Patent No. 5889870 Acoustic heterodyne device and method

 

Patent No. 5889870

Assignee:  American Technology Corporation, 15378 Avenue of Science, Suite 100. :: San Diego, CA 92128 USA

Acoustic heterodyne device and method (Norris, Mar 30, 1999) 

Abstract

The present invention is the emission of new sonic or subsonic compression waves from a region resonant cavity or similar of interference of at least two ultrasonic wave trains. In one embodiment, two ultrasonic emitters are oriented toward the cavity so as to cause interference between emitted ultrasonic wave trains. When the difference in frequency between the two ultrasonic wave trains is in the sonic or subsonic frequency range, a new sonic or subsonic wave train of that frequency is emitted from within the cavity or region of interference in accordance with the principles of acoustical heterodyning. The preferred embodiment is a system comprised of a single ultrasonic radiating element oriented toward the cavity emitting multiple waves.

Notes:

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and apparatus for indirectly emitting new sonic and subsonic wave trains from a region of air without using a direct radiating element to emit the wave trains.

It is another object to indirectly generate at least one new sonic or subsonic wave train by using a by-product of interference between at least two ultrasonic signals having different frequencies equal to the at least one new sonic or subsonic wave train.

It is still another object to cause at least two ultrasonic wave trains to interact in accordance with the principles of acoustical heterodyning to thereby extract intelligence from the interfering wave trains.

It is yet another object to indirectly generate new sonic or subsonic wave trains by combining them with an ultrasonic carrier wave using amplitude modulation, emitting the combined signal from an ultrasonic transducer, causing interference between the carrier wave and another ultrasonic frequency wave train, to thereby create the new sonic or subsonic wave trains.

It is still another object to affect a physical state of a living being utilizing an indirectly created compression wave.

It is still yet another object to generate a new compression wave which is perceptible to human senses using at least two imperceptible compression waves, but without directly propagating the new compression wave.

Yet another object of the invention is to generate a new sonic or subsonic wave train without having to overcome the mass and associated inertial limitations of a conventional direct radiating element.

Still another object of the invention is to generate a new sonic or subsonic wave train without introducing distortions or undesired harmonics otherwise inherent to a conventional direct radiating element.

Another object is to indirectly generate and enhance a new sonic or subsonic wave train from within a resonant cavity by emitting at least two ultrasonic wave trains into the resonant cavity.

Yet another object is to omni-directionally generate a high frequency wave train, thereby avoiding the highly focused and directional nature of high frequency signal emissions typical of a conventional loudspeaker.

Still yet another object is to generate a new sonic or subsonic wave train in a localized area without coupling to an associated environment or enclosure which would otherwise cause undesirable broadcasting of the sonic or subsonic wave train.

Yet another object is to generate a new sonic or subsonic wave train wherein characteristics of the new sonic or subsonic wave train are not limited by the characteristics of a direct radiating element.

Another object of the invention is to emulate a sound wave detection process typical of an approximate point-source detection device such as a microphone, but without providing a physical detection device at a detection location.

Another object is to control the volume of a new sonic or subsonic wave train by manipulating the degree of interaction of the at least two ultrasonic frequency wave trains.

Still another object is to emit a new sonic or subsonic wave train from a region of air as a by-product of modulating a single ultrasonic wave train emitted from a single ultrasonic transducer into the region in accordance with the principles of acoustical heterodyning.

The present invention is embodied in a system which indirectly generates new sonic or subsonic waves trains. In one embodiment, a new sonic or subsonic wave train is emitted from a region of interference of at least two ultrasonic wave trains emitted from at least two ultrasonic transducers. The principle of operation is based on incorporating retrievable intelligence onto an ultrasonic carrier wave. The intelligence is retrieved as the desirable by-product of interference of the ultrasonic carrier wave train and another ultrasonic wave train. The ultrasonic wave trains interfere within a region of non-linearity in accordance with principles identified by the inventor as "acoustical heterodyning," and thereby generate by-products which include the difference and the sum of the two ultrasonic wave trains.

A system which easily demonstrates the principle of acoustical heterodyning comprises two ultrasonic frequency transducers which are oriented so as to cause interference between emitted ultrasonic wave trains. When the difference in frequency between the two ultrasonic wave trains is in the sonic or subsonic frequency range, the difference in frequency is generated as a new, audible sonic or new subsonic wave train emanating outward from within the region of heterodyning interference.

A different embodiment of the system provides the advantage of being comprised of only one ultrasonic direct radiating element. The advantage is not only in the decreased amount of hardware, but the perfect alignment of the two interfering ultrasonic wave trains because they are emitted from the same radiating element. In effect, the new sonic or subsonic wave train appears to be generated directly from the ultrasonic emitter. If it were not for the inescapable conclusion that the ultrasonic emitter cannot itself generate sonic or subsonic frequencies, plus the audible evidence that the sound is not emanating directly from the emitter, one might be deceived.

The importance of the first embodiment is that it teaches the concept of generating a new sonic or subsonic wave train as a result of the interference between two ultrasonic wave trains in accordance with the principles of acoustical heterodyning. In essence, it is easier to see that two ultrasonic wave trains are coming from two ultrasonic emitters. But the principle of acoustical heterodyning taught by this first embodiment prepares the way for understanding how the second embodiment functions. It becomes apparent that the same acoustical heterodyning principle applies when it is understood which wave trains are interfering in space.

A key aspect of the invention is the discovery that by superimposing sonic or subsonic intelligence onto an ultrasonic carrier wave, this intelligence can be retrieved as a new sonic or subsonic wave train. Whether the ultrasonic wave trains are generated from two emitters or from a single emitter, the effect is the same.

Another aspect of the invention is the indirect generation of new compression waves without having to overcome the problems inherent to mass and the associated limitations of inertia of a conventional direct radiating element. The present invention eliminates a direct radiating element as the source of a new compression wave so that the desired sound is generated directly from a region of air and without the several forms of distortion all associated with direct radiating speakers.

Another aspect which is helpful to utilize the present invention is to understand the nature of the transmission medium. More specifically, the region of air in which an acoustical heterodyning effect occurs is referred to as the transmission medium. It is well known that the transmission medium of air provides an elastic medium for the propagation of sound waves. Thus, prior art research has treated air as a passive element of the sound reproduction process. Air simply waits to be moved by a compression wave.

Consequently, little practical attention has been devoted to the nature of air when it behaves non-linearly. In the past, such non-linearity has perhaps been perceived as an obstacle to accurate sound reproduction. This is because it is understood by those skilled in the art that in extreme conditions, air molecules are less and less able to follow the vibration of a compression wave, such as that produced by a diaphragm. Therefore, the tendency of research has been to avoid non-linear conditions.

In contrast, the present invention appears to favor the existence of a non-linear transmission medium in order to bring about the required heterodyning effect. Although air is naturally non-linear when a compression wave moves through it, the degree of non-linearity is relatively unobservable or inconsequential. However, when ultrasonic compression waves are emitted so as to interfere in air, the non-linearity causes a surprising and unexpected result which will be explained and referred to as the acoustical heterodyning effect or process.

The present invention draws on a variety of technologies and aspects which have sometimes perceived as unrelated topics. These aspects of the invention include 1) indirectly generating a new sonic, subsonic or ultrasonic compression wave, 2) superimposing intelligence on an ultrasonic carrier wave and retrieving the intelligence as the indirectly generated compression wave, 3) causing at least two ultrasonic compression waves to interact in air and using the by-product of the interference, 4) using the principle of acoustical heterodyning to indirectly generate the new compression wave, 5) generating the new compression wave from a relatively massless radiating element to avoid the distortion and undesirable harmonics of conventional direct radiating elements, 6) affecting a physical state of a living being by generating subsonic frequencies in close proximity thereto, 7) generating an approximate point-source of sound that is phase coherent over the entire audio spectrum, 8) eliminating distortion in playback or broadcasting of sound, 9) eliminating the "beaming" phenomenon inherent in emission of high frequency compression waves from a direct radiating element, 10) generating a new sonic or subsonic compression wave which is independent of the characteristics of the direct radiating element, and 11) the detection of sound without using a direct detection device at a detection location.

It should be remembered that all of these aspects of the present invention are possible without using a speaker or other form of direct radiating structure. Furthermore, these sonic or subsonic frequencies are generated absolutely free of distortion and in a generally omni-directional orientation. The surprising result is the ability to recreate "pure" sound in the same form as when it was originally captured at a microphone or other recording system.

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It is to be understood that the preceding description is given to illustrate various embodiments of the present inventive concepts. The specific examples are not to be considered as limiting, except in accordance with the following claims.