are used most often for animal tracking applications (e.g. pet tagging and livestock identification), but are also used in some access control applications.

LF tags are ideal for animal tracking applications because they are easily read through the animal’s body (containing water).

High Frequency (HF)

About the HF Band

The high frequency (HF) band on the RF spectrum extends from 3 MHz to 30 MHz.

The wavelength of a high frequency wave is much shorter than an LF wave, only around 22 meters, or a little less than 2 school buses in length.

High frequency, like low frequency, uses magnetic coupling to communicate between the tags and the RFID reader/antenna.

HF waves can pass through most materials except for water and dense metals.

Thin metals, like aluminum, can still be tagged with HF tags and function normally.

HF RFID tags usually have a general read range of a few centimeters up to about a meter in length depending on the setup of the system.

Within the high frequency band of the RF spectrum, near-field communication, or NFC, is a communication protocol approved by the International Organization of Standardization, or ISO (ISO 14443 & ISO 18000-3).

Because NFC is a global communication standard, and therefore regulated, it operates on a single frequency - 13.56 MHz.

HF Tags: * HF and NFC tags cost from about $0.35 - $10.00 per tag.
The tags are usually delivered as labels, cards, or plastic encased tags. * They are generally small in size so that they can be applied to many different items.
 HF tags rely on magnetic coupling as their power source so they tend to last the lifespan of the application unless damaged by wear and tear to the tag.

HF Readers: * HF RFID readers are used with HF tags and cost around a few hundred USD.
* NFC tags can be read with the same HF readers, including any smartphones that contain HF/NFC readers.

HF RFID Applications

HF and NFC RFID applications are continuously emerging from many companies looking to solve business problems using RFID technology.

NFC is particularly popular in marketing applications like advertising posters, smart items, and brand/item interactive experiences.

The most used applications for HF RFID are access control applications, data transfer applications, and some ticketing applications.

HF RFID tags are also used in passports across the world in countries like the United States, Norway, Japan, Australia, India, and more.

There has been criticism in the past about the security of these tags in passports.

This was later addressed by adding both a metal lining to lower the read range, and a password that has to be keyed into the RFID reader to read the tag.

Ultra-High Frequency (UHF)

About the UHF Band

tl;dr

  • The lower the frequency, the longer the wavelength
  • the longer the wavelength, the slower the data transmission and vice-versa

  • NFC is part of the High Frequency (HF) band at 13.56 MHz

  • LF can pass through water and metal (unique to LF)

  • HF can pass through most materials except water and dense metals.

Source: Atlas RFID Store