Patent Description:
It is desirable to ensure hearing safety of ground crew, maintenance personnel, or other persons near an aircraft that includes high decibel (dB) ultrasonic sound transmitters. Hearing safety can be a concern at high sound pressure levels, including those over <NUM> dB, for example, even with the use of hearing protection. In addition to hearing safety, other undesirable physiological effects can occur due to high decibel ultrasonic sound at lower levels, such as <NUM> dB, for example. These levels may be desirable in an aircraft sensing system to support high velocity measurements.

For systems that are critical to the operation of the aircraft, it may be impractical to simply turn the ultrasonic transmitters off while the aircraft is on the ground. Critical systems may need to provide, for example, power-up built-in-test results demonstrating that the system is functional prior to flight and may also need to begin providing preliminary measurement data to support maintenance, taxi, and takeoff operations. Thus, it is desirable to allow ultrasonic acoustic systems to begin operation and performance of fault checking while the aircraft is on the ground.

<CIT> discloses an acoustic manipulator element to split sound waves from an acoustic source.

<CIT> discloses a continuous wave ultrasonic wave transmitter which transmits waves in two opposite directions to determine the speed of an aircraft.

From a first aspect, the invention provides an acoustic sensor system for an aircraft as claimed in claim <NUM>.

The acoustic sensor system of the preceding paragraph can optionally include, any one or more of the following features, configurations and/or additional components:
A further embodiment of any of the foregoing acoustic sensor system, wherein the echo protector includes a housing that extends from a base to an end, and a directivity feature positioned within the housing and configured to direct the acoustic signals to the at least one microphone.

A further embodiment of any of the foregoing acoustic sensor systems, wherein the base includes an opening configured to permit the acoustic signals to reach the directivity feature.

A further embodiment of any of the foregoing acoustic sensor systems, wherein the directivity feature is an inverted pyramid connected to the end of the housing, and wherein each of a plurality of faces of the inverted pyramid are positioned to direct the acoustic signals.

A further embodiment of any of the foregoing acoustic sensor systems, wherein the at least one microphone comprises a plurality of microphones, and wherein each of the plurality of faces is configured to direct the acoustic signals to a respective one of the plurality of microphones.

A further embodiment of any of the foregoing acoustic sensor systems, wherein the transmitter is configured to protrude beyond a skin of the aircraft and emit the acoustic signals toward the at least one microphone such that the sound pressure level is maximized at the at least one microphone and minimized perpendicular to the aircraft.

A further embodiment of any of the foregoing acoustic sensor systems, wherein the transmitter is configured to emit the acoustic signals as ultrasonic signals.

From a further aspect, the invention provides a method of controlling the directivity of acoustic signals of an acoustic sensor system as claimed in claim <NUM>.

The method of the preceding paragraph can optionally include any one or more of the following features, configurations and/or additional components:
A further embodiment of any of the foregoing methods, wherein directing, using the echo protector fixed over the transmitter, the acoustic signals includes directing, by a directivity feature positioned within a housing of the echo protector, the acoustic signals.

A further embodiment of any of the foregoing methods, wherein directing, by the directivity feature positioned within a housing of the echo protector includes permitting the acoustic signals to reach the directivity feature from the transmitter through an opening in a base of the housing.

A further embodiment of any of the foregoing methods, wherein directing, by the directivity feature includes directing, by an inverted pyramid positioned within the housing, the acoustic signals, wherein the inverted pyramid includes a plurality of faces positioned to direct the acoustic signals.

A further embodiment of any of the foregoing methods, wherein the at least one microphone includes a plurality of microphones, and wherein directing, by the inverted pyramid positioned within the housing of the echo protector, the acoustic signals includes directing, by each one of the plurality of faces of the inverted pyramid, the acoustic signals to a respective one of the plurality of microphones.

A further embodiment of any of the foregoing methods, wherein the transmitter protrudes beyond the exterior of the aircraft, and wherein emitting, by the transmitter of the acoustic sensor, the acoustic signals about the exterior of the aircraft includes emitting, by the transmitter, the acoustic signals toward the at least one microphone such that the sound pressure level is attenuated perpendicular to the aircraft.

A further embodiment of any of the foregoing methods, wherein emitting, by the transmitter of the acoustic sensor, the acoustic signals comprises emitting the acoustic signals as ultrasonic signals.

Systems and methods are disclosed herein for ground operation safety of aircraft ultrasonic sensors. A control circuit monitors the acoustic response from microphones of the ultrasonic sensors and monitors aircraft parameters from other systems onboard the aircraft in order to detect an environmental condition. The control circuit detects that the aircraft is on the ground and reduces the intensity of the emitted acoustic signals to below <NUM> decibels (dB), for example. The control circuit detects a hard target, which may be indicative of a person, in the vicinity of the ultrasonic sensor by detecting an echo of an emitted acoustic pulse. In response to the detected hard target, the control circuit reduces the intensity of the acoustic signals and may terminate the acoustic signals.

In other example embodiments, the directivity of the emitted acoustic signals may be controlled to limit the intensity of the emitted acoustic signals at a threshold distance from the aircraft. In one embodiment, the ultrasonic transmitter may be designed to emit the acoustic signals out horizontally along the skin of the aircraft toward the microphones of the ultrasonic sensor such that the sound pressure level is highly attenuated at a short distance from the skin of the aircraft, where a person is most likely to be. In the invention, a fixed echo protector is placed over the ultrasonic transmitter that is configured to direct the acoustic signals horizontally along the skin of the aircraft such that the sound pressure level is also highly attenuated at a short distance from the skin of the aircraft.

<FIG> is a block diagram illustrating control loop <NUM> for an acoustic sensor system. Aircraft may employ acoustic sensor systems, for example, to determine air data parameters. These acoustic sensors may be placed on the exterior of the aircraft and may be utilized to determine, among other values, static air temperature, airspeed, angle of attack, and angle of sideslip. These air data parameters may be utilized by critical functions of the aircraft, such as flight control functions, which may make it necessary to test the acoustic sensor system while the aircraft is on the ground. While testing or performing maintenance, it is desirable that any persons in the vicinity of the acoustic sensors, such as ground personnel or maintenance personnel, do not experience any high sound pressure levels from the emitted acoustic signals.

Control loop <NUM> includes acoustic transmitter <NUM>, microphones 14a-14n, control circuit <NUM>, driver circuit <NUM>, receiver amplification stage <NUM>, and aircraft systems <NUM>. Transmitter <NUM> is configured to emit acoustic signals into the air about the exterior of the aircraft. Microphones 14a-14n are positioned on the exterior of the aircraft to sense the acoustic signals emitted by transmitter <NUM>. The sensed signals from microphones 14a-14n are amplified and conditioned by receiver amplification stage <NUM> and provided to control circuit <NUM> for processing. Control circuit <NUM> may be a standalone controller or may be a part of a larger aircraft control system. Control circuit <NUM> may be located in close proximity to transmitter <NUM> and microphones 14a-14n, or may be located remote from transmitter <NUM> and microphones 14a-14n in an avionics or other electronics bay, for example.

Control circuit <NUM> is configured to control the output of the acoustic pulses through driver circuit <NUM>. Control circuit <NUM> may include one or more of a microprocessor, application specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other circuit. Driver circuit <NUM> may be any electronic circuit configured to control the output of transmitter <NUM> based on input from control circuit <NUM>. For example, to increase the intensity of the acoustic signals, control circuit <NUM> can increase a control voltage provided by driver circuit <NUM>. In one example embodiment, the acoustic signals may be acoustic pulses emitted at any desired frequency. For example, acoustic sensor system <NUM> may be an ultrasonic acoustic sensor system, configured to emit acoustic pulses at greater than <NUM>. In other embodiments, acoustic sensor system <NUM> may be configured to emit a continuous sound wave rather than pulses.

Control circuit <NUM> may control transmitter <NUM> to emit signals at a desired intensity using closed-loop feedback control. Control circuit <NUM> can monitor the response from microphones 14a-14n to determine a present intensity of emitted signals. This way, if control circuit <NUM> desires transmitter <NUM> to emit a signal at a desired intensity, control circuit <NUM> can monitor the response from microphones 14a-14n to determine a present intensity and continue to adjust the voltage provided by driver circuit <NUM> until the response from microphones 14a-14n indicate that the present intensity is at the desired intensity.

With continued reference to <FIG>, <FIG> is a signal diagram illustrating signals produced and received by an aircraft acoustic sensor system. Signal <NUM> is a signal indicative of an acoustic signal emitted by transmitter <NUM>, and signal <NUM> is a signal indicative of an acoustic signal received by one of microphones 14a-14n. For example, signal <NUM> may be a voltage provided by driver circuit <NUM> and signal <NUM> may be a voltage received from one or more of microphones 14a-14n indicative of a sensed acoustic signal.

Pulse <NUM> is representative of an acoustic pulse emitted by transmitter <NUM>. During flight of an aircraft, pulse <NUM> may be at or about <NUM> dB and greater than <NUM> in order to ensure integrity of data throughout the flight envelope. Pulse <NUM> is sensed at microphones 14a-14n as pulse <NUM>. The distance between transmitter <NUM> and microphones 14a-14n is known and thus, the timing of pulse <NUM> is utilized by control circuit <NUM> to determine air data parameters, for example. However, regardless of environmental conditions, pulse <NUM> is expected to be sensed by microphones 14a-14n within an expected time-of-flight (TOF) window, which may be on the order of <NUM> microseconds, for example. The above factors, in addition to the flight envelope, can be utilized to determine a desired TOF window, for example.

The amplitude of pulse <NUM> is indicative of the sound pressure level of the acoustic signal at the respective microphone 14a-14n. A voltage threshold may be set and utilized to differentiate a pulse <NUM> from background noise. Depending upon the conditions of the environment, the sound pressure level of the emitted acoustic signal may need to be sufficiently high in order to ensure detection of pulses <NUM> at microphones 14a-14n and in turn, ensure the integrity of the air data parameters determined by the acoustic sensor system.

It may be desirable to operate in a low-decibel mode while the aircraft is on the ground. For example, it may be desirable to limit the intensity of the emitted acoustic signals to less than <NUM> dB to ensure hearing safety for any persons present in the vicinity of transmitter <NUM>. Control circuit <NUM> determines that the aircraft is on the ground based on parameters received from aircraft systems <NUM>. The parameters received may include, among others, weight-on-wheels (WOW), throttle position, or other aircraft parameters desired by control circuit <NUM>. In one embodiment, control circuit <NUM> may control transmitter <NUM> to emit signals at the reduced intensity any time the WOW parameter indicates the aircraft is on the ground. In another embodiment, control circuit <NUM> may also monitor the throttle position to determine both that the aircraft is on the ground, and that the aircraft is not accelerating down the runway. This is due to the fact that persons are unlikely to be in the vicinity of transmitter <NUM> while the aircraft is accelerating down the runway.

Control circuit <NUM> may control the intensity of the acoustic signals using a closed-loop control. For example, control circuit <NUM> can monitor the amplitude of pulse <NUM> to determine a present intensity of emitted acoustic signals (e.g., pulse <NUM>). If the amplitude of pulse <NUM> indicates that the intensity of acoustic signals emitted by transmitter <NUM> is below <NUM> dB, control circuit <NUM> can maintain the voltage provided by drive circuit <NUM>. If the amplitude of pulse <NUM> indicates that the intensity of acoustic signals emitted by transmitter <NUM> is above <NUM> dB, control circuit <NUM> can reduce the voltage provided by drive circuit <NUM> to further reduce the intensity of the emitted pulses, until the present intensity reaches the desired value.

Control circuit <NUM> is also configured to monitor for a hard target in close proximity to transmitter <NUM>. Pulse <NUM> is an unexpected pulse with respect to emitted pulse <NUM> as it occurs outside the expected TOF window. Pulse <NUM> may be indictive of a hard target in that the emitted pulse <NUM> reflected off of the hard target back toward microphones 14a-14n. A threshold (VTH) may be set with which control circuit <NUM> compares signal <NUM> in order to detect a hard target pulse <NUM> outside of the TOF window.

The threshold (VTH) for detecting a hard target (e.g., pulse <NUM>) may be set as the same value that control circuit <NUM> uses to detect an expected pulse (e.g., pulse <NUM>). In other embodiments, a separate threshold (VTH) may be set for detecting a hard object that takes into account, for example, an assumed safe distance and ambient parameters for atmospheric attenuation. For example, if a hard target is greater than <NUM> (<NUM> feet) from transmitter <NUM>, acoustic signals may be attenuated sufficiently such that control circuit <NUM> does not need to adjust the output of transmitter <NUM>. The threshold (VTH) could thus be set to ignore pulses that correspond to hard targets that are <NUM> (<NUM> feet), or any other safe distance, from transmitter <NUM>.

Detection of pulse <NUM>, which are indicative of the presence of a hard target, instructs control circuit <NUM> to reduce the intensity of the acoustic signal emitted by transmitter <NUM>. For example, if transmitter <NUM> is currently emitting acoustic signals at greater than <NUM> dB, control circuit <NUM> may reduce the voltage provided by driver circuit <NUM> to decrease the intensity of the acoustic signals to below <NUM> dB. In other examples, not forming part of the invention, upon detection of pulse <NUM>, control circuit <NUM> may simply command transmitter <NUM> off by terminating power to driver circuit <NUM>.

By reducing the emitted signal to less than <NUM> dB, the acoustic sensor system can still operate on the ground while reducing the exposure to any persons in the vicinity of the acoustic sensor system. While lowering the output intensity may increase the signal-to-noise ratio, which can limit performance, the performance may be sufficient to sense air data parameters or perform testing and/or maintenance while on the ground in low/zero speed conditions, for example.

<FIG> is a schematic diagram of an acoustic sensor system and <FIG> is a polar plot for an acoustic sensor system. In some embodiments, not within the scope of the present claims, rather than controlling an acoustic transmitter to reduce the intensity of emitted acoustic signals, the directivity of a transmitter may be controlled to ensure that while the sound pressure level at the microphones is high, the sound pressure level at a short distance from the body of the aircraft, perpendicular to the transmitter, is sufficiently attenuated. For example, hard target <NUM>, which may be a person outside of an aircraft, is positioned at a short distance perpendicular to the acoustic sensor system of aircraft <NUM>. The directivity of transmitter <NUM>' may be designed such that the sound pressure level present at hard target <NUM> is sufficiently attenuated while the sound pressure level at microphones 14a-14n is sufficiently high.

In one embodiment, as illustrated in <FIG>, transmitter <NUM>' may include a cylindrical piezo material configured to vibrate to emit acoustic signals into the airflow external to aircraft <NUM>. Microphones 14a and 14b are positioned within plate <NUM> to sense the acoustic signals emitted by transmitter <NUM>'. For example, the cylindrical piezo material may be configured to extend out from the skin of aircraft <NUM> in order to emit the acoustic signals horizontally along the skin of the aircraft as illustrated in the polar plot of <FIG>. In the polar plot illustrated in <FIG>, Sound Pressure Levels (SPL) <NUM> and <NUM> illustrate the sound pressure emitted by transmitter <NUM>'. As illustrated, the maximum SPL is out at an angle of <NUM>°, which is where microphones 14a and 14b are located on the exterior of aircraft <NUM>, and is where persons will not be located.

While illustrated in <FIG> as a cylindrical piezo material transmitter, transmitter <NUM>' may be designed in other ways to achieve the directivity illustrated in <FIG>. For example, a horn design may be used, or a plurality of low cost transmitters may be configured in an array that extend out from aircraft <NUM> and are pointed radially toward microphones 14a-14n. While not illustrated in the polar plot of <FIG>, these transmitter designs may also result in some lower intensity side lobes. By designing the acoustic sensor system to have the directivity illustrated in <FIG>, any exposure to high pressure sound levels by hard target <NUM> can be avoided.

<FIG> are schematic diagrams illustrating fixed echo protector <NUM> for an acoustic sensor system. Fixed echo protector <NUM> acts as a "hat" for transmitter <NUM>", which may be any type of acoustic transmitter configured to emit acoustic pulses external to aircraft <NUM>. Fixed echo protector <NUM> includes a directivity feature configured to direct the acoustic signals to microphones 14a and 14b. In the embodiment illustrated in <FIG>, the directivity feature is inverted pyramid <NUM>, which is positioned within housing <NUM>, above opening <NUM>. Opening <NUM> permits acoustic signals to reach inverted pyramid <NUM> from transmitter <NUM>". Inverted pyramid <NUM> includes one or more faces <NUM> positioned to direct acoustic signals out toward microphones 14a and 14b. Housing <NUM> extends from base <NUM> to opposite end <NUM>.

The one or more faces <NUM> are flat faces that direct acoustic signals from transmitter <NUM>" to each microphone 14a and 14b. Although not required, in the present embodiment, faces <NUM> may be flat rather than rounded so as not to affect the frequency response of the acoustic sensor system. Each microphone may include its own respective corresponding flat face <NUM>. For example, if the acoustic sensor system includes four microphones, inverted pyramid <NUM> may include four respective faces <NUM>. Each face <NUM> will direct acoustic signals from transmitter <NUM>" to the respective microphone 14a-14n. This allows a directivity similar to that illustrated in <FIG> to be achieved with any special transmitter design. In other embodiments, the directivity feature may be an inverted cone, or any other structure configured to direct the acoustic signals to microphones 14a-14n.

In the embodiment illustrated in <FIG>, inverted pyramid <NUM> has an angle between the apex of inverted pyramid <NUM> and base <NUM> that is sufficient to attenuate the emitted acoustic signals to safe levels. This angle may be <NUM>°, for example, or any other angle sufficient to attenuate the sound pressure levels for hard target <NUM>. For example, fixed echo protector <NUM> may direct acoustic signals emitted by transmitter <NUM>" at <NUM> dB such that hard target <NUM> receives the acoustic signals at less than <NUM> dB. This way, ground operation can occur without the need to reduce the intensity of signals emitted by transmitter <NUM>" as compared to in-flight use. In some embodiments, fixed echo protector <NUM> may be attached over transmitter <NUM>" while the aircraft is on the ground and may be removed while the aircraft is in-flight. For example, fixed echo protector <NUM> may be attached over transmitter <NUM>" during maintenance, and removed once maintenance is complete.

Claim 1:
An acoustic sensor system for an aircraft, the acoustic sensor system comprising:
a transmitter (<NUM>; <NUM>'; <NUM>") configured to be positioned on an exterior of the aircraft and configured to emit acoustic signals external to the aircraft;
at least one microphone (14A, 14B) configured to be positioned on an exterior of the aircraft and configured to sense the acoustic signals as sensed data;
an echo protector (<NUM>) fixed over the transmitter (<NUM>; <NUM>'; <NUM>") and shaped to direct the acoustic signals toward the at least one microphone (14A, 14B) such that the sound pressure level is attenuated perpendicular to the aircraft,
characterised in that the acoustic sensor system comprises:
a control circuit (<NUM>) configured to determine that the aircraft is on the ground based on parameters received from onboard aircraft systems (<NUM>) and to determine the presence of a hard target in proximity to the transmitter (<NUM>; <NUM>'; <NUM>") by detecting an echo of an acoustic emitted pulse, wherein the control circuit (<NUM>) is further configured to reduce the intensity of the acoustic signals emitted by the transmitter (<NUM>; <NUM>'; <NUM>") when the control circuit (<NUM>) determines that the aircraft is on the ground and determines the presence of a hard target in proximity to the transmitter (<NUM>; <NUM>'; <NUM>").