Browsing by Subject "Wide-band"

Now showing 1 - 6 of 6

Open Access
The design of a wideband and widebeam piston transducer in a finite closed circular baffle
(2008-06-07) Şahin, Z.; Köymen, Hayrettin
The design of a high power piezoelectric underwater transducer operating at frequency range 40 kHz-80 kHz with acoustic power capability in excess of 250W is described. The transducer consists of two back-toback elements. Each element is formed by stacked PZT-4 ceramic rings, a matching and a steel backing layer, and placed in a finite rigid circular baffle. We investigate the dependence of bandwidth and beamwidth to the combination of piston and baffle radii, a and b, respectively. With ka of 2.45 (κ is the wave number) at resonance and a b/a ratio of 2, the transducer resonates at 60kHz with 67% bandwidth and has a beamwidth of 60° at each half space. We show that when two transducers are placed at right angles spatially and driven in parallel, we can obtain an omnidirectional beam pattern in the lower frequency band. The beam pattern exhibits two dips in each quadrant at the higher end of the frequency band, which are within 8 dB. We also investigated power handling capability of the transducer from thermal point of view using finite element analysis. The input impedance measurements agree well with the numerical results within the pass band.
Open Access
Dispersion irrelevant wideband asymmetric transmission in dielectric photonic crystal gratings
(Optical Society of America, 2012-11-22) Serebryannikov, A. E.; Colak, E.; Cakmak, A. O.; Özbay, Ekmel
Wideband suppression of zero order and relevant strongly asymmetric transmission can be obtained in photonic crystal gratings that are made of linear isotropic materials and show the broken structural (axial) symmetry, even if zero diffraction order may be coupled to a Floquet-Bloch (FB) wave at the incidence and exit interfaces. The studied mechanism requires that the peculiar diffractions at the corrugated exit interface inspire strong energy transfer to higher orders, including those not coupled to an FB wave. At the opposite direction of incidence, transmission due to zero and some higher orders that may be coupled at the corrugated input interface can vanish. This leads to the alternative scenario of wideband unidirectional transmission, which itself does not need but can coexist with the other scenario based on the merging of asymmetric diffraction and dispersion of the FB mode.
Open Access
Kesirli fourier dönüşümünün zaman bölgesinde sonlu farklar yöntemine uygulanması
(IEEE, 2010-04) Sayın, I.; Arıkan F.; Arıkan, Orhan
Bilgisayarların hız ve belleklerinin gelişmesi ile birlikte elektromanyetik problemlerin çözümünde saysal yöntemler sıkça kullanılmaya başlanmış ve bu konuda çok sayda araştırma yapılmıştır. Saysal Elektromanyetik yöntemleri genel olarak zaman ve frekans tabanlı yöntemler olarak sınıflandırılabilir. Zaman tabanlı yöntemler geçici tepkilerin ve geniş bantlı problemlerin incelenmesinde kullanışlı olurken, frekans tabanlı yöntemler durağan hal tepkilerin ve dar bantlı problemlerin incelenmesinde en iyi çözümü vermektedir. Her iki yaklaşımın da avantajlarını ön plana çıkarabilecek bir yöntem geliştirilebileceği düşünülmektedir. Uzayda ve/veya zamanda Kesirli Fourier Dönüşümü uygulanarak bazı durumlarda hesaplama karmaşıklığı azaltılabilir. Kesirli Fourier Dönüşümü, sürekli Fourier Dönüşümünün genelleştirilmiş halidir. Son yıllarda bu konu üzerinde çeşitli çalışmalar yapılmakta ve uygulama alanları genişlemektedir. Genel olarak, sinyal işleme ve gürültü süzme gibi alanlarda kullanılmaktadır. Bu çalmada Kesirli Fourier Dönüşümü, ilk kez Maxwell denklemlerine zaman bölgesinde uygulanmış ve elde edilen diferansiyel denklemler sonlu farklar yaklaşımı ile ayrık hale getirilmiştir. Elde edilen ayrık sonlu fark denklemlerinin çözümü için öneriler sunulmuştur.
Open Access
A plasmonically enhanced pixel structure for uncooled microbolometer detectors
(SPIE, 2013) Erturk O.; Battal, Enes; Kucuk, S.E.; Okyay, Ali Kemal; Akin, T.
This paper introduces a method of broadband absorption enhancement that can be integrated with the conventional suspended microbolometer process with no significant additional cost. The premise of this study is that electric field can be enhanced throughout the structural layer of the microbolometer, resulting in an increase in the absorption of the infrared radiation in the long wave infrared window. A concentric double C-shaped plasmonic geometry is simulated using the FDTD method, and this geometry is fabricated on suspended pixel arrays. Simulation results and FTIR measurements are in good agreement indicating a broadband absorption enhancement in the 8 μm - 12 μm range for LWIR applications. The enhancement is attained using metallic geometries embedded in the structural layer of the suspended microbridge, where the metallic-dielectric interface increases the average absorption of a 35 μm pixel from 67.6% to 80.1%. © 2013 SPIE.
Open Access
Radiation impedance of an array of circular capacitive micromachined ultrasonic transducers in collapsed state
(IEEE, 2011-10) Özgürlük, Alper; Atalar, Abdullah; Köymen, Hayrettin; Olcum, Selim
Radiation impedance is one of the important parameters in designing efficient and wideband capacitive micro-machined ultrasonic transducer (CMUT) arrays. It determines how much acoustical power is generated in the surrounding medium given the membrane motion. Recently, considerable effort has been put to characterize the radiation impedance of CMUT arrays in conventional uncollapsed regime. However, the radiation impedance of an array of CMUT cells in collapsed state has not yet been investigated. To calculate the array radiation impedance in collapse mode, we first calculate the radiation impedance of a single cell CMUT. For the array case, the mutual impedances between the neighboring cells must also be taken into account.We consider an array of 7, 19, 37, and 61 cells placed in a hexagonal pattern and try to determine the radiation impedance for different degrees of collapse. We find that in the collapsed case the peak radiation resistance value is reached at higher kd values, where k is the wavenumber and d is the center to center cell spacing, compared to the uncollapsed regime.
Open Access
Stagger tuned cMUT array for wideband airborne applications
(IEEE, 2006-10) Olcum, Selim; Atalar, Abdullah; Köymen Hayrtettin; Şenlik, Muhammed N.
In this study, we explore the limits of cMUTs in air-borne applications. First we investigate the ways of increasing the bandwidth of a single cMUT cell in air. The effect of array operation is also considered in order to increase the radiation resistance seen by the transducer. We calculate the bandwidth of a stagger tuned cMUT array. It is shown in this paper that more than 60% bandwidth can be obtained by three staggered frequencies. © 2006 IEEE.