Systems and methods for controlling x-ray dosage

Abstract

Systems and methods for controlling the X-ray dosage by controlling anode current in the time domain are disclosed. In one of the aspects, a digitally switching X-ray emission system includes a digital switching unit operable to selectively connect a low voltage driving circuit to activate a field emission type electron emitting construct such that electrons are accelerated by a high gate voltage towards an anode target thereby generating a pulse of X-rays. The gate voltage is increased until a desired anode current is reached and PWM is used to slice the gate voltage in the time domain. The X-ray dose is controlled by slicing the anode current in time using PWM gate voltage.

Description

[0001] SYSTEMS AND METHODS FOR CONTROLLING X-RAY DOSAGE

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of priority from U.S. Provisional Patent Application No. 63 / 678,103, filed August 1 , 2025, the contents of which are incorporated by reference in their entirety.

[0004] FIELD OF THE DISCLOSURE

[0005] The disclosure herein relates to systems and methods for controlling X-ray dosage. In particular, but not exclusively, the disclosure relates to controlling the X-ray dose by controlling the anode current of the X- ray emitter device.

[0006] BACKGROUND

[0007] X-rays are created in X-ray tubes when electrons are accelerated towards an anode and hit the X- ray target on the anode at high kinetic energies. X-ray tubes conventionally use a filament as an electron emission element and use thermo-electrons emitted from the filament as an electron source. The emitted electrons interact with a bound electron of the target material and cause its ejection from the inner shell of the atom. Outer shell electrons then relax into this vacant energy level and release the energy difference as X- rays. The production of X-rays is conducted within a vacuum enclosure so that the electrons are not absorbed by the air before they strike the target material.

[0008] Controlled low dose X-ray is required in various X-ray applications such as for backscatter scanners used in security screening for example in handheld devices. Backscatter X-ray is an advanced X-ray imaging technology which detects the radiation that reflects from a target. However, flying-spot backscatter scanner which was earlier used in body scan at airports was prohibited for use considering public radiation safety concerns. It is still used in handheld applications. Some backscatter X-ray scanners can scan much larger objects, such as trucks and containers. This scan is much faster than a physical search and could potentially allow a larger percentage of shipping to be checked for smuggled items, weapons, drugs, or people.

[0009] In backscatter applications where low dose control is required in X-ray, the anode current is typically <100uA. In this operating range, almost 100% of the emission is redirected to the gate electrode while the emission is an exponential function of the gate voltage. It is difficult to measure such low return current with a portable High Voltage Power Supply (HVPS) in handheld device, and controlling gate voltage with precision employs costly circuit as well.

[0010] Further, it is difficult to control the anode current by adjusting gate voltage with any precision in the high gradient section of the graph of Gate Voltage vs Anode Current. It is also difficult to measure the anode current at such high voltage and such low current.

[0011] Therefore, there exists a need to control X-ray dose by controlling the anode current. Moreover, the effective anode current needs to be precisely calculated to allow the X-ray dosage to be known with enough precision to enable X-ray detection by back scattering. The present invention comes to address these needs.

[0012] SUMMARY OF THE EMBODIMENTS

[0013] It is therefore an object of the invention to control the X-ray dose by controlling anode current in the time domain by slicing a predetermined anode current in time using PWM of the gate voltage. The precise calculation of the effective anode current allows the X-ray dosage to be known with enough precision to enable Xray detection by back scattering.

[0014] The present disclosure provides systems and methods for precisely controlling a low-dose X-ray source and for transmitting digital information using an X-ray beam.

[0015] In a first aspect, the invention provides a system for controlling an X-ray dose. The system comprises an X-ray tube, which includes a cold cathode field emission electron source, a gate electrode, and an anode target. The system further includes a low voltage driver configured to provide a gate voltage to the gate electrode, a digital switching unit operatively connected to the low voltage driver and the gate electrode, and a controller. The controller is configured to perform a two-step process: first, it determines a gate voltage level that corresponds to a predetermined peak anode current (lp). Second, it controls the digital switching unit to modulate this gate voltage level with a pulse-width modulated (PWM) signal. This modulation effectively slices the predetermined peak anode current in the time domain to generate a controlled, lower effective anode current (le) and, consequently, a controlled X-ray dose. In some embodiments, the cold cathode field emission electron source is a Spindt type electron source. The system may be integrated as part of a handheld backscatter scanner.

[0016] In a further embodiment, the pulse-width modulated (PWM) signal comprises a series of gate pulses having a fixed pulse duration (5t1 ) generated at a regular interval (At). The system may further include a timer configured to generate a fixed clock signal for defining this regular interval (At). The fixed pulse duration (5t1) may be selected according to the relationship 5t1 = (le / lP)At, such that the effective anode current (le) is precisely determined by the formula le= (5t1 / At) * lP.

[0017] In another embodiment, the system further comprises a detector positioned to receive X-rays generated by the anode target, and a synchronizer. The synchronizer is configured to coordinate an acquisition signal for the detector with the pulse-width modulated (PWM) signal. This synchronization may be configured to enable either Synchronous detection or Heterodyne detection of the X-rays, thereby improving the signal-to-noise ratio. In embodiments where the detector comprises an optical imager, the synchronizer is configured to produce a controlled imaging rate.

[0018] A specific embodiment of the invention provides a system for controlling an X-ray dose comprising: an X-ray tube with a Spindt type cold cathode source; a low voltage driver; a digital switching unit; a timer generating a fixed clock signal; a detector, being an optical imager; a synchronizer; and a controller configured to determine the gate voltage for a peak current and then control the switching unit to modulate said gate voltage with a PWM signal composed of pulses with duration (5t1 ) at an interval (At) defined by the timer. The system may be part of a handheld backscatter scanner.

[0019] In another aspect, the invention provides a system for transmitting digital information. The system comprises the X-ray tube, low voltage driver, and digital switching unit. The controller in this aspect is configured to receive a digital data stream, generate a pulse-code modulated (PCM) gate signal based on said data stream, and control the digital switching unit according to the PCM signal, thereby encoding the digital information onto an X-ray beam. The controller may first determine a gate voltage for a predetermined peak anode current (lp), which the PCM signal then modulates. The system may be configured to establish a communication link to a satellite or to transmit information through an X-ray transparent medium, such as a metal wall or a concrete wall. The PCM gate signal may be generated using a line coding scheme that provides guaranteed signal transitions for clock recovery, such as a bipolar scheme like Alternate Mark Inversion (AMI) which produces a signal with substantially no DC component, or a self-clocking scheme like Delay Modulation where data is encoded by the timing of signal transitions.

[0020] In yet another aspect, the invention provides a system for controlling an X-ray dose which addresses the non-linear behavior of the source. The system comprises an X-ray tube where the source exhibits a nonlinear relationship between gate voltage and anode current. The system includes a current monitor configured to measure the anode current in real-time and generate a feedback signal. A controller is configured to receive a target anode current signal and execute an adaptive control algorithm. This algorithm dynamically adjusts the gate voltage based on the feedback signal to achieve the target current, thereby compensating for the non-linear relationship. In a further embodiment, the adaptive control algorithm comprises defining a plurality of quasi-linear operating regions within the non-linear relationship and applying a distinct set of control coefficients for each respective operating region to adjust the gate voltage. The invention further provides corresponding methods for the systems described above. A method for controlling an X-ray dose from an X-ray tube comprises the steps of: determining a gate voltage level corresponding to a predetermined peak anode current (lp); and modulating said gate voltage level with a PWM signal to slice the peak current, thereby generating a controlled effective anode current (le). The method may further include generating the PWM signal as a series of pulses, using a timer, and selecting the pulse duration based on the desired current ratio. The method can be performed in a handheld backscatter scanner. The method may also include detecting the X-rays and synchronizing an acquisition signal to enable Synchronous or Heterodyne detection, and to produce a controlled imaging rate if an optical imager is used.

[0021] A method for transmitting digital information using an X-ray system comprises the steps of: receiving a digital data stream; generating a PCM gate signal based on the data stream; and controlling a digital switching unit to apply the PCM signal to a gate electrode, thereby encoding the information onto the X-ray beam. The method may include the initial step of determining a gate voltage for a peak current, which is then modulated. The method may be used to establish a communication link to a satellite or transmit through a medium such as a metal wall or a concrete wall. The step of generating the PCM signal may involve using various line coding schemes, including bipolar or self-clocking schemes.

[0022] Finally, a method for controlling an X-ray dose from a tube with a non-linear response comprises the steps of: measuring an anode current in real-time to generate a feedback signal; comparing the feedback signal to a target current value; and executing an adaptive control algorithm to dynamically adjust a gate voltage based on the comparison, thereby compensating for the non-linear response to achieve the target current.

[0023] BRIEF DESCRIPTION OF THE FIGURES

[0024] For a better understanding of the embodiments and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings.

[0025] With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of selected embodiments only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects. In this regard, no attempt is made to show structural details in more detail than is necessary for a fundamental understanding; the description taken with the drawings making apparent to those skilled in the art how the various selected embodiments may be put into practice. In the accompanying drawings:

[0026] Fig. 1A illustrates a cross section through an example of a cold cathode X-ray tube 100 used for producing X-rays of the disclosure;

[0027] Fig. 1 B illustrates a graph 100’ of Gate Voltage vs Anode Current;

[0028] Fig. 2 is a block diagram representing selected elements of an embodiment of a switchable x-ray source;

[0029] Fig. 3 illustrates exemplary signal profiles of PWM gate signal and the anode current;

[0030] Fig. 4 illustrates exemplary signal profiles of PCM gate signal and the anode current;

[0031] Fig. 5 is a block diagram representing of another embodiments of a switchable X-ray source incorporating a synchronized detector and a closed-loop feedback mechanism;

[0032] Fig. 6 illustrates exemplary signal profiles of LV activation signal, HV gate signal and the acquisition signal which synchronizes to produce X-ray detection rate;

[0033] Fig. 7 is a flowchart illustrating an exemplary method for transmitting digital information using an X- ray system according to an embodiment of the disclosure; Fig. 8 is a flowchart illustrating an exemplary method and its alternative embodiments for controlling an X-ray source, corresponding to the methods claimed herein; and

[0034] Fig. 9 is a simplified, conceptual schematic of a closed-loop driver circuit used to provide fast, adaptive control of the gate voltage in accordance with an embodiment of the disclosure.

[0035] DETAILED DESCRIPTION

[0036] Aspects of the current disclosure relate to systems and methods for controlling X-ray dose by controlling anode current in the time domain by slicing a predetermined anode current in time using Pulse Width Modulation (PWM) of the gate voltage. This is enabled by the use of a switchable cold cathode field emission array electron source. The system may be calibrated by increasing gate voltage until a desired anode current is reached and then using PWM to slice this gate voltage in time.

[0037] Furthermore, the gate voltage signal can be synchronized with an acquisition signal of a detector such that Synchronous or Heterodyne detection is enabled for X-rays at frequencies in the kHz / MHz range which is only possible with FEA sources.

[0038] Additionally, X-ray Pulse Code Modulation (PCM) may be used to encode signals into the sliced gate voltage signal, such that the low power tube can transmit X-ray digital PCM signals.

[0039] In various embodiments of the disclosure, one or more tasks as described herein may be performed by a data processor, such as a computing platform or distributed computing system for executing a plurality of instructions. Optionally, the data processor includes or accesses a volatile memory for storing instructions, data or the like. Additionally, or alternatively, the data processor may access a non-volatile storage, for example, a magnetic hard-disk, flash-drive, removable media or the like, for storing instructions and / or data.

[0040] It is particularly noted that the systems and methods of the disclosure herein may not be limited in its application to the details of construction and the arrangement of the components or methods set forth in the description or illustrated in the drawings and examples. The systems and methods of the disclosure may be capable of other embodiments, or of being practiced and carried out in various ways and technologies.

[0041] Alternative methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the disclosure. Nevertheless, particular methods and materials are described herein for illustrative purposes only. The materials, methods, and examples are not intended to be necessarily limiting.

[0042] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0043] Reference is now made to Fig. 1 A which is a schematic cross section representation of an example of an x-ray vacuum tube 100 used for producing X-rays according to an aspect of the disclosure.

[0044] The x-ray vacuum tube 100 includes a cold cathode electron source 102, a gate electrode 104 and a target anode 106 all held within a sealed glass chamber 108 from which most of the air has been evacuated.

[0045] A beam of electrons may be produced by the cold cathode electron source 102 and directed towards a focal point on the anode target 106 such that x-rays may be produced.

[0046] The cold cathode electron source 102 may be a field array emission chip such as a gated cone electron source having cones (“emitter tips”) arranged in an array, each emitter tip being surrounded by an opening in the gate electrode (a “gate hole”), a Spindt type electron source, a carbon nanotube (CNT) type electron source, a metal-insulator-metal (MIM) type electron source or a metal-insulator-semiconductor (MIS) type electron source. In particular embodiments, the electron source may be a Spindt type electron source.

[0047] Referring to Fig. 1 B which illustrates a graph 100’ of Gate Voltage vs Anode Current. Initially, the anode current la is very low but increases exponentially with the increase of gate voltage Vg. The anode current in low dose applications like backscatter scanning is typically <100uA. In this operating range, almost 100% of the emission is redirected to the gate while the emission is an exponential function of the gate voltage.

[0048] Fig. 2 is a block diagram representing selected elements of an embodiment of a switchable X-ray source 200. The digitally switchable X-ray emission system 200 includes an electron emitter 204, an anode target 206, a high voltage supply 208, a low voltage driver 212, a switching unit 214 a controller 216 and a timer 218.

[0049] The electron emitter 204 may be a cold cathode such as a low voltage activated field emission type electron emitting construct configured and operable to release electrons when stimulated by a low voltage. Accordingly, the low voltage driver 212 may include a low voltage driving circuit for activating the electron emitting construct.

[0050] The anode target 206 may comprise a metallic target selected such that X-rays 210 are generated when it is bombarded by accelerated electrons from the electron emitter 204. The anode 206 may be constructed of molybdenum, rhodium, tungsten, or the like or combinations thereof.

[0051] The high voltage supply 208 wired between said electron emitting construct 204 and the anode 206 is provided for establishing an electron accelerating potential between said electron emitting construct 204 and the anode 206.

[0052] It is a particular feature of the digitally switchable X-ray emission system 200 that the digital switching unit 214 is provided to selectively connect and disconnect the low voltage driving circuit 212 thereby selectively activating and deactivating the electron emitting construct 204. Accordingly, emission of the electrons may be controlled by the digital switching system 214.

[0053] When the emitting construct 204 is activated, electrons are accelerated towards said anode target 206 and a pulse of X-rays 210 is generated. As a result, X-ray emission from the anode 206 may be controlled digitally by the switching unit 214.

[0054] The controller 216 may be provided to generate an activation signal which can control the switching rate of the digital switching unit 214. It is particularly noted that in contrast to high voltage switching systems, because the activation signal is a low voltage signal, the response time of the electron emitter is much shorter than the response time of switching the high voltage accelerating potential.

[0055] As a result of the reduced response time of the low voltage switching unit, a timer 218 may be provided to generate a fixed clock signal and a high frequency activation signal may be provided consisting of a series of short duration gate pulses at regular intervals.

[0056] The coordinated electrical activation of the driving circuit 212 and the electron emitter 204 results in its activation, i.e., electron emission 220. The activation signal may comprise a series of pulses generated at a regular intervals At and having a fixed pulse duration 5t1 . Accordingly, the electron emission 220 may follow a similar regular pattern of emission as shown in Fig. 3.

[0057] The gate signal from the emitter is modulated by the activation signal to produce Pulse Width Modulated (PWM) gate signal 302. The PWM gate signal comprise a series of gate pulses generated at regular intervals At and having a fixed gate-pulse duration 5t1 . A predetermined anode current Ip is achieved by increasing the gate voltage in accordance with the graph of Fig. 1 B. The anode current Ip is then sliced in time domain using PWM gate voltage. The anode current in applications such as backscatter scanning is typically <100uA. The plot of predetermined anode current Ip 304 in time is shown. The X-ray dose is controlled by slicing the anode current Ip 304 in time using PWM of the gate voltage 302. An effective anode current le 306 is given by the product of the predetermined anode current Ip and the ratio of the gate-pulse duration 5t1 and the regular interval At, Ie=(5t1 / At)*lp. The effective anode current 306 represents the current which effectively generated the X-ray pulses with the applied gate voltage over time. The precise calculation of the effective anode current le allows the X-ray dosage to be known with enough precision to enable X-ray detection by back scattering. Accordingly, for any required X-ray dosage, a corresponding required effective current le may be determined and a fixed gate-pulse duration 5t1 selected according to the formula: 5t1=(le / lp)At.

[0058] In an additional embodiment of the present invention, the system's capability for high-speed digital switching may be leveraged to transmit information, wherein X-ray Pulse Code Modulation (PCM) is used to encode a digital data stream into the sliced gate voltage signal, as illustrated in Fig. 4. The gate signal is pulse code modulated to produce the PCM gate signal 402, which in turn modulates the X-ray emission. The X-ray dose is thereby controlled by slicing the predetermined anode current lp404 in time using this PCM gate voltage signal 402.

[0059] The system can be configured to use any of a variety of known line coding schemes to generate the PCM gate signal, depending on the requirements of the communication channel. For instance, a simple Non- Return-to-Zero-Level (NRZ-L) waveform may be used, where a high voltage level represents a binary '1' and a low voltage level represents a binary 'O'. While conceptually simple, NRZ-L can present challenges in practical systems, as long sequences of identical bits (e.g., '111111 ' or '000000') produce no signal transitions, which can lead to a loss of clock synchronization at the receiver.

[0060] To address these limitations, more robust line coding schemes may be implemented by the controller. These schemes are designed to guarantee signal transitions for reliable clock recovery and to manage the signal's DC component. Such schemes include:

[0061] • Return-to-Zero (RZ) schemes: In these codes, the signal level returns to zero in the middle of each bit period. In Unipolar RZ, a binary '1 ' is represented by a pulse for the first half of the bit period followed by a return to zero, guaranteeing a transition for every '1 '.

[0062] • Bipolar RZ and Alternate Mark Inversion (RZ-AMI): These advanced bipolar schemes represent a binary 'O' with zero voltage and encode binary '1 's (or "marks") with alternating positive and negative voltage pulses. This alternating polarity ensures that the net DC component of the signal is zero, which is highly advantageous for many communication systems. Furthermore, this provides an inherent mechanism for error detection, as the reception of two consecutive pulses of the same polarity would indicate a transmission error.

[0063] • Delay Modulation (Miller Code): This is a self-clocking technique where data is encoded by the timing of the transitions themselves. A transition in the middle of a bit period indicates a '1 ', while the presence or absence of a transition at the end of the bit period encodes a 'O'. The resulting signal contains sufficient timing information for the receiver to robustly extract the clock signal directly from the data stream.

[0064] The flexibility of the system's digital control architecture allows for the implementation of any of these PCM techniques, thereby enabling the X-ray source to function as a robust data transmitter for applications such as secure communication links to satellites or through X-ray transparent media like metal or concrete walls.

[0065] In this way PCM modulated signals may be transmitted via x-ray carrier waves which may be useful for communication links to satellites or through x-ray transparent media such as metal or concrete walls or the like.

[0066] Accordingly, an x-ray signal transmission system is disclosed including a PCM unit for encoding signals into a carrier x-ray produced by an x-ray vacuum tube includes a cold cathode electron source, a switchable gate electrode and a target anode all held within a sealed glass chamber from which most of the air has been evacuated.

[0067] Referring now to the block diagram of Fig. 5, which represents another embodiment of a switchable X-ray source 500 incorporating a synchronized detector 528. The system includes an X-ray source 506 which emits X-rays 510 that may be directed towards a detector 528 for detecting, for example, backscattered X- rays. The operation of the system 500 is coordinated by a controller 516 and a synchronizer 522, which manage a high voltage (HV) signal 520, a low voltage (LV) activation signal 518, and an acquisition signal 524.

[0068] The individual roles of these signals are as follows:

[0069] • The high voltage signal 520, produced by the high voltage supply 508, determines the characteristics of the high voltage amplitude of the electron accelerating potential.

[0070] • The low voltage signal 518 determines the characteristics of the switching rate of the digital switching unit 514, which in turn activates the low voltage driver 512 to produce the activation potential for the electron emitting construct 504.

[0071] • The acquisition signal 524 determines the sampling rate of the detector 528.

[0072] The synchronizer 522 is operable to coordinate the signal profiles of the HV signal 520, the LV signal 518, and the acquisition signal 524 to achieve precise control over the entire X-ray device 500.

[0073] In a preferred embodiment, the controller 516 is configured to implement a closed-loop, adaptive control algorithm to achieve a fast and stable response. It is recognized that the relationship between the gate voltage and the resulting anode current is highly non-linear, as illustrated in Fig. 1 B. This non-linearity prevents the effective use of classical control algorithms, such as a standard Proportional-lntegral-Derivative (PID) controller, across the full operating range of the device.

[0074] To overcome this, as shown in Fig. 5, the system includes a current monitor 530 operatively connected to the electron emitter 504. The current monitor 530 measures the anode current and / or gate current in real-time and generates a feedback signal 532, which is sent to the controller 516. The controller utilizes an adaptive control strategy to manage the gate voltage based on this feedback. In one implementation, this strategy involves dividing the non-linear voltage-to-current response curve into a plurality of quasi-linear regions and storing a set of pre-determined control coefficients for each region, for instance in a look-up table (LUT). When operating within a specific region, the controller applies the corresponding coefficients to rapidly and accurately converge on the target current. This adaptive, gain-scheduling approach allows the system to maintain stability and achieve a fast response time despite the inherent non-linearity of the electron source.

[0075] A key advantage of this synchronized architecture is that it enables advanced detection schemes for X-rays at frequencies in the kHz / MHz range, which is only possible with FEA sources. The choice between implementing synchronous or heterodyne detection is determined by the specific configuration programmed into the controller 516 and synchronizer 522.

[0076] • For synchronous detection (also known as phase-sensitive or lock-in detection), the synchronizer 522 ensures that the acquisition signal 524 is generated at the exact same frequency and phase as the LV activation signal 518. The signal from the detector is then passed through a low-pass filter to extract the signal's amplitude from a high-noise environment, based on the frequency relationship: f acquisition=fx-ray-

[0077] • For heterodyne detection, the synchronizer 522 generates the acquisition signal 524 to act as a local oscillator (LO) signal, with a frequency intentionally offset from the X-ray modulation frequency by a precise, stable intermediate frequency (IF), based on the relationship: / acquisition = fx-ray + fip. The output from the detector is then passed through a sharp band-pass filter centered at the IF to recover the signal.

[0078] The flexibility of the system's digital control architecture allows the controller 516 to be programmed for either detection mode by controlling the frequency and phase relationships between the LV activation signal 518 and the acquisition signal 524. Fig. 6 illustrates exemplary signal profiles of the LV activation signal, HV gate signal, and the acquisition signal which are synchronized to produce an X-ray detection rate. In a particular embodiment where the detector 528 is an optical imager, this X-ray detection rate corresponds to a controlled imaging rate of the X-ray device.

[0079] Reference is now made to FIG. 7, which illustrates a flowchart of an exemplary method 700 for transmitting digital information using the X-ray system of the present disclosure. This method enables the X- ray source to function as a data transmitter, encoding a digital data stream onto the emitted X-ray beam.

[0080] The method 700 may begin with an optional but preferred calibration step 702, wherein the controller first determines the gate voltage level required to produce a known, predetermined peak anode current (lp). This step establishes the maximum signal amplitude for the "on" state of the digital signal, ensuring a consistent and predictable X-ray flux for each pulse.

[0081] In step 704, the controller receives a digital data stream that is intended for transmission. This data stream comprises a sequence of binary bits (1s and 0s).

[0082] Next, in step 706, the controller processes this data stream to generate a corresponding pulse-code modulated (PCM) gate signal. This step involves selecting an appropriate line coding scheme to convert the binary data into a physical voltage waveform. As previously described, this scheme may be chosen from various known techniques, such as a bipolar scheme like Alternate Mark Inversion (AMI) to eliminate any DC component, or a self-clocking scheme like Delay Modulation to ensure robust clock recovery at the receiver.

[0083] In step 708, the controller uses the generated PCM gate signal to control the digital switching unit. The switching unit, in turn, applies the modulated voltage waveform to the gate electrode of the X-ray tube.

[0084] Finally, in step 710, the application of the PCM gate signal to the gate electrode modulates the emission of electrons from the cold cathode source, thereby modulating the resulting X-ray beam. The sequence of X-ray pulses and absences directly corresponds to the original digital data stream, thus encoding the information onto the X-ray beam for transmission. This method may be employed to establish a communication link across various media, including to a satellite or through materials such as metal or concrete walls.

[0085] Reference is now made to FIG. 8, which provides a flowchart for an exemplary method 800 of operating the X-ray system, illustrating the primary control method and its key alternative embodiments. The method demonstrates the versatility of the system's digital controller in performing distinct functions such as precise dose control and data transmission.

[0086] The method begins at step 802, where an initial calibration may be performed. In this step, the controller determines the gate voltage level required to produce a predetermined peak anode current (lp). This establishes a consistent and known baseline for the maximum X-ray emission intensity.

[0087] Following the initial setup, the method proceeds to a decision block 804, which represents the selection of an operating mode. Depending on the application, the system can be configured for either dose control or data transmission.

[0088] If the system is configured for dose control, the method follows the path to step 806. Here, the controller modulates the established gate voltage using a Pulse-Width Modulated (PWM) signal. This PWM signal is preferably composed of a series of pulses with a fixed duration (5t1) occurring at a regular interval (At), thereby slicing the peak anode current in the time domain. The result, shown in step 808, is the generation of a precisely controlled, lower effective anode current and a correspondingly controlled X-ray dose.

[0089] From this dose control mode, a further operational choice is presented at decision block 810. If the application requires synchronized detection, the "Yes" path is taken to step 812. In this step, the acquisition signal of an associated detector is synchronized with the PWM signal from the X-ray source. This synchronization enables advanced, high-sensitivity detection schemes, such as Synchronous or Heterodyne detection, and can be used to establish a controlled imaging rate when the detector is an optical imager. If synchronization is not required, the "No" path is taken, and the process concludes.

[0090] Alternatively, if the system is configured for data transmission at decision block 804, the method follows the path to step 814. In this mode, the controller modulates the gate voltage using a Pulse-Code Modulated (PCM) signal that is generated from a digital data stream. The subsequent step, 816, shows the outcome: the X-ray beam is modulated according to the PCM signal, thereby encoding and transmitting the digital information, for example, through an X-ray transparent medium to a satellite.

[0091] The entire method 800, in any of its embodiments, may be advantageously implemented within a portable device, such as a handheld backscatter scanner.

[0092] Reference is now made to FIG. 9, which illustrates a simplified, conceptual schematic of a closed- loop driver and control circuit 900. This circuit embodies the principles of the fast-response feedback loop used to precisely control the gate voltage of the X-ray tube. It is to be understood that FIG. 9 is a functional representation, and a practical implementation may include additional components for protection, stabilization, and signal conditioning.

[0093] The core of the circuit is the Driver & Control Logic 902. This functional block represents the combination of signal processing and power amplification stages. In a practical embodiment, this logic may be implemented using operational amplifiers such as an LM358 for processing feedback signals and a power operational amplifier like an OPA547 for the final output driver stage, capable of providing the necessary current to drive the gate electrode quickly.

[0094] The circuit receives several inputs. The Gate Voltage Command 904 is a setpoint signal, typically provided by the main system controller (e.g., 516 in Fig. 5), which represents the desired gate voltage. The circuit also receives Feedback Signals 906, which are real-time measurements of the X-ray tube's operating state. This may include, for example, a signal proportional to the measured gate current or anode current.

[0095] The output of the circuit is the Gate Drive Signal 908, which is the final, conditioned voltage applied to the gate electrode of the X-ray tube.

[0096] Another aspect of the circuit is that a fast closed-loop feedback path may be provided in addition to or alternatively to digital logic or software. The fast closed-loop feedback path may include discrete and nonactive components for gain control, pulse shaping, such as resistors, capacitors, inductors and the like. The output signal 908 is fed back to an input of the control logic 902 through a network that may include a feedback resistor (R_f 910) and a feedback capacitor (C_f 912). This feedback loop allows the circuit to continuously compare the actual output state with the command signal 904 and make instantaneous corrections.

[0097] Furthermore, the feedback components are crucial for shaping the output pulse. The feedback capacitor C_f 912, in particular, influences the slew rate of the amplifier. By carefully selecting the value of C_f, the circuit can precisely control the rise and fall times of the Gate Drive Signal 908. This pulse-shaping capability is critical for generating clean, well-defined pulses for the PWM and PCM modulation schemes, minimizing overshoot and ringing, and ensuring reliable operation at high frequencies. This fast, feedback- controlled, and shaped driving signal is what enables the controller to effectively execute the adaptive control algorithms needed to manage the non-linear behavior of the electron emitter.

[0098] As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its essential characteristics. The present embodiments are, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within therefore intended to be embraced therein. Technical and scientific terms used herein should have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. Nevertheless, it is expected that during the life of a patent maturing from this application many relevant systems and methods will be developed. Accordingly, the scope of the terms such as computing unit, network, display, memory, server and the like are intended to include all such new technologies a priori.

[0099] As used herein the term “about” refers to at least ± 10 %.

[0100] The terms "comprises", "comprising", "includes", "including", “having” and their conjugates mean "including but not limited to" and indicate that the components listed are included, but not generally to the exclusion of other components. Such terms encompass the terms "consisting of" and "consisting essentially of".

[0101] The phrase "consisting essentially of' means that the composition or method may include additional ingredients and / or steps, but only if the additional ingredients and / or steps do not materially alter the basic and novel characteristics of the claimed composition or method.

[0102] As used herein, the singular form "a", "an" and "the" may include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

[0103] The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or to exclude the incorporation of features from other embodiments.

[0104] The word “optionally” is used herein to mean “is provided in some embodiments and not provided in other embodiments”. Any particular embodiment of the disclosure may include a plurality of “optional” features unless such features conflict.

[0105] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging / ranges between” a first indicate number and a second indicate number and “ranging / ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween. It should be understood, therefore, that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 3, 4, 5, and 6 as well as non-integral intermediate values. This applies regardless of the breadth of the range.

[0106] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the disclosure. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments unless the embodiment is inoperative without those elements.

[0107] Although the disclosure has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present disclosure. To the extent that section headings are used, they should not be construed as necessarily limiting.

[0108] The scope of the disclosed subject matter is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.

Claims

CLAIMS1 . A system for controlling an X-ray dose, the system comprising: a. an X-ray tube comprising a cold cathode field emission electron source, a gate electrode, and an anode target; b. a low voltage driver configured to provide a gate voltage to the gate electrode; c. a digital switching unit operatively connected to the low voltage driver and the gate electrode; and d. a controller configured to: i. determine a gate voltage level corresponding to a predetermined peak anode current (lp); and ii. control the digital switching unit to modulate said gate voltage level with a pulse-width modulated (PWM) signal, thereby slicing the predetermined peak anode current in the time domain to generate a controlled effective anode current (le) and a corresponding controlled X-ray dose.

2. The system of claim 1 , wherein the pulse-width modulated (PWM) signal comprises a series of gate pulses having a fixed pulse duration (5t1) generated at a regular interval (At).

3. The system of claim 2, further comprising a timer configured to generate a fixed clock signal for defining the regular interval (At) of the gate pulses.

4. The system of claim 2, wherein the fixed pulse duration (5t1) is selected such that the effective anode current (le) is determined by le= (5t1 / At) * lP.

5. The system of claim 1 , wherein the controller is further configured to control the digital switching unit to modulate the gate voltage level with a pulse-code modulated (PCM) signal to encode a digital signal into the X-ray dose.

6. The system of claim 5, wherein the PCM modulated signal is transmitted via X-ray carrier waves for communication through X-ray transparent media.

7. The system of claim 1 , further comprising: a. a detector positioned to receive X-rays generated by the anode target; and b. a synchronizer configured to coordinate an acquisition signal for the detector with the pulse-width modulated (PWM) signal.

8. The system of claim 7, wherein the synchronizer is configured to synchronize the acquisition signal and the PWM signal to enable Synchronous detection of the X-rays.

9. The system of claim 7, wherein the synchronizer is configured to synchronize the acquisition signal and the PWM signal to enable Heterodyne detection of the X-rays.

10. The system of claim 7, wherein the detector comprises an optical imager and the synchronizer is configured to produce a controlled imaging rate.11 . The system of claim 1 , wherein the cold cathode field emission electron source is a Spindt type electron source.

12. The system of claim 1 , wherein the system is part of a handheld backscatter scanner.

13. A system for controlling an X-ray dose, the system comprising: a. an X-ray tube comprising a Spindt type cold cathode field emission electron source, a gate electrode, and an anode target; b. a low voltage driver configured to provide a gate voltage to the gate electrode; c. a digital switching unit operatively connected to the low voltage driver and the gate electrode; d. a timer configured to generate a fixed clock signal; e. a detector, being an optical imager, positioned to receive X-rays generated by the anode target; f. a synchronizer; andg. a controller configured to:I. determine a gate voltage level corresponding to a predetermined peak anode current; and ii. control the digital switching unit to modulate said gate voltage level with a pulse-width modulated (PWM) signal, the PWM signal comprising a series of gate pulses having a fixed pulse duration (5t1) generated at a regular interval (At) defined by the fixed clock signal from the timer, thereby slicing the predetermined peak anode current in the time domain to generate a controlled effective anode current (le) and a corresponding controlled X-ray dose.

14. The system of claim 13, wherein the synchronizer is configured to synchronize an acquisition signal for the detector with the PWM signal to enable Synchronous detection of the X-rays.

15. The system of claim 13, wherein the synchronizer is configured to synchronize an acquisition signal for the detector with the PWM signal to enable Heterodyne detection of the X-rays.

16. The system of claim 13, wherein the system is part of a handheld backscatter scanner.

17. The system of claim 13, wherein the fixed pulse duration (5t1) is selected such that 5t1 = (le / lP)At.

18. A method for controlling an X-ray dose from an X-ray tube, the X-ray tube comprising a cold cathode field emission electron source, a gate electrode, and an anode target, the method comprising: a. determining a gate voltage level corresponding to a predetermined peak anode current (lp); and b. modulating said gate voltage level with a pulse-width modulated (PWM) signal to slice the predetermined peak anode current in the time domain, thereby generating a controlled effective anode current (le) and a corresponding controlled X-ray dose.

19. The method of claim 18, wherein the step of modulating comprises generating the pulse-width modulated (PWM) signal as a series of gate pulses having a fixed pulse duration (5t1) at a regular interval (At).

20. The method of claim 19, further comprising selecting the fixed pulse duration (5t1) such that 5t1 = (le / lP)At.21 . The method of claim 19, further comprising using a timer to generate a fixed clock signal to define the regular interval (At) of the gate pulses.

22. The method of claim 18, further comprising modulating the gate voltage level with a pulse-code modulated (PCM) signal to encode a digital signal into the X-ray dose.

23. The method of claim 22, further comprising transmitting the encoded digital signal via X-ray carrier waves for communication through X-ray transparent media.

24. The method of claim 18, further comprising: a. detecting the X-rays generated by the anode target using a detector; and b. synchronizing an acquisition signal for the detector with the pulse-width modulated (PWM) signal.

25. The method of claim 24, wherein the step of synchronizing enables Synchronous or Heterodyne detection of the X-rays.

26. The method of claim 24, wherein the detector is an optical imager and the step of synchronizing produces a controlled imaging rate.

27. The method of claim 18, wherein the method is performed within a handheld backscatter scanner.

28. An X-ray system for transmitting digital information, the system comprising: a. an X-ray tube comprising a cold cathode field emission electron source, a gate electrode, and an anode target; b. a low voltage driver configured to provide a gate voltage to the gate electrode; c. a digital switching unit operatively connected to the low voltage driver; and d. a controller configured to: i. receive a digital data stream; ii. generate a pulse-code modulated (PCM) gate signal based on said digital data stream; andiii. control the digital switching unit according to the PCM gate signal, thereby encoding the digital information onto an X-ray beam produced by the X-ray tube.

29. The system of claim 28, wherein the controller is configured to generate the PCM gate signal using a line coding scheme that provides guaranteed signal transitions for clock recovery at a receiver.

30. The system of claim 29, wherein the line coding scheme is a bipolar scheme, such as Alternate Mark Inversion (AMI), that encodes binary Ts with pulses of alternating polarity, thereby producing a signal with substantially no DC component.

31. The system of claim 29, wherein the line coding scheme is a self-clocking scheme, such as Delay Modulation, wherein the digital data stream is encoded by the timing of signal transitions.

32. The system of claim 28, wherein the controller is further configured to first determine a gate voltage level corresponding to a predetermined peak anode current (lp), and wherein the PCM gate signal modulates said gate voltage level.

33. The system of claim 28, wherein the system is configured to establish a communication link to a satellite.

34. The system of claim 28, wherein the system is configured to transmit the digital information through an X-ray transparent medium.

35. The system of claim 34, wherein the X-ray transparent medium is a metal wall.

36. The system of claim 34, wherein the X-ray transparent medium is a concrete wall.

37. A method for transmitting digital information using an X-ray system, the method comprising: a. receiving a digital data stream; b. generating a pulse-code modulated (PCM) gate signal based on said digital data stream; and c. controlling a digital switching unit to apply the PCM gate signal to a gate electrode of an X-ray tube, thereby modulating an X-ray beam produced by the X-ray tube to encode the digital information onto said beam.

38. The method of claim 37, wherein the step of generating the PCM gate signal comprises using a line coding scheme that provides guaranteed signal transitions for clock recovery at a receiver.

39. The method of claim 38, wherein the line coding scheme is a bipolar scheme, such as Alternate Mark Inversion (AMI), that encodes binary 'Ts with pulses of alternating polarity, thereby producing a signal with substantially no DC component.

40. The method of claim 38, wherein the line coding scheme is a self-clocking scheme, such as Delay Modulation, wherein the digital data stream is encoded by the timing of signal transitions.

41. The method of claim 37, further comprising the initial step of: determining a gate voltage level corresponding to a predetermined peak anode current (lp), wherein the generated PCM gate signal modulates said gate voltage level.

42. The method of claim 37, wherein the method is used to establish a communication link to a satellite.

43. The method of claim 37, further comprising transmitting the encoded digital information through an X-ray transparent medium.

44. The method of claim 43, wherein the X-ray transparent medium is a metal wall or a concrete wall.

45. A system for controlling an X-ray dose, the system comprising: a. an X-ray tube comprising a cold cathode field emission electron source, a gate electrode, and an anode target, wherein the source exhibits a non-linear relationship between a gate voltage applied to the gate electrode and a resulting anode current; b. a current monitor configured to measure the anode current in real-time and generate a feedback signal; and c. a controller configured to: i. receive a target anode current signal; andii. execute an adaptive control algorithm that dynamically adjusts the gate voltage based on the feedback signal from the current monitor to achieve the target anode current, wherein the algorithm is configured to compensate for the non-linear relationship.

46. The system of claim 45, wherein the adaptive control algorithm comprises: a. defining a plurality of quasi-linear operating regions within the non-linear relationship; and b. applying a distinct set of control coefficients for each respective operating region to adjust the gate voltage.

47. A method for controlling an X-ray dose from an X-ray tube having a non-linear voltage-to-current response, the method comprising: a. measuring an anode current in real-time to generate a feedback signal; b. comparing the feedback signal to a target anode current value; and c. executing an adaptive control algorithm to dynamically adjust a gate voltage based on said comparison, thereby compensating for the non-linear response to achieve the target anode current.

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