Parametric amplifier

A parametric surface-acoustic-wave amplifier which comprises:

• a surface acoustic wave propagation medium having a nature to produce a different between travelling velocities of surface acoustic waves having different frequencies and travelling therethrough;
• an input transducer provided on said medium to convert an input electric signal into a surface acoustic wave;
• an output transducer provided on said medium to convert said surface acoustic wave into an output electric signal;
• exciting means provided between said input and output transducers on said medium to give a parametric interaction to said surface acoustic wave supplied from said input transducer;
• and
• power source means to apply a pumping power to said exciting means,
• said exciting means including a plurality of parameter changing regions disposed in a periodic alignment having a cycle length l to change a parameter of said medium in response to said pumping power applied thereto, said cycle length being chosen such that for an angular signal input frequency .omega., equal to the sum of the frequency .omega..sub.s of the exciting source and the frequency .omega..sub.2 of the idler wave motion resulting from said parametric interaction, said cycle length of said parameter changing regions is related to the wave numbers .beta..sub.1 and .beta..sub.2 in said medium corresponding to the frequencies .omega..sub.1 and .omega..sub.2 respectively by the approximate relationship 2.pi./l.apprxeq..beta..sub.1 +.beta..sub.2.