Triboelectric vibration sensor

Abstract

A triboelectric vibration sensor comprises a first electrode 906 moveable relative to a second electrode 908, wherein the first electrode includes a charge-generating layer (104, figure 7) and the second electrode includes a charge-collecting layer. A charge-measuring component is connected to the first and second electrodes and is configured to measure charge generated when the first and second electrodes move relative to one another. An electric field-generating component 902, 904 is configured to generate and control an external electric field based on the charge measured, by controlling the external electric field so as to stabilise the charge measured by the charge-measuring component. A vibration measurement output component is configured to output a parameter based on the external electric field as a vibration measurement. In embodiments, the electric field-generating component is a pair of electrodes that control the capacitance of the TENG layers and produce a constant output voltage.

Description

CROSS-REFERENCE(S) TO RELATED APPLICATIONS This application claims priority from United Kingdom patent application number 2316463.5 filed on 27 October 2023, which is incorporated by reference herein. FIELD OF THE INVENTION The invention relates to vibration sensors. BACKGROUND TO THE INVENTION Vibrations are an inevitable phenomenon occurring in structures and machines, especially when the structure or machine is prone to experiencing external forces. Typically, vibrations are enhanced at connection points, such as joints, between two or more parts of the structure. Vibrations can have irregular patterns in which each phase may have a different amplitude, frequency, and intensity. Although not ideal, irregular vibratory patterns are typically not of great concern. Nevertheless, vibrations can be concerning when they build into oscillations. Oscillations have a dangerous characteristic whereby they may continually become more intense and stronger with each phase until the oscillations may become uncontrollable and the structure breaks or sustains other permanent damages. In mechanical devices, various factors such as engine operations, propeller rotation, aerodynamic forces, landing gear deployment, friction, inefficiencies, and the like, can cause vibrations. These vibrations can induce mechanical stress and fatigue in the structure which will eventually lead to cracks, fractures, or component failures. Moreover, vibrations can interfere with the accuracy and functionality of sensitive instruments and systems such as navigation, communications, control, durability, precision, measurement, and the like. Therefore, monitoring, measuring, and predicting these vibrations in a device, mechanism, apparatus, or structure during operation is essential to ensure their longevity. It can be difficult to implement vibration sensors over the entire body of devices or mechanisms which require a relatively light total body weight, such as in aircrafts and smaller airborne crafts such as unmanned aerial vehicles (UAVs). The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY OF THE INVENTION In accordance with an aspect of the invention there is provided a triboelectric vibration sensor comprising: a first electrode moveable relative to a second electrode, wherein the first electrode includes a charge-generating layer and the second electrode includes a charge-collecting layer; a charge-measuring component connected to the first and second electrodes and configured to measure charge generated when the first and second electrodes move relative to one another; an electric field-generating component configured to generate and control an external electric field based on the charge measured by the charge-measuring component, wherein the electric field-generating component is configured to control the external electric field so as to stabilise the charge measured by the charge-measuring component; and, a vibration measurement output component configured to output a parameter based on the external electric field as a vibration measurement. The parameter may be a potential difference value corresponding to a potential difference supplied to the electric field-generating component so as to control the external electric field to stabilise the charge measured by the charge-measuring component. The electric field-generating component may include a pair of external electrodes connected to a variable voltage source. The external electric field may be controlled to adjust a capacitance of a dielectric medium between the first and second electrodes. The capacitance may be tuned such that the charge-measuring component may output a desired stabilised charge signal. The first and second electrodes may be the charge-generating and charge-collecting layers of a triboelectric nanogenerator (TENG), respectively. The triboelectric vibration sensor may include a potential-measuring component which may be configured to measure a potential difference supplied to the electric field-generating component to control the external electric field so as to stabilise the charge measured by the chargemeasuring component. The triboelectric vibration sensor may include a feedback component which may be configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge. The feedback component may be configured to adjust the potential difference to reduce an error between a reference voltage and the measured charge. The potential-measuring component, charge-measuring component, feedback component, and electric field-generating components may form part of a voltage stabilisation component. The charge-measuring component may be configured to measure charge generated from the first and second electrodes when they move relative to one another. The electric field-generating component may be configured to generate an electric field based on the measured charge to stabilise the generated charge. The potential-measuring component may be configured to measure the potential difference supplied to the electric field-generating component. The feedback component may be configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge such that the error between the reference voltage and the measured charge may be reduced. The voltage stabilisation component may be configured to convert a fluctuating bi-polar output of the charge-measuring component and first and second electrodes into a unipolar pulsed signal. The potential-measuring component may be configured to output a vibration signal to the vibration measurement output component to output the parameter. The vibration measurement output component may include a comparing component which may be configured to compare the vibration signal to the stabilised charge signal to determine the intensity of a vibration causing the first and second electrodes to move relative to one another. The vibration measurement output component may be configured to output the parameter based on the comparison of the comparing component. The electric field-generating component may be electrically connected to the first and second electrodes and may be configured to use the generated charge as a source of power for generating the electric field. The electric field-generating component is connected to an external power source for generating the electric field. A capacitance of a dielectric medium between the first and second electrodes may be adjusted by the electric field. The dielectric medium may be air. Polarisation of the first and / or second electrode may induce an electric dipole moment which may create an internal electric field opposing the electric field. The internal electric field opposing the electric field may reduce a net electric field. A corelation between the potential difference supplied to the electric field-generating component and a force applied to the first or second electrode may be made to determine parameters of the force or vibration. The parameters may include a frequency, a phase, a magnitude, and an intensity. The triboelectric vibration sensor may be used to determine vibrations in the body or body parts of an unmanned aerial vehicle (UAV). In accordance with another aspect of the present disclosure there may be provided a voltage-controlled triboelectric nanogenerator. The voltage-controlled triboelectric nanogenerator may have two main components: a vertical contact mode triboelectric nanogenerator and an output voltage-controlling mechanism. The vertical contact mode triboelectric nanogenerator may consist of at least two layers of materials which may have different tendencies to gain or lose electrons when they come into contact. These materials may belong to a triboelectric series, forming a triboelectric charge when separated. The triboelectric nanogenerator may also have another dielectric medium between the two layers of the triboelectric series to enhance the charge separation. The output voltage-controlling mechanism may include at least two external electrodes that may be connected to an external voltage source. The external voltage source may apply a potential difference to the electrodes, which may affect the electric field inside the triboelectric nanogenerator. By changing the electric field, the output voltage-controlling mechanism may change a virtual thickness of the layers of the triboelectric nanogenerator. By adjusting the virtual thickness of one or more layers of the triboelectric nanogenerator, the output voltage-controlling mechanism may control the output voltage of the triboelectric nanogenerator. This way, the output voltage may be stabilised and optimised according to the requirements of different applications. Moreover, by applying the proposed mechanism for stabilising the output voltage / current of the TENG, it may be used as a vibration sensor with high sensitivity in LIAVs. The proposed TENG may be integrated with an aircraft or UAV structure or attached to a surface of the aircraft or UAV body. When the aircraft or UAV vibrates during operation, the TENG may generate steady electrical signals that may reflect the vibration characteristics, such as amplitude, frequency, phase, etc. The voltage-controlling mechanism disclosed in the current disclosure may control the steady electric signals. The electrical signals may be transmitted wirelessly or through wires to a receiver or processor that may analyse the vibration information and provide feedback or control for the aircraft or UAV system. By using TENG as vibration sensors for aircraft and UAVs, it may be possible to achieve real-time and continuous vibration monitoring and measurement without an external power supply or additional burden for the aircraft or UAV. This may improve performance, safety, and reliability of aircrafts and UAVs. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a three-dimensional view of an example embodiment of a triboelectric nanogenerator; Figure 2A shows an exemplary embodiment of a variable capacitor in use in an equivalent circuit model of a triboelectric nanogenerator; Figure 2B shows another exemplary embodiment of a variable capacitor in use in an equivalent circuit model of a triboelectric nanogenerator; Figure 20 shows yet another exemplary embodiment of a variable capacitor in use in an equivalent circuit model of a triboelectric nanogenerator; Figure 3 is a normalised graph of an output voltage with respect to time of an exemplary triboelectric nanogenerator; Figure 4 is a graphical representation of the relationship between an output voltage and a force of contact between plates of an exemplary triboelectric nanogenerator; Figure 5 illustrates an exemplary dielectric medium in the absence of an external electric field; Figure 6 illustrates the dielectric medium of Figure 5 in the presence of an external electric field; Figure 7 is a three-dimensional view of an exemplary embodiment of a triboelectric nanogenerator and electrodes connected to a variable voltage source; Figure 8 is an example embodiment of electrodes controlling a capacitance of an array of capacitors; Figure 9 is an example embodiment of separately applied external electrodes controlling an output voltage of a triboelectric nanogenerator; Figure 10 is an example embodiment illustrating an equivalent circuit model of the external electrodes and triboelectric nanogenerators of Figure 9; Figure 11 is an exemplary graphical representation of an output voltage obtained after applying an electric field via the external electrodes to the triboelectric generator of Figure 10; Figure 12A illustrates an exemplary mechanism of a constructive mechanism of electromagnetic (EM) waves; Figure 12B illustrates an exemplary mechanism of a destructive mechanism of electromagnetic (EM) waves; Figure 13A is a graph showing positive and negative peaks of a voltage cycle without an applied potential; Figure 13B is a graph showing the correlation between vibrations and applied potential; and Figure 14 is an exemplary feed-back loop in accordance with aspects of the description. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS A triboelectric vibration sensor is described. The sensor may include a triboelectric nanogenerator (TENG) and may be configured to sense a vibration. The sensor may include a first electrode which may be moveable relative to a second electrode. The first electrode may be a chargegenerating layer and the second electrode may be a charge-collecting layer. A charge-measuring component may be connected to the first and second electrodes. The charge-measuring component may be configured to measure a charge generated when the first and second electrodes move relative to one another. More specifically, the charge between the first and second electrodes may be generated when they contact and separate from one another. The first and second electrodes may be arranged face-to-face and may be closely spaced such that a vibration (or force applied to one or both electrodes) causes the electrodes to contact and separate from each other. Thus, the first and second electrodes may be spaced close to one another such that they almost touch and contact one another. The collected or stored charge may be channelled to another electric component configured to utilise the charge. The charge (or a parameter relating thereto, such as a quantity or other measure of charge) may be used to determine properties, parameters, stress, fatigues, forces, oscillations, vibrations, irregularities, or the like, of a structure, object, machine, device, apparatus, etc., to which the sensor is installed or mounted. The sensor includes an electric field-generating component configured to generate and control an external electric field based on the charge measured by the charge-measuring component. The electric field-generating component is further configured to control the external electric field so as to stabilise the charge measured by the charge-measuring component. Therefore, the external electric field may be configured to influence the charge generated by the first and second electrodes. The electric field-generating component may include at least a pair of external electrodes which may be connected to a variable voltage source. The external electrodes may be configured to generate the external electric field which may be used to polarise and / or tune the first and second electrodes. Therefore, the external electric field generated by the external electrodes and may be used to control a voltage output of the TENG and / or first and second electrodes. It may be appreciated that the first and second electrodes may be the charge generating and charge collecting layers of a triboelectric nanogenerator (TENG), respectively, and that the external electrodes do not form part of the TENG itself. Instead, they may influence the performance of the TENG. The TENG may have a dielectric medium which may be positioned between the first and second electrodes. The external electric field may adjust or influence the capacitance of the dielectric medium. The external electric field may be configured to adjust or tune the capacitance such that the charge-measuring component may output a desired stabilised charge signal. The desired stabilised charge signal may be associated with a reference voltage. More specifically, the external electric field may tune the capacitance of the dielectric medium such that the generated charge of the first and second electrodes may be reduced or altered. The generated charge may be altered such that the charge-measuring component outputs the desired charge signal. The dielectric medium may be air. Polarisation of the first and / or second electrodes may induce an electric dipole moment, which may create an internal electric field opposing the generated external electric field. The internal electric field opposing the generated external electric field may reduce a net electric field. This may, in turn, influence the output signal of the charge-measuring component. The triboelectric vibration sensor may further include a vibration measurement output component configured to output a parameter based on the external electric field. The parameter may be a potential difference value corresponding to a potential difference supplied to the electric fieldgenerating component so as to control the external electric field to stabilise the charge measured by the charge-measuring component. There may be a potential-measuring component configured to measure a potential difference supplied by the variable voltage source to keep the output voltage of the first and second electrodes constant. More specifically, the potential-measuring component may be configured to measure a potential difference supplied to the electric field-generating component to generate an external electric field for stabilising the generated charge. The potential-measuring component may for example include a vibration measurement output component which determines (or the potential-measuring component) may determine a vibration measurement based on a corelation between the potential difference supplied and a force applied to the first or second electrode to determine a magnitude of the force. More specifically, the potential-measuring component may determine the vibration measurement based on a correlation between the potential difference supplied and the movement of the first or second electrode to determine the parameters of a possible vibration. The parameters may include a frequency, a phase, a magnitude, and an intensity. The vibration measurement may be output as the vibration signal to the vibration measurement output component to output the parameter. There may be a feedback component configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge. The feedback component may be configured to adjust the potential difference to reduce an error between a reference voltage and the measured charge. The potential-measuring component, charge-measuring component, feedback component, and electric field-generating components form part of a voltage stabilisation component. In use, the charge-measuring component may be configured to measure charge generated from the first and second electrodes when they move relative to one another. The electric field-generating component may be configured to generate an external electric field based on the measured charge to stabilise the generated charge. The potential-measuring component may be configured to measure the potential difference supplied to the electric field-generating component. The feedback component may be configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge such that the error between the reference voltage and the measured charge may be reduced. The voltage stabilisation component may further be configured to convert a fluctuating bi-polar output of the charge-measuring component and first and second electrodes into a unipolar pulsed signal. A comparing component may be configured to compare the vibration signal to the stabilised charge signal to determine the intensity of a vibration causing the first and second electrodes to move relative to one another. The vibration measurement output component may include the comparing component. The vibration measurement output component may be configured to output the parameter based on the comparison of the comparing component. The electric field-generating component may be electrically connected to the first and second electrodes and may be configured to use the generated charge as a source of power for generating the external electric field. It may also be that the electric field-generating component may be connected to an external power source for generating the external electric field. Furthermore, there may be an embodiment where the electric field-generating component may use the external power source or the first and second electrodes as power sources simultaneously. In this manner, the triboelectric vibration sensor may be used to determine vibrations in the body or body parts of an unmanned aerial vehicle (UAV). However, it should be appreciated that the triboelectric vibration sensor may be suitable for use with various other devices, whether mechanical in nature or not. In fact, the sensor may be used for any device, apparatus, mechanism, structure, or the like, experiencing vibrations. In the following description, reference is made to the accompanying drawings that form a part of an example embodiment of a triboelectric vibration sensor. Therefore, the drawings representing the embodiments are shown for illustrative purposes only in which the invention may be practised. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilised and that structural, logical, and electrical changes may be made without departing from the scope of the present invention. Therefore, the following description of example embodiments is not to be taken in a limited sense. Embodiments of a method of controlling the output voltage of triboelectric nanogenerators are disclosed. The present disclosure is related to a mechanism of controlling the output voltage of triboelectric nanogenerators. A voltage-controlling mechanism may have a number of electrodes placed in a vicinity of the triboelectric plates through which an electric field may be applied. Referring to the drawings, Figure 1 is a three-dimensional view (100) of a contact mode triboelectric nanogenerator. The contact mode triboelectric nanogenerator (100) includes two triboelectric layers (106,108) with opposite polarities and are separated by another dielectric (102), usually air, with metal electrodes (104) attached to the top and bottom surfaces. The electrodes may be connected to an external load or electric circuit. When an external force causes the two layers to contact and separate periodically, the triboelectric effect may generate electric charges on the surfaces. Figures 2A to 2C show exemplary diagrams (200) demonstrating three exemplary equivalent circuit models (202, 204, 206) of a contact mode triboelectric nanogenerator (TENG). An equivalent circuit model of a TENG system is represented by an ideal voltage source with a capacitor (202) in Figure 2A. Figure 2B also shows a capacitance model of the TENG (204). Since every two nodes (206), as illustrated in Figure 2C, are connected by electric field lines, an equivalent capacitance may be formed between each of them. As the separation distance between the triboelectric layers may vary during contact and separation, this is modelled by a variable capacitor (208) in an equivalent circuit model (206). A normalised open circuit voltage graph of a TENG system having a voltage output is illustrated in Figure 3. A coupling of contact electrification and electrostatic induction may describe the operating principle of TENGs with vertical contact-separation mode. Prior to contact between the triboelectric layers, the electric potential difference between the layers may be zero. With an externally introduced displacement, such as a vibration, the triboelectric layers may be brought into contact with each other. Surface charge transfer may occur at the contact area due to the triboelectric effect. As force behind the externally introduced displacement releases, the TENG starts to be released and the open circuit voltage may keep increasing (302) until it reaches a maximum value when the triboelectric layers fully revert to their original position. When it is pressed again, the potential difference may start diminishing (304) as the triboelectric layers get closer to each other. A relation of output voltage (Vout) of a triboelectric nanogenerator (TENG) with applied force (F) and time (t) is illustrated in Figure 4. The graph consists of three sections labelled T1, T2, and T3, corresponding to three different levels of applied force on the TENG. In each section, the output voltage of the TENG is represented by a pulse waveform (402), which has a positive peak and lowest point. The amplitude and duration of the pulse waveform depend on the applied force. The higher the force, the higher the amplitude. The lower the force, the lower the amplitude. However, in this scenario, if the forces in all three sections are equal, the output voltage of TENG may still not be constant. A dielectric medium in the absence of any external electric field is illustrated in Figure 5. A dielectric material (502) may be composed of many polar molecules (504), which have a positive and a negative charge and which may be separated by a small distance. The polar molecules (504) may be randomly oriented in the absence of an external electric field, as represented by the positive (+) and negative (-) symbols on their surface. A net electric dipole moment of the dielectric material may be zero, as the positive and negative charges cancel each other out in all directions. Figure 5 shows that the dielectric material does not have any inherent electric polarisation or potential difference. Figure 6 shows the dielectric material (502) in the presence of an external electric field. The external electric field exerted through the electrodes (602,604) may create a potential difference between the two sides of the dielectric material. The external electric field may cause the polar molecules (504) to align themselves with the external electric field direction (606). The alignment of the polar molecules may create an induced electric dipole moment in the dielectric material. The induced electric dipole moment of the dielectric material may oppose the external electric field, which may create an internal electric field that may reduce a net electric field inside the dielectric material. An exemplary embodiment (700) of a triboelectric vibration sensor is illustrated in Figure 7. The triboelectric vibration sensor includes a mechanism or electric field-generating component for controlling the output voltage of TENG. The triboelectric vibration sensor includes first and second electrodes. The first and second electrodes may form part of a TENG. The electric field-generating component may include a pair external electrodes (702,704) connected to a variable voltage source (706). The external electrodes (702,704) may create an external electric field that may affect the electric field between the layers of the TENG (104) and the dielectric (102) therebetween, typically air. Through the application of this externally controlled external electric field, the capacitance of the layers of the TENG (104) may be controlled. The capacitance of the layers of the TENG may depend on the permittivity of the materials, the area of the layers, the electric field between them, and the like. The external electric field applied through an external source may change the capacitance by changing the electric field, the virtual thickness, the permittivity of the layers (104), and the like. Figure 8 shows an exemplary mechanism for controlling the output voltage of a TENG. The mechanism may be used to better understand the triboelectric vibration sensor of Figure 7. The mechanism (800) consists of a pair of external electrodes (802,804) connected to a variable voltage source (706) and several capacitors (806) placed inside it. Since the layers of TENG can be modelled by capacitors (806), by changing the potential of the external electrodes (802,804), the capacitance of the capacitors can be controlled, increased, or decreased as per requirements, as the external electrodes electric field interfere, constructive or destructive, with the electric field of the capacitors (806). Figure 9 shows an exemplary embodiment of a mechanism (900) for controlling the output voltage of a TENG. Figure 9 illustrates a preferred embodiment of a triboelectric vibration sensor including the mechanism (900) or electric field generating component and first (906) and second electrodes (908). The mechanism consists of a number of external electrodes (902,904) placed adjacent to the layers of a TENG (906, 908) in order to control the capacitance of these layers. The layers of the TENG (906, 908) are separated by air (102). In a typical scenario, the output voltage of a TENG may not have a constant value. Through the application of the external electrodes proposed in the current disclosure, a constant output voltage may be obtained from the TENG. An exemplary equivalent circuit model (1000) of the proposed triboelectric vibration sensor of Figure 7 or Figure 9 is shown in Figure 10. The equivalent circuit model (1000) of the proposed mechanism may be similar to that of a typical vertical contact mode TENG with the addition of making the capacitors (1002, 1004), which are static in the case of a typical TENG, variable through the application of external electrodes. By making the capacitors variable (1002, 1004) rather than static, the output voltage of the TENG may be controlled. This means, if desired, getting a constant output voltage from the TENG. Figure 11 is an exemplary graph (1100) showing a relation of output voltage (Vout) of a triboelectric nanogenerator (TENG) with applied force (F) and time (t) after applying the proposed mechanism. The graph consists of three sections labelled T1, T2, and T3, corresponding to three different levels of applied force on the TENG. In each section, the output voltage of the TENG is represented by a pulse waveform (1102), which has a positive peak and lowest point. The graph illustrates that a constant output voltage may be obtained through the application of the proposed mechanism of applying an external electric field using the electrodes, even when the external force varies from F± to F3. This response is different from Figure 4 in which the output voltage changes. Figures 12A and 12B are exemplary schematic diagrams (1200) showing an electric field (1202, 1204) inside a capacitor and the interference phenomena inside it. In the absence of an external electric field, as illustrated in Figure 12A, the electric field (1202) inside the plates of a capacitor may be directed from a higher potential to a lower potential plate. Through the application of an external dynamic electric field, as illustrated in Figure 12B, an electric field (1204) may be induced inside a region of the capacitor, which may interfere constructively or destructively with the dynamic field of the capacitor. In use, the triboelectric vibration sensor may maintain a constant voltage output of the first and second electrodes by introducing additional voltage through the external electric field generated by the electric field-generating component. It may be viewed that the amplitude of the added voltage or potential supplied to the electric field-generating component may be the amplitude of a vibration. In this manner, a very minute vibration may be detected by using this logic, and very low peaks may also be detected easily with basic electronics (like classical low-end microcontrollers or Digital Signal Processing (DSP) modules). There may be many different mechanisms that may be used for the quantification of vibration. A person skilled in the relevant field may come up with several algorithms for measuring the vibration using the triboelectric vibration sensor. For example, one such method which may be used is: In a typical contact-separation mode TENG, periodic contact and separation of the triboelectric layers may induce an alternating output voltage waveform across the load, as shown in the exemplary graph of Figure 13A. This output waveform may result from the coupling of triboelectric surface charge generation and electrostatic induction. On contact, surface charges may be created on the triboelectric layers due to electron transfer based on the triboelectric series. As the layers separate, the potential difference induced by the uncompensated surface charges may increase progressively up to a peak positive value. When the layers move back towards each other, the potential difference may start to decrease progressively to zero and then reach a negative peak. The amplitude and duration of the positive and negative peaks may correlate directly with the intensity and frequency of the external mechanical vibrations causing the periodic contact-separation motion. The triboelectric vibration sensor, as explained earlier, may include an electronic voltage stabilization mechanism or component to convert this fluctuating bi-polar output caused by the periodic contact-separation into a steady unipolar pulsed signal while still enabling vibration sensing. As illustrated in the exemplary graph of Figure 13B; by applying an optimized external electric field (Eext) across the triboelectric layers (or first and second sensors as described earlier) using stabilization electrodes connected to a voltage source (Vsource), the capacitance (C) of the layers may be precisely tuned. The stabilization electrodes may form part of the electric field-generating component as described earlier. By constructive / destructive superposition of the external electric field (Eext) with the triboelectric surface charge-induced field (Esurf), the net field (Enet) and output voltage (Vout) associated with the net field (Enet) across the load may be regulated to a steady level. Through the application of the external electric field (Eext), the negative peak (1304) may be mapped (1302) to the positive side by application of the disclosed mechanism or component. The negative peak (1304) may be part of the original negative cycle of voltage. As the vibration intensity varies randomly, the stabilization electronics must be dynamically tuned to dynamically change the external electric field (Eext) to maintain a steady voltage output (Vout). This is achieved using a feedback mechanism, an example of which is shown in Figure 14. The output voltage (Vout) may be fed back to a controller circuit, which may adjust the voltage (Vsource) applied to the stabilization electrodes in real-time to reduce any error between a set reference voltage (Vref) and measured voltage (Vout). By correlating the adjustments in the voltage applied (Vsource) needed to stabilize the measured voltage (Vout) under different vibration conditions, the vibration intensity may be quantified indirectly. This closed-loop feedback mechanism may therefore allow for self-powered vibration sensing using the disclosed triboelectric vibration sensor. A correlation may be made between the potential difference applied by the variable voltage source and the vibration magnitude. As the vibration intensity changes, the magnitude of voltage needed to apply different potential differences across the TENG layers to maintain a constant output voltage may also vary. By calibrating (balancing) this relationship between applied potential difference and vibration magnitude, the vibration intensity may be quantified indirectly by measuring the applied potential difference. The phenomenon taking place when the first and second electrodes are placed in the presence of an external electric field may be explained below: • The disclosed triboelectric nanogenerator (TENG) has triboelectric material layers made of substances like silicon and PTFE (i.e Triboelectric series materials). These materials may have an intrinsic ability to gain / lose electrons on contact due to the triboelectric effect. Triboelectric Layer Dipole Orientation: • At molecular level, the triboelectric layers may consist of many electric dipoles -atoms / molecules with inherent separation of positive and negative charge centers. By default, these numerous atomic / molecular dipoles may be randomly oriented. When the external stabilization electrodes apply an external electric field (Eext) across a triboelectric layer, the electric dipoles within the material layer may tend to orient their direction along the applied field, i.e. aligning with the external electric field. This rearrangement of electric dipoles may create a net dipole density in the triboelectric material. • In other words, the external electric field may polarize the triboelectric layer by realigning its internal electric dipoles, as illustrated in Figure 6. Change in Layer Capacitance: • The creation of net dipole density equals inducing bound charges in the triboelectric material layer, as illustrated in Figure 10. This may change the layer's capacitance (1004 and 1002 or Ctribo) which may depend on bound charge density. • By tuning the external field (Eext) appropriately, a desired dipole reorientation and capacitance (Ctribo) may be attained. Adjusting Output Voltage: • The capacitance (Ctribo) may directly influence the output voltage (Vout) harvested from the TENG. Therefore, by polarizing the triboelectric layers through optimized external field (Eext), the output voltage (Vout) may be stabilized at the required value. This dipole manipulation may form the basis of output voltage control in the disclosed triboelectric vibration sensor. As explained above, a classical approach requires highly sensitive sense electronics to detect the signal coming from the TENG generator, but if we look at the triboelectric vibration sensor according to aspects of the disclosure, an extra offset is given before it enters the DSP section which may make it more noticeable or detectable for the sense electronic. In other words, spatial resolution may be much increased by using the logic disclosed in the current disclosure. Typical vibration sensing TENGs (VS-TENGs) may directly measure open circuit voltage signals from the TENG, which fluctuate extensively with vibration intensity. This makes it difficult to quantify the vibration magnitude accurately. By stabilizing the output voltage through capacitance modulation of the tribolayers, the disclosed TENG vibration sensor provides superior vibration sensing resolution and calibration. The difference between traditional VS-TENG and the triboelectric vibration sensor of the invention may be: Traditional VS-TENG Operation: • The output voltage varies extensively with vibration intensity due to changing separation between the triboelectric layers. • There is no precise one-to-one correspondence between voltage fluctuations and applied vibration stimuli. • This makes accurate vibration quantification challenging. Disclosed TENG Sensor Advantage: • By introducing the electric field control mechanism, the capacitance of the triboelectric layers may be modulated precisely. • This may enable stabilizing the output voltage to a standardized reference level. • A closed-loop feedback mechanism that correlates adjustments in the external electric field required to stabilize the output voltage with the vibration intensity. The adjustments in the external electric field required to stabilize the output voltage (Vout) may provide an indirect measure of the vibration intensity. By mapping the relationships between the electronic and mechanical domains, the disclosed TENG vibration sensor may enable self-powered quantification of vibrations. In conventional vibration sensing TENGs (VS-TENGs), both the output voltage and currents exhibit large random fluctuations depending on the separation distance between the triboelectric layers caused by external vibrations. These uncontrolled simultaneous voltage and current fluctuations make it quite challenging to isolate and quantify the underlying vibration signals. The unstable outputs also potentially introduce electrical noise into connected electronics, decreasing resolution and false readings. The disclosed TENG vibration sensor uses an external electric field modulation method that may actively stabilize both voltage and current outputs at constant levels. This may enable clear device signal analysis by: a) Removing fluctuations that could mask vibration signatures. b) Enabling calibration between input vibrations and steady electrical outputs. Additionally, this triboelectric vibration sensor may utilize a feedback mechanism that may continually adjust the external electric field to maintain stable voltage output. The feedback loop correlates adjustments in the external electric field (through voltage fed to electrodes) required to sustain steady voltage under vibratory conditions as an indirect measure of vibration intensity. The calibration between input vibrations and steady electrical outputs can be further explained using external electric field modulation to stabilize the output voltage and current to standardized constant levels enables a calibration process as follows: 1. A set of controlled mechanical vibrations of known frequencies and intensities may be applied as input test signals to the TENG sensor over multiple trials. 2. For each trial mechanical vibration input, the electric stabilization (Feedback) circuitry may adjust the external electric field as necessary to maintain the steady predefined output voltage and current. 3. The adjustment in the external electric field to sustain the constant electrical outputs for each trial mechanical vibration may be recorded. 4. By correlating the various trial vibration intensities to the corresponding external electric field adjustments, a vibration intensity calibration profile may be mapped. 5. Once this input vibrations to output electric field relationship may be calibrated, an unknown real-world vibration signal may be quantified by: a) Allowing it to modulate the TENG sensor and alter its electrical response. b) The electric field modulation circuitry may adjust itself to re-stabilize the outputs. c) This required dynamic electric field adjustment may quantify the unknown vibration intensity through the established calibration profile. The disclosed triboelectric vibration sensor may be used to convert the AC output voltage obtained from a typical TENG to a DC voltage. Hence, a skilled person may appreciate the invention of a DC output Voltage TENG. Typically, contact-separation mode triboelectric nanogenerators (TENGs) may produce an alternating current (AC) output voltage that fluctuates with the frequency of the mechanical vibration inducing periodic contact and separation of its internal triboelectric layers. However, many self-powered electronic sensor applications may require a steady direct current (DC) voltage supply input. So, the fluctuating AC output of a TENG may need conversion to DC before powering devices. Additional electronics like rectifiers and capacitors may usually be needed to convert the AC to DC. This may increase system complexity and cost. The disclosed electric field modulation technique may present an elegant solution to convert the intrinsic AC outputs from a TENG into a regulated DC voltage without any additional components. This may be explained as follows: • In the contact-separation mode TENG, the periodic collision and separation of the triboelectric layers with opposite surface charge affinity may induce an AC output voltage across the load. • As the triboelectric layers come closer, negative voltage may build up across the load due to reversed potential difference caused by triboelectric surface charge rearrangement. • As they separate, a positive voltage may build up progressively due to surface charge-induced potential difference. • This may create the bi-directional AC output waveform with alternating positive and negative peaks. • Now, when the external parallel plate stabilization electrodes apply an external electric field across the TENG: > It may cause a realignment of electric dipoles within the dielectric triboelectric layers, modulating their capacitance. > Adjusting the external electric field may appropriately alter the triboelectric charge generation and induction process. > Carefully tuning this field through a feedback mechanism may enable selectively reducing the negative voltage peaks while retaining the positive peaks. > Further flattening the valleys may map the entire AC signal onto the positive voltage region. > This capacitive control and offset may effectively convert the intrinsic AC into a stable DC output voltage. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. Any of the steps, operations, components or processes described herein may be performed or implemented with one or more hardware or software units, alone or in combination with other devices. Components or devices configured or arranged to perform described functions or operations may be so arranged or configured through computer-implemented instructions which implement or carry out the described functions, algorithms, or methods. The computer-implemented instructions may be provided by hardware or software units. In one embodiment, a software unit is implemented with a computer program product comprising a non-transient or non-transitory computer-readable medium containing computer program code, which can be executed by a processor for performing any or all of the steps, operations, or processes described. Software units or functions described in this application may be implemented as computer program code using any suitable computer language such as, for example, Java™, C++, or Perl™ using, for example, conventional or object-oriented techniques. The computer program code may be stored as a series of instructions, or commands on a non-transitory computer-readable medium, such as a random access memory (RAM), a read-only memory (ROM), a magnetic medium such as a hard-drive, or an optical medium such as a CD-ROM. Any such computer-readable medium may also reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network. Flowchart illustrations and block diagrams of methods, systems, and computer program products according to embodiments are used herein. Each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, may provide functions which may be implemented by computer readable program instructions. In some alternative implementations, the functions identified by the blocks may take place in a different order to that shown in the flowchart illustrations. Some portions of this description describe the examples in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations, such as accompanying flow diagrams, are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. The described operations may be embodied in software, firmware, hardware, or any combinations thereof. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A triboelectric vibration sensor comprising:a first electrode moveable relative to a second electrode, wherein the first electrode includes a charge-generating layer and the second electrode includes a charge-collecting layer;a charge-measuring component connected to the first and second electrodes and configured to measure charge generated when the first and second electrodes move relative to one another;an electric field-generating component configured to generate and control an external electric field based on the charge measured by the charge-measuring component, wherein the electric field-generating component is configured to control the external electric field so as to stabilise the charge measured by the charge-measuring component; and,a vibration measurement output component configured to output a parameter based on the external electric field as a vibration measurement.

2. The triboelectric vibration sensor as claimed in claim 1, wherein the parameter is a potential difference value corresponding to a potential difference supplied to the electric fieldgenerating component so as to control the external electric field to stabilise the charge measured by the charge-measuring component.

3. The triboelectric vibration sensor as claimed in claim 1 or claim 2, wherein the electric field-generating component includes a pair of external electrodes connected to a variable voltage source.

4. The triboelectric vibration sensor as claimed in any one of claims 1 to 3, wherein the first and second electrodes are the charge-generating and charge-collecting layers of a triboelectric nanogenerator (TENG), respectively.

5. The triboelectric vibration sensor of any one of claims 1 to 4, wherein the external electric field is controlled to adjust a capacitance of a dielectric medium between the first and second electrodes.

6. The triboelectric vibration sensor of claim 5, wherein the capacitance is tuned such that the charge-measuring component outputs a desired stabilised charge signal.

7. The triboelectric vibration sensor of any one of the previous claims, including a potentialmeasuring component configured to measure a potential difference supplied to the electric fieldgenerating component to control the external electric field so as to stabilise the charge measured by the charge-measuring component.

8. The triboelectric vibration sensor as claimed in claim 7, including a feedback component configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge.

9. The triboelectric vibration sensor as claimed in claim 8, wherein the feedback component is configured to adjust the potential difference to reduce an error between a reference voltage and the measured charge.

10. The triboelectric vibration sensor as claimed in claim 8 or claim 9, wherein the potentialmeasuring component, charge-measuring component, feedback component, and electric fieldgenerating components form part of a voltage stabilisation component, wherein the chargemeasuring component is configured to measure charge generated from the first and second electrodes when they move relative to one another, the electric field-generating component is configured to generate an electric field based on the measured charge to stabilise the generated charge, the potential-measuring component is configured to measure the potential difference supplied to the electric field-generating component, and the feedback component is configured to dynamically adjust the potential difference supplied to the electric field-generating component to stabilise the generated charge such that the error between the reference voltage and the measured charge is reduced.

11. The triboelectric vibration sensor as claimed in claim 9 or claim 10, wherein the voltage stabilisation component is configured to convert a fluctuating bi-polar output of the chargemeasuring component and first and second electrodes into a unipolar pulsed signal.

12. The triboelectric vibration sensor as claimed in any one of claims 7 to 11, wherein the potential-measuring component is configured to output a vibration signal to the vibration measurement output component to output the parameter.

13. The triboelectric vibration sensor as claimed in claim 12, wherein the vibration measurement output component includes a comparing component configured to compare the vibration signal to the stabilised charge signal to determine the intensity of a vibration causing the first and second electrodes to move relative to one another.

14. The triboelectric vibration sensor as claimed in any one of the previous claims, wherein the electric field-generating component is electrically connected to the first and second electrodes and configured to use the generated charge as a source of power for generating the electric field.5 15. The triboelectric vibration sensor as claimed in any one of the previous claims, whereinthe electric field-generating component is connected to an external power source for generating the electric field.

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