While the reduction in weight of railway vehicles contributes to speed and energy saving, it is generally unfavorable in terms of internal noise generation. Since demand for on-board comfort is expected to grow in the future, the reduction of internal noise has become an important challenge.

      A noise reduction technique using piezoelectric devices was developed as a countermeasure to the problem. The technique avoids massive weight increases to reduce the floor board flexural vibrations that can lead to increased internal noise. Instead, a piezoelectric device attached to the floor board is used to generate electrical energy (voltage) when vibrations cause deformation. By dissipating the electrical energy as heat, floor board vibration is reduced leading to a decrease in on-board noise.

      The effectiveness of the technique was verified by applying it to an aluminum alloy floor board of approximately 3m²/20kg, representing the area of one Shinkansen seat (Fig.1). A piezoelectric device was attached to the center of the floor board where the amplitude of out-of-plane bending vibration was the strongest, and was then connected to an electric circuit made up of resistors and coils. The weight of the device and the circuit together is less than 1kg (at approximately 300g each), representing minimization of the increase in weight. Vertical vibration was applied to the floor board using a vibration generator mounted under the floor. Fig.2 shows values for the sound pressure of emitted noise, measured by a microphone placed above the set-up. Sound pressure at the frequency corresponding to the bending vibration was reduced to about half using the piezoelectric device technique, verifying its effectiveness in reducing emitted noise.

      Evaluation of the technique using actual vehicles is planned, and its areas of application will be extended to car roofs and side boards for wider use in the field of engineering.

Fig.1 Vibration test site	Fig.2 Reduction effect on the measured sound pressure of emitted noise