Preventing Radio and Light Signal Transmission Loss Through a Transmission Surface Due to Weather Environmental and Operational Conditions Using Active Flow Control Actuators

Abstract

Systems and methods for cleaning transmission surfaces for optical and sensor surfaces in order to maintain optimal performance under a variety of weather and environmental conditions using synthetic jet actuators. The actuators can emit a jet of water or air depending on environmental conditions and the waveform, frequency, amplitude of the actuator can be adjusted based on particle characteristics and transmission signal quality in order to better clean the surfaces.

Claims

1. A system for cleaning the surface of a vehicle vision sensor, the system comprising: a sensor cleaning unit, mounted on the vehicle, having at least one actuator configured to direct a fluid jet onto the vehicle vision sensor; a sensor cleaning unit sensor, mounted on the vehicle, having at least one environment sensor configured to capture environmental sensor data proximate the vehicle; a cleaning electronic control unit configured to receive the environmental sensor data from the sensor cleaning unit sensor and to determine at least one of a drive frequency and a drive amplitude for controlling at least one actuator of the sensor cleaning unit, based on the received environmental data.

2. The system of claim 1, wherein the environment sensor includes at least one of a precipitation sensor or an airflow sensor configured to determine apparent wind speed and wind direction.

3. The system of claim 2, wherein the precipitation sensor is configured to determine the diameter of rain droplet sizes during a precipitation event.

4. The system of claim 3, wherein the cleaning control unit sets a drive frequency ranging from 360 Hz for rain droplet diameter sizes of 0.01 mm to 1040 Hz for rain droplet diameter sizes of 4 mm.

5. The system of claim 4, wherein the actuator operates using pulse wave modulation.

6. The system of claim 5, further comprising a water source connected to the sensor cleaning unit, wherein the cleaning electronic control unit is further configured to choose to use one of either water from the water source or ambient air for use with the actuator of the sensor cleaning unit, based on the received environmental data.

7. A system for cleaning the surface of a vehicle vision sensor, the system comprising: a sensor cleaning unit, mounted on the vehicle, having at least one actuator configured to direct a fluid jet onto the vehicle vision sensor.

8. The system of claim 6, further comprising: a cleaning electronic control unit configured to receive vision sensor transmission surface obstruction level data from the vehicle vision sensor indicating an amount of obstruction of a transmission signal through the vehicle vision sensor transmission surface, wherein the cleaning electronic control unit determines at least one of a drive frequency and a drive amplitude for controlling at least one actuator of the sensor cleaning unit, when the amount of obstruction of the transmission signal exceeds a predetermined threshold.

9. A method for cleaning the surface of a vehicle vision sensor, the method comprising: capturing environmental sensor data proximate the vehicle from a sensor cleaning unit sensor mounted on the vehicle; determining, by a cleaning electronic control unit, at least one of a drive frequency and a drive amplitude for controlling at least one actuator of a sensor cleaning unit mounted on the vehicle, generating a fluid jet by the at least one actuator of the sensor cleaning unit to clean the surface of the vehicle vision sensor.

10. A system for cleaning the surface of a photovoltaic solar panel, the system comprising: a sensor cleaning unit, mounted on a peripheral edge of the photovoltaic solar panel, having at least one actuator configured to direct a fluid jet onto the photovoltaic solar panel; a cleaning electronic control unit configured to receive electricity generation efficiency data indicating obstruction of the photovoltaic panels from a control unit associated with the photovoltaic solar panel, or with an energy storage measuring device associated with the cleaning system, the cleaning electronic control unit determining at least one of a drive frequency and a drive amplitude for controlling the at least one actuator of the sensor cleaning unit, when the amount of generation efficiency falls below a predetermined threshold.

11. The system of claim 1, wherein the actuator includes at least one heating element in order to control the temperature of the fluid jet.

12. The system of claim 1, wherein the actuator includes a drainage and an electrically controlled nozzle cover to open or block the nozzle to prevent contaminants from entering the actuator when not in use.

13. The system of claim 1, wherein the actuator is supplied with water which, when combined with the fluid jet, generates a water spray.

14. The system of claim 1, wherein the actuator is mounted on or under a motorized plate in order to remove particles from a transmission surface which wraps 360 degrees around a vehicle mounted vision sensor and further wherein the actuator generates a fluid jet as it rotates around the circumference of transmission surface; and the rotating plate is controlled by an electronic control unit associated with one or more of the vision sensor, cleaning system or vehicle system in order to position the fluid jet in locations across the circumference of the transmission surface which encounter vision blockage by particles that adhere to it.

15. The system of claim 1, wherein the actuator is integrated with a vision sensor and the fluid jet is channeled through a transmission surface which is shaped as a curved surface to cover vision sensor for aerodynamic, optical, environmental or other purpose.

16. The system of claim 1, wherein the sensor cleaning unit further comprises two fluid jet nozzles wherein one water nozzle is located between the two fluid jet nozzles for the release of water, configured so that the fluid jets dispensed from the fluid jet nozzles are combined with water from the water nozzle to generate a water spray.

17. The system of claim 16, wherein the two fluid jets are each operated with a different voltage amplitude such that each air-jet reaches a maximum amplitude at a different time in an alternating manner.

18. The system of claim 17 wherein the flow rate in which water is released through the water nozzle is synchronized with the peak voltage amplitude of the two fluid jets in order to generate a water spray that has a lateral motion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The features and advantages of the present invention will be more fully understood by reference to the following detailed description of illustrative embodiments of the present invention when taken in conjunction with the following figures, wherein:

[0069] FIG. 1 is a schematic diagram illustrating an embodiment of the sensor cleaning system of the present invention where used in connection with a motor vehicle vision sensor.

[0070] FIG. 2 is a schematic diagram illustrating an embodiment of the sensor cleaning unit, a component of the sensor cleaning system of the present invention.

[0071] FIG. 3A is an illustration of the sensor cleaning unit where used with a vision sensor having a curved surface in accordance with an embodiment of the present invention.

[0072] FIG. 3B is an illustration of the sensor cleaning unit when used with a vision sensor having a flat surface in accordance with an embodiment of the present invention.

[0073] FIGS. 4A, 4B, 4C and 4D illustrate various air and water spray configurations of the sensor cleaning unit when used with a vision sensor having a flat surface in accordance with embodiments of the present invention.

[0074] FIGS. 5A and 5B illustrate packaging configurations of the sensor cleaning unit and vision sensor where used in connection with motor vehicles in accordance with an embodiment of the present invention.

[0075] FIGS. 6A, 6B and 6C illustrate the sensor cleaning unit when used with a 360-degree vision sensor in accordance with embodiments of the present invention.

[0076] FIG. 7 is an illustration of sensor cleaning system integration configurations where used in connection with a moving vehicle in accordance with an embodiment of the present invention.

[0077] FIG. 8 is a schematic illustration of the operation of the sensor cleaning system where used in connection with a moving vehicle in accordance with an embodiment of the present invention.

[0078] FIGS. 9A, 9B, 9C, 9D, 9E and 9F illustrate the dependency between water droplet size and actuation frequency using an actuator in accordance with embodiments of the present invention.

[0079] FIGS. 10A, 10B, 10C, 10D and 10E illustrate the interaction between air-jets using an actuator in accordance with embodiments of the present invention and water droplets of various diameters.

[0080] FIG. 11 is an illustration of a photovoltaic cleaning system used in connection with a photovoltaic panel in accordance with an embodiment of the present invention.

[0081] It is emphasized that, according to common practice, various features/elements of the drawings may not be drawn to scale. On the contrary, the dimensions of the various features/elements may be arbitrarily expanded or reduced for clarity.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0082] Initially referring to FIG. 1, a schematic diagram illustrating an embodiment of sensor cleaning system 100 of the present invention is shown. Sensor cleaning system 100 (SCS) is comprised of an electronic power supply unit 101 (EPSU), a cleaning electronic control unit 102 (CECU), and a sensor cleaning unit 103 (SCU). EPSU 101 and CECU 102 provide power and signal respectively to SCU 103 in order to clean transmission surface 104 of vision sensor (VS) 105.

[0083] For example, in a preferred embodiment where SCS 100 receives input from CECU 102 indicating the need to commence cleaning of transmission surface 104, EPSU regulates the amount of power to send to SCU 103. CECU 102 determines what type of signal to output depending on the input it receives from vehicle electronic control unit (VECU) (not shown) or the VS electronic control unit (VSECU) (not shown).

[0084] To illustrate the implementation of an embodiment, in one example, a vehicle is moving at a speed of 50 mph on a highway during heavy rain (about a 4 mm diameter droplet size). To provide enough time for the vehicle to brake in case of obstruction on the path of the vehicle, a roof mounted LiDAR maintains a certain detection distance across a certain field vision. When the field of vision, detection distance and generally the ability to detect objects falls below a required threshold (often due to a reduction in signal intensity which translates to less points on objects being detected), an electronic control unit (the vehicle's, vision sensor or cleaning system) commands the actuator to operate at a certain actuation frequency which has been tested and discovered to be most effective in removing 4 mm droplets.

[0085] In another example, there may no longer be a heavy rain, but the transmission surface can be covered by spray splash from passing vehicles (about a 0.01 mm droplet size). The change in droplet size from the prior rain event is detected by a sensor and a command is issued to change the actuation frequency to another frequency which was discovered to be more effective smaller droplets.

[0086] To provide power to SCU 103, EPSU 101 may receive power from a power source independent of the vehicle, such as a battery or generator, or from the vehicle battery (both not shown). To provide data to the SCU, the CECU receives data from the vehicle electronic control unit (VECU) or the VS electronic control unit (VSECU). The EPSU and CECU can operate a single SCU as shown in FIG. 1, or an array of SCUs simultaneously (not shown).

[0087] FIG. 2 provides detail into the subsystems comprising the sensor cleaning unit, such as found in SCU 103. The SCU receives power from EPSU 240 and data from CECU 250. The SCU includes actuator 200, heating element 210 and water spray unit 220. In embodiments, heating element 210 is used to raise the temperature expelled through the nozzle outside the actuator in order to accelerate the de-freezing process of the transmission surface. Actuator 200 includes drainage opening 204 to let out particles (such as water or melted ice) which entered into the actuator while not operating. Nozzle cover 203 covers nozzle 201 when it is not operating to prevent contaminants from getting into the actuator.

[0088] In embodiments, when the SCU is engaged, EPSU 240 powers actuator 200 to generate air-jet 202 directed at transmission surface 231 of vision sensor (VS) 230. Air-jet 202 removes particles from transmission surface 231. In embodiments, CECU sends a signal to the SCU to activate water spray unit 220. In that scenario, EPSU 240 powers water spray unit 220 which supplies water through water supply conduit 221 to an opening near actuator 200 to generate water spray 222. By providing water spray 222 on transmission surface 231, the SCU washes away particles such as dust, mud, ice, etc., from transmission surface 231 which may not be effectively washed away using air jet 202 on its own. By alternating between water spray 222 and air-jet 202, the SCU can both remove wet and dry particles off the transmission surface, like the combined function of a windshield wiper and water spray in existing vehicles.

[0089] In embodiments (not shown), SCU includes a pair or more actuators to generate air-jet 202 and water spray 222. CECU 250 controls actuator 200 parameters such as frequency, waveform, duty cycle, on/off, and power amplitude.

[0090] CECU 250 controls water spray unit 220 parameters such as on/off, and flow rate. Water spray provides water to water conduit 221 which brings water to nozzle 201 where the combination between the water and air-jet 202 creates water spray 222.

[0091] Adapter 260 shown not in use in FIG. 2, can be used in embodiments where the original articulation of air-jet 202 is not optimal for particle removal on transmission surface 231 due to SCU positioning constraints with respect to transmission surface 231. In such a scenario, adapter 260 is attached to actuator 200 such that air jet 202a is redirected through adapter 260 in order to reach transmission surface 231 (not shown in use with adapter 260) at the optimal angle for removing particles. In such an embodiment, the angle of air-jet 202a may be modified through channeling via adapter 260 until the optimal angle is obtained.

[0092] In other cases, adapter 260 is used to affect other parameters of air-jet 202 such as jet spread angle to cover a larger area of transmission surface 231. Spread angle through the use of adapter 260 can also be similarly adjusted through the use of channeling of adapter 260 until the optimal angle is reached.

[0093] In embodiments where a water spray is being generated with adapter 260 (not shown), water spray 222a (shown schematically) is generated by providing water through conduit 221 either into the adapter, using its internal channel as a mixing chamber, or next to its opening, as with nozzle 201, combining water and air-jet 202a to create water spray 222a.

[0094] Turning to FIG. 3A, an embodiment where the sensor cleaning unit is used with a vision sensor having a curved surface is shown. In embodiments, transmission surface 321 of vision sensor 320 is shaped as a curved surface for aerodynamic, optical, environmental or other purpose. In such an embodiment, nozzle 301 of actuator 300 may be integrated into transmission surface 321 such that air-jet 310 is channeled to cover transmission surface 321 to achieve particle removal across transmission surface 321. In embodiments, actuator 300 is integrated into the packaging of vision sensor 320 and its size may be dictated by constraints set forth by the sizing of vision sensor 320. In embodiments (not shown), actuator 300 may be part of a standalone SCU and not integrated into vision sensor 320. In embodiments where the actuator and vision sensor share packaging, the actuator is likely to be dedicated to the specific vision sensor. In that case, CECU and VSECU are the same and the vision sensor directly controls the operation of the cleaning process. In other words, the actuator is part of the vision sensor, and the vision sensor provides it with power and data to command its operation.

[0095] Turning to FIG. 3B, an embodiment where the sensor cleaning unit is used with a vision sensor having a flat surface is shown. In this embodiment, actuator 300 is located externally to the packaging of vision sensor 320. In other embodiments (not shown) actuator 300 may be integrated into the packaging of vision sensor 320. Turning to the operation of actuator 300, actuator 300 generates air-jet 310 and 311 in order to maintain transmission surface 321 clear of particles such that vision sensor 320 could detect objects in a manner required to maintain the safety of the vehicle. In one embodiment, particles 350 approach transmission surface 321 and adhere to its surface. In this case, actuator 300 generates air-jet 310 through nozzle 301 which removes particles 351 by blowing them away off the transmission surface. Actuator 300 can be engaged by the SCU (not shown) based on a variety of environmental factors, such as precipitation, water-based and dust-type particles and the interference caused to a transmission surface. In an alternative embodiment, actuator 300 can be programmed to actuate on a timed cycle, or in another embodiment on a continuous duty cycle.

[0096] In an alternate embodiment when actuator 300 operates on a continuous duty cycle (not shown), actuator 300 generates air-jet 311 through nozzle 301. Air-jet 311 is directed away from transmission surface 321 to create an air-curtain which deflects particles 352 from reaching transmission surface 321 such that they do not reach transmission surface 321. In this embodiment, air-jet 311 is created by an additional actuator. In such an embodiment, each actuator would be directed differently. One actuator would be directed towards the transmission surface and a second actuator would be directed away from the transmission surface at an angle of 0-45 degrees.

[0097] FIGS. 4A-4D, illustrate various configurations of the air and water spray configurations of the sensor cleaning unit when used with a vision sensor having a flat surface in accordance with embodiments of the present invention.

[0098] In the embodiment shown in FIG. 4A, water is released through nozzle 401a. Air-jet 404a is generated by actuator 400 through nozzle 403a. When air-jet 404a is combined with water through nozzle 401a, it generates water spray 402a in order to clean transmission surface 411 of vision sensor 410. In embodiments, air-jet 404a is controlled by the CECU in order to modify the properties of water spray 402a such as its spread, distance and particle size.

[0099] In the embodiment shown in FIG. 4B, water is released through nozzle 401b, located between air-jets 403b and 405b. Air-jets 404b and 406b are generated by actuator 400 through nozzles 403b and 405b, respectively. When air-jets 404b and 406b are combined with water through nozzle 401b it generates water spray 402b in order to clean transmission surface 411 of vision sensor 410. In this embodiment, air-jets 404b and 406b are operated with a phase angle difference and different voltage amplitude such that each air-jet reaches maximum amplitude at different times in an alternating manner. In an embodiment, the phase angle ranges from 0-180 degrees and the voltage ranges from 20-200 Vrms. In a preferred embodiment, the flow rate in which water is released through nozzle 401b is synchronized with the peak voltage amplitude of one or both of air jets 404b and 406b in order to provide water spray 402b with lateral motion 407b which has been shown to improve particle removal capability as compared without a lateral motion component.

[0100] In the embodiment shown in FIG. 4C, air-jet 404c is generated by actuator 400 through nozzle 403c in order to remove particles from transmission surface 411 of vision sensor 410. In embodiments, actuator 400 and its corresponding air-jet 404c could be part of a larger array of actuators that comprise an SCU.

[0101] In the embodiment shown in FIG. 4D, water spray 402d is generated by actuator 400 through nozzle 401d in order to remove particles from transmission surface 411 of vision sensor 410. In this case, water is supplied into the internal part of actuator 400 (not shown) and is pushed out along with the air expelled through nozzle 401d. In another embodiment (not shown), the water is supplied into an adapter attached to nozzle 401d. In another embodiment (not shown), water is supplied next to nozzle 401d such that water spray 402d is generated by the air-jet passing through nozzle 401d.

[0102] Turning to FIGS. 5A and 5B, embodiments of various packaging configurations of the sensor cleaning unit and vision sensor where used in connection with motor vehicles in accordance with an embodiment of the present invention are shown. In the embodiment depicted in FIG. 5A, packaging enclosure 530 includes both actuator 500a, and vision sensor 510a with transmission surface 520a. Actuator nozzle 501a is built into enclosure 530. In this embodiment, actuator 500a and vision sensor 510a are designed to work together where vision sensor 510a commands actuator 500a through its associated controls hardware and software which determine when navigation performance is below a certain safety threshold and cleaning of transmission surface 520a through the use of actuator 501a is required.

[0103] In the embodiment depicted in FIG. 5B, actuator 500b and vision sensor 510b are independent from each other in terms of packaging enclosure. In this embodiment, actuator adapter 501b is attached to actuator 500b to direct air-jet 502b to more effectively remove particles from transmission surface 520b.

[0104] FIGS. 6A-6C illustrate the sensor cleaning unit when used with a 360-degree vision sensor in accordance with embodiments of the present invention.

[0105] In the embodiment depicted in FIG. 6A, actuator 603a is mounted on or under vision sensor 600a to remove particles from transmission surface 610a which extends 360 degrees around vision sensor 600a. In this embodiment, actuator 603a is comprised of multiple nozzles 602a distributed along the circumference of vision sensor 600a in order to release air-jets 601a around the entire circumference of vision sensor 600a.

[0106] In the embodiment depicted in FIG. 6B, actuator 603b is mounted on or under vision sensor 600b to remove particles from transmission surface 610b which extends 360 degrees around vision sensor 600b. In this embodiment, actuator stack 603b includes several actuators where polar nozzle array 602b releases air-jets 601b around the entire circumference of vision sensor 600a.

[0107] In the embodiment depicted in FIG. 6C, actuator 603c is mounted on or under motorized plate 604c in order to remove particles from transmission surface 610c which extends 360 degrees around vision sensor 600c. In this embodiment, actuator 603c generates air-jet 601c through nozzle 602c as it rotates around the circumference of transmission surface 610. Rotating plate 604c is controlled, in embodiments, by the CECU, VSECU or VECU in order to position nozzle 602c to generate air-jet 601c in locations across the circumference of transmission surface 610c which encounter vision blockage by particles that adhere to it.

[0108] FIG. 7 is an illustration of sensor cleaning system integration configurations where used in connection with a moving vehicle in accordance with an embodiment of the present invention. In this embodiment, vehicle 700 can be either an autonomous or driver-assist vehicle. In embodiments, vehicle 700 is equipped with vehicle electronic sensor 701 (VES) which is tasked with providing required input for sensor cleaning purposes to the vehicle electronic control unit 702 (VECU) that is part of vehicle system (not the cleaning system); cleaning electronic control unit 705 (CECU); vision sensors 710, 720, 730, 740, 750 (VS). In embodiments, VS 710, 720, 730, 740, 750 can utilize vision sensing technologies such as Radar, LIDAR, or the visual light spectrum such as with cameras.

[0109] In embodiments, VS 710, 720, 730, 740, 750 are integrated into vehicle exterior surfaces such as the front and rear bumper, doors, wheel covers, roof and hood. In an alternate embodiment, VS 710, 720, 730, 740, 750 can be installed as stand-alone installations separate from vehicle body exteriors such as a pod installed on a roof rack or underbody of the vehicle. In an embodiment, certain VS are integrated into vehicle exterior surfaces and other VS are installed as stand-alone installations.

[0110] In embodiments, vehicle 700 is also equipped with sensor cleaning unit 715, 725, 735, 745, 755 (SCU) dedicated to cleaning the respective VS; sensor cleaning unit sensor 716 (SCUS), which in embodiments comprises a sensor such as a camera, precipitation sensor, airflow sensor, or the like, that provides the CECU required input for commanding the SCUS. In embodiments, vehicle 700 is also equipped with vision sensor 721 (VSS) and vision sensor electronic control unit 722 (VSECU).

[0111] Embodiments of the sensor cleaning system depicted in FIG. 7 can operate in various configurations. In one embodiment (the “Independent System approach”) the control authority of the cleaning system is independent from vehicle 700 or VS 710, 720,730,740, 750. In this case, CECU 705 receives data required for cleaning from SCUS 716. Data received from SCUS 716 includes the size of area blocked by particles on transmission surface. CECU 705 analyzes the data and provides commands such as start/shutoff, voltage amplitude, actuation frequency, duty cycle, and waveform type to an array of SCUs 715, 725, 735, 745, 755 associated with their respective vision sensors at different locations on vehicle 700. In accordance with this embodiment, CECU 705 commands either a full array of SCUs, part of the array or a single SCU. When controlling more than one SCU, CECU 705 provides simultaneously different commands to various SCUs depending on parameters such as the type of VS they are tasked to, location around the vehicle, and local airflow conditions the VS is exposed to.

[0112] In one embodiment (the “Tier 2 approach”), SCU 715, 725, 735, 745, 755 are controlled by VS 710, 720, 730, 740, 750 respectively which it is tasked to clean. Each SCU receives commands through the VS system which includes VSS 721 and VSECU 722. In accordance with this embodiment, VSS 721 or VS 720 provides data required for cleaning to VSECU 722. VSECU 722 commands the dedicated SCU 725. SCU 725 performs a cleaning action and can be stopped once the VSS 721 or VS 720 provide input to the VSECU 722 that required vision level or associated performance associated with VS 720 has been attained.

[0113] In one embodiment (the “OEM approach”) the cleaning system is controlled by the vehicle system including VES 721 and VECU 702. VECU 702 receives cleaning requests from VES 721. VECU 702 commands array of SCU 715, 725, 735, 745, 755 or one or more of SCU 715, 725, 735, 745, 755.

[0114] In one embodiment (the “Hybrid approach”) to control an array of SCUs, an individual or part of the SCU array is controlled by one of the approaches discussed above (e.g., the Independent System approach, the Tier 2 approach, or the

[0115] OEM approach) while one or more parts of the array are operated by the other approaches discussed above such that the entire array is controlled by at least two of the provided approaches.

[0116] FIG. 8 is a schematic illustration of the operation of the sensor cleaning system where used in connection with a moving vehicle in accordance with an embodiment of the present invention. In this embodiment, the sensor cleaning system adapts cleaning performance to dynamic vehicle conditions. In this embodiment, a series of external environmental, operational, mechanical inputs such as droplet size 840, driving speed 845, apparent wind direction speed 850, and object detection status 855 of transmission surface 800 are provided to cleaning electronic control unit 835 (CECU).

[0117] CECU 835 provides input such as a trapezoidal waveform 810 of a certain frequency with a short rise and a long fall, a sinusoidal waveform 820 of a low frequency, and a sinusoidal waveform 830 of a high frequency, and could also include additional signal conditioning parameters such as a modulation frequency and a duty cycle in order to control one or more sensor cleaning unit actuators 815 to remove particles 801, 802, or 803, such as droplets of different dimensions, contact angle, and density; which are located at various places across transmission surface 804, 805, 806 of different importance for vision sensor performance.

[0118] It has been discovered that cleaning performance is a function of actuation parameters such as actuation frequency and waveform. Accordingly, in an embodiment when the control system senses particles of a certain size, then it transmits instructions for a trapezoidal waveform with a short rise and fall. The shape of the waveform—a sudden increase from no voltage to peak voltage—transforms into an abrupt air-jet issued by the actuator. When the air-jet hits the transmission surface at high speed at a very short time period, the droplets located in vicinity to the area hit by the air-jet are excited out of equilibrium and coalesce with neighboring droplets to form larger wetted areas.

[0119] It has been discovered that the air-jet is more effective in transporting these coalesced wetted areas across the transmission surface for a longer distance compared to much smaller droplets. It has also been discovered that different actuation frequencies of the same waveform, such as a pure sine wave, transport better different droplet sizes across the transmission surface. In a preferred embodiment, pre-designed signals are used. These pre-designed signals are constructed to include a sequence of waveforms at specific frequency of frequency range to be customized for a certain scenario. For example, a pre-designed signal might start by a number of trapezoidal waves to break and coalesce the droplets followed by low frequency sine wave cycles in order to transport the droplets across the transmission surface while reducing the power consumed by the actuator. Once the droplets are removed from the surface, the signal might change to a pulse width modulation with a duty cycle of 25% as a maintenance mode, meaning low power consumption air-jet that doesn't remove the particles entirely but delays their accumulation.

[0120] Table 1, presents experimental data illustrating what is seen on the transmission surface when applying a cleaning cycle. The Y-axis shows the obstruction level assessment of a transmission surface. In other words, the cleaning system records (through its sensor) how much of the transmission surface is blocked by water droplets. The X-axis is time. Starting from left to right, there is no obstruction on the transmission surface until water droplets land on the surface. Once the actuator is applied, the obstruction level drops, meaning that the actuator is removing some of the droplets and clears parts of the surface. The curves represent cases where the droplets on the transmission surface are of different size. As illustrated by Table 1, the actuator has a different impact as to droplets of different sizes.

[0121] FIGS. 9A, 9B, 9C, 9D, 9E and 9F illustrate the dependency between water droplet size and actuation frequency using an actuator in accordance with embodiments of the present invention. FIGS. 9A, 9B and 9C illustrate a high frequency (1040Hz) actuator removing water droplets of 4 mm, 0.1 mm, 0.01 mm diameters respectively from a transmission surface. FIGS. 9D, 9E and 9F illustrate a low frequency (360 Hz) actuator removing water droplets of 4 mm, 0.1 mm, 0.01 mm diameters, respectively, from a transmission surface.

[0122] As seen in FIGS. 9A-9F, although a high frequency actuator has a higher speed, actuation frequency has a bigger impact on removing droplets of different sizes. Thus, while a high frequency actuator is very effective in removing large droplets and less effective with smaller droplets, a low frequency actuator has an opposite effect. Accordingly, in embodiments, a high frequency is used for an actuator to remove droplets of larger size (e.g., about 4 mm) while a low frequency is used to remove droplets of smaller size (e.g., about 0.01 mm). In embodiments, intermediate frequencies are chosen to remove droplets of intermediate size (e.g., between about 0.01 mm to about 4 mm).

[0123] FIGS. 10A, 10B, 10C, 10D and 10E illustrate the interaction between air-jets using an actuator in accordance with embodiments of the present invention and water droplets of various diameters. Specifically, FIGS. 10A, 10B, 10C, 10D, and 10E illustrate the interaction between the air-jet and 4 mm droplets covering a transmission surface. The initial impact of the air-jet leads nearby droplets to coalesce with other droplets in their vicinity.

[0124] Further, as illustrated in FIG. 10, using specific waveforms generates coalescence where the air-jet initially hits the optical surface. FIGS. 10A-10E illustrate actuation over a short amount of time. FIG. 10A shows a transmission surface with actuation of 0.7 seconds. FIG. 10B shows a transmission surface with actuation of 0.95 seconds. FIG. 10C shows a transmission surface with actuation of 1.24 seconds. FIG. 10D shows a transmission surface with actuation of 1.4 seconds. FIG. 10E shows a transmission surface with actuation of 4.51 seconds. As seen in FIG. 10E, after 4.51 seconds, the droplets have coalesced and cleaned the surface.

[0125] FIG. 11 illustrates a sensor cleaning unit using synthetic jet actuators in use with a photovoltaic panel 1100. In embodiments, actuators 1110 are mounted on a peripheral edge of photovoltaic solar panel 1100. In one embodiment, a cleaning electronic control unit (not shown) is configured to receive electricity generation efficiency data indicating obstruction of the surface 1111 of photovoltaic panels 1100. When the obstruction level reaches a certain threshold, actuators 1110 are initiated creating jet 1115 which is directed across surface 1111 of photovoltaic panel 1100 to clean the obstruction, such as dust, pollen and the like, from surface 1111.