Abstract: A control system includes a plant 56 having resonant modes and a controller 5 which receives plant input signals on lines 14,24 from the plant 56 and provides a controller output signal I, related to a filter output signal V, which controls the plant 6. The controller is provided with a non-linear notch filter 30 which receives a filter input signal x related to the plant input signals and provides the filter output signal V. The notch filter has at least one notch frequency near one of the resonant modes so as to attenuate one of the modes by a predetermined amount and has a phase lag a decade below the lowest notch frequency of said notch filter which is less than that of a corresponding linear notch filter, thereby allowing the control system 7 to exhibit faster time response and increased bandwidth than a system employing linear notch filters.

Abstract: A photo-acoustic leak detection system for detecting a gas leaking from a component 30, includes at least two laser beams 24,26, incident on the component 30 and disposed so as to completely illuminate an inspection region 159 around at least a portion 28 of the component 30, each beam having a corresponding wavelength .lambda..sub.1 which is absorbed by the gas, the gas emitting an acoustic signal 36 when the gas absorbs light from at least one of the beams, an acoustic sensor 40, which receives the acoustic signals 36 and provides a sensor signal indicative thereof on a line 42 to a bandpass filter 44 and a synchronous detector 18 which provide a filtered signal indicative of the acoustic signal 36 on a line 50 to a signal processor 52. The processor 52 provides an output signal indicative of the leak in the component 30.

Abstract: An active noise (or vibration) control system having an actuator 24 which provides an acoustic anti-noise signal in response to an drive signal (U), an error sensor 16 which senses the acoustic anti-noise signal from the actuator, senses disturbance noise (d), and provides an error signal (e) indicative of a combination thereof, and a controller 20, responsive to the error signal (e), which provides the drive signal (U) to the actuator 24, is provided with controller compensation 78 having energy states 112 and having non-linear reset logic 130 which temporarily resets the energy states 112 in the filter 78 to zero when the error signal crosses zero, thereby improving the bandwidth of the active noise control system.

Abstract: A photo-acoustic leak detection system for detecting a gas leaking from a component includes a beam, having a wavelength, incident on the component and producing an acoustic signal. A second acoustic signal is also produced when an air source dilutes the gas leaking from the component. A signal processor receives sensor signals indicative of both acoustic signals and uses the second sensor signal as a non-leak baseline measurement and provides an output signal indicative of whether a leak exists.

Abstract: A magnetic bearing with reduced control-flux-induced rotor loss includes a rotor 14, and a stator 12 having a plurality of slots S1-S16 around which coils 150-156 of a first Phase A and coils 160-166 of a second Phase B are wound. The winding configuration provides a two pole magnetic field around a rotor/stator gap 15 which is sinusoidal and which can be directed to any location along the gap 15. The configuration minimizes discontinuities or sharp changes in control flux in the gap which thereby reduces rotor losses. Also, the stator tooth gap g1 is minimized to provide smooth flux distribution along the rotor/stator gap 15. More phases and more or less stator slots may be used.

Abstract: A machine having protruding elements 26 and an adjacent abradable seal 18, which move relative to each other, an air-path clearance G between the seal 18 and the elements 26 and an element distance D2 between the sensor 10 and the elements 26, is provided with a sensor 10 which is recessed within the seal 18 by a recess distance D. A clearance/thickness circuit 14 provides transmitted and reflected microwave signals 30,32 along a coaxial cable 12 having a characteristic impedance, to the sensor 10, which has an impedance substantially matched to the characteristic impedance of the cable 12. The sensor 10 provides the reflected signal 32 which is indicative of the recess distance D when the elements 26 are not in front of the sensor 10 and is indicative of the blade distance D2 between the sensor 10 and the elements 26 when the elements 26 are in front of the sensor 10.

Abstract: A photo-acoustic leak detection system for detecting a gas leaking from a component (30), includes at least one laser beam (20), incident on the component (30) and having a wavelength which is absorbed by the gas, the gas emitting a photo-acoustic signal (36) when the gas absorbs light from the beam (20), the beam (20) being pulsed at a pulse frequency, the pulse frequency being related to a detection frequency of the photo-acoustic signal and being a frequency at which the magnitude of background acoustic noise at the detection frequency is at a predetermined low level, at least one acoustic sensor (40), which receives the photo-acoustic signal (36) and provides a sensor signal on the line (42) indicative thereof to a filter (44) and a synchronous detector (18), which provide a filtered signal on a line (50) to a signal processor (52). The processor (52) provides an output signal on a line (54) indicative of the leak in the component.

Abstract: An active noise control system includes sensors 16,26 which detects noise 114 and provides electronic signals to an active noise control (ANC) controller 20. The controller provides electronic anti-noise signals to a speaker 24 which is connected to, and provides acoustic anti-noise into, a plurality of active resonators 120-124. The resonators 120-124 are disposed successively along the propagation direction of the noise 114 and provide time-delayed anti-noise acoustic output signals each of which attenuates a portion of the noise 114. The phasing of the anti-noise signals from the resonators 120-124 may be accomplished by acoustic and/or electronic time delays.

Abstract: Resin curing of a composite laminated structure is monitored using an optical fiber 20 having a grating sensor 28 embedded therein. The fiber 20 is surrounded by upper and lower buffer regions 12,14 having a predetermined minimum number of layers 30 (or thickness) with uni-directional reinforcing filaments 32 and resin 34 therebetween. When the filaments 32 are oriented perpendicular to the longitudinal axis of the fiber 20, the buffer regions 12,14 allow the sensor 28 to exhibit maximum sensitivity to detection of the minimum resin viscosity and the gelation point (i.e., the onset of a rapid crosslinking rate) of the resin 34. The buffer regions 12,14 also have a minimum thickness which serve to isolate the sensor 28 from interfering stresses from arbitrarily angled filaments 32 in layers 30 of outer regions 10,16 which surround the buffer regions 12,14.

Abstract: An active noise control system is provided with a plurality of error sensor arrays 50,77 which provide signals on lines 64-74,90-100 to beam forming and beam steering logic 76 which cause the arrays 50,77 to exhibit acoustic response profiles 104,106, respectively. The profiles 104,106 intersect in a predefined region 116 to be quieted. The logic 76 provides signals on lines 118, one for each region to be quieted, to active noise control (ANC) logic 20 which also receives inputs from feedforward sensing microphones 10 and provides output signals to acoustic speakers 24 which generate anti-noise 26 to cancel the noise in the quiet region 116. The quiet region 116 may be selectively positioned to any region in the room by steering the beams 104,108. Alternatively, the system may have a plurality of distributed sensors which, when taken together, have an overall maximum (main lobe) acoustic response at a predetermined selectable quiet region.

Abstract: A reduced phase-shift nonlinear filter includes linear filter logic 10 responsive to a filter input signal x and having a linear transfer function G(s), which provides a linear filtered signal g, zero-cross sample-and-hold logic 16 responsive to the filter input signal x and the linear filtered signal g, which provides a square wave signal n which crosses zero at the same time and in the same direction as the filter input signal x and has an amplitude proportional to the value of the linear filtered signal g at that time, complementary filter logic 20 responsive to said square wave signal n and having a complementary transfer function (1-G(s)) which provides a complementary filtered signal c, and a summer 30 which adds the complementary filtered signal and the linear filtered signal to provide a filter output signal y which exhibits less phase shift over certain frequency bands than that of the linear transfer function.

Abstract: A fiber laser 26 including a rare-earth doped fiber laser cavity 32 delimited by a pair of reflective elements 28,30, such as Bragg gratings, is tuned by compressing the cavity 32 and the gratings 28,30. Because an optical fiber is a much stronger under compression than in tension, the laser 26 is tunable over a much broader range than conventional tension/stretching techniques.

Abstract: An efficient wavelength multiplexer/demultiplexer includes a plurality of 2.times.2 optical couplers 122,180,200,220, each having a pair of matched gratings 130,142; 182,184; 202,204; and 222,224, having bandpass wavelengths .lambda..sub.1, .lambda..sub.2, .lambda..sub.3, .lambda..sub.4, respectively, attached to two of the ports. An input signal 116 enters a port 120 and is split and reflected off the gratings 130,142 and then recombined so as to provide all the input signal 116 at an output port 150 and no reflection out of the port 120. Another input signal 154 is incident on the grating 142 which is passed by the grating 142 and is coupled onto the output port 150 with the signal 116 as a signal 160. A similar arrangement exists for the other couplers 180,200,220 connected in series, each of which adds another input wavelength. Alternatively, in a de-multiplexing application the signal 116 may be broadband and the signals 154,190,206,230 would be separate output wavelengths.

Abstract: A fiber optic sensor for magnetic bearings includes a stator 12, a rotor 14, and an optical transmit/receive fiber 50 which propagates transmit light 112 which is launched across a gap 15 between the stator and the rotor and which receives reflected light 114 that is reflected off of the rotor 14 and travels along the fiber 50 as the light 116. The gap 15 distance is determined by the change in intensity of the return light 114. The transmit/receive fiber 50 may be located radially through or longitudinally along the stator 12. The receive light 116 is detected by a photodetector 120 which provides an electrical signal to a control circuit 124 which controls electromagnetic coils 31-34 of the magnetic bearing. Alternatively, two separate fibers may be used for the transmit and receive light. Also, time or wavelength multiplexing may be employed to allow for remote optical source and detection/control of the gap 15 distance. Further, a plurality of such sensors may be used around the gap 15.

Abstract: A flywheel system having permanent magnets 20 disposed on a flywheel 10 rotating about a shaft 12 is provided with a stator 28 having an outer diameter which is oriented concentrically and shaped conically within a similarly shaped inner diameter of the flywheel 10 (and the magnets 20) and the stator 28 is slidably and rotatably mounted to a shaft 30 thereby allowing a gap g.sub.1 between the stator 28 and the rotor/flywheel 10 to be adjustable. When energy is being provided to (spin-up) or extracted from (spin-down) the flywheel 10, the stator is automatically forced to the left (FIG. 1) due to torque on the stator 28, thereby causing the gap g.sub.1 to be small to provide strong electromagnetic interaction between the stator 28 and the flywheel 10. Conversely, when the flywheel 10 is freewheeling, the stator 28 is forced to the right by a spring 40 causing the gap g.sub.1 to increase to a distance large enough to minimize electro-magnetic drag on the flywheel 10.

Abstract: An induction motor is provided with a secondary portion 20 comprising an interlaced conductor/back-iron (or ferromagnetic) portion 60 and a purely ferromagnetic back-iron portion 62. The interlaced portion 60 comprises an electrically conductive lattice (or foam) material 61 having pores 63 filled with a ferromagnetic material which results in two interlaced lattices 61,63 which are continuous through a shared volume. The interlaced region 60 provides both good magnetic permeability for passing magnetic flux 30 and good electrical conductivity for flowing induced electrical currents necessary for induction motors. As a result, the effective magnetic gap G1 is minimized while also providing a low-cost induction motor. Alternatively, the lattice 61 may be a ferromagnetic material which is embedded with a conductor.

Abstract: An optical fiber entry strain relief interface includes a composite structure (lay-up) 10 having an optical fiber 20 embedded therein. The optical fiber 20 enters (or exits) the lay-up 10 at at least one point 24 and passes through transition layers 47 comprising an adhesive film 42, a thin rubber sealing layer 44, and a thick rubber strain relief layer 46, and through a polymer plug 48 located above the layer 46. The lay-up is consolidated by heating the lay-up over a temperature profile and applying pressure through mostly closed compression molding tools 30,32.

Abstract: A birefringent active fiber laser sensor includes one or more fiber lasers 12, 14, 16, each having a pair of Bragg gratings 18, 20, embedded in a fiber 10 and excited by a common pump light 30. At least one of the lasers 12, 14, 16 has a laser cavity wit a predetermined birefrigence and a lasing light at a first lasing frequency along a first polarization axis, and at a second fusing frequency along a second polarization axis. A difference frequency between the first and the second lasing frequencies is related to the magnitude of the birefringence, and the birefringence varies in response to a perturbation. Output light 104 from each of the lasers 12,14,16 is fed to a defraction grating 106 which splits the beam 104 into different wavelength groups, each group having the two lasing frequencies and polarizations of a given laser.

Abstract: A single polarization fiber and/or amplifier includes a non-polarization preserving fiber 10 having a fiber grating tap 12 which has a predetermined length and strength (.DELTA.n/n) and is oriented at a predetermined angle .theta. and has a grating spacing D so as to couple-out of the fiber 10 a predetermined amount of one polarization 24 over a predetermined wavelength range of an input light 16 and pass the other polarization 28 as output light 26, the grating length being substantially the length of the fiber 10. Alternatively, all or a portion of the fiber 10 may be doped to form a polarization sensitive optical amplifier.

Abstract: An optical waveguide laser arrangement includes a solid optical waveguide having a waveguiding portion that extends along an axis between two spaced regions of the optical waveguide and is of a material capable of emitting stimulated light upon excitation by pumping light that is launched into the optical waveguide for axial propagation through the axially spaced regions of the optical waveguide. Two reflectors are provided, each being disposed at one of the axially spaced regions of the optical waveguide to delimit a laser resonator. At least one of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive periodic perturbations in the refractive index of the respective one of the axially spaced regions that cumulatively reflect the stimulated light at a reflectivity that decreases for adjacent longitudinal modes of the stimulated light with increasing deviation from a central wavelength.