Browsing by Author "Tekin, Ahmet"

Now showing 1 - 17 of 17

Metadata only
16-elements helical antenna system integration with a solar cell powered IoT collector
(IEEE, 2019) Ullah, Naveed; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Ullah, Naveed
An 868MHz-915MHz 16-elements helical wire antenna array design with a solar-cell integration is presented. Each element is designed to be omni-directional with the corresponding tuning stubs and ground substrate. This is shared with distributed solar cell array, powering 16- Internet of Things (loT) transceivers operating at multiple Industrial Scientific and Medical (ISM) bands. 370mmx400mm design including the antennas, solar cells, and the tuning stubs can generate 8-watts solar power under direct sun, charging Lithium batteries. 1.6-mm thick planner design with horizontal radiation pattern resulted in average -15dB return loss at 868 MHz without using any external matching elements.
Open Access
A 1GS/s, 9-bits DAC interleaved (2+1)-bit then 2-bit per cycle SAR ADC
(Istanbul University, 2020-07) El-Sawy, Salma; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; El-Sawy, Salma
This paper presents a high speed Successive Approximation Register Analog to Digital Converter (SAR ADC) for low-noise low-power satellite transceiver applications. The system is a (2+1) then 2-bit per cycle SAR ADC of 1GS/s sampling rate, 9-bits resolution designed in a 65nm standard CMOS technology. The system resolves 9 bits with a special switching scheme in a total of 4 cycles per sample. This is achieved by interleaving 4 Capacitive Digital to Analog Converter (C-DACs) of unit capacitance 1fF. Since the interleaving is limited to the DACs only which match well, the design does not suffer from the drawbacks of full interleaving. Hence, better power efficiency and performance metrics were obtained in comparison to regular interleaved ADCs. A special timing with an extra first bit comparator is optimized to leave proper timing margins for every step from a single 4-GHz low noise clock source which is readily available in the 8- GHz direct conversion front-end. This comparator is reused as all the other active comparators in the both interleaving phases. The proposed design achieved an effective number of bits (ENOB) of 8.2 bits at Nyquist with power consumption of 12mW, resulting in a Figure of Merit (FoM) of 38.37 fJ/conversion-step.
Metadata only
Adaptive 6.78-MHz ISM band wireless charging for small form factor receivers
(IEEE, 2017) Abouzeid, Mohamed Osama Hussein Soliman; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Abouzeid, Mohamed Osama Hussein Soliman
This paper presents a low cost wireless power transfer system tailored particularly for size limited insulation sealed wearable devices. The 5-V USB input system features a crystal oscillator as reference signal source, a class-E power stage, a transmit coil with tunable series resonance and a feedback path to tune the resonance for peak power transmission. Regardless of the receive coil, load, component variations or any external blockers, the system continuously targets peak power at the strict center frequency of 6.78 MHz for compliance with international frequency regulations. Design choices and experimental measurement results were presented along with detailed circuit diagrams. The design can transfer around 50mW power to a 15mm × 17mm × 1mm 40-turn receive coil in a charging pad area of as wide as 9cm × 9cm.
Metadata only
Class E resonant converter design for LED drivers
(IEEE, 2019-06) Zengin, Ö. Ö.; Boztepe, M.; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet
The LED (Light Emitting Diode) lighting technology has been becoming widespread rapidly due to having advantages such as extremely long lifetime, compact structure and very low energy consumption. In the literature, various LED driver topologies are proposed for controlling the LED's current and voltage. However, most of them require a large capacitor and inductor values due to low switching frequency operation. On the other hand, high capacitance with low volume can be achieved by using the electrolytic type capacitors which limits the lifetime and reliability of LED driver. By the help of high switching frequency, converter size can be reduced significantly. In addition, the capacitor size decreases and therefore electrolytic capacitors can be eliminated. In this study, isolated Class E resonant topology operating at 1 MHz is analysed and designed for 48 V/60 W offline LED driver. The design methodology is presented and verified by PSIM simulation.
Metadata only
Design and kinematics of 4- DoF multi-purpose wearable mechanical arm (MUWA) support for enhanced operation stability
(IEEE, 2019) Nomanfar, P.; Tekin, Ahmet; Bogosyan, S.; Şendur, Polat; Electrical & Electronics Engineering; Mechanical Engineering; TEKİN, Ahmet; ŞENDUR, Polat
A low-cost motor-less simple wearable mechanical arm support unit is presented as a viable alternative to todays assistive exoskeleton support units. By limiting the functionality of the device to stabilization rather than actuation, the cost could significantly be reduced while still maintaining a wide range of applications. The basic idea is to let the device follow the wearers actions freely without obscuring the motion in normal mode, while fixating the arm at the desired angle and location when the user expect to receive support; namely in lock mode. The lock-unlock mechanism is simple Bluetooth activated palm gesture of the non-operating arm while the support unit Bluetooth receiver stabilizes the arm at any desired angle or position in response to sensed gesture command. The lock-unlock mechanism is achieved by solely two solenoids, one at each of the joints; shoulder and elbow, with 3 Degree of Freedom (DoF) and 1 DoF respectively, leaving the wrist free to perform the desired hand operation and increasing the precision of the locking mechanism.
Open Access
Design and simulation of microfluidic device for metabolite screening and quantitative monitoring of drug uptake in cancer cells
(Sciendo, 2018) Asif, Afia; Khawaldeh, S.; Khan, Muhammad Salman; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Asif, Afia; Khan, Muhammad Salman
Although liquid-liquid extraction methods are currently being applied in many areas such as analytical chemistry, biochemical engineering, biochemistry, and biological applications, accessibility and usability of microfluidics in practical daily life fields are still bounded. Suspended microfluidic devices have the potential to lessen the obstacles, but the absence of robust design rules have hampered their usage. The primary objective of this work is to design and fabricate a microfluidic device to quantitatively monitor the drug uptake of cancer cells. Liquid-liquid extraction is used to quantify the drug uptake. In this research work, designs and simulations of two different microfluidic devices for carrying out multiplex solution experiments are proposed to test their efficiency. These simplified miniaturized chips would serve as suspended microfluidic metabolites extraction platform as it allows extracting the metabolites produced from the cancer cells as a result of applying a specific drug type for a certain period of time. These devices would be fabricated by making polydimethylsiloxane (PDMS) molds from the negative master mold using soft lithography. Furthermore, it can leverage to provide versatile functionalities like high throughput screening, cancer cell invasions, protein purification, and small molecules extractions. As per previous studies, PDMS has been depicting better stability with various solvents and has proved to be a reliable and cost effective material to be used for fabrication, though the sensitivity of the chip would be analyzed by cross contamination and of solvents within the channels of device.
Open Access
The design of a high gain dual-polarized quad-ridged circular horn antenna for wideband EMC test applications
(The Applied Computational Electromagnetics Society, 2018-09) Solak, Bekir; Seçmen, M.; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Solak, Bekir
This paper presents the design of a high gain broadband quadruple-ridged circular horn antenna for Electromagnetic Compatibility (EMC) testing. The proposed antenna contains a wideband feed structure as a transition between coaxial line and quad-ridged circular waveguide behind the conical horn antenna. The wideband matching between impedances at the apertures of the feed and the horn is achieved with a tapering at the flare section along the horn length, which is obtained after a detailed investigation of various tapering profiles. The antenna is designed to operate in horizontal and vertical polarizations (dual linear polarization) simultaneously in EMC tests. This implementation is found to present a return loss greater than 10 dB, isolation level higher than 28 dB, high-gain (minimum 13.6 dBi) and low-gain variation of 4.5 dBi within the frequency range of 1-6.75 GHz (6.75:1 bandwidth) at both polarizations, which is a desired feature in radiated emission and immunity tests.
Open Access
Dopamine detection using mercaptopropionic acid and cysteamine for electrodes surface modification
(Sciendo, 2018) Khan, Muhammad Salman; Asif, Afia; Khawaldeh, S.; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Khan, Muhammad Salman; Asif, Afia
Gold electrodes are often not suitable for dopamine measurements as dopamine creates a non-conducting polymer layer on the surface of the electrodes, which leads to increased amount of electrode passivity with the gradual increase in voltammograms measurement. This work presents the impedance spectroscopy and cyclic-voltammetry comparative study for dopamine detection with two modifications for the surface of Au electrodes; cysteamine and mercaptopropionic acid for thermally bonded and ultrasonically welded microfluidic chips, respectively. The effects of optimized tubing selection, bonding techniques, and cleaning methods of the devices with KOH solution played crucial role for improvements in dopamine detection, which are observed in the results. Furthermore, comparison for the modification with unmodified chips, and finding the unknown concentration of dopamine solution using flow injection techniques, is also illustrated.
Open Access
An experimental study of a bluetooth communication system for robot motion control
(IEEE, 2019) Dalgiç, Oğuzhan; Tekin, Ahmet; Uğurlu, Regaip Barkan; Electrical & Electronics Engineering; Mechanical Engineering; TEKİN, Ahmet; UĞURLU, Regaip Barkan; Dalgıç, Oğuzhan
This paper presents a method that aims to reduce the complex cabling problem in robotics applications, so as to prevent difficulties in troubleshooting processes and failures in case of cable breaks. Examples in the literature have proven the reliability of the Bluetooth Low Energy (BLE) based communication systems and indicated that it could be employed in sensor data transfer applications. Therefore, our solution to the aforementioned issue is independent joint modules that comprise a motor driver, a microcontroller for running servo control loops, and a BLE device that enables the module to communicate with the main processor of the robot without the need of bulky cabling. Target applications for this method are mobile robots that encapsulate onboard processors and actuators that are deployed within a short range.
Metadata only
An improved speed controller for PMSM drive with unbalanced load using load torque observer
(IEEE, 2019) Yoldaş, Koray; Tekin, Ahmet; Boztepe, M.; Electrical & Electronics Engineering; TEKİN, Ahmet; Yoldaş, Koray
In order to overcome disturbance effects as load torque variations in Permanent Magnet Synchronous Motor (PMSM) of washing machines, an improved controller with feed forward compensation is presented in this paper. A few load torque observer techniques have been studied and combined with several sensorless control techniques. The observed torque is used as feedforward in q-axis current PI controller to compensate the output of speed PI controller. Simulation and experimental results show that in an operating system with disturbances as washing machines, PI controller response time can be improved by adopting an accurate feedforward scheme.
Metadata only
Low-cost thin-film passive RFID circuits and detector system
(Cambridge University Press, 2020-06) El-Sawy, Salma; Nawaz, Wasim; Abouzeid, Mohamed Osama Hussein Soliman; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; El-Sawy, Salma; Nawaz, Wasim; Abouzeid, Mohamed Osama Hussein Soliman
This paper discusses the design of chip-less RFID tags of a standard pocket size of 69 mm by 156 mm. These tags are based on lumped elements of copper metal traces constructed on a thin polyamide flexible substrate. Moreover, a low-cost single-chip Bluetooth detector circuit system is demonstrated. Two different detection methods: variable coil load coupling and optical light intensity detection were combined to yield 256 unique ID codes. In the first method, by utilizing simple 4 MHz digital drivers and an integrated analog to digital converter (ADC) in the reader controller; various inductively coupled resonant loads corresponding to multiple distinct tags could be differentiated, yielding eight different (3-bit) ID codes. The additional via-based hole pattern reflectometer method creates additional 32 distinct levels (5-bit) utilizing 650 nm visible light-emitting diode and a simple trans-impedance operational along with the same analog ADC pins of a Bluetooth controller. The printed circuit board trace coil on the two-layer low-cost FR-4 waterproof sealed detector unit is simultaneously used as a Qi wireless power receiver to charge the120 mAh 2450 Lithium Polymer (LiR) battery. The device could remain operational for more than a month with a single charge; remaining connected with a mobile device and enabling 10 readouts daily.
Open Access
Omni-directional wideband antenna array with solar cells
(SciELO - Scientific Electronic Library Online, 2021-03) Ullah, Naveed; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Ullah, Naveed
Distributed sensor networks are becoming more and more widespread due to their substantial benefits to our daily lives. These sensors, in most cases, are distributed in nature and even may require mobility. This, in turn, implies omnidirectional collector units to collect the data from various sensors at arbitrary directions. This work summarizes the performance outcomes of various integrated wide-band antenna structures and solar power generation topologies to achieve equal gain in all directions. Purpose of the array in this instance is contrary to enhance the received signal levels in all directions. Low-cost solutions ranging from the planar helical printed circuit board (PCB) designs to vertical wire helical antennas were investigated. An optimum design structure for multiple ISM bands (868 MHz to 915 MHz) was proposed and characterized considering the cost, size, directional coverage and most significantly RF sensitivity and range of the overall design. The final water-resistant solarpowered wideband transceiver front-end has provided range improvement and omnidirectional radiation pattern. The system consists of a 190mm x 190mm low-cost FR4 substrate and a Wilkinson network to combine the power of 8 helical wire antennas sprinkled along with the solar cells. The self-contained, Sun-powered unit resulted in 4.5-dB sensitivity improvement in measurements.
Metadata only
Resonance-filtering combo system for continuous wireless charging range coverage
(Cambridge University Press, 2020-09) Sağlam, Üstün; Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet; Sağlam, Üstün
Distribution of wireless power charging field uniformly on a large area pad is critical for power receivers, particularly for wearable devices, wherein small form factor coils are involved. Since the receiver coil size is quite limited in these types of applications, the device is very sensitive to the amount of field it could retain and hence, it needs special placement or snapping mechanism to fix it at an optimum location for reliable wireless charging. In order to overcome this limitation for the end-user, a dual-mode multi-coil power transceiver system is proposed; utilizing resonance filtering to increase the amount of total power delivered with the rather uniform spatial distribution. Two concentric coils; center one driven by 6.78-MHz high-frequency driver (A4WP) and the outer larger one with a 200-KHz low-frequency driver (Q(i)) with resonant blocker could transfer up to 50 mW standards compliant flat power to a 13-mm radius 30-turns wearable receiver coil everywhere across an 8-cm radius charging pad area without any alignment requirement or snapping. Two different feedback topologies corresponding to each of the H-Bridge power drivers were also presented as an automatic series resonance coil drive frequency lock mechanism, extracting peak powers for each system individually from a standard 5 V-1A USB wall charger.
Metadata only
A robust voltage control method for universal EV battery charger LLC resonant converters
(IEEE, 2019) Daş, Y.; Tekin, Ahmet; Boztepe, M.; Tarhan, C.; Electrical & Electronics Engineering; TEKİN, Ahmet
In this study, a novel control method for LLC resonant converter with wide output voltage range and constant switching frequency is proposed targeting wide range of Electric Vehicle (EV) battery charger standards. In conventional LLC converter control topologies, in order to reach lower output voltage levels, switching frequency happens to move away from the resonance frequency, increasing in most of the cases. However, the switching losses due to switching devices start to become the main bottleneck at high switching frequency operation. Furthermore, high switching frequency operation may cause irreversible inrush current damage at the input terminals during the start-up with corresponding overshoot at the output voltage as well, risking the clients on this particular supply. The work presented in this paper proposes a robust and reliable control solution for these particular resonant converter drawbacks. Theoretical analysis for both conventional and proposed control methods are presented in detail. In order to show the effectiveness of the proposed technique, performance metrics of the both are compared experimentally on an LLC resonant converter specification having an output voltage range of 150-500 V with a maximum output power of 7.5 kW.
Metadata only
A sub-sampling pulse-resonance OOK modulated digital ultrasound communication system for biomedical IoT
(Elsevier, 2019-11-01) Abouzeid, Mohamed Osama Hussein Soliman; Tekin, Ahmet; Mohieldin, A. N.; Electrical & Electronics Engineering; TEKİN, Ahmet; Abouzeid, Mohamed Osama Hussein Soliman
A pulse-resonance On-Off keying ultrasound communication microsystem is presented. It is a viable alternative to today's widely used RF technologies in order to avoid the associated health risks for a specific group of interest, namely babies. Special signal processing and circuit techniques are proposed to overcome drawbacks of classical ultrasound communications; such as echoes and excess ringing, achieving a measured communication range of 28m with a 50bit/is data rate and bit error rate (BER) of 0.01. Targeting a biomedical sensory pacifier, the proposed design needs to be insulated, small size, and low power. Utilizing a 40 kHz ultrasound transducer and a 5-pin low-power controller, a wirelessly-charged high-accuracy remote temperature sensor system with nominal average current consumption of 0.416 mu A is designed and tested. Multiple subsystems were merged in total volume of 12mm diameter and 15mm height, excluding the charging coil, which is designed as the pacifier's handler. Thanks to echo avoidance, ringing suppression, dynamic detection threshold adjustment techniques along with 3-bit preamble synchronization; the proposed low-power sub-sampling IQ demodulation of OOK bits results in high-sensitivity robust ultrasound communication system without any alignment requirement for the transducers. The lifetime of the sensor prototype with 8mAh LiR battery is about 27 months.
Metadata only
Total harmonic distortion and power factor improvement technique for CRM flyback PFC converters
(IEEE, 2019) Kavcı, Mustafa; Tekin, Ahmet; Tarhan, C.; Electrical & Electronics Engineering; TEKİN, Ahmet; Kavcı, Mustafa
In many of today's solid-state lighting applications, Critical Conduction Mode (CCM) Flyback PFC converter is a popular solution due to its limited component count and simple structure with respect to other SMPS topologies. As described in international standards documents (IEC/EN 61000-3-2), drivers are required to demonstrate a power factor results greater than 0.9 and lower THD for power levels above 25W. Due to non-sinusoidal input current waveform of the traditional constant-on-time control method, achieving improved PF and THD is quite difficult. In this paper, a new control method is introduced in an effort to improve power factor and total harmonic distortion of Voltage Mode CRM Flyback PFC Converter. The work proposes injection of a compensating sin(ωt) signal component in the feedback path utilizing an additional primary transformer winding to linearize the current from the source. The detailed theoretical analysis is presented along with measurement results of a 30W high-power system prototype.
Open Access
A wideband smart EMF detector for mobile devices
(Istanbul University, 2021-01) Tekin, Ahmet; Electrical & Electronics Engineering; TEKİN, Ahmet
A wideband electromagnetic field (EMF) sensor system is introduced in this study. This small form factor, low-cost system is intended for use with smart mobile devices and can precisely measure the imminent field strength through the combination of a wideband omnidirectional receive antenna, RF, and audio mixing front-end as well as signal processing algorithm in the mobile unit. A detection dynamic range of 30 dB is shifted toward the high-field intensity regimes to enable its use as a hazardous EM field detector. The total diameter of the device was 13 cm with a cylindrical thickness of 1.6 mm (standard FR4), and it can interface with the audio port of any mobile device including cell-phones or tablets. Field strengths in the range of 5 V/m–50 V/m can be detected in approximately by 10 MHz–3 GHz RF transmission bands.