Laser-based gas detector

Abstract

A system for measuring the level of flammable gas, such as cooking gas, within an enclosed space and for issuing an alarm when the gas level exceeds a safety threshold. The system uses a laser beam to determine the presence of an intrusive flammable gas. The laser beam provides a convenient method for determining the gas absorptivity on the beam path since the beam is generally collimated, passing through a clear path, can cover a wide range of areas for monitoring gas contamination. The absorptivity of the light of the laser beam through the region depends on the gas content in the environment through which the beam passes. The wavelength of the laser beam used is selected such that there is a significant absorptivity in the laser beam of the gas used by the system for detection.

Description

Technical Field

[0001] The present disclosure describes technology related to the field of detecting foreign gases using laser beams, particularly for detecting flammable gases in domestic environments where gas appliances are used for cooking or heating. Background Art

[0002] There are many different types of gas detection sensors, including photoionization detectors, ultrasonic sensors, electrochemical sensors, and metal oxide semiconductor (MOS) sensors. A common method of detecting gas involves using a spectrophotometer to analyze the gas mixture, typically using a broadband near-infrared light source (such as a tungsten lamp, mercury lamp, or incandescent lamp). This broadband light source is able to measure over a wide range of wavelengths, allowing the absorption spectrum to cover different gases. One such spectrophotometer measurement system is shown in an article by JJ Rohwedder et al., published in The Analyst, 139.10.1039 / c4an00556b (2014), entitled "A miniaturized near-infrared gas sensor based on substrate-integrated hollow waveguides coupled to a micro-NIR-spectrophotometer."

[0003] Most such sensors are mounted in a specific location, usually in the center of the ceiling of the space to be protected, and provide warning of gas leaks in the vicinity of the sensor. However, with the increasing use of wireless laser power transmission (such as it is used in systems for charging mobile electronic devices), there has arisen a need to provide a specific indication of the presence of intrusion of flammable gas (such as that which may come from a gas leak in a domestic environment) in the path of the laser beam itself, which may have a power density high enough to cause ignition of the flammable gas released by the leak. For this reason, it is important to determine the gas concentration in the laser beam path and over the entire length of the laser beam path, as the gas concentration may be different at different locations in the same room (such as at a detector mounted in the ceiling of the room). The ceiling mounting location is to prevent furniture and other objects from obstructing the flow of air or gas, while cooking gases can accumulate in the lower parts of the room and are particularly dangerous at bed height when gas heaters may be used at night. Even more importantly, gas concentrations within the beam are particularly prone to becoming a safety issue because the beam is a potential ignition threat localized in a very specific location (i.e., the beam path). This danger is even more acute because installations of today's increasingly common wireless laser power charging systems often start from the ceiling, but cooking gases, which are heavier than air and usually originate at table height or lower, typically accumulate near the floor. Therefore, it is important to be able to measure and detect gas contamination close to its source, which may be far from a ceiling mounted detector.

[0004] The disclosures of each of the publications mentioned in this section and other sections of this specification are each incorporated herein by reference in their entirety. Summary of the invention

[0005] The present disclosure attempts to provide novel systems and methods that overcome at least some of the shortcomings of the systems and methods of the prior art. The present disclosure describes new example systems for measuring the level (extent, grade) of impurity gases, and in particular flammable gases (such as cooking gases), in an enclosed space, and for providing a warning, or even taking safety measures, when the gas level exceeds a predetermined threshold (considered a safe level). The systems and methods of the present disclosure differ from previously used gas detection systems in that they use a laser beam to determine the presence of an intrusive gas. Laser beams provide a convenient way to determine the absorptivity of a gas in the beam path because the beam is typically collimated and passes through a well-defined path that covers a large area of ​​the area to be monitored for gas contamination. The absorptivity of the laser beam to light as it passes through the area depends on the gas content in the environment through which the beam passes. As long as there is no gas contamination in the beam path, the power level transmitted by the beam will not change significantly because the composition of the air through which the beam passes remains fairly stable, and humidity may be the main factor that changes the absorptivity of the beam. Thus, the presently described gas detector system is advantageous over gas monitors mounted at a single location (e.g., at a ceiling location) because the sensitivity of the detection mechanism of the laser-based system does not drop significantly over the entire path of the laser beam. Such a laser beam can be extended from one end of a large room or hall to the other, thereby providing substantially undiminished sensitivity over the entire distance. In addition, the laser beam can be scanned at different locations in the room, thereby covering a larger area of ​​the room.

[0006] Laser systems are becoming increasingly popular for the remote transmission of energy from a transmitter to a receiver, where the energy is used to power mobile personal electronic devices or charge their batteries, or to power electronic devices installed in locations where battery replacement or charging or connection to a mains power source may be problematic, such as bathrooms or movable room installations, such as doors or curtains. Such remote laser wireless power transmission systems have been described in, for example, some patents and patent applications with some common inventors and co-owned with the present applicant, such as WO 2017 / 009854 for "A System for Optical Wireless Power Supply", WO 2017 / 033192 for "Wireless Power Distribution System", WO 2018 / 158605 for "System for Optical Wireless Power Supply", WO 2017 / 179051 for "System for Optical Wireless Power Supply", and WO 2018 / 211506 for "Flexible Management System for Optical Wireless Power Supply". Many such systems are used in domestic environments, including kitchens or homes where gas is used for cooking or for heating. In this case, the presence of leaking gas in the laser beam field creates a serious safety hazard, as the power density of the laser beam may ignite the gas leaking into the environment and cause an explosion. In addition, the laser beam may also be used as a critical component of security systems, smoke detectors, alarm systems and medical equipment, so it should only be powered when it is safe to do so. In any of the above cases, when the flammable gas level exceeds a certain safety threshold, the laser beam should be shut off and a warning alarm should be issued to the user and / or the fire department and / or gas supply company.

[0007] Since a common need for such gas detection systems is for detecting dangerous concentrations of cooking gases, the systems and methods of the present disclosure will be described below using this application, but it should be understood that this is not intended to limit the invention, but rather to illustrate its use. The system and method utilizes a laser beam that is transmitted from a transmitter to a beam detector located in a room or space where gas concentrations need to be monitored. According to one aspect of the gas detection system currently described, the laser beam used to determine the concentration of intrusive gases in the environment can be the same laser beam used to transmit wireless laser charging power to the receiver, because the system's detection of, for example, flammable cooking gases is then performed just in the path of the laser beam, which may be the cause of igniting the cooking gases if such a gas leak is present. However, whether or not the laser beam is related to gas ignition, the currently described system also provides general detection of related gases in the beam path.

[0008] Therefore, the gas detection system of the present application includes a laser transmitter and a receiver, wherein the transmitter directs a laser beam to a receiver, and the receiver converts the energy in the beam into an electrical signal, the level of which depends on the absorptivity of the laser beam in the space between the transmitter and the receiver. The wavelength of the laser beam used in the system must be selected so that there is a beam in the laser beam that is significantly absorbed by the gas to be detected by the system. The gas detectors of the prior art generally use a broadband light source, so that the broadband light source can detect different gases by the absorptivity of different wavelengths covered by the broadband light source. Once it is detected that there is any gas whose absorptivity wavelength falls within the wavelength band of the light source exceeds a predetermined threshold, the detector is set to provide a warning signal, or shut down any system that may potentially contribute to igniting the gas, or even shut down the gas supply. However, since they do not use a guided beam, but detect the gas reaching the detector in the entire volume around the detector, such prior art volumetric gas detectors are rarely able to detect dangerous gas levels within the laser beam path itself.

[0009] While a laser beam can be directed along a narrow path along which it is desired to detect concentrations of hazardous gases, lasers are inherently narrowband and therefore provide much less gas detection data than broadband light sources. Therefore, an intelligent system is required to detect gases when using laser beams. The choice of wavelength for absorbing the detection light is critical and in many cases may be different from the wavelength at which the laser beam is used for power transmission, as many laser power transmission wavelengths are either not sufficiently absorbed by cooking gases and therefore cannot be used to detect gases, or are absorbed by other compounds in the air, such as nitrogen, oxygen, water vapor, carbon dioxide, etc., and are therefore insensitive to small proportions of cooking gases. Therefore, the system must operate at wavelengths where there is a high absorption rate for the main cooking gas components (butane and propane). These wavelength ranges are between 850-950 nanometers, 1120-1220 nanometers, and 1280-1440 nanometers. Therefore, the transmitter may advantageously include one or more lasers that emit one or more laser beams in a wavelength range such as the above-mentioned 850-950 nanometers, 1120-1220 nanometers, or 1280-1440 nanometers range. For beam ranges of several meters (such as beams commonly found in domestic environments), absorbances between 5% and 10% fall within these ranges and enable higher sensitivities, thereby enabling simpler and more accurate gas detection. In order to cover any of these wavelength ranges, a system with more than one laser can be used so that the system can cover a wider wavelength band. In the case of multiple beams using multiple wavelengths, the laser beams are advantageously arranged collinearly. In the case of multiple lasers, at least one laser is typically modulated to distinguish the measured powers of the different lasers. This modulation is also useful in the case of a single laser, and noise can be better reduced using processes such as phase and frequency locking or other mode-sensitive methods (Optical Code Division Multiple Access (CDMA) is an extreme example).

[0010] The system should also include a beam deflection unit for aiming the laser beam at the receiver, and a controller for controlling both the laser(s) and the beam deflection system and also ensuring safe operation in the event of a warning of high gas concentration. The receiver typically uses a photovoltaic cell of a type suitable for the wavelength(s) of the laser to detect the laser beam(s). The receiver should also include a digital communication channel for communicating information about the received radiation to the transmitter. The communication channel can also be used to transmit information from the transmitter to the receiver. In addition, information about the radiation received by the receiver can be input to the transmitter unit controller to determine when the laser beam optimally impacts the beam detector in the receiver. The controller can adjust the aiming direction of the beam deflection unit to ensure optimal impact of the beam.

[0011] When the detection system is implemented on a laser wireless power transmission system for providing power to a remote device (whether mobile or stationary), the receiver will include a DC / DC converter for providing power used by the device receiving the wireless laser power transmission. To improve conversion efficiency, a maximum power point tracking system (MPPT) may be included.

[0012] Both the transmitter and receiver should include power measurement devices to determine the power of the transmitted and received beams. The transmitted power can be simply represented by measuring the excitation current into the laser, and the total received power can be represented by the output current of the photovoltaic cell. The system can then calculate the power absorbed in the transmission between the transmitter and the receiver by the difference between the power received by the receiver and the power transmitted by the transmitter. This may overestimate the absorption rate of the laser light by the gas in the beam between the transmitter and the receiver, because other factors such as beam scattering, beam expansion, reflections from the exit window of the transmitter or the entrance window of the receiver, and other power dispersion effects may also cause the power between the transmitter and the receiver to be reduced. By calculating the power absorbed or scattered along the laser path between the transmitter and the receiver, the gas absorption rate between the transmitter and the receiver can be measured. The system controller will usually receive the power measurements of both the transmitter and the receiver and calculate the difference using at least one preliminary calibration measurement to obtain the actual power measured. The receiver's power measurements are typically transmitted to the transmitter (where the controller is typically located) via a wireless or partial wireless communication channel, the latter being a configuration in which the data can be sent using conventional wireless communication protocols to an intermediate wireless access station from which the transmitter can access the data, for example, over the Internet.

[0013] The controller can then use data relating to the power loss of the transmission, and the known absorption coefficients of the gases expected to be found in the volume, to determine the concentration of the detected gas along the entire length of the laser transmission path from the transmitter to the receiver. In order to convert the power loss to gas concentration, it is generally necessary to determine the length of the path along which the laser beam travels. Although the detected gas may be slightly more concentrated in a particular portion of the length of the beam path, this effect may be minor since the air movement within the volume being detected is assumed to result in a fairly uniform volume concentration of the gas throughout the volume, but the advantage of having particularly localized gas concentrations within certain portions of the laser beam is not insignificant. Thus, an estimate of the distance between the transmitter and receiver can be used to determine the average gas concentration over the entire path. The controller can receive distance measurements from the receiver by knowing the layout of the room and the location of the receiver, or it can estimate the distance by measuring different properties, such as the strength of a test signal transmitted to or reflected from the receiver, or by the size or shape of an optical pattern on the receiver, or by a time-of-flight measurement of the signal from the transmitter to the receiver and back. As an alternative to methods involving path length measurements, the controller can assume a maximum distance based on system design and parameters.

[0014] A controller, which is also typically connected to the laser source(s), is able to modulate the laser in a specific pattern or modulation, making signal detection easier and more sensitive, and may also be able to shut down the entire system when measurements are not needed.

[0015] The measured absorbance is proportional to the absorbance of the gaseous medium along the length of the beam. Certain wavelength bands are more sensitive to the presence of cooking gases, while others may be sensitive to water vapor content. Similarly, certain bands may be sensitive to carbon dioxide in the air, while most bands can be used to detect smoke. When the controller detects that the absorbance exceeds a threshold (the threshold is usually predetermined, but may also be calculated on the fly based on the results of other parameters detected), it can respond by performing any of the following actions:

[0016] 1. Turn off the laser or significantly reduce its power

[0017] 2. Alert the user

[0018] 3. Alert an automated system (e.g. alarm system or smart center) of the situation

[0019] 4. Call the fire department.

[0020] 5. Sound an alarm

[0021] 6. Turn on illuminated warnings, such as LED lights

[0022] 7. Cut off the gas supply by issuing a command to the electronically controlled gas supply valve.

[0023] Typically, a laser is turned off by issuing a command to the laser driver, but it can also be turned off by closing an optical or mechanical shutter to block the beam, or by switching a semiconductor switch in the laser power supply to a non-conducting state.

[0024] Once the laser is terminated or switched to low power mode, the controller may initiate a recovery protocol after a predetermined time interval or after the warning is cancelled by the user or fire department or remote server or by a secondary measurement of the absorption rate between the transmitter and receiver, indicating that the risk condition has ceased.

[0025] Therefore, according to an exemplary embodiment of the apparatus described in the present disclosure, there is provided a system for securely transmitting laser power to at least one remote receiver, the system comprising:

[0026] A transmitter unit comprising:

[0027] (a) at least one laser emitter for generating a laser beam;

[0028] (b) a beam aiming element adapted to direct the beam toward the at least one receiver; and

[0029] (c) a laser power meter positioned so that it determines the power of the laser beam;

[0030] wherein at least one receiver comprises: a beam sensor adapted to receive a laser beam; a power meter configured to measure a power level input to the receiver by an incident laser beam; and a communication link configured to send a signal corresponding to the power level input to the receiver by the incident laser beam back to the transmitter; and

[0031] wherein the system further comprises a control unit adapted to determine whether a difference between the power of the emitted laser beam and the power input to the receiver exceeds a predetermined level, and

[0032] The wavelength of at least one laser transmitter is selected so that the absorption rate of the laser beam to the flammable gas is high enough so that the system can detect a predetermined minimum concentration of the gas in the air through which the laser beam passes, thereby enabling the system to detect the flammable gas along the entire path of the laser beam in an area where a remote receiver may be found.

[0033] In such a system, the absorption rate of the laser beam by water vapor should advantageously not exceed a predetermined fraction of the absorption rate by the flammable gas.

[0034] In any of the above systems, the control system should be adapted to adjust the beam aiming element using a signal corresponding to the power level input to the receiver to ensure optimal incidence of the laser beam on the beam sensor.

[0035] In any of the above systems, the control system may be further adapted to reduce the power emitted by the laser if the difference between the power of the emitted laser beam and the power input to the receiver exceeds a predetermined level. In this case, if the difference between the power of the emitted laser beam and the power input to the receiver exceeds a predetermined level, the control system is adapted to perform at least one of the following actions:

[0036] a. Turn off the laser or reduce its power to a predetermined safe level;

[0037] b. Alert the user;

[0038] c. Sending an alert to an automatic warning system, such as an alarm system or a smart center;

[0039] d. Call the fire department;

[0040] e. sound an alarm;

[0041] f. Turn on the visual warning signal; and

[0042] g. Cut off the gas supply by issuing a command to the controlled gas supply valve.

[0043] Additionally, in any of the foregoing systems, the light beam sensor is a photovoltaic cell.

[0044] In addition, any of these systems may also include a DC / DC converter circuit that is suitable for converting the output current of the beam sensor into a current at a higher voltage so that the current is at a voltage suitable for powering an externally connected electronic device. Alternatively, the system may then further include a DC / DC converter circuit that is suitable for converting the output current of the beam sensor into a current at a higher voltage so that the current is at a voltage suitable for charging a battery of an externally connected electronic device. In any of these cases, the system may further include a maximum power point tracking system to ensure optimal efficiency of the DC / DC converter circuit.

[0045] In any of the above systems, the control unit may be located in the transmitter unit. Furthermore, the difference between the power of the emitted laser beam and the power input to the receiver is a fractional difference.

[0046] Furthermore, the wavelength of at least one laser emitter may fall within at least one of the wavelength ranges of 820-935 nanometers, 970-1125 nanometers, 1170-1350 nanometers, 1515-1545 nanometers, and 1620-1700 nanometers.

[0047] Finally, according to another embodiment of the present application, a method for safely transmitting laser power to at least one remote receiver in a space where at least one gas powered device can be used is also provided, the method comprising:

[0048] (i) measuring the power of a laser beam transmitted from a transmitter through the space to a receiver,

[0049] (ii) measuring the power of the laser beam received by the receiver after passing through the space; and

[0050] (iii) determining the difference between the power of a laser beam emitted from a transmitter into the space and the power input to a receiver after traversing the space, and, if the difference exceeds a predetermined level, shutting down the laser, or reducing its power to a predetermined safe level,

[0051] Therein, the wavelength of the laser beam is selected so that the absorption rate of the laser beam by the gas used in the instrument is high enough so that a predetermined minimum concentration of the gas in the space through which the beam travels to the receiver is sufficient to cause the power difference to reach a predetermined level, thereby enabling the method to detect dangerous levels of gas in the instrument along the entire path of the laser beam in a space where a remote receiver can be found. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention may be more fully understood and appreciated from the following detailed description in conjunction with the accompanying drawings, in which:

[0053] Figure 1 An example system according to the present disclosure is schematically shown for providing safe laser wireless power transmission in an environment where flammable gas contamination may be present;

[0054] Figure 2 is a description such as Figure 1 a flow chart showing how the system shown operates in use;

[0055] Figure 3 is a graph showing the absorbance level of a humid air sample as a function of wavelength over the visible and near infrared regions; and

[0056] Figure 4 is a graph showing the spectral absorbance of four different flammable gases (methane, ethane, propane, and butane) as a function of wavelength in the near infrared region. DETAILED DESCRIPTION

[0057] View Now Figure 1 , which schematically illustrates an example system for detecting the presence of flammable gas contamination in an environment, such as in a domestic environment where gas is used for cooking and / or heating. A gas leak may create a flammable atmosphere in the environment, which may be ignited and exploded if exposed to a spark or any other ignition process. This is particularly true if the gas detector system is integrated into a laser wireless power transmission system, where the concentrated power density of the collimated laser beam is substantially higher than a laser system used only for gas detection. Such a system differs from prior art gas detection systems in that it detects the presence of flammable gas specifically along areas where flammable gas may be ignited, i.e., exactly along the path of the laser beam. The system thus provides a self-protection safety feature to enable transmission of the laser power beam in an environment where a dangerous explosive atmosphere may be present.

[0058] exist Figure 1 In FIG. 1 , a transmitter 1 is shown for generating a laser power beam 7 and emitting the laser power beam 7 into a space where a receiver 10 is located, and a receiver for receiving the power beam 7 and converting it into electrical energy, which can optionally be used by an external device 19 to be powered or charged. Figure 1 , the path of the light beam is represented by the thicker black line, while the power of the electrical or electronic signal is represented by the thinner line. The transmitter 1 includes a laser beam generator 2, which outputs a light beam having a wavelength or wavelength range between 820-935 nanometers, or between 970-1125 nanometers, or between 1170-1350 nanometers, or between 1515-1545 or 1620-1700 nanometers, or any combination of these ranges. The reasons for selecting these preferred wavelength ranges will be further explained below. The optical system 3 collimates or focuses the light beam to a distance of at least 1 meter from the transmitter 1. The output coupler 4 splits off a portion of the light beam, typically up to about 15% of the light beam, to enable the power output of the light beam to be measured by a power meter 9. The light beam then passes through a beam deflecting element 5, such as a controlled collimator or MEMS actuated mirror, which directs the light beam 7 through an output window 6 towards a receiver 10 located away from the transmitter. A controller 8 in the transmitter may be used to control the direction of the beam deflecting element 5 , the power level and any modulation applied to the output beam of the laser transmitter 2 .

[0059] The power beam 7 is incident on a receiver 10 and is absorbed by a beam sensor, typically in the form of a photovoltaic cell 11, which is protected behind a receiver entrance window 12. The photovoltaic cell 11 absorbs a large portion of the laser beam 7 and, if the detection system is also used to detect the laser beam 7 for a client device 19 ( Figure 1If wireless power is provided by a device (not shown), a DC / DC converter 13 is used to convert the output current of the photovoltaic cell 11 into a current with a higher and more suitable voltage for charging or operating such a device. An optional maximum power point tracking system 18 (MPPT) can be used to ensure that the photovoltaic cell output reaches the optimal impedance to maximize the power extracted from the photovoltaic cell 7. The power meter 15 is used to estimate the power level of the received laser beam 7, which can be done by directly measuring the optical power of the beam, or by measuring the current generated by the photovoltaic cell 7, or the voltage generated by the photovoltaic cell 7, or the power generated by the MPPT 18 (because they are all purely electronic methods, so it is more convenient, such as Figure 1 The power meter 15 reports the received power level to the receiver controller 14, which wirelessly transmits the power data or a calculated result based on the measurement of the power data back to the transmitter via the communication channel transmitter 16, where it is received by the communication channel receiver 17 and input to the controller 8. Although the system controller 8 is most conveniently located within the transmitter 1 itself, it may be located in the transmitter 1 or any other suitable location remote from the transmitter.

[0060] When the system controller 8 detects that the power detected at the receiver 10 is lower than the power transmitted by the transmitter as measured by the power meter 9 by more than a predetermined level, this may indicate a gas leak, as the displacement of air in the laser beam path by flammable gas may result in an increased absorption rate of the laser beam. This is particularly true if the power detected at the receiver decreases over time, while the power output by the transmitter does not. This situation would appear to indicate that the level of contaminated gas in the laser beam path is slowly increasing. If this situation is detected, and there is no indication that the received power is decreasing due to other known causes, then the system controller may determine that a gas leak exists and, depending on the level of contamination, either terminate the beam emitted by the transmitter by shutting down the laser 2, or reduce the power level emitted by the laser 2 to a safe level until the source of the power absorption is verified. Thus, the system is specifically designed to detect the presence of flammable gas in the laser path itself, where the flammable gas may be ignited by the power density of the collimated or focused laser beam. Furthermore, in certain embodiments of these systems, once such detection of a potential flammable gas leak is determined, it is important for the system to shut down completely to prevent any risk of sparks from the electronic circuits igniting the gas. Before shutting down, or after, or simultaneously with the reduction of laser power, the system can electronically alert any of a security system, a host server, an alarm system, or a fire prevention or detection system. The system can also be configured to signal danger to nearby persons by activating warning lights, or sounding warning sounds, or by calling the gas company and / or the local fire department.

[0061] Reference now Figure 2 , Figure 2 is a flow chart showing the Figure 1 Exemplary operation of the system as it transmits laser power to a remote receiver is shown.

[0062] In step 21, the current level of transmitted laser power is measured for entry into the control system.

[0063] At the same time, in step 22, the level of laser power received in the receiver is also measured for input into the control system.

[0064] In step 23, the power difference between the transmitted and received beams is calculated, which represents the power loss during transmission. In order to take into account different operating conditions, this power loss is usefully determined as a percentage of the transmitted power, since the power loss to be expected under normal operating conditions and without any unsafe conditions being implied will depend on such factors as the distance of the receiver from the transmitter, the level of any contamination on the optical surfaces of the receiver or the transmitter, etc.

[0065] In step 24, the controller determines whether the power loss between the transmitter and the receiver exceeds a predetermined level. This predetermined level should have been determined in the preliminary calibration of the system to determine the expected power drop due to replacing the air in the path of the transmitted laser beam with different proportions of the specific gas or gas mixture whose presence is being detected, while taking into account the absorption rate of the specific gas or gas mixture for the laser wavelength or wavelengths used. In step 24, if it is determined that the power loss does not exceed the predetermined safe level, the system returns to steps 21 and 22 and continues to continuously monitor the power of the transmitted and received laser beams. If continuous monitoring is not considered necessary, a short delay can be introduced in step 29 before returning to steps 21 and 22.

[0066] However, if it is determined in step 24 that the power loss does exceed the predetermined safety level, this means that there may be flammable gas leaking into the space through which the laser beam passes, and in step 25 the controller is instructed to reduce the laser power to a lower standby configuration, or more preferably to shut down the laser completely. This decision may depend on the extent to which the detected power loss exceeds the predetermined safety level. At the same time, the system may issue a warning or alarm to the user or the entire electronic security system, and may optionally also alert the fire department or gas company.

[0067] Step 29 is also performed when the system is in its initial low power startup mode (e.g., during initial startup), or after it has been shut down due to a detected safety hazard (as explained below in step 27). Step 29 will then use this delayed step for the system's safe startup procedure. The system should always be started up in a safe low power mode, not only to ensure that there are no people or other objects in the beam path, but also in the context of this application to ensure that there are no dangerous levels of gas that would have been present before the laser was turned on. In this case, the system startup is terminated while the laser beam is still in the low power configuration, thereby avoiding any danger that might occur if the laser was initially turned on at full power.

[0068] In step 26, after the laser has been shut down due to a danger warning issued by the system, the controller waits for a predetermined recovery time, which is selected according to the specific conditions on site, in order to determine whether the atmosphere has recovered from the gas contamination, or whether the contamination is still present or has even increased.

[0069] In step 27, once the predetermined recovery time has been reached, the laser system is restarted, as described above, at a lower power setting to prevent the laser beam power from potentially igniting the flammable gas (if the flammable gas is still present), and control is passed back to steps 21 and 22, where the transmitted and received power levels are again measured. At this reduced power setting, the safety threshold of the difference in power transmitted and received will of course be reduced in accordance with the reduction in power transmitted in the low power mode. The determination of the lost power as a percentage of the transmitted power in step 23 enables this step to be simply performed at the reduced power setting. If the system detects in step 24 that the explosion hazard has now passed, the laser power can be increased to its desired level by step 29.

[0070] The wavelength or wavelengths of the generated laser beam must be carefully selected to ensure that the absorbance of the gas to be detected is large enough to enable accurate determination of the percentage of contaminating gas in the laser beam, as outlined above in the Abstract section of this disclosure.

[0071] The above described systems employ a laser generator having a laser wavelength adapted to provide sufficient absorptivity to detect the gas or gases of interest. In residential environments, it is often desirable to detect cooking gases, which are typically composed of propane or butane or a mixture thereof. These systems may also be used as smoke detectors, in which case the laser wavelength is less important, since smoke is largely specific, scattering the laser radiation as particles rather than absorbing it. Cooking gases are efficiently absorbed by the following wavelength ranges (with high levels of absorptivity for butane and / or propane gases): 850-950 nanometers, 1120-1220 nanometers, and 1280-1440 nanometers. However, certain laser wavelengths within these ranges are also strongly absorbed by moisture in the air, and this creates uncertainty as to the power loss due to the absorptivity of butane and / or propane gases compared to the absorptivity due to water vapor in the ambient air. Therefore, the gas detection systems of the present disclosure should not use those spectral regions where the water vapor absorption level is high.

[0072] Reference now Figure 3 , which is a graph showing the absorbance level of humid air as a function of wavelength in the visible and near infrared regions. The absorbance data was obtained for air samples at a relative humidity of 33.6% at 27°C at a distance of 1 meter. Figure 3 As can be seen in the figure, there are water absorption regions over a considerable wavelength range in the near infrared, so these wavelengths should not be used in the system of the present application. Specifically, the preferred wavelengths are those between the water vapor absorption bands, such as between 700-935 nanometers and 970-1125 nanometers, and the bands between 1170-1350 nanometers and 1515-1700 nanometers. In these ranges, the laser beam is not strongly absorbed by air humidity. Since low water vapor absorption and good propane or butane absorption do not completely overlap, some compromise is used to select the appropriate wavelength to provide good detection efficiency. Propane and butane absorb strongly in the ranges 820-935 nm and 970-1125 nm, and therefore these two bands are preferred in addition to the bands between 1170-1350 nm and 1515-1545 nm as well as 1620-1700 nm, since in these bands the laser beam is not strongly absorbed by air humidity but is reasonably absorbed by cooking gases in the case of gas leaks, thus enabling detection with good risk reduction.

[0073] Reference now Figure 4, which is a graph showing the spectral absorbance of two flammable gases (propane and butane) in the near infrared region as a function of wavelength. These gases are commonly used as domestic cooking gases. The lighter, thinner trace represents propane, and the thicker, heavier trace represents butane. The most efficient laser wavelengths to be used are those that fall within the following ranges: (i) Figure 4 The wavelength in the high absorbance spectral region shown in FIG. 1 makes the absorption rate of the laser beam change sufficiently with the change of the concentration of the detected gas; (ii) not Figure 3 The wavelength in the high water absorption region of the laser beam is such that the beam absorption rate of the ambient humidity does not significantly interfere with the detection of the detected gas. It is understood that in order to detect other flammable or dangerous gases, such as some of the gases in FIG. 5 , lasers of other wavelengths should be used.

[0074] Finally, some explanation is now provided on the dependence of the properties of flammable gases and the possibility of explosive mixtures as a function of the concentration of these gases in air.

[0075] Reference is now made to the Appendix Table below, which summarizes a list of common flammable gases and their concentration in air as a function of the explosion hazard level. Under normal oxygen conditions, when the concentration of the gas in the air is above the Lower Explosion Limit (LEL) expressed as a volume percentage in the Appendix Table below and below the Upper Explosion Limit (UEL), if a spark occurs or some material is heated to a high temperature by the laser beam, then a dangerous explosion is likely to occur. In a typical residential or commercial environment, such danger mainly comes from cooking gas leaks, which mainly include propane or butane or a mixture thereof. For common gases, it can be seen from the Appendix that a volume concentration above 1% may pose a risk of such an explosion.

[0076] Example embodiments are provided to make the present disclosure exhaustive and fully convey its scope to those skilled in the art. Many specific details, such as examples of specific components, devices, and methods, are listed to provide a comprehensive understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that the example embodiments may be embodied in a variety of different forms without the use of specific details, and should not be construed as limiting the scope of the present disclosure. In addition, those skilled in the art will recognize that the present invention is not limited to what is particularly shown and described above. On the contrary, the scope of the present invention includes both combinations and sub-combinations of the various features described above, as well as changes and modifications that would occur to those skilled in the art when reading the above description and that are not in the prior art.

[0077] appendix

[0078]

[0079]

Claims

1. A system for safe laser power transmission to at least one remote receiver, the system comprising: A transmitter unit comprising: at least one laser emitter that generates a laser beam; a beam aiming element adapted to direct said beam toward said at least one receiver; and a laser power meter positioned such that it determines the power of said laser beam; wherein at least one of the receivers comprises: a beam sensor adapted to receive the laser beam; a power meter configured to measure a power level input to the receiver by an incident laser beam; and a communication link configured to transmit a signal back to the transmitter corresponding to a power level input to the receiver by the incident laser beam, wherein the system further comprises a control unit adapted to determine whether a difference between the power of the emitted laser beam and the power input to the receiver exceeds a predetermined level, and Wherein, the wavelength of at least one of the laser emitters is selected so that the laser beam has a sufficiently high absorption rate by the flammable gas so that the system can detect a predetermined minimum concentration of the gas in the air through which the beam passes, and the system can detect flammable gas along the entire path of the laser beam in an area where a remote receiver can be found.

2. The system according to claim 1, wherein: The laser beam also has an absorption rate by water vapor which does not exceed a predetermined fraction of the absorption rate by the flammable gas.

3. The system according to any one of claims 1 and 2, wherein: The control system is adapted to adjust the beam aiming element using a signal corresponding to a power level input to the receiver to ensure optimal incidence of the laser beam on the beam sensor.

4. A system according to any one of the preceding claims, wherein: The control system is adapted to reduce the power emitted by the laser if the difference between the power of the emitted laser beam and the power input to the receiver exceeds the predetermined level.

5. The system according to any one of claims 1 to 3, wherein: If the difference between the power of the emitted laser beam and the power input to the receiver exceeds the predetermined level, the control system is adapted to perform at least one of the following actions: a. Turn off the laser or reduce its power to a predetermined safe level; b. Alert the user; c. issuing an alarm to an automatic warning system, such as an alarm system or a smart center; d. Call the fire department; e. sound an alarm; f. Turn on the visual warning signal; and g. Cut off the gas supply by issuing a command to the controlled gas supply valve.

6. A system according to any one of the preceding claims, wherein the light beam sensor is a photovoltaic cell.

7. A system according to any of the preceding claims, further comprising a DC / DC converter circuit suitable for converting the output current of the light beam sensor into a current at a higher voltage so that the current is at a voltage suitable for powering externally connected electronic devices.

8. The system according to any one of claims 1 to 6 further comprises a DC / DC converter circuit suitable for converting the output current of the light beam sensor into a current at a higher voltage so that the current is at a voltage suitable for charging a battery of an externally connected electronic device.

9. The system according to any one of claims 7 and 8, further comprising a maximum power point tracking system to ensure optimal efficiency of the DC / DC converter circuit.

10. A system according to any one of the preceding claims, wherein: The control unit is located in the transmitter unit.

11. A system according to any one of the preceding claims, wherein: The wavelength of the at least one laser emitter falls within at least one of the wavelength bands ranging from 820-935 nanometers, 970-1125 nanometers, 1170-1350 nanometers, 1515-1545 nanometers, and 1620-1700 nanometers.

12. A system according to any one of the preceding claims, wherein: The difference between the power of the emitted laser beam and the power input to the receiver is a fractional difference.

13. A method of safely transmitting laser power to at least one remote receiver in a space where at least one flammable gas powered device may be used, the method comprising: Measuring the power of a laser beam transmitted from a transmitter through the space to a receiver, measuring the power of the laser beam received by the receiver after passing through the space; as well as determining a difference between the power of a laser beam emitted from a transmitter into the space and the power input to said receiver after traversing the space, and, if said difference exceeds a predetermined level, shutting down said laser, or reducing its power to a predetermined safe level, Wherein, the wavelength of the laser beam is selected so that the laser beam has a sufficiently high absorption rate by the flammable gas used in the appliance so that the predetermined minimum concentration of the gas in the space passed by the beam to the receiver is sufficient to achieve a predetermined level of power difference, thereby enabling the method to detect dangerous levels of the appliance gas along the entire path of the laser beam in a space where a remote receiver may be present.

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