Abstract:
A system and method for generating X-rays are provided. The X-ray source includes an X-ray chamber including a sidewall formed of a piezoelectric material at least partially surrounding an evacuated chamber, a cathode positioned at a first end of the evacuated chamber, an anode positioned at a second opposite end of the evacuated chamber, and a window positioned at the second end, the window substantially transparent to X-ray radiation. The window includes a target layer at least partially covering a surface of the window. The target layer is configured to receive a flow of electrons from the cathode and to generate a flow of X-rays from an interaction with the flow of electrons. The X-ray source includes an actuator coaxially aligned with the X-ray chamber and configured to generate a stress in the sidewall.

Description:
BACKGROUND 
       [0001]    This description relates to X-ray generators, and, more particularly, to a method and system for a high voltage piezoelectric generator and X-ray source combination. 
         [0002]    At least some known X-ray generators use a high voltage power supply to provide a stream of electrons, which are accelerated toward a target material. The accelerated electrons interact with the target material to generate a stream of X-rays, which exit the X-ray generator to be used by a process. The high voltage is typically supplied by a high voltage power supply connected to the X-ray generator via an electrical cable. Moreover, the high voltage components of the X-ray generator require additional space or insulators to accommodate the high voltage. Such considerations increase the size and weight of typical X-ray generators such that they prevent further miniaturization. 
       BRIEF DESCRIPTION 
       [0003]    In one aspect, an X-ray source includes an X-ray chamber including a sidewall formed of a piezoelectric material at least partially surrounding an evacuated chamber, a cathode positioned at a first end of the evacuated chamber, an anode positioned at a second opposite end of the evacuated chamber, and a window positioned at the second end, the window substantially transparent to X-ray radiation. The window includes a target layer at least partially covering a surface of the window. The target layer is configured to receive a flow of electrons from the cathode and to generate a flow of X-rays from an interaction with the flow of electrons. The X-ray source includes an actuator coaxially aligned with the X-ray chamber and configured to generate a stress in the sidewall. 
         [0004]    In another aspect, a method of generating X-rays includes applying a force to a piezoelectric sidewall of an X-ray chamber, generating an electric field in the piezoelectric sidewall relative to the applied force, and generating a flow of electrons from a cathode of the X-ray chamber. The method also includes accelerating the flow of electrons towards a target, and generating a flow of X-rays from the target using electrons from the flow of electrons that interact with the target. 
         [0005]    In yet another aspect, an X-ray generating system includes a housing including a pistol-grip configured to receive a hand of a user and an X-ray generator positioned at least partially within the housing. The X-ray generator includes a sidewall formed of piezoelectric material, the sidewall configured to generate electric charge in response to a stress applied to the sidewall, a cathode configured to concentrate the charge at a first end of the sidewall, and a target assembly positioned at a second opposite end of the sidewall. The target assembly includes a target window, a target material deposited on the target window, and an anode positioned adjacent the target window. The anode is configured to accelerate a flow of electrons from the cathode toward the target material. The X-ray generating system an actuator configured to generate a stress in the sidewall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1-4  show example embodiments of the method and apparatus described herein. 
           [0007]      FIG. 1  is a side elevation view of an X-ray generator in accordance with an example embodiment of the present disclosure. 
           [0008]      FIG. 2  is a side elevation view of an X-ray generator in accordance with another example embodiment of the present disclosure. 
           [0009]      FIG. 3  is a side elevation view of an X-ray generator in accordance with another example embodiment of the present disclosure. 
           [0010]      FIG. 4  is a flow diagram of a method of generating a flow of 
           [0011]    X-rays. 
       
    
    
       [0012]    Although specific features of various embodiments may be shown in some drawings and not in others, this is for convenience only. Any feature of any drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
         [0013]    Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of the disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of the disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
       DETAILED DESCRIPTION 
       [0014]    The following detailed description illustrates embodiments of the disclosure by way of example and not by way of limitation. It is contemplated that the disclosure has general application to analytical and methodical embodiments of generating X-rays in a portable hand-held X-ray generator in industrial, commercial, and residential applications. 
         [0015]    The following description refers to the accompanying drawings, in which, in the absence of a contrary representation, the same numbers in different drawings represent similar elements. 
         [0016]      FIG. 1  is a side elevation view of an X-ray generator  100  in accordance with an example embodiment of the present disclosure. In the example embodiment, a cylindrical shaped X-ray chamber  102  includes a sidewall  104  that surrounds an evacuated volume  106 . Sidewall  104  is formed of a piezoelectric material sensitive to a compressive force applied in an axial direction  108  along a longitudinal axis  110  of X-ray generator  100 . The compressive force exerted over an area of an end face  111  of sidewall  104  defines a stress in sidewall  104 . 
         [0017]    X-ray chamber  102  includes a cathode  112  enclosing a first end of X-ray chamber  102 . Cathode  112  includes a generally planar cross-section and a charge concentrator  114  extending from a first face  115  of cathode  112 . In the example embodiment, charge concentrator  114  includes a triangular cross-section with an apex of the triangle extending farthest into volume  106 . A second opposite end of X-ray chamber  102  is enclosed by a window  116  formed of, for example, but, not limited to, beryllium. A target material  118 , such as, but, not limited to silver, rhodium, copper, tungsten, or combinations thereof, is deposited onto window  116  by, for example, a sputtering process. An anode  120  is positioned within evacuated volume  106  adjacent window  116 . 
         [0018]    During operation, a compressive force, typically in the form of an impulse or series of impulses is applied axially to sidewall  104 . The compressive force impulses cause the piezoelectric material of sidewall  104  to generate an electrostatic charge proportional to the stress exerted on sidewall  104  due to the input force. The electrostatic charge accumulates on charge concentrator  114  until the charge reaches a dielectric breakdown potential. A stream or burst of electrons  122  are then emitted from charge concentrator  114  and are accelerated towards anode  120 . A large number of electrons  122  strike target material  118  with enough energy to generate X-rays  124 , which continue outwardly from X-ray chamber  102  towards a sample material  126 . 
         [0019]    Piezoelectric ceramic under stress generates an electrical charge proportional to the applied stress, this charge accumulates on the outer electrodes to build up a voltage proportional to the stress and inversely proportional to capacitance between the electrodes. The voltage or electrical potential E can be found from equation (1): 
         [0000]        E=L·g   33   ·σ,   (1)
 
         [0000]    where
       E—output potential (V),   L—Piezoelectric Ceramic Length (m),       g33—Piezoelectric material constant (V·m/N), and   σ—Stress in Piezoelectric Ceramic (N/m 2 ).   
 
         [0024]    In an example: if, L=0.04 m, g33=25×10 −3  V·m/N and σ=1/6·amax=100×10 6  N/m 2 , E will be approximately 100 kV. Other combinations of the length of sidewall  104 , the piezoelectric constant of the material of sidewall  10 , and the amount of stress applied to sidewall  104  will provide other voltage output levels for sidewall  104 . The stress applied to sidewall  104  is controllable to provide a selectable output level. In various embodiments, a length  127  of sidewall  104  and the piezoelectric constant are selected to provide an output potential of between approximately 80 kV and approximately 120 kV with a stress applied that does not damage sidewall  104 . Stress in piezoelectric ceramic has limits and beyond those limits, the material will fracture. Due to the nature of the exemplary material, tensile and compression stress limits differ by about 18-20 times. Average tensile stress is 15-20×10 6  N/m 2  and compression stress is about 100-600×10 6  N/m 2 . 
         [0025]    The force is applied to sidewall  104  through an insulator  128  from an actuator  130 . In the example embodiment, insulator  128  is cylindrical about axis  110  and axially aligned with X-ray chamber  102 . Insulator  128  is formed of an insulative material that is also capable of transferring a compressive force from actuator  130  to sidewall  104 . In the example embodiment, insulator  128  is formed of alumina, for example, but not limited to Al 2 O 3 , Al 3 O 2 . A diode  132  facilitates recovering the potential across insulator  128 . In the example embodiment, diode  132  is illustrated in close proximity to insulator  128 , such as, positioned in a channel formed in insulator  128 . In various embodiments, diode  132  is positioned remotely from insulator  128  and coupled electrically between cathode  112  and a ground electrode  136  positioned between actuator  130  and insulator  128 . 
         [0026]    In the example embodiment, actuator  130  is embodied in a second piezoelectric ceramic material formed as a cylinder. An electrical source  137  is electrically coupled to actuator  130  through a conduit  138 . In one embodiment, electrical source  137  supplies electrical energy to actuator  130 . Actuator  130  deforms under the influence of the electrical energy to press on sidewall  104  through insulator  128 . In various embodiments, electrical source  137  supplies the electrical energy at approximately 150 volts to approximately 200 volts. In other embodiments, electrical source  137  supplies the electrical energy at approximately 75 volts to approximately 300 volts. In still other embodiments, electrical source  137  supplies the electrical energy at approximately 48 volts to approximately 440 volts. In various embodiments, electrical source  137  supplies the electrical energy at approximately 800 Hz to approximately 20 kHz. In other embodiments, electrical source  137  supplies the electrical energy at approximately 500 Hz to approximately 30 kHz. In still other embodiments, electrical source  137  supplies the electrical energy at approximately 200 Hz to approximately 40 kHz. In various embodiments, a frequency of the applied force is selected to coincide with a resonant frequency of X-ray generator  100 . 
         [0027]    In various embodiments, actuator  130  is other than a piezoelectric material. For example, actuator  130  is any device that can impart an axial force into sidewall  104 . Actuator  130  can be, for example, but not limited to an electric linear motor, mechanical oscillator, or other electrical device that converts electrical energy into motion or a force. Actuator  130  can also be pneumatic, hydraulic, or mechanical. In one embodiment, actuator  130  is a trigger-activated bias member that provides an impulse or series of impulses after the bias member has charged to a predetermined amount. 
         [0028]    A rigid outer shell  140  surrounds X-ray chamber  102 , insulator  128 , and actuator  130 . In the example embodiment, outer shell  140  is formed of a ceramic material. In various embodiments, outer shell  140  is formed of a metallic material. 
         [0029]      FIG. 2  is a side elevation view of an X-ray generator  100  in accordance with another example embodiment of the present disclosure. In the example embodiment, anode  120  includes a cylindrical axially extending portion  142  that accelerates stream of electrons  122  towards target material  118 , which in this embodiment is angled with respect to longitudinal axis  110 . In the example embodiment, window  116  is positioned radially outward from target material  118  in a sidewall  144  of anode  120 . 
         [0030]      FIG. 3  is a side elevation view of an X-ray generator  200  in accordance with an example embodiment of the present disclosure. In the example embodiment, X-ray generator  200  includes an X-ray chamber  202  including a sidewall  204  that surrounds an evacuated volume  206 . Sidewall  204  is formed of a piezoelectric material sensitive to a compressive force applied in an axial direction  208  along a longitudinal axis  210  of X-ray generator  200 . 
         [0031]    X-ray chamber  202  includes a cathode  212  enclosing a first end of X-ray chamber  202 . A second opposite end of X-ray chamber  202  is enclosed by a window  216  having a target material  218  deposited thereon. An anode  220  is positioned within evacuated volume  206  adjacent window  216 . A rigid outer shell  238  surrounds X-ray chamber  202 , an insulator  228 , and an actuator  230 . 
         [0032]    Actuator  230  includes a vibrator  240  and an energy storage device  242 . In the example embodiment, vibrator  240  is a mechanical vibrator and energy storage device  242  is, for example, but not limited to a spring. The spring may be charged using a trigger  244 , which is mechanically connected by a link  243  to energy storage device  242 . In some embodiments, a single pull of trigger  244  charges and discharges energy storage device  242 . In other embodiments, many pulls of trigger  244  are used to charge the spring until a predetermined amount of energy is stored. Energy storage device  242  is then discharged manually or automatically when the predetermined amount of energy is available. Vibrator  240  uses the stored energy to generate a series of vibrations or a single vibration or impulse, which is transmitted to sidewall  204  through insulator  228 , cathode  212 , and any other intervening components, such as, but not limited to a ground electrode (not shown in  FIG. 2 ). 
         [0033]    During operation, the vibrations or impulse is applied axially to sidewall  204 . The compressive vibrations or impulse cause the piezoelectric material of sidewall  204  to generate an electrostatic charge proportional to a stress caused by the input force of the vibrations or impulse. The electrostatic charge accumulates on cathode  212  until the charge reaches a dielectric breakdown potential. A stream or burst of electrons  222  are then emitted from cathode  212  and are accelerated towards an anode  220 . A large number of electrons  222  strike target material  218  with enough energy to generate X-rays  224 , which continue outwardly from X-ray chamber  202  towards a sample material  226 . 
         [0034]    In various embodiments, actuator may be electrical such as a motor with an eccentric wheel to generate vibrations, in which case energy storage device  242  could be a battery, a supercapacitor, or other electrical storage device. In other embodiments, is a fluid-driven vibrator, in which case energy storage device  242  could be a store of compressed gas, for example, but not limited to a CO 2  cartridge. Moreover, in some embodiments, actuator  230  or parts of actuator  230 , such as, vibrator  240  are formed around a radially outer surface of sidewall  204  and configured to impart a radially inward stress on sidewall  204  to generate liberate charge in the piezoelectric material. 
         [0035]    A pistol grip  246  facilitates X-ray generator  200  being a hand-held device and generating a high voltage operating voltage onboard X-ray generator  200  using stored energy or energy applied by a human operator permits use in remote locations. 
         [0036]      FIG. 4  is a flow diagram of a method  300  of generating a flow of X-rays. In the example embodiment, method  300  includes applying  302  a force to a piezoelectric sidewall of an X-ray chamber. In various embodiments, the force is applied using an actuator mechanically coupled to the sidewall. The force is applied axially or radially. Moreover, the force applied may be applied as a vibratory force occurring many times a second or may applied as an impulse force only one time with a relatively longer time between applications of the force. Method  300  further includes generating  304  an electric field in the piezoelectric sidewall relative to the applied force, and generating  306  a flow of electrons from a cathode of the X-ray chamber. Method  300  also includes accelerating  308  the flow of electrons towards a target, and generating  310  a flow of X-rays from the target using electrons from the flow of electrons that interact with the target. 
         [0037]    Method  300  further includes storing energy in a hand-held housing surrounding at least a portion of the X-ray chamber. The X-ray chamber is configured to be housed in a hand-held device that is self contained to convert a force generated in the actuator into a stress in the sidewall, which in turn generates charge in the sidewall. In various embodiments, energy used to power the actuator is stored onboard the hand-held device. In some embodiments, the energy is stored as electrical energy in, for example, but, not limited to, batteries and/or supercapacitors. In other embodiments, the energy is stored as mechanical energy in, for example, a spring or compressed fluid. In an embodiment, the energy stored is generated by a human user by, for example, charging the spring or squeezing a trigger mechanism to pressurize a fluid. 
         [0038]    The above-described embodiments of a method and system of generating X-rays using a hand-held X-ray generator provides a cost-effective and reliable means generating a stream of X-rays without external sources of energy or high voltage outside of the X-ray generator. More specifically, the methods and systems described herein facilitate generating a high voltage within an X-ray generating chamber. In addition, the above-described methods and systems facilitate providing an actuating force to the X-ray generating chamber from an actuator on-board the hand-held X-ray generator. As a result, the methods and systems described herein facilitate processes using X-rays in remote locations in a cost-effective and reliable manner. 
         [0039]    This written description uses examples to describe the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.