**3. Challenges of traceability in the Nordic forest industry**

**2.2. Possibilities and benefits with wood traceability**

304 Radio Frequency Identification from System to Applications

**Figure 4.** Collection and utilisation of information in the wood supply chain [2].

tion related to the wood cannot be traced along the chain.

**•** Increased quality of the products

**•** Reduced production costs.

**•** Increased yields

Figure 4.

Currently, the wood material properties are measured when needed in the wood conversion chain and the gathered data is usually lost between the processing steps as illustrated in

As the collected information is lost between the processing steps, measurements need to be repeated - such as the measurement of the log dimensions in the forest by the harvester dur‐ ing cutting and the re-measurement of the dimensions in log sorting in the saw mill to deter‐ mine the volume of the wood for the second time. The lost information also naturally means reduced control over the wood conversion chain from forest to end product as the informa‐

The traceability of the wood and the associated information can be achieved by identifying the individual wood items – logs and boards, instead of relying on classification of wood and processing in batches of the same class of wood. The benefits of the traceability include:

The quality of the products can be increased with improved control of the production proc‐ esses by effectively utilising the information collected in the previous stages of the conver‐ sion chain. The production process can be optimised based on the individual properties of the wood - processing parameters can be adjusted to better suit the material in question and

the most suitable raw material can be used for the product in question.

The forest industry presents some unique challenges to the traceability – item marking and identification, and information storage, retrieval and exchange between the different actors in the supply chain. Different supply chains with somewhat different challenges exist for different wood products e.g. pulp and paper, sawn timber, other wood products and energy wood. For simplicity, the discussion is limited here on the sawn timber supply chain with the focus on the round wood.

The wood harvesting takes place in the forest outdoor conditions in rough terrain. The wood is stored outdoors where there is ice, snow, rain, water, dirt, mud, etc. The transporta‐ tion is by trucks, train or by flotation in bunches from forest to the saw mills. The logs are subjected to impacts with machinery parts, other logs, rocks and the ground. At the saw mill the logs are handled with cranes and conveyors. These conditions are challenging for the log markings and their identification, and for the electronic hardware to be used.

The logs are sawn into boards, which usually destroys the physical markings in the wood and the boards have to be re-marked if full traceability over the chain is targeted. Board marking represents a different challenge from the log marking – the boards are handled in a more con‐ trolled industrial environment mostly indoors but the number of boards is larger than that of the logs as each log is sawn in to several boards and the value of each board is lower. Thus the board marking and identification needs to be very inexpensive to be feasible.

In the following Sections, the approaches considered for log marking and identification are discussed together with the specific challenges and limitations related to the use of UHF RFID technology in the forest industry.

#### **3.1. Wood traceability techniques**

The traceability can be based on marking and identifying the wood items such as logs and boards. Several methods have been considered for marking tree trunks and logs including painted markings, engraved markings, attached labels with a printed serial number (or oth‐ er alphanumerical data) or a bar code, fingerprinting techniques based on physical, chemical and/or genetic properties of the wood, and RFID [3]. Markings can be painted or printed on the wood surface and they can be read either by personnel or automatically using machine vision technology (cameras and software). Different coding schemes from simple colour co‐ des to serial numbers and to more advanced codes such as 2D matrix codes have been used. A medium-sized saw mill in Nordic countries typically processes a few million logs per year and thus individual identification of the logs requires a large number of unique codes to be available as the harvested logs may be also transported to several saw mills. Therefore, for unique identification only the more complex codes such as long serial numbers, barcodes or data matrices are feasible. Figure 5 shows examples of a bar code and a matrix code.

the contrast between the markings and the wood surface [5]. Matrix codes allow also for er‐ ror correction algorithms for improved readability. The achievable identification rate in the

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The use of visual markings on round wood, such as logs and tree trunks, is more complicat‐ ed than on boards. Logs have to be marked and identified outdoors where the environment is more challenging due to the more frequent occurrence of dirt, water, snow, ice and other materials obscuring the marking. The wood surface also varies more on logs than on sawn boards. In the Indisputable Key –project two log marking methods based on visual mark‐ ings were tested: luminescent nanoparticle (LNP) ink codes with a handheld marking device and harvester saw integrated printer that sprayed a matrix code or a custom bar code con‐ sisting of ink dots or stripes onto the log end [6]. The LNP ink dot or the line markings were read using an infrared camera. The trial achieved 75 % readability of the log markings. The harvester saw integrated marker was tested in marking logs in the forest that we identified using a camera at the log sorting station in a saw mill. Automatic detection rate of the cor‐ rect identity of the marked logs was nearly 40 % and by eye 74 % of the markings were read‐

To overcome the readability problems with visual marking techniques radio frequency iden‐ tification (RFID) has been tested for log identification. The main advantage of RFID technol‐ ogy is the capability for very high readability – radio waves do not require a line-of-sight and they propagate through most materials excluding highly conductive materials. Thus RFID technology is insensitive to the commonly found dirt, snow, ice and other opaque ma‐ terials on wood. In the past, RFID trials have used commercial transponders – mainly low frequency (LF, 125 kHz) and high frequency (HF, 13.56 MHz) tags. LF and HF tags have been available much longer and were considered to be better suited for wood marking than UHF (ultra high frequency, ~860-960 MHz) transponders with known problems on moist

Examples of the LF and HF transponder trials are described in [8,9]. In [8] logs were marked by inserting 23 mm long LF tags by Texas Instruments into logs in the forest using a proto‐ type applicator in the harvester. The reading range is reported to have been up to 0.5 m and reading accuracies in the range of 80-90 % were reported at the saw mill. Korten et al [9] report trials with HF transponder cards that were stapled on the logs and read using loop antennas in the forwarder, in a timber truck and at the saw mill. The reported reading range was 0.5-1 m depending on the reading location. Reading is reported to have been reliable.

Reliable automatic log identification is the basis for the traceability in the wood supply chain. UHF RFID technology offers the potential for high readability as the reading range is typically much longer than at LF and HF. Also, a few years ago GS1 introduced standardisa‐ tion for UHF RFID which facilitates the implementation of the RFID systems. The challenges related to the use of UHF RFID technology in wood supply chain are discussed in the next

board marking with visual codes seems to be in the range of 90-95 % [6].

able [7].

Section.

surfaces e.g. on wet wood and near metal.

**Figure 5.** Examples of a GS1-128 code and GS1 DataMatrix [4].

The code markings can be painted, printed, engraved, punched or otherwise imprinted on wood. The main attraction of this kind of markings is the low cost of the marking as each individual marking is inexpensive to make. The most common application of these visual marking codes is printing them onto the boards as the large number of the items and their relatively low value emphasizes the need for low cost marking. The main weakness of the visual markings is their readability – the codes can be obscured by dirt, snow and moisture. A line-of-sight is needed for the camera and optical equipment may need frequent mainte‐ nance in dusty industrial environments. Printing of the codes on the surface of wood is also challenging; the surface of wood varies and clear markings are difficult to achieve consis‐ tently. For example, markings printed accidentally on dirt or other material on the wood come of when this material comes of the wood. The drying of the wood may distort the shape of the marking and the wood may crack under it.

Multiple techniques have been developed to overcome the problems with visible markings on wood surfaces. One can use attachable labels for smooth printing surface but these labels may also be detached from the wood during the processing steps and the labels can also be covered by dirt, saw dust or other opaque material preventing their reading. Special lumi‐ nescent inks have been used to improve the readability of the visual markings by increasing the contrast between the markings and the wood surface [5]. Matrix codes allow also for er‐ ror correction algorithms for improved readability. The achievable identification rate in the board marking with visual codes seems to be in the range of 90-95 % [6].

**3.1. Wood traceability techniques**

306 Radio Frequency Identification from System to Applications

**Figure 5.** Examples of a GS1-128 code and GS1 DataMatrix [4].

shape of the marking and the wood may crack under it.

The traceability can be based on marking and identifying the wood items such as logs and boards. Several methods have been considered for marking tree trunks and logs including painted markings, engraved markings, attached labels with a printed serial number (or oth‐ er alphanumerical data) or a bar code, fingerprinting techniques based on physical, chemical and/or genetic properties of the wood, and RFID [3]. Markings can be painted or printed on the wood surface and they can be read either by personnel or automatically using machine vision technology (cameras and software). Different coding schemes from simple colour co‐ des to serial numbers and to more advanced codes such as 2D matrix codes have been used. A medium-sized saw mill in Nordic countries typically processes a few million logs per year and thus individual identification of the logs requires a large number of unique codes to be available as the harvested logs may be also transported to several saw mills. Therefore, for unique identification only the more complex codes such as long serial numbers, barcodes or

data matrices are feasible. Figure 5 shows examples of a bar code and a matrix code.

The code markings can be painted, printed, engraved, punched or otherwise imprinted on wood. The main attraction of this kind of markings is the low cost of the marking as each individual marking is inexpensive to make. The most common application of these visual marking codes is printing them onto the boards as the large number of the items and their relatively low value emphasizes the need for low cost marking. The main weakness of the visual markings is their readability – the codes can be obscured by dirt, snow and moisture. A line-of-sight is needed for the camera and optical equipment may need frequent mainte‐ nance in dusty industrial environments. Printing of the codes on the surface of wood is also challenging; the surface of wood varies and clear markings are difficult to achieve consis‐ tently. For example, markings printed accidentally on dirt or other material on the wood come of when this material comes of the wood. The drying of the wood may distort the

Multiple techniques have been developed to overcome the problems with visible markings on wood surfaces. One can use attachable labels for smooth printing surface but these labels may also be detached from the wood during the processing steps and the labels can also be covered by dirt, saw dust or other opaque material preventing their reading. Special lumi‐ nescent inks have been used to improve the readability of the visual markings by increasing

The use of visual markings on round wood, such as logs and tree trunks, is more complicat‐ ed than on boards. Logs have to be marked and identified outdoors where the environment is more challenging due to the more frequent occurrence of dirt, water, snow, ice and other materials obscuring the marking. The wood surface also varies more on logs than on sawn boards. In the Indisputable Key –project two log marking methods based on visual mark‐ ings were tested: luminescent nanoparticle (LNP) ink codes with a handheld marking device and harvester saw integrated printer that sprayed a matrix code or a custom bar code con‐ sisting of ink dots or stripes onto the log end [6]. The LNP ink dot or the line markings were read using an infrared camera. The trial achieved 75 % readability of the log markings. The harvester saw integrated marker was tested in marking logs in the forest that we identified using a camera at the log sorting station in a saw mill. Automatic detection rate of the cor‐ rect identity of the marked logs was nearly 40 % and by eye 74 % of the markings were read‐ able [7].

To overcome the readability problems with visual marking techniques radio frequency iden‐ tification (RFID) has been tested for log identification. The main advantage of RFID technol‐ ogy is the capability for very high readability – radio waves do not require a line-of-sight and they propagate through most materials excluding highly conductive materials. Thus RFID technology is insensitive to the commonly found dirt, snow, ice and other opaque ma‐ terials on wood. In the past, RFID trials have used commercial transponders – mainly low frequency (LF, 125 kHz) and high frequency (HF, 13.56 MHz) tags. LF and HF tags have been available much longer and were considered to be better suited for wood marking than UHF (ultra high frequency, ~860-960 MHz) transponders with known problems on moist surfaces e.g. on wet wood and near metal.

Examples of the LF and HF transponder trials are described in [8,9]. In [8] logs were marked by inserting 23 mm long LF tags by Texas Instruments into logs in the forest using a proto‐ type applicator in the harvester. The reading range is reported to have been up to 0.5 m and reading accuracies in the range of 80-90 % were reported at the saw mill. Korten et al [9] report trials with HF transponder cards that were stapled on the logs and read using loop antennas in the forwarder, in a timber truck and at the saw mill. The reported reading range was 0.5-1 m depending on the reading location. Reading is reported to have been reliable.

Reliable automatic log identification is the basis for the traceability in the wood supply chain. UHF RFID technology offers the potential for high readability as the reading range is typically much longer than at LF and HF. Also, a few years ago GS1 introduced standardisa‐ tion for UHF RFID which facilitates the implementation of the RFID systems. The challenges related to the use of UHF RFID technology in wood supply chain are discussed in the next Section.

#### **3.2. Challenges of UHF RFID technology in wood traceability**

Economically viable utilisation of the traceability requires that the wood items can be auto‐ matically identified. The item marking should not reduce their value or limit their use as a high quality raw material. The identification of wood items, the marking and reading, should be done without reducing the production efficiency e.g. by slowing it down and the costs related to the traceability should be reasonable to allow the benefits of the traceability to be utilised. The most significant part of the RFID system is the transponder as they are the most numerous component in the system and their performance is the basis of the overall system performance.

In paper making certain materials even in small concentrations are banned from the wood used as the raw material in pulping as they may cause problems in the quality of the paper produced. These materials include most plastics, coal and metal. This represents a challenge in the manufacturing of the transponders as the commonly used materials cannot be used. When round logs are sawn into rectangular boards some of the wood is left over and this wood is commonly chipped and sold to pulp mills. These wood chippings are a high quality raw material for paper making and a valuable by-product for saw mills. As transponders and their pieces may end up into these chippings, the same restrictions on the tag materials apply also to their use in the sawn timber supply. Thus conventional plastics cannot be used in the tags to avoid possible plastics contamination of the wood. The transponder design and materials have to be suitable for inexpensive mass production of the tags as the costs of

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the transponders typically forms the largest part of a RFID based traceability system.

The past RFID trials have focused on using available commercial RFID transponders to mark logs or other wood items. The results of these trials have varied, but in general the transponders intended for other applications have not been optimal for the needs of the for‐ est industry. Therefore, a custom made RFID solution was considered advantageous and was developed in an EU FP6 funded project called Indisputable Key [10]. The following Sec‐ tions describe the passive UHF RFID solution developed for the supply chain of the forest

The basis of the traceability utilising RFID is the transponder used to mark the wood items. The requirements for the transponder to be used in log marking in the Nordic sawn timber

These requirements are discussed in Section 3. The required compatibility of the material used with the pulp and paper making processes is perhaps the most constricting require‐ ment for the transponder. Typically a UHF RFID transponder consists of a thin plastic inlay with a metal foil for the antenna to which the microchip is connected and of a hard plastic casing. As common plastics are not accepted in the wood used for pulping, alternative mate‐ rials were considered. Biopolymers offer an interesting alternative to conventional plastics. In addition to the chemical compatibility with the paper making processes, the transponder material has to be suitable for insertion into the wood to ensure tag survival in the logs in

**4. RFID implementation for forest industry**

wood supply chain can be summarised as follows:

**•** Harmlessness in pulp and paper making

**•** Suitability for inexpensive mass production.

**4.1. RFID transponder for log marking in sawn timber supply chain**

industry.

**•** High readability

**•** Easy attachment into a log

Wood is a natural material with varying properties between the trees, logs and boards – and within them. The density of the wood, the grain orientation and the moisture content vary and thus the electromagnetic properties (the complex permittivity) also vary. The varying moisture content has the greatest effect on the permittivity and loss in the wood. The per‐ mittivity variation can lead to transponder antenna detuning and the high loss due to the high moisture content attenuates the radio signal. These effects have to be taken into ac‐ count in the design of the UHF RFID transponder to guarantee a sufficient reading range in all conditions in the wood supply chain. UHF label tags are therefore not suitable for mark‐ ing fresh wood with high moisture content. In practice, the reading of the tags at saw mills has to be done at distances up to 1 m. The reading range depends mostly on the transponder as the reader operation is governed by the radio regulations defining for example the maxi‐ mum allowed radiated power.

Reliable identification of the wood items requires that the tags have a high survival rate in the wood processing steps as transponders that have been destroyed or have been detached from the logs or boards cannot be read. In the RFID trials it has been frequently found out that tags glued, stapled or otherwise attached on the logs may be lost in the wood process‐ ing – especially during transportation, on conveyors and in debarking. In [9] it is reported that some 75 % of tags attached to the front-end of the log were lost in debarking at the saw mill. In trials carried out by the authors with tags attached onto the surface of the log ends typically up to a few per cent of the transponders were lost in each processing step which results in a significant loss of tags over the supply chain. Therefore, in order to ensure the transponder survival through the whole supply chain the tags has to be inserted inside the wood. Inside the wood the tag is protected from impacts which will improve the transpond‐ er survival rate considerable.

The transponder has to be attached on or preferably inserted into the wood by an applicator tool or machine and the tag has to be suitable for reliable and quick application. The applica‐ tion of the transponder should not reduce the production efficiency i.e. the application should not introduce significant delays. The application has to be done automatically where the wood processing is automatic and manual application is possible only if the wood is handled manually, e.g. felled with a chain saw or a reasonably small number of logs are marked. The transponder has to withstand the application to be readable.

In paper making certain materials even in small concentrations are banned from the wood used as the raw material in pulping as they may cause problems in the quality of the paper produced. These materials include most plastics, coal and metal. This represents a challenge in the manufacturing of the transponders as the commonly used materials cannot be used. When round logs are sawn into rectangular boards some of the wood is left over and this wood is commonly chipped and sold to pulp mills. These wood chippings are a high quality raw material for paper making and a valuable by-product for saw mills. As transponders and their pieces may end up into these chippings, the same restrictions on the tag materials apply also to their use in the sawn timber supply. Thus conventional plastics cannot be used in the tags to avoid possible plastics contamination of the wood. The transponder design and materials have to be suitable for inexpensive mass production of the tags as the costs of the transponders typically forms the largest part of a RFID based traceability system.
