Acoustic sensors using microstructures tunable with energy other than acoustic energy

A sensor for detecting acoustic energy includes a microstructure tuned to a predetermined acoustic frequency and a device for detecting movement of the microstructure. A display device is operatively linked to the movement detecting device. When acoustic energy strikes the acoustic sensor, acoustic energy having a predetermined frequency moves the microstructure, where the movement is detected by the movement detecting device.

TECHNICAL FIELD

The present invention relates generally to a method and apparatus for detecting acoustic energy and relates more specifically to microstructures that are tunable with energy other than acoustic energy.

BACKGROUND OF THE INVENTION

Many acoustic sensors include sound-responsive elements that resonate when they are exposed to acoustic energy. Such sound-responsive elements are typically mechanical structures that include any one of the following: a stretched membrane, a clamped diaphragm, a magnetic diaphragm held in place by magnetic forces, conical diaphragms, circular pistons, and corrugated-ribbon conductors. To transform the acoustic energy detected by the aforementioned sound-responsive elements, transducers are coupled to the sound-responsive elements. Typical transducers include the following: loose-contact transducers; moving-iron transducers; electrostatic transducers; piezoelectric transducers; and moving coil transducers.

The transducers and their corresponding sound-responsive elements have inherent size limitations as well as acoustic frequency response limitations. For example, a carbon microphone employs a diaphragm that vibrates in accordance with impulses of sound and then turns the vibrations into electric energy. The vibrations are converted into electrical energy by a piezoelectric transducing method where the diaphragm compresses the carbon granules which in turn changes the electrical resistance of the carbon granules. The electrical resistance of the carbon granules is detected by a voltage measuring device and can be processed by a correlating device which can associate the measured resistance to an acoustic frequency and acoustic intensity. With the voltage measuring device and piezoelectric tranducing method, the operating range for a carbon microphone is typically between 100 and 5,000 hertz (Hz). The carbon microphone is typically used in the mouth piece or transmitter of a telephone handset.

Carbon microphones have a finite length, width, and height that are dependent upon the range of acoustic frequencies that are intended to be detected by the carbon microphone. Due to this physical size dependency on the range of acoustic frequencies intended to be detected, a carbon microphone is typically bulky. Another drawback of a carbon microphone is that it can generate noise. The noise is typically a result of carbon granules that are packed too loosely. Another disadvantage of the carbon microphone is that if an acoustic frequency of interest lies outside the operating range of the carbon microphone, the actual physical dimensions of the carbon microphone and more specifically the sound-responsive element and transducers of the carbon microphone, must be changed or resized in order to detect such a frequency,

Unlike the transducers of the carbon microphone, a dynamic microphone includes a moving coil transducer to convert the movement of a pole into electrical energy. The pole is attached to a diaphragm and is moved by sound waves striking the diaphragm. A dynamic microphone typically includes many parts: a large base permanent magnet, a coil, a diaphragm held in place by a ring, a washer, and large air spaces disposed within the permanent magnet. The dynamic microphone typically has an acoustic frequency response of 30 Hz to 18 kHz. While the dynamic microphone may a large acoustic frequent response range relative to the carbon microphone, the number and size of the dynamic microphone's operating components render it impractical for use in acoustic arrays and other array like applications. Similar to the carbon microphone, the dynamic microphone is typically designed for a set or fixed acoustic frequency range and therefore, requires substantial mechanical retrofitting or resizing to alter its acoustic frequency range response.

In addition to the size and frequency response limitations of both the dynamic microphone and carbon microphone, these microphones can cause mutual interference in large array applications. For example, if several carbon or dynamic microphones having the same frequency range are placed adjacent to one another, neighboring microphones may interfere with one another due to the sound-responsive elements of each of these microphones being tuned to the same acoustic frequency. Vibrations of one sound responsive element of a microphone may generate acoustic energy or noise relative to a neighboring microphone having a similar size sound-responsive element.

Thus there is a need for an acoustic sensor which avoids the drawbacks of the size and sensitivity of conventional acoustical sensors. There is further need for an acoustic sensor having reduced number of sound-responsive elements. Another need exists for an acoustic sensor that can reduce mutual interference between acoustic sensors placed in an array.

SUMMARY OF THE INVENTION

The present invention overcomes the problems associated with conventional acoustic detectors which have inherent limitations based on their size and sensitivity. The acoustic sensor of the present invention detects acoustic energy by entirely different sound-responsive elements and transducers. Consequently the size and frequency response limitations associated with conventional acoustic sensors are substantially eliminated by the present invention. Further, the acoustic sensor of the present invention has a reduced number of moving parts for the sound responsive element and also has the capability of substantially reducing or eliminating mutual interference between neighboring sound responsive elements in acoustic sensor array applications. The acoustic sensor of the present invention has increased sensitivity over a wide range of acoustic frequencies and has dimensions that are orders of magnitude smaller than conventional acoustic sensors. Additionally, the frequency range of the acoustic sensor of the present invention can be modified without changing the actual size of the sound responsive element.

Stated more specifically, the present invention relates generally to an acoustic sensor using microstructures tunable through energy being applied to the microstructure to create stress within the microstructure. The acoustic sensor of the present invention comprises a microstructure tuned to a predetermined acoustic frequency. The sensor also includes a device for detecting movement of the microstructure caused by acoustic energy. The sensor further includes a display device operatively linked to the detecting device. When acoustic energy strikes the sensor, acoustic energy having the predetermined frequency moves the microstructure and the movement is detected by the movement or deflection detecting device.

In addition to the movement detecting device, the acoustic sensor of the present invention can include a device for associating movement of the microstructure with a predetermined acoustic energy level. With such a correlating device, the sensor can output an intensity level of the acoustic energy being detected.

To determine the acoustic intensity energy level and presence of an acoustic frequency, the acoustic sensor detects acoustic energy with a microstructure that has a predetermined acoustic resonant length. The microstructure of the present invention can be any one of the various structures that make-up microelectromechanical systems (MEMS). Specifically, the microstructure of the present invention can be a microbar/microcantilever, a microbridge, or a microplate.

While the aforementioned microstructures of the present invention can be tuned to a predetermined acoustic resonant length, the present invention can also include a device for tuning a microstructure above or below the predetermined acoustic resonant length of a respective microstructure. This tuning device produces energy other than acoustic energy that is focused on the microstructure such that the natural acoustic resonant frequency that is dependent on the length of microstructure is altered. The energy that alters the natural acoustic resonant frequency of the microstructure can be either light energy, thermal energy, energy derived from an electric field, or mechanical energy.

Similar to the various energy forms available to the tuning device, the movement detecting device of the present invention can measure movement of the microstructure through a variety of measuring techniques. In one embodiment, the detecting device can include a laser device and light detector. In another embodiment, the movement detecting device of the present invention can include a capacitive sensing device. And further, the movement detecting device can include a voltage measuring device when the microstructure is made from piezoresistive materials. Alternatively, the detecting device can include a mechanism that monitors a change of resonance of the microstructure itself.

In another aspect of the present invention, the acoustic sensor includes a microstructure array tuned for a predetermined acoustic frequency range. The detecting device of this aspect of the present invention detects movements of individual microstructures in the microstructure array. The acoustic sensor further includes a correlating device that associates movement of individual microstructures with corresponding acoustic resonant frequencies. The acoustic sensor also includes a display device operatively linked to the movement detecting device.

According to this aspect of the invention, the detecting device monitors a selected microstructure at one time in the microstructure array. In order to monitor a selected microstructure, the acoustic sensor can further include a detuning device that detunes or tunes neighboring microstructures away from a natural acoustic resonant frequency of a selected microstructure in the microstructure array. The detuning device exposes the neighboring microstructures with energy other than acoustic energy. This energy can either be light energy, thermal energy, energy derived from an electric field, or mechanical energy.

The microstructure array can also be a two dimensional microstructure array or a three dimensional microstructure array. With a three dimensional microstructure array, the correlating device of the acoustic sensor can determine a direction of a source of the acoustic energy.

In another aspect for the present invention, the acoustic sensor can identify a target based upon a target's acoustic signature. More specifically, the target sensor includes a microstructure array tuned for a predetermined acoustic frequency range and a detecting device which detects movement of individual microstructures in the microstructure array. The sensor of this aspect of the present invention includes a correlating device that associates movement of the individual microstructures with corresponding acoustic frequencies. The correlating device further associates the detected acoustic frequencies with stored acoustic frequencies of targets in a data base. The sensor further includes a display device that displays detected acoustic frequencies and target identification received from the correlating device.

In yet another aspect of the present invention, a method for detecting acoustic energy includes tuning a microstructure to a predetermined acoustic frequency and exposing the microstructure to acoustic energy. The acoustic sensor then detects movement of the microstructure and then activates a display device to indicate that a predetermined acoustic frequency has been detected.

According to another aspect of the present invention, a method for detecting acoustic energy includes the steps of tuning a microstructure array for a predetermined acoustic frequency range and exposing the microstructure array to acoustic energy. The acoustic sensor detects movement of individual microstructures in the microstructure array and associates the movement of the individual microstructures with corresponding acoustic resonant frequencies. After some calculations or signal processing or both, the sensor displays detected acoustic frequencies on a display device.

In an additional aspect of the present invention, a method for identifying a target employs a microstructure array tuned for a predetermined acoustic frequency range. The microstructure array is then exposed to acoustic energy generated by a target. The target sensor of the method for identifying a target then detects movement of individual microstructures in the microstructure array and associates the movement of the individual microstructures with corresponding acoustic resonant frequencies. The target sensor then associates detected acoustic frequencies with stored acoustic frequencies which targets in a database. The target sensor then displays detected acoustic frequencies in identification of the target on a display device.

Thus it is an object of the present invention to provide an improved acoustic sensor.

It is another object of the present invention to tune an acoustic sensor having a microstructure by stressing the microstructure with energy other than acoustic energy with out altering or changing the physical dimensions of the microstructure. A further object of the present invention is to provide an array of microstructures that detect acoustic energy where performance of a selected microstructure is not affected by neighboring microstructures.

Other objects, features, and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the drawings and dependent claims.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

Referring now to the drawings in which like numerals indicate like elements throughout the several views,FIG. 1Ashows a microstructure10according to one embodiment of the present invention. The microstructure10in this embodiment is a microbar or microcantilever. The microstructure10ofFIG. 1Ais a bimetallic microcantilever that includes a first portion12made from silicon (Si) or silicon nitride (Si3N4). The materials for the second portion14will be discussed in further detail below. Materials for microcantilevers include galium arsenide (GaAs). Microcantilevers are typically 100-200 micrometers (μm) long, 0.3-3 micrometers thick, and 10-30 micrometers wide, and can be fabricated from various dielectric or semiconducting materials. Microcantilevers made out of galium arsenide can be fabricated with a thickness of 100 nanometers (nm) or less. Microcantilevers are typically manufactured such that they are attached to a large rectangular chip (approximately 1 millimeter wide by 3 millimeters long by 1 millimeter thick). The rectangular chip can be used to facilitate manipulation and mounting of the microcantilevers. The present invention is not limited to the geometry of the microstructure illustrated in FIG.1. Microcantilevers can have several geometries that are not illustrated in FIG.1. For example, other geometries include, but are not limited to, triangular cantilevers, and other like geometries.

The present invention is also not limited to the microstructure10illustrated in FIG.1. The microstructure10can be microstructures other than cantilevers. For example, other microstructures include, but are not limited to, microbars, microbridges, and microplates. The difference between microbars and microcantilevers lies in their respective width dimensions. The width dimension of a microbar is typically greater than that of a microcantilever. However, microcantilevers are sometimes referred to as falling into a class of microbars. A microbridge is a microstructure similar to a microcantilever where both ends of the microstructure are fixed. A microplate is microstructure that has both length and width dimensions and edge regions rigidly secured to prevent deflection thereof.

The microstructure10ofFIG. 1Ais sized according to an acoustic frequency of interest. The natural acoustic resonant frequency of a microstructure (in absence of applying tuning energy that can stress the microstructure as will be explained below) corresponds to the length of the microstructure. An acoustic resonant length of a microstructure can be calculated from the following equation:
f=(1/2π)(t/L2)√(E/ρ)
where f is the frequency of interest, L is the length of the microstructure, t is the thickness of the microstructure, E is Young's modulus of the structure, and ρ is the mass density of the microstructure.

The microstructure10further includes a second portion14made of the material that absorbs energy other than acoustic energy. F or example, the second portion14is preferably made from an infrared absorbing material such as gold black. However, other energy absorbing materials are not beyond the scope of the present invention. Other energy absorbing materials include, but are not limited to, aluminum (Al) coatings, as well as gold/chromium films or other semi-conductor materials.

In the absence of tuning energy being applied to second portion14, surface stress forces S1and S2are balanced and are at equilibrium as illustrated in FIG.1A. Surface stress forces S1and S2generate a radial force Fr along a medial plane of the microstructure10. As illustrated inFIG. 1B, the stress forces S1and S2become unequal when the microstructure is exposed to acoustic energy AEhaving a frequency substantially close to or equal to the acoustic resonant frequency of the microstructure10.

The natural acoustic resonant frequency of microstructure10can be modified or changed by applying energy other than acoustic energy to the either the first portion12or second portion14of the microstructure10. The energy other than acoustic energy can be any one of the following energy forms: electromagnetic energy that includes light energy such as infrared radiation or light in the visible spectrum; thermal energy such as infrared radiation at a predetermined wavelength; mechanical energy; energy derived from an electric field or magnetic field; and other like energy forms. The applied energy interacts with the microstructure10in such a way as to create stress, which can tune microstructure10to frequencies other than its natural acoustic frequency. Stress in the microstructure10can be created by making either the first portion12or second portion14or both portions from a material that is sensitive to or reacts with the applied energy. In a preferred embodiment, such materials of the microstructure10are designed to absorb the applied energy.

In one embodiment, the first portion12is made from a semiconductor material such as silicon. When tuning energy TEin the form of photon radiation at a predetermined frequency, intended to excite semiconductor material, is applied to the first portion12of microstructure10, free charge carriers13(such as electrons and holes as illustrated inFIG. 1B) are created in the semiconductor material of the first portion12. The photon radiation can be infrared, visible, ultraviolet, X-ray, gamma rays, x-rays, and microwave type photons. In a preferred embodiment, visible photons are used. The generation of free charge carriers results in the development of local mechanical stress. This photo-induced stress will cause an expansion or contraction of the lattice of the semiconductor material in the first portion12similar to thermal expansion or contraction. However, charge carriers can be generated in a very short time to produce photo-induced stress much faster than the creation of thermal-induced stress.

In another embodiment, the second portion14is made from an infrared absorbing material or coating, such as gold black. When tuning energy TEin the form of infrared radiation at a predetermined frequency, intended to thermally excite infrared absorbing material, is applied to the second portion14of microstructure10, the temperature of the second portion14increases due to absorption of this optical tuning energy TE. The infrared radiation at the predetermined frequency intended to thermally excite infrared absorbing material typically does not excite or produce charge carriers in the semi-conductor material. Thus, photo-induced stress is not created in the first semi-conductor portion12. Generally, infrared radiation intended to thermally excite infrared absorbing material has a larger wavelength (lower frequency) than infrared radiation intended to excite semiconductor materials. When infrared radiation intended to thermally excite infrared absorbing material is applied to the second portion, and since the first portion12and second portion14are constructed from materials having dissimilar thermal expansion properties, a “bimaterial” effect will cause the microstructure10to deflect in response to this temperature variation.

Therefore, while it is possible to detect acoustic energy AEwith the microstructure10due to the displacement or deflection of microstructure10as a result of the microstructure's natural acoustic resonant frequency, it is also possible to tune the microstructure10away from its natural acoustic resonant frequency by applying energy other than acoustic energy (such as optical energy in the form of photons from an infrared radiating device) so that the microstructure10can detect other acoustic frequencies.

In order to isolate the microstructure10and its tuning/detuning devices from the surrounding environment, the microstructure10can be coupled to an acoustic energy collector or sound-responsive element such a diaphragm. In this way, the microstructure10and its corresponding tuning/detuning devices can be operate in a self-contained environment so that they are protected from external environmental elements, such as water, dust, dirt, etc.

InFIG. 1B, tuning energy TEin the form of infrared radiation produces a bending force (FZ) that opposes the bending force generated by acoustic energy AE. In this way, it is possible to tune the microstructure10without actually resizing or adjusting the physical dimensions of microstructure10. InFIG. 1, infrared radiation at a predetermined frequency intended to excite semiconductor materials is applied to the first portion12in order to create photo-induced stress.

The present invention is not limited to the tuning or detuning energy (TE) illustrated inFIG. 1where this tuning energy TEis in the form of light energy, and more specifically infrared radiation at a predetermined frequency intended to excite semiconductor material. Other tuning or detuning energy (TE.) includes, but is not limited to, thermal energy (such as infrared radiation having large wavelengths relative to radiation intended to excite semiconductor material), energy derived from an electric field, and mechanical energy. The only requirement of the detuning or tuning energy (TE) is that it interacts with the microstructure10in such a way as to alter the natural acoustic resonant frequency of the microstructure10without actually changing or adjusting any of its physical dimensions.

Tuning energy improves sensitivity of microstructures in array applications. A plurality of microstructures10can be disposed in a microstructure array20as illustrated inFIG. 2to detect a range or band of acoustic frequencies. Each microstructure10of the microstructure array20has a predetermined acoustic resonant length that resonates at a predetermined acoustic frequency (f). In the microstructure array20, each microstructure10has a different acoustic resonant length with respect to a neighboring microstructure10. Therefore, each microstructure10in the microstructure array20resonates at a different acoustic frequency relative to a neighboring microstructure10. However, the present invention is not limited to this geometry of microstructure array20. Other geometries of microstructure array20include, but are not limited to, multiple microstructures grouped together having the same resonant length, placing microstructures having different acoustic resonant frequencies in a random order, and other like arrangements. Also, the microstructure array20is not limited to the microcantilevers shown in FIG.2. As noted above, other microstructures10include, but are not limited to, microbars, microplates, and microbridges.

With the arrangement of the microstructures10in the microstructure array20shown inFIG. 2, neighboring microstructures10may interfere or degrade the sensitivity of a microstructure102having a frequency of interest f2. For example, if a third microstructure103having a acoustic resonant frequency f3is substantially close to the acoustic resonant frequency f2of a second microstructure102, and if a first microstructure101having an acoustic resonant frequency f1is substantially close to the acoustic resonant frequency f2of the second microstructure102, then both the first and third microstructures101and103may interfere with the operation and thus affect the sensitivity of the second microstructure102. The first and third microstructures101and103may resonate at frequencies so close to the acoustic resonant frequency f2that they may cause the second microstructure102to vibrate or resonate in response to vibrations caused by their movement. The present invention is designed to substantially reduce or eliminate such mutual interference between microstructures10in acoustic sensor array applications.

In order to substantially reduce or eliminate mutual interference between neighboring microstructures10in a microstructure array20, the acoustic sensor30of the present invention has a detuning device32as illustrated in FIG.3. In a single microstructure10embodiment, the detuning device33can be used to tune the single microstructure10to other acoustic frequencies other than the natural acoustic frequency of the microstructure10that is dependent upon the physical length of the microstructure10.

The acoustic sensor30further includes a movement or deflection detector34that monitors or measures the amount of deflection of a particular microstructure10of interest. The movement detector34communicates deflection and data to a correlation device36. The correlation device36associates the movement of an individual microstructure10in an array20with a corresponding acoustic resonant frequency of the microstructure10and a predetermined acoustic energy level. After associating the movement of an individual microstructure10with its corresponding acoustic frequency and intensity level, the correlation device36outputs an acoustic frequency identification and/or intensity level38.

The detuning device32can produce any one of the tuning or detuning energies TEdiscussed above with respect toFIG. 1above. For example, the detuning device32may produce light energy, thermal energy, energy derived from an electric field, or mechanical energy as long as such energy can alter the natural acoustic resonant frequency of the microstructure10without resizing or changing the physical dimensions of the microstructure10. Further, the detuning device32may apply tuning energy TEto a microstructure102having a frequency of interest f2in order to tune such a microstructure to a predetermined acoustic frequency while applying energy at different magnitudes to neighboring microstructures10and103such that the neighboring microstructures101and103are detuned or substantially tuned away from the microstructure102having the acoustic resonant frequency of interest f2.

In a microstructure array20of a preferred embodiment, each of the microstructures in the microstructure array20may have acoustic resonant lengths from 100 micrometers (μm) to a few millimeters (mm) such that acoustic energy having a frequency of 100 Hz to 10 Kilohertz (kHz) can be detected. However, with detuning device32, the exemplary frequency range can be expanded or contracted according to the amount of tuning or detuning energy TEapplied to the microstructures10of the microstructure array20having the frequency of interest.

Similar to the detuning device32, the movement or deflection detector34can be any one of a number of movement detection devices. For example, the movement detector34can include a laser38operatively linked to a photodetector40as illustrated in FIG.4. However, other deflection detection devices34are not beyond the scope of the present invention. Other deflection detection devices34include voltage measuring devices that are coupled to a microstructure10made of piezoresistive materials. Other deflection detection devices34include devices that sense a change in capacitance due to displacement of the microstructure10or devices that measure or monitor a change of resonance of the microstructure10. For example, changes in resonance of a microstructure can be detected by measuring the change in the degree of bending of a microstructure as a function of frequency. When the deflection of a microstructure peaks at a certain frequency, resonance of the microstructure has been detected.

InFIG. 4, a microstructure array20includes a plurality of microstructures10N. Each of these microstructures10Nresonates at a discrete acoustic resonant frequency fx. The resonant frequency fxof neighboring microstructures10Nrelative to a microstructure10ihaving a frequency of interest fiare detuned by tuning energy TE. Tuning energy generators42produce the tuning energy TE.

The tuning energy generators42are controlled by a tuning energy generator controller44. This controller tunes away the neighboring microstructures10Nrelative to the microstructure10ihaving the frequency of interest fi. By detuning the neighboring microstructures10N, the microstructure10ihaving the resonant frequency of interest fican readily detect acoustic energy from an acoustic energy source if the acoustic energy source produces acoustic energy having the predetermined frequency of interest fi. The detuning of neighboring microstructures10Nsubstantially increases the sensitivity of the microstructure10ihaving the frequency of interest fisince noise or mutual interference of neighboring microstructures is substantially reduced or eliminated. Therefore, the movement detector34only detects deflections of microstructure10ihaving the frequency of interest fithat are directly attributed to the acoustic energy source.

In the exemplary embodiment illustrated inFIG. 4, the movement detector34includes a bandpass filter46to block scattered light from the laser38. The photodetector40can include a dual element photodiode displacement detector to collect the reflected light energy from the microstructure10; having the having the frequency of interest fi. The dual element photodiode photodiode displacement detector40produces a difference signal that is digitized by a digitizer48. The digitizer48then forwards this signal to a lock-in amplifier50where the difference signal is extracted and averaged.

The lock-in amplifier50then can feed the averaged signal to a microprocessor or correlation device36. While the correlation device36is preferably a microprocessor in this embodiment, other correlation devices are not beyond the scope of the present invention. Such correlation devices36can be either hardwired or be made of application specific integrated chips (ASIC), and other like devices. The correlation device36associates the movement of the microstructure10ihaving the frequency of interest fiwith the corresponding acoustic resonant frequency intended to be detected. The correlation device36can also calculate the intensity of the detected acoustic energy based upon the amount of deflection of the microstructure10ihaving the frequency of interest fi.

By employing rapid scanning of the microstructures10of the microstructure array20, the correlation device36of the acoustic sensor30ofFIG. 4can match and measure a plurality of acoustic frequencies generated by the acoustic energy source AE. The tuning energy controller44can activate and deactivate tuning energy generators42very quickly (such as in time increments of milliseconds—ms or microseconds—μs). Further, the laser38can include multiple focusing devices (not shown in the drawings) such that the laser38can irradiate the microstructure10ihaving the frequency of interest. The rapid scanning of the microstructure array20permits the acoustic sensor30to perform a spectral analysis of the acoustic energy being detected where movement or deflection of each microstructure10of the microstructure array20related to a frequency of interest is evaluated. The acoustic sensor30has substantially increased sensitivity relative to conventional acoustic sensors by having a substantially reduced packaging size where the largest microstructure10is only a few millimeters in length. Further, the acoustic sensor30ofFIG. 4has a substantially reduced number of moving parts that are seldom prone to mechanical degradation over the life of the acoustic sensor30.

Description of Operation of the Preferred Apparatus With Reference to the Logic Flow Diagrams

FIG. 5is a logic flow diagram of the process of detuning neighboring microstructures in a microstructure array20. Step100inFIG. 5is the first step of the process of the detuning neighboring microstructures in microstructure array20. In step100, each of the microstructures10is tuned to a predetermine acoustic frequency. In step102the detuning device32identifies a microstructure10ihaving a frequency of interest fi. In routine104, the detuning device32tunes or detunes neighboring microstructures10Naway from the microstructure10ihaving the acoustic frequency of interest fi. Further details of routine104are described with respect toFIG. 6below. The method then proceeds to step106where the microstructures10of the microstructure array20are exposed to acoustic energy.

In routine108, the deflection detector detects the movement or deflection of the microstructure10ihaving the acoustic frequency of interest fi. Further details of routine108will be described with respect toFIG. 7below.

Following routine108, in step110, the correlation device36associates the deflection data received from the deflection detector34with acoustic frequencies that are set to be detected. The correlation device36can associate an intensity level of acoustic energy with the measured deflection. In step112, the acoustic sensor30identifies the detected acoustic frequency and intensity level of the acoustic frequency.

InFIG. 6, routine104is illustrated where neighboring microstructures in a microstructure array20are tuned away from a microstructure10; having a frequency of interest fi. Step200is the first step of routine104. In step200, the detuning device32activates tuning energy generators42to produce tuning or detuning energy TE. This detuning energy can be in the form of optical energy (such as photons), thermal energy, energy in the form of an electric field, and mechanical energy. In step202, the tuning energy controller44focuses detuning energy TEon neighboring microstructures10Nof the microstructure array20. In step204, the tuning energy control44detunes the neighboring microstructures to acoustic frequencies substantially higher or lower than the microstructure101having the acoustic frequency of interest fiin order to substantially reduce or eliminate any interfering mechanical oscillations from the neighboring microstructures. In step206, the process returns to step106illustrated in FIG.5.

InFIG. 7, routine108where deflection of the microstructure10; having the frequency of interest fi, is illustrated. Step302is the first step in routine108. In step302, the acoustic sensor30activates the movement or deflection detection device34. As noted above, the movement detection device34can employ optical, capacitive, piezoresistive, or resonance measuring techniques to measure the deflection of the microstructure107having the frequency of interest fi. In step304, the movement detection device34monitors and records the deflection of the microstructure10ihaving the acoustic frequency of interest fi. In step306, the process returns to step110as illustrated in FIG.5.

Three Dimensional Microstructure Array

InFIG. 8, another embodiment of the acoustic sensor30is illustrated.

In this embodiment, the acoustic sensor30includes a three dimensional microstructure array54that includes microstructure arrays20arranged in an orthogonal manner with respect to each other. However, other geometrical configurations are not beyond the scope of the present invention where the microstructure arrays20are aligned at angles other than 90 degrees. The 3-D microstructure array54may include any geometrical configuration where it is possible to triangulate or detect the direction of an acoustic energy source AE. In one embodiment as illustrated inFIG. 8, the microstructure arrays20are oriented such that the larger microstructures of each individual array20are positioned adjacent to the origin of orthogonal axes that make up the 3-D microstructure array54. With such an orientation, interfering vibrations from the larger/longer microstructures relative to the smaller/shorter microstructures is substantially reduced, which in turn improves the sensitivity and overall performance of the 3-D microstructure array54.

In this embodiment, the acoustic sensor30includes detuning devices34and movement detectors32that correspond to respective microstructure arrays20of the three dimensional microstructure array54. With this embodiment, the correlation device36can identify acoustic frequencies being detected, their respective intensity levels, and additionally, the direction or bearing of the acoustic energy source AE. The correlation device36is able to identify direction of an acoustic energy source AEby utilizing data from each of the arrays in the three dimensional microstructure array arrangement54. As noted above, the present invention is not limited to a three dimensional embodiment and can include any number of microstructure arrays20so long that direction or bearing data of acoustic energy is possible.

Target Identification and Identification of Target Direction

FIG. 9illustrates another embodiment of the present invention where a target sensor58employs detuning devices32, a three dimensional microstructure array54, movement detectors34, and a correlation device36to identify a target as well as a direction of movement of a target. In this embodiment, the three dimensional microstructure array54is exposed to target noise TN. Then, the detuning devices32rapidly scan the microstructure arrays of the three dimensional microstructure array54such that the movement detectors34can sense deflection of respective individual microstructures of each microstructure array. The correlation device36then associates movement of individual microstructures10with corresponding acoustic frequencies and then associates these detected acoustic frequencies with stored acoustic frequencies of targets in a database.

For example, a database for the present invention may provide matching spectral analyses for automobiles, tanks, submarines, aircraft, missiles, torpedoes, and bullets. After identifying a match of acoustic energies, the correlation device36outputs to a display device60the name of the target and its corresponding acoustic spectral analysis. The correlation device36also outputs the results of its location calculations to a the display device60where a target's bearing relative to the three dimensional microstructure array54is displayed.

Target Identification and Bearing Based Upon Acoustic Signature

FIG. 10illustrates a process where an target sensor58determines the bearing and identification of a target based upon an acoustic signature of the target. Step402is the first step in the target bearing and identification process400. In step402, a plurality of microstructure arrays20are tuned for a predetermined number of acoustic frequencies. In step404, the target sensor58identifies a microstructure on each array having a frequency of interest. In step406, the target sensor58tunes neighboring microstructures10Non each array away from a corresponding microstructure10ihaving an acoustic frequency of interest fi. Following step406, in step408, the microstructure arrays20are exposed to a target noise. In step410, the target sensor58detects deflection of each microstructure10ion each array20having the frequency of interest fi. In step412, the correlation device36of the target sensor58associates the deflection data received from the deflection detectors34with acoustic frequencies set to be detected and intensity levels of acoustic energy. In step414, the correlation device36compares the detected target acoustic noise/energy with acoustic energy data in a database. In step416, the correlation20are disposed in orthogonal manner in order to form a three dimensional microstructure array54as illustrated in FIG.9. In step418, the target sensor outputs the target's acoustic energy frequency identification, the identification of the target, the bearing of the target, and the target's noise intensity level.

With the present invention, the size of an acoustic sensor is substantially reduced while sensitivity of the sensor is substantially increased through the generation of tuning energy TE. Further, the present invention provides an acoustic sensor with substantially fewer moving parts relative to the conventional art.

While the foregoing embodiment has been disclosed with respect to a target sensor that employs a three dimensional microstructure array54in order to identify a target, it would be understood that the microstructures disclosed in this embodiment and other embodiments can be employed for different acoustic sensing applications. For example, the three dimensional microstructure array54can be employed as part of an acoustic sensing device of a sonogram apparatus. Further, the microstructures of the present application and the rapid scanning thereof can be employed to produce an acoustic spectrometer that performs spectral analysis of acoustic energy. Other applications of the microstructures of the present application in combination with the detuning device34are not beyond the scope of the present invention.

Finally, it will be understood that the preferred embodiments have been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.