@inproceedings{Dokhanchi,
  author    = {Dokhanchi, Najmeh Sadat},
  title     = {Acoustic travel time tomography: Applicability of an array of directional sound sources},
  editor    = {Arnold, J{\"o}rg},
  doi       = {10.25643/bauhaus-universitaet.4658},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46589},
  abstract  = {The technique of Acoustic travel-time TOMography (ATOM) allows for measuring the distribution of air temperatures throughout the entire room based on the determined sound-travel-times of early reflections, currently up to second order reflections. The number of detected early reflections in the room impulse response (RIR) which stands for the desired sound paths inside the room, has a significant impact on the resolution of reconstructed temperatures. This study investigates the possibility of utilizing an array of directional sound sources for ATOM measurements instead of a single omnidirectional loudspeaker used in the previous studies [1-3]. The developed measurement setup consists of two directional sound sources placed near the edge of the floor in the climate chamber of the Bauhaus-University Weimar and one omnidirectional receiver at center of the room near the ceiling. In order to compensate for the reduced number of sound paths when using directional sound sources, it is proposed to take high-energy early reflections up to third order into account. For this purpose, the simulated travel times up to third-order image sources were implemented in the image source model (ISM) algorithm, by which these early reflections can be detected effectively for air temperature reconstructions. To minimize the uncertainties of travel-times estimation due to the positioning of the sound transducers inside the room, measurements were conducted to determine the exact emitting point of the utilized sound source i.e. its acoustic center (AC). For these measurements, three types of excitation signals (MLS, linear and logarithmic chirp signals) with various frequency ranges were used considering that the acoustic center of a sound source is a frequency dependent parameter [4]. Furthermore, measurements were conducted to determine an optimum excitation signal based on the given condition of the ATOM measurement set-up which defines an optimum method for the RIR estimation correspondingly. Finally, the uncertainty of the measuring system utilizing an array of directional sound sources was analyzed.},
  subject      = {Bauphysik},
  language  = {en}
}
@inproceedings{Dokhanchi,
  author    = {Dokhanchi, Najmeh Sadat},
  title     = {Reconstruction of the indoor air temperature distribution using acoustic travel-time tomography},
  editor    = {Arnold, J{\"o}rg},
  doi       = {10.25643/bauhaus-universitaet.4659},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220622-46593},
  abstract  = {Acoustic travel-time tomography (ATOM) is being increasingly considered recently as a remote sensing methodology to determine the indoor air temperatures distribution. It employs the relationship between the sound velocities along sound-paths and their related travel-times through measured room-impulse-response (RIR). Thus, the precise travel-time estimation is of critical importance which can be performed by applying an analysis time-window method. In this study, multiple analysis time-windows with different lengths are proposed to overcome the challenge of accurate detection of the travel-times at RIR. Hence, the ATOM-temperatures distribution has been measured at the climate chamber lab of the Bauhaus-University Weimar. As a benchmark, the temperatures of NTC thermistors are compared to the reconstructed temperatures derived from the ATOM technique illustrating this technique can be a reliable substitute for traditional thermal sensors. The numerical results indicate that the selection of an appropriate analysis time-window significantly enhances the accuracy of the reconstructed temperatures distribution.},
  subject      = {Bauphysik},
  language  = {en}
}
@article{DokhanchiArnoldVogeletal.2020,
  author    = {Dokhanchi, Najmeh Sadat and Arnold, J{\"o}rg and Vogel, Albert and V{\"o}lker, Conrad},
  title     = {Measurement of indoor air temperature distribution using acoustic travel-time tomography: Optimization of transducers location and sound-ray coverage of the room},
  series = {Measurement},
  volume    = {2020},
  journal   = {Measurement},
  number    = {Volume 164, article 107934},
  publisher = {Elsevier},
  address   = {Amsterdam},
  doi       = {10.1016/j.measurement.2020.107934},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20220524-46473},
  year      = {2020},
  abstract  = {Acoustic travel-time TOMography (ATOM) allows the measurement and reconstruction of air temperature distributions. Due to limiting factors, such as the challenge of travel-time estimation of the early reflections in the room impulse response, which heavily depends on the position of transducers inside the measurement area, ATOM is applied mainly outdoors. To apply ATOM in buildings, this paper presents a numerical solution to optimize the positions of transducers. This optimization avoids reflection overlaps, leading to distinguishable travel-times in the impulse response reflectogram. To increase the accuracy of the measured temperature within tomographic voxels, an additional function is employed to the proposed numerical method to minimize the number of sound-path-free voxels, ensuring the best sound-ray coverage of the room. Subsequently, an experimental set-up has been performed to verify the proposed numerical method. The results indicate the positive impact of the optimal positions of transducers on the distribution of ATOM-temperatures.},
  subject      = {Bauphysik},
  language  = {en}
}