Beam-steering, active electronic scanning using directed surface-acoustic- waves in ultra-subwavelength antenna using magnetostrictive magnonic crystal on piezoelectric substrate

Abstract

Embodiments provide active beam steering in an extreme sub-wavelength nano-antenna using directed surface acoustic waves (SAWs). A SAW launched in the substrate excites resonant spin waves in the nanomagnets of a nanomagnet array at specific (GHz) frequencies via magnon-phonon coupling, which radiate electromagnetic waves at those frequencies via magnon-photon coupling. These specific frequencies are determined by the size and the shape of the nanomagnets and hence can be altered by changing the size and / or the shape. Normally, one would expect such an ultrasmall antenna to behave as a point source that radiates isotropically. Surprisingly, it does not because of the intrinsic anisotropy in the phonon-magnon and magnon photon coupling in this system. The radiation pattern (both elevation and azimuthal) is anisotropic. By changing the direction of SAW propagation, one can change the pattern. A multiphase clock excites the electrodes pairwise sequentially to scan the beam electronically, thereby realizing the function of an active electronically scanned array (AES A).

Description

[0001] BEAM STEERING AND ACTIVE ELECTRONIC SCANNING USING DIRECTED SURFACE ACOUSTIC WAVES IN AN ULTRA-SUB WAVELENGTH ELECTROMAGNETIC ANTENNA IMPLEMENTED WITH A MAGNETOSTRICTIVE MAGNONIC CRYSTAL ON A PIEZOELECTRIC SUBSTRATE

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 625,457, filed January 26, 2024, the complete contents of which are incorporated by reference herein.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0005] This invention was made with government support under grant number ECCS-2235789 awarded by the National Science Foundation (NSF). The US government has certain rights in the invention.

[0006] BACKGROUND

[0007] Conventional antennas radiate electromagnetic waves via fluctuating charges or electric dipoles in a metallic or non-metallic structure. Recently a new genre of antennas was demonstrated that operates on a different principle. The antenna consists of a periodic array of magnetostrictive nanomagnets (a “magnonic crystal”) deposited on a piezoelectric substrate. A surface acoustic wave launched in the substrate with electrodes or interdigitated transducers generates time varying strain in the magnetostrictive nanomagnets that makes their magnetizations precess and radiate electromagnetic waves. These antennas can be aggressively miniaturized to dimensions much smaller than the radiated wavelength and yet they radiate efficiently with radiation efficiencies that are few orders of magnitude larger than those of conventional antennas of the same dimensions. Drobitch, J. L., De, A., Dutta, K., Pal. P. K., Adhikari, A., Barman, A. and Bandyopadhyay, S., “Extreme sub-wavelength magnetoelastic electromagnetic antenna implemented with multiferroic nanomagnets”, Adv. Mater. Techno , vol. 5, 2000316 (2020), present an antenna consisting of a two-dimensional periodic array of magnetostrictive cobalt nanomagnets (~ 300 nm lateral dimension and 6 nm thickness) on a LiNbCh piezoelectric substrate. A surface acoustic wave (SAW) is launched in the substrate with side electrodes. At a SAW frequency of 144 MHz, emitted electromagnetic (EM) radiation of the same frequency as the SAW had an intrinsic radiation efficiency of 0.036%. Despite this small value, it was still 144,000x larger than the theoretical limit for conventional antennas at 144 MHz since the antenna’s emitting area was a mere 10-8m2.

[0008] Fabiha, R., Lundquist, J., Majumder, S., Topsakal, E., Barman, A. and Bandyopadhyay, S., “Spin wave electromagnetic nano-antenna enabled by tripartite phonon-magnon-photon coupling”, Adv. Sci., vol. 9, 2104644 (2022), demonstrate a mechanism that could produce much higher absolute efficiencies at certain discrete frequencies in the same type of samples. SAWs of certain discrete frequencies could excite resonant spin waves in the nanomagnets via phononmagnon coupling. These frequencies are such that the spin waves they excite in the nanomagnets have wavelengthsswthat fulfill the condition m / .sw— 2L, where L is a lateral dimension of the nanomagnet and m is an integer. These spin waves are resonant cavity modes and they can efficiently radiate electromagnetic waves via magnon-photon coupling. The measured gain (assuming isotropic radiation) and the intrinsic radiation efficiency at a resonant frequency (14 GHz) exceeded the Harrington limits by two and five orders of magnitude, respectively, and the absolute value of the intrinsic radiation efficiency was measured as ~50% at 14 GHz. The efficiency, however, was much less at non-resonant frequencies. The emitting area A of this antenna was ~ 10,000 pm2, making A / A2= 10-5at 14 GHz where A is the electromagnetic wavelength at 14 GHz.

[0009] Though the foregoing works represent significant advancements in small antennas, there is no report of any antenna orders of magnitude smaller than the wavelength that has any directivity at all for beam steering or beam scanning applications. SUMMARY

[0010] According to an aspect of some exemplary embodiments, an exemplary beam steering apparatus comprises a subwavelength antenna and a multiphase clock.

[0011] An exemplary subwavelength antenna comprises a piezoelectric substrate, a nanomagnet array of magnetostrictive nanomagnets deposited on the piezoelectric substrate, and an electrode array. Electrodes of the electrode array are positioned to different sides of the nanomagnet array. Different pairs of electrodes of the electrode array are configured to launch surface acoustic waves (SAWs) in different directions in the piezoelectric substrate when activated. The nanomagnet array is configured to radiate an electromagnetic beam by phonon-magnon-photon coupling when exposed to the SAWs.

[0012] An exemplary multiphase clock is configured to sequentially activate different electrodes in an electrode array deposited on the piezoelectric substrate and surrounding the nanomagnets on all sides to change the direction of the SAW propagation in the substrate which then changes the direction of the radiated electromagnetic beam emanating from the nanomagnets. This enables “beam steering” which is directing the beam in different directions, which is the hallmark of an active electronically scanned array (AES A). The antenna here is orders of magnitude smaller than the wavelength which effectively makes it a “point source”. Normally a point source will radiate isotropically so that the beam is not directed in any particular direction, making beam steering moot or impossible. The radiated beam here is not isotropic or omnidirectional because of the “internal anisotropy” associated with the nature of the magnonic (or spin) waves created within the nanomagnets. The spin wave patterns are anisotropic and their amplitudes are different in different directions as verified by Landau-Lifshitz-Gilbert simulations. Insofar as it is the spin waves that radiate the electromagnetic waves, the radiated beam is also “anisotropic” and has a directionality or directivity, meaning that the beam intensity varies with direction.

[0013] An exemplary method of beam steering is the following. A multiphase clock is used to sequentially activate adjacent electrodes (e.g., contact pads or interdigitated transducers), and that changes the direction of the beam radiated from the nanomagnet array continuously in time, resulting in beam steering. Interdigitated transducers can be used if a single frequency is desired (since these transducers are narrow band filters) while solid electrodes or contact pads can be used if multiple frequencies are desired. Activating different pads causes the surface acoustic wave to be launched in different directions in the substrate, and this changes the direction of the primary lobe in the radiated beam. Exemplary methods may apply a signal such as but not limited to a microwave frequency voltage between different electrode pairs to launch SAWs in multiple different directions. The radiation patterns of the antenna are different depending on the direction of SAW propagation. By changing the direction of the SAW by exciting different electrode pairs, exemplary embodiments steer the beam to different directions.

[0014] The surface acoustic wave in the piezoelectric substrate subjects the nanomagnets to periodic time-varying strain. Strain acts like an effective magnetic field in a magnetostrictive nanomagnet and in the case of SAW, an effective periodic magnetic field will appear in the nanomagnet. This periodic field makes the magnetization precess and oscillate in time, thereby producing a spin wave. The direction of the effective magnetic field is along the direction of SAW propagation. Therefore, if the direction of SAW propagation is changed, the direction of the effective time- varying magnetic field in the nanomagnet is changed, and this will change the axis of precession of the magnetization within the nanomagnet, resulting in a change in the oscillations of the x-, y- and z-components of the magnetization, i.e. the spin wave pattern will change. The change in the spin wave pattern results in a change in the direction of the electromagnetic radiation emitted by the spin waves.

[0015] An exemplary ultra-sub-wavelength antenna with continuous beam steering is an active electronically scanned antenna (AESA). Using a multiphase clock to excite the electrodes pairwise sequentially, the beam is scanned electronically, similar to a phased array scan, thereby effectively realizing an active electronically scanned antenna (AESA), except in this case, the AESA element is sub-mm in size and is a single antenna rather than an array of antennas used in conventional phased arrays to steer beams. Conventional phased arrays for beam steering consist of multiple antenna elements each much larger than the wavelength. In contrast, this device enables beam steering with a single element that is much smaller than the wavelength.

[0016] Exemplary antennas have two advantages over prior antennas that use thin films and ferromagnetic resonance. First, in thin films, there can be considerable eddy current loss that degrades the intrinsic radiation efficiency. Nanomagnets, on the other hand, are too small to allow many eddy current loops to form within them and hence the eddy current loss is significantly suppressed. Second, the actuation principle in nanomagnets is not ferromagnetic resonance, and hence exemplary antennas of this disclosure are not restricted to just the ferromagnetic resonance frequency. Exemplary antennas work very efficiently at multiple frequencies (not just one frequency) where cavity spin wave modes form within the nanomagnets. This offers more versatility.

[0017] Exemplary antennas beat the theoretical limits of conventional antennas on the gain and radiation efficiency by at least two orders of magnitude, at least three orders of magnitude, at least four orders of magnitude, and / or at least five orders of magnitude.

[0018] An exemplary magnetostrictive nanomagnet array (magnonic crystal) may comprise, for example, a two dimensional periodic array of magnetostrictive nanomagnets. The nanomagnets may vary in size and shape depending on a particular implementation. Nanomagnets may be elliptical or any other anisotropic shape. The nanomagnet array does not have rotational symmetry in space. Vertical edge-to-edge separation of vertically adjacent magnetostrictive nanomagnets differs from a horizontal edge-to-edge separation of horizontally adjacent magnetostrictive nanomagnets. The edge-to-edge separation between nearest neighbors along the major axes differs from the edge-to-edge separation between nearest neighbors along the minor axes (e.g., by at least 40% or by at least 50%). The edge-to-edge separation can have significant tolerance. As long as it is different along the major and minor axes of the nanomagnets, the precise value of the separation is not critical. An exemplary nanomagnet array may radiate electromagnetic waves with a continuously changing radiation pattern in any plane to implement beam steering.

[0019] In some exemplary antennas, nanomagnets of different sizes and shapes may be arranged on the same wafer (i.e. , same piezoelectric substrate). Since the resonant frequencies are determined by the relation msw= 2L, where L is a lateral dimension of the nanomagnet (e.g., largest lateral dimension) and m is an integer, an antenna comprising some nanomagnets with significantly different L from one another will allow a much broader range of resonant frequencies and hence a larger bandwidth. However, since this configuration can result in fewer nanomagnets radiating at a given resonant frequency (for an antenna design with limited size and thus a limit to the number of nanomagnets which may be included), the output power at that frequency will be less than if the entirety of the nanomagnet array radiated at that frequency. The radiation efficiency is thus lessened for such particular frequency under this circumstance. Thus, there is a trade-off and the design considerations will be dictated by the requirements of the intended use for a particular antenna embodiment.

[0020] In some exemplary embodiments, a beam steering device may include means for applying an external magnetic field (e.g., one or more electromagnets adjacent to the nanomagnet array configured to produce a magnetic field in the region of the nanomagnets when activated) to the nanomagnet array to allow reconfigurability of the nanomagnets after manufacture. Once the nanomagnets are fabricated, it is no longer possible to change the dimensions (L) and hence the resonant “wavelengths” determined by the condition msw= 2L cannot be changed post-fabrication. However, the frequency-wavelength relation may be changed with an external magnetic field. Application of an external magnetic field may thus change the resonant “frequencies” post-fabrication even though we cannot change the resonant “wavelengths”. An external magnetic field may change the frequency of the resonant spin wave mode at a given wavelength by introducing additional (magnetic-field-dependent) Kittel-type modes that couple with the resonant modes via magnon- magnon coupling. This can enable some degree of reconfigurability.

[0021] Exemplary ultra-sub-wavelength high-gain and high-efficiency nano-antennas have disruptive technological applications in medically implanted devices which monitor patient health and communicate that information to outside monitors. They also have obvious applications in wearable electronics, personal communicators, and stealth devices for defense and crime-fighting.

[0022] Beam steering methods and devices according to this disclosure can find applications in wireless local area network (WLAN) and mobile multi-input-multi-output (MIMO) antennas, as well as on-chip communications. Embodiments can be used in many communication systems - cell phones, low-power radars, etc. and this technology allows all of them to be aggressively miniaturized because the antenna can be orders of magnitude smaller than the wavelength. The ability to steer a radiated electromagnetic beam emanating from an antenna is extremely valuable in all manner of applications - cell phones, radars, stealth devices, body sensor networks, etc. Exemplary embodiments of this disclosure offer a novel modality of achieving this objective in an aggressively miniaturized extreme sub-wavelength antenna based on coupling between phonons, magnons and photons. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A is an exemplary beam steering apparatus in block diagram format;

[0024] Figure IB is a diagram of a single nanomagnet the magnetization of which is precessing as a result of a SAW in the piezoelectric substrate with which the nanomagnet is in elastic contact;

[0025] Figure 2 is another exemplary beam steering apparatus;

[0026] Figure 3 is a diagram of a prototypical antenna the testing of which is described in Example 1;

[0027] Figure 4A is exemplary test results of the antenna from Figure 3 discussed in Example 1;

[0028] Figure 4B is further exemplary test results of the antenna from Figure 3 discussed in Example 1;

[0029] Figure 5 is a diagram of a prototypical antenna the testing of which is described in Example 2;

[0030] Figure 6 is a scanning electron microscope (SEM) image of the prototypical antenna the testing of which is described in Example 2;

[0031] Figure 7 A is exemplary test results of the antenna of Figures 5 and 6 discussed in Example 2;

[0032] Figure 7B is further exemplary test results of the antenna of Figures 5 and 6 discussed in Example 2;

[0033] Figure 8 A is further exemplary test results of the antenna of Figures 5 and 6 discussed in Example 2;

[0034] Figure 8B is further exemplary test results of the antenna of Figures 5 and 6 discussed in Example 2.

[0035] DETAIEED DESCRIPTION

[0036] Figure 1A is a block diagram of an exemplary apparatus 100 for electronic beam steering and / or scanning. The apparatus 100 comprises a subwavelength antenna 101 and control circuitry 102. A power source 103 may be integral with or simply connectable with elements 101 and 102, depending on the intended application of apparatus 100. The power source 103 may be any alternating current source, for example.

[0037] The subwavelength antenna 101 comprises a piezoelectric substrate 111, at least one nanomagnet array 112 of magnetostrictive nanomagnets deposited on the piezoelectric substrate 111, and an electrode array 113. The electrode array 113 comprises different pairs 113a, 113b, 113c, 113d, etc. of electrodes. The electrodes may be configured as pads (i.e., contact pads) but, for at least this exemplary embodiment, are not interdigitated transducers (IDTs) since IDTs are frequency filters that are efficient only at the resonant frequency of the IDT and inefficient at all other frequencies. IDTs can be used if a single frequency is desired, but of multiple frequencies are desired, solid contact pads will be preferred. The electrode pairs of the electrode array 113 are configured to launch surface acoustic waves (SAWs) in different directions in the piezoelectric substrate 111 when activated. Electrode pairs with different positions relative to the nanomagnet array 112 radiate SAWs in different directions. The at least one nanomagnet array 112 is configured to radiate an electromagnetic beam (i.e., electromagnetic waves) by phonon- magnon-photon coupling initiated by the SAWs.

[0038] The control circuitry 102 comprises at least one clock 121 and at least one signal source 122. In some configurations, the clock and signal source may be integral with one another. The power source 103 may be separate or integral with the signal source 122. The clock 121 is preferably a multiphase clock. The control circuitry 102 further includes elements such as but not limited to a non-transitory data storage medium for storing antenna control instructions and one or more processors 124 for executing such instructions to operate the antenna 101. In some implementations, control circuitry 102 and antenna 101 may be configured together in a single device, e.g., arranged together on a single printed circuit board (PCB). In such a case one or more (or all) elements of the control circuitry 102 may be considered parts of the antenna 101.

[0039] The multiphase clock 121 is configured to sequentially activate the different pairs of adjacent electrodes in the electrode array 113 (with a micro wave electrical signal) to change direction of the radiated electromagnetic beam radiated by nanomagnet array 112. Sequential activations and corresponding changes in beam direction may be carried out continuously in time. An exemplary signal source is a microwave source capable of sending microwave frequency electrical signals (microwave frequency voltages) to the electrodes of the electrode array 113 in accordance with the timing supplied by the multiphase clock 121. When a surface acoustic wave is launched in the substrate 111 by applying a microwave electrical signal (from signal source 122) between two adjacent electrodes, the SAW reaches the nanomagnet array 112 and triggers the nanomagnet array 112 to radiate electromagnetic waves into the surrounding medium (e.g., surrounding air) by virtue of phonon-magnon-photon coupling taking place within the nanomagnets. The antenna 101 is much smaller than the wavelength of frequencies of electromagnetic waves it radiates. The antenna 101 does not operate as a “point source” which radiates equally in all directions (omnidirectional antenna). Instead, the antenna 101 radiates anisotropically because of the nature of the spin waves excited in the nanomagnets due to phonon-magnon coupling. The nanomagnet array 112 of magnetostrictive nanomagnets is configured to (i) convert phonons of the SAWs to magnons via phonon-magnon coupling and (ii) convert the magnons to photons of the electromagnetic waves via magnon-photon coupling. Each SAW periodically strains the nanomagnets, causing their magnetizations to precess owing to the inverse magnetostriction (Villari) effect. Figure IB is a diagram of a single nanomagnet 151 the magnetization 152 of which is precessing as a result of a SAW in the piezoelectric substrate 153 with which the nanomagnet 151 is in elastic contact. The precessions generate spin waves of the same frequency as the SAW and these spin waves (rotating / oscillating magnetizations) radiate electromagnetic waves, again with the same frequency as the SAW. The phonons from the SAW couple into magnons in the spin wave (phonon-magnon coupling) and the magnons then couple into photons in the electromagnetic wave (magnon-photon coupling). The antenna therefore works on the principle of tripartite phonon-magnon-photon coupling.

[0040] The nature of the spin waves excited in the nanomagnets depends on the direction of SAW propagation. Accordingly, the direction of the electromagnetic beam radiated by antenna 101 depends on the direction of surface acoustic wave propagation. SAW propagation direction is changed by switching activation among different pairs of electrodes (e.g., by applying the activating micro wave signal between different pairs of pads).

[0041] Exemplary embodiments sequentially activate different pairs by using the multiphase clock 121, and this allows steering the beam electronically. That ability results in an active electronically scanned antenna without using multiple antennas (as in an antenna array). Electronic beam steering is achieved in a single aggressively miniaturized antenna. Antenna “gain” is the product of the radiation efficiency and directivity. The radiation efficiency is a measure of how efficiently the antenna radiates (it is the ratio of the energy radiated to the input energy) while the directivity is a measure of its directionality. Hence, it is possible to direct the beam in two very different directions by choosing to activate different pairs of electrodes arranged at different angles relative to the nanomagnet array 112.

[0042] According to some embodiments, the gain of antenna 101 is frequency-dependent. Leveraging this feature, an exemplary beam steering method involves changing direction (of a primary lobe) of a radiated beam of the subwavelength antenna by one or both of: sequentially activating different pairs of electrodes causing surface acoustic waves to be launched in different directions in the piezoelectric substrate, and using frequency modulation to change excitation frequencies used to activate pair(s) of electrodes which launch a surface acoustic wave in the piezoelectric substrate. The frequency modulation may be performed by signal source 122, for example. Hence by using frequency modulation to change the frequency, an exemplary embodiment can direct the principle lobe in different directions and this also achieves beam steering.

[0043] Figure 2 is another exemplary beam steering antenna 201. The antenna 201 comprises an array 212 of magnetostrictive nanomagnets (e.g., cobalt) deposited on a piezoelectric substrate 211 surrounded by an array of electrodes 1-8 of any metal (e.g. aluminum). The nanomagnet array 212 may be, for example, a two dimensional periodic array of nanomagnets deposited on the piezoelectric substrate 211. The nanomagnets may vary in size and shape depending on a particular implementation. As non-limiting but illustrative examples, nanomagnets may be ~ 100 nm sized and be elliptical or any other anisotropic shape. The nanomagnet array does not have rotational symmetry in space. No nanomagnet is circular. Each nanomagnet is slightly elliptical in antenna 201. The edge-to-edge separation between nearest neighbors along the major axes differs from the edge-to-edge separation between nearest neighbors along the minor axes (e.g., by at least 40% or by at least 50%). As a result, the dipole coupling between nearest neighbors is anisotropic. All these anisotropies introduce anisotropy in the nature of the phonon-magnon coupling in exemplary systems. That, in turn, makes the spin wave spectra as well as the power and phase profiles of the spin waves excited in the nanomagnets anisotropic. Consequently, the electromagnetic radiation pattern becomes different when the SAW is launched parallel to the major axes of the elliptical nanomagnets from that when the SAW is launched parallel to the minor axes. The SAW propagation direction does not have to be parallel to either the major or the minor axis. The SAW can be launched in any arbitrary direction that is not parallel to the major or minor axes. The radiation pattern will again change if the direction is changed.

[0044] EXAMPLES

[0045] Example 1.

[0046] A sample antenna was made consistent with Figure 3 (not to scale). The antenna 301 comprises an array of magnetostrictive nanomagnets (Co) deposited on a piezoelectric substrate (LiNbOa) surrounded by an array of electrodes 1-10 of aluminum.

[0047] When a surface acoustic wave is launched in the substrate by applying a microwave electrical signal (from a signal source) between two adjacent pads (numbered 1-8), the sample radiated electromagnetic waves into the surrounding medium by virtue of phonon-magnon- photon coupling taking place within the nanomagnets. The radiated beam is however not omnidirectional because of the nature of the magnonic waves created within the nanomagnets. The beam has a directionality or directivity, meaning that the beam intensity varies with direction.

[0048] The antenna “gain” is the product of the radiation efficiency and directivity. The radiation efficiency is a measure of how efficiently the antenna radiates (it is the ratio of the energy radiated to the input energy) while the directivity is a measure of its directionality. Figures 4A and 4B show two measured polar plots of the gain in the plane perpendicular to the sample’s plane for horizontal polarizations of the electric field in the radiated beam, when contact pads (3,4) and (7,8) were activated, respectively. The plots are shown for ten different excitation frequencies. Note that the plots are very different because in the two cases. In each case the surface acoustic wave is launched in a different direction. In Figure 4A, at 5.47 GHz frequency, the radiated beam has a low intensity of -20 db at 240° angle, whereas in Figure 4B, the radiated beam has a much higher intensity of +5 db at that same angle. At the frequency of 8.16 GHz, the primary lobe with the highest intensity is directed at an angle of 30° in Figure 4A, while the primary lobe is directed at an angle of 0° in Figure 4B. These experimental results demonstrate directing the beam in two very different directions by choosing to activate either contact pads (3,4) or contact pads (7,8). The gain plots of Figures 4A and 4B also show that the gain plot is frequency-dependent. Hence by using frequency modulation to change the frequency, it is possible to direct the principle lobe in different directions, and this also achieves beam steering.

[0049] Example 2.

[0050] A sample antenna was prepared consistent with Figure 5 (not to scale). The antenna included a two-dimensional periodic array of magnetostrictive nanomagnets on a piezoelectric substrate. The different pairs of electrodes, such as (3,4) or (5,6) were connected to a microwave voltage source to launch surface acoustic waves in different directions. Figure 6 is a scanning electron micrograph (SEM) of the nanomagnet array showing that the major axis is ~ 92 nm, the minor axis is ~ 86 nm, the edge-to-edge separation is ~53 nm along the major axes and ~79 nm along the minor axes. The array does not have rotational symmetry in space.

[0051] Because the dimensions of the sample antenna are so much smaller than the wavelength, one would expect them to be-have as “point sources” that should radiate omnidirectionally and isotropically. Surprisingly, they do not. The nanomagnet array does not have rotational symmetry in space, as can be seen from the scanning electron micrograph in Figure 6. No nanomagnet is circular; each is slightly elliptical with major axis dimension of ~92 nm and minor axis dimension of ~86nm. Furthermore, the edge-to-edge separation between nearest neighbors is ~53 nm along the major axes and ~79 nm along the minor axes. As a result, the dipole coupling between nearest neighbors is anisotropic. All these anisotropies introduce anisotropy in the nature of the phonon-magnon coupling in these systems. That, in turn, makes the spin wave spectra, as well as the power and phase profiles of the spin waves excited in the nanomagnets anisotropic. Consequently, the electromagnetic radiation pattern becomes different when the SAW is launched parallel to the major axes of the elliptical nanomagnets from the electromagnetic radiation pattern when the SAW is launched parallel to the minor axes.

[0052] A microwave frequency voltage was applied between either electrode pairs (3,4) or (5,6) to launch SAWs in two different directions. The radiation patterns (both azimuthal and elevation) were measured in an anechoic chamber for these two different directions of SAW propagation. The results are shown in Figures 7 A, 7B, 8 A, and 8B. The results are shown for the vertical polarization, but similar features were observed for the horizontal polarization as well (not shown here). The radiation patterns were measured in an AMS-8701 Anechoic Chamber, Antenna Measurement System using a 3164-10 Open Boundary Quad-ridged Horn Antenna and a 3115 Standard Gain Horn.

[0053] Figures 7 A and 7B show elevation radiation patterns (gain in db for vertical polarization) at different SAW excitation frequencies when the microwave source to launch the SAW was connected between two different electrode pairs. Figure 7A shows the results when the microwave source was connected between electrodes 3 and 4 in Figure 5. Figure 7B shows the results when the microwave source was connected between electrodes 5 and 6. In the former case, the peak radiation at 5.47 GHz frequency was at an angle of 325°, while in the latter case, it was at an angle of 35°.

[0054] Figures 8A and 8B show azimuthal radiation patterns (gain in db for vertical polarization) at different SAW excitation frequencies when the microwave source to launch the SAW was connected between two different electrode pairs. Figure 8 A shows the results when the microwave source was connected between electrodes 3 and 4 in Figure 5. Figure 8B shows the results when the microwave source was connected between electrodes 5 and 6. In the former case, the peak radiation at 8.55 GHz frequency was at 70°, while in the latter case, it was at 330°.

[0055] The plots in Figures 7A, 7B, 8 A, and 8B show that the radiation patterns are different depending on the direction of SAW propagation in these samples. This is due to the fact that the array does not have rotational symmetry in space so that the nature of the spin waves excited in the nanomagnets depends on the direction of SAW propagation. What this Example has shown is that by changing the direction of the SAW by exciting different electrode pairs, it is possible to steer the beam to different directions.

[0056] Some embodiments of the present invention may be a system, a device, a method, and / or a computer program product. A system, device, or computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention, e.g., processes or parts of processes or a combination of processes described herein.

[0057] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[0058] Processes described herein, or steps thereof, may be embodied in computer readable program instructions which may be paired with or downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and / or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device.

[0059] Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Java, Python, Smalltalk, C++ or the like, and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

[0060] Aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer readable program instructions and in various combinations.

[0061] These computer readable program instructions may be provided to one or more processors of one or more general purpose computers, special purpose computers, or other programmable data processing apparatuses to produce a machine or system, such that the instructions, which execute via the processor(s) of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and / or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function / act specified in the flowchart and / or block diagram block or blocks.

[0062] The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks. The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, and combinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

[0063] Where a range of values is provided in this disclosure, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0064] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are described.

[0065] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely ,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0066] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of steps recited or in any other order which is logically possible. Alternative methods may combine different elements of specific detailed methods described above and in the figures. While exemplary embodiments of the present invention have been disclosed herein, one skilled in the art will recognize that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A beam steering apparatus, comprising an extreme subwavelength antenna, comprising a piezoelectric substrate, a nanomagnet array of magnetostrictive nanomagnets deposited on the piezoelectric substrate, and an electrode array surrounding the nanomagnet array, wherein different pairs of electrodes of the electrode array are configured to launch surface acoustic waves (SAWs) in different directions in the piezoelectric substrate when activated, wherein the nanomagnet array is configured to radiate an electromagnetic beam by phonon-magnon-photon coupling; and a multiphase clock configured to sequentially activate the different pairs of electrodes in the electrode array to change direction of the radiated electromagnetic beam.

2. The beam steering apparatus of claim 1, wherein the magnetostrictive nanomagnets are elliptical or any other anisotropic shape.

3. The beam steering apparatus of claim 1, wherein a vertical edge-to-edge separation of vertically adjacent magnetostrictive nanomagnets differs from a horizontal edge-to-edge separation of horizontally adjacent magnetostrictive nanomagnets.

4. The beam steering apparatus of claim 1, wherein the electrode array comprises nanomagnets of different sizes and / or shapes arranged on the same piezoelectric substrate.

5. A method of electronically beam steering a sub wavelength antenna, the sub wavelength antenna comprising a piezoelectric substrate, a nanomagnet array of magnetostrictive nanomagnets deposited on the piezoelectric substrate, and an electrode array about the nanomagnet array, wherein different pairs of electrodes of the electrode array are configured to launch surface acoustic waves (SAWs) in different directions in the piezoelectric substrate whenactivated, wherein the nanomagnet array is configured to radiate an electromagnetic beam by phonon-magnon-photon coupling, the method comprising changing direction of a radiated beam of the subwavelength antenna by one or both of: sequentially activating different pairs of electrodes, causing surface acoustic waves to be launched in different directions in the piezoelectric substrate, and using frequency modulation to change excitation frequencies used to activate a pair of electrodes which launch a surface acoustic wave in the piezoelectric substrate.

6. The method of claim 5, wherein the direction is changed by using frequency modulation to change excitation frequencies used to activate the pair of electrodes which launch a surface acoustic wave in the piezoelectric substrate.

7. The method of claim 5, wherein the direction of the radiated beam is changed continuously in any plane to implement beam steering.

8. The method of claim 5, wherein beam steering is achieved with a single antenna in contrast to multiple antennas needed in conventional phased arrays used for beam steering.

9. An antenna orders of magnitude smaller than wavelengths emittable by the antenna, which makes it effectively a “point source” and yet the antenna emits an anisotropic radiation pattern which is alterable by changing a direction of surface acoustic wave (SAW) propagation in a piezoelectric substrate of the antenna to implement beam steering.

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