WIRELESS POWER TRANSMISSION SYSTEM WITH ADAPTIVE DYNAMIC SAFETY MANAGEMENT

Abstract

Methods and systems for safely and effectively supplying a beam of wireless power from a transmitter to at least one receiver. A delta signal is generated by repeatedly calculating the difference in power between the power of the beam emitted by the transmitter and the amount of power received at the receiver. The system dynamically generates a time delay, which is a time period shorter than the maximal exposure duration relating to safe exposure durations for the power level of the delta signal. If the time delay is exceeded, the system changes an operational parameter of the system, such as terminating the beam. Because of limitations to building a perfect timing system, the system is built to be more sensitive to time delays having longer safe exposure durations, with large delta signals having short safe exposure durations being responded to immediately and without significant regard to the time delay.

Claims

1. A system for providing wireless power supply to at least one receiver, the system comprising: (a) a transmitter adapted to emit a beam of wireless power; (b) a power meter configured to generate a first signal corresponding to the power level of the emitted beam; (c) a detector associated with the at least one receiver, and configured to generate a second signal corresponding to the power of the beam received at the receiver; (d) at least one controller, the at least one controller adapted to: (i) generate a time period T.sub.delay, being less than the maximal safe exposure duration for the difference in power measured by the power meter and the detector; (ii) dynamically generate a new T.sub.delay if the difference in power has changed by more than a significant amount; and (iii) modify at least one operational parameter of the transmitter to reduce the difference in power, should T.sub.delay be exceeded.

2. A system according claim 1 wherein a frequency selective signal processor is used to process a signal corresponding to the difference in power, prior to the generation of T.sub.delay.

3. A system according to either claim 1 or claim 2 wherein, if the difference is above a predetermined level of power, the controller is configured to respond without waiting for T.sub.delay to be exceeded, before modifying the operational parameters of the transmitter to reduce the delta signal.

4. A system according to either of claim 2 or 3 wherein the frequency selective processor is configured such that its pass-band is set to cover frequencies significantly lower than the range that would be required to respond within a time period mandated by the maximal level of difference signals expected.

5. A system according to either of claim 2 or 3, wherein the frequency selective processor is configured such that its frequency response curve is shifted to lower frequencies than those indicated by the center of the range of frequencies which would be required to provide amplification over the range of exposure durations expected from the power transmission system.

6. A system according to claim 5, wherein the shift of the frequency response curve provides increased amplification to low level power difference signals, such that the processor can respond to changes in these low level signals.

7. A system according to claim 5, wherein the shift of the frequency response curve provides increased amplification to low level power difference signals, such that those low level power difference signals can generate a sufficiently high processor output above the noise level, to trigger the laser safety routine.

8. A system according to any of the previous claims, wherein the controller is further configured to calculate T.sub.delay as a function of difference signals previously generated.

9. A system according to claim 8 wherein difference signals below a predetermined ambient level are indicative of no significant beam obstructions between the at least one transmitter and the at least one receiver.

10. A system according to claim 9 wherein if the difference signal falls below the ambient level for a pre-determined amount of time, the generation of T.sub.delay is not significantly based on any previous difference signals.

11. A system according to claim 8 wherein the system is configured to respond to any difference signals above the ambient level by either calculating T.sub.delay for signals below a predetermined level and above the ambient level, or by responding without relating to T.sub.delay should the difference signal be above the predetermined level.

12. A system according to claim 8 wherein the system is configured to respond to any difference signals above the ambient level by either calculating T.sub.delay for signals below a predetermined level and above the ambient level, or by modifying the operational parameters of the transmitter to reduce the delta signal.

13. A system according to any of claims 2 to 12, wherein the frequency selective processor comprises an amplifier.

14. A system according to any of the previous claims, wherein step (iii) is performed should the elapsed time from step (i) exceed T.sub.delay.

15. A system according to any of the previous claims wherein the modifying of at least one operational parameter of the transmitter comprises at least one of: modifying the power level of the beam; terminating lasing completely; changing the beam profile of the beam emitted; blocking the beam; directing the beam to a different location, by using a scanning mirror to steer the beam; scanning the area around the current scan position to better align the beam onto the receiver; and recording the scan position of the location that signified an object in the beam path.

16. A method for safe wireless power supply to at least one receiver, the method comprising: (a) transmitting power from at least one transmitter to at least one receiver; (b) generating a first signal corresponding to the level of power emitted by the at least one transmitter; (c) generating a second signal corresponding to the level of power received at the at least one receiver; (d) generating a difference signal, the difference signal being the difference between the second signal and the first signal; (e) generating a time period T.sub.delay, being less than the maximal exposure duration relating to a safe exposure duration for the power indicated by the difference signal; (f) monitoring whether the difference signal has changed by a predetermined amount, and if so, returning to step (e); and (g) should T.sub.delay be exceeded, modifying at least one operational parameter of the wireless power supply in order to reduce the difference signal.

17. A method according to claim 16 wherein the system responds to difference signals above a predetermined level without using T.sub.delay to determine the time period to wait before the modification of at least one operational parameter of the wireless power supply.

18. A method according to claim 16 wherein the T.sub.delay is calculated by averaging the difference signal for an amount of time dependent on the level of power indicated by the difference signal, such that difference signals indicating a high level of power have a shorter averaging time than difference signals showing a lesser amount of power.

19. A system for laser power transmission from a transmitter to at least one receiver, the system comprising a hazard prevention system comprising: a power monitor measuring the laser's optical power emitted from the transmitter; and a power sensor for measuring the laser's optical power at the at least one receiver; the hazard prevention system being configured to cause the laser's power to be reduced or terminated in response to an increase in the difference between the measurements of the power monitor and the power sensor, after a time delay after the occurrence of the difference increase, the time delay, measured in seconds, being: $\frac{1.5*10^{-10}*{\left(8+e^{\left(\frac{\lambda }{10.857}-115.129255\right)}\right)}^4}{{\left(P_{\mathrm{transmitter}}-P_{\mathrm{receiver}}\right)}^4}>{\tau }_{\mathrm{delay}}>\frac{1.5*10^{-12}*{\left(8+e^{\left(\frac{\lambda }{10.857}-115.129255\right)}\right)}^4}{{\left(P_{\mathrm{transmitter}}-P_{\mathrm{receiver}}\right)}^4}.Math.$ where P.sub.transmitter is the laser power measured by the power monitor, measured in Watts; where P.sub.receiver is the laser power measured at the power sensor, measured in Watts; and where λ is the laser wavelength measured in nanometers.

20. A system for safe wireless power supply to at least one receiver, the system comprising: (a) a transmitter adapted to emit a beam; (b) a power meter for measuring the power level of the emitted beam; (c) a detector associated with a receiver, and configured to detect at least a portion of the beam received at the receiver; and (d) a frequency selective signal processor adapted to: (i) generate an output signal representing a time period T.sub.delay, being less than the maximal exposure duration relating to safe exposure durations for the difference in power measured by the power meter and the detector; and (ii) monitor the elapsed time since the generation of the T.sub.delay and modify at least one operational parameter of the transmitter to reduce the difference, should T.sub.delay be exceeded; wherein the frequency selective processor is configured such that if the output signal is above a first predetermined level, the frequency selective processor has a response characteristic such that it modifies an operational parameter of the system without significant processing.

21. The system of claim 20, wherein the frequency selective processor has a frequency response biased towards low frequencies, such that the difference signals having levels less than a second predetermined level, and associated with exposure durations, significantly longer than the allowed exposure duration levels of power exposures above the first predetermined level, are amplified more than signals above the first predetermined level.

22. A system for safe wireless power supply to at least one receiver, the system comprising: (a) a transmitter adapted to emit a beam of wireless power; (b) a power meter configured to generate a first signal corresponding to the power level of the emitted beam; (c) a detector associated with the at least one receiver, and configured to generate a second signal corresponding to the power of the beam received at the receiver; (d) at least one controller, adapted to: (i) determine an energy limit for accumulated exposure permitted for the power level relating to the difference in power measured by the power meter and the detector; (ii) dynamically generate a new energy limit if the difference has changed by more than a significant amount; and (iii) modify at least one operational parameter of the transmitter to reduce the difference, should the energy limit be exceeded.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

[0078] FIG. 1 shows a typical example of a wireless power supply system, according to the present application;

[0079] FIG. 2 illustrates one particular regulation for the permissible exposure duration at different laser beam power levels;

[0080] FIG. 3 shows a schematic representation of the response curve of a prior art amplifier, processor or control system over the entire range of frequencies shown in FIG. 2;

[0081] FIG. 4 shows a schematic representation of the response curve of an amplifier, processor or control system constructed such that its frequency response curve is shifted to lower frequencies than those indicated in the curve of FIG. 3;

[0082] FIG. 5A is an exemplary plot of the differential power signal obtained in a typical detection scenario, as a function of time; FIG. 5B shows the resulting control signal generated by the power profile shown in FIG. 5A; and FIG. 5C illustrates a situation in which a short noise spike “A” is ignored by the system;

[0083] FIGS. 6A and 6B illustrate various scenarios having hazardous situations which may necessitate curtailment or diversion of the laser transmission, to avoid potential laser damage;

[0084] FIG. 7 is a flow chart which illustrates one implementation of the methods used in operating the currently disclosed system; and

[0085] FIGS. 8A and 8B illustrate the permissible exposure time allowed for different power levels, according to a US regulation.

DETAILED DESCRIPTION

[0086] Reference is now made to FIG. 1, which illustrates a typical setup of a wireless power supply system. A transmitter 10 is shown, comprising a beam generator 12, for example a laser, directing an optical beam 17 towards a receiver 15. In order to measure the power level of the laser beam emitted by the transmitter, the system comprises a first power meter 13, called the transmission power meter. The transmission power meter 13 may be situated inside the transmitter 10, or in the beam path at the exit of the transmitter. This power meter may sample the emitted beam at a high sampling rate, for example at a frequency of 5 kHz or more, such that changes in power of the beam being emitted are obtained by the system in real-time, without delay.

[0087] Typically, the receiver 15 contains a photovoltaic cell 16, which converts the optical energy of the beam into usable electric energy, usually for charging or powering a device associated with the receiver. Should portions of the beam be directed at surfaces other than the receiver power absorbing aperture, the stray beam may cause dangerous, laser generated damage. Any surface, whether fully reflective or only partially reflective, or absorptive, such as mirrors, human body, animals, cameras, glass surfaces, metallic surface and sensitive equipment, could present a hazardous situation should a beam be mistakenly directed onto them.

[0088] Thus, a second power meter 14 associated with the receiver, the receiver power meter, may be incorporated to measure whether the receiver is receiving all, or at least a large portion of the beam directed at it, such that the system can determine whether an appreciable portion of the beam, or even any portion of the beam, is being directed elsewhere, with potentially dangerous consequences. The receiver power meter 14 may receive a portion of the beam from a beam splitter (not shown) located in the receiver, or, in other cases, a current meter, voltage meter or the photovoltaic cell itself may be used as a power meter in the receiver. The portion of the beam received by the receiver power meter is proportional to the beam power impinging on the receiver.

[0089] The system also includes a controller 18. The controller 18 receives a signal 14.sub.sig from the receiver power meter 14 representing the amount of power detected at the receiver. The controller also receives a signal 13.sub.sig from the transmission power meter 13 representing the amount of power of the laser beam 17 exiting the transmitter 10.

[0090] The controller 18 compares the signal 14.sub.sig of the beam detected by the detector 14 to the signal 13.sub.sig representing the amount of power emitted by the laser 12. Should the difference between these measured powers be significant, an indication of a hazardous situation may be generated by the system, since a significant amount of power emitted by the transmitter is unaccounted for by the receiver device, and thus may be impinging on a surface other than the receiver device where it could cause damage. Therefore the system continuously performs a check to ascertain the level of the unaccounted-for power. The controller is configured so that if the level exceeds a predetermined threshold, the controller responds in order to reduce or eliminate this unaccounted-for beam power by causing at least one of the following: [0091] Modifying the power level of the beam; [0092] Terminating lasing completely; [0093] Changing the beam profile of the beam emitted; [0094] Blocking the beam; Directing the beam to a different location, for example to a beam dump, typically by using a scanning mirror to steer the beam; [0095] Scanning the area directly around the current scan position in order to attempt to better align the beam onto the receiver, and, should the scan find a position at which the difference signal drops, instructing the transmitter to use that more optimal scan direction; [0096] Recording the scan position of the location that signified an object in the beam path; and [0097] Changing any other operational parameter of the system.

[0098] During lasing, a reduced level of power impinging on the receiver is generally associated with an object traversing the path of the beam. The controller should thus be able to modify the laser output according to the level of power indicated as lost between the trasnmitter and the receiver device, to protect any such objects which have entered the path of the beam. Sampling of the power at the transmitter and receiver should be performed at a high enough rate to ensure that indications of changes in the portion of beam received, are obtained sufficiently rapidly to comply with the safety regulations mandating such protection. There will be explained hereinbelow, the implications of the sampling rate on the ability of the system to respond correctly temporally, both to low leakage powers occurring over long periods, and to high leakage powers, which have to be curtailed rapidly and therefore require a fast time response of the system.

[0099] Reference is now made to FIG. 2, which illustrates one particular regulation for the permissible exposure duration at different laser beam power levels. The particular graph shown gives the maximum permitted exposure level in dbm, for exposure to illumination having a wavelength of 1050 nm and for a beam diameter of 7 mm, and having a Gaussian profile. The abscissa, shows the bandwidth in Hz. required of an amplifier or processor, in order to successfully handle the response time implicit by the maximum exposure time permitted for the plotted exposure levels.

[0100] The system as shown in FIG. 1 must ensure that those portions of the beam that are not accounted for, namely the difference between the signal received at the detector and the amount of power emitted by the transmitter, and which therefore may impinge on humans or other object in the field of view, do not exceed the guidelines for maximal permissible exposure durations, as permitted by the various national regulations. The curve in FIG. 2 is obtained from the US Code of Federal Regulations Title 21, Volume 8 Revised as of Apr. 1, 2018 [CITE: 21CFR1040.10]. The graph shows the permitted time of exposure, expressed as an effective frequency of response of the measurement system, as a function of the power level to which the object is exposed, expressed in dbm, for a 7 mm Gaussian beam at 1050 nm wavelength.

[0101] As the power level of the beam increases, the permissible time of exposure decreases. Thus, should the controller indicate that a large portion of the power of a high power beam is unaccounted for, it is necessary to modify the system parameters very rapidly. Alternatively, should the controller signify that only a small portion of the beam power is missing, a longer period of time is allowed to elapse before the controller must instruct the laser to moderate or divert its beam, as shown in FIG. 2. Thus, for instance, for the 7 mm. beam whose allowable exposure level is shown in FIG. 2, for a power level of 0 dbm (1 mW), the allowed exposure time according to the above referenced regulation, is of the order of 10 seconds, so the bandwidth of the control loop required to respond within that 10 seconds should extend up to at least 0.1 Hz. Likewise, for the same beam but having a power of 10 dbm, the allowed exposure time is of the order of 5 ms, so the bandwidth of the control loop required to respond within that time should extend to at least 200 Hz.

[0102] To provide more non-limiting examples of these levels of protection according to the above referenced regulation, and to show how the level of protection required depends on several parameters of the beam, if a system using a circular beam having a diameter of 10 mm, and a uniform beam profile, which is the preferred beam profile for conversion by a photovoltaic cell to electric energy, and with a wavelength of 1050 nm, shows that 6.8 milliwatts of power are unaccounted for, the beam needs to be terminated within a time period of 1 second.

[0103] On the other hand, should the beam profile be Gaussian, if the system would show only 5.35 milliwatts of missing beam power, the laser beam would need to be terminated or modified within 1 second.

[0104] Similarly, should a similar system using a Gaussian beam having a diameter of 7 mm indicate that only 3.3 milliwatts of the beam are unaccounted for, that beam would need to be terminated within 1 second.

[0105] Should the wavelength of the beam change from 1050 to 1060 nm, as may be the case due to changes in laser temperature, the permissible exposure duration for a 10 mm Gaussian beam in a system showing that 5.6 milliwatts of power are unaccounted for is 1 second

[0106] It should be noted that the term “safe exposure time” for exposure to a specific beam power, is understood in this disclosure to refer to any time period less than the maximal permissible exposure time allowed by regulations in force at the time of use, for that beam power. As is observed in the full extent of the graph of FIG. 2, the permissible exposure duration may vary from nanoseconds to tens of hours, depending on the level of power lost during transmission of the laser beam, and the range of power levels to be monitored ranges from a few microwatts to the order of 10 watts.

[0107] Thus, the requirement of a signal handling system that can handle the required response to a signal representing a missing power of 10 W, is that it must have a dynamic range typically exceeding 60 dB and a frequency response extending to approximately 10 Mhz, corresponding to a response time of the order of 0.1 microsecond. Such a large signal dynamic range, in combination with a bandwidth which covers up to such a high frequency are practically impossible to achieve in presently available electronic technology, whether analog or digital. Therefore, it is an objective of the present invention to provide a system that has the capacity to be sensitive to all power levels within such a large dynamic range of the power, and to react within the most efficient time given by the regulation requirements for the maximum power measurement expected, namely as fast as 100 nanoseconds or so for the above mentioned 10 W power range.

[0108] Reference is now made to FIG. 3 which shows a schematic representation of the response curve of a prior art amplifier, processor or control system over the entire range of frequencies shown in FIG. 2. The axes are logarithmically plotted because of the very large ranges involved. In the example chosen, the peak amplification stretches around a central frequency of 10 Hz, and is shown as having significantly useful response covering two decades or slightly more, both above and below that frequency. This range of response is not intended to be limiting, but just shows a typical range illustrative of the problem which the current methods and systems attempt to solve. As is indicated in FIG. 3, the typical time exposures corresponding to the response frequencies where there is significant amplification, range from several hundred microseconds or so, to a few tens of seconds, or so. Outside of that range, the amplification, or, at the low frequency end of the spectrum, the ability of the amplification system to distinguish a real signal from the noise level of the signal, may be too small to be able to provide proper warning of the need to trigger the safety features of the system if the allowed power is exceeded. In practice, speed of response of the amplifier system is implemented not only by the electronic response characteristics of the amplifying and control circuits, but also by the sampling rate at which the system samples the measured power to determine whether the threshold has been reached.

[0109] It should be emphasized that the frequency ranges discussed in this example are levels which may be typical for everyday domestic situations, but are not meant to be limiting for every situation.

[0110] Referring back now to the levels of errant beam power exposure, associated with which the safety regulations define the maximum exposure times allowed, as shown in FIG. 2 for instance, it is seen that the range of beam powers whose levels permit the above exemplary range of exposure times, range from several hundred microwatts to a few tens of milliwatts, for such typically sized beams. Thus, powers falling outside of this range will likely not be sufficiently amplified by the system, which will not therefore be able to generate the correct instruction to the system to reduce or divert the beam should the power threshold for the errantly directed beam be exceeded for longer than the permitted time. There are two distinctly different situations with regard to this lack of the ability to respond.

[0111] At the high power end of the response curve, where only very short exposure is allowed, and the amplifying system must respond very quickly to shut down or divert the beam transmission should that power be exceeded, the situation is such that although the amplification is very low, the lack of amplification is more than made up by the magnitude of the signal input to the amplifier, resulting from a significantly high level of power. Therefore, despite the apparent insufficient amplification level of the system at those high frequencies, the high signal level makes up for that low amplification, thus providing sufficient output signal to trigger the safety regulation steps for reducing the radiation. However, at the low power end of the response curve, where long exposure can be allowed, running into many hours and even days for the very lowest powers regulated, there is no such compensating mechanism whereby the power level itself makes up for the drawbacks in the amplification at such low frequencies, as reflected in the inability of the amplification system to differentiate the signal from the noise level. Furthermore, although the power levels involved may sound almost negligible, there is still a maximum regulatory period allowed for exposure of a human to such low powers, and the safety system of the transmitter must be able to ensure that that criterion is properly complied with. Additionally, at these low powers, the system must still be capable, as at all times, to be able to respond rapidly to a large increase in leaked power which must trigger the safety actions within the permitted exposure time.

[0112] In order to achieve that aim, according to a first implementation of the system of the present disclosure, as shown in FIG. 4, the amplifier is constructed such that its frequency response curve is shifted to lower frequencies than those indicated by the center of the range of frequencies which should be handled by the amplifier. By virtue of this shift to lower frequencies, the very small signals generated at the power meter by the low power levels associated with long allowable exposure periods, undergo a larger level of amplification above the noise level, than they would using prior art amplifier selection criteria, and hence, compensation is provided for that low signal level, to enable them to generate a sufficiently high output above the noise level, to trigger the laser safety routine. Thus, in FIG. 4, it is clear that by shifting the center of the frequency response to 0.1 Hz. instead of 10 Hz., the amplification in the very low frequency ranges is substantially increased, thereby providing a sufficient output signal for those low power stray beams to actuate the beam safety system.

[0113] On the other hand, as previously explained, at the high power end of the spectrum of beam powers, the shift of the amplifier frequency response curve to a lower frequency, thereby reducing even further the low amplification provided at that end of the spectrum, has a lesser effect on the efficiency of the safety warning system, since the signal generated by the high stray beam power is so large, that even the reduced amplifier sensitivity in that high frequency range, will still generate sufficient output to operate the safety system.

[0114] However, there still remains a functional problem of how to implement this increase in sensitivity at low powers while ensuring that the system responds to high powers sufficiently speedily. The need to respond speedily to a large increase in detected power essential remains, whether the power being detected is low or high. The response time manifests itself in the form of the sampling rate which the system uses in order to measure the power. The shorter the power measurement response time required, the higher is the sampling rate which the system must use to measure that power. Therefore, the fast response time of the system to an increase in power to the maximum expected by the system, must be maintained even when very low powers are being detected. The sampling rate may typically be chosen to be three or more times the maximal permitted exposure duration for a power difference signal showing a complete beam obstruction. A system using a sampling rate at this frequency would allow a sudden spike in the power difference signal to be monitored for at least one more sample before required modification of lasing, thus allowing for an albeit short averaging calculation to be made before a response is acquired, in which the signal may drop down to an acceptably low amount.

[0115] On the other hand, the sampling rate may be chosen to be substantially the same, but never less than, what is equivalent to the maximal permitted exposure duration for full loss of the beam. The sampling rate may even be chosen to be two or less samples within this time limit.

[0116] However, as previously mentioned, a fast response time, and thus a high sampling rate, brings with it an increase in the sensitivity to noise. The increase in amplifier sensitivity at low powers, as mentioned above, increases this effect.

[0117] In order to achieve these aims, an effectively variable sampling rate may be used in the systems of the present disclosure. The response time manifests itself in the form of the sampling rate which the system uses in order to measure the power. The shorter the power measurement response time required, namely, the higher the errant power level to be detected, the higher the sampling rate which the system must use to measure that power. Therefore, to ensure that the highest powers capable of being emitted by the system are acted upon within the permitted time limit for that power level, the sampling rate must be maintained at a high rate, typically a few times faster than the rate at which the time between samples would be the maximum allowed safe time for the maximum system power. However, as already mentioned, a fast sampling rate leads to excessive sensitivity to noise, and at low emitted powers, the signal generated by the detected power may be difficult to extract from the noise level, possibly resulting in premature activation of the threshold shutdown or beam diversion procedure.

[0118] In order to overcome this problem, the control may be designed such that for low levels of the measured power signal, the sampling rate may be reduced, and the power signal responded to with less urgency. However, the sampling rate must still be maintained at above that required to respond within the maximum time allowed for the maximum exposure expected. When the system power itself is low, the sampling rate may be less frequent, since the maximal permissible time of exposure for that beam is longer, thus changes in the power signal do not need to be responded to in such a short time.

[0119] The controller can be advantageously configured such that there may be a time delay between receiving an indication of a loss of power, and the controller actually acting on the signal level received, and modifying the system. This time delay enables the system to determine whether the signal detected really is due to the power loss continuing over the entire sampling period, indicating a probably real instance of power being diverted somewhere along its transmission path, or whether it is a result of excessive noise detected at those low signal levels. This is achieved by averaging the power signal up to the end of the time delay and using that averaged signal to come to the decision whether the threshold has been reached and that the laser should be terminated or diverted, or whether the signal is just due to noise pickup, or results from a transient event, and can be ignored for the considerations of determining whether a real safety threshold time has been reached. The time delay is a function of the maximal permissible duration for the power loss detected at the power signal. The time delay must be slightly less than the maximal permissible duration for that loss of power.

[0120] The advantageous outcome of this procedure is now demonstrated in FIGS. 5A, 5B and 5C. FIG. 5A is an exemplary plot of the differential power signal, namely the power level of the beam power lost during transmission, obtained in a typical detection scenario, as a function of time. The symbol Δ represents the differential power as measured by the difference between the transmitted power, and the actual power incident on the receiver. Δ is plotted as a function of the elapsed time, t. The average or ambient power level Δ1 shown in the regions of the graph marked A, C and E, is so low that the permitted exposure to that level of leakage power is long, and would extend way beyond the total time shown in the graph of FIG. 5A, if no other event involving a larger level of differential power occurred. The sampling rate is maintained at a sufficiently high rate rate, commensurate with the need to respond to a sudden increase of Δ to the maximum power emitted by the system, such that such an increase in power would result in the system maintaining proper safety protection.

[0121] However, at the point in time marked T.sub.1s, an event occurred, possibly the short term intrusion of a partially absorbing object into the path of the transmitted beam, causing the Δ to rise to a level Δ.sub.2 which, according to the mandated regulations for a beam having an average power of Δ.sub.2, has a maximum permitted period of exposure extending up to the point T.sub.1r, such that the difference between T.sub.1r and T.sub.1S is the time for which the level of exposure Δ.sub.2 is permitted. According to the present described system, for such a moderate detected power difference as represented by Δ.sub.2, the decision as to whether the increased Δ represents a significant change that requires a response from the system is delayed by the controller, such that the system is adapted to wait for a delay time before terminating the beam, in order to determine whether the change in the signal is a significant, or real rise in the signal, or whether the spike was caused by noise or a short lived anomalous reading in the system. The delay is determined by the level of lost power which the system is showing, which in the case of moderate power level Δ.sub.2, extends to T.sub.1d, such that the difference in time between T.sub.1s and T.sub.1d is the delay during which the system is permitted to wait in order to establish whether the change in the signal to Δ.sub.2 needs responding to, before the permitted exposure time T.sub.1r is reached. Indeed, it can be seen that the jump in signal to Δ.sub.2, marked by time period “B”, does not require the modification of an operational parameter of the system, such as termination of the beam, since before T.sub.1d is reached, the beam obstructive event causing the jump to power level Δ.sub.2 has passed, and the power detected has again dropped to its low level, to approximately Δ.sub.1, at time T.sub.2. As a result of this method of signal averaging over the complete time period between T.sub.1s and T.sub.1d, extending into time period C, the control system does not prematurely activate the system trigger for removing the laser emission, as would be performed without the use of such a time delay criterion, and charging service is not prematurely terminated.

[0122] In a similar manner, at the time T.sub.3s, a large spike of lost power is suddenly detected by the system, having a substantially increased detected power level of Δ.sub.3. Such a pulse of power, using a prior art control system, would be rapidly detected, and would immediately shut the lasing down (as an example of the action to be taken) because the high level is indicative that a large amount of the beam is unaccounted for and may be impinging on dangerous targets. This would be done in prior art systems without consideration of the length of the pulse. Using the control system of the present disclosure, the threshold decision is delayed beyond the sampling time, to T.sub.3d, in order to correctly appraise the level of danger presented by the increased power. It is noted that T.sub.delay for this spike in region D is shorter than that for the power increase in region B, since the power level is higher, and hence, the permitted exposure time shorter. By using such a delayed decision response time, the sharp power spike is averaged out over its temporal environment, allowing for a waiting period to determine whether the signal's overall average level falls below that which would mandate a shutdown of the system.

[0123] FIG. 5B now shows the resulting control signal generated by the power profile shown in FIG. 5A. Both the moderate level event as shown by time period “B” and the larger jump to Δ.sub.3 during time period “D” are processed by the system, such that they are averaged before inputting into the control system. Neither of the events now trigger the safety threshold, thereby enabling the system of the present disclosure to continue providing charging service without interference, where, in previous systems, the threshold criterion would have been triggered as soon as the first sampling period occurred, and the system shut down.

[0124] FIG. 5C illustrates a situation in which a short spike “A” is ignored by the system, since the sampling of the signal and its ensuing averaging, enables the determination that no significant change has occurred since the signal quickly drops down to a low level.

[0125] However, when spike “B” is amplified, the system can determine that this increased Δ signal is rapidly exceeding the permitted duration for such a level of unaccounted-for beam power. Subsequently, the system terminates lasing, and therefore no power is received at the receiver, therefore the Δ signal drops to zero as shown at the end of time period “B”.

[0126] Reference is now made to FIGS. 6A and 6B, which illustrate various scenarios having hazardous situations which may necessitate curtailment or diversion of the laser transmission, to avoid potential laser damage.

[0127] FIG. 6A illustrates an exemplary scenario in which a person 60 traverses the beam 67. In such a case, before the person walked into the beam path, the signal received by the receiver power meter would be at its regular high level, and therefore the Δ, or loss of power between transmitter 61A and receiver 65A, calculated by the controller, would be low. Thus, the transmitter 61A may direct a full power beam at the receiver prior to the person walking into the beam.

[0128] When the person 60 then enters the beam path 67, the power level received by the detector would drop drastically and thus the difference Δ between the power detected leaving the transmitter 61A, and that detected at the receiver 65A would be high. That means that a high level of power is being dissipated somewhere in the transmission space, without reaching the receiver, and this potentially presents a high level exposure to the beam. In keeping with the regulations, such a high power exposure must result in reduction of the stray beam in a very short time. Because of the large change in power level and the short period of time in which the system amplification must respond, the system amplifier may not be able to faithfully handle the corresponding change in signal and issue the shutdown or beam diversion instruction within the time required. However, the Δ signal would be high enough to ensure that the system responds within the small permissible time for that loss of power, despite lack of meaningful amplification at such a high frequency.

[0129] FIG. 6B now illustrates a scenario in which a transparent object 64, or an object which only partially blocks the beam, partially obstructs the beam path. Since the change in detected power may be small, such a stray beam power may be acceptable according to the regulations, for a comparatively long period.

[0130] The characteristic time period of this event may be long, since, for a low level of errant power exposure, the object may be in the beam path for minutes, or even hundreds of minutes, thus lasing may continue uninterrupted. Prior art systems would not be sensitive to such a small loss of power between the transmitter and receiver over such a long period of time, as the effective frequency of this power change would be too low for them to detect. However, even if Δ, which symbolizes the unaccounted portion of the beam, is very small, and thus its permissible exposure time may be very long, the maximum permissible time level may be exceeded should transmission of power from a transmitter to a receiver occur for an extended period of time.

[0131] In the system of the current disclosure, the amplification of frequencies related to very slow changes of input signal and over long periods, is increased in comparison to prior art systems, such that it is more sensitive to events occurring over a long period of time. Combination of these features therefore enables the system to respond correctly over long periods of time, in spite of the increased sensitivity to noise at those low detection levels.

[0132] Therefore, the controller shows an increase in signal associated with Δ should a transparent or partially blocking object be in the beam path over a long period of time. The controller may be characterized to have a limited response, as the permissible level of exposure to such a weak beam may be minutes or even hours. This allows the controller to continue accurate monitoring of this Δ signal over a long time period to ensure that it does not exceed the time limit for this power level required by guidelines.

[0133] In the example shown in FIG. 6B, the vase 64 may be removed from the beam path before the maximal permitted period of time for the power level lost due to object 64 has been exceeded. Thus, the delay time or waiting period utilized by the system, ensures that no changes to the system may be performed unnecessarily.

[0134] Alternatively, should the vase 64 remain in the beam path for close to the maximal permitted exposure for loss of that level of power, such that the maximum “waiting period” or delay time allowed before the need to activate the shut-down or beam deviation system, is nearly exceeded, such action may be necessary before that maximal permissible exposure time is exceeded.

[0135] Thus, the currently disclosed system ensures that small losses of power between the transmitter and the receiver are accounted for, and an object traversing the beam for a short time would not be subject to as much attention as an object in the path of the beam for a long time. Moreover, the sensitivity of the currently disclosed system to the large dynamic range required is achieved, with the large dynamic range required taken into account.

[0136] Reference is now made to FIG. 7, which is a flow chart which illustrates one implementation of the methods used in operating the currently disclosed system.

[0137] In step 701, the “event clock” is started, and the system calculates a “waiting period”, called T.sub.delay, this being the length of time which the system will wait from the starting point of this “event clock” before terminating or diverting the beam should the Δ signal not show a significant change, as will be explained hereinbelow. T.sub.Δ is determined in accordance with the permitted exposure time at the Δ power currently received, according to regulations. According to one exemplary method, in order to calculate the T.sub.delay, an averaging of the delta signal is performed, with the time over which the averaging is performed being less than the max permissible duration for this power loss. This ensures that anomalous readings such as spikes arising from short noise interferences, do not unnecessarily cause the “event clock” to re-set.

[0138] In step 702, the Δ signal is continually measured.

[0139] In step 703, the system determines whether the level of the Δ signal has changed by more than a predetermined amount, shown as Δ.sub.ch. An increase in the Δ signal indicates that more beam loss is occurring than that calculated at step 701, and therefore a different and shorter T.sub.delay must be calculated based on this increase of Δ signal and the “event clock” or timing system must be reset to reflect this change. Conversely, a decrease in the Δ signal indicates a drop in beam loss occurring, and therefore a new longer T.sub.delay may be calculated based on this decrease of Δ signal and the “event clock” or timing system must be reset to reflect this change.

[0140] In an alternative embodiment of the system, should the loss of power indicated be greater than a predetermined saturation level, above which all signals are responded to identically, with the event clock rendered essentially irrelevant in this case, since the system should terminate, the system blocks or diverts the beam without delay. For example, a delta signal indicating 95% beam blockage may cause the system to respond in the same time as a delta signal indicating 99% beam blockage. The saturation level may be chosen to be 10 W or higher, or 9 W or higher, or at other power levels. The saturation level may be dependent on the environment of the wireless power system, or on other parameters.

[0141] In step 704, if no change in the Δ signal, greater than Δ.sub.ch, is indicated, the system evaluates whether the current T.sub.delay has been exceeded. If not, control passes back to step 702, and measurement of the Δ signal is continued. On the other hand, should it be indicated that T.sub.delay is exceeded, thus the required permissible exposure duration for the current loss of power will shortly be surpassed, control passes to step 705.

[0142] In step 705, an operation parameter of the system is activated, in order to prevent excessive beam exposure, such as by blocking, diverting or terminating the beam.

[0143] Reference is now made to FIGS. 8A and 8B, which illustrate the permissible exposure time allowed for different power levels, according to the above referenced US regulation. FIG. 8A is the response time required for a beam having a wavelength of 1050 m beam, and FIG. 8B for a beam having a wavelength of 2600 nm. Thus the waiting period or delay time of the controller, may be set such that the maximal delay before terminating the beam or affecting another parameter of the system is within the maximal permitted time for that loss of power.

[0144] It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.