Keywords: noise reduction, piezoelectric elements, railway vehicle, interior noise, transmitted noise, inductance circuit.

As a result of the speed up of railway vehicles and the reduction of vehicle mass it is important to reduce the interior noise of railway vehicles to improve the ride comfort [1]. Acoustic materials, damping materials and passive control based on the mass law have been widely adopted to reduce the interior noise. However, the reduction effect of such countermeasures is insufficient for low-frequencies (below 1 kHz) noise. An alternative cost-effective and lightweight countermeasure for reducing the interior noise with low-frequency is therefore required.

The authors have developed a new type of noise reduction system to reduce the transmitted noise through plates by fixing noise reduction panels. The panels consist of thin metal plates on which piezoelectric elements were stuck. These were called noise insulation panels that were designed to reduce the noise, the frequency of which corresponds to a (1,1) vibration mode. It is possible to reduce the transmitted noise without identifying the response of the target plate by installing an air layer between the noise reduction panel and the target plate. In addition, a resonant circuit is created between the capacitor of the piezoelectric elements and the inductance circuit by employing an inductance circuit as a control apparatus. It follows that the transmitted noise can be reduced in the frequency range near the resonant frequency [2]. This is equivalent to installing a virtual dynamic vibration absorber to the noise insulation panel [3].

In order to evaluate the noise reduction performance, a noise measurement test during the actual running was carried out for a Shinkansen vehicle with and without the proposed system. The interior noise measured below the pantograph had a peak at around 200 Hz, which is likely to be caused by noise transmitted through the ceiling panels from the pantograph. For the case of installing the noise reduction system to the ceiling panels beneath the pantograph the A-weighted sound pressure levels (SPLs) at just below the ceiling panels and at 1200 mm above the floor were reduced by approximately 5 dB and 4 dB, respectively.

In addition, the system was applied to the noise radiating from a transformer. The noise had peaks at frequencies of 100 Hz (double that of the commercial power frequency) and its integral multiples, and the A-weighted SPL of the radiated noise at 200Hz was the highest. When the noise reduction system was applied to the outside wall of transformer, the peak of the 200Hz decreased by about 7dB, and all passing values were reduced by approximately 3dB.

Consequently, the proposed system has a capability to reduce the low-frequency transmitted noise in an economical and lightweight manner.

1

K. Yamamoto, "Interior Noise Reduction of Railway Vehicle", The Journal of the INCE of Japan, 31(5), 368-373, 2007.

2

N.W. Hagood, A. Von Flotow, "Damping of Structural Vibrations with Piezoelectric Materials and Passive Electrical Networks", Journal of Sound and Vibration, 146(2), 243-268, 1991. doi:10.1016/0022-460X(91)90762-9

3

K. Yamada, H. Matsuhisa, H. Utsuno, "Equivalent Mechanical and Electrical Models of the Vibration Suppression System Using Piezoelectric Elements", Transactions of the Japan Society of Mechanical Engineers, Series C, 73(730), 1625-1632, 2007. doi:10.1299/kikaic.73.1625

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