Understanding and Analysis of Common Problems in UHF RFID System Application

- Nov 27, 2018-

I. Overview

Radio frequency identification (RFID) technology will be ubiquitous, which is undoubted, because it brings convenience and timeliness, that is, efficiency, and ultimately wealth!

However, there are many kinds of RFID technologies, the frequency is from 125KHz to 5.8GHz, the tags are divided into active and passive, and there are dual-frequency chips and active passive combination systems. Each technology has different characteristics, so it must be based on The application needs different technologies. At the same time, because it is a wireless communication technology, it is easily affected by various wireless signals in the air and the space environment. Therefore, its application effect is related to the on-site space environment, and it is difficult to have A unified performance indicator, therefore, application technology research for different application environments is indispensable, which determines that RFID technology can not be quickly popularized at once, it needs a process of continuous exploration and accumulation.

Second, read and write distance

When people understand UHF RFID products, the first question usually asked is how far your readers can read. In fact, such a problem is difficult to simply answer how far is the distance, because the actual read and write distance is determined by the reader's RF power, antenna gain and polarization direction, and feeder. The unit length attenuation and total length, the performance of the tag, the relative position angle of the tag and the reader antenna are determined. Of course, the surrounding physical environment will also affect the distance between reading and writing. However, if it is not a particularly harsh environment, the impact is not the main one, and the impact cannot be predicted in advance. Only the actual field test can be known.

From the perspective of commercial propaganda, people usually say how many meters my reader can read. In fact, this is only measured under a specific condition and environment. Leaving this particular environmental condition, such a number is strictly speaking. It doesn't make sense, and it can only be used as a reference at most, because there is no unified testing environment and authoritative testing department.

There are two other points that need to be explained: First, the distance from the data to the label is generally 40%-70% of the distance from the data read by the label, because writing requires more energy than reading. Second, the average person thinks UHF RFID. It is only suitable for long-distance applications. In fact, it can be used from zero distance to long distance, and the closer the distance is, the easier it is to achieve.

Third, the read rate or miss rate

The read rate is the ratio of the number of tags that can be correctly read after passing through the read/write area and the total number of tags passed. The miss rate is the ratio of the number of unread words to the total number. This indicator is also subject to a variety of conditions. It is meaningless to say in general terms how much the reading rate is, and even the reference value is not because it is affected by more uncertain factors. In addition to the above-mentioned factors related to the read/write distance, it also relates to how many labels pass at the same time, the relative position between the label and the label, the distance between the label and the reader antenna, the label and the reader antenna. The relative movement speed between the two is related. Of course, the performance of the reader and tag is the basis, but once selected, they are ok.

Fourth, the number of tags read at the same time

This indicator is also very much concerned by many people, because people often want to be able to read as much as possible. Some manufacturers use people's psychology. For the purpose of commercial hype, this indicator is said to be readable hundreds of times per second. 1000 labels, I think this is an irresponsible propaganda, there is no benefit to the promotion of RFID applications, it will only fight the confidence of people who really want to try the app! The number of propaganda is officially measured, it is also in Results under very harsh conditions, rather than test results under general conditions, are not universal. I even think that this indicator has no meaning for practical application! It can only be used as a theoretical indicator.

I also want to tell you that this indicator is not the bigger the value, the better, but it should be suitable for a specific application. Why? Because, the greater the requirement of this indicator, the higher the probability of missed reading under other conditions, this is determined by objective laws, as can be seen from Table 2. I think that in practical applications, we should pay attention to the study of reading rate. Another point is, what should we do if we miss reading? This kind of problem must be considered when we are actually applying it. The input of remedial measures is also required to read at the same time. The number is related.

The above questions are not difficult for the relevant professionals to understand, but for non-professional customers with various application needs, it is necessary to figure out.