Transparent Antenna Research Articles

Compact, Flexible, and Transparent Antennas Based on Embedded Metallic Mesh for Wearable Devices in 5G Wireless Network

Compact, transparent, and flexible 5G multiple-input multiple-output (MIMO) and millimeter wave (mmW) array antennas with Ni-based embedded metallic mesh (EMM) nanotechnology are presented for the next-generation wireless communication in emerging applications, such as smart wearable devices, vehicle radars, and smart 5G remote devices. The EMM has the advantages of high conductivity, superior transparency, and mechanical stability. To simultaneously enhance the transparency and radiation efficiency, the selected structures of EMM are proposed and analyzed. The designed 5G MIMO antenna based on the EMM exhibits superior transparency of 93%, optimal radiation efficiency up to 85%, isolation above 20 dB, envelope correlation coefficient (ECC) under 0.005, and operation in 5G n79 band (4.4-5 GHz). The measured results are in good agreement with the simulated results. In addition, transparent and flexible 5G mmW arrays with a maximum gain of 9.6 dBi and a scanning angle of approximately ±75° are demonstrated in the 26 and 28 GHz bands.

Optically Transparent Flexible Robust Circularly Polarized Antenna for UHF RFID Tags

Optically transparent flexible tag antennas are highly desired for some applications, where unobtrusiveness and capability of mounting on curved surfaces are required. On the other hand, circular polarization minimizes signal degradation due to polarization mismatch between the reader and tag antennas, thus ensuring good communication quality and accuracy. In this letter, we present an optically transparent and flexible radio frequency identification passive tag antenna operating in the ultrahigh frequency band and exhibits circular polarization. It is thin, lightweight, and completely encapsulated inside transparent polymer, which protects it against dust, water, heat, and mechanical stress. The tag antenna is made by utilizing highly flexible and transparent conductive-mesh-polymer composite through a simple and low-cost manufacturing process. The antenna design is based on a planar square ring. It achieves a measured maximum read range of about 8.3 m and approximately 47 MHz (885-932 MHz) 3 dB axial-ratio bandwidth (ARBW).

A Method to Develop Flexible Robust Optically Transparent Unidirectional Antennas Utilizing Pure Water, PDMS, and Transparent Conductive Mesh

A method to realize low-cost, optically transparent, flexible, and unidirectional antennas is presented in this article. The key to the method is making a flexible transparent reflector made using a new method—injection of pure water into a flexible transparent cavity that is made out of polydimethylsiloxane (PDMS) polymer and integrating the flexible reflector with a flexible dipole made of transparent conducting mesh. This method is simple and inexpensive. Hence, it is useful for large-scale production of transparent, flexible, robust, and low-cost antennas as well as RF/microwave components for wearable body-area networks and other such systems that require flexible and transparent components. To validate the method, an antenna operating in the 2.45 GHz band was designed, fabricated, and tested under various conditions. Its measured gain is 3.2 dBi and efficiency is 51%. To the best of our knowledge, this is the first water-based transparent flexible antenna. Due to the shielding effect of the water-based reflector, it produces a low specific absorption rate (SAR) in the human body when it is worn, as expected from a unidirectional antenna. Furthermore, it is investigated and confirmed that the use of pure water in the reflector makes the antenna significantly more efficient as opposed to salt water.

Increasing the transparency of compact flexible antennas using defected ground structure for unobtrusive wearable technologies

In this paper, new designs of optically transparent wearable antennas have been presented. The explored antennas have the excellent features of high flexibility, small size, low specific absorption rate (SAR) and high optical transparency. The proposed antennas are realised by utilising highly flexible, optically transparent and low-cost materials. For achieving compactness in antenna dimension and for improved transparency, square-ring-shaped radiator is used in the antenna design. To improve the efficiency and gain of the square-ring patch antennas, a new technique is proposed in this paper. The proposed technique utilises a strip line that connects the middle of the two opposite sides of the ring. Full ground plane is used in antenna design to reduce the back radiation. However, full ground plane reduces optical transparency. To elevate optical transparency without affecting antenna's back radiation significantly, a new technique of defected ground structure is investigated in this study. With this defected ground structure, the optical transparency is improved by about 6% without significantly compromising the SAR. The compatibility of the proposed antennas for wearable applications are investigated by examining the performances on flat and bent phantoms. Moreover, the robustness of the antennas are studied by subjecting the prototypes to multiple bending operations.

CPW-Fed Transparent Antenna for Vehicle Communications

In this paper, a fully transparent multiband antenna for vehicle communications is designed, fabricated, and analyzed. The antenna is coplanar waveguide-fed to facilitate its manufacture and increase its transmittance. An indium-tin-oxide film, a type of transparent conducting oxide, is selected as the conductive material for the radiation path and ground plane, with 8 ohms/square sheet resistance. The substrate is glass with a relative permittivity of 5.5, and the overall dimensions of the optimized design are 50 mm × 17 mm × 1.1 mm. The main antenna parameters, namely, sheet resistance, reflection coefficient, and radiation diagram, were measured and compared with simulations. The proposed antenna fulfills the frequency requirements for vehicular communications according to the IEEE 802.11p standard. Additionally, it covers the frequency bands from 1.82 to 2.5 GHz for possible LTE communications applied to vehicular networks.

Study of the Impact Between a Triple Junction Space Solar Cell and the Antenna Integrated on Top of It

Solid and meshed patch antennas integrated on the cover glass of a commercial space solar cell were examined. The effect of the solar cell on the antenna was analyzed and validated. The impact of the antenna on the efficiency of the solar cell was quantified through experiments. It has been found that while the active semiconductor junction in a solar cell severely reduces the gain of the antenna in many space communication bands, the electrode lattice in the solar cell can potentially act as an isolation between the solar cell and the antenna, preventing the gain worsening. The effect of the lattice also promises a potential application in lab-grown solar cells such that one may carefully design the size and number of the electrodes to ensure the best gain for the integrated antenna. The main factor that impacts the efficiency of the solar cells was found to be the cover glass rather than the shadow from the antenna. These results can serve as design guidelines when integrating optically transparent antennas on solar panels of small satellites to reduce payload and to achieve reliable communication link. One may balance the selection of solar cells, cover glass, and antenna geometry to achieve the optimal link budget.

An ultra‐wideband rectenna using optically transparent Vivaldi antenna for radio frequency energy harvesting

This paper presents a novel ultra-wideband rectenna which consists of a transparent Vivaldi antenna and a wideband rectifying circuit for radio frequency energy harvesting. The antenna is realized on a 2.2-mm-thick soda-lime glass substrate coated with fluorine-doped tin oxide of thickness 650 nm. It provides an optical transmittance greater than 80% in the visible region. The rectifying circuit with a cascaded matching network and the Greinacher doubler circuit are fabricated on an FR4 substrate with a thickness of 0.8 mm. The antenna provides the best matching characteristics and the realized peak gain is 3.2 dBi. The designed matching network enables maximum power transfer from the antenna to the rectifier. The rectenna provides a peak power conversion efficiency of 69% for −10 dBm input power. The proposed antenna can be realized on the windscreen of automobiles and glass windows without causing any obstruction to normal view.

Highly Transparent Planar Dipole Using Liquid Ionized Salt Water Under Surface Tension Condition for UHD TV Applications

In this article, a feasibility study on an optically transparent planar dipole antenna using liquid salt water at wide ultra-high frequency (UHF) band (470-771 MHz) for application in external antenna of ultra-high-definition television (UHD TV) is presented. The most significant reason behind using liquid salt water for transparent antenna applications is its excellent average optical transparency (OTav) (>95% at salinity of 40 ppt) compared with other typical solid transparent thin-film electrodes such as indium tin oxide (>73%) or multilayer films (>78%). Each conductive arm of the proposed dipole is constructed from a salt-water layer held between two clear planar acrylic layers (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 2.61, tan δ = 0.01, OT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">av</sub> > 90%) (acrylic/salt water/acrylic; ASA) due to surface tension. To investigate the electrical and optical properties of the ASA structure, we analyze the surface tension to determine the thickness of the salt-water layer that finalizes its sheet resistance and OT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">av</sub> . The average gain and efficiency of the antenna are 1.72 dBi and 74%, respectively, in the operating UHF band. This makes the proposed antenna a good candidate for application as a transparent external antenna in UHD TVs and proves that it is possible to use salt water for high-frequency devices.

Smart, soft contact lens for wireless immunosensing of cortisol.

Despite various approaches to immunoassay and chromatography for monitoring cortisol concentrations, conventional methods require bulky external equipment, which limits their use as mobile health care systems. Here, we describe a human pilot trial of a soft, smart contact lens for real-time detection of the cortisol concentration in tears using a smartphone. A cortisol sensor formed using a graphene field-effect transistor can measure cortisol concentration with a detection limit of 10 pg/ml, which is low enough to detect the cortisol concentration in human tears. In addition, this soft contact lens only requires the integration of this cortisol sensor with transparent antennas and wireless communication circuits to make a smartphone the only device needed to operate the lens remotely without obstructing the wearer's view. Furthermore, in vivo tests using live rabbits and the human pilot experiment confirmed the good biocompatibility and reliability of this lens as a noninvasive, mobile health care solution.

Highly transparent and conductive electrodes enabled by scalable printing-and-sintering of silver nanowires

Silver nanowires (Ag NWs) have good promised for flexible and transparent electronics. However, It remains an open question on how to achieve large-scale printing of Ag NWs with high optical transparency, electrical conductivity, and mechanical durability for practical applications, though extensive research has been conducted for more than a decade. In this work, we propose a possible solution that integrates screen printing of Ag NWs with flash-light sintering (FLS). We demonstrate that the use of low-concentration, screen-printable Ag NW ink enables large-area and high-resolution patterning of Ag NWs. A critical advantage comes from the FLS process that allows low-temperature processing, short operational time, and high output rate—characteristics that fit the scalable manufacturing. Importantly, we show that the resultant Ag NW patterns feature low sheet resistance (1.1–9.2 Ohm sq−1), high transparency (75.2–92.6%), and thus a remarkable figure of merit comparable to state of the art. These outstanding properties of Ag NW patterns, together with the scalable fabrication method we propose, would facilitate many Ag NW-based applications, such as transparent heaters, stretchable displays, and wearable devices; here, we demonstrate the novel design of flexible and transparent radio frequency 5G antennas.

Experimental studies of the robustness of the conductive-mesh-polymer composite towards the development of conformal and transparent antennas

One of the key challenges of the development of flexible and optically transparent antennas and sensors is the limited availability of the suitable materials. The traditional transparent conductors suffer from the drawback of instability in repeated bending and twisting and, thus, are not appropriate candidates for flexible transparent antenna development. Integration of flexible conductors with flexible substrates is another challenge not only for the realization of flexible transparent antennas but also for other types of flexible antennas, radio-frequency (RF) devices and sensors. Apart from the traditional flexible conductive and substrate materials, Conductive-Mesh-Polymer composite can be an efficient alternative for the realization of flexible transparent antennas. The polymer proposed here is Polydimethylsiloxane (PDMS), which is a flexible transparent substrate and the proposed transparent conductor is mesh-structured flexible conductive textile, VeilShield from Less EMF Inc. USA. Uncured PDMS is a sticky liquid and after curing, it makes a strong attachment with VeilShield. Due to the mesh-structured configuration of this conductor, uncured PDMS penetrates through the gaps among the threads and after curing of the PDMS, a composite is formed that has high optical transparency, flexibility and robustness against repeated mechanical deformations. For these attractive features, this composite material is a good candidate for the realization of optically transparent antennas, sensors and RF devices. In this paper, the feasibility of the VeilShield-PDMS composite towards the realization of flexible, robust and transparent antennas is assessed by investigating the morphology of the composite and exploring the RF performance of a microstrip patch antenna, fabricated using this composite, through 50 times bending cycle. The investigated results demonstrate the suitability of the VeilShield-PDMS composite towards the realization of flexible transparent antennas as well as other electronic components that are frequently exposed to repeated physical deformations.

Miniature water monopolar patch antenna using transparent high‐permittivity liquid substrate

A miniature water patch antenna using high-permittivity liquid substrate is demonstrated. The utilised liquid substrate is ethyl acetate, which is an optically transparent liquid with permittivity of 7.8 over microwave frequencies. It turns out that when using ethyl acetate as the middle substrate, the diameter of the circular water patch can be decreased by 48% compared with the case using air as the middle substrate, and a wide bandwidth of 36% can be obtained. The results show that the ethyl acetate is an optional candidate to realise a compact transparent antenna.

Transparent Conductive Oxide-Based Multiband CPW Fed Antenna

In this paper, a novel multiband coplanar waveguide-fed slotted transparent antenna is presented. The structural design of the radiating element is based on the semicircular curves in the form of slots on the patch to achieve multi-band characteristics with improved bandwidth. The overall structure having a size of λ0/2.67 × λ0/2.11 achieves transparency and a lightweight due to the presence of Plexiglas as a substrate material and AgHT-8 as a conductive material including the circular slotted patch and related CPW feeding line at the center frequency of the lowest operation band. The proposed antenna has the multiband operation characteristics with the center frequencies of 2.58 GHz, 3.67 GHz, 6.2 GHz having the impedance bandwidth of 19.84% (2.27—2.77 GHz), 1.76% (3.61—3.74 GHz) and 53.58% (4.50–7.79 GHz) respectively. The agreement between the numerical computation and measurement results of RF performance characteristics point out the technical potential of the proposed optically transparent antenna for short range multiband versatile wireless applications.

Optical Transparent Antenna Array Integrated With Solar Cell

This letter presents an optical transparent antenna array integrated with solar cell. Metal-meshed structure is used in the transparent antenna array, which achieves a balance between radiation efficiency and optical transparency. The meshed patches have equidistant distribution in the array and are fed by coaxial probes. A meshed ground, which has the same grid size as the meshed patch, is introduced and aligned with the patch. Cheap coating technology is utilized in printing silver-meshed patch and ground on the two surfaces of a glass substrate. A commercial monocrystalline silicon solar cell is closely assembled under the transparent antenna array. The proposed antenna array operates from 8.51 to 9.10 GHz (VSWR $\leq 2$ ) with low cross-polarization levels, and obtains an 88% optical transparency. The transparent antenna array achieves a good radiation performance with little effect on solar photovoltaic generation.

Design of Transparent Rectangular Patch Antenna for 5G Applications

Transparent antennas are meant for their optical transparency. This paper analyzes the rectangular patch antenna designed using meshed conductors and solid ground planes. Meshing the antennas makes it as optically transparent and the antenna’s transparency is based on the mesh geometry. Even there is a tradeoff between the antenna’s efficiency and the visual see-through ability of the patch antenna with meshed structure, it is able to tune the antenna by refining mesh lines. Material handling, fabrication process and the increased impedance are the important factors limiting the refining of the mesh lines, which also cause loss in efficiency of the antenna. Both the performance and antenna transparency is improved by a mesh refined with small line width (q). Also, by removing certain mesh lines, the antenna transparency is improved without affecting the antenna efficiency. This paper briefly explains the relation between the gain, transparency and the mesh structure of the antenna.

Infrared transparent millimeter wave antenna based on sapphire substrate

AbstractWe describe a novel millimeter wave antenna based on sapphire substrate. An infrared transparent millimeter wave antenna and the characterization of its radiation pattern, gain, main frequency, and dielectric infrared transmission were reported. The proposed antenna was constructed from several infrared transparent dielectric materials with thin gold film array elements using a photolithographic process. Several single‐layer infrared‐transparent substrates were stacked. As a infrared transparent window, the antennas have applications in multimode communications, navigation, and detection, particularly for millimeter wave and infrared wavelength in a common aperture system.

Flexible CPW fed transparent antenna for WLAN and sub‐6 GHz 5G applications

AbstractA transparent flexible co‐planar waveguide fed patch antenna using polyethylene terephthalate substrate is presented. The wideband high gain antenna having an overall dimension of 0.48λ × 0.64λ at the center frequency of 4.28 GHz is fabricated using a transparent sheet made up of Silver Tin Oxide (AgHT‐8). The performance of the proposed antenna is compared with four other nontransparent nonflexible and semitransparent flexible antennas. For the engineered design, patch geometry and feeding mechanism are kept constant whereas the substrate and patch materials are varied. Simulations are carried out using finite element method‐based full wave high‐frequency structure simulator after which the antennas are fabricated and tested. The proposed flexible transparent antenna has bandwidth in order of 40%, ranging from 3.89 to 5.9 GHz, with a notable gain over 3 dBi and efficiency greater than 80% for the entire frequency band. The bending conditions are also tested for the flexible transparent antenna which showed decent performance for sub‐6 GHz 5G and WLAN applications.

A Wideband and Optically Transparent Water Patch Antenna With Broadside Radiation Pattern

A wideband and optically transparent water patch antenna with a broadside radiation pattern is presented. Both the patch and the ground plane are composed of distilled water, enclosed by the transparent plexiglass container. Air is utilized as the middle substrate so that highly optical transparency can be achieved with low-cost materials. A metallic L-shaped probe is employed in the air substrate to excite the water patch. The performance turns out that a wide impedance bandwidth of 34.9% (from 1.61 to 2.29 GHz with standing wave ratio (SWR) < 2), the maximum gain of 6.6 dBi and a radiation efficiency up to 75% can be achieved.

Compact Wideband Four Element Optically Transparent MIMO Antenna for mm-Wave 5G Applications

A four-element compact wide-band optically transparent MIMO antenna with a full ground plane is proposed. The four elements transparent MIMO system has a compact size of 24 × 20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with the undivided ground plane as most of the real-time systems demand a common reference. The complete antenna system achieves around 85% transparency due to a combination of AgHT-8 and Plexiglas which forms the transparent conductive patch/ground and substrate, respectively. The antenna geometry leads dual-band operation ranging from 24.10 - 27.18 GHz (Impedance bandwidth = 12%) and 33 - 44.13 GHz (Impedance bandwidth =28.86$ %) targeting the mm-wave 5G applications. The 4-element antenna system achieves isolation between inter-elements >16 dB and maximum gain value of greater than 3 dBi with more than 75% efficiency. The proposed transparent MIMO antenna is evaluated in terms of diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC), and mean effective gain (MEG) where decent MIMO performance with isolation more than >16 dB between the adjacent and other elements is achieved. Transparent MIMO antenna achieves directional patterns for the operating band with the value of DG >9, ECC <; 0.1, TARC value less than -15dB, and the ratio of MEG within the agreed limit of ±3 dB confirming acceptable MIMO/diversity performance.

Optically Transparent 24 GHz Analog Front-End Based on Meshed Microstrip Lines for the Integration in a Self-Sufficient RFID Sensor Tag

This paper presents a 24 GHz Radio Frequency IDentification (RFID) sensor tag including an optically transparent patch antenna and an RF circuit. These components are placed on a single efficient solar cell and the transparency is achieved by realizing metal patches and lines as grid structure. Since the analog front-end is implemented in the microstrip line technology, the impact of the grid structure on the characteristic impedance and the propagation constant of microstrip transmission lines is studied in detail. The knowledge derived are taken into account in the design process of the meshed patch antenna as well as the modulator and demodulator circuit. Furthermore, the influence of the solar cell on the characteristics of the analog front-end is investigated. The overall dimensions of the sensor tag are $13\times 13\times 4$ mm3 including the aforementioned components, a microcontroller, an acceleration sensor and an energy storage. The perforated analog front-end fabricated on quartz glass has an overall transparency of 75 % and an antenna efficiency of 49 %. The achieved sensitivity value of the developed RFID sensor tag is −36 dBm resulting in a maximum communication range of approximately 1.3 m.