Browsing by Subject "Periodic structures"

Now showing 1 - 6 of 6

Open Access
Breathing detection based on the topological features of IR sensor and accelerometer signals
(IEEE, 2017) Erden, Fatih; Çetin, A. Enis
This paper describes a non-contact breathing detection system using a pyro-electric infrared (PIR) sensor and an accelerometer. The multi-sensor system can be used to detect the respiratory disorders. A PIR sensor is placed onto a stand near a bed and an accelerometer is placed on the mattress. We recently developed a PIR sensor which is capable of producing 1-D time-varying signals corresponding to the motions in its field of view. The PIR sensor signal due to the thoracic movements turns out to be an almost periodic signal. Similarly, the accelerometer produces an almost periodic signal in response to vibrations in bed. Sensor signals are processed using a topological approach. Point clouds are constructed from the delay-coordinate embedding of the time series sensor data first. Then, periodic structures in the point clouds are detected using persistent homology. The sensors, with the proposed method, complement each other to produce more accurate decisions in different lying positions.
Open Access
Doppler effect on nanopatterning with nonlinear laser lithography
(OSA, 2017) Yavuz, Özgün; Kara, Semih; Tokel, Onur; Pavlov, Ihor; İlday, Fatih Ömer
Summary form only given. Just five years after invention of the laser, laser induced periodic structures (LIPSS) had been reported. However, the structure period is not very uniform in LIPSS. Recently, with nonlinear laser lithography (NLL), long range ordered periodic surface structures had been maintained by exploiting various feedback mechanisms and nonlinearities. Albeit, fine tuning of structure period remains challenging. Here, we present an analogy between Doppler effect and structure period of the NLL which adds a capability of changing the structure period.
Open Access
Highly stable periodic structures using nonlinear laser lithography
(IEEE, 2016) Yavuz, Oğuzhan; Pavlov, Ihor; Tokel, Onur; Ergeçen, E.; Rızaoğlu, Anıl; İlday, Fatih Ömer
Nonlinear laser lithography (NLL) emerged as a novel surface structuring method allowing long-range periodic order. We present mathematical formalism for NLL, analysis of structure stability to perturbations and a way to control final tiling patterns.
Open Access
A novel approach for the efficient computation of 1-D and 2-D summations
(Institute of Electrical and Electronics Engineers Inc., 2016) Karabulut, E. P.; Ertürk, V. B.; Alatan, L.; Karan, S.; Alisan, B.; Aksun, M. I.
A novel computational method is proposed to evaluate 1-D and 2-D summations and integrals which are relatively difficult to compute numerically. The method is based on applying a subspace algorithm to the samples of partial sums and approximating them in terms of complex exponentials. For a convergent summation, the residue of the exponential term with zero complex pole of this approximation corresponds to the result of the summation. Since the procedure requires the evaluation of relatively small number of terms, the computation time for the evaluation of the summation is reduced significantly. In addition, by using the proposed method, very accurate and convergent results are obtained for the summations which are not even absolutely convergent. The efficiency and accuracy of the method are verified by evaluating some challenging 1-D and 2-D summations and integrals. © 2016 IEEE.
Open Access
Optimal sampling of multidimensional periodic band-limited signals
(IEEE, 2005) Korkmaz, Sayit
In this paper, we present an algebraic description of the aliasing phenomena evident in the linear sampling process of multidimensional periodic band limited signals. Opposed to the classical Shannon sampling, periodic band limited signals underlie a different aliasing structure providing further freedom in the sampling strategy due to the discreteness of the spectrum. An algebraic formulation of the optimal sampling problem is also presented.
Open Access
Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process
(Springer New York LLC, 2017) Ramzan, Mehrab; Khan, Talha Masood; Bolat, Sami; Nebioglu, Mehmet Ali; Altan, Hakan; Okyay, Ali Kemal; Topallı, Kağan
This paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-μm-thick glass substrate is formed through the HF etching of a standard 500-μm-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30° angle of incidence. The second design consists of a tripole structure on top of a 100-μm-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30° angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20° angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-μm-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations. © 2017, Springer Science+Business Media New York.