Drone Noise Reduction through Acoustic Engineering

Reducing noise in audio signals captured by microphones on unmanned aerial vehicles (UAVs) using state information about the UAV itself. The noise reduction is done by processing the audio signal using neural networks with inputs from the UAV's motor speeds, control signals, position estimates, and other state data. This allows more accurate estimation and removal of the UAV's own noise compared to just using the audio signal alone. The state information provides additional context about the UAV's motion, environment, and operation that can improve noise reduction performance.

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An unmanned aerial vehicle (UAV) that can actively cancel noise generated by its rotors without being affected by wind noise. The UAV has a processor that acquires operational information related to the rotor forces. It then generates an opposite phase signal based on this information. The UAV's speakers play back this opposite phase sound. This cancels out the rotor noise since it has an opposite phase to the actual rotor noise. By generating the canceling signal based on rotor operation, it avoids wind noise since the wind doesn't have the same phase as the rotor noise.

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Active noise cancellation of rotor noise for drones and other rotorcraft. It uses sensors to detect rotor noise, then modulates the rotor rotation electronically to produce anti-noise that cancels out the noise. This is done using coils around the rotor and magnets on the blades that can be driven to alter the blade rotation based on sensed noise.

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Active noise cancellation for drones to reduce the loud buzzing sound they make. The drone has microphones to capture environmental sounds, processing to analyze them, and speakers to emit cancellation sounds. This cancels out the original noise heard by people near the drone.

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Active noise cancellation (ANC) on unmanned aerial vehicles (UAVs) to reduce noise generated by the rotor. The UAV has a processor that acquires operational information about the rotor and generates an opposite-phase signal to cancel the rotor noise. This is then output through a speaker to reduce the rotor noise. The key idea is to use ANC to specifically cancel the rotor noise by generating an opposite-phase sound signal based on the rotor operational data.

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Thrust generating device for VTOL aircraft that reduces noise compared to conventional propeller ducts. The device has a duct with stators surrounding the propeller, but unlike conventional ducts that have stators in front of the propeller, the stators are placed behind the propeller. This avoids obstructing the airflow into the propeller and disrupting the propeller's airflow, which creates noise. The stators are located aft of the propeller to still provide thrust and improve efficiency.

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Ducted propeller for unmanned aerial vehicles (UAVs) that improves efficiency compared to open propellers. The ducted propeller has a ducted body with a cavity containing the propeller. The inner wall of the duct has clearance grooves matching the blade outer edge path. The blade rotates into the grooves during operation. This reduces tip clearance compared to unducted propellers. The clearance grooves allow the blade to fully fill the duct volume for higher efficiency. The grooves simplify design compared to adhesive tapes used in prior art ducted propellers.

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Optimized blade and hub design for ducted fan blades in ducted motors that improves airflow efficiency and reduces noise. The blade roots have upper and lower arc radii of 6mm and 20mm respectively, while the blade tips have radii of 10mm and 26mm. This specific radius ratio provides better airflow displacement and stability. The total blade diameter is 27mm, hub diameter is 17mm, and hub height is 6mm.

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A three-bladed roots blower with twisted blades and shaped outlet to reduce noise compared to conventional roots blowers. The blades are twisted relative to the shaft from one end to the other along the extending direction. This spirally extrudes the airflow into the intake. The outlet is shaped to gradually change volume instead of a sudden change. This prolongs the time of backflow impact and reduces strength/noise. The blower also has features like silencers, filters, and perforated plates to further reduce noise.

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Ducted fan assembly with a double-layer propeller for improved efficiency and reduced noise in applications like vertical takeoff and landing aircraft. The ducted fan has a housing, double-layer propeller blades on a central shaft, and covers at the ends. The double-layer blades consist of an inner and outer set that compress air. The housing has split sections that join with bolts. The duct inside has guide vanes to smooth airflow between the layers. This reduces airflow interference and improves compression compared to a single-layer propeller.

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Reducing noise from drones through propeller design. The drones have propellers with treatments that disrupt airflow or absorb sound. By using propellers with different treatments on the same drone, their sounds interfere and cancel out to reduce overall noise. Machine learning can be used to optimize the propeller treatments and speeds for specific drones to minimize sound.

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Aerial vehicles that actively abate the noise they generate during flight. The vehicles capture data on acoustic energies encountered during flight, correlate it with environmental and operational data, and use machine learning to predict future noise. They then emit anti-noise to counteract the predicted noise.

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Active noise abatement for aerial vehicles like drones by predicting and cancelling airborne noise during flight. The method involves capturing acoustic data from drones during operations along with environmental, operational, and position data. This training data is used to train machine learning models to associate acoustic signals with environmental conditions, drone behavior, and positions. Once trained, the models can predict expected noise levels during future flights based on planned routes, conditions, and drone behavior. The drones can then emit anti-noise signals to cancel out the predicted noise during flight.

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Reducing the noise generated by aerial vehicles like drones by using propellers with treatments that disrupt airflow and absorb sound. The idea is to have multiple propellers on an aerial vehicle with different blade treatments that generate destructive interference when they rotate, cancelling out the overall noise. A trained machine learning system predicts the sound profiles of different propeller blade shapes, treatments, and positions at different speeds for specific environments, operational conditions, and locations. It uses this data to determine anti-sounds that can be generated by adjusting the blade treatments. The aerial vehicle's propeller controllers then select blade treatment positions and speeds to match the anti-sounds and commanded lift.

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A propeller for an aircraft that reduces noise without sacrificing efficiency compared to conventional unducted fan propellers. The propeller has an upstream row of rotating blades and a fixed downstream row. The blades in the downstream row are positioned in a specific angular region around the propeller axis. This configuration allows the downstream blades to avoid interference with vortices generated by the upstream blades. The blades in the downstream row are truncated to reduce noise, but by positioning them in a way that avoids vortex interactions, the noise reduction is more effective than just blindly truncating them. This reduces noise levels without compromising efficiency compared to untruncated blades.

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Reducing noise from unmanned aerial vehicle propellers to improve safety and stealthiness. The propeller blades have a special sound absorbing coating applied using a spray welding process. The coating is made by mixing sound absorbing materials like cellulose fibers and melamine resin, and applying it to the blade surfaces using a thermal spray welding process. This coating absorbs and dissipates sound energy instead of reflecting it, reducing the overall noise produced by the propellers.

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A noise-reducing blade design for unmanned aerial vehicles (UAVs) to reduce the loudness of rotor blades. The blade has features like protrusions to cut and break up large vortices into smaller ones, zigzag concave sections to prevent tip stall noise, and a distorted 8-shape to reduce impact with objects. The blade shape, protrusions, and concave sections are designed to reduce aerodynamic noise compared to conventional UAV blades.

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A high-efficiency, low-noise, high-load, and high-safety factor unmanned aerial vehicle (UAV) lifting hook for industrial applications like construction and rescue. The UAV has a unique four-propeller design where the sum of the blade areas exceeds the circular area formed by rotation. This provides better lift efficiency, reduced vibration, and lower noise compared to conventional UAVs. The UAV also has a detachable lifting hook for carrying cargo. The UAV uses a battery, motor, and flight control system like a conventional UAV but with larger blade areas. This allows heavier loads and better lifting performance. The UAV can also tilt and turn like a helicopter for maneuverability.

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Unmanned aerial vehicle (UAV) propeller design that reduces noise compared to conventional propellers. The propeller has a curved upper surface with variable thickness along the length. The curved shape and thickness variation are based on principles of acoustic black holes. This design aims to absorb and cancel out noise generated by the propeller blades as they move through the air. The curved upper surface and variable thickness propeller blades are intended to reduce the UAV's flight noise.

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A noise reduction system for urban air mobility (UAM) vehicles like drones that land and take off from hubs. The system uses active noise control and AI to cancel out the loud noise generated during the vertical takeoff and landing of UAMs. The system has noise-canceling devices at the hubs that receive rotation speed and location data from the UAMs during takeoff/landing. It uses AI to predict the canceling sound wave amplitude based on this data. When sufficient data is accumulated, it stores the factors used for prediction. If not enough data, it calculates the canceling sound wave using recorded noise. The predicted canceling sound wave is then output to the UAM speakers to counteract the takeoff/landing noise. This reduces the overall noise level at the hubs.

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A drone with an active noise cancellation system that allows it to surreptitiously follow and monitor targets without being detected. The drone can detect its own noise from the motor vibration and generate a directed sound beam that cancels out the noise at the target location. This allows the drone to approach and track targets without them hearing it. The drone also has a camera, distance sensor, and image analysis to identify and follow targets. It can also receive instructions wirelessly with target information and extract voice messages from target sounds.

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Acoustic system for Urban Air Mobility (UAM) vehicles like flying taxis to reduce noise levels compared to traditional helicopters. The system uses shrouds around the rotor blades that have perforated inner walls and hollow chambers. The shrouds act as resonating chambers that attenuate low frequency rotor noise. Without the shrouds, the blade tips would generate more noise. The perforations in the inner wall allow airflow through the chamber. An acoustic liner can further enhance noise reduction. The shrouds are annular and extend radially outward from the blades.

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Flight planning for aerial vehicles that reduces community noise by dynamically selecting flight paths based on environmental conditions. The method involves estimating perceived noise at ground locations along proposed flight paths using factors like weather and foliage. A noise abatement function then assigns a value to each path based on the ground noise. Flight plans are chosen with the highest abatement values to reduce noise impacts on communities.

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Taking measures against noise generated by unmanned aerial vehicles (UAVs) by adaptively controlling flight based on local noise restrictions. The UAV acquires allowable noise levels based on factors like time, altitude, location, and weather. It then adjusts flight parameters like altitude, propulsion, and transfer methods to stay within the allowed noise limits. This allows UAVs to operate in areas with noise constraints without exceeding the permitted noise levels.

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Aircraft with reduced noise characteristics by using different propeller designs on the same vehicle to distribute energy over a wider spectrum and reduce perceived noise annoyance. The aircraft has multiple electric motors driving propellers with distinct blade geometries that deliver equal thrust at a predetermined RPM. This avoids constructive interference of tonal noise from multiple propellers spinning at the same RPM. Dynamic RPM monitoring and adjustment compensates for deviations.

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Reducing the noise generated by multiple propellers on aerial vehicles like drones by phasing their blade movements. The propellers have the same number of blades, rotate at the same speed, and are offset by a phase angle determined by the blade count. This reduces the radiated sound power at the blade passing frequency. The phase locking can be achieved mechanically or electronically. The propeller axes can be parallel. The phase offset angle is around 180 degrees divided by the blade count.

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Reducing noise generated by unmanned aerial vehicles (UAVs) while they are flying by adjusting the position of the propeller blades. The propeller blades can be extendable or retractable relative to the motor. Changing the blade position alters the lifting force without changing motor RPM, but also changes the sound profile due to blade tip vortex interaction and blade pitch variation. By positioning the blades so they are out-of-phase, destructive interference cancels out some of the noise.

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Reducing noise generated by unmanned aerial vehicles (UAVs) while they are in flight by adjusting the position of the propeller blades. The blades can be extended or retracted laterally relative to the motor. This alters the lifting force without changing the motor RPM. It also changes the noise profile because the blade tip velocities and spacing are different at different extensions. By positioning the blades so they are out-of-phase, the sounds they generate interfere destructively to cancel out some noise.

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Controlling the acoustic radiation emitted by an aircraft's rotors to reduce noise pollution. The system uses a controller to regulate the rotor settings and modify the acoustic behavior. This involves adjusting rotor parameters like frequency, phase, and directionality to change the sound characteristics. By dynamically tuning the rotor operation, the radiation can be modified to be less annoying or perceptible to people on the ground. The controller modifies the commanded flight settings from the flight control system to achieve the desired acoustic characteristics.

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Noise-reducing propeller for indoor drones to significantly reduce the noise generated by drones when flying indoors. The propeller is designed using the Betz minimum energy loss criterion and blade theory. The blade chord lengths and pitch angles are calculated to minimize energy loss and noise. The chord length distribution is weighted with 0.18 at the tip and 0.46 at the root. This reduces the tip chord length for lower energy loss and less noise conversion. The pitch angles gradually decrease from the root to tip. This noise-reducing propeller can be used on indoor drones to significantly lower their indoor noise levels.

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A noise-reducing and efficiency increasing propeller blade design for drones and other applications. The blade has a pattern of serrations covering the entire surface, as well as serrations on the leading and trailing edges. The serrations on the surface are angled relative to the blade axis when viewed from the side. The serration pattern reduces noise by keeping the flow attached and preventing separation. The angled surface serrations also improve efficiency. The edge serrations further reduce noise by reducing flow separation. The combined serration pattern provides both noise reduction and efficiency improvement compared to plain blades.

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Low noise, high efficiency propellers for unmanned aerial vehicles (UAVs) that reduce noise and power requirements compared to conventional propellers. The propellers have blades with tapered angles near the tips that decrease below zero lift. This unloaded region reduces vortex formation and induced drag, lowering noise and power. The propellers also have shorter overall length than conventional propellers to further reduce noise. The propellers maintain high efficiency without needing higher rotational speeds to compensate for reduced lift.

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Propeller design for rotorcraft that improves aerodynamic efficiency and reduces noise compared to conventional propellers. The propeller has blades with specific twist angles at three radial locations: 36°, 59.5°, and 83.3% of the radius. This twist distribution reduces power consumption for the same lift and allows lower rotational speeds. The swept-back blade tip further reduces tip vortex turbulence and noise.

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Propeller blade design for unmanned aerial vehicles that reduces noise and improves efficiency compared to conventional propellers. The propeller blade is a swept shape with torsion angles between the wing sections. This creates a more aerodynamic and tensioned blade profile that reduces noise compared to straight blades. The swept blade shape also improves lift and thrust at lower speeds, making it suitable for unmanned aerial vehicles.

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A high-efficiency, low-noise rotor wing design for unmanned aerial vehicles that improves flight efficiency and reduces noise compared to traditional rotor blades. The wing has a unique shape with a sequential connection of a smooth section and a sweepback section. The sweepback section has an anti-paddle tip, a sweep upper arc, and a sweep lower arc that meet at a pointed end. This configuration provides higher lift-drag ratio, better stability, and reduced noise compared to symmetrical blades. The sequential connection allows smooth airflow transition between the sections. The anti-paddle tip prevents stall vortices. The pointed end reduces noise by smoothing airflow separation.

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Shrouds for aircraft, especially drones, to reduce noise from propellers. The shrouds have features like baffles inside to dissipate sound by reflection and refraction, as well as outside shapes that redirect sound in desired directions. The shrouds also absorb sound. The aim is to significantly reduce noise heard by people around the drone and improve audio recording quality by minimizing propeller noise.

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Attenuating noise generated by open rotor aircraft propulsion systems without using nacelles. The aircraft has a fuselage or body with an acoustic panel to reduce noise from the open rotors mounted on a pylon. This provides an alternative to conventional nacelles for noise reduction in open rotor aircraft since they lack shrouds around the rotors.

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Reducing noise in aircraft like gyroplanes by adding a sound-absorbing structure at the connection point between the fuselage and tail unit. This reduces noise emissions from the connection area that would otherwise transmit through the aircraft. The sound-absorbing structure can be a separate component or integrated into the connection. It helps mitigate noise without impacting flight performance or adding significant weight. The noise reduction is surprising since it was expected that complex propeller-connection interactions would be difficult to tackle.

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Aerial vehicles like drones with rotor units having asymmetric blade shapes to reduce perceived noise compared to symmetric blades. The asymmetric blades are designed such that their vortex interactions cause the rotor unit to emit a broader spectrum of softer frequencies instead of just strong fundamentals. This makes the overall sound output less objectionable to humans. The asymmetry is selected based on blade area relationships to achieve this acoustic behavior.

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Blade design for unmanned aerial vehicles (UAVs) propellers that reduces vortex interference between blades and improves stability. The blade has a dihedral-angled tip that offsets vortex formation downwards. The chord length and installation angle of the blade sections gradually decrease towards the tip. This offsets vortex tracks away from following blades, reducing disturbance and flapping.

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An aircraft shaped to reduce noise generation has a recessed inlet, protrusions forward of the inlet, and an outlet nozzle at the rear. The inlet is recessed from the leading edge and surrounded by forward protrusions. The wings extend from the main body. This shaping and ducted inlet/outlet configuration reduce noise propagation to the ground compared to conventional UAV designs.

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Engine mufflers reduce noise from small internal combustion engines, particularly for unmanned aerial vehicles (UAVs). The muffler has a body with an interior chamber, a first-end section that attaches to the engine exhaust outlet, and a second-end section that mounts to the engine to resist movement. This prevents the muffler from detaching due to thermal expansion or vibration. The second-end section mounting can use a resilient coupling or preload force.

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Noise reduction systems for air mobility like drones efficiently reduce various types of noise generated during flight. The system uses PWM control of power to propeller inverters and motors to mitigate carrier frequencies from inverters and fundamental frequencies from motors. It also detects noise from sensors and filters it into a carrier and fundamental frequencies. By selecting the longer wavelength frequency, it reduces the corresponding noise. This reduces noise transmitted to nearby objects like people.

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