Broad band flueric amplifier

A broad band flueric amplifier is disclosed which comprises means to incre the deflection of the fluid jet within the amplifier at higher frequencies of oscillation of the jet. The means for increasing jet deflection comprises vanes or protrusions positioned closely adjacent the jet path at selected distances from the nozzle. Acoustic feedback from these vanes or protrusions will assist the control pulse in deflecting the jet at selected frequencies of oscillation.

BACKGROUND OF THE INVENTION 
Typically, the bandwidth of AC fluidic or flueric amplifiers has been 
limited by the dynamic response of the input impedance. This impedance is 
such that the input control signal is generally attenuated significantly 
at higher frequencies. Often the bandwidth of available devices is 
insufficient for many purposes. Particularly, the increasing use of 
flueric amplifiers for FM and speech processing requires a wider band of 
operating frequencies. 
Accordingly, it is an object of the invention to overcome the deficiencies 
of the prior art devices noted above. 
Specifically, it is an object of the invention to provide a flueric or 
fluidic amplifier having a significantly increased bandwidth. 
It is an object of the invention to provide a fluidic amplifier which will 
operate at a broad range of frequencies yet be simple in structure, having 
no moving parts. 
SUMMARY OF THE INVENTION 
Fluidic amplifiers such as the laminar proportional amplifier (LPA) are 
generally designed with a low aspect ratio (height/width ratio) to get 
wide bandwidth. This invention makes use of observed performance of high 
aspect ratio devices, having an aspect ratio greater than two. By placing 
multiple protrusions in an LPA amplifier, multiple peaks in gain can be 
achieved. Pressure feedback from the protrusions provides an amplification 
of jet deflection. This is the result of a phenomenon not unlike edgetones 
except that there is no instability present. This results in a device 
which has an order of magnitude wider bandwidth. Data shows that a device 
normally having a bandwidth of 300 Hz can exhibit a bandwidth of 3,000 Hz 
when this feedback is provided. 
Several of the amplifiers of the invention can be operated in parallel, the 
peaks in gain of one amplifier being shifted in relation to the peaks in 
gain of another amplifier. The result will be an output which is smoother, 
having increased gain across a broad continuum of frequencies.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown an amplifier comprising the essential 
features of the present invention. Supply 3 comprises a pressurized source 
of fluid which directs a jet out of nozzle 4. Control inputs 6 and 8 
direct control pressure pulses through outlets 10 and 12, respectively. 
Vents 14 and 16 are maintained at constant pressure in the usual and well 
known manner for such devices. Either or both of outlets 18 and 20 will 
receive the fluid of the jet depending upon the position of the jet 
resulting from deflection by pressure pulses through outlets 10 or 12. 
Vanes 1 and 2 are placed within the vent region between nozzle 4 and 
splitter S which separates outputs 18 and 20. The vanes extend to a 
position closely adjacent the path of the jet. The outer-most edge of each 
vane should extend to a position which is at a distance from the edge of 
the undeflected jet which does not exceed one-half the width of nozzle 4. 
The deflected jet should just touch the vane when the output of the 
amplifier is fully saturated. 
In operation, fluid from supply 3 exits as a jet through nozzle 4 toward 
splitter S. Control pressures through inputs 6 and 8 generate control 
pulses at ports 10 and 12, respectively. These control pulses act to 
deflect the jet toward either output 18 or output 20. As the control 
pulses at ports 10 and 12 are reversed due to a frequency input, the jet 
will oscillate back and forth between the outputs 18 and 20 at the same 
frequency. 
As the jet passes closely adjacent the edge of one of the vanes 1 or 2 
acoustic energy will be generated and fed back toward the nozzle 4. This 
will also occur as the jet passes closely adjacent the splitter S. This 
acoustic energy will provide a pressure on the side of the jet adjacent 
the protrusion or vane. This pressure, along with the pressure pulses from 
ports 10 and 12, will act on the jet to determine the deflection thereof. 
If the acoustic feedback pulse and the control pulse from the port 10 or 
12 are exactly in phase with one another, the two will combine to 
significantly increase the deflection of the jet. However, since there is 
a finite transport time for the fluid of the jet from nozzle 4 to any 
point downstream of the nozzle the acoustic pulse cannot be precisely in 
phase with the pulse from the control port. Therefore, the two pulses will 
combine to increase the deflection of the jet when they are 360.degree. 
out of phase with one another, or exactly one wavelength apart. 
At low frequencies of oscillation of the control pulse the position of the 
jet with respect to the outputs will always be substantially in phase with 
the control pulse. For example, when a positive pulse is applied at port 
10, the jet will follow a path through output 20. As the frequency of 
oscillation of the control pulse is increased, the downstream position of 
the jet moves out of phase with the control pulse. As seen in FIG. 1, the 
control pulse P.sub.j is applied through port 10 while the downstream 
position of the jet, shown by dashed lines, is at output 18. The position 
of the jet at splitter S is therefore 180.degree. out of phase wtih the 
pressure pulse P.sub.j. Also, there is a normal phase lag between the jet 
position downstream and the control signal of 180.degree. due to the 
finite jet transport time between the upstream and downstream positions. 
(This lag can be observed in a stream of water exiting from the nozzle of 
a garden hose as the hose is rapidly moved back and forth.) The result is 
that the acoustic feedback, shown by arrow F in FIG. 1, generated at the 
splitter is 360.degree. out of phase with the control impulse at port 10. 
Since the acoustic energy travels at the speed of sound, much more rapidly 
than does the jet, the acoustic pressure may be considered to instantly 
combine with the pulse from port 10 to increase the deflection of the jet. 
The manner in which this phenomenon increases the operation bandwidth of 
the amplifier will be described with reference to FIGS. 2 and 3. In FIG. 
2, P.sub.c represents the control pressure which exists at input 6 or 8 of 
the amplifier, while P.sub.j represents the actual pressure pulse 
generated at the output ports 10 and 12. Since the input signal P.sub.c is 
fed through an impedance, the signal P.sub.j becomes significantly 
attenuated at higher frequencies. This is illustrated in FIG. 2 by the 
rapidly decreasing ratio of P.sub.j to P.sub.c at increasing frequencies. 
Due to this loss of control pressure at higher frequencies, the gain of 
prior art amplifiers significantly diminished or disappeared at such 
frequencies. The present invention alleviates this problem by providing 
the above discussed acoustic pressure signals in the higher frequency 
range, thus increasing the gain of the amplifier in this range. 
FIG. 3 graphically illustrates the relationship between frequency and the 
ratio of the output pressure to the control pressure (gain) in the 
amplifier of the present invention. At lower frequencies the device 
operates substantially in the same manner as the prior art devices. This 
can be seen in that portion of the gain curve which terminates at point N 
along the axis which represents frequency. Point N signifies the normal 
bandwidth of a prior art amplifier since it is at this point where the 
gain diminishes substantially due to the loss of pressure at the control 
port, as discussed with reference to FIG. 2. In this device of the present 
invention, as the frequency increases beyond the value N, the wavelength 
of the deflected jet becomes such that the position of the wave at the 
splitter S becomes 180.degree. out of phase with the control pulse, as 
discussed with reference to FIG. 1. At that point the acoustic pressure 
signal is 360.degree. out of phase with the control pulse, and combines 
therewith to increase the deflection of the jet, thereby increasing the 
gain of the amplifier. The acoustic signal generated by the device 
compensates for the loss in pressure at the control ports. 
As the frequency of oscillation increases still further, the acoustic pulse 
generated at the splitter moves further out of phase with the pulse at the 
control port, and therefore will not combine therewith to effectively 
increase the deflection of the jet. However, the increasing frequency will 
shorten the wavelength of the deflected jet to the extent that the jet 
position at vane 2 will then be 180.degree. out of phase with the pulse at 
the control port. The acoustic signal generated at vane 2, as shown by 
arrow H in FIG. 1, will then be 360.degree. out of phase with the signal 
at the control port, and will combine therewith to again increase the 
deflection of the jet. The result will be a second increase in the gain of 
the amplifier, as shown by point 2 in FIG. 3. The same will again occur as 
the frequency is increased to bring the deflected jet 180.degree. out of 
phase with the control signal at vane 1. 
As can be seen in FIG. 3, the successive peaks in the gain of the amplifier 
at higher frequencies extend the operational bandwidth of the device to a 
frequency represented by point B. While FIG. 1 illustrates a device having 
two sets of vanes 1 and 2, it is to be noted that any number of vanes may 
be used. The position of the vane, that is the distance of the vane from 
the nozzle 4, will determine the frequency at which the acoustic energy 
will be effective to assist the control pulse in deflecting the jet. 
Therefore, an amplifier may be readily designed which will generate peaks 
in the gain thereof at preselected frequencies. 
FIG. 4 illustrates an embodiment of the invention which comprises two 
amplifiers of the invention operating in parallel. It is to be understood 
that three or more amplifiers may also be operated in parallel as shown in 
the drawing. The embodiment of FIG. 4 comprises common inputs 6 and 8 for 
the control pulses of the respective amplifiers, and common outputs 18 and 
20. The upper-most amplifier comprises vanes 1 and 2 positioned at 
distances d.sub.1 and d.sub.2 from the nozzle 4, respectively. The 
lower-most amplifier comprises nozzles 31 and 32 set at distances d.sub.31 
and d.sub.32 from nozzle 4, respectively. It is noted that the distances 
d.sub.1, d.sub.2, d.sub.31, d.sub.32 are all different from one another. 
Assuming that the velocities of the respective jets in the amplifiers are 
equal the peaks in gain generated by vanes 1 and 2 will be generated at 
frequencies different from the peaks in gain generated by vanes 31 and 32. 
FIG. 5 graphically illustrates the gain of the composite amplifier of FIG. 
4. The lower curves marked LPA 1 and LPA 2 signify the gain curves of the 
respective individual amplifiers of FIG. 4. It is noted that each of these 
lower curves corresponds in shape generally to that of FIG. 3. The 
composite curve of FIG. 5 illustrates the effective gain of the composite 
device shown in FIG. 4. Note that since the peaks in gain of the 
respective lower curves are shifted relative one another the summation of 
the two results in a curve which is much smoother, having less sharply 
defined peaks and valleys. The result is an amplifier which has a much 
more even operation across a wide continuum of frequencies. 
As noted above the frequency at which an amplifier of the invention will 
generate a peak in amplifier gain is determined by the position of the 
protrusions or vanes in the device. This frequency may also be affected by 
varying the velocity of the jet from nozzle 4. The velocity of the jet 
determines the transport time of the fluid to a position adjacent one of 
the protrusions or vanes, thereby affecting the time at which the jet will 
be in or out of phase with the pulse at the control port. 
While the invention has been disclosed with reference to the specification 
and attached drawings, I do not wish to be limited to the specific details 
disclosed therein as obvious modifications can be made by one of ordinary 
skill in the art.