Card with metal layer and an antenna

Patent metadata

Field	Value
Publication number	US-9721200-B2
Application number	US-201414543495-A
Country	US
Kind code	B2
Filing date	Nov 17, 2014
Priority date	Nov 18, 2013
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

In a smart card having an antenna structure and a metal layer, an insulator layer is formed between the antenna structure and the metal layer to compensate for the attenuation due to the metal layer. The thickness of the insulator layer affects the capacitive coupling between the antenna structure and the metal layer and is selected to have a value which optimizes the transmission/reception of signals between the card and a card reader.

First claim

What is claimed is:

1. A method for determining a preferred range of thickness for an insulator layer formed between an antenna structure and a metal layer comprising the steps of:
forming said insulator layer between said antenna structure and said metal layer, with said insulator layer being in direct contact with said antenna structure and said metal layer; where said insulator layer exhibits capacitance coupling the antenna structure and the metal layer; and wherein the thickness of the insulator layer affects the value of the capacitance between said antenna structure and said metal layer;
varying the thickness of the insulator layer over a range extending between a first, minimum, value and a second, higher, value for varying the capacitance exhibited between said antenna structure and said metal layer;
transmitting RF signals to the combination of the antenna structure, the insulator layer and the metal layer for selected values of insulator thickness within said range;
sensing the amplitude of the signals received at the antenna structure for said selected values of thickness of the insulator layer; and
identifying the insulator thickness which results in the highest amplitude of signal being received at the antenna structure.

2. A method as claimed in claim 1 further including the step of forming a smart metal card including the insulator layer formed between the antenna structure and the metal layer and wherein said insulator layer has a thickness corresponding to that which results in the highest amplitude of signal being received at the antenna structure.

3. A method as claimed in claim 2 wherein the step of transmitting RF signals includes a transponder located at a prescribed distance from the smart metal card and also includes the step of applying the RF signals at a prescribed operating frequency.

4. A method as claimed in claim 2 wherein said smart metal card includes a chip and a plurality of other layers to form a sturdy and reliable card.

5. A method as claimed in claim 1 wherein the metal layer is a holographic film and wherein the antenna structure is coupled to an RFID chip; and
further including the step of forming a number of plastic layers above the antenna structure and a like number of plastic layers below the metal layer.

6. A method as claimed in claim 1 wherein said second higher value is a maximum value of insulator thickness and wherein the value of insulator thickness which provides the highest amplitude of signal received is a thickness less than said maximum value of insulator thickness.

7. A smart card comprising:
an insulator layer formed between a metal layer and an antenna structure; said insulator layer having first and second surfaces, said first surface being in direct contact with said antenna structure and said second surface being in direct contact with said metal layer; and said insulator layer exhibiting a coupling capacitance between said antenna structure and said metal layer whose value is a function of the thickness of the insulator layer; said metal layer tending to attenuate the amplitude of radio frequency signals received at the antenna structure;
the thickness of the insulator layer being selected to have a value determined by analyzing the results obtained from testing corresponding structures by varying the insulator thickness which varies the value of the coupling capacitance and identifying for which value of insulator thickness best reception is obtained at the antenna structure; and
the selected thickness of the insulator layer being such that the amplitude of the received signal at the antenna structure is maximized.

8. A smart card as claimed in claim 7 wherein said antenna structure is coupled to an RFID chip; and wherein said smart card can transmit and receive signals to and from a card reader located at a predetermined distance from the smart metal card.

9. A smart card as claimed in claim 8 wherein said metal layer also tends to attenuate signals emitted via said antenna structure and wherein the thickness of the insulator layer is selected such that the amplitude of the transmitted signal from the antenna structure is maximized.

10. A smart card as claimed in claim 8 wherein said smart card includes the RFID chip coupled to said antenna structure and wherein said smart card also includes additional plastic and buffer layers.

11. A smart card as claimed in claim 7 wherein the selected value of insulator thickness is less than a possible thicker value for the insulator layer.

12. A method for forming a smart metal card comprising the steps of:
forming a combination including an antenna structure and a metal layer with an insulator layer formed in direct contact between the antenna structure and the metal layer; wherein said metal layer tends to attenuate the amplitude of radio frequency signals received at the antenna structure; where said insulator layer exhibits capacitance coupling the antenna structure and the metal layer; and wherein the thickness of the insulator layer affects the value of capacitance between said antenna structure and said metal layer;
and
forming the insulator layer with a thickness selected to provide a quasi-resonant frequency response such that the amplitude of the signal received at the antenna structure is maximized; and
wherein the value of said insulator thickness is obtained by testing a number N of different combinations, similar to said combination, in which the thickness of the insulator is varied and identifying which thickness provides the best reception to RF signals.

13. A method as claimed in claim 12 wherein the smart card can be formed with a thicker insulator layer, but the selected value of thickness provides better reception to RE signals.

14. A method for making smart metal cards including the steps of:
forming N test cards, where N is an integer greater than 1, each one of said N test cards including an insulator layer formed in direct contact between an antenna structure and a metal layer; where said insulator layer exhibits capacitance coupling the antenna structure and the metal layer; and wherein the thickness of the insulator layer controls to a great degree the value of capacitance between said antenna structure and said metal layer; and wherein the thickness of the insulator layer of the N test cards have different values;
transmitting selected RF signals to each one of said N test cards;
sensing the amplitude of the signals received at the antenna structure of each one of said N test cards; and
identifying the test card having the highest amplitude of signal received at the antenna structure.

15. A method as claimed in claim 14 wherein the step of transmitting RF signals includes a transponder located at a prescribed distance from the smart metal card.

16. A method as claimed in claim 15 wherein the step of transmitting RF signals includes the step of applying the RF signals at a prescribed operating frequency; and
further including the step of forming a number of plastic layers above the antenna structure and a like number of plastic layers below the metal layer.

Assignees

• Composecure Llc
• Composecure L L C

Inventors

• Herslow John
• Logan Michele
• Finn David

Classifications

• H01Q1/2225

  used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal · CPC title

• H01Q1/38 Primary

  formed by a conductive layer on an insulating support {(patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface  H01Q15/142)} · CPC title

• G06K19/07783

  the coil being planar · CPC title

• G06K19/07722 Primary

  the record carrier being multilayered, e.g. laminated sheets (flat articles in general, see B32B37/00) · CPC title

• Y10T29/49016

  Antenna or wave energy "plumbing" making · CPC title