Browsing by Subject "Acoustic impedance"

Now showing 1 - 3 of 3

Open Access
Acoustical tuning of CMUT receiver arrays
(IEEE, 2016) Taşdelen, Akif Sinan; Atalar, Abdullah; Enhoş, Kerem; Köymen, Hayrettin
Cell placement in an element and structural modifications on the array baffle significantly change the bandwidth, band shape and signal to noise ratio of a CMUT receiver array. In this paper, optimum receiver performance tailoring by means of cell placement, cell size variation and use of dummy cells in the array elements is discussed. The performance of the array is modified acoustically at the acoustic port of the elements.
Open Access
Developing wideband acoustic absorbers in interior spaces: modelling, measurements and applications
(2024-01) Fasllija, Ela
This study aims to develop wideband acoustic absorbers in interior spaces for speech purposes, through the use of Micro-Perforated Panels (MPPs) arranged in different configurations. The research has involved theoretical modelling, measurements, and applications in interior spaces. The initial phase focused on modelling various MPP arrangements and predicting their sound absorption coefficients using the Electric Equivalent Circuit Model (ECM) under normal and oblique incidence conditions. Small samples with different geometric parameters were then manufactured and tested for their absorption coefficients at the Turkish Standards Institute, following the impedance tube method (ISO 10534-2:1998). The preliminary results showed a good agreement with the numerical predictions. Furthermore, the random incidence absorption coefficient of a parallel arranged MPP structure was measured in a Small-Scale Reverberation Room (SSRR) at Bilkent University to evaluate the proposed structure in a diffuse field. The results obtained by using ISO 354:2003 showed lower values than the predicted ones by a range of 0.1- 0.3. However, there was a better alignment between the ECM predictions and experimental results for 30-degree oblique incidence. Regarding interior applications, a classroom with poor acoustics was treated in ODEON 16 using the proposed material in the form of a wall panel. The effect of the developed material on objective room acoustics parameters was examined, revealing improvements in the Reverberation Time and Speech Intelligibility Index values. Lastly, the Turkish versions of Perceived Affective Qualities outlined in the ISO/TS 12913-2:2018 standard were developed to assess the subjective perception of the material following the soundscape approach.
Open Access
Equivalent circuit-based analysis of CMUT cell dynamics in arrays
(IEEE, 2013) Oğuz, H. K.; Atalar, Abdullah; Köymen, Hayrettin
Capacitive micromachined ultrasonic transducers (CMUTs) are usually composed of large arrays of closely packed cells. In this work, we use an equivalent circuit model to analyze CMUT arrays with multiple cells. We study the effects of mutual acoustic interactions through the immersion medium caused by the pressure field generated by each cell acting upon the others. To do this, all the cells in the array are coupled through a radiation impedance matrix at their acoustic terminals. An accurate approximation for the mutual radiation impedance is defined between two circular cells, which can be used in large arrays to reduce computational complexity. Hence, a performance analysis of CMUT arrays can be accurately done with a circuit simulator. By using the proposed model, one can very rapidly obtain the linear frequency and nonlinear transient responses of arrays with an arbitrary number of CMUT cells. We performed several finite element method (FEM) simulations for arrays with small numbers of cells and showed that the results are very similar to those obtained by the equivalent circuit model.