WO2021064742A1

WO2021064742A1 - Zns nano particle thin film deposited metamaterial antenna for notch frequency application

Info

Publication number: WO2021064742A1
Application number: PCT/IN2020/000020
Authority: WO
Inventors: Kumaresh Sarmah; Sivaranjan Goswami; Angana Sarma; Kumar Kandarpa SARMA; Sunandan Baruah
Original assignee: Kumaresh Sarmah; Sivaranjan Goswami; Angana Sarma; Sarma Kumar Kandarpa; Sunandan Baruah
Priority date: 2019-09-30
Filing date: 2020-09-29
Publication date: 2021-04-08

Abstract

A ZnS Nanoparticle Thin Film Deposited Metamaterial Antenna For Notch Frequency Application comprising of a 20-25 nm ZnS nanomaterial thin film grown in the gap(1) of a complementary split ring resonator (CSRR) unit cell(2). The method comprises of the steps- (a)boiling Zn salt solution at 100°C and then adding 1/5th the volume of 1.1%, chitosan in mild acetic acid (1-2%) and then adding aqueous Na₂S in stoichiometric amounts; (b) allowing the solution to cool and then centrifuging the solution at 4000-5000 rpm to obtain a ZnS colloid which is then electrosterically stabilized by chitosan capping; (c)covering the conducting portion of the CSRR unit cell with a tape and then dropping ZnS colloid obtained from step (b) on it and then drying the unit cell at 80°-90°C; (d) repeating the step(c) for 3 to 5 times. This antenna results in the return loss parameter (S₁₁) getting significantly improved at its resonant frequency.

Description

DESCRIPTION

Title of the Invention:

ZnS Nano Particle Thin Film Deposited Metamaterial Antenna For Notch Frequency Application.

Technical Field:

This invention relates to a Complementary Split Ring Resonator (CSRR) microstrip antenna having ZnS nanomaterial-based thin film deposited between the rings of the CSRR. Such an antenna can greatly enhance the return loss(S 11) at both the resonant and notched frequency.

Background Art:

Antennas are basically classified into either resonating type or non-resonating type. To achieve more than one band of operations, typically a single band microstrip antenna can be converted to the multiband antenna by modifying the dimensions, of the antenna or by applying different cut slots along with introducing resonating structures such as CSRR in the ground plane of the antenna. To achieve multiple resonating frequencies over a single band antenna, designers need to compromise with either the bandwidth of operation or the directivity of the antenna at a resonating frequency.

Metamaterial etched antennas can give dual-band frequency application, by compromising the return loss (Sn) of the antenna. Complementary split ring resonator(CSRR) is a pair of narrow opening loops with splits in them at opposite ends. CSRR is etched at the ground plane of a microstrip antenna to introduce metamaterial effect in the overall structure. CSRR is planar metamaterial structures that can yield effectively negative permittivity of material in narrow bands near its resonant frequencies. Due to this negative value of permittivity the radiation property such as bandwidth, gain and return loss of an antenna is found to be enhanced with the application of CSRR based structures.

US Patent No. 9019160B2 (Mohammad S. Sharawi, Muhammad Umar Khan, Ahmad Bilal Numan, 2015) provides CSRR loaded MIMO antenna for wireless communication. Here CSRR is loaded at the ground plane of the antenna to achieve desired frequency isolation between closely placed 2x2 MIMO patch antenna. The MIMO antenna has four elements of raditing patch with overall dimensions of 100x50x0.8 mm². Four CSRR strucures are fabricated at the bottom side of the antenna substrate to obtained desired isolation of -10 dB between the closely spaced patch elements. However, in the case, there is a requirement of rejection of unwanted frequency recived by the individual antenna elements apart from its resonating frequency. As the four elements of CSRR are used for the purpose to provide isolations from all other frequency except the resonating frequency of the antenna at 2.45 GHz ISM band. Such isolation demands more space in the antenna system. However, in our present invention is a single antenna system where two possible unwanted signals can be prevented from causing interference at the receiver system.

US patent no. US7233296B2 ( Hyok J. Song, Tsung Yuan Hsu, Daniel F.

Sievenpiper, Timothy J. Talty, Hui-pin Hsu, 2005) discues the invention about an optically transparent thin film of conductive surfaces over which antenna structure is grown. Here in this invention antenna is fabricated over a surfaces made up of transparent thin-film conducting material using indium tin oxide (ITO). AgHT™-4 type film substrate material is used to fabricate the transparent antenna. Such transparent antenna can be easyly mounted over transparent galss windows. In this case thin film deposited conducting material is acting as an electromagnetic radiator mounted over the glass window. However, in our case semiconducr thin film of ZnS nano particle is used to improve the metamaterial behaviour of the CSRR based antenna. In our case thin film of ZnS nano particle is deposited between the gaps of CSRR structure to improve the impedance of the antenna at notched frequency.

Such improvent in the impedance can significantly enhance the attenuation of the antenna at notched bands.

US patent no. US7261916B1 (Kun-Ta Lu, Hsin-Chun Lu, Han-Lun Lin, 2006) presents a method of manufacturing a thin-film antenna system. In this invention, the antenna substrate is coated with a layer of organic material. The typically used substrate materials are polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), glass, acrylic resin or other materials with similar properties. Here the radiating antenna fabricated over such substrate is made from conducting organic polymer materials. This invention describes only the deposition method of an organic polymer as an antenna system which can be applicable for communication system. However, in our present invention semiconducting nano praticel such as ZnS thin film is deposited to improve the radiation performance of a microstrip patch antenna fabricated over a FR4 substrate. As this CSRR structure at ground plane produces notching behavior in the microstrip antenna along with the resonating frequency, therefore there is a need to enhance the return loss(Si i) parameter of the antenna at its operating frequency as well as at notched frequency. By modifying the geometry and varying the dimension of the CSRR and the microstrip antenna, improvement in return loss parameter of the antenna is not significant. Therefore, there is a need for introducing alternate technology to enhance the return loss of an antenna at its resonating frequency. Due to the presence of gaps between the circular conducting loops in the CSRR geometry, the impedance at desired notched frequencies and the resonant frequency is not matched. If the gap between the conducting circular loops of CSRR can be filled with some nanomaterial-based artificial material the impedance at resonating as well as notched frequency can be enhanced. In our invention, we introduce ZnS nanomaterial- based thin film between the narrow opening gaps of the CSRR metallic structures

Disclosure of Invention:

The present invention provides a metamaterial based microstrip patch antenna loaded with a Complementary Split Ring Resonator (CSRR) unit cell(2) at the ground plane of the antenna with a 20nm to 25 nm ZnS nanomaterial thin film deposited in the gap(l) of the said CSRR. It enables the return loss (Su) at the resonant frequency as well as at a notched frequency of the antenna to be enhanced without changing the shape or size of the same. Further, this invention also relates to a method of depositing the said ZnO thin film in the said gap of the said antenna. The said method comprises of the following steps of- (a)boiling the salt solution at 100°C and then adding l/5th the volume of 1.1%, chitosan in mild acetic acid (1-2%) and then adding aqueous Na2S in stoichiometric amounts; (b)Removing heat and allowing the solution to cool and then centrifuging the solution at 4000-5000 rpm to obtain a ZnS colloid which in turn is then electrosterically stabilized by chitosan capping; (c)covering the conducting portion of the CSRR unit cell with a tape and then dropping ZnS colloid obtained from step (b) on it and then the unit cell is dried at about 80-90°C; (d) repeating the step(c) for 3 to 5 times.

Brief Description of Drawings:

Figure 1. Shows the thin film of ZnS nanoparticle deposited Complementary Split Ring Resonator unit cell(2).

Figure 2. Shows a comparison of return loss (Si i) parameter of the antenna with and without ZnS nano-thin film.

Figure 3. TEM image of the ZnS nanoparticles for deposition of the thin film at CSRR. Figure 4. XRD image of the nano ZnS particles.

Figure 5: Practical antenna top view.

Figure 6: Practical Antenna bottom view. Figure 7. The radiation pattern of the antenna at 2.4 GHz, the operating frequency of the antenna.

Figure 8. The radiation pattern of the antenna at 3.6 GHz, the notched frequency of the antenna.

Best Mode for Carrying Out the Invention:

In the present invention, a planar microstrip antenna comprising of a microstrip patch with an inset feed line on one side and a ground plane having a Complementary Split Ring

Resonator[CSRR] on the other side is used. Here, a thin film of ZnS nanomaterial is grown or deposited in the gap(l) typically being 0.5 mm wide, of the CSRR unit cell(2) at the ground plane of the antenna. The deposited film has a thickness of 20-25 nanometers and the ZnS nanoparticles used for making the said thin film are in the size range of 5 to 7 nanometres. The said antenna is typically fabricated over a glass epoxy laminated dielectric substrate and has an operating frequency of 2.4 GHz and create a notch at 3.6GHz.

The method employed in the invention for preparing and depositing the ZnS nanoparticles is to be carefully followed. It comprises of the following steps- Step (a): ZnS nanoparticles are synthesized through a chemical precipitation method where Zn²⁺ ions are dissociated in water from a corresponding salt under stirring at room temperature. Here, salt such as Zn(C¾COO)2 or Z^h(Nq3)2 or ZnCh is used. The salt solution is first boiled at 100° C and then added l/5th the volume of 1.1%, chitosan in mild acetic acid (1-2%) and then added aqueous Na2S in stoichiometric amounts (~5 times the concentration of the salt solution). ZnS forms immediately and the macroparticles settle down while the nanoparticles remain suspended.

Step (b): Next, the heat is removed from the solution and it is allowed to cool to room temperature. Then the solution is centrifuged at 4000-5000 rpm for 20 minutes to obtain a ZhS colloid which in turn is then electrosterically stabilized by chitosan capping.

Step (c): In this step, the conducting portion of the CSRR unit cell is covered with a scotch tape of thickness 0.5 mm and then the ZnS colloid obtained from step(b) is dropped to cover and fill the gap(l). Next, the unit cell is dried at 80-90°C resulting in a thin film of ZnS nanoparticles.

Step (d): The step(c) is repeated for 3 to 5 times until the deposited ZnS film thickness of 20-25nm is achieved.

With the thin film of ZnS nanoparticle, the return loss of the CSRR antenna at 2.4 GHz is found to be -24 dB. The presence of nano thin film at the gaps of CSRR improves the impedance matchning of the antenna at its operating frequency of 2.4 GHz. At the same time antenna impedance at the notched frequency of 3.6 GHz is improved to -34 dB. It is because, ZnS thin film at the gaps of CSRR causes better absorption of electromagnetic signal at notched band. This results in enhanced attenuation of signal by -3dB at 3.6 GHz. At the same time at operating frequency of 2 GHz the gain of the antenna is enhanced by 2 dB.

To evaluate the invention performance, the following examples have been successfully performed and supporting results enclosed as diagrams-

Bxample 1: It is to study the return loss and notching behavior of the CSRR microstrip antenna without deposition of the ZnS nanomaterial thin film. Here, the said antenna with metamaterial unit cell at the ground plane is simulated using High-Frequency Structural

Simulator (HFSS) software and all the parameters such as return loss, gain and radiation pattern was studied. Further, the antenna Was fabricated practically using LPKF ProtoMat

S62 PCB fabrication unit procured from Germany. Vector Network Analyser (Rohde &

Schwarz, ZNB20) is used to measure the return loss of the practical antenna. The radiation pattern of the practical antenna measured using an automated system from DAMS 6000 Antenna Measurement system. The reference antenna is a broadband HF-907 (Rohde & Schwarz) Double-ridged waveguide hom operating from 800MHz to 18 GHz. The practical antenna is placed on an automated turntable and a signal is fed from the vector network analyzer. The measurement results from VNA shows that the return loss of the practical antenna at 1.4 GHz, 2.4 GHz is well below -10 dB mark. At 3.6 GHz the return loss shows a dip below -20dB. Figure 2, gives the comparison of measured return loss(Sn) of the fabricated antenna with and without depositing the nano thin film at the gap of the CSRR. Radiation pattern at 2.4 GHz shows a gain enhancement of the antenna by around 2 dB. In the other hand at 3.6 GHz, the radiation pattern shows significant attenuation by -3 dB. Figure 7 and Figure 8 shows the measured radiation pattern of the proposed antenna at 2.4 GHz and 3.6 GHz respectively. The frequency at 3.6 GHz can be considered as the image rejection frequency or notched frequency of the designed antenna operating at 2.4 GHz.

Example 2: To study the return loss and radiation pattern of the CSRR microstrip antenna with deposition of the nanomaterial thin film at the gap of the CSRR unit cell. Here, a thin film of ZnS nanomaterial is grown between the gaps of the CSRR at the ground plane of the practical antenna. The thin film of ZnS is deposited by covering the conducting part of the metallic CSRR. The thin film was deposited at a hot plate at a temperature of 70°-80° Celsius. The gap between the CSRR is now covered with a thin film of ZnS nanomaterial. The return loss of the thin film deposited antenna is measured with a vector network analyzer (Rohde & Schwarz, ZNB20). The measured results show significant improvement in the return loss well below -10 dB at 2.4 GHz and 3.6 GHz. The radiation pattern of the thin film deposited antenna is carried out using the DAMS 6000 Antenna Measurement system considering the HF-907 (Rohde & Schwarz) Double-ridged waveguide horn antenna as the reference antenna. The radiation pattern sholvs significant improvement in the operating frequency of the antenna at 2.4 GHz. The measured gain of the antenna is improved by 3 dB. Figure 7 shows the improvement in gain at 2.4 GHz and Figure 8 shows attenuation at notched frequency at 3.6 GHz. At notched frequency of 3.6 GHz, the antenna shows significant attenuation around - 3 dB.

Industrial Applicability:

The invention can find its application in wireless communication where the current technology has to deal with the elimination of unwanted frequency from the receiving signal at the antenna terminal.

Claims

CLAIMS We claim:

1. A ZnS Nanoparticle Thin Film Deposited Metamaterial Antenna For Notch Frequency Applicationcomprising of a 20-25 nm thick ZnS nanoparticle thin film deposited at the gap(l) of a Complementary Split Ring Resonator unit cell(2) at the ground plane of die said antenna, and a method of depositing the said thin film in the said gap of the said antenna comprising of the following steps-

(a) boiling a Zn(CH3COO)2 or Zn(N03)₂ or ZnCh salt solution at 100° C and then adding l/5^th the volume of 1.1%, chitosan in mild acetic acid (1-2%) and then adding aqueous Na2S in stoichiometric amounts to 5 times the concentration of the salt solution obtaining ZnS nanoparticles;

(b) removing the heat from the solution obtained in step(a) and then allowing it to cool to room temperature and then centrifuging it at 4000-5000 rpm for 20 minutes to obtain a ZnS colloid which in turn is then electrosterically stabilized by chitosan capping;

(c) covering the conducting portion of the CSRR unit cell(2) with a scotch tape of thickness 0.5 mm and then depositing the ZnS colloid obtained from step(b), in the gap(l) to fill it and then drying the unit cell at 80-90°C obtaining a thin film deposit in the said gap;

(d) repeating the step(c) for 3 to 5 times until the deposited ZnS film thickness of 20-25nm is achieved.

2. A. ZnS Nanoparticle Thin Film Deposited Metamaterial Antenna For Notch Frequency Application as claimed in Claim 1 wherein the size of the ZnS nanoparticle used is in the range of 5-7 nm.

3. A ZnS Nanoparticle Thin Film Deposited Metamaterial Antenna For Notch Frequency Application as claimed in Claim 1 wherein the return loss at its resonant frequency 2.4 GHz and at the notched frequency of 3.6 GHz is below -10 dB.