Abstract: An active noise control subassembly for reducing noise caused by a source (such as an aircraft engine) independent of the subassembly. A noise radiating panel is bendably vibratable to generate a panel noise canceling at least a portion of the source noise. A piezoceramic actuator plate is connected to the panel. A back plate is spaced apart from the first plate and the panel with the panel positioned between the source noise and the back plate. A pair of spaced-apart side walls each generally abut the panel and the back plate so as to generally enclose a back cavity. A mechanism is provided for varying the panel resonating frequency by varying the state of the back cavity (such as by varying its fluid pressure and/or volume) while the panel is undergoing bending vibrations.

Abstract: An active noise control subassembly array for reducing noise caused by a source (such as an aircraft engine). A pair of subassemblies each has a piezoceramic-driven noise radiating panel to generate a panel noise canceling at least some of the source noise. A front plate is spaced apart from the panel and has a sound exit port. A first pair of spaced-apart side walls each generally abuts the panel and the front plate so as to generally enclose a front cavity to define a resonator. A back plate is spaced apart from the panel by a second pair of side walls. The pair of subassemblies are spaced apart to create a space between their adjacent side walls. A third subassembly is similar to the pair of subassemblies but may have a different resonant frequency and is positioned such that the back plates of the subassembly pair serve as the front plate of the third subassembly with the space between the subassembly pair serving as the sound exit port of the third subassembly.

Abstract: An active noise control subassembly for reducing noise caused by a source (such as an aircraft engine) independent of the subassembly. A noise radiating panel is bendably vibratable to generate a panel noise canceling at least a portion of the source noise. A piezoceramic actuator plate is connected to the panel. A front plate is spaced apart from the panel and the first plate, is positioned generally between the source noise and the panel, and has a sound exit port. A first pair of spaced-apart side walls each generally abut the panel and the front plate so as to generally enclose a front cavity to define a resonator.

Abstract: An active noise control subassembly for an aircraft engine. An aircraft engine noise radiating panel is bendably vibratable to generate a canceling noise generally opposite in phase to at least a portion of the discrete tonal noise produced by the engine. A piezoceramic actuator plate is vibratable by an applied electric AC signal. The plate is connected to the panel such that vibrations in the plate cause bending vibrations in the panel and such that the plate is compressively prestressed along the panel when the panel is free of bending vibrations. The compressive prestressing increases the amplitude of the canceling noise before the critical tensile stress level of the plate is reached. Preferably, a positive electric DC bias is also applied to the plate in its poling direction to increase the amplitude of the canceling noise before the sum of the AC signal and DC bias exceeds the depolarization voltage in a direction opposite to the poling direction.

Abstract: The output of a second sensor is matched to the output of a first sensor. The sensors, such as two microphones, are generally identically and simultaneously exposed to a physical quantity which they have been designed to sense. Their outputs are presented as digital outputs. The second sensor's digital output is numerically adaptively filtered using an adaptive filter having adaptive filtering coefficients. The filter's output is equal to the sum of the products of the second sensor's digital outputs and the associated adaptive filtering coefficients, with the sum taken over a predetermined number of sampling intervals. The adaptive filtering continues until the adaptive filtering coefficients are determined such that the filter's output matches the first sensor's digital output to within a predetermined value. Thereafter, the second sensor's digital output is filtered with fixed coefficients which are equal to the adaptively-determined coefficients.

Abstract: The output of a second sensor is matched to the output of a first sensor. The sensors, such as two microphones, are generally identically and simultaneously exposed to a physical quantity which they have been designed to sense. Their outputs are presented as digital outputs. The second sensor's digital output is numerically adaptively filtered using an adaptive filter having adaptive filtering coefficients. The filter's output is equal to the sum of the products of the second sensor's digital outputs and the associated adaptive filtering coefficients, with the sum taken over a predetermined number of sampling intervals. The adaptive filtering continues until the adaptive filtering coefficients are determined such that the filter's output matches the first sensor's digital output to within a predetermined value. Thereafter, the second sensor's digital output is filtered with fixed coefficients which are equal to the adaptively-determined coefficients.

Abstract: An active vibration control subassembly for a structure (such as a jet engine duct or a washing machine panel) undergoing bending vibrations caused by a source (such as the clothes agitator of the washing machine) independent of the subassembly. A piezoceramic actuator plate is vibratable by an applied electric AC signal. The plate is connected to the structure such that vibrations in the plate induced by the AC signal cause canceling bending vibrations in the structure and such that the plate is compressively pre-stressed along the structure when the structure is free of any bending vibrations. The compressive prestressing increases the amplitude of the canceling bending vibrations before the critical tensile stress level of the plate is reached. Preferably, a positive electric DC bias is also applied to the plate in its poling direction.

Abstract: A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of noise radiating structure is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating structure is tuned by a plurality of drivers arranged to contact the noise radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the noise radiating structure. The drivers are actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the drivers, causing them to expand or contract. The noise radiating structure may be either the outer shroud of the engine or a ring mounted flush with an inner wall of the shroud or disposed in the interior of the shroud.

Abstract: A signal enhancement system for separating a composite diagnostic signal detected in a rotating machine into component signals representative of the contributions to the composite signal of a number of independent sources. The signal enhancement system includes at least one signal subtraction loop having a transducer which produces a reference signal based on the rotational speed of a rotating shaft in the machine and an adaptive filter connected to the transducer. The adaptive filter processes the reference signal to produce a component signal which closely approximates the contribution of the rotating shaft to the composite signal. A summer is also included which subtracts the component signal from the composite diagnostic signal to produce a second component signal. Both the first and second component signals are provided as outputs of the system.

Abstract: A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by an expandable ring embedded in the noise radiating element. Excitation of the ring causes expansion or contraction of the ring, thereby varying the stress in the noise radiating element. The ring is actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the ring, causing the ring to expand or contract. Instead of a single ring embedded in the noise radiating panel, a first expandable ring can be bonded to one side of the noise radiating element, and a second expandable ring can be bonded to the other side.

Abstract: A method for matching the second output of a second sensor to the first output of a first sensor wherein a source transducer is driven by a reference analog or digital electrical signal to produce the physical quantity (e.g., acoustic pressure) the sensors (e.g., pressure sensors, such as microphones) can sense. A reference adaptive filter determines filtering coefficients to match the reference electrical signal to the first output of the first sensor and therefore models the source transducer and the first sensor (which typically is an independently-calibrated sensor). Thereafter, a second adaptive filter compensates the second output of the second sensor to match the output from a fixed filter having filtering coefficients identical to those determined by the reference adaptive filter, such output compensation of the second sensor not requiring the presence of the first sensor.

Abstract: A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency is tuned by adjusting the size of a frame which encloses the noise radiating element. One or more expandable elements are disposed in the frame to produce expansion and contraction of the frame. The elements are actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the frame to expand or contract.

Abstract: A fan assembly has a fan motor and first and second generally identical and spaced apart fans each rotationally attached to the fan motor to turn at the same rotational speed. Each fan has an equal number of generally identical fan blades and produces noise including a tone having a frequency equal to its rotational speed times its number of fan blades. The fan blades of one fan are angularly offset at a relative phase angle with respect to the fan blades of the second fan such that the tones of each fan generally cancel each other out. An equation is provided for a ducted fan assembly relating the relative phase angle to the rotational speed of the fans, the number of fan blades of each fan, the geometry of the duct, and the speed of sound in air within the duct.

Abstract: A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied.

Abstract: An active noise control system which minimizes noise output by creating a secondary, cancelling noise field using vibrational inputs. The system includes one or more piezoceramic actuators mounted to the inner surface of the shroud of an aircraft engine. The actuators can be either mounted directly to the shroud or to one or more noise cancelling members which are resiliently mounted the shroud. Transducers are also provided for sensing the noise generated by the engine and producing an error signal corresponding to the level of noise sensed. A controller sends a control signal to the actuators in response to the error signal, thereby causing the actuators to vibrate and generate a noise field which minimizes the total noise emanating from the engine. The piezoceramic actuators can be thin sheets of piezoceramic material or can be in the form of a piezoelectric-driven mechanical lever arrangement.

Abstract: A system for reducing noise created by multiple rotating machines by synchronizing the machines so as to establish a phase relationship between the machines which minimizes the noise. One or more feedback sensors, such as microphones, are placed so as to sense the noise to be reduced. The noise signals from the microphones are sent to a controller. Tachometer signals of the rotational speed of each machine are also sent to the controller. The controller generates an output signal in response to the inputs from the microphones and the tachometers that is fed to one or more of the rotating machines in order to establish the desired phase relationships.