Acoustic variable focal length lens assembly

Claim 2

An acoustic variable focal length lens assembly exhibiting a certain fixed relative aperture, said assembly comprising first and second serially spaced acoustic lenses for focusing acoustic wave energy of a predetermined wavelength, wherein said first acoustic lens has a given physical aperture and a single relatively short predetermined focal length, and wherein said second acoustic lens includes means for electronically controlling the focal length of said second acoustic lens to have any selected one of a predetermined plural number of different preselected discrete focal lengths, each of said discrete focal lengths being substantially larger than said predetermined focal length, and simultaneously controlling the size of the physical aperture of said second lens, in correspondence with the selection of each different discrete focal length, to have those respective values of size, no greater than said given physical aperture, which result in said assembly exhibiting substantially the same certain relative aperture for all of said different discrete focal lengths, whereby both the depth of field and the imaging resolution of said lens assembly at said predetermined wavelength and at all of said different discrete focal lengths have substantially fixed values that depend solely on said certain relative aperture of said lens assembly.

Claim 3

The acoustic lens assembly defined in claim 1, wherein the respective values of said discrete focal lengths are preselected such that the location of said respective depths of field of said lens assembly at said different discrete focal lengths are in abutting or overlapping relationship.

Claim 4

The acoustic lens assembly defined in claim 1, wherein said first acoustic lens is comprised of material exhibiting an index of refraction to said acoustic wave energy propagated therethrough which is different from that of its surroundings, and wherein said second acoustic lens comprises an electro-acoustic transducer including a piezoelectric slab having at a face thereof a plurality of separate spatially distributed electrodes and said second acoustic lens further comprises signal coupling means, including phase delay means and switch means, selectively connecting any of certain combinations of said electrodes to a common terminal to thereby select a corresponding one of said predetermined plural number of different preselected discrete focal lengths.

Claim 5

The acoustic lens assembly defined in claim 3, wherein said first lens has a given physical aperture, wherein said plurality of electrodes comprise a central electrode having a circular cross section of a preselected diameter surrounded by a certain plural number of contiguous annular electrodes with the outer diameter of the outermost one of said electrodes defining a maximum physical aperture for said second lens which is no greater than said given physical aperture, each of said annular electrodes having a preselected inner diameter and a preselected outer diameter, wherein said coupling means, when selecting the largest of said preselected discrete focal lengths, couples all of said electrodes to said common terminal and thereby exhibits a certain numerical aperture for said lens assembly, wherein said coupling means, when selecting any non-longest preselected discrete focal length, couples some given combination of electrodes, consisting of a certain non-outermost annular electrode and those electrodes surrounded by that certain non-outermost annular electrode, to said common terminal, and wherein said electrode diameters are preselected so that said combination exhibits substantially said certain numerical aperture for said lens assembly.

Claim 6

The acoustic lens assembly defined in claim 4, wherein said combination of electrodes comprises an inner group of one or more contiguous electrodes and an outer group of one or more contiguous electrodes, and wherein, in response to the selection of said non-longest preselected discrete focal length, said switch means includes means for respectively connecting in parallel said electrodes of said inner group to said common terminal and connecting in parallel said electrodes of said outer group to said common terminal and said phase delay means includes means for phase delaying signals at the freqency of said acoustic wave energy which are coupled between said electrodes of said inner group and said common terminal substantially an integral number of quarter wavelengths with respect to signals at the frequency of said acoustic wave energy which are coupled between said electrodes of said outer group and said common terminal.

Claim 7

The acoustic lens assembly defined in claim 5, wherein the electrodes of said inner and said outer groups are in contiguous serial relationship, and wherein said phase delay means includes means for phase delaying said signals coupled between electrodes of said inner group and said common terminal substantially one-quarter wavelength with respect to said signals coupled between said electrodes of said outer group and said common terminal.

Claim 8

The acoustic lens assembly defined in claim 5, wherein said given combination of electrodes further comprises an intermediate group of one or more contiguous electrodes situated between the electrodes of said inner group and the electrodes of said outer group in contiguous serial relationship therein, and wherein, in response to the selection of said nonlongest preselected discrete focal length, said switch means includes means for connecting in parallel said electrodes of said intermediate group to said common terminal and said phase delay means includes means for respectively phase delaying signals at the frequency of said acoustic wave energy which are coupled respectively (1) between said electrodes of said intermediate groups and said common terminal and (2) between said electrodes of said inner group and said common terminal by (1) substantially one-quarter wavelength and by (2) substantially onehalf wavelength with respect to signals at the frequency of said acoustic wave energy which are coupled between said electrodes of said outer group and said common terminal.

Claim 9

In an ultrasonic pulse-echo imaging system for imaging a deep structure insonified with a pulse of ultrasonic wave energy of a predetermined wavelength, the combination including: an acoustic variable focal length lens assembly situated in spaced relationship with said deep structure so as to receive ultrasonic echoes from said insonified deep structure during a certain time interval following the insonification of said deep structure, wherein said lens assembly has a certain fixed relative aperture and comprises first and second spaced acoustic lenses, said first lens having a given physical aperture and a single relatively short predetermined focal length, and said second lens having a variable physical aperture and being electronically controlled to have any selected one of a predetermined plural number of different discrete focal lengths, each of said discrete focal lengths being substantially larger than said predetermined focal length, the respective values of said discrete focal lengths being selected such that at said predetermined wavelength the respective depths of field of said lens assembly at the respective different discrete focal lengths include separate contiguous portions of the entire depth of said deep structure to be imaged, said variable physical aperture of said second lens being controlled, in correspondence with the selection of each different discrete focal length, to have those respective values of size, no greater than said given physical aperture, which result in said assembly exhibiting substantially the same certain relative aperture for all of said different discrete focal lengths, and time-control means responsive to the time of transmission of said pulse of ultrasonic wave energy, said time-control means being coupled to said second lens for sequentially selecting each of the different discrete focal lengths during successive portions of said certain time interval to provide an effective resultant depth of field for said lens assembly which includes the entire depth of said deep structure to be imaged.

Claim 10

In an ultrasonic pulse-echo imaging system for imaging a deep structure insonified with a pulse of ultrasonic wave energy of a predetermined wavelength, the combination including: an acoustic variable focal length lens assembly situated in spaced relationship with said deep structure so as to receive ultrasonic echoes from said insonified deep structure during a certain time interval following the insonification of said deep structure, wherein said lens assembly has a certain fixed relative aperture and comprises first and second spaced acoustic lenses, said first lens having a given physical aperture and a single relatively short predetermined focal length, and said second lens having a variable physical aperture and being electronically controlled to have any selected one of a predetermined plural number of different discrete focal lengths, each of said discrete focal lengths being substantially larger than said predetermined focal length, the respective values of said discrete focal lengths being selected such that at said predetermined wavelength the respective depths of field of said lens assembly at the respective different discrete focal lengths include separate contiguous portions of the entire depth of said deep structure to be imaged, said variable physical aperture of said second lens being controlled, in correspondence with the selection of each different discrete focal length, to have those respective values of size, no greater than said given physical aperture, which result in said assembly exhibiting substantially the same certain relative aperture for all of said different discrete focal lengths, and time-control means responsive to the time of transmission of said pulse of ultrasonic wave energy, said time-control means being coupled to said second lens for sequentially selecting each of the different discrete focal lengths during successive portions of said certain time interval to provide an effective resultant depth of field for said lens assembly which includes the entire depth of said deep structure to be imaged.