On-Chip Integration of a Plasmonic FET Source and a Nano-Patch Antenna for Efficient Terahertz Wave Radiation.

Graphene-based Field-Effect Transistors (FETs) integrated with microstrip patch antennas offer a promising approach for terahertz signal radiation. In this study, a dual-stage simulation methodology is employed to comprehensively investigate the device's performance. The initial stage, executed in MATLAB, delves into charge transport dynamics within a FET under asymmetric boundary conditions, employing hydrodynamic equations for electron transport in the graphene channel. Electromagnetic field interactions are modeled via Finite-Difference Time-Domain (FDTD) techniques. The second stage, conducted in COMSOL Multiphysics, focuses on the microstrip patch antenna's radiative characteristics. Notably, analysis of the S11 curve reveals minimal reflections at the FET's resonant frequency of 1.34672 THz, indicating efficient impedance matching. Examination of the radiation pattern demonstrates the antenna's favorable directional properties. This research underscores the potential of graphene-based FETs for terahertz applications, offering tunable impedance matching and high radiation efficiency for future terahertz devices.

Tunable topological charge vortex microlaser.

The orbital angular momentum (OAM) intrinsically carried by vortex light beams holds a promise for multidimensional high-capacity data multiplexing, meeting the ever-increasing demands for information. Development of a dynamically tunable OAM light source is a critical step in the realization of OAM modulation and multiplexing. By harnessing the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking, we demonstrate an OAM-tunable vortex microlaser, providing chiral light states of variable topological charges at a single telecommunication wavelength. The scheme of the non-Hermitian-controlled chiral light emission at room temperature can be further scaled up for simultaneous multivortex emissions in a flexible manner. Our work provides a route for the development of the next generation of multidimensional OAM-spin-wavelength division multiplexing technology.

Nanonetworks in Biomedical Applications.

By interconnecting nanomachines and forming nanonetworks, the capacities of single nanomachines are expected to be enhanced, as the ensuing information exchange will allow them to cooperate towards a common goal. Nowadays, systems normally use electromagnetic signals to encode, send and receive information, however, in a novel communication paradigm, molecular transceivers, channel models or protocols use molecules. This article presents the current developments in nanomachines along with their future architecture to better understand nanonetwork scenarios in biomedical applications. Furthermore, to highlight the communication needs between nanomachines, two applications for nanonetworks are also presented: i) a new networking paradigm, called the Internet of NanoThings, that allows nanoscale devices to interconnect with existing communication networks, and ii) Molecular Communication, where the propagation of chemical compounds like drug particles, carry out the information exchange.

Security and eavesdropping in terahertz wireless links.

Resiliency against eavesdropping and other security threats has become one of the key design considerations for communication systems. As wireless systems become ubiquitous, there is an increasing need for security protocols at all levels, including software (such as encryption), hardware (such as trusted platform modules) and the physical layer (such as wave-front engineering)1-5. With the inevitable shift to higher carrier frequencies, especially in the terahertz range (above 100 gigahertz), an important consideration is the decreased angular divergence (that is, the increased directionality) of transmitted signals, owing to the reduced effects of diffraction on waves with shorter wavelengths. In recent years, research on wireless devices6-8 and systems9-11 that operate at terahertz frequencies has ramped up markedly. These high-frequency, narrow-angle broadcasts present a more challenging environment for eavesdroppers compared to the wide-area broadcasts used at lower frequencies12,13. However, despite the widespread assumption of improved security for high-frequency wireless data links14-16, the possibility of terahertz eavesdropping has not yet been characterized. A few recent studies have considered the issue at lower frequencies5,12,13,17,18, but generally with the idea that the eavesdropper's antenna must be located within the broadcast sector of the transmitting antenna, leading to the conclusion that eavesdropping becomes essentially impossible when the transmitted signal has sufficiently high directionality15. Here we demonstrate that, contrary to this expectation, an eavesdropper can intercept signals in line-of-sight transmissions, even when they are transmitted at high frequencies with narrow beams. The eavesdropper's techniques are different from those for lower-frequency transmissions, as they involve placing an object in the path of the transmission to scatter radiation towards the eavesdropper. We also discuss one counter-measure for this eavesdropping technique, which involves characterizing the backscatter of the channel. We show that this counter-measure can be used to detect some, although not all, eavesdroppers. Our work highlights the importance of physical-layer security in terahertz wireless networks and the need for transceiver designs that incorporate new counter-measures.

End-to-End Noise Model for Intra-Body Terahertz Nanoscale Communication.

In vivo wireless nanosensor networks (iWNSNs) are paving the way toward transformative healthcare solutions. These networks are expected to enable a plethora of applications, including drug-delivery, bio-sensing, and health monitoring. With the development of miniature plasmonic signal sources, antennas, and detectors, wireless communications among intrabody nanodevices will expectedly be enabled in the terahertz (THz) frequency band (0.1-10 THz). Several propagation models were recently developed to analyze and assess the feasibility of intra-body electromagnetic (EM) nanoscale communication. The emphasis of these works has mainly been on understanding the propagation of EM signals through biological media, with limited focus on the intra-body noise sources and their impact on the system performance. In this paper, a stochastic noise model for iWNSNs is presented in which the individual noise sources that impact intra-body systems operating in the THz frequency band are analyzed. The overall noise contributions are composed of three distinctive constituents, namely, Johnson-Nyquist noise, black-body noise, and Doppler-shift-induced noise. The probability distribution of each noise component is derived, and a comprehensive analytical approach is developed to obtain the total noise power-spectral density. The model is further validated via 2-D particle simulations as the active transport motion of particles is conveyed in the presented framework. The developed models serve as the starting point for a rigorous end-to-end channel model that enables the proper estimation of data rate, channel capacity, and other key parameters, which are all factors of the noise environment.

Photothermal Modeling and Analysis of Intrabody Terahertz Nanoscale Communication.

Wireless communication among implanted nano-biosensors will enable transformative smart health monitoring and diagnosis systems. The state of the art of nano-electronics and nano-photonics points to the terahertz (THz) band (0.1-10 THz) and optical frequency bands (infrared, 30-400 THz, and visible, 400-750 THz) as the frequency range for communication among nano-biosensors. Recently, several propagation models have been developed to study and assess the feasibility of intra-body electromagnetic (EM) nanoscale communication. These works have been mainly focused on understanding the propagation of EM signals through biological media, but do not capture the resulting photothermal effects and their impact both on the communication as well as on the body itself. In this paper, a novel thermal noise model for intra-body communication based on the diffusive heat flow theory is developed. In particular, an analytical framework is presented to illustrate how molecules in the human body absorb energy from EM fields and subsequently release this energy as heat to their immediate surroundings. As a result, a change in temperature is witnessed from which the molecular absorption noise can be computed. Such analysis has a dual benefit from a health as well as a communication perspective. For the medical community, the presented methodology allows the quantization of the temperature increase resulting from THz frequency absorption. For communication purposes, the complete understanding of the intra-body medium opens the door toward developing modulations suited for the capabilities of nano-machines and tailored to the peculiarities of the THz band channel as well as the optical window.

Cooperative Raman Spectroscopy for Real-Time In Vivo Nano-Biosensing.

In the last few decades, the development of miniature biological sensors that can detect and measure different phenomena at the nanoscale has led to transformative disease diagnosis and treatment techniques. Among others, biofunctional Raman nanoparticles have been utilized in vitro and in vivo for multiplexed diagnosis and detection of different biological agents. However, existing solutions require the use of bulky lasers to excite the nanoparticles and similarly bulky and expensive spectrometers to measure the scattered Raman signals, which limit the practicality and applications of this nano-biosensing technique. In addition, due to the high path loss of the intra-body environment, the received signals are usually very weak, which hampers the accuracy of the measurements. In this paper, the concept of cooperative Raman spectrum reconstruction for real-time in vivo nano-biosensing is presented for the first time. The fundamental idea is to replace the single excitation and measurement points (i.e., the laser and the spectrometer, respectively) by a network of interconnected nano-devices that can simultaneously excite and measure nano-biosensing particles. More specifically, in the proposed system, a large number of nanosensors jointly and distributively collect the Raman response of nano-biofunctional nanoparticles (NBPs) travelling through the blood vessels. This paper presents a detailed description of the sensing system and, more importantly, proves its feasibility, by utilizing the accurate models of optical signal propagation in intra-body environment and low-complexity estimation algorithms. The numerical results show that with a certain density of NBPs, the reconstructed Raman spectrum can be recovered and utilized to accurately extract the targeting intra-body information.

Terahertz Channel Model and Link Budget Analysis for Intrabody Nanoscale Communication.

Nanosized devices operating inside the human body open up new prospects in the healthcare domain. Invivo wireless nanosensor networks (iWNSNs) will result in a plethora of applications ranging from intrabody health-monitoring to drug-delivery systems. With the development of miniature plasmonic signal sources, antennas, and detectors, wireless communications among intrabody nanodevices will expectedly be enabled at both the terahertz band (0.1-10 THz) as well as optical frequencies (400-750 THz). This result motivates the analysis of the phenomena affecting the propagation of electromagnetic signals inside the human body. In this paper, a rigorous channel model for intrabody communication in iWNSNs is developed. The total path loss is computed by taking into account the combined effect of the spreading of the propagating wave, molecular absorption from human tissues, as well as scattering from both small and large body particles. The analytical results are validated by means of electromagnetic wave propagation simulations. Moreover, this paper provides the first framework necessitated for conducting link budget analysis between nanodevices operating within the human body. This analysis is performed by taking into account the transmitter power, medium path loss, and receiver sensitivity, where both the THz and photonic devices are considered. The overall attenuation model of intrabody THz and optical frequency propagation facilitates the accurate design and practical deployment of iWNSNs.

Wireless Optogenetic Nanonetworks for Brain Stimulation: Device Model and Charging Protocols.

In recent years, numerous research efforts have been dedicated toward developing efficient implantable devices for brain stimulation. However, there are limitations and challenges with the current technologies. They include neuron population stimulation instead of single neuron level, the size, the biocompatibility, and the device lifetime reliability in the patient's brain. We have recently proposed the concept of wireless optogenetic nanonetworking devices (WiOptND) that could address the problem of long term deployment, and at the same time target single neuron stimulation utilizing ultrasonic as a mode for energy harvesting. In addition, a number of charging protocols are also proposed, in order to minimize the quantity of energy required for charging, while ensuring minimum number of neural spike misfirings. These protocols include the simple charge and fire, which requires the full knowledge of the raster plots of neuron firing patterns, and the predictive sliding detection window, and its variant Markov-chain based time-delay patterns, which minimizes the need for full knowledge of neural spiking patterns as well as number of ultrasound charging frequencies. Simulation results exhibit a drop for the stimulation ratio of ~ 25% and more stable trend in its efficiency ratio (standard deviation of ~0.5%) for the Markov-chain based time-delay patterns protocol compared with the baseline change and fire. The results show the feasibility of utilizing WiOptND for long-term implants in the brain, and a new direction toward precise stimulation of neurons in the cortical microcolumn of the brain cortex.

Intra-Body Optical Channel Modeling for In Vivo Wireless Nanosensor Networks.

In vivo wireless nanosensor networks (iWNSNs) consist of nanosized communicating devices, which can operate inside the human body in real time. iWNSNs are at the basis of transformative healthcare techniques, ranging from intra-body health-monitoring systems to drug-delivery applications. Plasmonic nanoantennas are expected to enable the communication among nanosensors in the near infrared and optical transmission window. This result motivates the analysis of the phenomena affecting the propagation of such electromagnetic (EM) signals inside the human body. In this paper, a channel model for intra-body optical communication among nanosensors is developed. The total path loss is computed by taking into account the absorption from different types of molecules and the scattering by different types of cells. In particular, first, the impact of a single cell on the propagation of an optical wave is analytically obtained, by modeling a cell as a multi-layer sphere with complex permittivity. Then, the impact of having a large number of cells with different properties arranged in layered tissues is analyzed. The analytical channel model is validated by means of electromagnetic simulations and extensive numerical results are provided to understand the behavior of the intra-body optical wireless channel. The result shows that, at optical frequencies, the scattering loss introduced by cells is much larger than the absorption loss from the medium. This result motivates the utilization of the lower frequencies of the near-infrared window for communication in iWNSNs.