JP2022114701A - Ultrasonic liquid crystal lens and method for controlling the same - Google Patents

Abstract

To provide an ultrasonic liquid crystal lens capable of expanding a lens diameter.SOLUTION: An ultrasonic liquid crystal lens 1 includes: an annular ultrasonic transducer 3; a lens 4 including a liquid crystal layer; and a drive unit 5 for applying an electric signal to the ultrasonic transducer 3 to generate an ultrasonic wave. The ultrasonic transducer 3 includes four electrodes 31-34 divided into four in a circumferential direction; and the drive unit 5 applies the electric signal obtained by shifting a phase for every 90° in the circumferential direction to the four electrodes 31-34 to generate an ultrasonic progressive wave propagated in the circumferential direction of the lens 4 and form a progressive wave mode changing an orientation of a liquid crystal molecule in a peripheral part of the liquid crystal layer.SELECTED DRAWING: Figure 1

Description

Patent Law Article 30, Paragraph 2 application filed (1) Date of publication, September 6, 2020, IEEE International Ultrasonics Symposium 2020 Proceedings (2) Date of publication, September 11, 2020 Meeting at the IEEE International Ultrasonics Symposium 2020 (held in Las Vegas, Nevada, USA)

The present invention relates to an ultrasonic liquid crystal lens and a control method for an ultrasonic liquid crystal lens.

As an ultrasonic liquid crystal lens, for example, one described in Patent Document 1 is known. The ultrasonic liquid crystal lens described in Patent Document 1 includes an annular ultrasonic transducer having a central opening, and a lens including a liquid crystal layer disposed in the central opening. The ultrasonic liquid crystal lens described in Patent Document 1 can function as a lens by changing the orientation of liquid crystal molecules in a liquid crystal layer by flexural vibration of ultrasonic waves generated by an ultrasonic oscillator. The focal length can be controlled by controlling the voltage value of the electrical signal applied to the vibrator.

However, in the ultrasonic liquid crystal lens described in Patent Document 1, since the pressure due to bending vibration concentrates on the center of the lens, the orientation of the liquid crystal molecules changes only in the center of the lens, and as a result, the lens diameter ( There is a problem that the area functioning as a lens is miniaturized.

JP 2018-92069 A

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic liquid crystal lens capable of enlarging the lens diameter and a method for controlling the ultrasonic liquid crystal lens. be.

In order to solve the above problems, the ultrasonic liquid crystal lens according to the present invention includes:
an annular ultrasonic transducer having a central opening;
a lens comprising a liquid crystal layer disposed in said central opening and having a central portion and a peripheral portion around said central portion;
a driving unit that applies an electric signal to the ultrasonic transducer to generate ultrasonic waves;
An ultrasonic liquid crystal lens comprising
The ultrasonic transducer includes N electrodes (N is an integer of 3 or more) divided into N in the circumferential direction,
The drive unit
Applying the electrical signal whose phase is shifted by integral multiples of (360/N)° in the circumferential direction to the N electrodes to generate a traveling wave of the ultrasonic wave that propagates in the circumferential direction of the lens. and a traveling wave mode for changing the orientation of liquid crystal molecules in the peripheral portion of the liquid crystal layer.

According to this configuration, the lens diameter can be increased by increasing the pressure on the peripheral portion of the liquid crystal layer by the traveling wave of the ultrasonic wave to change the orientation of the liquid crystal molecules in the peripheral portion.

In the ultrasonic liquid crystal lens,
The drive unit
The electrical signals in phase are applied to the N electrodes to generate a standing wave of the ultrasonic waves in the liquid crystal layer, thereby changing the orientation of the liquid crystal molecules in the central portion of the liquid crystal layer. It can be configured to have modes.

In the ultrasonic liquid crystal lens,
The N electrodes may have the same shape.

In order to solve the above problems, a method for controlling an ultrasonic liquid crystal lens according to the present invention includes:
An ultrasonic vibrator formed in an annular shape having a central opening and having N electrodes (N is an integer of 3 or more) divided in the circumferential direction, and a liquid crystal layer disposed in the central opening. A control method for an ultrasonic liquid crystal lens comprising a lens and a driving unit for applying an electric signal to the ultrasonic transducer to generate ultrasonic waves,
The driving unit applies the electrical signals whose phases are shifted by integral multiples of (360/N)° in the circumferential direction to the N electrodes, and the traveling wave of the ultrasonic wave propagates in the circumferential direction of the lens. to change the orientation of the liquid crystal molecules in the periphery around the center of the liquid crystal layer.

According to this configuration, the lens diameter can be increased by increasing the pressure on the peripheral portion of the liquid crystal layer by the traveling wave of the ultrasonic wave to change the orientation of the liquid crystal molecules in the peripheral portion.

The method for controlling the ultrasonic liquid crystal lens includes:
The electric signals having the same phase are applied to the N electrodes by the driving unit, and the standing wave of the ultrasonic wave is generated in the liquid crystal layer to change the orientation of the liquid crystal molecules in the central portion of the liquid crystal layer. A second step of allowing the

According to the present invention, it is possible to provide an ultrasonic liquid crystal lens capable of enlarging the lens diameter and a method for controlling the ultrasonic liquid crystal lens.

1A is a plan view of an ultrasonic liquid crystal lens according to the present invention, and FIG. 1B is a cross-sectional view thereof. FIG. FIG. 4 is a diagram showing the orientation of liquid crystal molecules when no electrical signal is applied; It is a figure which shows the orientation of a liquid crystal molecule, and a lens diameter, (A) is a figure in standing wave mode, (B) is a figure in traveling wave mode. FIG. 10 is a diagram showing the vibration amplitude of a lens in traveling wave mode; It is a figure which shows the retardation change of the lens in standing wave mode. It is a figure which shows the retardation change of the lens in traveling wave mode.

Embodiments of an ultrasonic liquid crystal lens and an ultrasonic liquid crystal lens control method according to the present invention will be described below with reference to the accompanying drawings.

[Ultrasonic liquid crystal lens]
FIG. 1 shows an ultrasonic liquid crystal lens 1 according to one embodiment of the present invention. The ultrasonic liquid crystal lens 1 includes a substrate 2 , an ultrasonic transducer 3 , a lens 4 and a driving section 5 .

The substrate 2 is a disk-shaped glass substrate. The substrate 2 has a diameter of 30 [mm] and a thickness of 0.5 [mm].

The ultrasonic transducer 3 is an annular piezoelectric ultrasonic transducer having a central opening, and is made of lead zirconate titanate (PZT). The ultrasonic transducer 3 has an inner diameter of 20 [mm], an outer diameter of 30 [mm], and a thickness of 1 [mm].

The ultrasonic transducer 3 has four aluminum electrodes (a first electrode 31, a second electrode 32, a third electrode 33 and a fourth electrode 34) divided into four in the circumferential direction. The four aluminum electrodes consist of a positive electrode and a negative electrode insulated from each other, and have the same shape.

The first electrode 31 consists of a first positive electrode 31a and a first negative electrode 31b. The second electrode 32 consists of a second positive electrode 32a and a second negative electrode 32b. The third electrode 33 consists of a third positive electrode 33a and a third negative electrode 33b. The fourth electrode 34 consists of a fourth positive electrode 34a and a fourth negative electrode 34b. The first negative electrode 31b, the second negative electrode 32b, the third negative electrode 33b, and the fourth negative electrode 34b are connected to a common negative electrode formed on the lower surface side (substrate 2 side) of the ultrasonic transducer 3. there is

A lens 4 is arranged in the central opening of the ultrasonic transducer 3 . As shown in FIG. 2, the lens 4 includes a first substrate 41 and a second substrate 42 facing each other, a first alignment film 43 provided on the lower surface side of the first substrate 41, and an upper surface of the second substrate 42. It includes a second alignment film 44 provided on the side and a liquid crystal layer 45 . Liquid crystal layer 45 includes liquid crystal molecules 46 .

The first substrate 41 is a disk-shaped glass substrate having a diameter of 15 [mm] and a thickness of 0.5 [mm]. The second substrate 42 is a portion of the substrate 2 facing the first substrate 41 .

The first alignment film 43 and the second alignment film 44 are vertical alignment films in which the pretilt angle of the liquid crystal molecules 46 is 90 degrees, and are made of a polyimide-based material.

The liquid crystal layer 45 includes liquid crystal molecules 46 of nematic liquid crystal, and has a thickness of 200 [μm] by spacers (for example, PET film). The periphery of the liquid crystal layer 45 is sealed with a sealing material (for example, epoxy resin). The liquid crystal molecules 46 stand vertically with respect to the first alignment film 43 and the second alignment film 44 when the ultrasonic oscillator 3 does not generate ultrasonic waves.

The driving unit 5 has a traveling wave mode and a standing wave mode, and is configured to apply an electric signal (AC voltage signal) to the ultrasonic transducer 3 to generate ultrasonic waves. The driving unit 5 includes a first driving unit 51 connected to the first electrode 31, a second driving unit 52 connected to the second electrode 32, a third driving unit 53 connected to the third electrode 33, and a fourth driving portion 54 connected to the fourth electrode 34 . The first driving section 51 to the fourth driving section 54 can independently control the phase, voltage value and frequency of the electric signal.

In the standing wave mode, the drive unit 5 applies in-phase electric signals to the ultrasonic transducer 3 . That is, the first driving section 51 to the fourth driving section 54 apply electric signals of the same phase to the first electrode 31 to the fourth electrode 34 to which they are connected. The first to fourth electrodes 31 to 34 generate ultrasonic waves of a predetermined frequency according to the electric signal. For example, the first to fourth electrodes 31 to 34 generate ultrasonic waves having a frequency matching the resonance frequency of the lens 4 .

When the ultrasonic waves generated by the first electrode 31 to the fourth electrode 34 propagate to the lens 4, the standing wave (acoustic standing wave) of the ultrasonic wave, specifically the flexural vibration of the primary mode, occurs in the lens 4. waves are generated. The flexural vibration in the primary mode refers to vibration in which the vibration intensity continuously decreases from the center of the lens 4 toward the outer peripheral surface. In the present invention, the center of the lens 4 and its vicinity are defined as the central portion, and the area around the center (out of the entire lens 4 other than the central portion) is defined as the peripheral portion.

When a standing wave of flexural vibration is generated in the lens 4 , a constant Pressure due to the acoustic radiation force of existing waves acts. The pressure due to the acoustic radiation force of standing waves is higher at the center of the lens 4 .

As shown in FIG. 3(A), the pressure due to the acoustic radiation force of the standing wave changes the orientation of the liquid crystal molecules 46 at the center of the lens 4 . For example, the pressure due to the acoustic radiation force of the standing wave can be adjusted by slightly changing (in this embodiment, slightly increasing) the thickness of the liquid crystal layer 45 at the center of the lens 4, so that the liquid crystal molecules at the center 46 orientation is changed. Note that FIG. 3 does not show changes in thickness. In addition, since the liquid crystal molecules 46 positioned at the center of the central portion are axially symmetrical and stable, the alignment does not change.

In the standing wave mode, the orientation of the liquid crystal molecules 46 at the center of the lens 4 is changed, so only the center of the lens 4 functions as a lens. In other words, the central portion of the lens 4 has the lens diameter D1.

In the traveling wave mode, the drive unit 5 applies electrical signals whose phases are shifted by 90° in the circumferential direction to the first electrode 31 to the fourth electrode 34 . That is, the electric signal applied to the first electrode 31 by the first driving unit 51 has a phase difference of 90° between the electric signal applied to the second electrode 32 by the second driving unit 52, and the electric signal applied to the second electrode 32 by the first driving unit 51 has a phase difference of 90°. The electrical signal applied by the 53 to the third electrode 33 has a phase difference of 180°, and the electrical signal applied to the fourth electrode 34 by the fourth driver 54 has a phase difference of 270°. The first to fourth electrodes 31 to 34 generate ultrasonic waves corresponding to the electrical signals.

When the ultrasonic waves generated by the first electrode 31 to the fourth electrode 34 propagate to the lens 4, the lens 4 generates a traveling wave (acoustic traveling wave) of the ultrasonic wave propagating in the circumferential direction, that is, a traveling wave of flexural vibration. do.

When a traveling wave of flexural vibration is generated in the lens 4, the traveling wave occurs in the lens 4 (for example, at the interface between the liquid crystal layer 45 and the first alignment film 43 and the interface between the liquid crystal layer 45 and the second alignment film 44). pressure due to the acoustic radiation force of The pressure due to the acoustic radiation force of the traveling wave is higher at the periphery of the lens 4 .

As shown in FIG. 3B, the pressure due to the acoustic radiation force of the traveling wave mainly changes the orientation of the liquid crystal molecules 46 in the peripheral portion of the lens 4 . The liquid crystal molecules 46 located in the center of the center do not change their orientation due to the axial symmetry, but the liquid crystal molecules 46 located on the peripheral side of the center slightly change their orientation. As a result, in traveling wave mode, the central and peripheral portions of lens 4 function as lenses. In other words, the center and peripheral portions of the lens 4 have the lens diameter D2.

[Method of controlling ultrasonic liquid crystal lens]
A control method for an ultrasonic liquid crystal lens according to an embodiment of the present invention is the control method for the ultrasonic liquid crystal lens 1 described above. That is, the control method mainly includes a first step of changing the orientation of the liquid crystal molecules 46 in the peripheral portion of the lens 4 and a second step of changing the orientation of the liquid crystal molecules 46 in the central portion of the lens 4 .

In the first step, the driving section 5 (the first driving section 51 to the fourth driving section 54) applies electrical signals whose phases are shifted by 90° in the circumferential direction to the first electrode 31 to the fourth electrode 34. , produces a traveling wave of flexural vibration that propagates in the circumferential direction of the lens 4 . The electrical signals output by the first driving section 51 to the fourth driving section 54 differ only in phase, and have the same voltage value and frequency.

When a traveling wave of flexural vibration is generated in the lens 4 , pressure due to the acoustic radiation force of the traveling wave acts on the lens 4 , and the pressure increases in the peripheral portion of the lens 4 . As a result, the orientation of the liquid crystal molecules 46 in the peripheral portion of the lens 4 changes, and the orientation of the liquid crystal molecules 46 in the central portion of the lens 4 also slightly changes, so that the central portion and the peripheral portion of the lens 4 function as lenses.

In the second step, the drive unit 5 (first drive unit 51 to fourth drive unit 54) applies in-phase electrical signals to the first electrode 31 to fourth electrode 34, and the lens 4 is subjected to constant bending vibration. cause a wave. The electrical signals output by the first driving section 51 to the fourth driving section 54 have the same voltage value and frequency.

When a standing wave of flexural vibration is generated in the lens 4 , pressure due to the acoustic radiation force of the standing wave acts on the lens 4 , and the pressure increases at the center of the lens 4 . As a result, the orientation of the liquid crystal molecules 46 at the central portion of the lens 4 changes, and only the central portion of the lens 4 functions as a lens.

In the first step and the second step, when the first driving section 51 to the fourth driving section 54 change the voltage value of the electric signal, the magnitude of the pressure due to the acoustic radiation force changes, and the focal length of the lens 4 changes. Change. Further, when the amount of change in the voltage value of each electric signal by the first driving section 51 to the fourth driving section 54 is different, it is possible to control not only the focal length but also the focal position on the XY plane.

[Evaluation experiment]
Next, an evaluation experiment for the ultrasonic liquid crystal lens 1 and its control method will be described.

FIG. 4 shows the vibration amplitude of the lens 4 in traveling wave mode. The horizontal axis of FIG. 4 indicates the position of the lens 4 in the radial direction (X direction), with the center of the lens 4 being 0. As shown in FIG. From FIG. 4, it can be seen that the vibration intensity of the flexural vibration is high at the periphery of the lens 4 and low at the center.

5 and 6 are images of the upper surface of the lens 4 when orthoscopic observation is performed under crossed Nicols using a polarizing microscope. 5 is an image in the standing wave mode, and FIG. 6 is an image in the traveling wave mode. 5 shows the lens diameter D1 of the lens 4 at 0.42 [mm] in the drawing, and FIG. 6 shows the lens diameter D2 of the lens 4 at 0.83 [mm] in the drawing. indicates that That is, it can be seen that the lens diameter is enlarged by switching from the standing wave mode to the traveling wave mode.

[Modification]
Although the embodiments of the ultrasonic liquid crystal lens and the ultrasonic liquid crystal lens control method according to the present invention have been described above, the present invention is not limited to the above embodiments.

An ultrasonic liquid crystal lens according to the present invention includes a ring-shaped ultrasonic oscillator, a lens including a liquid crystal layer disposed in a central opening of the ultrasonic oscillator, and an ultrasonic wave by applying an electric signal to the ultrasonic oscillator. an ultrasonic liquid crystal lens that generates sound waves, wherein the ultrasonic transducer includes N electrodes (N is an integer of 3 or more) divided in the circumferential direction, and the driving unit includes: , N electrodes are applied with electrical signals whose phases are shifted by integral multiples of (360/N)° in the circumferential direction to generate traveling waves of ultrasonic waves that propagate in the circumferential direction of the lens. As long as it has a traveling wave mode that changes the orientation of the liquid crystal molecules in the peripheral portion, the configuration can be changed as appropriate.

In the above-described embodiment, the drive unit 5 applies electrical signals whose phases are shifted by 1 times 90° in the circumferential direction to the first electrode 31 to the fourth electrode 34. Electrical signals shifted by a factor of two may be applied. In this case, the electric signal applied to the first electrode 31 by the first driving unit 51 has a phase difference of 180° between the electric signal applied to the second electrode 32 by the second driving unit 52, and the third driving unit 51 applies the electric signal to the second electrode 32. The electric signal applied to the third electrode 33 by the unit 53 has a phase difference of 360°, and the electric signal applied to the fourth electrode 34 by the fourth driving unit 54 has a phase difference of 540°.

In the method for controlling an ultrasonic liquid crystal lens according to the present invention, an electrical signal whose phase is shifted by an integral multiple of (360/N)° in the circumferential direction is applied to N electrodes by a driving unit, The configuration can be modified as appropriate so long as it includes a first step of generating a traveling wave of ultrasonic waves propagating in a direction to change the orientation of the liquid crystal molecules in the periphery around the center of the liquid crystal layer.

1 Ultrasonic Liquid Crystal Lens 2 Substrate 3 Ultrasonic Vibrator 31 First Electrode 31a First Positive Electrode 31b First Negative Electrode 32 Second Electrode 32a Second Positive Electrode 32b Second Negative Electrode 33 Third Electrode 33a Third Positive Electrode 33b Third negative electrode 34 Fourth electrode 34a Fourth positive electrode 34b Fourth negative electrode 4 Lens 41 First substrate 42 Second substrate 43 First alignment film 44 Second alignment film 45 Liquid crystal layer 46 Liquid crystal molecules 5 Driving unit 51 Third 1 driving section 52 2nd driving section 53 3rd driving section 54 4th driving section

Claims (5)

an annular ultrasonic transducer having a central opening;
a lens comprising a liquid crystal layer disposed in said central opening and having a central portion and a peripheral portion around said central portion;
a driving unit that applies an electric signal to the ultrasonic transducer to generate ultrasonic waves;
An ultrasonic liquid crystal lens comprising
The ultrasonic transducer includes N electrodes (N is an integer of 3 or more) divided into N in the circumferential direction,
The drive unit
Applying the electrical signals whose phases are shifted by integral multiples of (360/N)° in the circumferential direction to the N electrodes to generate traveling waves of the ultrasonic waves that propagate in the circumferential direction of the lens. 9. An ultrasonic liquid crystal lens, characterized by having a traveling wave mode for changing the orientation of liquid crystal molecules in said peripheral portion of said liquid crystal layer. The drive unit
The electrical signals in phase are applied to the N electrodes to generate a standing wave of the ultrasonic waves in the liquid crystal layer, thereby changing the orientation of the liquid crystal molecules in the central portion of the liquid crystal layer. 2. The ultrasonic liquid crystal lens according to claim 1, having a mode. 3. The ultrasonic liquid crystal lens according to claim 1, wherein said N electrodes have the same shape. An ultrasonic vibrator formed in an annular shape having a central opening and having N electrodes (N is an integer of 3 or more) divided in the circumferential direction, and a liquid crystal layer disposed in the central opening. A control method for an ultrasonic liquid crystal lens comprising a lens and a driving unit for applying an electric signal to the ultrasonic transducer to generate ultrasonic waves,
The driving unit applies the electrical signals whose phases are shifted by integral multiples of (360/N)° in the circumferential direction to the N electrodes, and the traveling wave of the ultrasonic wave propagates in the circumferential direction of the lens. , to change the orientation of the liquid crystal molecules in the periphery around the center of the liquid crystal layer. The electric signals having the same phase are applied to the N electrodes by the driving unit, and the standing wave of the ultrasonic wave is generated in the liquid crystal layer to change the orientation of the liquid crystal molecules in the central portion of the liquid crystal layer. 5. The method of controlling an ultrasonic liquid crystal lens according to claim 4, comprising a second step of allowing

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