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What are architectural acoustics?
Published in Samuel L. Hurt, Building Systems in Interior Design, 2017
It is possible to have too much absorption, which causes rooms to sound “dead.” The ultimate example of this is an anechoic chamber, a room that is designed to absorb all sound that hits its surfaces. Such a room has no normal floor because a normal floor cannot be made to be both 100% acoustically absorptive and walkable, so these rooms have narrow catwalks out to very small platforms in the center of the room. The experience of being in one of these rooms is very odd, even a little disturbing, mostly because one does not hear oneself talking as usual. Because there are no reflections, little to no sound enters the ears, which is mostly how we hear ourselves talk. Instead, in an anechoic chamber, we only hear ourselves through the vibrations in our heads—a strange sensation indeed.
Basic Instrumentation
Published in Vinayak Bairagi, Mousami V. Munot, Research Methodology, 2019
Pradeep B. Mane, Shobha S. Nikam
The laboratory based experimental setup to test antenna parameters includes anechoic chamber. An anechoic chamber is a huge Faraday enclosure, which eliminates reflection, external noise and interference caused by electromagnetic waves. All inner surfaces of the chamber are lined with RF/microwave absorbers, which minimize the amplitude and phase ripples in the test zone. Hence, an anechoic chamber provides accurate and precise measurement of antenna parameters such as antenna far-field patterns, gain, directivity, radiation efficiency, input impedance and polarization. It provides controlled electromagnetic environment. A picture of an anechoic chamber is shown in the Figure 4.10 along with experimental setup to measure antenna parameters.
Motor Vibration and Acoustic Noise
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
An acoustic anechoic chamber is a specially designed room that can completely absorb reflections of sound waves and insulate testing equipment from environmental sources of noise. To absorb sound waves, the interior surfaces of the acoustic anechoic chamber are covered with acoustically absorbent materials. One of the most effective types of absorbent materials comprises arrays of pyramid-shaped pieces, each of which is constructed from a suitably lossy material. To get the best results, all internal surfaces of the acoustic anechoic chamber must be entirely covered with the pyramids (Figure 12.48).
A Quadrilateral Shaped Fractal Slot Planar Antenna for Ultra-Wide Band Applications
Published in Australian Journal of Electrical and Electronics Engineering, 2022
Ranjeet Kumar, Rashmi Sinha, Arvind Choubey, Santosh Kumar Mahto
Inspired by the encouraging performance of fractal design techniques in these literatures, a miniaturised and low-profile fractal slot planar antenna is proposed here. The self-similarity fractal geometry is introduced by iterating circular, triangular and hexagonal patches. The structure thus obtained is cost-effective and compact with dimension 33 × 22 mm2. It exhibits an enhanced performance with bandwidth, gain and radiation efficiency equal to 15.5 GHz, 6.8 dBi, and 90%, respectively. The consistent performance of this novel fractal structure is well suited for various UWB applications such as WLAN, WiMAX, 5 G, X-band, C-band, S-band and Ku-band. The proposed fractal-shaped monopole antenna is compared with other similar works reported in available literature. The comparative results show that the proposed design has much better performance in terms of return loss, VSWR, radiation pattern and gain. The results are also verified by experimental measurements performed in an anechoic Chamber.
Printed λ/4 folded monopole with printed circuit board slot for penta-band
Published in Electromagnetics, 2018
Figure 5 shows the photograph of the proposed gap-coupled folded monopole with a PCB slot. The proposed antenna was fabricated on FR4 substrate, and the overall dimension of the antenna is 37.5 mm (length) × 8 mm (width) × 0.8 mm (height). Also, the dimension of the PCB ground is 70 mm in width and 140 mm in length. The simulated and measured reflection coefficients of the antenna are compared, as shown in Figure 6. The measured results were obtained using Agilent 8510C vector network analyzer. The −6 dB bandwidths (VSWR 3:1) in low and high band are measured to be 160 MHz (830–990 MHz) and 550 MHz (1,550–2,100 MHz), respectively. The measured results are in good agreement with the simulated results except for a down-shifted resonance frequencies due to the fabrication tolerance. The far-field radiation pattern and total efficiency are measured in the full anechoic chamber system. The anechoic chamber is composed of shield enclosure (size 4 m× 2.5 m × 2.5 m), 18-inch pyramidal absorber, network analyzer, wireless communication test set, positioner, turn table, and dual-polarized transmit antenna. Figure 7 shows the measured far-field radiation patterns in the x–y, y–z, and x–z planes at 890, 960, 1,640, and 2,010 MHz. For lower resonant frequencies at 890 and 960 MHz, monopole-like radiation patterns are seen, and this pattern characteristic is similar to those observed for the conventional internal mobile phone antenna for a low band. On the other hand, more variations are observed in the radiation pattern at 1,640 and 2,010 MHz. This is because the length of the PCB ground is longer than the wavelength of higher bands, and there are nulls of a surface current on the PCB ground. The measured total efficiency of the proposed antenna is larger than 60% over the penta-band including GSM 850/900/1800/1900 bands, and WCDMA 2100 band, as shown in Figure 8. Also, the simulated and measured results all agree very well. Thus, the total efficiency of the proposed antenna is acceptable for practical application.