Abstract. In this technical note, the acoustic echo cancellations by a piezoelectric layer, coated to a rigid acoustic surface and shunted with various combinations of resistor, capacitor and inductor in series, have been investigated. A one-dimensional electro-acoustic model, enabling us to calculate the acoustic echo reduction for different shunting circuits, is established for the electrically shunted piezoelectric layer. It will be seen that shunting the piezoelectric layer with a resistor and an inductor can achieve good echo reduction only in a very narrow frequency bandwidth. In order to achieve broadband echo reduction, an inductor, a resistor and a capacitor in series shall be used. The formulae for calculating the inductance, resistance and capacitance of the shunting circuit have been derived. Numerical simulations show that the capacitance of the optimal shunting circuit can be negative for most commercial piezoelectric materials, although the inductance can be designed to be positive by adjusting the acoustic impedance of the piezoelectric materials. Realization of a capacitive circuit with negative capacitance has been proposed.

Print publication: Issue 2 (April 2001)
Received 25 August 2000, in final form 27 November 2000