WO2018222727A1

WO2018222727A1 - Multidimensional piezoelectric actuator having enhanced actuation range

Info

Publication number: WO2018222727A1
Application number: PCT/US2018/035150
Authority: WO
Inventors: Chris Xu; Najva AKBARI
Original assignee: Cornell University
Priority date: 2017-05-31
Filing date: 2018-05-30
Publication date: 2018-12-06

Abstract

A piezoelectric actuator including a base, a first piezoelectric bending actuator connected to the base having a first actuation axis, a second piezoelectric bending actuator having a second actuation axis that is non-parallel to the first actuation axis, the first axis and the second axis defining a plane and a third piezoelectric bending actuator having a third actuation axis. The third actuation axis may extend parallel to a plane formed by the first actuation axis and the second actuation axis, such that the bending actuators constitute a course actuation module and fine actuation module. The actuator may include a fiber optic to form an optical scanner. The actuator may comprise a rod to enhance the actuation range. The bending actuators may form a 3D scanner.

Description

MULTIDIMENSIONAL PIEZOELECTRIC ACTUATOR HAVING ENHANCED

ACTUATION RANGE

CROSS REFERENCE

[0001] This application claims the benefit of the filing date of U.S. Provisional Patent Application Serial No. 62/512,905 filed May 31, 2017, which is hereby incorporated by reference in its entirety.

GOVERNMENT RIGHTS

[0002] This invention was made with government support under grant number

EY027568 awarded by THE NATIONAL INSTITUTES OF HEALTH. The govemment has certain rights in this invention.

FIELD

[0003] Methods and apparatus for multidimensional actuation using a piezoelectric material, and in particular methods and apparatus for enhancing actuation range of multidimensional actuator using piezoelectric material.

BACKGROUND

[0004] The piezoelectric effect is the well-known phenomenon occurring in selected materials (known as piezoelectric materials) where the materials deform upon the application of a voltage thereto. The use of a piezoelectric materials to form a bending actuator is also well known. As shown in FIG. 1, in one example of such an actuator 10, a bilayer structure is formed with a first layer 12 of piezoelectric material located adjacent a second layer 14 of piezoelectric material, having a width W and a combined thickness T. As shown in FIG. 1, if the bilayer structure is fixed at only one end E_1; upon the application voltages (V_out +, Vi_n-) causing opposite biasing of the first layer and the second layer, the free end E₂ of the structure bends about the fixed end E₁ to achieve a deflection ΔΧ. Bending actuators may have other configurations including one or more layers of piezoelectric material. Bending actuators, referred to as composite bending actuators, may have one or more passive layers (e.g., a metal layer or ceramic layer) to tune the bending characteristics of the actuator.

[0005] As illustrated in FIG. 2 and described in United States Patent No. 8,705, 184, piezoelectric actuators can be combined to form a multidimensional piezoelectric actuator 20 by connecting two or actuators 22,24 together with the actuation axes being perpendicular to one another. Also, As illustrated in FIG. 2 and described in U.S. 8,705,184 bending actuators can be operated as scanner by adding functionality to distal end DE of the bending actuator. For example, as shown, if an optical source (not shown) and/or an optical receiver (not shown) is coupled to the free end of a bending actuator, optical scanning can be performed. The substance of U.S. 8,705,184 is hereby incorporated by reference in its entirety.

SUMMARY

[0006] Conventional actuation apparatus using the piezoelectric effect have a relatively small actuation range. Although an actuation range can be increased by increasing the length of the piezoelectric material of a bending actuators, such modifications tend to greatly reduce the actuation speed of the actuators. Aspects of the present invention are directed to methods and apparatus for enhancing actuation range of multidimensional piezoelectric actuators while limiting the impact on actuation speed.

[0007] An aspect of the present invention is directed to a piezoelectric actuator, comprising a base, a first piezoelectric bending actuator, a second piezoelectric bending actuator, and a third piezoelectric bending actuator. The first piezoelectric bending actuator has a first actuator first end and a first actuator second end. The first bending actuator is connected to the base at the first actuator first end. The first bending actuator has a first actuation axis. The second piezoelectric bending actuator has a second actuator first end and a second actuator second end. The second bending actuator first end is connected to the first actuator second end. The second bending actuator has a second actuation axis that is non- parallel to the first actuation axis. The first axis and the second axis define a plane. The third piezoelectric bending actuator has a third actuator first end and a third actuator second end. The third bending actuator first end is connected to the second actuator second end. The third bending actuator has a third actuation axis that extends parallel to the plane.

[0008] In some embodiments, a rod is connected between the first bending actuator and the second bending actuator.

[0009] In some embodiments, a rod is connected between the second bending actuator and the third bending actuator.

[0010] The actuator may further comprise a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end. The fourth bending actuator first end is connected to the third bending actuator second end. The fourth bending actuator has a fourth actuation axis that extends parallel to the plane. The fourth actuation axis is non- parallel to the third actuation axis.

[0011] The first actuation axis and the second actuation axis may be perpendicular to one another. [0012] The third actuation axis may be parallel to a first of the first actuation axis and the second actuation axis.

[0013] In some embodiments, the actuator further comprises a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end. The fourth bending actuator first end is connected to the third bending actuator second end. The fourth bending actuator has a fourth actuation axis that is parallel to the plane. The fourth actuation axis is non-parallel to the third actuation axis. In such embodiments, the fourth actuation axis is parallel to a second of the first actuation axis and the second actuation axis.

[0014] The first actuation axis and the second actuation axis may be perpendicular to one another.

[0015] In some embodiments, the actuator further comprises a fiber optic connected to the fourth piezoelectric bending actuator, whereby the actuator forms an optical scanner.

[0016] In some embodiments, the first bending actuator has a first length, the second actuator has a second length and the third actuator has a third length, and at least one of the first length and the second length is greater than the third length.

[0017] In some embodiments, the at least one of the first length and the second length is at least twenty percent greater than the third length.

[0018] In some embodiments, the actuator further comprises a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end. The fourth bending actuator first end is connected to the third bending actuator second end. The fourth bending actuator has a fourth actuation axis that extends parallel to the plane, and the fourth actuation axis is non-parallel to the third actuation axis.

[0019] The first actuation axis and the second actuation axis may be perpendicular to one another.

[0020] The third actuation axis may be parallel to a first of the first actuation axis and the second actuation axis.

[0021] The second bending actuator first end may be directly connected to the first bending actuator second end, and the third bending actuator first end is directly connected to the second bending actuator second end.

[0022] Another aspect of the invention is directed to an actuator comprising a base, a first piezoelectric bending actuator, a second piezoelectric bending actuator, and a third piezoelectric bending actuator. The first piezoelectric bending actuator has a first actuator first end and a first actuator second end. The first bending actuator is connected to the base at the first actuator first end. The first bending actuator has a first actuation axis. The second piezoelectric bending actuator has a second actuator first end and a second actuator second end. The second bending actuator first end is connected to the first actuator second end. The second bending actuator has a second actuation axis that is non-parallel to the first actuation axis. The first axis and the second axis define a plane. The third piezoelectric bending actuator has a third actuator first end and a third actuator second end. The third bending actuator first end is connected to the second actuator second end. The third bending actuator has a third actuation axis that extends through the plane.

[0023] In some embodiments of this aspect, the third actuation axis extends

perpendicular to the plane.

[0024] In some embodiments of this aspect, the first actuation axis, the second actuation axis and the third actuation axis are mutually perpendicular.

[0025] In some embodiments of this aspect, the actuator further comprises a fiber optic connected to the third piezoelectric bending actuator, whereby the actuator forms an optical scanner.

[0026] The term "proximal" refers to a location that is in a location tending toward a base of an actuator; and the term "distal" refers to a location tending away from a base (toward a functional end) of an actuator. For example, a bending actuator has a proximal end PE nearer to a base, and a distal end DE further from the base.

[0027] The term "rod" as used herein refers to a thin straight bar. A rod need not have any particular cross-sectional shape.

[0028] These and other aspects of the present invention will become apparent upon a review of the following detailed description and the claims appended thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 illustrates an example of a piezoelectric bending actuator having a bilayer structure;

[0030] FIG. 2 illustrates a multidimensional piezoelectric actuator comprising two piezoelectric bending actuators;

[0031] FIG. 3 is a schematic illustration of an example of an optical scanner according to aspects of the present invention, having a course actuation module and a fine actuation module;

[0032] FIG. 4 is schematic illustration of larger area of a cross section of a brain and multiple smaller areas that are scannable using a scanner according to aspects of the present invention, the larger area being accessible using the course actuation while the smaller areas, disposed within the larger area, are scannable using a fine scanning module of the scanner;

[0033] FIG. 5 is a schematic illustration of an example of an embodiment of an actuator including a rod to increase a scanning range, according to aspects of the present invention; and

[0034] FIG. 6 is a schematic illustration of an example of an optical scanner providing three-dimensional (3D) scanning capability, according to aspects of the present invention.

DETAILED DESCRIPTION

[0035] Aspects of the invention are directed to multidimensional actuators having a course actuation module and a fine actuation module. Each module has one or more piezoelectric bending actuators, each bending actuator scans in a given direction. By dividing the actuator into a course actuation module and a fine actuation module, a relatively large range of motion can be achieved using a course actuation module while also maintaining an ability for high speed actuation over a smaller range within the larger range.

[0036] An actuator may have a base that provides a reference location about which the actuator moves. The course actuation module is connected between the base and the fine actuation module. As a result of the location of the course actuator (i.e., more proximal than the fine actuation module), actuation of the course actuator can move a functional feature disposed at a distal end of fine actuation module over a greater range than the fine actuation module; however, fine actuation module operates with a smaller moment of inertia than the course actuation arm and therefore can move the functional feature faster (but over a smaller range).

[0037] The invention will be further discussed with reference to the following specific examples. It is understood that these examples are given by way of illustration and are not meant to limit the disclosure or the claims to follow to any particular example. Although aspects of the invention are described with reference an optical scanner, other functionalities may be used with actuators according to aspects of the present invention.

[0038] FIG. 3 is a schematic illustration of an example of an optical scanner 100 according to aspects of the present invention having a course actuation module 130 and a fine actuation module 140. Scanner 100 comprises a multidimensional actuator 110 and a fiber optic 120. Actuator 110 comprises a base 102, a first piezoelectric bending actuator 104, a second piezoelectric bending actuator 106 and a third piezoelectric bending actuator 108. [0039] Base 102 is a structure to which the remaining components of an actuator are attached. Typically, a bending actuator of actuator 1 10 is fixed to the base at a location L. The first bending actuator 104 bends about location L.

[0040] First piezoelectric bending actuator 104 has a first actuator first end 104ei and a first actuator second end 104e2. First bending actuator 104 is connected to base 102 at the first actuator first end 104ei. First bending actuator 104 has a first actuation axis A₁.

[0041] Second piezoelectric bending actuator 106 has a second actuator first end 106ei and a second actuator second end 106e2. Second bending actuator first end 106ei is connected to the first actuator second end 104e2. Second bending actuator 106 has a second actuation axis A₂ that is non-parallel to the first actuation axis A₁. First axis A₁ and second axis A₂ defining a plane P. It will be understood that a plane defined by the first actuation axis and the second actuation axis is any plane where one or both the first actuation axis and the second actuation axis are translated while maintaining the direction of the axis (or axes), to a location where the first actuation axis and the second actuation axis intersect.

[0042] Third piezoelectric bending actuator 108 has a third actuator first end 108ei and a third actuator second end 108e₂. Third bending actuator first end 108ei is connected to the second actuator second end 106e₂. Third bending actuator 108 has a third actuation axis A₃ that extends parallel to plane P.

[0043] Actuator 1 10 includes an, optional, fourth piezoelectric bending actuator 109 having a fourth actuator first end 109ei and a fourth actuator second end 109e₂. Fourth bending actuator first end 109ei is connected to the third bending actuator second end 108e₂. Fourth bending actuator 109 has a fourth actuation axis A₄ that extends parallel to plane P. The fourth actuation axis A₄ is non-parallel to the third actuation axis A₃. A bending actuator may be made of any suitable piezoelectric material (e.g., Lead Zirconate Titanate).

Typically, a bending actuator is rod-shaped, with the length from first end to the second end of the bending actuator being longer than the cross sectional dimensions of the bending actuator, and often several times longer (e.g., 2, 3, 4 or more times as long).

[0044] Although not illustrated, actuator 110 includes one or more voltage generators to produce the voltages needed to actuate each of bending actuators 104, 106, 108 and 109. The voltages are applied to the bending actuators in a conventional manner. The voltages may be in the form of an oscillating signal, a direct current bias or a combination of both. For example, the signals applied to the bending actuators 104, 106 of the course actuation module 130 will have time periods with a fixed DC biasing voltage to cause the functional end of the actuator (i.e., distal end DE) to locate proximate a given location in a larger area LA (shown in FIG. 4), and the signals applied to the bending actuators 108, 109 of the fine actuation module 140 will be oscillatory to achieves scanning of a relatively small area (e.g., area SAi shown in FIG. 4).

[0045] FIG. 4 is schematic illustration of larger area LA of a cross section of a brain that is scannable using a course scanning module of a scanner according to aspects of the present invention, and having smaller areas SA_1; SA₂, SA₃ disposed within large area LA, that are scannable using a fine scanning module of the scanner. As shown in FIG. 4, the course actuation module can position the functional end of an actuator proximate a first location in large area LA and the fine actuation module can scan a first, relatively small area SA₁ proximate the first location. Subsequently, the course actuation module can position the functional end proximate one or more additional locations in large area LA and the fine actuation module can scan a second, relatively small area SA₂ proximate the second location. Although scanning of the small area can be achieved in an x -y partem as shown, voltages may be applied to the bending actuators of the fine actuation module to achieve any suitable scanning pattern.

[0046] Referring again to FIG. 3, as indicated above, fourth piezoelectric bending actuator 109 is optional. In embodiments where fourth actuator 109 is omitted, one of the first actuator 104 and the second actuator 106 having a scan axis that is non-parallel to third actuator 108, may be operated to provide the functionality of omitted bending actuator 109. For example, if fourth bending actuator 109 were omitted from actuator 110, second actuator 106 could be operated with a DC bias to select a location within area LA, and oscillating signal to provide a component of the scanning pattern in the manner shown in FIG. 4.

[0047] In some embodiments, because first actuator 104 and the second actuator 106 operate in a relatively slow manner, and the primary function of the first actuator and the second actuator is to provide scanning range, it is advantageous if at least one of length Li of first actuator 104 and second length L₂ of the second actuator 106 is greater than length L₃ of third actuator 108 and/or length L₄ of fourth actuator 109. Such a configuration provides added scanning range without a loss of scanning speed over the smaller area. For example, the length of the first actuator or second actuator may be at least 10%, 20% or 50% longer than the length of the third actuator and/or the fourth actuator.

[0048] In the illustrated embodiment, the first actuation axis A i and second actuation axis A₂ are perpendicular to one another which can be used to achieve a conventional x - y movement/scanning partem. However, the first actuator and the second actuator can be arranged to achieve any suitable angular relationship between first actuation axis A₁ and second actuation axis A₂. In addition, the voltage signals applied to the actuators 104, 106, and the angular relationship between the actuation axes Ai A₂ can be selected to achieve a desired movement/scanning pattern.

[0049] Similarly, in the illustrated embodiment, the third actuation axis A3 and fourth actuation axis A₄ are perpendicular to one another which can be used to achieve a

conventional x - y scanning partem. However, the third actuator and the fourth actuator can be arranged to achieve any suitable angular relationship between third actuation axis A₃ and fourth actuation axis A₄. In addition, the voltage signals applied to the actuators 108, 109, and the angular relationship between the actuation axes A_3i A₄ can be selected to achieve a desired scanning pattern.

[0050] Also, in the illustrated embodiment, the third actuation axis A₃ is parallel to a first of the first actuation axis A₁ and the second actuation axis A₂ and the fourth actuation axis A₄ is parallel to a second of the first actuation axis Ai and the second actuation axis A₂. Accordingly, in the illustrated embodiment, both the course scanning module and the fine scanning module achieve a conventional scanning pattern.

[0051] First bending actuator 104 may be connected to base 102 and the second bending actuator 106 is connected to first bending actuator 106 using any suitable adhesive (e.g., a glue) or mechanical connector. Typically, second bending actuator first end 106ei is directly connected to first bending actuator second end 104e2, and the third bending actuator first end 108ei is directly connected to the second bending actuator second end 106e2, with nothing between said components other than, perhaps, adhesive.

[0052] Although actuator 1 10 is illustrated as an optical scanner (i.e., imaging and/or illuminating), it will be appreciated that an actuator according to aspects of the present invention may be used to achieve any suitable functionality by providing a suitable operative element at the functional end and/or another suitable location on a bending actuator. Any suitable fastening technique (e.g., adhesive or mechanical connection) may be used to form a connection.

[0053] In some embodiments, it is advantageous to include a lens 122 on the distal end of fiber 120. The lens focuses the beam of light out of the fiber to decrease of the illumination spot size and/or to decrease the spot size of the light gathered into the fiber optic, thereby improving the resolution of the scanner. It will be appreciated that, in some embodiments, by using such a fiber lens, the need to use optics external to the fiber to de- magnify the beam of light output from the fiber or decrease the spot size of the light gathered by the fiber may be eliminated. It will also be appreciated that, in some embodiments, such demagnification using external optics may result in an undesirable decrease in scan range of a scanner.

[0054] According to an aspect of the invention, a scanning range achievable by a bending actuator is increased while only requiring a relatively small increase in the moment of inertia of the bending actuator (i. e., less than the increase that would result from increasing the length of a piezoelectric material to attain the increased scanning range). As described in greater detail below, in such embodiments, a light weight rod is added between one or more bending actuators and the distal end of the actuator.

[0055] FIG. 5 is a schematic illustration of an example of an embodiment of an actuator 500 including a rod 550 to increase a scanning range of the actuator. In the illustrated embodiment, actuator 500 comprises a rod 550 connected between second bending actuator 106 and third bending actuator 108. A suitable rod has a rigidity suitable for moving distal end DE to perform any function the actuator is to designed to perform (e.g., optical scanning), and have a suitable weight. The weight of the rod is typically less than the weight of an equal length of piezoelectric material that would be used to achieve the scanning range. For example, the rod may be made of carbon fiber or a magnesium alloy.

[0056] It is to be appreciated that rod 550 increases the scanning range of any bending actuator that is located proximal to the rod (e.g., bending actuators 104 and 106). In actuator 500, the scanning range is increased relative to a same actuator without rod.

[0057] In an alternative embodiment, rod 550 may be connected between the first bending actuator 104 and the second bending actuator 106. In such an actuator, only the scanning range of bending actuator 104 is increased relative to a same actuator without a rod.

[0058] As described above, actuator 500 may include an optional fourth piezoelectric bending actuator (not shown). Also as described above, first actuation axis A_1; second actuation axis A₂, third actuation axis A₃, and the fourth actuation axis can have any orientation relative to one another (e.g., parallel or perpendicular to one another).

[0059] In some embodiments including a rod, a fiber optic 120 is connected to the fourth piezoelectric bending actuator to form an optical scanner.

[0060] FIG. 6 is a schematic illustration of an example of an optical scanner 600 according to aspects of the present invention providing three-dimensional (3D) scanning capability. Scanner 600 comprises a multidimensional actuator 610 and a fiber optic 120. Like scanner 100, scanner 600 comprises an actuator 610 comprising a base 102, a first piezoelectric bending actuator 104, a second piezoelectric bending actuator 106 and a third piezoelectric bending actuator 608. [0061] Unlike scanner 100, in scanner 600, the third bending actuator 608 has a third actuation axis A₃ that extends through a plane P formed by axis Ai and A₂. In some embodiments, as illustrated in FIG. 6, third actuation axis A₃ extends perpendicular to plane P, and the first actuation axis A_1; second actuation axis A₂ and the third actuation axis A₃ are mutually perpendicular.

[0062] In the illustrated embodiment, a fiber optic 120 is connected to the third piezoelectric bending actuator 608, whereby the actuator forms an optical scanner. However, as indicated above other functionality may be provide on the actuator.

[0063] Example # 1 - A Mesoscope

[0064] In one example application of a scanner as described above, the scanner operates as a mesoscope having relatively small size and low cost. It will be appreciated that such a design can be pre-assembled, portable and not require re-alignment on site. It will be appreciated that designs as described herein are unaffected by magnetic fields and are therefore MRI-compatible, thereby enabling new forms of multi-modal imaging. In some embodiments, designs as described herein provide a mesoscope with a field of view as large as ~ 5 mm, and have sub-μιη spatial resolution.

[0065] Example #2 - Endoscope

[0066] In a second example application of a scanner as described above, the scanner operates as an endoscope having relatively small size and low cost. The fiber optic is an air core, photonic bandgap fiber (PBGF) to deliver excitation light for imaging of tissue (e.g., an animal brain, such as a zebra fish brain). A system may include several fibers designed for various excitation wavelengths, the fibers being glued together to form a fiber array with a width and thickness of 1.0 mm and 250 μιτι, respectively. Further details of such a fiber array are given in U. S. 8,705, 184. The bending actuators are a bimorph structure including two layers of PZT material of equal thickness.

[0067] The thickness and the overhang length of bending actuators are designed so that its lowest mechanical resonant frequency is approximately 4.0 KHz, allowing a bi-directional line-scan rate at approximately 8 kHz. In some embodiments, the combined transmission range of 4 or 5 of these fibers will essentially cover all useful wavelengths for two-photon and three-photon imaging.

[0068] In some embodiments, the proximal bending actuators (i.e., the course actuation module) of the tandem, piezo-fiber scanner (PFS) are two piezo bending actuators made of thicker and wider materials than the bending actuators of the fine actuation module, to generate larger bending forces. In order to significantly reduce the total weight and increase the stiffness, a rod comprising a thin- walled square tube made of high-modulus carbon fiber composite material is used to form a connecting rod. It will be appreciated that carbon fiber materials have much higher elastic modulus than piezo materials, and have a density of approximately 1.5 g/cm³ (approximately 20% of the density of piezoelectric material PZT). Since the mass of the optical fiber is negligible (approximately 34 mg/m), the combined mass of the fine actuation module and the carbon tube is less than 0.25 gram, ensuring the targeted re-positioning time of -10 ms with ample margin.

[0069] Example design parameters are as follows -

*Values are determined by measuring deflection while only the identified bending actuator is operated, and with an optical fiber overhang beyond the distal end of the last bending actuator about 10mm (e.g., bending actuator 109 in FIG. 3)

** This deflection indicates the movement of the fiber optic at resonance, and includes deflection resulting from deflection of the distal end of the last bending actuator (e.g., bending actuator 109 in FIG. 3)

[0070] The scan engine covers a large FOV of 3.8 mm (i.e., (71 + 72) / 3) by 3.2 mm (i.e., (XI + 0.6 * X2) 13 ). The length and thickness of the materials are chosen to have resonant frequencies at 300 Hz or higher, with the resonant axis, X2, having a resonant frequency well above 25 kHz. The thickness and width of the materials are selected for generating sufficient fiber optic tip deflection and blocking force. The system provides Yl, XI, and Y2 scan range values of 10 mm, 8 mm, and 3.5, respectively. It is to be appreciated that the 3.8 mm by 3.2 mm FOV is designed for imaging adult zebrafish brain, and that a larger FOV is possible by adjusting the design parameters. In the present example, the bending actuators XI, Yl and Y2 are driven linearly (i.e., not at a resonant frequency) by voltages applied thereto; and bending actuator X2 is driven resonantly using a sinusoidal signal, to achieve an increased scan range.

[0071] Example #3 - Endoscope

[0072] In a third example application of a scanner as described above, the scanner operates as an endoscope having relatively small size and low cost. The fiber optic is an air core, photonic bandgap fiber (PBGF) to deliver excitation light for imaging of tissue (e.g., an animal brain, such as a zebra fish brain). A system may include several fibers designed for various excitation wavelengths, the fibers being glued together to form a fiber array with a width and thickness of 1.0 mm and 250 μιτι, respectively. Further details of such a fiber array are given in U. S. 8,705, 184. The bending actuators of the course actuation module are a trimorph structure including two PZT layer that are 0.27 mm thick sandwiching a carbon fiber layer that is 0.24 mm thick; and the fine actuators are a bimorph structure including two layers of PZT material of equal thickness.

[0073] The thickness and the overhang length of bending actuators are designed so that its lowest mechanical resonant frequency is approximately 2.0 KHz, allowing a bi-directional line-scan rate at approximately 8 kHz. In some embodiments, the combined transmission range of 4 or 5 of these fibers will essentially cover all useful wavelengths for two-photon and three-photon imaging.

[0074] In some embodiments, the proximal bending actuators (i.e., the course actuation module) of the tandem, piezo-fiber scanner (PFS) are two piezo benders made of thicker and wider materials than the bending actuators of the fine actuation module, to generate larger force. In order to significantly reduce the total weight and increase the stiffness, a rod comprising a thin- walled square tube made of high-modulus carbon fiber composite material is used to form a connecting rod. It will be appreciated that carbon fiber materials have much higher elastic modulus than piezo materials, and have a density of approximately 1.5 g/cm³ (approximately 20% of the density of piezoelectric material PZT). Since the mass of the optical fiber is negligible (approximately 34 mg/m), the combined mass of the fine actuation module and the carbon tube is less than 0.25 gram, ensuring the targeted re-positioning time of -10 ms with ample margin. [0075] Example design parameters are as follows -

[0076] The scan engine covers a large FOV of 2.3 mm (i.e., (71 + 72) / 3) by 1.7 mm (i.e., (XI + 0.6 * X2) 13 ). The length and thickness of the materials are chosen to have resonant frequencies at 250 Hz or higher, with the resonant axis, X2, having a resonant frequency well above 25 kHz. The thickness and width of the materials are selected for generating sufficient fiber optic tip deflection and blocking force. The system provides Yl, XI, and Y2 scan range values of 5.6 mm, 4.1 mm, and 1.2, respectively. It is to be appreciated that the 2.3 mm by 1.7 mm FOV is designed for imaging adult zebrafish brain, and that a larger FOV is possible by adjusting the design parameters.

[0077] In the present example, the bending actuators XI, Yl and Y2 are driven linearly (i.e., not at a resonant frequency) by voltages applied thereto; and bending actuator X2 is driven resonantly using a sinusoidal signal, to achieve an increased scan range.

[0078] Although various embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.

Claims

WHAT IS CLAIMED

1. A piezoelectric actuator, comprising:

a base;

a first piezoelectric bending actuator having a first actuator first end and a first actuator second end, the first bending actuator connected to the base at the first actuator first end, the first bending actuator having a first actuation axis;

a second piezoelectric bending actuator having a second actuator first end and a second actuator second end, the second bending actuator first end connected to the first actuator second end, the second bending actuator having a second actuation axis that is non- parallel to the first actuation axis, the first axis and the second axis defining a plane; and a third piezoelectric bending actuator having a third actuator first end and a third actuator second end, the third bending actuator first end connected to the second actuator second end, the third bending actuator having a third actuation axis that extends parallel to the plane.

2. The actuator of claim 1, further comprising a rod connected between the first bending actuator and the second bending actuator.

3. The actuator of claim 1, further comprising a rod connected between the second bending actuator and the third bending actuator.

4. The actuator of claim 3, further comprising a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end, the fourth bending actuator first end connected to the third bending actuator second end, the fourth bending actuator having a fourth actuation axis that extends parallel to the plane, the fourth actuation axis being non-parallel to the third actuation axis.

5. The actuator of claim 3, wherein the first actuation axis and the second actuation axis are perpendicular to one another.

6. The actuator of claim 3, wherein the third actuation axis is parallel to a first of the first actuation axis and the second actuation axis.

7. The actuator of claim 6, further comprising a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end, the fourth bending actuator first end connected to the third bending actuator second end, the fourth bending actuator having a fourth actuation axis that is parallel to the plane, the fourth actuation axis being non-parallel to the third actuation axis,

wherein the fourth actuation axis is parallel to a second of the first actuation axis and the second actuation axis.

8. The actuator of claim 6, wherein the first actuation axis and the second actuation axis are perpendicular to one another.

9. The actuator of claim 4, further comprising a fiber optic connected to the fourth piezoelectric bending actuator, whereby the actuator forms an optical scanner.

10. The actuator of claim 1, wherein the first bending actuator has a first length, the second actuator has a second length and the third actuator has a third length, at least one of the first length and the second length being greater than the third length.

11. The actuator of claim 10, wherein the at least one of the first length and the second length is at least twenty percent greater than the third length.

12. The actuator of claim 10, further comprising a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end, the fourth bending actuator first end connected to the third bending actuator second end, the fourth bending actuator having a fourth actuation axis that extends parallel to the plane, the fourth actuation axis being non-parallel to the third actuation axis.

13. The actuator of claim 1, wherein the first actuation axis and the second actuation axis are perpendicular to one another.

14. The actuator of claim 1, wherein the third actuation axis is parallel to a first of the first actuation axis and the second actuation axis.

15. The actuator of claim 14, further comprising a fourth piezoelectric bending actuator having a fourth actuator first end and a fourth actuator second end, the fourth bending actuator first end connected to the third bending actuator second end, the fourth bending actuator having a fourth actuation axis that extends parallel to the plane, the fourth actuation axis being non-parallel to the third actuation axis,

16. The actuator of claim 14, wherein the first actuation axis and the second actuation axis are perpendicular to one another.

17. The actuator of claim 1, wherein the second bending actuator first end is directly connected to the first bending actuator second end, and the third bending actuator first end is directly connected to the second bending actuator second end.

18. The actuator of claim 12, further comprising a fiber optic connected to the fourth piezoelectric bending actuator, whereby the actuator forms an optical scanner.

19. An actuator, comprising:

a base; a first piezoelectric bending actuator having a first actuator first end and a first actuator second end, the first bending actuator connected to the base at the first actuator first end, the first bending actuator having a first actuation axis;

a second piezoelectric bending actuator having a second actuator first end and a second actuator second end, the second bending actuator first end connected to the first actuator second end, the second bending actuator having a second actuation axis that is non- parallel to the first actuation axis, the first axis and the second axis defining a plane; and a third piezoelectric bending actuator having a third actuator first end and a third actuator second end, the third bending actuator first end connected to the second actuator second end, the third bending actuator having a third actuation axis that extends through the plane.

20. The actuator of claim 19, wherein the third actuation axis extends perpendicular to the plane.

21. The actuator of claim 19, wherein the first actuation axis, the second actuation axis and the third actuation axis are mutually perpendicular.

22. The actuator of claim 19, further comprising a fiber optic connected to the third piezoelectric bending actuator, whereby the actuator forms an optical scanner.