Characteristics of a high power ultrasonic array transmitter in air
A high-power ultrasonic array transmitter with 144 transmitting elements for 3D measurements in air has been developed. The sound pressure level of 126 dB was obtained at a distance of 5 m in the air with an ultrasonic frequency of 40 kHz. This value is approximately 32 dB higher than that obtained using a single transmitting element. The characteristics of the array transmitter were studied and compared with simulation results. The experimental results were in good agreement with the simulation results.
Imaging sensor system using dispersed ultrasonic array
Imaging sensor system using dispersed ultrasonic array is described in this paper. Although ultrasonic elements are generally mounted on a plane or curved surface with separation shorter than half the wavelength of the ultrasonic wave for synthetic aperture systems, the elements can be distributed on any position and wide separations are acceptable for our system. Although delay-and-sum operations are used for synthetic aperture systems, delayed-and-multiplication operations were also used in our system to make the side lobe in the sensor directivity spectra small, and to obtain high resolution for the sensor array of the small number of ultrasonic elements. Furthermore, the intensities of the reflected wave differ based on the shape, material, direction, and distance to the object. Therefore, the signals are corrected by labeling the signals from each element. The characteristics of the system are studied by numerical simulation and experimentally. Since this system minimizes the possibilities of violation of privacy, it is suitable for shape measurement of three-dimensional objects in the residential areas.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.