Circulating acoustic surface wave

Claim 2

A circulating acoustic surface wave device which comprises, an anisotropic elastic medium formed to enable propagation of an acoustic surface wave around its peripheral surface, and means for establishing an acoustic surface wave on said elastic medium so as to propagate therearound.

Claim 3

A circulating acoustic surface wave device according to claim 1 wherein, the peripheral surface of said medium along which the acoustic wave propagates has at no point a radius of curvature less than two acoustic wavelengths.

Claim 4

A circulating acoustic surface wave device according to claim 1 wherein, said elastic mEdium constitutes a piezoelectric crystal.

Claim 5

A circulating acoustic surface wave device according to claim 3 wherein, said piezoelectric crystal has high crystalline anisotropy.

Claim 6

A circulating acoustic surface wave device according to claim 3 wherein, said wave establishing means includes an interdigital transducer disposed on said piezoelectric crystal to generate an acoustic surface wave beam along a major crystal axis.

Claim 7

A circulating acoustic surface wave device according to claim 1 wherein, said wave establishing means forms an acoustic beam in a direction to propagate around said medium in a closed loop.

Claim 8

A circulating acoustic surface wave device according to claim 6 wherein, said wave establishing means includes a single transducer arranged to generate the acoustic beam and to receive echo signals separated by the transit time of the beam around said propagating medium.

Claim 9

A circulating acoustic surface wave device according to claim 6 wherein, the closed loop along which the acoustic beam propagates has a length equal to an integral number of acoustic wavelengths.

Claim 10

A circulating acoustic surface wave device according to claim 6 wherein, said wave establishing means includes a first transducer and which comprises, a second transducer disposed along the closed loop to receive time-delayed signals from the propagating wave.

Claim 11

A circulating acoustic surface wave device according to claim 9 wherein, said first transducer establishes acoustic beams propagating in both directions along the closed loop path to said second transducer and wherein the acoustic distance in both directions is equal wherefore the two acoustic beams arrive at said second transducer with the same instantaneous phase.

Claim 12

A circulating acoustic surface wave device according to claim 1 which comprises, amplifying means arranged adjacent the propagation path of the acoustic surface wave.

Claim 13

A circulating acoustic surface wave device according to claim 11 wherein, said amplifying means includes a semiconductor strip extending along the direction of acoustic wave propagation, and means for applying a direct current voltage on said strip to generate drifting carriers therealong.

Claim 14

A circulating acoustic surface wave device which comprises an anisotropic elastic medium formed to enable propagation of an acoustic surface wave around its peripheral surface, means including a transmitting transducer angularly disposed on the peripheral surface of said elastic medium relative to a major axis for establishing an acoustic surface wave beam which propagates along a generally helical path, and a receiving transducer disposed on said medium along said helical path to intercept the acoustic beam.

Claim 15

A circulating acoustic surface wave device which comprises an anisotropic elastic medium formed to enable propagation of an acoustic surface wave around its peripheral surface, means including a transmitting transducer angularly disposed on the peripheral surface of said elastic medium relative to a major axis for establishing an acoustic surface wave beam which propagates along a generally helical path, and a receiving transducer disposed on said medium along said helical path to intercept the acoustic beam.

Claim 16

A circulating acoustic surface wave device according to claim 13 wherein, said transmitting transducer is disposed so that adjacent turns of the acoustic beam along its helical path are separated by a distance of the order of the beam width.