Unidirectional surface wave transducers

Claim 2

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel electrodes defined on one surface of said substrate; c. a second array of substantially parallel electrodes defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel electrodes defined on said one surface interleaved with said first and second arrays of electrodes, said first, second and third arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer; and e. means for simultaneously applying voltages of a preselected different phase to each array of electrodes to generate driving electric fields of different phases between sequential pairs of adjacent electrodes, whereby the acoustic wave generated in the surface of said substrate propagates unidirectionally.

Claim 3

A unidirectional transducer as set forth in claim 1 wherein the voltages applied to the respective arrays are mutually out of phase by 120*.

Claim 4

A unidirectional transducer as set forth in claim 1 wherein there are four arrays of electrodes forming an interdigitated pattern having four electrodes for each acoustic wavelength and wherein the voltages applied to successive electrodes within a given acoustic wavelength are out of phase by 90*.

Claim 5

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel elongated electrodes defined on one surface of said substrate; c. a second array of substantially parallel elongated electrodes defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel elongated electrodes defined on said one surface interleaved with said first and second arrays of electrodes, said first, second and third arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-third of said acoustic wavelength; and e. means for simultaneously applying a voltage of different phase to each of said arrays, to generate driving electric fields of different phases between sequential pairs of adjacent electrodes, the phase difference between the voltage applied to respective arrays being substantially 120*.

Claim 6

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel elongated electrodes defined on one surface of said substrate; c. a second array of substantially parallel elongated electrodes defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel elongated electrodes defined on said one surface interleaved with said first and second arrays of electrodes, said first, second and third arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-third of said acoustic wavelength; and e. means for simultaneously applying a voltage of different phase to each of said arrays, to generate driving electric fields of different phases between sequential pairs of adjacent electrodes, the phase difference between the voltage applied to respective arrays being substantially 120*.

Claim 7

A unidirectional transducer as set forth in claim 4 wherein said means for applying a voltage of different phase to each of said first, second and third arrays of electrodes comprises a 60* phase shifter.

Claim 8

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel elongated electrodes defined on one surface of said substrate; c. a second array of substantially parallel elongated electrodes defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel elongated electrodes defined on said one surface interleaved with said first and second arrays of electrodes, said first, second and third arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-third of said acoustic wavelength; and e. means for simultaneously applying a voltage of different phase to each of said arrays, said means comprising 60* phase shifting circuits which include impedance matching networks.

Claim 9

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel elongated electrodes defined on one surface of said substrate; c. a second array of substantially parallel elongated electrodes defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel elongated electrodes defined on said one surface interleaved with said first and second arrays of electrodes, said first, second and third arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-third of said acoustic wavelength; and e. means for simultaneously applying a voltage of different phase to each of said arrays, said means comprising 60* phase shifting circuits which include impedance matching networks.

Claim 10

A unidirectional transducer as set forth in claim 6 wherein said means for applying a voltage of different phase to each array of electrodes comprises: a. a first input terminal and a second input terminal for receiving a single phased input voltage from a suitable voltage source; b. a first inductor connected between said first input terminal and said first array of electrodes operable to match the impedance of said input source to the impedance of said transducer; c. a second inductor connected between said first array of electrodes and said second array of electrodes; and d. a third inductor connected between said second array of electrodes and said third array of electrodes, said third array of electrodes also being connected to said second input terminal, said second and third inductors being operable to match the impedance of the internal capacitance of said transducer and to provide a 60* phase shift to said input voltage whereby the phase of the voltage applied to said third array of electrodes lags the phase of the voltage applied to said second array of electrodes by 120*, and the phase of the voltage applied to said second array of electrodes lags the phase of the signal applied to said first array of electrodes by 120*.

Claim 11

A unidirectional transducer as set forth in claim 6 wherein said means for applying a voltage of different phase to each array of electrodes comprises: a. a first input terminal and a second input terminal for receiving a single phase input voltage from a suitable voltage source; b. a tapped inductor connected between said first array of electrodes and said third array of electrodes, said first input terminal being connected to the tap of said tapped inductor and said second input terminal being connected to the junction of said third array of electrodes and said tapped inductor, said tapped inductor being operable to match the impedance of said voltage source to the impedance of said transducer; c. a first inductor connected between said first array of electrodes and said second array of electrodes; and d. a second inductor connected between said second array of electrodes and said third array of electrodes, said first and second inductors being operable to match the impedance of the internal capacitance of said transducer and to provide a 60* phase shift to said input voltage.

Claim 12

A unidirectional transducer as set forth in claim 6 wherein said means for applying a voltage of different phase to each array of electrodes comprises: a. a first input terminal and a second input terminal for receiving a single phase input voltage from a suitable voltage source; b. a first tapped inductor connected between said first array of electrodes and said third array of electrodes, and second input terminal also being connected to said third array of electrodes; c. a second tapped inductor connected between said second array of electrodes and third array of electrodes; d. a first inductor connected between said first array of electrodes and said second array of electrodes, said first inductor and said first and second tapped inductors being operable to match the impedance of the internal capacitance of said transducer; e. a third inductor connected between said first input terminal and the tap of said first tapped inductor; and f. a capacitor connected between the junction of said third inductor and said first input terminal and the tap of said second tapped inductor, said third inductor and capacitor being operable to provide a 60* phase shift to said input voltage.

Claim 13

A unidirectional transducer as set forth in claim 6 wherein said means for applying a voltage of different phase to each of said arrays comprises: a. a first input terminal and a second input terminal for receiving a single phase input voltage from a suitable voltage source; b. a first inductor having two taps; c. a capacitor, said first inductor and capacitor being connected in series between said second array of electrodes and said third array of electrodes, said first input terminal being connected to one of said taps and said second input terminal being connected to the junction of said first tapped inductor and said third array of electrodes; and d. a second inductor connected between the other of said two taps of said first inductor and said first array of electrodes, said second inductor and said capacitor being operable to provide a 60* phase shift to said input voltage, and said first inductor being operable to match the impedance of the internal capacitance of said transducer and to match the overall impedance of said transducer to the impedance of said input voltage source.

Claim 14

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel electrodes defined on one surface of said substrate; c. a second array of electrodes substantially parallel defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel electrodes defined on said one surface interleaved with said first and second arrays of electrodes; e. a fourth array of substantially parallel electrodes defined on said one surface interleaved with said first, second and third arrays of electrodes, said first, second, third and fourth arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-fourth of said acoustic wavelength; and f. means for simultaneously applying to each of said arrays a voltage of different phase to generate driving electric fields of different phases between sequential pairs of adjacent electrodes, the phase of the voltage applied to successive electrodes within a given acoustic wavelength lagging the preceding voltage by 90* whereby the acoustic waves produced in said substrate in response to said phased voltage add in one direction of propagation but substantially cancel in the other direction of propagation.

Claim 15

A unidirectional interdigitated surface wave transducer having a preselected resonance frequency comprising: a. a piezoelectric substrate; b. a first array of substantially parallel electrodes defined on one surface of said substrate; c. a second array of electrodes substantially parallel defined on said one surface interleaved with said first array of electrodes; d. a third array of substantially parallel electrodes defined on said one surface interleaved with said first and second arrays of electrodes; e. a fourth array of substantially parallel electrodes defined on said one surface interleaved with said first, second and third arrays of electrodes, said first, second, third and fourth arrays of electrodes respectively having a periodicity corresponding to one acoustic wavelength of the resonance frequency of said transducer, successive electrodes of said interleaved arrays of electrodes being substantially equidistantly spaced apart by one-fourth of said acoustic wavelength; and f. means for simultaneously applying to each of said arrays a voltage of different phase to generate driving electric fields of different phases between sequential pairs of adjacent electrodes, the phase of the voltage applied to successive electrodes within a given acoustic wavelength lagging the preceding voltage by 90* whereby the acoustic waves produced in said substrate in response to said phased voltage add in one direction of propagation but substantially cancel in the other direction of propagation.