the substrate where rbaw signals launched from the input idt 10 1 are reflected from the bottom surface 29 to the output idts 10 2 1 and 10 2 n the angle of reflection u03b8 n is a function of the dc voltage applied across the terminals 20 3 and 22 3 as shown in fig7 b in both this configuration and that of fig6 the idt 11 may be considered a control idt whereas in the first two embodiments shown in fig4 and 5 the control is additionally provided both in the input idt or in both the input and output idts thus the magnification of the electroacoustic effect can be used not only to alter the acoustic velocities of the waves propagated as well as the device resonant frequency or time delay provided thereby but also the critical angles of reflection may be altered moreover the various disturbances such as provided by the environmental parameters or aging can be sensed by including a sensor on the devices of the subject invention to sense a particular disturbance and generating a signal in accordance therewith this signal then may be utilized to control the magnitude of the dc bias voltage applied furthermore when desirable ac signals can be applied in place of or in addition to the dc bias potentials for providing.