IL33964A - Signal processing apparatus and method - Google Patents

Description

R1NES Ten Post Office i SIGNAL PROCESSING APPARATUS AND METHOD Abstract of This disclosure involves a novel and compact pulse compression filter and the employing elastic transduction by means of a varying magnetic providing power handling capability and greater compression ratios than The present Invention relates to being more though not directed to producing controlled time delay time inversion or other delay of electric preferably of the type volving such as pulses and the like useful radar and similar as for the Proceedings of the pages Numerous types of filters have been proposed and used for such including delay as described said networks and other All such have heretofore had serious limitations in handling achievable pulse compression and in application to wideband It thus to the obviating of these limitations that the present invention is primarily it being an objeot of the invention to provide a new and improved processing apparatus of this character that has vastly creased and wideband A further object to provide a new and improved time filter apparatus of more general as well as a novel method or signal An additional object is to provide new and improved Other and further objects will be hereinafter and more fully delineated in the appended In from one of its broad aspects the tion contemplates an apparatus in an elastic input and output transducer means disposed at the device for respectively coupling electric Impulses thereto to generate and propagate waves therein and for transducing such waves electric output and means for applying a energy field to the device during the coupling of said electrio impulses into the device by the input transducer means in order to cause different frequencies in waves to be advanced or delayed in time by different thereby to introduce processing the output Preferred details are hereinafter set The invention will now be described with reference to the accompanying the single figure of which a longitudinal section and schematic circuit diagram of a preferred It has been determined that microwave waves can be converted into spin waves and vice by means of a spatially uniform but magnetic bias field in a single crystal yttrium iron garnet aa in my article entitled Modulated appearing the Journal of Applied July pages Experiments have verified the theoretical prediction that such conversion occurs at constant wave number and momentum but with variable energy and power Advantage is taken of this when modified accordance with the present to among other a novel pulse compression or delay filter that is affords greater compression ratios than conventional and is suitable for wideband microwave radar systems and the For purposes of the invention will be described in connection with its application as a chirp impulse compression In its simplest the filter consists of a single crystal rod as capable of supporting waves and provided with piezoelectric shear and longitudinal elastic wave transducers deposited respectively on the input and output end regions of the A wound around the crystal used to produce a transient or magnetic energy field If the bias is a ramp turned on after an Input electric chirp signal la or coupled to the oan serve to oonvert each frequency component of the input shear elastic first to a magnetic wave and then to a longitudinal elastic wave of relatively fast velocity compared to the shear wave and of higher frequency that will couple to the output Because components spend more tranelt time in the proper choice of bias ramp will produce a matched filter output with noise factor In and because of the frequency translation of the output impulse the pulse compression factor is creased by a factor that the ratio of the longitudinal to shear wave velocities g normally a factor of about Such a filter is flexible because the bias current ramp can be altered to match a variety of chirp and it is compact because for input pulses of microsecond the crystal may be about one centimeter Such a filter is potentially wide band the limits of the because the linearity of the filter is as good as that of the bias ramp In microsecond to nanosecond compression is The bias energy required to filter one such is typically a few Referring to the a preferred version such a filter is shown in section comprising a sphere of for diametrically cored and provided with a high quality cylindrical rod as of disposed within the the appropriate and elastic wave transducers as CdS or are deposited on the parallel and optically flat end faces at 2 and A solenoid 3 is wound about the sphere 1 such that the number of turns per unit length as projected along the sphere axis is a The entire structure is magnetized to saturation either by a permanent magnet or an Current is passed through the coil 3 from a ramp generator the waveform being shown as the t produolng a substantially uniform spatial magnetio field inside of the sphere which adds a oomponent to the bias field provided by magnet The pulse applied to the transducer as schematically illustrated by the arrow during such the magnetic energy produced by the solenoid coil 3 acts upon the In consider a frequency oomponent entering the rod via the input transducer 2 from the chirp impulse time At a later time the current ramp from generator 5 will have produced a ficient magnetic energy field in the solenoid 3 to cause conversion of the shear elastic wave to a spin The component travels a distance as a shear and then stops propagates at a finite small for a further time interval until longitudinal wave conversion oocurs at the oomponent travels a distance as a longitudinal elastic wave until exiting at the output transducer 4 at time T as an output electric labelled For wave propagation parallel to the field is parallel to the rod the dispersion relation vs has the form of a first rising followed by a horizontal as disclosed my said and then by a continuing or second rising The plateau region can be moved up and down by varying the magnetic field at such the spin waves 3erve as a elevating the frequency from the first rising curve to the second curve where the frequenoy thus on the removal of the causing the to drop again or reverse The final frequency that at when the ramp has caused the magnon elevator thus to is thus higher than the input frequency at 2 by the factor a as before and Vg are respectively the longitudinal and velocities suoh higher frequency delayed longer in the device compression is effected by this changing time signal Power gain a l3 o results from this elevating or conversion action The power handling is inherently about 30 db greater than prior art magnetoelastlc devices The time signal is in accordance with the by both the conversion between the of waves the conversion and by the ences in velocity therebetween Considering a one centimeter long ferrimagnet magnetized in a plane at the axis or a microsecond chirp pulse with ω variation from to 3 a relatively fast longitudina l wave velocity of directed along sa id a lower velocity of 725 ampere turns in the eolenoid coil a ramp duration of sec for each successive input a magnetic field of the order of 400 and a peak energy delivered to the 3 of joules the following results are The critical gradients for longitudinal wave conversion will range linearly with frequency from about 157 oe at GHz to 235 at The s ponding values of the conversion efficiencies range from d at to at The average conversion loss for the signal pulse is approximately In there due to the frequency translation and change in group For this the shear elastic wave transducer 2 should be flat over the frequency range 1 and the longitudinal transducer over the frequency range It been found that at substantially the mentioned magnetizing angle of to the axis in the maximum interaction or splitting between the longitudinal and spin wave occurs in the YIG Up to about Improvement in such coupling and conversion has been determined for magnetizing and propagating the wave at an angle of substantially to the axis or direction in the In a novel and pulse compression filter employing elastic shear elastic longitudinal wave transduction by means of a varying magnetic field bias been The linearity of the filter is as good as the current ramp function can be and the bandwidth as wide aa that of the input and output to microsecond input oan be For 500 chirp compression into the nanosecond range is pression is Increased by the factor over conventional Another outstanding advantage is the ease and rapidity with which the filter may be matched to various input pulses by merely altering the The peak bias energy required to filter one pulse is typically a few and while other ferrlmagnetlo and similar devices may be the single orystal appears to be a most suitable device for these While the spatial gradient of the magnetic field has been described as it may also be varied or along the crystal and other fleld3 besides magnetic fields in certain be employed to create the uniform conversion Further modifications will also occur to those skilled in this and all 3uoh are considered to fall within the spirit and of the invention as defined in the appended What is claimed insufficientOCRQuality

Claims (19)

1. An electric -impulse signal-processing apparatus having, in combination, an elastic-wave-supporting device, input and output transducer means disposed at the device for respectively coupling electric impulses thereto to generate and proga ate elastic waves therein and for transducing such waves into electric output impulses, and means for applying a time-varying energy field to the device during the coupling of said electric impulses Into the device by the Input transducer means In order to cause different frequencies in said wavee to be advanced or delayed In time by different amounts, thereby to Introduce time signal-processing into the output impulses .

2. An electric -impulse signal-processing apparatus as claimed in claim l and in which said field Is magnetic and means is provided for converting said elastic waves to spin waves upon which the time-varying energy field acts in the manner of a raa non elevator.

3. An electric-impulse signal-processing apparatus as claimed in claim 2 and in whioh means Is provided for converting said spin waves to elastic waves for transduolng Into said electric output impulses.

4. An electric -impulse signal-processing apparatus ae claimed in claim 2 and in which the time-varying field la applied and removed to cause the magnon elevator action to reverse.

5. An electric-impulse signal-processing apparatus having, in combination, an elas ic -wave-supporting device capable of supporting relatively slow and fast elastic waves, input and output transducer means disposed at the device for respectively coupling electric impulses thereto in order to generate and propagate therein one of the aaid elastic waves and for transducing the other of said elastic waves into electric output impulses, and means for applying a time-varying energy field to the device during the coupling of said electric impulses into the device by the input transducer means in order to cause the said one elastic waves propagating in said device to become converted into the aaid other elastic waves, thereby to introduce time signal-processing into the output impulses caused both by the conversion from the said one to the said other elastic waves ■ and by the difference in velocity therebetween.

6. An apparatus as claimed in claim 5 and in which said device comprises magnetic crystal means and said time-varying energy field is produced by time-varying magnetic field-producing means,

7. An apparatus as olaimed in claim 6 and in which aaid crystal means comprises a YIQ crystal and said transducer means comprise shear and longitudinal elastic-wave transducers.

8. An apparatus as claimed in claim 7 and in which the said YIG crystal is a single rod dis osed within an outer polyorystal YIQ structure about which the magnetic field-producing means is disposed.

9. An apparatus as claimed 3n claim 8 and in which the outer YIQ structure Is substantially spherical and the said YIG crystal is disposed substantially diametrically therein.

10. An apparatus as claimed in claim 5 and in which the said electric impulses comprise a frequency-modulated pulse, the said one and other elastic waves are respectively the said slow and fast waves, and the said signal processing results in compression of the input electric impulses.

11. An apparatus as claimed In claim 6 and in which the said magnetic field is oriented relative to said crystal means in one of a substantially 22.5° angle to the "100" axis in the " 100" plane and a substantially 25.52° angle to the " 100" axis in the "llO" plane.

12. Apparatus as claimed in claim 2 and in which means is provided for spatially varying field along the device.

13. An electric -impulse signal-processing apparatus comprising a magnetic crystal including YIQ, and a magnetic- field-producing means oriented to set up its field at one of a substantially 22.5° and a 25.52° angle with respect to the "100" axis in the respective "100" and "110" planes.

14. 1 . Apparatus as claimed in claim 13 and in which means is provided for propagating elastic waves in said crystal substantially along said "100" axis.

15. A method of changing the transit time of relatively low and high frequency components of elastic impulses, that comprises, propagating 3uch impulses in an elastic-wave-supporting medium, and, during the propagating, subjecting the medium to a time-varying energy field apart from said impulses.

16. A method as claimed in claim 15 and in which said field 13 magnetic and said propagating comprises introducing one type of elastic wave into said medium and converting the same to a spin wave therein upon which the time-varying energy field acts in the manner of a magnon elevator.

17. A method as claimed in claim 16 and in which the spin wave conversion Is followed by conversion Into a second type of elastic wave.

18. A method as claimed in claim 17 and In which the said types are relatively slow and fast elastic waves.

19. A method as claimed in claim 16 and in which there i3 further effected spatial varying of field along the medium.