WO2001092846A2

WO2001092846A2 - Acustic sensor for localization

Info

Publication number: WO2001092846A2
Application number: PCT/IL2001/000488
Authority: WO
Inventors: Haim Azhari; Baruch Berdugo
Original assignee: Technion Research And Development Foundation Ltd.
Priority date: 2000-05-29
Filing date: 2001-05-29
Publication date: 2001-12-06
Also published as: AU6263301A; IL136429A0; WO2001092846A3

Abstract

A system for the localization of target objects (105) using acoustic signals is disclosed. The system comprises an acoustic transducer (101); acoustic reflecting means (100); processing means and output means. The transducer (101) is adapted to transmit acoustic signals to a target object (105), receive superposed echoes (104) from the target object (105); directly from the target object (105) and indirectly, reflected by said acoustic reflecting means (100), and transmit an electrical signal corresponding to the received superposed acoustic signal to said processing means. The processing means is adapted to compute the position of the target object (105) and output the position through said output means.

Description

ACOUSTIC SENSOR FOR LOCALIZATION

FIELD OF THE INVENTION

This invention relates to reflecting devices, and more particularly it relates to an artificial pinna for the location of an acoustic signal by reflecting the incoming waves into a sensor and analyzing the reflected data.

BACKGROUND OF THE INVENTION

Accurate localization of reflected echoes can be important in medical, military, geological and other applications. Ultrasound-based systems usually utilize the transmit-receive (pulse-echo) mode. The system transmits an ultrasonic pulse and "observes" the received echoes reflected from the studied objects. Commonly, the same transducer is utilized for transmitting and receiving the acoustic signals. Range measuring systems simply translate the time delay between the transmitted pulse and the received echoes into distance by multiplying the delay by the corresponding sound propagation speed.

Common engineering solutions to improve resolution of localization systems utilize focusing devices such as lenses or phase array systems. An example for the use of lenses is disclosed in US patent no. 4,370,654 titled "APPARATUS FOR PRODUCING A FREQUENCY CHANGE OF A WAVE PROPAGATING SIGNAL" by K. Thomas, filled in 1980. This patent discloses an apparatus for producing a frequency change of wave propagating energy including microwave radar beams, electro-optical signals, other electromagnetic signals, acoustic signals, and other wave propagating energy. In a first embodiment, the apparatus includes a self-directive reflecting device, which may be a plurality of trihedral corner reflectors, Lumberg lenses, etc., and a motion-imparting device for imparting motion to the reflecting device. The motion-imparting device includes a supporting member and an axial member, which is rotatably coupled to the supporting member. The motion- imparting device also includes a mounting member, which is rigidly coupled to the axial member and on which a plurality of corner reflectors is mounted.

In medical imaging systems, cross-sectional images (B-scan in linear or sector modes) are obtained by insonifing the object from various locations or directions and using the pulse-echo approach. Data is collected from multiple points either by using an array of receivers, or a single moving transducer. An example of such an approach is disclosed in US patent no. 3,918,025 titled "ULTRASONIC IMAGING APPARATUS FOR THREE-DIMENSIONAL IMAGE DISPLAY" by K. Kageyoshi et al. This improved ultrasonic imaging apparatus utilizes ultrasonic waves for obtaining an image of a target object, which comprises a transmitting transducer radiating ultrasonic waves whose direction of radiation varies depending on the input frequency, a receiving transducer receiving reflected acoustic waves from a target plane, a frequency analyzer converting the output signal of the receiving transducer into a signal representing the position of the target plane on the basis of the frequency-and the position of the received acoustic waves on the receiving transducer, and an image display unit displaying the output signal of the frequency analyzer. In this apparatus, in order to obtain three-dimensional images including depthwise image information in addition to plane image information of the target object, the frequency analyzer is constructed so that a plurality of image information successively obtained from a plurality of target planes of different depths can be converted into signal representative of different depths to be displayed in superposed relation on the display unit.

The lateral resolution using this method and similar methods is one of the major factors effecting and limiting image quality. Methods for improving lateral resolution have been investigated. An example for focusing method is disclosed in US patent no. 5,301 ,674 titled "METHOD AND APPARATUS FOR FOCUSING TRANSMISSION AND RECEPTION OF ULTRASONIC BEAMS" by E. Kenneth et al., filled in 1992. This patent discloses an ultrasound imaging system for performing dynamic focusing of ultrasonic waves during transmit and receive. This invention includes a method and a means for transmitting ultrasonic waves to multiple depths within a body. This invention optimizes the transmit frequency for each of the multiple depths to localize the energy of the ultrasonic waves. This invention also includes a method and means for performing a dynamic receive focusing of the reflected ultrasonic waves produced by discontinuities in the body, such that it is focused to receive ultrasonic waves from the depth at which the transmitted ultrasonic waves are focused. The human hearing system uses only two acoustic sensors (the ears), and still has an impressive capability of space perception. Several aspects express the space perception capability: a. the ability to locate acoustic source in the horizontal and vertical planes; b. the ability to focus a single source and to ignore interference; and c. the ability to hear and locate sources in a reverberant environment.

Basically, the ear pinna modifies the received acoustic waves before reaching the eardrum. Thus, forming direction dependency. The brain utilizes these acoustic cues to perform source localization. This frequency modulation principle is a major factor in the head related transfer function (HTRF). The pinna acts as an acoustic reflector, where the interaction between the direct wave and the reflected waves is frequency and direction dependent.

Attempts were made at producing artificial hearing devices or hearing aids that imitate pinna. An example for an artificial pinna is disclosed in US patent no. 4,997,056 titled "EAR-FOCUSED ACOUSTIC REFLECTOR" by R. Michael, filled in 1989. This patent discloses an acoustic device for mechanically reflecting sound waves into the ear in an undistorted and directionally selective manner. The device has a pair of movable acoustic reflectors constructed, configured and mounted to preserve accurately phase, frequency and image information in the sound waves of interest to the front of the user. The reflectors are secured to a headband or helmet in position that place the focal points of the reflectors beyond the base of the lenses within the user's ear. BRIEF DESCRIPTION OF THE INVENTION

It is a purpose of the present invention to imitate the pinna principle and utilize it for mono-sensor echo direction finding and for frequency focusing acoustic signals, either in a simple transducer case or as a part of an array of such transducers.

It is another purpose of the present invention to provide a reflecting wall imitating roughly an animal ear to be used for ultrasonic imaging and acoustic tracking applications.

There is thus provided, in accordance with a preferred embodiment of the present invention, a system for the localization of target objects using acoustic signals comprising:

• an acoustic transducer;

• acoustic reflecting means;

• processing means;

• output means

wherein said transducer is adapted to transmit acoustic signals to a target object, receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means, and transmit an electrical signal corresponding to the received superposed acoustic signal to said processing means;

wherein said processing means is adapted to compute the position of the target object and output the position through said output means. Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic reflecting means comprises a flat reflecting plane.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic reflecting means comprises a concave reflecting plane.

Furthermore in accordance with yet another preferred embodiment of the present invention, said reflecting means comprises a hollow cylinder partially cut along the longitudinal axis of the cylinder, so as to present semi-circular cross-section.

Furthermore in accordance with yet another preferred embodiment of the present invention, said reflecting means comprises a reflector made from a metal such as aluminum or stainless steel.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic transducer has a cylindrical cross section

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic reflecting means is mounted on said acoustic transducer.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic reflecting means is a hollow cylinder cut along a diagonal cross-section.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic transducer is adapted to translate pressure to an electric voltage.

Furthermore in accordance with yet another preferred embodiment of the present invention, acoustic transducer is connected to a cable adapted to transmit the electric voltage received by said acoustic transducer to the processing means. Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic transducer is a piezo-electric transducer.

Furthermore in accordance with yet another preferred embodiment of the present invention, said processing means is adapted to calculate the direction of the target object with respect to the perpendicular line at the center of said acoustic transducer by dividing the sound propagation speed by two, divide the resultant by the central frequency of the incoming signal and than divide the resultant by the distance between the reflector and the transducer's center, wherein the resultant is multiplied by one minus the division of the frequency of the maximal amplitude in the spectrum of the incoming signal by the central frequency of the incoming signal.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic transducer is an ultrasonic transducer.

Furthermore in accordance with yet another preferred embodiment of the present invention, said ultrasonic transducer is adapted to receive superposed echoes from a target object situated up to 40 centimeters from said acoustic reflecting means, directly from the target object and indirectly, reflected by said acoustic reflecting means.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic transducer is a sonar system.

Furthermore in accordance with yet another preferred embodiment of the present invention, said sonar system is adapted to receive superposed echoes from a target object situated up to several kilometers from said acoustic reflecting means, directly from the target object and indirectly, reflected by said acoustic reflecting means.

Furthermore in accordance with yet another preferred embodiment of the present invention, said acoustic reflecting means is a rectangular plate, said plate is further provided with two triangular plates on both sides of said plate substantially perpendicular to the rectangular plate. Furthermore in accordance with yet another preferred embodiment of the present invention, said two triangular plates are made from an absorbing material.

Furthermore in accordance with yet another preferred embodiment of the present invention, the longitudinal dimension of said acoustic reflecting means in the anticipated direction of use is substantially twice as large as the wavelength of the incoming signal.

Furthermore in accordance with yet another preferred embodiment of the present invention, the longitudinal dimension of said acoustic reflecting means in the anticipated direction of use is substantially twice as large as the distance between said acoustic reflecting means and the center of said acoustic transducer.

Furthermore in accordance with yet another preferred embodiment of the present invention, a plurality of said acoustic reflecting means is aligned and adapted to reflect waves incoming from a reflecting object.

Furthermore in accordance with yet another preferred embodiment of the present invention, the plurality of said acoustic reflecting means is mounted on a plurality of said acoustic transducer, each of said acoustic reflecting means is mounted on each of said acoustic transducer.

Furthermore in accordance with yet another preferred embodiment of the present invention, the plurality of said acoustic transducer is adapted to transmit the electrical signals corresponding to the received superposed acoustic signal from each of said acoustic transducer to said processing means.

Furthermore in accordance with yet another preferred embodiment of the present invention, each of said acoustic reflecting means is a plate, said plate is provided with a prism on its backside.

Furthermore in accordance with yet another preferred embodiment of the present invention, said prism is made from an absorbing material. Furthermore, in accordance with yet another preferred embodiment of the present invention, a sensor for the localization of target objects using acoustic signals comprising:

• an acoustic transducer; and

• acoustic reflecting means;

wherein said acoustic transducer is adapted to transmit acoustic signals to a target object, receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means.

Furthermore, in accordance with another preferred embodiment of the present invention, said acoustic transducer receive superposed echoes from the target object, directly from the target.object and indirectly, reflected by said acoustic reflecting means, and wherein said sensor is further provided with an acoustic transducer adapted to transmit acoustic signals to a target object.

Finally, there is thus provided, in accordance with a preferred embodiment of the present invention, a method for the localization of target objects using acoustic signals comprising the following steps:

i. providing an acoustic transducer; acoustic reflecting means; processing means and output means, wherein said transducer is adapted to transmit acoustic signals to a target object, receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means, and transmit an electrical signal corresponding to the received superposed acoustic signal to said processing means; and wherein said processing means is adapted to compute the position of the target object and output the position through said output means;

ii. calculating the azimuth of the target object with respect to the perpendicular line at the center of said acoustic transducer by dividing half the sound propagation speed by the central frequency of the incoming signal and than divide the resultant by the distance between the reflector and the transducer's center, wherein the resultant is multiplied by one minus the division of the frequency of the maximal amplitude in the spectrum of the incoming signal by the central frequency of the incoming signal.

BRIEF DESCRITION OF THE FIGURES

J

Figure 1 illustrates a schematic description of an acoustic ray model that is implemented in the present invention.

Figure 2 illustrates an isometric view of an artificial pinna for localization of an acoustic signal in accordance with a preferred embodiment of the present invention.

Figure 3 shows a two-dimensional spectrogram depicting the theoretical transfer function of a single perfect reflector.

Figure 4 llustrates a schematic description of the experimental set-up used n accordance with a preferred embodiment of the present nvention.

Figure 5A illustrates a spectrogram of a received signal from a single sphere target scanned by a regular transducer (with a center frequency of about 1 MHz) without a pinna.

Figure 5B illustrates a spectrogram of a received signal from a single sphere target scanned by the same regular transducer with a pinna in accordance with a preferred embodiment of the present invention. Figure 5C illustrates a spectrogram of a received signal from two spheres target scanned by a regular transducer without a pinna.

Figure 5D illustrates a spectrogram of a received signal from two spheres target scanned by the same regular transducer with a pinna in accordance with a preferred embodiment of the present invention.

Figure 6A illustrates the energy of the back-scattered echoes from a single sphere target registered without a pinna.

Figure 6B illustrates the energy of the back-scattered echoes from a single sphere target registered with a pinna in accordance with a preferred embodiment of the present invention.

Figure 6C illustrates the energy of the back-scattered echoes from two spheres target registered without a pinna.

Figure 6D illustrates the energy of the back-scattered echoes from two spheres target registered with a pinna in accordance with a preferred embodiment of the present invention.

Figure 7 illustrates an isometric view of a reflector in accordance with another preferred embodiment of the present invention.

Figure 8 illustrates an isometric view of a reflector in accordance with yet another preferred embodiment of the present invention.

Figure 9 illustrates an array of reflectors in accordance with yet another preferred embodiment of the present invention.

Figure 10 illustrates an array of reflectors in accordance with yet another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel design for a reflecting device predesigned to imitate an ear pinna, mounted on or next to an acoustic sensor. The artificial pinna reflects the incoming waves into the sensor in a predetermined manner. Consequently, it modifies the input signal so that its spectrum is direction dependent. Using this relationship, the direction of the acoustic signal relative to the sensor can be analyzed and estimated from the measured spectrum.

Reference is made to Figure 1 illustrating a schematic description of an acoustic ray model that is referred to in the present invention. The schematic description considers the simplest pinna model which has a single infinite perfect reflector 100 located adjacent to an ultrasonic transducer 101. The transducer is adapted to transmit acoustic signals to a target object 105, receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means, and transmit an electrical signal corresponding to the received superposed acoustic signal.

There are known several kinds of acoustic transducers, such as a piezoelectric transducer, electromagnetic membrane, etc., which may serve in the design of the system according to the present invention. An example of a transducer that may be employed in the acoustic sensor of the present invention is manufactured by "Panametrics". The model of the "panametrics" transducer that was used for the experiments described hereafter is 0.5" - V303SU, 1-MHz).

The waves reaching the transducer surface 102 comprise of two components: the waves arriving along the direct path 103 and the waves arriving along the reflected (indirect) path 104.

Reference is now made to Figure 2 illustrating an isometric view of an artificial pinna for localization of an acoustic signal in accordance with a preferred embodiment of the present invention. A transducer 1 in the shape of a cylinder transmits acoustic pulses towards an object (not shown in the figure) located within the insonified region. An artificial pinna 2 that is mounted on top of transducer 1 is a hollow cylinder whose wall was partially removed, along the longitudinal axis of the sensor, to present semi-circular cross-section. This type of structure roughly imitates the pinna of a rabbit's ear. Artificial pinna 2 directs the reflected waves arriving from the reflecting object back to the transducer. The pinna is predesigned to direct as much indirect waves as possible to the transducer.

Transducer 1 is connected by a connector 3 to a cable 4 adapted to transmit the electric signal generated by transducer 1 to a processing means such as an analyzer (not shown in Figure 2. See Figure 4). In the case of an acoustic transducer, the transducer is adapted to translate pressure to an electric voltage, which is transmitted to the analyzer via the connecting cable.

It is not essential to use the transducer both as a pulse generator and as a receiver. It is optional to use another transmitter to transmit the acoustic pulses towards an object while the transducer that is adjacent to the reflector acts as the receiver of the arriving waves.

The signal (such as a signal generated by a sonar or an ultrasonic or any other wave generator) received by the transducer is a superposition of two signals: the signal arriving directly from the reflecting object and the signal reflected from artificial pinna 2. The relation between the frequency of the maximal amplitude in the spectrum of the incoming wave and the direction of the object can be calculated by

Δf _{= 1 Q} 2f₀d fo c

where fo is the central frequency of the incoming signals, θ is the direction of the signal source with respect to the perpendicular line at the center of the transducer, d is the distance between the reflector and the transducer and c is the sound propagation speed. The calculation is based on the simplified model shown in Figure 1.

The echoes received from a reflecting object are registered as a spectrum. An analyzer analyzes the spectrum of the received signal, which determines the frequency of the maximal amplitude. This information can be translated to the azimuth of the target object to be detected, as explained herein.

Theoretically, there is an infinite number of maxima of the spectrum for each direction (defined by the time delay between the direct and indirect waves). However, the response of a specific transducer is band limited both in frequency and direction. Therefore, by proper selection of the system's parameters, i.e., frequency bands, beam width, and the distance between the pinna reflector and the transducer center, one can design a system for which only one solution is relevant, and a unique almost linear mapping between the maximal amplitude frequency and direction is obtained.

An example of a two-dimensional spectrogram depicting the theoretical transfer function of a single perfect reflector is shown in Figure 3. The horizontal axis refers to the time delay between the direct wave and the reflected wave, which is related to the target's azimuth. The vertical axis refers to the frequency, and the gray scale refers to the amplitude, darker regions corresponding to greater amplitudes. Linear relationship between the frequency and the time delay within the transducer band-width can be observed (marked by a box).

An experimental set-up was built according to a preferred embodiment of the present invention and is shown in Figure 4. The purpose of the experiment was to demonstrate the performance of the artificial pinna shown in Figure 1. The experimental system comprises a computer-controlled mechanism that has the capability to scan a cylindrical volume (with a diameter of about 20 cm and a height of about 30 mm) located in the center- of a water tank 50. The target objects 51 are placed within this volume. A pulser-receiver 52 (Parametric model 5800) was used to excite the transducer 53 and amplify the received signals. An A D converter 54 (Rapid System R2000) was used to digitize the reflected waves. The system was controlled by a personal computer 55 wherein data acquisition and image reconstruction was compiled. A step motor controller 56 and a set of motors 57 were used to move the transducer.

The artificial pinna 1 that was used in the experimental set-up is similar to the embodiment shown in Figure 2. Artificial pinna 2 is an aluminum cylinder whose wall was partially removed so as to present a concave cross section along its longitudinal dimension, of about 16 mm in diameter. The whole length of the pinna is about 30 mm in length and is provided with a cylindrical connector to allow its mounting over an ultrasonic transducer. Artificial pinna 1 is mounted on top of an ultrasonic transducer with a central frequency of about 1 MHz, having the same diameter, and which was connected to an A/D convertor 54. In the experimental set-up shown in Figure 4, the first target object was a single glass sphere 15 mm in diameter that was placed at a distance of about 100 mm from transducer 53.

Two B-scans were performed, one with the artificial pinna mounted on the transducer and one with the artificial pinna removed. The scan resolution was 0.25 mm, i.e., an A-line was acquired every 0.25 mm. An ultrasonic pulse was transmitted from pulser-receiver 52 and 256 data samples of the reflected echoes were collected. The received signal (A-line) at each position was then zero padded and transformed to the frequency domain via a 1024 points FFT (Fast Fourier Transform). A two-dimensional image depicting the spectrogram as a function of the transducer position was then obtained for each case (with and without the artificial pinna).

The results of a scan performed using a regular transducer are shown in Figure 5A illustrating a spectrogram of a received signal from a single sphere target scanned by a transducer without a pinna. The X-axis is the displacement between the center of the object and the center of the transducer in mm. The Y-axis is the frequency in MHz. The Z-axis, which represents the intensity, is the magnitude of the Fourier transform. The regular transducer has a symmetric response about its axis. The beam width is about 10 mm and the frequency band is about 0.8-1.4 MHz. It can also be observed that the frequency response is almost constant for a wide range of displacements (within the beam-width), indicating a significant blurring.

The results of a scan performed using a transducer with a pinna in accordance with a preferred embodiment of the present invention mounted over it, are shown in Figure 5B illustrating a spectrogram of a received signal from a single sphere target. As can be noted, the experimental results are in accordance with the analytical prediction. The frequency of the maximal value of the Fourier transform is varying almost linearly as a function of the displacement. There is no energy at negative displacement since the reflector is "shadowing" the transducer.

In a second set of experiments, two targets, which were two glass spheres, each of 15 mm in diameter, were placed in water tank 50. The distance between the sphere's centers was 15 mm, i.e., there was no gap between the two spheres. The scan results of the targets using the regular transducer and the transducer with the pinna in accordance with a preferred embodiment of the present invention are shown in Figures 5C and 5D, respectively. From Figure 5C it can be noted that the objects are represented by two blurred images partially overlapping and there is no obvious distinction between the two spheres. Figure 5D illustrates a spectrogram of a received signal from two spheres target scanned by a transducer with a pinna in accordance with a preferred embodiment of the present invention. It can be observed that the images of the objects are very well distinct and separated.

In order to show the potential of increasing the resolution for medical imaging application, for example, the following frequency focusing algorithm was implemented to analyze the data.

a) Collect the echoes signal at each transducer location.

b) Extract the relevant temporal window that corresponds to the analyzed range from the transducer. c) Perform a Fast Fourier Transform (FFT) to the window data, find the frequency where the absolute value of the spectrum is maximal, and calculate the shift (delta) relative to the central frequency fo.

d) Calculate the azimuth θ using the equation

that expresses the relation between the azimuth (direction) θ and the frequency for which the amplitude response is maximal.

e) Accumulate the echo energy into the image buffer using the corresponding frequency range and azimuth information.

f) Repeat the above analysis for each transducer location and each frequency range.

The results obtained by applying the above algorithm are plotted in Figure 6A-6D. The graphs in Figures 6A and 6C depict the reflected echo energy as a function of the transducer location without the artificial pinna. The graphs in Figures 6B and 6D depict the output curves for the frequency focusing algorithm when implemented on the data collected by the transducer with the artificial pinna in accordance with a preferred embodiment of the present invention mounted on it. It can be observed that the two targets are clearly separated and the energy signature is about five folds enhanced. Furthermore, the target's location is accurately detected. The contrast between these results and the results obtained with the regular transducer (Figures 6A and 6C), where the target signatures are smeared, is evident.

The distance of the object from the reflector from which the sensor may receive signals ranges in accordance with the application. When using ultrasonic imaging, for instance, the distance between the reflector and the source may be up to about 30 cm. In sonar systems the distance may be in the range of a few kilometers. Generally, any flat or concave plane can be suitable for the construction of the artificial pinna reflector. Reference is now made to Figure 7 illustrating an isometric view of a reflector in accordance with another preferred embodiment of the present invention. A hollow cylinder 10 is diagonally cut off 11 so that a part of the internal plane is exposed to reflect the incoming waves and direct them to the transducer that is at the bottom of the reflector.

Reference is now made to Figure 8 illustrating an isometric view of a reflector in accordance with yet another preferred embodiment of the present invention. The reflector comprises three flat planes connected perpendicularly to each other. The middle plate 20 serves as a reflector while two triangular plates 21 and 22 on the sides can be made of an absorbing material so as to prevent reflection from these plates. Plates 21 and 22 are adapted to limit the transducer's field of view. The transducer is positioned at the bottom (the shaded area 23).

Any other flat or concave plane or an arrangement of planes that may serve as a reflector is covered by the scope of the present invention.

The physical parameters for the design of an acoustic sensor for localization are dependent on the application of the sensor. A preferred procedure for the selection of the system parameters is given in the next scheme:

Select central frequency

For medical imaging 1 -10 MHz For sonar systems 1 -100 KHz i

I

Set the system physical dimension d = t x c/sin θ where d is twice the distance between the transducer center and the reflector. c is the sound speed θ is nominal azimuths angle (typically half the transducer beam width)

An example for a specific selection of physical parameters for ultrasonic medical imaging system is given below:

Central frequency 1 MHz

Nominal time delay 0.5 μsec

c = 1500 m/s (sound speed in water)

nominal azimuth 0.5 degrees

The distance between the transducer center and the reflector is

d = 17/2 mm It should be noted that there are two recommendations to consider in determining the reflector size. First, the reflector's height (i.e. the longitudinal dimension of the reflector's plane in the anticipated direction of use) should preferably be greater than the wavelength of the acoustic pulse employed, at least twice the wavelength. Second, the reflector's height should preferably be greater than the distance between the reflector and the center of the transducer, again, at least twice the distance.

In order to improve the localization performance, a plurality of sensors can be arranged in an array. Reference is now made to Figure 9, illustrating an array of reflectors in accordance with yet another preferred embodiment of the present invention. Each reflector 30 is similar in shape to the reflector shown in Figure 2, while all reflectors are aligned facing to the right. The array of sensors can be arranged to face any direction from which signals are anticipated. Each reflector is mounted on a cylindrical transducer that receives the incoming waves. Eventually, the signals received from the plurality of sensors are transmitted to an analyzer that registers the contribution of each sensor to the total signal to be analyzed.

Reference is now made to Figure 10 illustrating an array of reflectors in accordance with yet another preferred embodiment of the present invention. A rectangular plate 40 serves as a reflector that is mounted on a transducer 41 of rectangular cross section. The array of reflectors faces to the right. At the back of each reflector, a prism 42 is attached. The prism disperses waves arriving from the left-hand side of the reflector's array, so as to prevent them from interfering with the reflector's readings. Prism 42 may preferably be made from or coated with an absorbing material, apart from the reflecting surface 40 on the right hand-side.

Accurate localization of reflected echoes can be important in medical and other applications. Common engineering solutions utilize focusing devices such as lenses or phase array systems. Nature on the other hand has provided alternative efficient solutions. The pinna organ modifies the spectrum of the received signal in a direction dependent manner. The brain utilizes the additional information to localize sound source and it can do so even in a monaural scenario.

Possible implementation of this principle can be found in ultrasonic imaging and acoustic tracking applications, such as security systems and perhaps passive sonar. The principle shown here can also be implemented for the electromagnetic spectrum.

The analyzed results of localization or any other processed information needed may be represented as an output and presented by an output means such as a printer or a computer monitor. Alternatively, the output may be transferred to another device.

It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of ^• the invention, without limiting its scope as covered by the following Claims.

It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the following Claims.

Claims

C L A I M S

A system for the localization of target objects using acoustic signals comprising:

an acoustic transducer;

acoustic reflecting means;

processing means;

output means

wherein said processing means is adapted to compute the position of the target object and output the position through said output means.

A system as claimed in Claim 1 , wherein said acoustic reflecting means comprises a flat reflecting plane.

A system as claimed in Claim 1 , wherein said acoustic reflecting means comprises a concave reflecting plane.

A system as claimed in Claim 1 , wherein said reflecting means comprises a surface having a semi-circular cross-section.

A system as claimed in Claim 1 , wherein said reflecting means comprises a reflector made from a metal such as aluminum or stainless steel.

6. A system as claimed in Claim 1 , wherein said acoustic reflecting means is mounted on said acoustic transducer.

7. A system as claimed in Claim 1 , wherein said acoustic reflecting means is a hollow cylinder cut along a diagonal cross-section.

5 8. A system as claimed in Claim 1 , wherein said acoustic transducer is adapted to translate pressure to an electric voltage.

9. A system as claimed in Claim 1 , wherein said acoustic transducer is a piezo-electric transducer.

10. A system as claimed in Claim 1 , wherein said processing means is 10 adapted to calculate the azimuth of the target object with respect to the perpendicular line at the center of said acoustic transducer by dividing half the sound propagation speed by the central frequency of the incoming signal and than divide the resultant by the distance between the reflector and the transducer's center, wherein the resultant is 15 multiplied by one minus the division of the frequency of the maximal amplitude in the spectrum of the incoming signal by the central frequency of the incoming signal.

11. A system as claimed in Claim 1 , wherein said acoustic transducer is an ultrasonic transducer.

20 12. A system as claimed in Claim 13, wherein said ultrasonic transducer is adapted to receive superposed echoes from a target object distanced not more than 40 centimeters from said acoustic reflecting means, directly from the target object and indirectly, reflected by said acoustic reflecting means.

25 13. A system as claimed in Claim 1 , wherein said acoustic transducer is a sonar transducer.

14. A system as claimed in Claim 15, wherein said sonar system is adapted to receive superposed echoes from a target object distanced up to not more than a few kilometers from said acoustic reflecting means, directly from the target object and indirectly, reflected by said acoustic reflecting means.

system as claimed in Claim 1 , wherein said acoustic reflecting means is a rectangular plate, said plate is further provided with two triangular plates on both sides of said plate substantially perpendicular to the rectangular plate.

system as Claimed in Claim 17, wherein said two triangular plates are made from an acoustically absorbing material.

system as claimed in Claim 1 , wherein the longitudinal dimension of said acoustic reflecting means in the anticipated direction of the incoming acoustic signal is substantially twice as large as the wavelength of the incoming acoustic signal.

system as claimed in Claim 1 , wherein the longitudinal dimension of said acoustic reflecting means in the anticipated direction of the incoming acoustic signal is substantially twice as large as the distance between said acoustic reflecting means and the center of said acoustic transducer.

system as claimed in Claim 1 , wherein a plurality of said acoustic reflecting means is aligned and adapted to reflect waves incoming from a reflecting object.

system as claimed in Claim 21 , wherein the plurality of said acoustic reflecting means is mounted on a plurality of said acoustic transducer, each of said acoustic reflecting means is mounted on each of said acoustic transducer.

system as claimed in Claim 22, wherein the plurality of said acoustic transducer is adapted to transmit the electrical signals corresponding to the received superposed acoustic signal from each of said acoustic transducer to said processing means. A system as claimed in Claim 21 , wherein each of said acoustic reflecting means is a plate, said plate is provided with a prism on its backside.

A system as claimed in Claim 24, wherein said prism is made from an absorbing material.

A sensor for the localization of target objects using acoustic signals comprising:

• an acoustic transducer; and

• acoustic reflecting means;

A sensor as claimed in Claim 24, wherein said acoustic reflecting means comprises a flat reflecting plane.

A sensor as claimed in Claim 24, wherein said acoustic reflecting means comprises a concave reflecting plane.

A sensor as claimed in Claim 24, wherein said reflecting means comprises a hollow cylinder partially cut along the longitudinal axis of the cylinder, so as to present semi-circular cross-section.

A sensor as claimed in Claim 24, wherein said acoustic transducer has a cylindrical cross section.

A sensor as claimed in Claim 24, wherein said acoustic reflecting means is mounted on said acoustic transducer.

A sensor as claimed in Claim 24, wherein said acoustic reflecting means is a hollow cylinder cut along a diagonal cross-section. A sensor as claimed in Claim 24, wherein said acoustic transducer is adapted to translate pressure to an electric voltage.

A sensor as claimed in Claim 24, wherein said acoustic reflecting means is a rectangular plate, said plate is further provided with two triangular plates on both sides of said plate substantially perpendicular to the rectangular plate.

A sensor as Claimed in Claim 32, wherein said two triangular plates are made from an absorbing material.

A sensor as claimed in Claim 24, wherein a plurality of said acoustic reflecting means is aligned and adapted to reflect waves incoming from a reflecting object.

A sensor as claimed in Claim 24, wherein said wherein said acoustic transducer receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means, and wherein said sensor is further provided with an acoustic transducer adapted to transmit acoustic signals to a target object.

A method to determine the localization of target objects using acoustic signals comprising the following steps:

i) providing an acoustic transducer; acoustic reflecting means; processing means and output means, wherein said transducer is adapted to transmit acoustic signals to a target object, receive superposed echoes from the target object, directly from the target object and indirectly, reflected by said acoustic reflecting means, and transmit an electrical signal corresponding to the received superposed acoustic signal to said processing means; and wherein said processing means is adapted to compute the position of the target object and output the position through said output means; ii) calculating the azimuth of the target object with respect to the perpendicular line at the center of said acoustic transducer by dividing half the sound propagation speed by the central frequency of the incoming signal and than divide the resultant by the distance between the reflector and the transducer's center, wherein the resultant is multiplied by one minus the division of the frequency of the maximal amplitude in the spectrum of the incoming signal by the central frequency of the incoming signal.

A system for the localization of target objects using acoustic signals substantially as described in the above specification, attached

Figures and appending Claims.

A method for the localization of target objects using acoustic signals substantially as described in the above specification, attached Figures and appending Claims.