Implanted Miniaturized Antenna for Brain Computer Interface Applications: Analysis and Design

Implantable Brain Computer Interfaces (BCIs) are designed to provide real-time control signals for prosthetic devices, study brain function, and/or restore sensory information lost as a result of injury or disease. Using Radio Frequency (RF) to wirelessly power a BCI could widely extend the number of applications and increase chronic in-vivo viability. However, due to the limited size and the electromagnetic loss of human brain tissues, implanted miniaturized antennas suffer low radiation efficiency. This work presents simulations, analysis and designs of implanted antennas for a wireless implantable RF-powered brain computer interface application. The results show that thin (on the order of 100 micrometers thickness) biocompatible insulating layers can significantly impact the antenna performance. The proper selection of the dielectric properties of the biocompatible insulating layers and the implantation position inside human brain tissues can facilitate efficient RF power reception by the implanted antenna. While the results show that the effects of the human head shape on implanted antenna performance is somewhat negligible, the constitutive properties of the brain tissues surrounding the implanted antenna can significantly impact the electrical characteristics (input impedance, and operational frequency) of the implanted antenna. Three miniaturized antenna designs are simulated and demonstrate that maximum RF power of up to 1.8 milli-Watts can be received at 2 GHz when the antenna implanted around the dura, without violating the Specific Absorption Rate (SAR) limits.     

FDTD assessment of human exposure to electromagnetic fields from WiFi and bluetooth devices in some operating situations

In this work, the numerical dosimetry in human exposure to the electromagnetic fields from antennas of wireless devices, such as those of wireless local area networks (WLAN) access points or phone and computer peripherals with Bluetooth antennas, is analyzed with the objective of assessing guidelines compliance. Several geometrical configurations are considered to simulate possible exposure situations of a person to the fields from WLAN or Bluetooth antennas operating at 2400 MHz. The exposure to radiation from two sources of different frequencies when using a 1800 MHz GSM mobile phone connected via Bluetooth with a hands-free car kit is also considered. The finite-difference time-domain (FDTD) method is used to calculate electric and magnetic field values in the vicinity of the antennas and specific absorption rates (SAR) in a high-resolution model of the human head and torso, to be compared with the limits from the guidelines (reference levels and basic restrictions, respectively). Results show that the exposure levels in worst-case situations studied are lower than those obtained when analyzing the exposure to mobile phones, as could be expected because of the low power of the signals and the distance between the human and the antennas, with both field and SAR values being far below the limits established by the guidelines, even when considering the combined exposure to both a GSM and a Bluetooth antenna.     

Studies in RF Power Communication,SAR, and Temperature Elevation in Wireless Implantable Neural Interfaces

Implantable neural interfaces are designed to provide a high spatial and temporal precision control signal implementing high degree of freedom real-time prosthetic systems. The development of a Radio Frequency (RF) wireless neural interface has the potential to expand the number of applications as well as extend the robustness and longevity compared to wired neural interfaces. However, it is well known that RF signal is absorbed by the body and can result in tissue heating. In this work, numerical studies with analytical validations are performed to provide an assessment of power, heating and specific absorption rate (SAR) associated with the wireless RF transmitting within the human head. The receiving antenna on the neural interface is designed with different geometries and modeled at a range of implanted depths within the brain in order to estimate the maximum receiving power without violating SAR and tissue temperature elevation safety regulations. Based on the size of the designed antenna, sets of frequencies between 1 GHz to 4 GHz have been investigated. As expected the simulations demonstrate that longer receiving antennas (dipole) and lower working frequencies result in greater power availability prior to violating SAR regulations. For a 15 mm dipole antenna operating at 1.24 GHz on the surface of the brain, 730 uW of power could be harvested at the Federal Communications Commission (FCC) SAR violation limit. At approximately 5 cm inside the head, this same antenna would receive 190 uW of power prior to violating SAR regulations. Finally, the 3-D bio-heat simulation results show that for all evaluated antennas and frequency combinations we reach FCC SAR limits well before 1 °C. It is clear that powering neural interfaces via RF is possible, but ultra-low power circuit designs combined with advanced simulation will be required to develop a functional antenna that meets all system requirements.     

Emission and Transmission Properties of a Doubly Resonant 3D Nanodisk Yagi–Uda Antenna for Wireless Optical Communications

In this paper, a novel doubly resonant three-dimensional (3D) nanodisk Yagi–Uda antenna, conceived for realizing wireless optical links within electronic circuits, is proposed. The prominent emitting properties of this nanoantenna have been deeply investigated both in the near and far field through a useful comparison with a more traditional 3D nanorod Yagi–Uda antenna. The behavior of the nanodisk antenna, both configured as a single nanoantenna and arranged in planar arrays, have been illustrated, emphasizing its improved performances with relation to crucial aspects as directional features, wavelength bands of operation, frequency tuning, and polarization influence on radiation. In particular, the single nanodisk antenna has been accurately designed to enhance the transmission feature in the near field at the wavelengths λ?=?1.3 and λ?=?1.55 μm. Also, the emission pattern of the array of nanodisk antennas has been properly tailored to ensure high peaks of directivity and narrow beam width in those ranges. Hence, efficient unidirectional angle patterns have been shaped for any operation wavelength and dimensions of the array, reaching extremely effective outcomes for a 3?×?3 array, which exhibits a maximum of directivity of 19 and 17.6 and ?3 dB points at 18° and 21° for λ?=?1.3 and λ?=?1.55 μm, respectively.     

Size variability of the unit building block of peripheral light-harvesting antennas as a strategy for effective functioning of antennas of variable size that is controlled in vivo by light intensity

This work continuous a series of studies devoted to discovering principles of organization of natural antennas in photosynthetic microorganisms that generate in vivo large and highly effective light-harvesting structures. The largest antenna is observed in green photosynthesizing bacteria, which are able to grow over a wide range of light intensities and adapt to low intensities by increasing of size of peripheral BChl c/d/e antenna. However, increasing antenna size must inevitably cause structural changes needed to maintain high efficiency of its functioning. Our model calculations have demonstrated that aggregation of the light-harvesting antenna pigments represents one of the universal structural factors that optimize functioning of any antenna and manage antenna efficiency. If the degree of aggregation of antenna pigments is a variable parameter, then efficiency of the antenna increases with increasing size of a single aggregate of the antenna. This means that change in degree of pigment aggregation controlled by light-harvesting antenna size is biologically expedient. We showed in our previous work on the oligomeric chlorosomal BChl c superantenna of green bacteria of the Chloroflexaceae family that this principle of optimization of variable antenna structure, whose size is controlled by light intensity during growth of bacteria, is actually realized in vivo. Studies of this phenomenon are continued in the present work, expanding the number of studied biological materials and investigating optical linear and nonlinear spectra of chlorosomes having different structures. We show for oligomeric chlorosomal superantennas of green bacteria (from two different families, Chloroflexaceae and Oscillochloridaceae) that a single BChl c aggregate is of small size, and the degree of BChl c aggregation is a variable parameter, which is controlled by the size of the entire BChl c superantenna, and the latter, in turn, is controlled by light intensity in the course of cell culture growth.     

High detectability with low impact: Optimizing large PIT tracking systems for cave‐dwelling bats

Passive integrated transponder (PIT) tag technology permits the “resighting” of animals tagged for ecological research without the need for physical re‐trapping. Whilst this is effective if animals pass within centimeters of tag readers, short‐distance detection capabilities have prevented the use of this technology with many species. To address this problem, we optimized a large (15 m long) flexible antenna system to provide a c. 8 m² vertical detection plane for detecting animals in flight. We installed antennas at two roosting caves, including the primary maternity cave, of the critically endangered southern bent‐winged bat (Miniopterus orianae bassanii) in south‐eastern Australia. Testing of these systems indicated PIT‐tags could be detected up to 105 cm either side of the antenna plane. Over the course of a three‐year study, we subcutaneously PIT‐tagged 2,966 bats and logged over 1.4 million unique detections, with 97% of tagged bats detected at least once. The probability of encountering a tagged bat decreased with increasing environmental “noise” (unwanted signal) perceived by the system. During the study, we mitigated initial high noise levels by earthing both systems, which contributed to an increase in daily detection probability (based on the proportion of individuals known to be alive that were detected each day) from <0.2 (noise level ≥30%) to 0.7–0.8 (noise level 5%–15%). Conditional on a low (5%) noise level, model‐based estimates of daily encounter probability were highest (>0.8) during peak breeding season when both female and male southern bent‐winged bats congregate at the maternity cave. In this paper, we detail the methods employed and make methodological recommendations for future wildlife research using large antennas, including earthing systems as standard protocol and quantifying noise metrics as a covariate influencing the probability of detection in subsequent analyses. Our results demonstrate that large PIT antennas can be used successfully to detect small volant species, extending the scope of PIT technology and enabling a much broader range of wildlife species to be studied using this approach.     

Multilayer Hybrid Plasmonic Nano Patch Antenna

This is the first report of a hybrid plasmonic nano patch antenna having metal insulator metal (HMIM) multilayer configuration. It is designed in a footprint area of 1.7 × 1.175 μm² to resonate at 1.55 μm wavelength. The proposed antenna is inset fed by an HMIM plasmonic waveguide for achieving proper impedance matching. It is observed, through electromagnetic numerical simulation, that the proposed plasmonic nano patch antenna emits a directional beam with a bandwidth, gain, and efficiency of 0.194 μm, 8.3 dB, and 96% respectively, which are significantly higher than previously reported designs. Since inset-fed antennas are suitable for developing high-gain antenna array, hence further, we examined antenna performance by designing antenna array. The proposed antenna is practically realizable and can be fabricated using standard semiconductor fabrication process. Moreover, it could be used for numerous chip scale applications such as wireless interconnects energy harvesting, photoemission, photo detection, scattering, heat transfer, spectroscopy, and optical sensing.

     

All‐Solid‐State Fiber Supercapacitors with Ultrahigh Volumetric Energy Density and Outstanding Flexibility

Fiber supercapacitors (FSCs) represent a promising class of energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. One of their main limitations, however, is the low volumetric energy density when compared with those of rechargeable batteries. Considering the energy density of FSC is proportional to CV² (E = 1/2 CV², where C is the capacitance and V is the operating voltage), one would explore high operating voltage as an effective strategy to promote the volumetric energy density. In the present work, an all‐solid‐state asymmetric FSC (AFSC) with a maximum operating voltage of 3.5 V is successfully achieved, by employing an ionic liquid (IL) incorporated gel‐polymer as the electrolyte (EMIMTFSI/PVDF‐HFP). The optimized AFSC is based on MnO_x@TiN nanowires@carbon nanotube (NWs@CNT) fiber as the positive electrode and C@TiN NWs@CNT fiber as the negative electrode, which gives rise to an ultrahigh stack volumetric energy density of 61.2 mW h cm^?3, being even comparable to those of commercially planar lead‐acid batteries (50–90 mW h cm^?3), and an excellent flexibility of 92.7% retention after 1000 blending cycles at 90°. The demonstration of employing the ILs‐based electrolyte opens up new opportunities to fabricate high‐performance flexible AFSC for future portable and wearable electronic devices.     

Analysis of the effect of mobile phone base station antenna loading on localized SAR and its consequences for measurements

In this work, the effect of antenna element loading on the localized specific absorption rate (SAR) has been analyzed for base station antennas. The analysis was conducted in order to determine whether localized SAR measurements of large multi-element base station antennas can be conducted using standardized procedures and commercially available equipment. More specifically, it was investigated if the antenna shifting measurement procedure, specified in the European base station exposure assessment standard EN 50383, will produce accurate localized SAR results for base station antennas larger than the specified measurement phantom. The obtained results show that SAR accuracy is affected by the presence of lossy material within distances of one wavelength from the tested antennas as a consequence of coupling and redistribution of transmitted power among the antenna elements. It was also found that the existing standardized phantom is not optimal for SAR measurements of large base station antennas. A new methodology is instead proposed based on a larger, box-shaped, whole-body phantom.     

Insights into the evolution of the antenna domains of Type-I and Type-II photosynthetic reaction centres through homology modelling

The (bacterio)chlorophylls of photosynthetic antenna and reaction centre complexes are bound to the protein via a fifth, axial ligand to the central magnesium atom. A number of the amino acids identified as providing such ligands are conserved between the large antenna of the cyanobacterial Type-I reaction centre and smaller antennas of the Type-I reaction centres of green sulphur bacteria and heliobacteria, and these numbers match closely the estimated number of antenna bacteriochlorophylls in the latter. The possible organisation of the antenna in the latter reaction centres is discussed, as is the mechanism by which the more pigment-rich antenna of the cyanobacterial reaction centre evolved. The homology modelling approach is also extended to the six-helix antenna proteins CP47 and CP43 associated with the Photosystem II reaction centre.     

Design and realisation of tissue-equivalent dielectric simulators for dosimetric studies on microwave antennas for interstitial ablation

Thermal ablation therapies, based on electromagnetic field sources (interstitial or intracavitary antennas) at radio and microwave frequencies, are increasingly used in medicine due to their proven efficacy in the treatment of many diseases (tumours, stenosis, etc). Such techniques need standardized procedures, still not completely consolidated, as to analyze the behaviour of antennas for treatment optimisation. Several tissue-equivalent dielectric simulators (also named phantoms) have been developed to represent human head tissues, and extensively used in the analysis of human exposure to the electromagnetic emissions from hand-held devices; yet, very few studies have considered other tissues, as those met in ablation therapies. The objective of this study was to develop phantoms of liver and kidney tissue to experimentally characterise interstitial microwave antennas in reference conditions. Phantom properties depend on the simulated target tissue (liver or kidney) and the considered frequency (2.45 GHz in this work), addressing the need for a transparent liquid to easily control the positioning of the probe with respect to the antenna under test. An experimental set-up was also developed and used to characterise microwave ablation antenna performances. Finally, a comparison between measurements and numerical simulations was performed for the cross-validation of the experimental set-up and the numerical model. The obtained results highlight the fundamental role played by dielectric simulators in the development of microwave ablation devices, representing the first step towards the definition of a procedure for the ablation treatment planning.     

Numerical simulation of the electromagnetic fields excited by loop antennas in plasma in the whistler frequency range

The electromagnetic fields excited by circular loop antennas in a magnetized plasma in the whistler frequency range are simulated by the finite-difference time-domain method. The spatial structure of quasi-monochromatic fields excited in the near- and far-field zones by an antenna with a harmonic current, as well as the dynamics of the electromagnetic field excited by an antenna with a current in the form of a single video pulse, is studied. Simulations performed for a uniform plasma and uniform ambient magnetic field agree well with the results of theoretical analysis and model laboratory experiments performed on large-scale plasma devices.     

Wireless Electric Energy Transmission through Various Isolated Solid Media Based on Triboelectric Nanogenerator

Wireless electric energy transmission is an important energy supply technology. However, most wireless energy supply based on electromagnetic induction cannot be used for energy transmission through a metal chamber. Herein, a novel idea for wireless electric energy transmission through various isolated solid media based on triboelectric nanogenerator (TENG) is presented. The electric energy is first transformed into mechanical vibration energy in mechanical wave that can propagate well in solid medium, and then the vibration energy is harvested by a TENG. By employing the spring steel sheets and freestanding triboelectric‐layer structure, the vibration TENG as an energy conversion unit has the advantages of high efficiency and facilitation, boosting this wireless energy transmission technology to be an alternative way of delivering electric energy through metal medium. The working principle and output performance have been systematically studied. A commercial capacitor can be charged from 0 to 10 V in 33 and 86 s isolated by an acrylic plate and a copper plate in thickness of 3 mm, respectively. The wireless electric transmission technology is also applied to deliver electric energy into a vacuum glove box and across glass wall successfully. This novel technology has great potential applications in implantable microelectronic devices, encrypted wireless communication, and even nondestructive testing.     

Catheter microwave ablation therapy for cardiac arrhythmias

This article describes three microwave catheter antennas for percutaneous cardiac ablation. A particular design feature of these antennas is that there is no reflected microwave current from the antenna flowing up the transmission line. Thus, it minimizes heating of the coaxial cable. The power reflection coefficients are very low (4% or less) in phantom equivalent materials. These antennas can also serve as bipolar electrodes for sensing endocardiac electrograms. Our studies in dogs, during both cardiopulmonary bypass and closed‐chest operations via the femoral vein, have shown microwave energy greater than 200 joules (J) delivered to the heart through a split‐tip dipole catheter antenna can produce irreversible block of the heart rhythms. This energy was achieved either by increasing the delivered power from 20 to 40 watts or by increasing the treatment duration from 7 to 11 s (210 to 330 J per application). It produced an endocardium temperature of about 65 ºC. We found that the percutaneous, transcatheter microwave system is capable of inducing AV blocks consistently in dogs using the flexible, curved tip, split‐tip catheter antenna. In addition, our studies have shown that the width and height of SAR distributions for cap‐choke and split‐tip catheter antennas are similar for the same antenna length. The cap‐slot design had a much longer SAR distribution compared to the others. Moreover, a longer (4 mm) split‐tip antenna can also induce larger lesions. These results suggest that it could be possible to ablate a ventricular tachycardia focus using the 4 mm split‐tip as well as the cap‐slot microwave catheter antennas. Bioelectromagnetics 20:120–132, 1999. © 1999 Wiley‐Liss, Inc.     

Comprehensive Surface-Wave Description for the Nano-scale Energy Concentration with Resonant Dipole Antennas

Resonant optical dipole nano-antennas allow giant field enhancement within nano-gaps. To show how the energy of external illumination waves is delivered and concentrated in nano-gaps, we build up a model by considering the dynamical launching and multiple scattering processes of surface plasmon polaritions (SPPs) on both antenna arms. The model captures the main feature of the antenna resonance as evidenced by comparison of the model prediction with fully vectorial numerical results and provides an intuitive picture that the energy of external wave is initially transferred into SPP and is then coupled into the nano-gap. The enhanced field in the nano-gap oscillates quasi-periodically with the increase of the antenna-arm length, and the resonance peaks can be predicted with a phase-matching condition derived from the model, showing that antenna resonance is due to a constructive interference of the multiple-scattered SPPs. Analytical equation for determining the complex resonance wavelength and the quality factor of the resonant modes is obtained. The model however exhibits observable deviation from fully vectorial numerical results for the lowest resonance order (for antenna with the shortest arms), evidencing that, for this case, surface waves other than SPPs contribute to the antenna resonance. The present results are helpful for clarifying the underlying physics for the energy concentration with resonant dipole antennas and may provide recipes for intuitive design of antenna devices, such as those used for optical nonlinearity enhancement and biochemical sensing.     

Exogenous quinones inhibit photosynthetic electron transfer in Chloroflexus aurantiacus by specific quenching of the excited bacteriochlorophyll c antenna.

In the photosynthetic green filamentous bacterium Chloroflexus aurantiacus, excitation energy is transferred from a large bacteriochlorophyll (BChl) c antenna via smaller BChl a antennas to the reaction center. The effects of substituted 1,4-naphthoquinones on BChl c and BChl a fluorescence and on flash-induced cytochrome c oxidation were studied in whole cells under aerobic conditions. BChl c fluorescence in a cell suspension with 5.4 microM BChl c was quenched to 50% by addition of 0.6 microM shikonin ((R)-2-(1-hydroxy-4-methyl-3-pentenyl)-5,8-dihydroxy-1, 4-naphthoquinone), 0.9 microM 5-hydroxy-1,4-naphthoquinone, or 4 microM 2-acetyl-3-methyl-1,4-naphthoquinone. Between 25 and 100 times higher quinone concentrations were needed to quench BChl a fluorescence to a similar extent. These quinones also efficiently inhibited flash-induced cytochrome c oxidation when BChl c was excited, but not when BChl a was excited. The quenching of BChl c fluorescence induced by these quinones correlated with the inhibition of flash-induced cytochrome c oxidation. We concluded that the quinones inhibited electron transfer in the reaction center by specifically quenching the excitation energy in the BChl c antenna. Our results provide a model system for studying the redox-dependent antenna quenching in green sulfur bacteria because the antennas in these bacteria inherently exhibit a sensitivity to O(2) similar to the quinone-supplemented cells of Cfx. aurantiacus.     

Combined ICR heating antenna for ion separation systems

A combination of one- and two-wave antennas (one and two turns of conductors around a plasma cylinder, respectively) is proposed. This combined antenna localizes an RF field within itself. It is shown that spent nuclear fuel processing systems based on ICR heating of nuclear ash by such a combined antenna have high productivity. A theory of the RF field excitation in ICR ion separation systems is presented in a simple and compact form.     

Quantifying the Volumetric Performance Metrics of Supercapacitors

Nanostructured materials have greatly improved the performance of electrochemical energy storage devices because of the increased activity and surface area. However, nanomaterials (e.g., nanocarbons) normally possess low packing density, and thus occupy more space which restricts their suitability for making electrochemical devices as compact as possible. This has resulted in their low volumetric performance (capacitance, energy density, and power density), which is a practical obstacle for the application of nanomaterials in mobile and on‐board energy storage devices. While rating electrode materials for supercapacitors, their volumetric performance is equally important as the gravimetric metrics and more reliable in particular for systems with limited space. However, the adopted criteria for measuring the volumetric performance of supercapacitors vary in the literature. Identifying the appropriate performance criteria for the volumetric values will set a universal ground for valid comparison. Here, the authors discuss the rationale for quantifying the volumetric performance metrics of supercapacitors from the three progressive levels of materials, electrodes, and devices. It is hoped that these thoughts will be of value for the general community in energy storage research.     

Changes in antenna of photosystem II induced by short-term heating

Changes in antenna of photosystem II, induced by short-term heating, were studied using characteristics of a short-wavelength band in low-temperature fluorescence spectra (77 K) of pea chloroplasts. Heating for 5 min was carried out at 25 and 45°C in the darkness or in the presence of white light with intensity of 260 or 1,400 μmol/m²s. Most modes of thermal treating induced a decrease in integral intensity of the band and an increase of its half-width. The changes were more prominent at high-temperature heating. The second derivative of the contour of a short-wavelength band showed its three components around 680, 685, and 693 nm, the first of which belongs to emission of the outer antenna of Photosystem II, and the other two to its inner antenna. As the fourth derivative shows, high-temperature heating in the presence of light evokes an appearance of some additional components in a short-wavelength region (654, 658, 661, 666, 672, and 675 nm) as well as of two additional components, 682 and 689 nm, in the region of 685-nm peak. Two subcomponents, 692 and 694 nm, can be detected in the 693-nm component. The results are discussed on the basis of the data concerning energy levels and pathways of energy transfer in pigment–protein complexes of the outer and the inner antennas of photosystem II. It is assumed that a protective role of low light relates to inducing of an essential disarrangement in the outer and the inner antennas and of a subsequent decrease in energy funneling to reaction centers, which, in turn, lowers the extent of photoinhibition.     

Recent Progress in Biomass‐Derived Electrode Materials for High Volumetric Performance Supercapacitors

Tremendous efforts have been spent on the development of electrical energy storage (EES) systems with high volumetric performance in the past few years due to the evergrowing demand of miniaturized, portable electronic devices, and electric vehicles. Among all the EES devices, supercapacitors with electrode materials derived from biosources have attracted special attention due to their eco‐friendliness, natural abundance, their intrinsic porous structures as well as their renewable and sustainable features. However, the relatively low packing densities make their specific volumetric capacitance intrinsically low, which has largely limited their further application in the supercapacitors. To address these issues, various promising approaches ranging from structural manufacture to compositional design are applied and significant breakthroughs are witnessed in recent years. In this progress report, key factors influencing the volumetric performance of biomass‐derived electrode materials are systematically discussed with a particular focus spanning from fundamental to operational aspects. This work provides insights into the development of high‐volumetric‐performance biomass‐derived supercapacitors by comprehensively summarizing recent advances in the rational structural design and fabrication. Perspectives regarding the future challenges and promising research directions on the design of next‐generation EES devices are also provided.