Performance analysis trivial RFID system

TPA - Assignment 2 Korneel Melkebeke, Pieter-Jan Steenbeke

Assignment 3: RFID

Total Plant Automation

1 Introduction

Radio-frequency identification (RDIF) is a wireless technology to transfer data in order to

automatically identify and track objects by means of tags attached to these objects. RFID systems

invariably comprise two components, tags and readers. A tag, or transponder, contains electroni-

cally stored data and hence resembles a label of the corresponding object. A reader, or interrogator,

predominantly both transmits and receives radio signals.

The remainder of this paper is structured as follows. The rest of this chapter gives a brief

summary of RFID systems concerning its classifications, selection criteria, and some typical appli-

cations. In order to scrutinise to what extent particular materials may disrupt the performance of

the system, Chapter 2 will present the configuration of the RFID system utilised in the lab. Fur-

thermore, Chapter 3 will examine the results and Chapter 4 will outline the conclusions.

RFID systems can be classified by the type of tag and reader. First, dependent of the power

supply, tags can be active or passive. Active tags have a local power source such as a battery, and

may hence operate at a much larger distance from the reader. Passive tags uses the radio energy

transmitted by the reader, and is therefore smaller and cheaper. The required energy to light up the

tags, however, is roughly a thousand times stronger than for signal transmission. The latter has a

direct relation to interference and radiation exposure, which will be described in further [1]. Second,

the system's operating frequency is the transmission frequency of the reader and can be categorised

in four ranges, see Table 1. Generally, the transmission frequency of the transponder equals the

operating frequency.

Next, another property to distinguish RFID systems is the type of main communication

procedure utilised to transfer data between transponder and reader, i.e. full/half duplex and se-

quential mode. In the former, the transfer of energy from the reader to the transponder is contin-

uous, whereas in the latter, the transfer of energy occurs in intervals. A direct drawback of those

pauses in the sequential system is a loss of energy. Dependent on the utilised communication pro-

cedure, the reading distance can either be in close range (0-1 cm), remote (0-1 m), or long range

(>1 m). Furthermore, there are two types of communication between transponder and reader,

broadcast and multi-access. In the former, the data of the reader is transmitted to all the transpond-

ers. In the latter, only transponders within the reach of a reader will transmit data to the reader. In

order to prevent collision, the channel capacity must thus be divided over the various members

TPA - Assignment 2 Korneel Melkebeke, Pieter-Jan Steenbeke 2

within the reader's reach. There are several anti-collision mechanisms to allow multiple systems

communicate with solely one reader as transponders cannot communicate with one another.

Apart from the aforementioned properties, some other properties of RFID systems are (i)

the possibility to write data to the transponder, i.e. read-only or writeable tags; and (ii) data capacity

of the tag, i.e. some bytes to multiple kilobytes, with the known 1-bit transponder as exception.

Table 1 - Properties in function of operating frequency

Operational frequency LF HR (RF) UHF W

Frequency band 30-300 kHz 3-30 MHz 300 MHz-3 GHz >3 GHz

Reach1


Third, the degree the housing of the tags are protected against deformation is directly pro-

portional to the system's resistance against pressure and vibrations. Here, the antenna of the tran-

sponder is the most sensitive part. For instance, the antenna can disconnect.

Next, ambient moisture and neighbouring metals may alter the transmitted signals. The

main difference with temperature exposure is that the sensitivity to moisture and metals varies

according to the operating frequency. As depicted by Table 1, low and high frequencies do not

encounter an inferior operation of the system. At higher frequencies, the ambient moisture starts

to absorb the transmitted signals and neighbouring metals may interfere with the signals. Thereby,

the signals either arrive incorrectly or do not arrive at all. In designing an RFID system, it is thus

important to examine what objects are in near proximity of the RFID tags. If a tag must be attached

to a metal object, a LF system will primarily utilised. However, in case of higher frequencies, there

must be some clearance distance between the tag and the metal object. Occasionally, tags utilise

the metal construction in order to transmit and receive signals. Here, also, neighbouring metal

objects may still cause reflections of the signals.

In case two or more RFID systems are nearby operating at the same operating frequency,

the antennas of the readers may interfere with each other. Therefore, there must be some clearance

distance between the readers in order to avert those interferences. This distance depends on the

type of readers and the size of their antennas, and is specified on the reader's datasheet. Another

way to diminish those interferences, is by governing the RFID systems such that they are never

active simultaneously. Note that some readers are competent to administer several antennas by

alternately transmitting signals.

The application determines the time the tag is attached to the object. For instance, tags are

attached permanently in closed loop applications whereas tags are attached to the object that leave

permanently in open loop applications. In the former case, the tags are attached to the objects upon

entering the production system. In the latter case, there are several possible times in the production

process where the tag can get attached to the object. Upstream, the probability the tag may get

damaged is higher.

In addition to the six main criteria, some supplementary criteria will be described below.

There are a variety of security threats, such as viruses and worms, which can significantly damage

the RFID system's performance. To avoid the majority of those threats, the incoming must be

examined. The cost price of an RFID system, i.e. material, equipment, installation, can be rather

extensive. The tags and the software development account for the largest part of the overall cost

structure. Further, the cost price depends on properties such as the operating frequency, the order


quantity, material, temperature resistance, power supply. Moreover, the positioning of tag must be

conducted such that the tag is readable, taking into account all the aforementioned altering mech-

anisms. In behalf of completeness, the system's data capacity, standardisation, and read rates are

also criteria to determine the appropriate RFID system.

RFID systems has a variety of applications such as commercial, security, agricultural, and

transport. Commercial applications include automated inventory control, ticketless entry, produc-

tion progress assembly line. Security applications include theft prevention in stores. Agricultural

applications include electronic tracking of livestock and improvement of food traceability.

Transport applications include automated toll collection, airline baggage tracking and vehicle man-

agement systems.

2 Set up

The assignment was performed in the software RF-MANAGER Basic V3.0, a user-friendly

instrument to configure and commission RFID readers. Figure 1 depicts the SIMATIC RF670R

reader and the two RF660A antennas that were used. The antennas are configured in the Anten-

nas menu, see Figure 2 for an example. For this assignment, the gain was set at 7 dB, and the cable

loss was set to 2.0 dB. Furthermore, the diagnosis view enables the reader to test the accuracy of

tag detection in the following scenarios: (i) commissioning of the reader and testing of the loaded

configuration; and (ii) checking and testing the reader on commissioning in the plant. Here, the

diagnosis view was utilised to determine the maximum read distance in order to scrutinise to what

extent particular materials may disrupt the performance of the system. This was conducted by

monitoring whether tags were detected in the diagnosis view and which colour was assigned to the

tags. Figure 3 depicts an illustration. The colours represent whether a tag was recently detected by

the reader, as described by Table 2.

(a)

(b)

Figure 1 - SIMATIC RF670R reader (a) and RF660A antenna (b)


Figure 2 - Antennas menu

Figure 3 - Example diagnosis view [2]

Table 2 - Meaning of colour type in diagnosis view [2]

Colour Meaning

Dark green The tag was detected in the current read cycle

Light green The tag was detected in the previous read cycle, but not in the present read cycle

Red The tag has not been detected since at least the previous read cycle and in the current read cy-cle


For a variety of surfaces, the maximum reach distance perpendicular in front of the antenna

was measured for various tags in order to determine the interference of the surface. Six different

tags were compared, see Figure 4. Tags (a), (b), and (c) of Figure 4 represent metal-on tags, indi-

cating that they can be attached on metal surfaces in order to identify and track metal objects. On

metal, the maximum read distance2 of tag (a) equals 10 m, of (b) 6 m, and of (c) 8 m - according to

their datasheets [3], [4], and [5]. As surfaces, the human body, paper, metal, and water were exam-

ined, see Figure 5. Important to note here is that the tags were hold against the surfaces and were

not mounted on the surfaces as well as the abundance of metal devices present in the lab. Initially,

this was conducted for different power levels. The power levels were set to 50; 100; 200; 500; 1,000;

and 2,000 mW. Due to technical issues, however, the software did not update the power level and,

in fact, all measurements were conducted at a power level of 2000 mW. Therefore, the tests were

conducted once more, with just one tag and some additional surfaces. Figure 6 depicts the utilised

the tag for the additional measurements. In total, nine surfaces were compared. In addition to the

three initially used surfaces depicted in Figure 5, and the option of no surface, textile and four extra

surfaces, as illustrated in Figure 7, were utilised. Specifically, four parameters were examined. First,

at a power level of 1,000 mW the influence of various surfaces was analysed. Second, for the textile

surface, the gain level was set to different levels to examine its influence. Next to the standard level

of 7 dB, the gain was set to 2, 5, and 20 dB. Third, also for a textile surface, the read distance was

measured for the aforementioned power levels. Finally, fourth, without use of a surface, the reach

distance was determined at two other positions, i.e. perpendicular left of and behind the antenna

in order to examine the equivalence with the theoretical spatial directional radiation pattern of the

RF660A antenna in free space and in the absence of reflecting/absorbing materials. Figure 8 illus-

trates the main, i.e. processing, and the auxiliary fields of this pattern. Note that the diagram is not

to scale.

(a) Xerafy MicroX II (b) Xerafy Xylinder (c) Confidex Ironside Slim

2 Read ranges are theoretical values that are calculated for non-reflective environment, in where antennas with optimum directivity are used with maximum allowed operating power according to ETSI EN 302 208 (2W ERP). EU = 865 - 868 MHz, US = 902 - 928 MHz, JPN = 952-956 MHz. Different surface materials may have an effect on performance.


(d) (e) (f)

Figure 4 - Initially utilised tags

(a) paper (b) metal (c) water

Figure 5 - Initially utilised surfaces, the human body excluded

Figure 6 - Tag utilised in the supplementary tests

(a) coffee mug (b) cardboard (c) archive folder (d) mobile phone

Figure 7 - Supplementary surfaces


Figure 8 - Spatial directional radiation pattern of the RF660A antenna, showing main (green) and auxiliary (blue) fields [6]

3 Analysis

As previously mentioned, the read distance was first determined for six tags attached to

four distinct surfaces. Figure 9 shows the influence of the surface for the various tags. Here, dashed

lines represent the on-metal tags (a), (b), and (c) - see Figure 4. Deceptively, of those on-metal tags,

tag (a) had a negligible to zero read distance for the different surfaces, regardless of a metal or non-

metal surface. Tag (b), however, did show an enhanced read distance in case of the metal surface

compared to the non-metal surfaces. Moreover, its maximum read distance approximately equates

the maximum read distance of 6 m listed on its datasheet [4]. Despite its lower read distances in

case of metal and water, tag (c) shows an adequate and equivalent read distance for human body

and for paper as surface. Tag (c) does not equate its maximum read distance of 8 m listed on its

datasheet [5]. In fact, tag (c) rather resembles a tag sensitive to both metal and moisture, as will be

illustrated by tags (e) and (f). Furthermore, the read distances of tag (d) for the distinct surfaces do

not comply with the anticipated disturbances by both metal and moisture whereas the read dis-

tances of tags (e) and (f) do comply. For the latter two, Figure 9, on the one hand, clearly illustrates

a read distance of 6.4 m and 3.8 m for tag (e) and (f), respectively, in case the tags was attached to

a human body or to paper. On the other hand, Figure 9 depicts that the tags are highly sensitive to

both metal and moisture, as stipulated by Table 1.


Figure 9 - Influence initial surfaces on maximum read distance for various tags,

dashed lines represent the on-metal tags with additional data labels for metal surface

For the second experiment, Figure 10 shows, in increasing order, the read distances for the

distinct surfaces. As the new tag is not explicitly designed for usage on metals, the tag is not visible

at any distance in case of the metal surface as well as when attached to a mobile phone. The sensi-

tivity to moisture is once more apparent, since the maximum read distance equates 1.0 m when

attached to water. Furthermore, the maximum read distance increases linearly in case of the ceramic

coffee mug, paper, cardboard, and textile. However, the read distance displays no difference in

maximum read distance when the tag was attached to either no surface or to an archive folder.

Figure 10 - Influence type of surfaces on maximum read distance for new tag, in increasing order

0

6.4

3.8

-1

0

1

2

3

4

5

6

7

8

human body paper metal water

Read d

ista

nce (

m)

(a) (b) (c) (d) (e) (f)

-1

0

1

2

3

4

5

6

7

8

metal mobilephone

water coffee mug paper cardboard textile none archivefolder

Read d

ista

nce (

m)


Next, Figure 11 and Figure 12 respectively depict the influence of both the antennas power

level and the antennas gain on the maximum read distance. They clearly show direct and inverse

proportionality, respectively.

Figure 11 - Influence antenna's power level on maxi-

mum read distance for the new tag on a textile surface

Figure 12 - Influence antenna's gain on maximum read

distance for the new tag on a textile surface

Finally, Table 3 shows that the maximum read distance behind the antenna is larger than at

its lateral read distance. This does not resemble the spatial directional radiation pattern as illustrated

in Figure 8.

Table 3 - Read distances for different orientations with respect to the antenna, for the new tag without a surface

orientation read distance (m)

front 6.6

left 0.8

back 1.1

4 Conclusions

In this paper, the performance of an RFID system was scrutinised in terms of maximum

read distance. The following four parameters were examined: (i) influence of surface to which the

tag is attached; (ii) power level and (iii) gain of the antenna; and (iv) orientation with respect to the

antenna. First, a brief introduction is presented comprising the standard classification, several se-

lection criteria, and some typical applications. Next, the RFID configurations of the experiments

are described, followed by the results. This chapter summarises the paper and articulates a few

conclusions.

From the first experiment, it cannot be entirely speculated that tags that are specifically

designed to be attached on metal surfaces, are insensitive of the metal surface. Of the three on-

0

1

2

3

4

5

6

7

0 500 1000 1500 2000 2500

Read d

ista

nce (

m)

antenna's power level (mW)

0

1

2

3

4

5

6

7

0 5 10 15 20 25

Read d

ista

nce (

m)

Antenna's gain (dB)


metal tags examined in this experiment, for instance, one tag showed a maximum read distance for

metal approximately half as large as the read distances of the surfaces human body and paper. In

fact, due to its additional sensitivity to water, this tag bore a resemblance to a tag not specifically

designed for on-metal surfaces. Another on-metal tag was never detected when attached to the

metal object. That tag was also not detected when attached to water whereas for paper and the

human body, it was practically undetectable. Therefore, the results for this tag are a bit inconclusive.

A reasonable cause for those ambiguous results may be the improper way of attaching the tag to

the surface. In this experiment, the tag was held against the surface, and not mounted which may

not furnish the synergy with metal surfaces.

For the three other tags, one tag did not show a significant variation in its maximum read

distance when attached to the various surfaces. In contrast, the two other did comply with the

anticipated disturbances by both metal and moisture as described in the introduction. In the second

experiment, those anticipated disturbances were considerably perceptible. In increasing order of

maximum read distances, the surfaces metal and water ended up at the bottom, followed by ceramic

coffee mug, paper, cardboard, and textile. Remarkably, the maximum read distance when the tag

was attached to an archive folder was equivalent to the case when no surface was utilised. A rea-

sonable cause for the latter assertion was probably the improper way of attaching the tag to the

surface in combination with the lack of a sufficient amount of material to induce an inferior oper-

ation of the system. Therefore, it can be confirmed that the surface on which the tag is mounted

as well as the accuracy of the attachment, does have an influence despite some contradicting results.

Next, it can be conjectured that the power level and the gain of the antenna have a direct

relation to the maximum read distance. Specifically, the read distance increased (decreased) with

increasing power level (gain) of the antenna. Therefore, the maximum read distance is, respectively,

directly and inversely proportional to the antenna's power level and gain.

Concerning the compliance with the theoretical spatial directional radiation pattern, the

empirical results of this experiment were not entirely equivalent. Particularly, the maximum lateral

read distance was not larger than the read distance at the back of the antennas. The read distance

in front of the antenna, however, was notably larger.

To conclude, from the empirical results, it can be asserted that the system's performance is

dependent on the type of tag; the surface to which the tag is mounted and the degree of the attach-

ment; the antenna's power level and gain; and the orientation of the tag with respect to the anten-

na's.

References

[1] Radio-frequency identification, Wikipedia, [Online]. Available: http://en.wikipedia.org/wiki/Radio-frequency_identification#Tags. [Accessed 3 May 2015].

[2] Siemens, SIMATIC RF-MANAGER Basic Configuration and Operating Manual, Germany: Siemens AG, 2012.

[3] Xerafy, MicroX II Datasheet, 3 July 2014. [Online]. Available: http://www.xerafy.com/userfiles/uploads/datasheets/Micro%20X%20II%20Datasheet.pdf. [Accessed 12 May 2015].

[4] Xerafy, Xylinder Brochure, 20 December 2013. [Online]. Available: http://www.xerafy.com/userfiles/uploads/brochures/Xylinder%20Brochure.pdf. [Accessed 12 May 2015].

[5] Confidex, Ironside Slim Datasheet, April 2015. [Online]. Available: http://www.confidex.com/application/files/3914/3074/4660/Ironside_Slim_Datasheet.pdf. [Accessed 12 May 2015].

[6] Siemens, SIMATIC RF600 System Manual, Germany: Siemens AG, 2012.

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Performance analysis trivial RFID system

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