Browsing by Subject "Wireless"

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Open Access
60 GHz wireless data center networks: A survey
(Elsevier BV * North-Holland, 2021-02-11) Terzi, Çağlar; Körpeoğlu, İbrahim
Data centers (DCs) became an important part of computing today. A lot of services in Internet are run on DCs. Meanwhile a lot of research is done to tackle the challenges of high-performance and energy-efficient data center networking (DCN). Hot node congestion, cabling complexity/cost, and cooling cost are some of the important issues about data centers that need further investigation. Static and rigid topology in wired DCNs is an other issue that hinders flexibility. Use of wireless links for DCNs to eliminate these disadvantages is proposed and is an important research topic. In this paper, we review research studies in literature about the design of radio frequency (RF) based wireless data center networks. RF wireless DCNs can be grouped into two as hybrid (wireless and wired) and completely wireless data centers. We investigate both. We also compare wireless DCN solutions in the literature with respect to various aspects. Open areas and research ideas are also discussed.
Open Access
Design and development of an SSVEP based low cost, wearable, and wireless BCI system
(2019-08) Waheed, Abdul
It has become a challenging research topic to design and develop cheap and wearable brain-computer interface (BCI) systems but not compromising the performance. In this thesis, the design and development of a steady state visually evoked potential (SSVEP) based BCI system has been presented which is a low cost, wearable BCI system and gives highly accurate target identi cations with good information transfer rate (ITR). It is a battery powered, wireless BCI system and ensures the complete isolation to the subject. Like all the BCI systems, it is designed and implemented in ve major parts: (i) stimulator which is a microcontroller based circuit and provides the frequency modulated visually evoked potential (f-VEP) and code-modulated visually evoked potential (c-VEP) stimulations (ii) dry active electrodes which capture the electroencephalography(EEG) signals from the O1, O2, and Oz head positions (iii) high sampling rate, 4-channel EEG data acquisition hardware which acquires the EEG signals, amplify them, converts them to digital data, and transmits the data using wi communication (iv) the data processing unit (DPU) which is a MATLAB script to process the raw EEG data and displays the results and (v) the headset which mounts all the components except DPU and is developed using 3D printing technology. The rst prototype of the proposed BCI system has been developed in 331 USD and tested for both the f-VEP and c-VEP modalities on six human subjects. For f-VEP modality, it exhibits an average accuracy (live accuracy) of 92.1% and average ITR (live ITR) of 69.5 bits/min on the basis of target identi cations done on 1:04 s data recordings. If we extract one message character from ve consecutive target identi cations, the average message accuracy goes to 98.8% and average message ITR to 17.2 bits/min. In case of c-VEP modality, it exhibits live accuracy of 70.1 % and live ITR of 23.5 bits/min while message accuracy of 90.7 % and message ITR of 12.4 bit/min.
Open Access
Improved selectivity from a wavelength addressable device for wireless stimulation of neural tissue
(Frontiers Research Foundation, 2014) Seymour, E. Ç.; Freedman, D. S.; Gökkavas, M.; Özbay, Ekmel; Sahin, M.; Ünlü, M. S.
Electrical neural stimulation with micro electrodes is a promising technique for restoring lost functions in the central nervous system as a result of injury or disease. One of the problems related to current neural stimulators is the tissue response due to the connecting wires and the presence of a rigid electrode inside soft neural tissue. We have developed a novel, optically activated, microscale photovoltaic neurostimulator based on a custom layered compound semiconductor heterostructure that is both wireless and has a comparatively small volume (<0.01 mm3). Optical activation provides a wireless means of energy transfer to the neurostimulator, eliminating wires and the associated complications. This neurostimulator was shown to evoke action potentials and a functional motor response in the rat spinal cord. In this work, we extend our design to include wavelength selectivity and thus allowing independent activation of devices. As a proof of concept, we fabricated two different microscale devices with different spectral responsivities in the near-infrared region. We assessed the improved addressability of individual devices via wavelength selectivity as compared to spatial selectivity alone through on-bench optical measurements of the devices in combination with an in vivo light intensity profile in the rat cortex obtained in a previous study. We show that wavelength selectivity improves the individual addressability of the floating stimulators, thus increasing the number of devices that can be implanted in close proximity to each other. © 2014 Seymour, Freedman, Gökkavas, Özbay, Sahinand Ünlü.