RAIN RFID Near-Field Antenna: How to create a close proximity read zone

By Times 7, Apr 15, 2020

Exploring what antenna is right for your project is an essential step to ensure that your application meets its desired outcome. There will be many antenna characteristics you will need to consider including whether you want a near-field or far-field antenna. In this blog, we want to explain when to choose near-field and how to create a real close-proximity read zone.

Why Choose Near-Field

RAIN Near-field antennas are often recommended for use cases that track metals or liquids (which are usually very tricky to track). Far-field electromagnetic fields get absorbed by liquid assets such as pharmaceutical drugs, shampoos or soaps, while the near-field's magnetic field is not subject to RF absorption.

Near-field antennas are also a preferred choice to create very defined read zones to limit stray reads. However, as opposed to other NF technologies, such as NFC, the RAIN near-field zone is not limited to the antenna’s surface and can read at a greater distance (learn more about NFC vs. RAIN NF here). RAIN Near-field is designed to offer a wider range of read-zones to fit specific requirements.

But, if you are looking to create a real close proximity read zone, which is limited to the antenna's surface, here are some tips:

1. Turn down the reader power

2. Use an NF only tag, such as the Smartrac NF Trap

3. Lower the RSSI threshold setting in the RFID reader

If you need further assistance, don't hesitate to contact us at sales@times-7.com.

For those amongst you that want a more technical read…

Near-Field vs. Far-Field

The concept of near-field and far-field plays a significant role in RAIN RFID applications. When a reader antenna is energized by an RFID reader, the antenna transmits electromagnetic waves (fields) into the free space. Dependant on where the waves move in this free space, and the distance they travel from the transmitting antenna, they will be classified as near-field or far-field. RAIN tags can be powered by the far-field electromagnetic fields or by the near-field magnetic fields.

The electromagnetic waves are a combination of electric (E) and magnetic (H) fields that are orthogonal and are in-phase with each other. The electromagnetic fields vary as a function of distance from the transmitting antenna. This is broadly classified as the near-field region and the far-field region.

Near-Field

The near-field region is the region next to the antenna and can further be classified into the reactive near-field and the radiative near-field. Near-field applications are used for close proximity tag reading and have a narrower beam to focus on specific areas.

Reactive Near-Field: This region lies right next to the antenna. The region is reactive as the E-field, and the H-field are 90° out of phase with each other. Propagation does not happen in this region as the E and H fields are out-of-phase.

Radiative Near-Field: This is the region between the near-field and the far-field. This transitional zone is also known as the ‘Fresnel region’. The radiation starts to happen in this region, but it is still immature. The radiation pattern of an antenna will vary with respect to distance in this region.

Far-Field

In this region, the E-fields and the H-fields are orthogonal to each other and are in-phase. Electromagnetic waves propagate in this region, and a meaningful antenna radiation pattern can be obtained in this region.

The reach of RAIN Near-field zones is relative to the antenna's gain and will increase or decrease with the reader's power input. However, due to the excellent design of the Times-7 True NearField antennas, they have a very low gain with only a few far-field components. Thus, resulting in a powerful magnetic field and an even energy distribution on the antenna's surface, showing no dead zones.