Patent GB-1159613-A (GB)
Title: Pure Fluid Acoustic Amplifier, Transmitter, Modulator and Demodulator.
IPC: H04R1/42
Filed: 1966-09-30
Abstract: 1,159,613. Signalling by audible signals. MATTEL Inc. 30 Sept., 1966 [30 Sept., 1965], No. 43744/66. Heading G4F. [Also in Divisions G3 and H4] In a fluid amplifier, which may be used as a communication device, a free fluid jet is modulated by an acoustic signal and a hydrodynamic oscillator derives an acoustic carrier wave from the modulated free jet. The modulated free jet is then demodulated to regenerate the acoustic signal. In a " walkie-talkie " type device 10 (Fig. 1) a horn 28 receives speech which is conveyed by conduit 22 to a non-electronic modulator 16. A free jet is established in the modulator 16 from a fluid source 20 (e.g. a toy balloon) and this jet is made to oscillate to provide a sonic carrier wave. The carrier wave, modulated by the speech, is directed through an outlet 30 to a parabolic reflector 32 which may beam the carrier to a similar device 10 acting as a receiver several hundred feet away. The carrier is received by a horn 34, travels through a passage 40 between the reflector 32 and horn 34 and is passed to a non-electronic demodulator 42 which transmits an audio output to a receiver 44. The demodulator is connected to a fluid source 48 (e.g. a toy balloon). A jet oscillating at the frequency of the carrier is produced in the modulator 42. The operator of the device 10 receives "sidetone" through the receiver 44. The transmitted carrier is unintelligible and may be of ultrasonic frequency. If the carrier is audible a low-pass filter may be used at the output of the demodulator 42. Using a carrier at 20 kcps, the frequency band 15 kcps to 30 kcps may be utilized. Preferably A.M. is used, although F.M. or both A.M. and F.M. may be utilized. Single stage modulator.-A conduit 62 (Fig. 13) terminates in a nozzle 64 and has an end 66 connected to conduit 18 (see Fig. 1) receiving compressed air. The nozzle 64 leads to a circular orifice 68 and then to a cavity 70. Conditions are such that self-sustained oscillations are set up in the cavity by the flow of compressed air. A sonic carrier is thereby obtained. Two waveguides 84 connected to the input horn deliver a modulating signal 85 (e.g. speech) and an A.M.C.W. 83 is delivered. Such a modulator is a " pressure disturbance " type. A " velocity disturbance " modulator is similar but the two waveguides 84 are replaced by a single waveguide 84a (Fig. 14) which extends well into the cavity 70 and adjacent the orifice 68. An A.M.C.W. 83a is again obtained. Acoustic efficiency may be improved, together with stabilization of the carrier frequency, by the inclusion of an acoustic resonator. Thus the modulator may be similar to that of Fig. 13 but have a cylindrical housing (80c), Fig. 17 (not shown) provided with a resonant chamber (62c) having a rigid wall (102) remote from the nozzle (64). A compressed air inlet (66c) is in the side wall (104) spaced #/4 from the rigid wall (102) and a distance ##(where “<#<¢) from the orifice (68). An output horn may be provided (Fig. 18, not shown). In a " velocity disturbance " type modulator (16d), Fig. 19 (not shown), a radial mode resonator (70d) comprises a cylindrical chamber in which is a waveguide (84d). The radius is such that the first radial acoustic mode corresponds to the frequency of the A.M.C.W. (83d). A modulator (16e), Fig. 20 (not shown) is similar to that of Fig. 13, but has a horn (110) downstream of the orifice (72d). Two-stage modulator.-Compressed air is introduced into a circular conduit 62# (Fig. 21), which communicates with a nozzle 64# having an orifice 68# establishing a free jet 82# within a cavity 70#. The flow from orifice 68# enters cavity 70# and passes through a second orifice 113. An audio modulating signal 85# is admitted to the cavity 70# through two waveguides 84# and acts on the stream 82# in the " pressure disturbance" " fashion. From orifice 113 the flow enters a radial mode resonator 114 before exhausting through a third orifice 72# and into a coupling horn 110#. Resonator 114 is relatively large and is free from flow disturbance due to waveguide 84#. An alternative modulator (16g), Fig. 22 (not shown) has a single waveguide (84g) to obtain "velocity disturbance" operation. A bias leak (116) communicates with the cavity (70g) to minimize displacement of the axis of the stream (82g) by influx of fluid through the waveguide (84g). Another modulator (16h), Fig. 23 (not shown) is similar to Fig. 21, but the waveguides 84# are replaced by a passage (84h) which communicates with the cavity (10h). The passage (84h) has an entrance (118) mounting a diaphragm (120) to form a blocking compliance sealing the cavity (70h). The diaphragm (120) constrains the frequency response of the modulator (16h) and minimizes uncontrollable aspiration in the cavity (70h). Demodulator.-A cylindrical housing 140 (Fig. 38) has an input conduit 148 connected to a compressed air source (e.g. balloon 48, Fig. 1) by conduit 50. Fluid leaves through a nozzle 146 and enters a long cylindrical channel 148, helping to ensure laminar flow at the exit 150. The laminar flow enters a cylindrical vortex chamber 152 from whence it passes through an orifice 130 in a flow divider plate 128. The flow divider plate 128 is carried by a cylinder 153 reciprocably mounted in the chamber 152 to vary the gain of the demodulator depending on the level of the A.M.C.W. 83 transmitted by the modulator. The A.M.C.W. 83 enters the chamber 152 through a conical horn waveguide 154, the end 158 being closely adjacent the boundary of the jet 160 issuing from exit 150. The plate 128 has a sharp but contoured leading edge 132. With the jet 160 operating so that it is unstable to the A.M.C.W. 83, vortices 162 form which are proportional to the input signal at any point h and are chopped off by orifice 130. A demodulated sound wave plus air thereby passes through conduit 46 and an amplified sound corresponding to the audio input is heard at the horn 44. An alternative demodulator (42a), Fig. 39 (not shown) has an orifice (172) in a circular plate (170) in the chamber (152) immediately downstream of the waveguide (154) serving as an anti-feedback plate which prevents the flow from oscillating. Exhaust passages (174) are symmetrically spaced downstream of the plate (170) while a bias passage (176) is upstream of the plate (170). A bulletshaped object (180) downstream of the flow divider plate (128) reduces the velocity of the flow downstream of the plate (128). The demodulators of Figs. 38, 39 operate as " velocity disturbance" devices. In a " pressure disturbance " demodulator (42b), Fig. 40 (not shown) the conical horn waveguide (154) is replaced by a waveguide (154a) which communicates with a cavity (182) of minimum volume immediately downstream of the channel exit (150). An anti-feedback plate (170) may be provided. A unified amplifier is produced by directly coupling a modulator and demodulator. In Fig. 4 (not shown), a modulator (16i) essentially that of Fig. 22, is integral with a demodulator (42c) similar to that of Fig. 39. In a negative feedback amplifier 192 (Fig. 42), the signal in vortex chamber 152a is out of phase with the input signal 85 and a portion of this signal is supplied by a conduit 194 which includes a variable orifice or acoustic resistance 196 for attenuating the signal. For obtaining positive feedback, the waveguide 194 is connected to the output of the amplifier 192 where signal 87 emerges. The power gain of an amplifier is improved by having several (e.g. twelve) demodulators (42d), Fig. 43 (not shown) connected in parallel with the signal (83i) from the modulator (16j).