Person:
TEKİN, Ahmet

Profile Picture

Email Address

Birth Date

WoSScopusGoogle ScholarORCID

Name

Job Title

First Name

Ahmet

Last Name

TEKİN
OrgUnit Logo
Organizational Unit

Filters

2017 - 2019122020 - 20215
Reset filters

Settings

Publication Search Results

Now showing 1 - 10 of 17
  • Placeholder
    ArticlePublicationMetadata 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.
  • Thumbnail Image
    ArticlePublicationOpen 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.
  • Placeholder
    Conference ObjectPublicationMetadata 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.
  • Placeholder
    Conference ObjectPublicationMetadata 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.
  • Thumbnail Image
    ArticlePublicationOpen 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.
  • Placeholder
    Conference ObjectPublicationMetadata 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.
  • Placeholder
    ArticlePublicationMetadata 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.
  • Thumbnail Image
    ArticlePublicationOpen 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.
  • Placeholder
    Conference ObjectPublicationMetadata 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.
  • Thumbnail Image
    ArticlePublicationOpen 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.