The present disclosure is related to pending U.S. patent application Ser. No. 12/561,498, filed Sep. 9, 2009, entitled “Multiferroic Antenna/Sensor which is assigned to the same assignee as the present application and is incorporated herein in its entirety by reference.
The present disclosure is related to antennas, and more particularly to a multiferroic antenna and transmitter.
Conventional antennas, such as dipoles, slots and patches that receive an electric field or magnetic field of an incident signal and convert it to an output signal must either protrude from the surface to which they are mounted or require a cavity in the surface behind them. Protruding antennas on aircraft increase drag and present anti-icing and other challenges. Antenna cavities on aircraft also add weight (reducing aircraft range/payloads), take up valuable space, result in holes through structural skins of the aircraft that are subject to lightning and fluid penetration, and are costly to integrate into the structure of the aircraft.
According to one aspect of the present disclosure, a multiferroic element may include a substrate formed on an electrically conductive ground plane. The substrate may be formed from a material having a predetermined elastic modulus. A layer of piezoelectric material may be formed on the substrate. A layer of magnetostrictive material may be bonded to the layer of piezoelectric material. A mechanical strain is created in the layer of piezoelectric material in response to a voltage signal being applied to the multiferroic element. The mechanical strain in the layer of piezoelectric material causes a mechanical strain in the layer of magnetostrictive material to produce a radio frequency magnetic field that is proportional to the voltage signal for generating a radio frequency electromagnetic wave. The predetermined elastic modulus of the substrate is substantially lower than an elastic modulus of the layer of piezoelectric material.
According to another aspect of the present disclosure, a multiferroic antenna may include an electrical conductive ground plane. A plurality of multiferroic elements may be formed on the ground plane and may be configured in an array to form the multiferroic antenna. Each of the multiferroic elements may include a substrate formed on the ground plane. Each multiferroic element may also include a layer of piezoelectric material formed on the substrate. Each multiferroic element may additionally include a layer of magnetostrictive material bonded to the layer of piezoelectric material. A mechanical strain is created in the layer of piezoelectric material in response to a voltage signal being connected across the ground plane and the layer of magnetostrictive material. The mechanical strain in the layer of piezoelectric material causes a mechanical strain in the layer of magnetostrictive material to produce a radio frequency magnetic field that is proportional to the voltage signal for generating a radio frequency electromagnetic wave.
According to a still further aspect of the present disclosure, a vehicle may include a skin. A transmitter may be mounted in the vehicle for communications and a transmit multiferroic antenna may be connected to the transmitter and mounted on the skin. The transmit multiferroic antenna may include an electrical conductive ground plane. A plurality of multiferroic elements may be formed on the electrically conductive ground plane and configured in an array to form the multiferroic antenna. Each of the multiferroic elements may include a substrate formed on the ground plane. Each of the multiferroic elements may also include a layer of piezoelectric material formed on the substrate. Each of the multiferroic elements may also include a layer of magnetostrictive material bonded to the layer of piezoelectric material. A mechanical strain is created in the layer of piezoelectric material in response to a voltage signal being connected across the ground plane and the layer of magnetostrictive material. The mechanical strain in the layer of piezoelectric material causes a mechanical strain in the layer of magnetostrictive material to produce a radio frequency magnetic field that is proportional to the voltage signal for generating a radio frequency electromagnetic wave.
According to another aspect of the present disclosure, a method for generating a radio frequency electromagnetic wave may include applying a voltage signal to a multiferroic element to create a mechanical strain in a layer of piezoelectric material bonded to a layer of magnetostrictive material of the multiferroic element in response to the voltage signal being applied. The mechanical strain in the layer of piezoelectric material causes a mechanical strain in the layer of magnetostrictive material to produce a radio frequency magnetic field that is proportional to the voltage signal for generating the radio frequency electromagnetic wave. The piezoelectric material may be formed on a substrate on an electrically conductive ground plane. The substrate may be formed from a material having a predetermined elastic modulus that is substantially lower than an elastic modulus of the layer of piezoelectric material.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings.
The present disclosure is further described in the detailed description which follows in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present disclosure in which like reference numerals represent similar parts throughout the several views of the drawings and wherein:
The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the disclosure. Other embodiments having different structures and operation do not depart from the scope of the present disclosure.
The transmitter 100 may include a user interface 104 for controlling the transmitter 100 and inputting information or signals for transmission by the transmitter 100. Audio signals, video signals, a combination of audio and visual signals or other electrical signals may be received by the user interface 104. The transmitter 100 may also include a RF transmitter circuit 106 for converting electrical signals from the user interface 104 into RF signals for transmission by the multiferroic transmit antenna 102.
The transmitter 100 may also include an impedance matching circuit 108 to match an impedance of the transmitter 100 to an input of the antenna 102. The antenna 102 may include a plurality of inputs or drive ports 110. As described in more detail herein, the antenna 102 or antenna array may be subdivided into groups of elements. The groups of elements may be driven by different drive ports 110 or inputs. The groups of elements may be driven either in-phase or out-of-phase to control a direction of the transmitted signal or electromagnetic wave. The groups of elements may be driven in parallel similar to that illustrated in
The multiferroic element 200 may include an electrically conductive ground plane 202. A substrate 204 may be formed on the electrically conductive ground plane 202. A layer of piezoelectric material 206 may be formed on the substrate 204. As described in more detail herein the substrate 204 is preferably a low-modulus substrate to substantially prevent distortion of the multiferroic element 200 when a signal voltage is applied.
A layer of magnetostrictive material 208 may be formed on the layer of piezoelectric material 206. The layer of magnetostrictive material 208 may be bonded to the layer of piezoelectric material 206. A mechanical strain is created in the layer of piezoelectric material 206 in response to a signal voltage (“V”) being connected across the ground plane 202 and the layer of magnetostrictive material 208. The layer of magnetostrictive material 208 may be an electrically conductive material and may act as electrode for applying the signal voltage to the layer of piezoelectric material 206. The mechanical strain in the layer of piezoelectric material 206 causes a mechanical strain in the adjacent layer of magnetostrictive material 208 bonded to the layer of piezoelectric material 206. The mechanical strain in the layer of magnetostrictive material 208 may produce a radio frequency magnetic field (“M”) that is proportional to the signal voltage (“V”). Lateral dimensions or a size of each multiferroic element 200 on the ground plane 202 is smaller than a wavelength of a lowest mechanical resonance of the multiferroic element 200 to substantially prevent any distortion of the multiferroic element 200 that could affect an electromagnetic wave generated by an antenna containing the multiferroic element 200 or an array of multiferroic elements 200. For example, a multiferroic element made of typical materials as described herein that is designed for 100 MHz operation should be smaller than about 10 microns depending upon material properties. A sufficiently large array of such multiferroic elements 200 may radiate an electromagnetic wave and act as a transmitter.
The substrate 204 may be formed from a material having a predetermined elastic modulus or mechanical modulus. The predetermined elastic modulus of the substrate 204 may be substantially lower than an elastic modulus of the layer of piezoelectric material 206 and the layer of magnetostrictive material 208 to substantially prevent distortion of the multiferroic element 200.
The signal voltage “V” from a transmitter electronics or circuit, such as circuit 106 in
A time-varying magnetic field “H” is produced by the voltage V and is equivalent to a radiating magnetic dipole source. Such a source will generate radiating magnetic and electric fields. The applied radio frequency voltage thereby produces radio frequency magnetic and electric fields that are transmitted as an electromagnetic wave.
The layer of piezoelectric material 206 may be any piezoelectric material, such as lead zirconium titanate (PZT), lead-magnesium-niobium-lead titanate (PMN-PT) or other piezoelectric material. Use of piezoelectric materials designed for power applications (such as actuators) may be preferred for generating high amplitude transmitted signals. The thickness of the layer of piezoelectric 206 may be large enough and the modulus high enough that the strain is efficiently transferred to the adjacent layer of the magnetostrictive material 208. The optimum thickness ratio of the layer of magnetostrictive material 208 to the layer of piezoelectric material 206 depends on the relative mechanical modulii of the layers but is typically about ½.
The layer of magnetostrictive material 208 may be any magnetostrictive material, such as for example Terfenol, nickel, Metglas or other magnetostrictive material. The layer of magnetostrictive material 208 may be biased with a static magnetic field (MS) 210 to maximize the radio frequency magnetic field that is generated by the strain. The bias field may be generated by small conventional permanent magnets or by small conventional electromagnets. Bias fields as small as a few Oersteds are sufficient (depending on choice of magnetostrictive materials). For example the bias field may be a direct current (DC) field of about 8 Oersteds for Metglas and up to about 400 Oersteds for Terfenol-D. Lower values may be possible. The magnets or electromagnets may bias single elements 200 or multiple elements. The layer of magnetostrictive material 208 may be formed with a predetermined thickness such that the stress applied by the layer of piezoelectric material 206 causes a uniform strain throughout the layer of magnetostrictive material 208. For example, the layer of magnetostrictive material 208 may be formed with a thickness that is sufficiently small that the stress applied by the layer of piezoelectric material 206 leads to a uniform strain throughout the magnetostrictive layer 208.
Similar to a conventional antenna, the array 300 of multiferroic elements 302 may be narrow in a predetermined dimension or direction, such as for example in the “y” direction as illustrated in the example of
While the array 300 illustrated in
The multiferroic elements 302 of the array 300 may form a rectangle or any other convenient shape consistent with any antenna requirements for directionality of the antenna 304. The multiferroic elements 302 may be closely packed or dispersed to facilitate integration with other features, such as features of the vehicle or aircraft 400 in which the antenna 304 is associated or attached as illustrated in the example of
The antenna assembly 404 or array may be very thin (a few mils) and may be applied as an appliqué to the aircraft 400. The antenna assembly 404 or array does not require a radome or antenna cavity, nor does it have to protrude from the surface of the aircraft 400. The antenna 404 does not require large penetrations through the aircraft 400 or other skin and only requires small penetrations for coax line ports similar to ports 306 of
The receiver 506 and multiferroic receiver antenna assembly 508 may be similar to that described in pending U.S. patent application Ser. No. 12/561,498, filed Sep. 9, 2009, and entitled “Multiferroic Antenna/Sensor which is incorporated herein in its entirety by reference. The multiferroic antennas described herein and those in U.S. patent application Ser. No. 12/561,498 may be combined to form a transmit/receive antenna. Referring also to
Each multiferroic stack 602 and 604 may include multiple stacked multiferroic layers-pairs where each multiferroic layer-pair consists of an alternating layer of the magnetostrictive material 606 and a piezoelectric material 608 bonded together enabling a high signal sensitivity. A magnetic field of an incident signal on each multiferroic layer-pair of magnetostrictive material 606 and piezoelectric material 608 causes mechanical strain in the magnetostrictive material 606 layers that strain adjacent piezoelectric material layers 608 producing an electrical voltage from each multiferroic layer-pair proportional to the magnitude of the incident signal. A built-in mechanical polarization (i.e., a bias strain) yields increased sensitivity to an incident signal's magnetic field. A sum of the voltages from all multiferroic layer-pairs is the multiferroic sensor output voltage 612. Therefore, the multiferroic sensor output voltage 612 consists of the electrical voltage from each multiferroic layer-pair amplified proportional to a total number of multiple connected multiferroic layered-pairs in the multiferroic stacks 602 and 604. In this exemplary embodiment of the present disclosure, with the two multiferroic stacks 602 and 604 are connected in series, an output voltage from each stack is added together to produce the total output voltage 612 from the multiferroic sensor or antenna 600.
The multiferroic antenna described herein is capable of operating over a wide frequency band, power levels, directionality and temperature extremes. For example, a 1 meter long array may transmit efficiently from about 50 MHz to about 18 GHz with the low frequency limit determined by the requirement for the length to be at least ¼ wavelengths and the high frequency limit by the number of drive ports. The power level is determined by the size of the array and by the material properties. For example a 0.0014 volt signal applied to a 1 micron thick PMN-PT having a piezoelectric coefficient of about −7e−10 m/V will generate a strain parallel to the surface of the array of approximately 1 microstrain. This strain will transfer to the magnetostrictive layer with about a 0.5 coupling factor resulting in a strain of about 0.5 microstrains. If the magnetostrictive material is, for example, 45 Permalloy having a magnetostriction coefficient of about 7e−8 m/A with a 5 A/m bias field then the strain-induced magnetization in the Permalloy is about 1 Gauss and this creates an external magnetic field parallel to the surface of approximately 5 A/m. Then a 1 m by 2 cm well-matched antenna consisting of an array of closely spaced elements will emit about 100 watts of transmitted power. Typical magnetostrictive and piezoelectric materials are capable of much higher strains and magnetizations leading to expectation that much larger power levels can be transmitted. At some point cooling may be appropriate to prevent overheating above the piezoelectric “Curie point” which is typically about 150° C. The temperature range of the array described herein may range from near-absolute zero to the Curie point.
Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art appreciate that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown and that the disclosure has other applications in other environments. This application is intended to cover any adaptations or variations of the present disclosure. The following claims are in no way intended to limit the scope of the disclosure to the specific embodiments described herein.
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