US3366922A

US3366922A - Blind aid

Info

Publication number: US3366922A
Application number: US541851A
Authority: US
Inventors: Kay Leslie
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1965-04-29
Filing date: 1966-04-11
Publication date: 1968-01-30
Anticipated expiration: 1985-01-30
Also published as: DE1548479B2; ES326146A1; GB1098927A; NL6605777A; AT273247B; CH443069A; JPS5027736B1; DE1548479A1

Description

L. KAY

Jan. 30, 1968 BLIND AID 6 Sheets-Sheet- 1 Filed April 11, 1966 AMPLITUDE OF SIGNAL.

COMPENSATED.

L. KAY

BLIND AID Jan. 30, 1968 6 Sheets-Sheet 2 Filed April 11, 1966 b S C K C K O 0 7 (s w \l M ll:

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Jan. 30, 1968 L. KAY 3,

BLIND AID Filed April 11, 1966 6 Sheets-Sheet. 5

L. KAY

BLIND AID Jan. 30, 1968 6 Sheets-Sheet 4 Filed April 11, 1966 Fig. 7.

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Jan. 30, 1968 L. K AY BLIND AID Filed April 11, 1966 6 Sheets-Sheet 5 Jan. 30, 1968 Filed April 11, 1966 L. KAY

BLIND AID 6 Sheets-Sheet 6 19 2| H 22 23 I g I I z aa Aa miaiz FE E RANGE RECEIVING CHANGER, TRANSDUCER. EOUAL'SER' lb )5 1/4 IO 2 l3 24 H EAD N PHONES POW R O P SS L M TRANSMTTING AMP LIFIER -QDK C SFFREOUENCY SAW-TOOTH 24 SWEPT GENERATOR. TRANSDUCER. OSCILLATOR l7 l8 19 2| ll 22 23 5mm Ra's? RECEIVING FREQUENCY RANGE TRANSDUCER. CHANGER. EOUALISER.

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United States Patent 3,366,922 BLIND All) Leslie Kay, Christchurch, South island, New Zealand, as-

signor to National Research Development Corporation, London, England, a corporation of Great Britain Filed Apr. 11, 1966, Ser. No. 541,851 Claims priority, application Great Britain, Apr. 29, 1965, 17,933/65 11 Claims. (Cl. 340-1) ABSTRACT OF THE DISCLUSURE A blind aid in which frequency swept acoustic wave energy, preferably ultrasonic, is radiated from a transmitting transducer carried by a spectacle type head set and received by laterally spaced receiving transducers on the head set the outputs of which feed two channels in which a locally generated frequency swept signal heterodynes with the received signal to provide audible beat signals in two earphones, and wherein the receiving transducers have divergent polar lobes which in combination with the polar lobe of the transmitting transducer simulate the characteristics of a normal human auditory system.

This invention relates to a new or improved blind aid of the kind wherein acoustic wave energy, preferably at a frequency above the audible range, is radiated to a field of view and is received therefrom upon reflection from an object therein by means of a transmitter-receiver system incorporating two receiving channels fed from respective transducers carried on a head set and connected to respective aural elements for furnishing audible signals to the left and right hand ears of the user.

This invention has been developed primarily in relation to a particular form of blind aid as set forth in the foregoing paragraph and which comprises transmitting means for generating an electrical carrier wave signal of ultrasonic frequency, means for frequency modulating said carrier wave signal in accordance with a saw-tooth frequency-time characteristic to sweep said carrier wave through a range of frequencies whereof the highest value is at least one half an octave higher than the lowest value, transducer means connected with said transmitting means for radiating acoustic wave energy of the frequency of said carrier signal to a field of view and for receiving a reflection of said acoustic wave energy from an object therein, receiving means also connected with said transducer means for receiving therefrom an incoming electrical signal of the frequency of said reflection and including at least one receiving channel, modulating means in said channel, means for feeding a local electrical signal to said modulator means of a frequency varying cyclically in conformity with that of said carrier wave signal to heterodyne with said incoming signal and produce a beat signal of difference frequency proportional to the range of the object and varying through a range of values as the range of said object varies from maximum to minimum, filter means in said channel for passing in a single continuous band only beat signals of less than a predetermined frequency corresponding to said maximum range down to those corresponding to said minimum range, the former having a value a plurality of times smaller than said range of values through which said carrier wave signal is varied, means for presenting said beat signal, consisting only of sound reproducing means, connected to said filter means for generating an audible signal of the frequency of all of said beat signals concurrently passed by said filter means, and portable mounting means movable by 35,366,922 Patented Jan. 30, 1968 said person into different orientations and carrying at least said transducer means.

This particular form of blind aid is described and claimed in my prior US. Patent 3,172,075.

Use of this blind aid by a blind person to obtain information as to the direction of an object in the field of view is achieved primarily by recognition of a difference in the frequency of the beat signals in the two channels and reproduced by the aural indicator elements connected thereto, the user turning his head to equalize the beat frequencies and when this is obtained looking in a direction towards the object. Assistance in this respect is also gained from the fact that the beat frequency audio signal fed to each aural indicator element consists of a series of pulses during which the particular frequency is maintained and intervening intervals when it ceases (zero audio signal) producing a pulsing effect. When the users head is turned towards the object the pulses produced by the two aural indicator elements should be in synchronism with each other.

In this prior form of the apparatus, however, the directional characteristics of the two receiving transducers (as represented by their polar diagrams drawn in an azimuthal plane) were not correlated to those average or normal auditory neural characteristics of the human system which enable persons to recognize the direction from which sounds are radiated towards them from a distant object, by virtue of the amplitude differences of the signal to which the ear drums are subjected.

These characteristics are such that when the source of sound lies at a point directly ahead of the observer the latter having his face turned forwardly towards this source, the amplitude of the audible signal applied to each ear drum is less than that which is applied to one of the ear drums when the observer turns hi head to present this car directly towards the source of sound. This effect is due to the formation of the outer ear, but the observer retains the sensation of hearing a sound of the same amplitude or strength irrespective of whether he is facing towards the source or turns his head to present one ear towards it because of compensation occurring in the nervous system between the ears and the brain or in the latter. Recognition of the direction of the sound source is therefore achieved by virtue of the different contribution to the overall sensation of sound proceeding from the two ears respectively. This contribution is equal when the observer is facing towards the sound source and is unequal in other orientations of the users head, although over approximately the overall sensation is one of equal mtensity or strength of sound.

This effect is known psychologically as localization, which term is used to describe the sensation experienced by the observer when the source of sound appears to him to be an external source, that is to say, situated outside his own head.

There is another known effect psychologically termed lateralization in which the observer experiences the sensation that the source of sound is within his own head, and this sensation is frequently experienced when the observer is listening to sounds applied to his ears by means of headphones. Use of the particular form of apparatus described and claimed in the prior patent hereinbefore mentioned gave rise to a lateralization effect so that in order to recognize the direction of the source of sound, i.e. the object, the user had to rely entirely upon the frequency difference and pulsing effect. Consequently, the users inate ability to recognize direction, and which is dependent upon the existence of a localization effect could not be made use of, and was even interfered with, so far as audible sounds emanating from sound emitting objects in the field were concerned.

The object of the present invention is to provide an improved form of blind aid which is adapted to give rise to a localization eifect and to enable the user to recognize the direction of an object in the field of view by employment of his normal binaural sense of direction.

According to the invention a blind aid wherein acoustic wave energy is radiated to a field of View, and is received therefrom upon reflection from an object therein by means of a transmitter-receiver system incorporating two receiving channels fed from respective transducers carried on a head set, such channels feeding respective aural elements for furnishing audible signals to the left and right hand ears of the user, is characterised in that these transducers are so constructed or mounted as to have receiving characteristics represented by polar lobes of which the principal axes diverge and lie on opposite sides of a reference axis extending medially of the field of view such lobes overlapping with each other along the reference axis.

The term principal axis as used herein is to be deemed to mean the direction in which the radius vector of the lobe concerned has maximum amplitude irrespective of whether the lobe is symmetrical or assymetrical about this vector.

It will be understood that the angular limits which represent the lateral boundaries of the field of view can be varied to suit particular requirements.

In general these limits will lie in a range of from about 30 to about 60 to each side of the reference axis so that the angular width of the field of view in azimuth is from about 60 to about 120.

The amplitude or strength of the signal reproduced audibly by each of the aural elements diminishes as the object from which the reflection is received is displaced angularly towards the reference axis from the position on the principal axis of the lobe concerned. The extent of the diminution should ideally be such as to correspond with that which occurs at the ear drum when a normal sound source is moved in a corresponding manner. Thus, when the compensation is superimposed on this characteristic by the observers neural system and brain, the observer will experience the sensation of an approximately constant amplitude or strength of sound over the displacement angle above mentioned. Such sensation will also remain constant over the outer par-ts of the field of view.

A further advantage of the present invention is that it enables the user to resolve ambiguities as to the direction of an object which could not be resolved by the form of aid as described in the prior patent. When two objects were present in the field of view the user was confused because, theoretically, it can be shown that there were four signals, two of which correspond to the objects in their correct positions, and two which corresponded to objects in imaginary positions. It was necessary for the user to turn the head to resolve these, and, when there were more than two such objects present the situation was impossible of resolution. With the present apparatus which makes use of the normal binaural sense of direction the latter will enable the user to recognize the respective directions of the two objects even without turning his head.

In the apparatus described and claimed in the prior patent previously mentioned, the transmitting transducer which it was proposed to employ had a radiating surface of relatively small area and of plane circular form. The polar diagram representing the directional characteristics (in azimuth) of such a surface consisted of a main lobe subtending a fairly narrow angle (typically 40) flanked at both sides by a number of secondary lobes of the smaller size with intervening cusps or zeros.

In order to provide a wider field of view the area of the radiating surface could have been reduced, but to do so would have involved a corresponding reduction in the power of the wave energy radiated to the field of view as a whole and having regard to the angular enlargement of the latter this effect would have been most undesirable 4 since it would have seriously reduced the effective range of the aid.

Thus, this directional characteristic of the transmitting transducer operating in combination with the directional characteristics produced by the polar lobes of the receiving transducers disclosed in said prior patent inevitably produced a sharply directional characteristic having its maximum coincident with the reference axis.

One disadvantage of this was that the effective field of view was reduced to too small an angle. Further, the peaking of the amplitude or strength of the sound pro duced by both aural elements when the observer was facing directly towards an object was an imposed phenomenon differing in character fundamentally from the normal 7 V W 7 V Such directional characteristic may be provided by utilizing for the transmitting transducer a radiating element or a plurality of radiating elements which presents, or present collectively, a radiating surface of convex arcuate form as viewed in an azimuthal cross sectional plane.

This form of transmitting transducer is especially advantageous in that it provides a very simple means of irradiating a field of view bounded by selected or predetermined angular limits merely by making the angle subtended at the ends of the radiating surface equal or approximately equal to the included angle of the field of view. Moreover, it will be evident that the power radiated is increased as the angle is increased.

The invention further resides in the provision of an improved form of blind aid wherein acoustic wave energy is radiated to a field of view and is received therefrom upon reflection from an object therein by means of a transmitter-receiver system incorporating a transmitting transducer and two receiving transducers all carried by a head set, the receiving transducers feeding respective receiving channels of the system to which are connected respective aural elements on the head set for applying audible signals to the left and right hand ears of the user, characterised in that the transmitting transducer includes a radiating element or a plurality of radiating elements presenting or collectively presenting as the case may be, a radiating surface of convex arcuate form. in an azimuthal plane, and the receiving transducers have receptive surfaces presented towards the field of view in directions which diverge to opposite sides of a reference axis extending medially of such field, the whole arrangement being such as to avoid any pronounced forward peak of sensitivity along the reference axis.

While the invention is applicable with especial advantage to the particular form of blind aid as defined in the second paragraph of this specification, and one form of which is described and claimed in the prior patent hereinbefore mentioned, it will be understood that the invention may be applied to forms of blind aid in which the transmitter-receiver system is not necessarily one which involves production of a frequency modulated transmitted signal heterodyned with the received signal. Such system may involve transmission of an amplitude modulated signal, for example a pulsed signal, range determination being then effected by measurement of the time interval elapsing between transmission of a given pulse and its reception after reflection from an object in the field of view. Such measurement could be impressed upon the sensibility of the user by means of a variable frequency circuit producing an audible frequency of a value correlated to the range at which the object is situated.

The invention will now be described by way of example with reference to the accompanying drawings wherein:

FIGURE 1 is a simplified and idealized polar diagram illustrating the desired directional characteristics in azimuth for the transmitting transducer and receiving transducers of a blind aid incorporating the present invention.

FIGURE 2 is an idealized graphical representation of characteristics of the human auditory neural system in which amplitude of sound signal or strength is plotted as ordinate against angular position of the source of sound relative to a reference axis.

FIGURE 3 is a polar diagram of the actual directional characteristic in azimuth attained by a transmitting transducer and receiving transducers constructed and arranged in accordance with the invention.

FIGURE 4 is a diagrammatic view in front elevation showing the form and arrangement of transducers.

FIGURE 5 is a diagrammatic plan view of the parts shown in FIGURE 4.

FIGURE 6 is a perspective view of one form of head set on which transmitting and receiving transducers are mounted, such transducers being constructed and arranged in accordance with the present invention.

FIGURE 7 is a fragmentary perspective view on an enlarged scale showing the construction of one of the parts of the transmitting transducer.

FIGURE 8 is a view in front elevation showing an alternative embodiment of head set incorporating transmitting and receiving transducers constructed and arranged in accordance with the present invention.

FIGURE 9 is a plan view partly in cross section on the line 9-9 of FIGURE 8 of the same embodiment, and

FIGURE 10 is a schematic circuit diagram showing one form of circuit which may be employed in the apparatus.

Referring firstly to FIGURE 2 of the drawings, the curves (A) (A) shown therein in full lines illustrate diagrammatically the amplitude or strength of the sound signal which is incident at the ear drums of the left and right hand ears of a normal human observer as the users head is turned to one side and the other side through angles of 90 from a straight ahead position in which the observer is looking straight towards the source of sound. The characteristics represented by these curves (A) and (A) are produced by the particular form. of outer ear and shadow effect of the head. The curve (A) and (A) are typical for a median range of frequencies, e.g. 3 kc./s. to 7 kc./s. Curves similar to (A) and (A) have been reproduced by setting up a receiving transducer, amplifier, and amplitude measuring instrument with the transducer situated at the inner end of the passageway presented by an artifically constructed outer ear formation and moving a source of sound angularly relatively to the latter. The broken line curve B represents the subjective sensation experienced by the observer as to the amplitude or strength of sound which he actually hears (with both ears), the nervous system and the brain producing compensation for the cusp presented by the curves (A) (A) so that as the user turns his head through 180 from one side to the other of the reference axis upon which the source of sound lies he experiences a sensation of approximately uniform amplitude or strength.

Ability to recognize the direction of the source is derived from subconscious assessment of the relative contributions made by the two ears, which is approximately equal when the observer is looking straight ahead towards the source of sound, and which increases for the particular ear turned to present its aperture towards the source of sound.

The present invention is based on the concept that the strength or amplitude of the beat frequency signals reproduced audibly by the aural elements of a blind aid of the kind specified should, so far as possible, conform to the curves (A) (A) represented in FIGURE 2, so that the user experiences a sensation as to the amplitude or strength of the sound signal as represented by curve B, and will hence be able to exercise his normal faculties of recognizing the direction in which the source of sound is situated rather than being under the necessity of developing a different and possibly unnatural faculty for recognizing such direction, as would be the case were the blind aid to have a pronounced forward peak of sensitivity.

These features are particularly important inasmuch as the hearing faculties of blind persons tend to become highly developed. It would therefore be confusing to such person if his auditory system were under the necessity of simultaneously receiving two sets of sound signals, one set consisting of the ordinary environmental sounds with respect to which such person would utilize his normal directional recognition faculties, and the other set being the audibly produced beat signals fed to the users left and right hand ears from the blind aid and with respect to which the user would be under the necessity of developing an artificial or unnatural directional recognition faculty.

The general form of blind aid of the kind specified and incorporating the present improvements designed to allow the user to exercise his normal directional recognition faculties with respect to the audibly produced beat signal frequencies may be as described and illustrated in FIGURES 1, 2, 3 and 6 to- 11 of the specification of the prior patent previously referred to. For convenience the schematic circuit diagram of this apparatus is shown in FIGURE 10 hereof. Such apparatus comprises a transmitting channel 10 and two receiving channels 11, the former containing a frequency swept oscillator 12 having a saw tooth frequency sweep fed through a low pass filter 14 and power amplifier to a transmitting transducer 16 and each of the latter channels 11 being fed from a receiving transducer 17 and containing a pre-amplifier 18, a frequency changer or modulator 19 fed with a frequency swept signal from the transmitting channel through a conductor 20, a low pass filter 21, range equaliser 22 and audio amplifier 23 feeding aural elements 24 incorporated in a head set.

As disclosed in the aforementioned specification the frequency of the radiation from the transmitting transducer is above the audible range.

To assist the user in recognizing the character of objects from which reflections are obtained the frequency sweep is selected as disclosed in the prior specification referred to, so that the upper limit is at least one half an octave above the lower limit of frequency, a preferred value being about one octave above this lower value. Typically a frequency sweep of from 45 kc./s. to kc./s. may be employed. Also to assist recognition of the type of object the maximum beat frequency corresponding to maximum distance or range of the object from which reflections are obtained has a low value relative to the frequency sweep, the latter being a plurality of times greater, so that even at maximum range, the audible signals consist of relatively long pulses of the beat frequency separated by relatively short intervals. These features enable the user to differentiate by tonal differences between refiections received from different types of surface.

Ideally the directivity of the receiving transducers 17 in azimuth would be as represented by the lobes C and D in FIGURE 1. The principal axes of these lobes as represented at E and F are disposed in divergent relation to each other symmetrically on opposite sides of the reference axis G.

The angle of divergence is selected having regard to the shape of the lobes to ensure that the portions of the two lobes within the field of view provide as good an approximation as possible to the characteristics represented by the curves (A) and (A) of FIGURE 2. Portions of the lobes which lie laterally beyond the lines H and I representing the lateral limits of the field of view are comparatively unimportant for the reason that the transmitter radiates only a small amount of power outside these limits. The principal axes of the lobes are represented by the lines E and F coincident with the points on these lobes where the radius vector has its maximum value.

The directional characteristic in azimuth of the transmitting transducer is represented ideally by a sector shaped lobe bounded by the lines H and J representing the lateral boundaries of the field of view and which typically would 'be from 60 to 120 and by a circular arc K centered on the origin L of the polar diagram.

These characteristics can be attained to a good degree of approximation by utilization of a transmitting transducer and receiving transducers as shown diagrammatically in FIGURES 4 and 5. In these figures parts corresponding to those already referred to in FIGURE 10 are indicated by like numerals of reference with the prefix 1. The transmitting transducer 116 is in the form of an arcuate strip presenting a continuous convex radiating surface 116a towards the field of view. The surface 116a may have a constant curvature, that is to say it may be part circular, the center of curvature being situated at 125.

The radius of curvature is selected to provide over the frequency range a sector shaped polar lobe approximating as nearly as possible to that represented at K in FIGURE 1. In practice the radius of curvature of the strip 116 producing a satisfactory result will normally be found to exceed about eight times the wave length (in air) of the lowest frequency radiated.

The ends of the transducer may subtend an angle 5 which is approximately equal to the angular width of the field of view required, e.g., 60 to 120 all portions of the surface 116 being energized to radiate at uniform intensity.

The receiving transducer elements 117 may have plane circular receptive surfaces 117a which are presented towards the field of view in directions which are divergent to opposite sides of the reference axis 126 symmetrically in relation thereto. Normals 127 drawn through the centers of the surfaces 117:: intersect with each other at a point 128 on the reference axis and define an included angle a.

The angle on may be varied to suit the particular requirements of individual users. Thus for a user whose outer ears are so formed as to produce a very pronounced cusp A as represented in FIGURE 2 and who may have correspondingly pronounced compensation in the brain and nervous system to achieve the curve B, it would bev necessary for the angle of splay a to be increased from the average or normal value in order to produce a correspondingly pronounced cusp in the amplitude or strength of reproduced beat frequency signal, this being achieved as a result of greater divergence of the principal axis E and F of the two lobes C and D. For a user having a cusp A which is less pronounced than normal the angle of splay on would require to be correspondingly reduced so that in both cases the sound signals presented to the user by the blind aid conforms as closely as possible to the natural sound signals which he would receive at his ear drums.

In general, satisfactory results are attained when the angle on has a value which lies somewhere between (5 and 3/2. Thus on may have a value which is equal or approximately equal to 6 when the latter is at the lower end of its range, e.g., in the region of 60, and may have a value of approximately [3/2 when ,8 is at or near the upper end of its range, e.g., about 120.

In general terms, the maximum splay angle a should not exceed the value at which straight ahead or forward sensitivity diminishes so as seriously to impair the detec' tion performance of the aid, while the angle of splay should not be reduced below a value which will produce a forward peak of sensitivity seriously interfering with, or preventing, the user exercising his natural auditory directional faculties.

The lateral separation of the receiving transducers 117 measured between the centers of their surfaces 117a may be varied to suit the head dimensions of various users. The distance between centers may advantageously approximate to the separation of the users cars, a typical value being 5 to 6 inches. If desired the receiving transducers may be mounted in such a manner as to permit the distance between them to be adjusted.

The polar lobes of both the transmitting transducer and receiving transducers undergo variations in shape and dimensions as the frequency of the signal radiated therefrom and received thereat respectively changes through the range of values employed in the aid. Typical variations which are attained in practice are illustrated in FIGURE 3. The full line M and the broken line N are the polar diagrams for the transmitting transducer of the form as shown in FIGURES 4 and 5 at the frequencies of kc./s. and 70 kc./s. respectively. It will be observed that while both these polar diagrams depart from the ideal sector-shaped diagram as shown in FIGURE 1, the local peaks and troughs change position as the frequency varies, and in practice the overall effect obtained is a good approximation to the sector shaped polar diagram L in FIGURE 1 over a field of View of about Full lines P and Q show the polar diagrams of the two receiving transducers of the form illustrated in FIGURES 4 and 5 at a frequency of 50 kc./s., and broken lines R and S show these polar diagrams respectively at a frequency of kc./s.

The polar diagram produced by both the transmitting transducer and the receiving transducers in elevation consists of a polar lobe the angular width of which undergoes Some appreciable variation through the frequency range. Inasmuch, however, as the raising and lowering of the users head to direct such lobe towards an object from which a reflection of the radiated wave energy is obtained is more easily performed, and is a more natural movement than turning of the head, the necessity for making such adjustments in elevation is not in practice a serious disadvantage.

Reference is now made to a practical embodiment of the aid as illustrated in FIGURES '6 and 7.

Parts already referred to are designated in this construction by like reference with the prefix 2.

The head set is in the form of a spectacle structure including a front piece 229 to which side arms 230 are connected.

The front piece 229 is in the form of an arcuate strip the upper part of which embodies the transmitting transducer 216.

As disclosed in the aforementioned specification such transducer may be of the general type disclosed in Acustica, volume IV, 1954, No. 5, pages 519 to 532, and comprise a diaphragm 21Gb in the form of a film of insulating material such as that known under the registered trademark Melinex having a thickness of 50 to microns and the outer radiating surface 216a of which is coated with metal such as aluminum. Melinex is a polyester film of polyethylene terepthalate. Underlying the strip 216 the front piece 229 is formed with, or incorporates an insert formed with, a plurality of projections 216a which may be produced by cutting or otherwise forming horizontally extending grooves or channels such as 216d intersecting with vertical grooves or channels such as 216e.

The exposed surfaces on the projections and the bases of the channels are metalized (for example with aluminum), or the insert, if employed, which incorporates the 9 projections in the grooves or channels may be formed of an electrically conductive metal, for example aluminum.

The strip 216 may be secured along its margins in position by adhesive or other convenient retaining means. In FIGURE 6 a portion of the strip 216 is shown pulled away from the front piece to disclose the underlying construction of projections and intersecting horizontal and vertical grooves or channels. When the strip is fully applied to the front piece a gaseous medium, for example air, is enclosed in the intersecting horizontal and vertical channels.

The receiving transducers 217 may be of similar construction to that already disclosed in the aforementioned specification. The outer film is shown removed from one of these to expose an underlying system of concentric ribs and grooves 217:: and 217d. By virtue of the curvature of the front piece 229 the receptive surfaces 217a of the receiving transducers have an angle of splay which is somewhat less than the angle subtended by the ends of the transmitting transducer, and consequently the embodiment is in conformity with the geometry of the arrangement illustrated diagrammatically in FIGURES 4 and 5. The receiving transducer may be above or below the transmitting transducer. The angle of splay may be controlled by forming the part of the front piece on which the receiving transducers are mounted to a curvature different from that presented by the part which incorporates or on which the transmitting transducer is mounted.

The side arms 230 serve to carry the aural elements 224. The side arms 230 may also accommodate the whole or part of the circuit components other than the transducers as shown in FIGURE 10 hereof. Such circuit may, for this purpose, be formed utilizing known micro-miniture techniques. The side arms may be formed as housings to accommodate such circuits.

In the embodiment illustrated in FIGURE 8 parts corresponding to those already described are designated by like reference numerals with the prefix 3.

In this embodiment the front piece 329 comprises a generally conventional spectacle frame incorporating D- shaped eye pieces 329a and a bridging piece 32%. Within each eye piece is mounted a transmitting transducer 316 and a receiving transducer 317. If desired a single piece of Melinex may be employed within each eye piece. This piece may be so coloured a to have the appearance of the lens of a conventional pair of sun glasses.

Because of the gap between the transmitting transducers 316 the inner margins 316 of their radiating surfaces 31611 are directed angularly inwardly towards the reference axis as represented by the line 326 or may be approximately at right angles thereto, thus preventing a local decrease in value of the radius vector, of the transmitting polar lobe on and near the reference axis. The receiving transducers 317 are inset laterally from the outer lateral extremities of the corresponding transmitting transducers 316 so that their angle of splay would in any case be somewhat less. If desired the angle of splay may be further reduced by the shape of a mounting member 3294' fitted in each eye piece and which incorporates a protruberent boss 329d. The forwardly presented surfaces of these, 329e, with which the receptive surfaces of the receiving transducers 317 may be flush, are parallel to the tangent which can be drawn to the radiating surface of the associated transmitting transducer 316 at a position such as that indicated at 316g considerably inset.

The side arms 330, as before, carry the aural elements (not illustrated in FIGURE 9) and micro-miniature circuits as in the case of the side arms 230.

What I claim then is:

1. A blind aid comprising:

(A) a head set including;

(i) a front piece for overlying part of the face of a user,

(ii) means for holding said front piece in said overlying relation to the users face,

(iii) a transmitting transducer means on said front piece for radiating acoustic wave energy to a field of view extending forwardly of the front piece on each side of a medial longitudinal reference axis normal to said front piece, the said transmitting transducer having transmitting characteristics represented by a lobe having an approximately uniform level of field strength over said field of view,

(iv) receiving transducers on said front piece having receiving characteristics represented by respective polar lobes having respective principal axes divergent from each other and lying on opposite sides of said medial longitudinal reference axis and overlapping with each other along the reference axis.

(B) transmitting means for generating an electrical signal of the frequency of said acoustic wave energy and connected to said transmitting transducer means,

(C) receiving means including two receiving channels connected respectively to said receiving transducers for passage of electrical signals through said channels in response to reception at said receiving transducers of wave energy reflected from an object in said field of View,

(D) means for reproducing said signals audibly and including aural elements connected respectively to said channels and including means for supporting said aural elements in respective positions to furnish audible signals to the left and right hand ears of the user.

2. A blind aid according to claim 1 wherein:

(A) the polar lobes of the receiving transducers define angular limits to said field of view,

(B) the means for radiating acoustic wave energy comprise transmitting transducer means having a characteristic represented by a polar lobe providing an approximately uniform level of field of strength within said angular limits.

3. A blind aid according to claim 2 wherein:

(A) said transmitting transducer means present an effective radiating surface of convex arcuate form in an azimuthal plane,

(B) said receiving transducers have receptive surfaces presented towards said field of view in directions which diverge to opposite sides of said reference axis,

(C) said polar lobe of said transmitting transducer and said polar lobes of said receiving transducers are shaped in combination to avoid any pronounced forward peak of sensitivity alOng said reference axis.

4. A blind aid comprising:

(A) a head set,

(E) means for radiating acoustic wave energy to a field of View on opposite sides of a reference axis extending medially of such field and comprising a transmitting transducer means carried by said head set and including a plurality of radiating elements:

(i) positioned to afford a gap between them extending on each side of said reference axis,

(ii) having respective radiating surfaces which collectively are of convex arcuate form in an azimuthal plane and which respectively include marginal portions adjacent to said gap having respective normals which have an angular relation to said reference axis between parallelism and convergence in a direction towards said field of view,

(iii) having a characteristic represented by a polar lobe providing an approximately uniform level of field strength within angular limits of said field of view,

(C) means for receiving a reflection of said wave energy from an object in said field of view, means including:

(i) receiving transducers carried by said head set and having:

(a) resmctive receptive surfaces presented towards said field of view in directions which diverge to opposite sides of said reference axis,

(b) receiving characteristics represented by respective polar lobes having respective principal axes divergent from each other and lying on opposite sides of said reference axis, defining said angular limits of said field of view, and being shaped to avoid presenting in combination with said polar lobe of said transmitting transducer any pronounced forward peak of sensitivity along said reference axis,

(ii) two receiving channels for the passage of respective electrical signals therethrough in response to the reception of said reflection and to which said receiving transducers are connected respectively,

' (D) means for reproducing said signals audibly and including aural elements connected respectively to said channels for furnishing audible signals to left and right hand ears of a user.

5. A blind aid comprising:

(A) a head set comprising a spectacle type structure having a front piece formed of a piece of strip material of bowed arcuate form presenting a convex face forwardly towards said field of view in a continuous arcuate zone extending laterally of said front piece, and having a conductive surface formed with projecting parts and intervening spaces containing a gaseous medium,

(B) means for radiating acoustic wave energy to a field of view on opposite sides of a reference axis extending medially of such field and comprising transmitting transducers means:

(i) including a radiating element in the form of a dielectric film overlying said front piece and presenting an effective radiating surface of convex arcuate form in an azimuthal plane,

(ii) having a characteristic represented by a polar lobe providing an approximately uniform level of field strength within angular limits of said field of view,

\C) means for receiving reflection of said wave energy from an object in said field comprising (i) two receiving channels for the passage of respective electrical signals therethrough in response to the reception of said reflection,

(ii) receiving transducers connected respectively to said receiving channels and having:

(a) respective receptive surfaces presented towards said field of view in directions which diverge to opposite sides of said reference axis,

(b) receiving characteristics represented by respective polar lobes having respective principal axes divergent from each other, lying on opposite sides of said reference axis, defining said angular limits of said field of view, and being shaped to avoid presenting in combination with said transmitting transducer any pronounced forward peak of sensitivity along said reference axis,

(D) means for reproducing said signals audibly and including aural elements connected respectively to said channels for furnishing audible signals to left and right hand ears of a user.

6. A blind aid according to claim wherein said projecting parts are separated from each other by sets of 12 channels extending in respective transverse directions and intersecting with each other to define said spaces.

7. A blind aid according to claim 5 wherein:

(A) said receiving transducers are mounted on said front piece in a laterally extending zone offset vertically from said radiating element,

(B) said receiving transducers are spaced apart laterally by a distance less than that between outer lateral boundaries of said radiating element,

(C) said receiving transducers present receptive surfaces having respective normals which are divergent with respect to each other in a direction towards said field of view,

(D) marginal portions of said radiating element ad- 'jacent to' said outer lateral boundaries also have' normals which are divergent with respect to each other in a direction towards said field of view,

(E) the included angle between the first said normals is less than the included angle between the second said normals.

8. In a blind aid for detecting the presence of an object by reflection of wave energy, and comprising means for generating a carrier wave, means for varying the frequency thereof cyclically through a range of values, means for radiating said carrier wave to a field of view in the form of acoustic wave energy, means for receiving reflections of said wave energy from an object in the field of view and including two receiving transducers having directional receptivity represented by polar lobes having principal axes both extending forwardly into said field of view on opposite sides of a longitudinally extending reference axis therein, head set means for supporting said radiating means and said receiving transducers to present a radiating surface on the former and receptive surfaces on the latter towards said field of view, two receiving channels connected respectively to said receiving transducers, modulator means in each of said channels, means for feeding a local signal to each of said modulator means of a frequency varying cyclically in conformity with that of said carrier wave to heterodyne with an incoming signal in each of said channels and produce respective beat signals therein of a difference frequency varying through a range of values as the range of the.

object varies from maximum to minimum, the improvement wherein:

(A) said receiving transducers are mounted on said head set relatively to each other in positions such that the principal axes of their respective polar lobes are divergent from each other in a direction forwardly of the field of view and lie on opposite sides of said reference axis,

(B) the angle of divergence between the lobes is such that they overlap with each other along the reference axis,

(C) the transmitting transducer has a directional radiating characteristic which, in combination with the directional receptivities of the receiving transducers, provides an overall directional characteristic simulating that of the auditory system of a normal person.

9. The improvement according to claim 8 wherein the receiving transducers are mounted on the head set relatively to each other in positions such that the principal axes of their respective polar lobes diverge from each other at an angle in the region of degrees.

10. The improvement according to claim 8 wherein the receiving transducers are mounted on the head set relatively to each other at positions spaced laterally apart by a distance at least approximately equal to the lateral separation of the ears of a normal person.

11. A blind aid comprising:

(A) a head set including:

(i) a front piece for overlying part of the face of a user,

(iii) a transmitting transducer means on said front piece for radiating acoustic wave energy to a field of view extending forwardly of the front piece on each side of a medial longitudinal reference axis normal to said front piece,

(iv) receiving transducers on said front piece having receiving characteristics represented by respective polar lobes having respective principal axes divergent from each other and lying on opposite sides of said reference axis and overlapping with each other along the reference axis,

(D) means for reproducing said signals audibly and including aural elements connected respectively to said channels and including means for supporting said aural elements in respective positions to furnish audible signals to the left and right hand ears of the user,

(E) and wherein the transmitting transducer has a directional radiating characteristic which, in combination with the directional receptivities of the re ceiving transducers, provides an overall directional characteristic simulating that of the auditory system of a normal person.

References Cited UNITED STATES PATENTS 2,467,368 4/ 1949 Batchelder 340-3 3,107,351 10/1963 Milam 343-16 3,172,075 3/1965 Kay 340-1 RICHARD A. FARLEY, Primary Examiner.