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Nonlinear optoacoustics enable effective communication across the air-water interface. However, the requirement of a high-power laser and the vapor cloud buildup can limit the power efficiency and data rate. Thus, a proper modulation and encoding scheme is necessary. This article tackles this issue by presenting an optical focusing-based adaptive modulation (OFAM) technique that can dynamically control the underwater acoustic source (plasma) and acoustic pressure. Specifically, the article describes two variants of OFAM for a single laser transmitter with stationary focusing (OFAM-1D) and dynamic focusing (OFAM-3D). The data rate of OFAM-1D and OFAM-3D is approximately 6 and 4.4 times higher than peak detection based on-off keying (PDOOK). Furthermore, both techniques are 137% more power efficient than PDOOK. Studying the bit error rate (BER) in the presence of ambient underwater noises for different node positions has indicated that OFAM can achieve low BER even at a 300-m depth for 50- and 60-mJ laser pulse energy. Moreover, machine learning (ML) techniques have been leveraged in the demodulation process for increased robustness. Specifically, the random forest (RF) model could yield up to 94.75% demodulation accuracy. Our results indicate that OFAM can lead to a new paradigm of air to underwater wireless communication. 

In an application involving Autonomous Underwater Vehicles (AUV) it is important to track the trajectory and spatially correlate the collected data. Relying on an Inertial Navigation System (INS) while factoring in the initial AUV position would not suffice given the major accumulated errors. Employing surface nodes is a logistically complicated option, especially for missions involving emerging events. This paper proposes a novel localization approach that offers both agility and accuracy. The idea is to exploit a communication mechanism across the air-water interface. In particular, we employ an airborne unit, e.g., a drone, that scans the area of interest and uses visual light communication (VLC) to reach the AUV. In essence, the airborne unit defines virtual anchors with known GPS coordinates. The AUV uses the light intensity of the received VLC transmissions to estimate the range relative to the anchor points and then determine its own global coordinates at various time instances. The proposed approach is validated through extensive simulation experiments. The simulation results demonstrate the viability of our approach and analyze the effect of the VLC parameters. 

Wireless communication from air-to-underwater is quite challenging because of the lack of proper physical signal that propagates well in both air and water medium. Photoacoustic energy transfer mechanism is the most promising method for such cross-medium communication, where a high energy pulsed light is focused on the water surface, causing the generation of an acoustic signal inside the water. Since acoustic signals can travel a long distance inside the water, this method enables an airborne unit to reach nodes at increased underwater depth. Yet the achievable bit rate for this process is very low. When a pulsed laser light with a higher repetition rate is focused inside the water, a vapor cloud is generated around the focus point, which blocks subsequent generation of acoustic signal and consequently limits the achievable bit rate. This paper opts to overcome such a limitation by proposing a novel pulse position modulation technique which can avoid such generation of vapor cloud and increases the bit rate significantly. 

The current era is notably characterized by the major advances in communication technologies. The increased connectivity has been transformative in terrestrial, space, and undersea applications. Nonetheless, the water medium imposes unique constraints on the signals that can be pursued for establishing wireless links. While numerous studies have been dedicated to tackling the challenges for underwater communication, little attention has been paid to effectively interfacing the underwater networks to remote entities. Particularly it has been conventionally assumed that a surface node will be deployed to act as a relay using acoustic links for underwater nodes and radio links for air-based communication. Yet, such an assumption could be, in fact, a hindrance in practice. The paper discusses alternative means by allowing communication across the air–water interface. Specifically, the optoacoustic effect, also referred to as photoacoustic effect, is being exploited as a means for achieving connectivity between underwater and airborne nodes. The paper provides background, discusses technical challenges, and summarizes progress. Open research problems are also highlighted. 

Transcranial magnetic stimulation (TMS) is gaining increasing attention for therapeutic treatment of mental illnesses. However, a clear understanding of its impact to the underlying brain mechanisms is critical for its effective application. For this, we analyze electroencephalography (EEG) response to TMS subthreshold pulse at the left motor cortex from 6 healthy controls and 6 schizophrenia patients. We use principal component analysis (PCA) along sparse nonnegative matrix factorization (NMF), an unsupervised machine learning technique, on brain connectivity data established by sliding window coherence of EEG based source localized data. The source localization was achieved by using the sLORETA algorithm on our EEG data after artifact removal. This, hence, provides high temporal and spatial resolution in the connectivity analysis results, giving advantage over other neuroimaging modalities. PCA aids in establishing the number of common underlying connected subnetworks (say k) across subjects whereas NMF is employed to derive these k spatial and temporal signature subnetwork response to the stimulus. Within these signatures, we studied motor cortical connectivity and found that schizophrenia patients exhibited sensory gating deficits as compared to controls. These findings can act as potential biomarkers to monitor TMS for clinical therapeutic techniques in the future. 

In recent years, there is an increasing interest in noninvasive treatments for neurological disorders like Alzheimer and Depression. Transcranial magnetic stimulation (TMS) is one of the most effective methods used for this purpose. The performance of TMS highly depends on the coils used for the generation of magnetic field and induced electric field particularly their designs affecting depth and focality tradeoff characteristics. Among a variety of proposed and used TMS coil designs, circular coils are commonly used both in research and medical and clinical applications. In current study, we focus on changing the outer and inner sizes (diameter) and winding turns of ring coils and try to reach deeper brain regions without significant field strength decay. The induced electric field and the decay rate of the generated field with depth were studied with finite element method calculations. The results of the performed simulations indicate that larger diameter coils have a larger equivalent field emission aperture and produce larger footprint of induced electric field initially. However, their emission solid angles are smaller and, as a result, the field divergence or the decay rates of the generated field with depth are smaller as well, which give them a good potential to perform better for deep brain stimulation compared with that of smaller coil.