Patent Application
20230312866
The present disclosure relates to an isolation sheet, the preparation method thereof and an ultra-high frequency (UHF) radio frequency identification (RFID) tag that uses the isolation sheet for reducing interference from the metal attached to or near the UHF RFID tag when the RFID tag is in UHF environment, thereby improving the recognition efficiency.
UHF refers to electromagnetic waves with frequencies ranging from 300 MHz to 3 GHz and UHF technology has been widely used in RFID tags, such as UHF RFID tags used in warehouse management. “UHF RFID tag” refers to an RFID tag that can be used in the UHF frequency band. This is because UHF RFID tags have the characteristics of non-contact sensing, a wide reading range and multiple tags can be read by a UHF RFID reader (or RFID read-write device) at once, thereby shortening operation time.
When a UHF RFID tag is attached to or near the surface of a typical non-metallic product, such as a plastic tray, the UHF RFID reader can start reading the UHF RFID tag from a relatively long distance, which is known as the “original reading distance”. However, when the UHF RFID tag is attached to or near a metal product, such as a stainless steel or aluminum pot placed on a warehouse shelf, or a bottle of water or glass bottle, the input impedance of the UHF RFID tag will rapidly decay due to its proximity to the metal or bottle surface. In this case, the UHF RFID reader must be closer to the tag than the “original reading distance” to have a chance of reading the UHF RFID tag, which is called the “maximum reading distance”. That is the position starting from the UHF RFID tag and gradually moving farther from the UHF RFID tag until the farthest position that the UHF RFID tag can still be read. Any position beyond the position the data cannot be read from the UHF RFID tag. Thus, when the UHF RFID tag is attached to or near the surface of the non-metallic product, the “original reading distance” is greater than the “maximum reading distance” when the UHF RFID tag is attached to or near the surface of the metallic product. Sometimes, if the UHF RFID tag's input impedance decay is too severe, it will cause the UHF RFID tag to be unreadable and the maximum reading distance will be marked as zero.
Currently, in order to overcome the problem of UHF RFID tags being attached to or near metal objects, an isolation sheet is typically placed between the metal object and the UHF RFID tag to reduce the impact of the metal object on the maximum reading distance. For example, in prior art 1 (China Patent Publication No. CN109713427B), a multilayer composite comprising a polymer film and a foam medium layer is used as the isolation sheet. However, the thickness of the foam medium layer alone must be greater than 0.5 mm to achieve isolation effect (i.e., the UHF RFID reader can read the data from the UHF RFID tag) and the double-layer design generates the complexity and difficulty for manufacturing processes. Additionally, prior art 2 (China Patent Publication No. CN103401055B) uses magnetic materials as a single-layer isolation sheet to improve the above-mentioned problems in prior art 1. However, the same problem also occurs in prior art 2. The thickness of the magnetic material must be greater than 0.5 mm (millimeters), and at this time, the maximum reading distance is only 1.5 m (meters). Even if the thickness of the magnetic material is increased to 5 mm, the maximum reading distance is only 5 m.
With the miniaturization of both metal products and UHF RFID tags, the thickness of the isolation sheet also becomes crucial. In other words, the thickness of the isolation sheet must be reduced. The thickness of the isolation sheet used in the prior arts 1 and 2, which is greater than 0.5 mm, is no longer sufficient for the industry's needs. In fact, the industry has already faced the need to read UHF RFID tags when the thickness of the isolation sheet is less than 0.5 mm.
Although prior art 2 describes the numerical ranges of the real and imaginary parts of the dielectric constant and the loss tangent, as well as the real and imaginary parts of the magnetic permeability and the loss tangent, prior art 2 did not pay attention to the mutual influence of the dielectric constant and the magnetic permeability. This is also a major factor that caused prior art 2 failing to reduce the thickness of the isolation sheet to less than 0.5 mm under the circumstances that the UHF RFID tag still is able to be read.
Based on the rich professional knowledge and practical experience over the years, the inventor has improved the invention in order to solve various problems caused by conventional isolation sheets. Therefore, the inventor has come up this disclosure with the assistance of rich professional knowledge and practical experience.
The isolation sheet provided by the present disclosure, even when its thickness is less than 0.5 mm and is applied between the back of the antenna of the UHF RFID tag and a metal product, the information stored in the UHF RFID tag can still be read by the UHF RFID reader at a predetermined distance in front of the antenna of the UHF RFID tag that operates within the frequency bandwidth of 860 MHz to 960 MHz, thereby achieving the effect of thinning. The isolation sheet is an integrated molding single-layer structure. “Integrated molding” means that the isolation sheet is formed by the same process without assembly, therefore having the advantage of simple manufacturing process. In addition, the isolation sheet is composed of a resin layer and a plurality of insulated soft magnetic particles dispersed in the resin layer. The shape of the insulated soft magnetic particles is selected to be spherical and the weight percentage of the insulated soft magnetic particles in the isolation sheet can be adjusted so that the product of the imaginary part of the dielectric constant (ϵ′), the dielectric quality factor (Qϵ), the real part of the magnetic permeability (μ′) and the magnetic quality factor (Qμ) confined to this single-layer structure is between two predetermined different values, thereby achieving the effect of simultaneously matching the electrical and magnetic properties in the single-layer structure. The dielectric quality factor (Qϵ) and the magnetic quality factor (Qμ) are described later.
This invention provides an isolation sheet, includes a resin layer and a plurality of insulated soft magnetic particles dispersed in the resin layer; the isolation sheet has a real part of dielectric constant (ϵ′), an imaginary part of dielectric constant (ϵ″), a dielectric quality factor (Qϵ), a real part of magnetic permeability (μ′), an imaginary part of magnetic permeability (μ″) and a magnetic quality factor (Qμ). The dielectric quality factor (Qϵ) is the quotient obtained by dividing the real part of the dielectric constant (ϵ′) with the imaginary part of the dielectric constant (ϵ″), the magnetic quality factor (Qμ) is the quotient obtained by dividing the real part of the magnetic permeability (μ′) with the imaginary part of the magnetic permeability (μ″), wherein the product of the imaginary part of dielectric constant (ϵ″), dielectric quality factor (Qϵ), real part of magnetic permeability (μ′), and magnetic quality factor (Qμ) is between 3000 and 4500.
In one embodiment of the isolation sheet, wherein the product of the imaginary part of the dielectric constant (ϵ′), the dielectric quality factor (Qϵ), the real part of the magnetic permeability (μ′) and the magnetic quality factor (Qμ) is between 3522.40 and 4460.50.
In one embodiment of the isolation sheet, wherein the product of the imaginary part of the dielectric constant (ϵ′), the dielectric quality factor (Qϵ), the real part of the magnetic permeability (μ′) and the magnetic quality factor (Qμ) is between 3550 and 4000.
In one embodiment of the isolation sheet, wherein the real part of the dielectric constant (ϵ′) is between 10 and 20, the imaginary part of the dielectric constant (ϵ″) is between 0.8 and 1.5, the real part of the magnetic permeability (μ′) is between 5.0 and 6.5, the imaginary part of the magnetic permeability (μ″) is between 1.0 and 2.5, the dielectric quality factor (Qϵ) is between 10 and 20 and/or the magnetic quality factor (Qμ) is between 2.0 and 5.0.
In one embodiment of the isolation sheet, wherein the real part of the dielectric constant (ϵ′) is between 11.15 and 16.53, the imaginary part of the dielectric constant (ϵ″) is between 0.8 and 1.33, the real part of the permeability (μ′) is between 5.23 and 6.12, the imaginary part of the permeability (μ″) is between 1.23 and 2.42, the dielectric quality factor (Qϵ) is between 12.43 and 19.50 and/or the magnetic quality factor (Qμ) is between 2.16 and 4.69, the product of the real part of the dielectric constant (ϵ′) and the dielectric quality factor (Qϵ) is between 155.40 and 311.81 and/or the product of the real part of the permeability (μ′) and the magnetic quality factor (Qμ) is between 11.30 and 28.70.
In one embodiment of the isolation sheet, wherein the insulated soft magnetic particles are spherical in shape, the insulated soft magnetic particles have a core part and a shell part surrounding the core part; the core part is a soft magnetic material made of carbonyl iron powder, and the shell part is made of an insulating material and sequentially coats the core part with a phosphate film and a silicate film by overlay coating from the inside out.
In one embodiment of the isolation sheet, the plurality of insulated soft magnetic particles accounts for 70 wt % to 87 wt % of the isolation sheet, the resin layer is composed of a resin material, the resin material accounts for 13 wt % to 30 wt % of the isolation sheet, the resin material and the plurality of insulated soft magnetic particles account for 100 wt % of the isolation sheet in total, and the particle size of the insulated soft magnetic particles is between 1 μm and 5 μm.
In one embodiment of the invention, wherein the plurality of insulated soft magnetic particles accounts for 70 wt % to 77.5 wt % of the isolation sheet, and the resin material accounts for 22.5 wt % to 30 wt % of the isolation sheet.
In one embodiment of the disclosure, the isolation sheet is an integrated molding single-layer structure.
The present disclosure also provides a UHF RFID tag, includes an antenna and the aforementioned isolation sheet disposed below the antenna.
In one embodiment of the UHF RFID tag, wherein the thickness of the isolation sheet is less than 0.5 mm.
In one embodiment of the UHF RFID tag, wherein the UHF RFID tag and/or the isolation sheet are suitable for a working bandwidth of 860 MHz to 960 MHz.
The present disclosure also provides a method for manufacturing the isolation sheet, includes mixing a thermoplastic elastomer with a plurality of insulated soft magnetic particles after weighing, then milling the mixture into a flexible rolled body for the ease of printing and bonding with the antenna of a UHF RFID tag, and subsequently cutting into sheet-shaped isolation sheets. Since the thickness is less than 0.5 mm, it is more suitable for making flexible rolled body (commonly known as rolled materials), which can be automatically bonded with tags and is suitable for mass production.
In one embodiment of the manufacturing method of an isolation sheet, wherein the plurality of insulated soft magnetic particles accounts for 70 wt % to 87 wt % of the isolation sheet, the thermoplastic elastomer accounts for 13 wt % to 30 wt % of the isolation sheet, the thermoplastic elastomer and the plurality of insulated soft magnetic particles account for 100 wt % of the isolation sheet in total, and particle size of the insulated soft magnetic particles is between 1 μm and 5 μm.
In one embodiment of the manufacturing method of an isolation sheet, the thickness of the isolation sheet is less than 0.5 mm.
Accordingly, the present disclosure provides a flexible integrated molding single-layer isolation sheet made of insulated soft magnetic particles and thermoplastic elastomer. By adjusting the weight percentage of the insulated soft magnetic particles in the isolation sheet, the product of the imaginary part (ϵ′) of the dielectric constant, the dielectric quality factor (Qϵ), the real part (μ′) of the magnetic permeability and the magnetic quality factor (Qμ) is limited to a range between two different predetermined values, thereby achieving the effect of simultaneously matching the electrical and magnetic properties in the single-layer structure of the isolation sheet. Thereby even if the thickness of the isolation sheet is less than 0.5 mm and the isolation sheet is placed between the back of the antenna of a UHF RFID tag and a metal product, an RFID reader located in front of the antenna of the UHF RFID tag and at a predetermined distance away may still read the information stored in the antenna of the UHF RFID tag at a working frequency band of 860 MHz to 960 MHz.
The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
In order to understand the technical features, contents, advantages and effects that can be achieved by the present disclosure, the expression of the present disclosure in conjunction with the attached drawings will be described in detail below. The purpose of the drawings used is only for illustrating and assisting the specification and may not necessarily represent the actual proportion and precise configuration after the implementation of the present disclosure. Therefore, the interpretation of the proportion and configuration relationship of the attached drawings should not limit the scope of the present disclosure in actual implementation, which is hereby stated.
In order to make the description of the content disclosed by the present disclosure more detailed and complete, the following description provides explanatory descriptions for the embodiment and specific examples of the present disclosure. However, these are not the only forms of implementation or application of the specific embodiments of the present disclosure. In addition, the use of “˜” and “between . . . and . . . ” in this specification and the claims refers to a numerical range that includes the values before and after the “˜” and “. . . and . . . ” as the lower limit and upper limit values. The term “wt %” in this specification and the claims refers to weight percent and the term “particle size” refers to the particle size measured using a laser particle size analyzer.
<Structure of the Isolation Sheet and UHF RFID Tag>
Referring to
The resin layer 321 is composed of a resin material that can be a thermoplastic polyurethane elastomer or a thermoplastic polyolefin elastomer. The resin material accounts for 13 wt % to 30 wt % of the isolation sheet.
The insulated soft magnetic particles 322 are spherical in shape. Each insulated soft magnetic particle 322 has a core part 3221 and a shell part 3222 surrounding the core part 3221. The core part 3221 is made of a soft magnetic material. The core part 3221 is a carbonyl iron powder ball. The shell part 3222 is made of an insulating material and sequentially coats the core part 3221 with a phosphate film and a silicate film by overlay coating from the inside out. The phosphate film accounts for 0.5 wt % to 5 wt % of the core part 3221 and the silicate film accounts for 0.5 wt % to 3 wt % of the core part 3221. The particle size of the insulated soft magnetic particles 322 is between 1 μm and 5 μm. The plurality of insulated soft magnetic particles 322 account for 70 wt % to 87 wt % of the isolation sheet. Preferably, the resin material and the plurality of insulated soft magnetic particles account for 100 wt % of the isolation sheet in total.
<Manufacturing Method of the Isolation Sheet>
After a thermoplastic polyurethane elastomer and insulated soft magnetic particles are weighed and mixed according to the weight percentages listed in the following Table 1 (comprising Table 1-1 and Table 1-2), put into a mixing mill for mixing. After fully mixing the thermoplastic polyurethane elastomer and the insulated soft magnetic particles to form a uniform gel material, the material is discharged. Next, the gel material is passed through a rolling mill and is milled according to the thicknesses listed in Tables 1 and 2 to form a flexible rolled body and then cut into sheets to prepare the isolation sheets of Embodiments 1-3 and Comparative Examples 1-2. Therefore, the isolation sheet is an integrated molding single-layer structure. Integrated molding means that the isolation sheet is formed by the same process (rolling mill) without assembly. Among them, Comparative Examples 1-2 use insulated soft magnetic particles with sheet-shaped FeSiCr (D) and with sheet-shaped FeSiAl (E) instead of spherical carbonyl iron powder for the core parts.
<Evaluation and Testing for the Performance of the Isolation Sheet>
Referring to
In table 1 (comprising Table 1-1 and Table 1-2), ϵ′ represents the real part of the dielectric constant, ϵ″ represents the imaginary part of the dielectric constant, Qϵ represents the dielectric quality factor, μ′ represents the real part of the permeability μ″ represents the imaginary part of the permeability and Qμ represents the magnetic quality factor. The dielectric quality factor (Qϵ) is the quotient obtained by dividing the real part of the dielectric constant (ϵ′) with the imaginary part of the dielectric constant (ϵ″). The magnetic quality factor (Qμ) is the quotient obtained by dividing the real part of the permeability (μ′) with the imaginary part of the permeability (μ″). ϵ′×Qϵ represents the product of the real part of the dielectric constant (ϵ′) and the dielectric quality factor (Qϵ) and μ′×Qμ represents the product of the real part of the permeability (μ′) and the magnetic quality factor (Qμ).
It may be known from Table 1 (comprising Table 1-1 and Table 1-2) that when the thickness of the isolation sheet is 0.5 mm as shown as Examples 1 to 3, the recovery percentage is greater than 40% and the maximum reading distance is greater than 1.50m, so they are qualified products. On the other hand, in Comparative Examples 1 and 2, when the thickness of the isolation sheet is 0.5 mm, the recovery percentage is less than 40% and the maximum reading distance is less than 1.50 m, so they are unqualified products. Table 1 (comprising Table 1-1 and Table 1-2) further shows that the “electromagnetic factor” of Examples 3, 2, and 1 are 3522.40, 3834.82, and 4460.50, respectively. The electromagnetic factor is the product of the imaginary part of the dielectric constant (ϵ′), the dielectric quality factor (Qϵ), the real part of the magnetic permeability (μ′) and the magnetic quality factor (Qμ). Therefore, the electromagnetic factor of the isolation sheet of the present disclosure ranges from 3000 to 4500, preferably from 3522.40 to 4460.50 and more preferably from 3550 to 4000. As shown in Table 1 (comprising Table 1-1 and Table 1-2), the higher the value of the electromagnetic factor, the higher the recovery percentage. For example, the electromagnetic factors of Examples 3, 2 and 1 are 3522.403834.82
4460.50 respectively that gradually increases, the recovery percentages of Examples 3, 2, and 1 are 40.2%, 51.3%, and 53.1% respectively, also gradually increases. Therefore, the “electromagnetic factor” mentioned in the present disclosure is highly positively correlated with the recovery percentage. In other words, the isolation sheets may be designed with specific thickness and recovery percentages based on the electromagnetic factor, which is a major creative aspect of the present disclosure. The “electromagnetic factor” indicates that the isolation sheet of the present disclosure takes into account the combined effects of electrical and magnetic properties in the integrated molding single-layer structure, rather than separately considering the electrical or magnetic effects in each layer before stacking and assembling in the multi-layer structure.
Moreover, ϵ′ may be between 10 and 20, ϵ″ may be between 0.8 and 1.5, μ′ may be between 5.0 and 6.5, μ″ may be between 1.0 and 2.5, Qϵ may be between 10 and 20 and/or Qμ may be between 2.0 and 5.0. As shown in Table 1 (comprising Table 1-1 and Table 1-2), preferably, ϵ′ may be between 11.15 and 16.53, ϵ″ may be between 0.8 and 1.33, μ′ may be between 5.23 and 6.12, μ″ may be between 1.23 and 2.42, Qϵ may be between 12.43 and 19.50, Qμ may be between 2.16 and 4.69 and the product of ϵ′ and Qϵ may be between 155.40 and 311.81 and/or the product of μ′ and Qμ may be between 11.30 and 28.70.
Additionally, it is preferable that the plurality of insulated soft magnetic particles account for 70 wt %˜77.5 wt % of the isolation sheet and the resin material accounts for 22.5 wt %˜30 wt % of the insulating sheet. The resin material and the plurality of insulated soft magnetic particles account for 100 wt % of the isolation sheet in total.
<Unexpected Effect 1>
Table 2 shows the production of isolation sheets of different thicknesses using the thermoplastic polyurethane elastomer and insulated soft magnetic particles of Example 1 in Table 1 (comprising Table 1-1 and Table 1-2) and the maximum reading distance and recovery percentage are measured according to the aforementioned method and equipment.
When the thickness of the isolation sheet is 1.0 mm, the recovery percentage may reach 100% and the maximum reading distance has been restored to 3.76 m (i.e., the “original reading distance” of the UHF RFID tag). However, the unexpected discovery from table 2 is that when the thickness of the isolation sheet reaches 2.0 mm and 3.0 mm, the maximum reading distance exceeds 3.76 m and reaches 5.82 m and 7.33 m, respectively. When converted to recovery percentage, they are 154.7% and 194.7%, respectively. In other words, the surprising finding is that when the thickness of the isolation sheet of the present disclosure exceeds a specific thickness, it will cause a gain effect on the isolation sheet, which will make the maximum reading distance exceed or equal the original reading distance. This breaks the limitation mentioned in the prior art or literature, which previously believed that the maximum reading distance cannot be greater than the original reading distance.
Table 2 further shows that when the thickness of the isolation sheet is 0.4 mm, the recovery percentage is 42.4%, which is greater than the passing standard of 40%, and the maximum reading distance is 1.60 m, which is also greater than the passing standard of 1.50 m. In other words, the surprising finding is that the isolation sheet of the present disclosure breaks the limitations mentioned in the prior arts 1 and 2. The prior arts 1 and 2 both believe that the isolation sheet must be greater than 0.5 mm to allow the UHF RFID reader to read the data of the UHF RFID tag.
Furthermore, table 2 shows that even when the thickness of the isolation sheet is 0.1 mm, the data of the UHF RFID tag can still be read within a distance of 0.33 m, even if its recovery percentage is only 8.7%. In other words, the surprising finding is that the isolation sheet of the present disclosure breaks the limitations mentioned in the prior arts 1 and 2. The prior arts 1 and 2 both believe that when the thickness of the isolation sheet is less than 0.5 mm, the UHF RFID reader cannot read the data of the UHF RFID tag.
<Unexpected Effect 2>
Based on the obtained commercially available isolation sheet (composition unknown) with a thickness of 5 mm, the isolation sheet with a thickness of 5 mm in Example 1 was further used on intention, the instrument and method described in the <Evaluation and testing for the performance of the isolation sheet>section are used for testing the isolation sheets but the operating bandwidth is changed to 850 MHz˜950 MHz. The test results are combined and plotted in
According to
In addition, it is further known from
<Proportion of Resin Material and Insulated Soft Magnetic Particles in the Isolation Sheet>
The present disclosure further produces isolation sheets of different proportions of resin material and insulated soft magnetic particles and different thicknesses according to Table 3 below and measures the maximum reading distance and recovery percentage using the aforementioned method and equipment.
As previously described, when the thickness of the isolation sheet is 0.5 mm, a recovery percentage greater than 15% or a maximum reading distance greater than 0.5 m is acceptable. Therefore, in Embodiments 1-1, 1, 1-2 and 1-3, the recovery percentages measured with a thickness of 0.5 mm are all greater than 15% and the maximum reading distances are all greater than 0.5 m. Thus, the resin material accounts for 13 wt % to 30 wt % of the isolation sheet and the plurality of insulated soft magnetic particles 322 account for 70 wt % to 87 wt % of the isolation sheet. The resin material and the plurality of insulated soft magnetic particles account for 100 wt % of the isolation sheet in total.
In summary, the present disclosure has the following advantages: (1) The electromagnetic factors of the isolation sheet in the present disclosure are limited to the product of the imaginary part of the dielectric constant (ϵ′), the dielectric quality factor (Qϵ), the real part of the permeability (μ′) and the magnetic quality factor (Qμ) between 3000 and 4500, preferably between 3522.40 and 4460.50 and more preferably between 3550 and 4000, to achieve the effect of simultaneously matching the electrical and magnetic properties in the single-layer structure. (2) Placing the isolation sheet of the present disclosure correspondingly between the antenna of the UHF RFID tag and the metal product, excellent recovery rates may be measured. (3) When the thickness of the isolation sheet of the present disclosure exceeds a specific thickness, a gain effect is generated, which allows the maximum reading distance to exceed or be greater than the original reading distance. The limitations mentioned in prior art or literature is broken through. (4) The isolation sheet of the present disclosure has broken through the limitation that the isolation sheet must be larger than 0.5 mm in the prior arts. (5) By using the isolation sheet of the present disclosure for the UHF RFID tags, when the UHF RFID tag reader reads the antenna data, the effect of high stability and the antenna data may be read throughout the full frequency domain is achieved.
The above-described embodiments are only intended to illustrate the technical ideas and features of the present disclosure and their purpose is to enable those skilled in the art to understand the contents of the present disclosure and implement them. They cannot limit the scope of the present disclosure and any equal changes or modifications made based on the spirit of the present disclosure should still be within the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 111112956 | Apr 2022 | TW | national |
