Optically Transparent Antenna for Smart Glasses

This article introduces different types of transparent antennas to the readers. To begin, the electrical and optical properties of some of the commonly seen transparent dielectrics and transparent conducting thin films are discussed. Focus will be given to their microwave characteristics. Two types of transparent antennas, namely, conductive and nonconductive antennas, are covered in this article. In the first part, transparent antennas that are made of conducting thin film and meshed conductor are presented. The conductive thin‐film antenna usually has low antenna radiation efficiency because its film thickness, which is usually less than skin depth, causes the electron conductivity to reduce. Meshed antenna also experiences efficiency deterioration due to metal removal. The design issues and compromises for both types of conductive transparent antennas are discussed. In the second part, the transparent dielectric resonator antenna (DRA) is explored. Regardless of its shape and thickness, the transparent DRA can have good radiation efficiency and optical transparency at the same time. Additional advantages such as using the antenna as a decorative art piece or as a multifunctional component are also possible with the transparent DRA. The optical and antenna performances will be studied. We have prepared this article in a language comprehensible to both antenna and microwave engineers.

Dr Yongjin Kim of Inha Technical College, Korea, talks about the work behind the paper ‘Design of transparent multilayer film antenna for wireless communication’, page 12. Dr Yongjin Kim I received my B.S. degree in electrical engineering from Inha University in Inchon, and my M.S. and Ph.D. from Ohio State University, Columbus. During graduate school, in the ElectroScience Laboratory at Ohio, I joined several projects involving design of conformal antennas, subsurface target detection/identification, ground bound reduction for outdoor range measurement and radar systems. Then, from 2003 to 2007, I was a senior engineer in the communication and networking laboratory at the Samsung Advanced Institute of Technology in Korea, where I conducted research into the design of various antennas for communication devices, including cellular phones and UWB and RFID antennas. Since then, I have been an associate professor at Inha Technical College. My principle area of research is the design of modern communication antennas and my current interests include a smart antenna system and the development of conductive file antennas with composite materials and structures. A variety of studies using transparent electrodes and transparent conductive films have been conducted in RF applications. If the RF performance of a transparent antenna can be made similar to that of a conventional antenna, a wide range of applications in wireless communication become possible, including for the Internet of things (IoT) and RFID. I was interested in the study of this idea and I thought it could lead to a breakthrough in the antenna field. In the paper, we propose a multilayer thin film antenna for mobile devices. The proposed antenna consists of an IZTO/Ag/IZTO multilayer film that is fabricated on polyimide substrate and a copper layer. The center frequency of the antenna is 1260 MHz. The proposed antenna using an IZTO (indium zinc tin oxide) electrode has an excellent resistive characteristic and high flexibility. Also, it shows a transmittance of 86%. The proposed antenna is made by inserting a thin Ag layer between two layers of IZTO. We placed the IZTO/Ag/IZTO 3-layer structure over a polyamide substrate. The antenna is designed as an IFA type structure with a coupled loop and two branches. Our antenna has very high transparency and good radiation efficiency, showing an excellent balance with regard to the trade-off between the two. It is also the first antenna model for a mobile hand set using an IZTO/Ag/IZTO 3-layer structure. I think this will be a good basis of research for the future development of the transparent antenna. Of course, the strength of transparent antennas is transparency, they can be attached to many kinds of objects requiring antennas, including TVs, cellular phone displays, automobile glass, etc; and for RFID and IoT applications, where making the antenna inconspicuous may be desirable for a range of different reasons. The interest for transparent wireless communication devices is increasing due to the demands from a variety of designs and developments in communication services, both from the perspective of visual design and being able to integrate device components more efficiently. Thus, I think the research into transparent electronic components and materials will continue. There are several challenges in this research. One of them is the fine manufacturing process, which is a key point of determining antenna performance. The next one is increasing the conductivity of the 3-layer structure without decreasing the transparency of the antenna. There is also a simulation modelling issue for designing the antenna structure. In the transparent and flexible antenna area, one of my related projects is in the use of composite materials of carbon nanotube and other polymer materials such as a poly-vinylidence fluoridle for antenna applications.

A dual‐band optically transparent antenna having two slotted circular rings with partial ground plane is proposed for smart applications. The antenna has circular split ring resonators (SRRs) array which offers negative refractive index properties to the resonator. The antenna is fed using microstrip feed line which is matched at 50 Ω. The conducting patch, partial ground plane and two circular SRRs are made up of transparent conducting thin film AgHT‐8 having transparency of above 80%. Substrate in the form of Plexiglas is used for making the antenna structure completely transparent. Metamaterial is incorporated for achieving acceptable values of antenna gain. The patch design is engineered for antenna operation in IEEE a/b/g/n frequency bands working at 2.4 GHz and 5.5 GHz, respectively. The size of the proposed transparent antenna is 35 × 35 × 1.84 mm3 with measured impedance bandwidth of 13.27% and 5.28% achieved for lower frequency band of 2.4 GHz and the upper frequency band of 5.5 GHz, respectively. The proposed antenna is useful for smart devices communicating over WLAN frequency bands without need of extra board space due to the optical transparency of antenna.

This paper presents a systematic parameter study on mesh pattern for optically transparent flexible antenna with feedline. In implementing a transparent flexible antenna using a metal mesh, transparency and performance of antenna and feedline are opposite factors. To understand how both elements are affected by the design parameters of the mesh, we analyze the performance of the feedlines and antennas according to the design parameters of diamond and square meshes. Moreover, the effect of the difference in the shape of diamond mesh and square mesh on performance is analyzed. The measured results of the fabricated samples offer the feasibility of implementing transparent feedlines and antennas with similar performance to nontransparent feedlines and antennas.

Current radio frequency (RF) sensors at the Edge lack the computational resources to support practical, in-situ training for intelligent spectrum monitoring. This is true for sensor data classification in general. We propose a solution via Deep Delay Loop Reservoir Computing (DLR), a processing architecture that supports general machine learning algorithms on compact mobile devices by leveraging delay-loop reservoir computing in combination with innovative electro-optical hardware. With both digital and photonic realizations of our design of the loops, DLR delivers reductions in form factor, hardware complexity and latency, compared to the State-of-the-Art (SoA). The main impact of the reservoir is to project the input data into a higher dimensional space of reservoir state vectors in order to linearly separate the input classes. Once the classes are well separated, traditionally complex, power-hungry classification models are no longer needed for the learning process. Yet, even with simple classifiers based on Ridge regression (RR), the complexity grows at least quadratically with the input size. Hence, the hardware reduction required for training on compact devices is in contradiction with the large dimension of state vectors. DLR employs a RR-based classifier to exceed the SoA accuracy, while further reducing power consumption by leveraging the architecture of parallel (split) loops. We present DLR architectures composed of multiple smaller loops whose state vectors are linearly combined to create a lower dimensional input into Ridge regression. We demonstrate the advantages of using DLR for two distinct applications: RF Specific Emitter Identification (SEI) for IoT authentication, and wireless protocol recognition for IoT situational awareness.

In this paper, we propose a printed circuit board (PCB)-based planar antenna pair, operating at 2.4 GHz and 5.0 GHz frequency bands, respectively, for dual-band routers. The antennas are both rectangular and consist of twisted radiating elements and microstrips etched on an FR4 dielectric substrate. Etching slots on the radiating elements and adjusting the serpentine microstrips influence surface current distribution and therefore effectively reduce antenna size and enhance antenna gain. The proposed antenna features a compact size compared to general router antennas and demonstrates high gain characteristics compared to dipole antennas. In the 2.3–2.5 GHz band, the simulated S11 of the 2.4 GHz antenna was lower than -10 dB, while the gain was 3.9 dBi at 2.4 GHz. In the 5.1–5.9 GHz band, the simulated S11 of the 5.0 GHz antenna was lower than -10 dB, and the gain was greater than 4.8 dBi. The proposed antenna has potential for application to router antennas.

The transparent flexible plastic antenna was fabricated. Indium tin oxide (ITO) thin film was deposited on flexible plastic substrate at room temperature by radio frequency (RF) magnetron sputtering with a new technique, called gas-timing. By using the X-ray diffraction (XRD) measurement of the ITO thin film grown by this technique, a cubic nanocrystalline structure with predominant (222) orientation was observed. The technique of gas-timing we used, the ITO thin film on flexible substrate was achieved with high transmittance in visible region of 90% and low resistivity. The performance of the new film antenna was studied experimentally with its return loss and radiation patterns.

This paper presents a miniaturized, wideband, and optically transparent antenna with high efficiency, designed using the optimized wired metal mesh (WMM) for Internet of Things (IoT) applications. The performance of transparent antennas based on conductive oxides (TCOs) or metal meshes (MMs) is fundamentally determined by the optical transparency (OT) and sheet resistance (SR) of the material. Although OT and SR can be tuned using various fabrication techniques, conventional SR values provided by existing studies do not accurately represent the loss behavior at GHz frequencies. In this paper, an effective SR material model for the WMM is developed with consideration of high-frequency losses and applied in electromagnetic (EM) simulations. Using this model, the proposed antenna is systematically designed to achieve an impedance bandwidth of 66.3% and peak total efficiency of 92.4% over 2.61-5.2 GHz, in a compact 55×40 mm2 form. In addition to intrinsic antenna performance, practical robustness is evaluated under bending deformation, temperature variation, and indoor propagation environments. In the indoor scenarios having multipath effects, Error vector magnitude measurements at 3.5 GHz and 5.15 GHz demonstrated its suitability for IoT communication environments.

Intelligent transportation services are being developed to enhance road safety, increase traffic efficiency, achieve higher speeds, and alleviate traffic congestion. This article presents the design and simulation results of a novel, compact, transparent patch antenna. The suggested design is designed to cover vehicular communication standards such as DSRC/IEEE 802.11p at 5.9 GHz and cellular V2X (C-V2X) bands. Additionally, it supports other frequency bands, including the C-Band (5.925–6.425 GHz, 7.25-7.75 GHz) and X-Band (7.250-7.750 GHz, 7.90–8.40 GHz, 8.0–8.5 GHz). The antenna operates within the frequency ranges of 5.11–6.44 GHz and 7.25–9.06 GHz, achieving a gain of 2–5 dB and a radiation efficiency of approximately 90% at 5.9 GHz. The antenna is enhanced by adding slots to the patch and utilizing a modified ground plane.

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. ing the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system with a sensing capability for developing varifocal augmented reality glasses and naturally fit haptic gloves. Here, we design a shape memory alloy-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified shape memory alloy actuator. Despite its light weight (0.22 g), the actuator has a high power density of 1.7 kW/kg, an actuation strain of 300% under 80 g of external payload. We show how the actuator enables image depth control and an immersive tactile response in the form of augmented reality glasses and two-way communication haptic gloves whose thin form factor and high power density can hardly be achieved by conventional actuators.

While the potential of mobile information visualisation is widely recognized, there is still relatively little research in this area and few practical guidelines for the design of mobile information visualisation interfaces. Indeed, it would appear that there is still a general feeling in the interface design community that mobile visualisation should be limited to simple operations and small scale data. Information visualisation research has concentrated thus far on desktop PCs and larger displays while interfaces for more compact mobile device have been neglected. This is in spite of the increasing popularity and widespread use of smart-phones and other new mobile technologies. In this paper we address this issue by developing a set of low-level interface design guidelines for mobile information visualisation development. This is done by considering a basic set of interactions and relating these to mobile device limitations. Our results suggest that the mindful application of existing information visualisation techniques can overcome many mobile device limitations and that proper implementation of interaction mechanisms and animated view transitions are key to effective mobile information visualisation. This is illustrated with case studies looking at a coordinated map and timeline interface for geo-temporal data, a distorted scatter-plot, and a space filling hierarchy view.

Low operating temperature micro solid oxide fuel cell (micro-SOFC) systems which utilize liquid fuels are attractive for high energy efficiency and density. Long time operation is possible for micro-SOFCs by refueling and it is not restricted by battery charge. Hence, it is expected to alternative power source for compact mobile electronic devices which consume a large amount of power. In previous, diverse types of micro-SOFCs focused on its performance was reported and a maximum power density of 1 W/cm2 at 500oC was achieved. However, they have many problems of durability and repeatability for practical use. Additionally, it is necessary to consider how to heat up micro-SOFC cells to operating temperature, compatibility with other electronic circuits and thermally self-sustained condition. In this study, micro-SOFC system was proposed in order to adopt the micro-SOFCs into a power source of compact mobile electric devices. We designed the micro-SOFC package with thermal insulation and heat exchanger. Its insulation performance was experimentally confirmed and power generation test with micro heater in the micro-SOFC package was performed. Micro-SOFC packages require thermal insulation to keep the surface temperature below about 85oC, which is the maximum operating temperature of other electronic circuits. We applied vacuum insulation widely used for thermal insulation in MEMS devices to the package. The heat of the exhaust gas was recovered by the liquid fuel through heat exchanger. From the calculation of temperature distribution by the finite element method, surface temperature of the package was kept from 57 to 88oC when operating temperature is 500oC. As long as the liquid is evaporated, temperature of the heat exchanger is kept constant. Therefore, heat conduction from high temperature glass flow channels to vacuum insulator was prevented and low surface temperature was achieved. Applying micro-SOFC system as independent power sources, thermally self-sustained condition is required, i.e. micro-SOFC packages should keep operating temperature more than 300oC only by the generated heat from reaction of fuel cells during power generation. For thermally self-sustained condition, the amount of heat generated during power generation needs to exceed that of heat loss from surface of the package and transferred heat by exhaust gas. We calculated thermally self-sustained condition of a micro-SOFC system with 4 W output fueled by methanol and water that has reformer and heat exchanger from exhaust gas. From the result, generated heat from reaction of fuel cells was 4.8W, heat loss from surface was 1.5 W and transferred heat by exhaust gas was 4.6 W at 500oC. The result confirmed that transferred heat by exhaust gas was dominated in this system. Hence, recovering the heat of exhaust gas with the gas-liquid heat exchanger was essential to achieve thermally self-sustained condition. Micro-SOFC cells and micro heater were fabricated in general MEMS technology. Power generation test and electrochemical impedance spectroscopy of micro-SOFC (Pt-Pd | 15 mol% Y-doped BaZrO3 | Pt-Pd) by micro heater were measured in the temperature range of 200-330oC. A maximum power density of 1.12 mW/cm2 and open circuit voltage of 1.09 V at 330oC were obtained using wet H2 as fuel and air as the oxidant. As a result of impedance measurement, electrode reaction resistance was very high in cell total resistance. Therefore, the improvement of electrode will reduce cell resistance to a level for actual utility. We actually fabricated the micro-SOFC package installed vacuum structure and heat exchanger to evaluate cooling performance of the insulation package and performed power generation test in the package. In the case of heat exchanger filled with 50 vol% ethanol solution, surface temperature was 89.6oC when micro heater temperature was 500oC. In accordance with the result, it was possible to keep surface temperature of the package sufficiently low with heat exchanger. As a result of power generation test of micro-SOFC inside the package, a maximum power density of 1.27 mW/cm2 and open circuit voltage of 0.94 V at 300oC were obtained using wet 25% or 50% H2 as fuel and air as the oxidant. Additionally, surface temperature of the package was kept under 80oC. Therefore I achieved power generation in compact micro-SOFC system with thermal insulation. The micro-SOFC package was designed for applying micro-SOFCs to power source of mobile electronic devices in this study. As a result of calculation, the package installed vacuum insulation and heat exchanger could achieve thermally self-sustained condition and low surface temperature. Power generation test of micro-SOFC inside the prototype package was achieved and the package kept low surface temperature. Hence, this study presented that applicability of micro-SOFC system to power source for compact mobile electronic devices.

Transparent microstrip antenna with fluorine‐doped tin oxide (FTO or SnO 2 :F) patch is studied here. The authors make use of spray pyrolysis technique to deposit FTO transparent patch on a Pyrex glass substrate. The deposited FTO patches show high optical transmittance (about 80–90%) and low electrical surface resistance (as low as 7 Ω/□). Two transparent microstrip patch antennas (with conventional conductor as ground plane), which are fed by proximity coupling at 2.5 and 5 GHz resonance frequencies, are fabricated and their radiation properties are presented and compared with copper patch antenna counterparts. In order to reduce the conductor loss of the antenna and ameliorate antenna efficiency, thick substrates should be used. The 2.5 GHz antenna shows low efficiency and significant loss in transparent layer but the 5 GHz one shows 3.63 dBi maximum gain and only ∼0.83 dB degradation in comparison with the copper patch antenna.

The performances of two microstrip patch antennas with low visual impact are presented in this paper and compared to an opaque solution. These consist in a copper film deposited on a Borofloat 33 glass substrate through a thin titanium gripping layer. The mesh is obtained by wet chemical etching. Antennas differ by the dimensions in the ground plane mesh pattern.

통신의 흐름은 빠르게 변하고 있으며, 최근에는 스마트 안경과 스마트 시계와 같은 인간의 삶을 윤택하게 하는 다채로운 웨어러블(Wearable) 기기들이 출현하고 있다. 웨어러블 기기에는 필수적으로 통신을 지원하는 안테나가 설치되어야 한다. 본 논문은 스마트 안경에 적용할 수 있으며 투명한 소재로 제작하여 광 투과성이 우수한 특성을 지닌 웨어러블 안테나에 관하여 연구한 논문이다. 투명한 안테나는 차기 웨어러블 기기인 스마트 유리에도 적용이 가능하며, 투명한 장점을 활용하여 시야를 가리지 않으면서 통신을 지원할 수 있는 장점이 있다. IZTO/Ag/IZTO(IAI) 다층구조의 투명전극 박막은 단일구조의 박막보다 전기전도도가 높으며 광 투과성이 우수하다. 이러한 다층구조의 투명전극 박막을 활용하여 제작한 안테나는 우수한 전기전도도로 인하여 안테나로 활용이 가능하다. 본 논문에서는 다층구조의 투명전극 박막을 활용하여 투명한 소자가 적용 가능한 깨끗한 안경렌즈에 부착하여 안테나의 성능을 측정하였다. 안테나는 여러 기판 위에 올려진 것을 가정하여 시뮬레이션 되었으며, 안테나의 폭과 길이를 적절히 활용하여 안테나의 임피던스를 매칭하였다. 제작한 안테나의 전기전도도와 투명도는 각각 홀 효과 측정기(HMS-3000)과 광 투과율 측정기(UV-Spectrometer)로 측정하였으며, 안테나의 성능을 비교하기 위하여 은(Ag)을 40 nm 두께로 증착한 안테나를 대조군으로 사용하었다. 제작한 안테나는 일반 웨어러블 안경에서 지원하는 Wi-fi 통신 대역인 주파수 2.4~2.5GHz 범위에서 사용가능하며, 최대 이득 2.89 dBi, 효율 34%의 성능을 보인다. Communication flow is changing rapidly. Recently, a range of wearable devices such as wearable glasses and wearable watch, have been launched. These kinds of wearable devices help people to live a more comfortable life. Wearable devices most have an antenna for wireless communication. This paper reports a transparent antenna that is made of an optically transparent material for wearable glasses. Transparent antenna can be applied to smart windows and will not disturb the view of user. IZTO/Ag/IZTO multilayer electrode has higher electrical and optical properties. This antenna is available because of its good electrical properties. This study measured the performance of the proposed transparent antenna, which is made of a multilayer electrode, applied to a lens. The proposed antenna was simulated with several substrates. The antenna impedance was matched with length and width of the antenna. The antenna's conductivity and transparency was measured using a HMS-3000 and UV-spectrometer. A 40nm thick Ag single layer antenna was fabricated on a flexible polyimide substrate for comparing the antenna performances. The fabricated antenna is useable at a frequency of 2.4-2.5GHz, which is suitable for Wifi communications and has peak gain of 2.89dBi and an efficiency of 34%.