X-ray diagnostics and computed tomography (CT) are the most commonly used medical imaging modalities. Currently, there are two ways to detect x-rays for medical imaging purposes: either using direct solid-state detectors (1, 2) (semiconductors based) or using indirect detectors based on the scintillators (3). However, the radiation dose associated CT scans is extremally high and, therefore, increase of detector sensitivity and performance speed is required. X-ray detectors can be characterized by a dead-time—the time that needs to be spent for collection of the electric charge which is proportional to the intensity of the detected radiation. Modern detectors are operated with dead-time of 10−6-10−7 s (corresponding to the processing frequency of MHz) (4).
According to a first aspect of the invention, there is provided a method for determining intensity of electromagnetic radiation at at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure comprising:
providing at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure having a control resonance frequency;
exposing the suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure to electromagnetic radiation of unknown intensity or variable intensity such that the at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure undergoes an internal photoelectric effect;
measuring an irradiated resonance frequency of the irradiated at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure; and
determining the intensity of the electromagnetic radiation irradiating the at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure from the control resonance frequency and the irradiated resonance frequency.
In some embodiments of the invention, there is more than one ferrimagnetic crystal, ferromagnetic crystal, and/or ferro(ferri)magnetic-photostrictive material heterostructure.
In some embodiments of the invention, wherein there is more than one ferrimagnetic crystal, ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure, each respective ferrimagnetic crystal ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure has a different control resonance frequency.
In some embodiments of the invention, wherein there is more than one ferrimagnetic crystal, ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure, the ferrimagnetic crystals, ferromagnetic crystals, and/or ferro(ferri)magnetic-photostrictive material heterostructures are arranged in an array, as discussed herein.
In some embodiments of the invention, the suitable crystal is a hexaferrite crystal, as discussed herein.
According to another aspect of the invention, there is provided a detector comprising:
a plurality of suitable ferrimagnetic crystals, suitable ferromagnetic crystals, and/or suitable ferro(ferri)magnetic-photostrictive material heterostructures arranged in an array,
said array within a magnetic field such that each respective one suitable ferrimagnetic crystal, suitable ferromagnetic crystal and/or suitable ferro(ferri)magnetic-photostrictive material heterostructure has a unique resonance frequency; and
a microwave spectrometer for measuring resonance frequencies.
In some embodiments, the magnetic field is a two-dimensional magnetic field gradient.
In addition to radiation detection, the described photoinduced nonlinear magnetoelectric effect can be utilized to create optically coupled ferromagnetic resonators with radiation source such as, but not limited to, light-emitting diode (LED) that emits ultraviolet, visible, or infrared light. These coupled resonators can then be used in various microwave signal processing devices including, but not limited to, filters, phase shifters, and delay lines. For example, by alternating the voltage applied to the LED, the spectral characteristics and phase characteristics of the resonators can be tuned. As will be understood by one of skill in the art, this will increase the dynamic range of the microwave devices incorporating these resonators and will increase the quality factor of the microwave devices. As will be understood by one of skill in the art, these LED-coupled ferromagnetic resonators could be used as adaptive microwave antennas as well.
Accordingly, in some embodiments of the invention, there is provided use of at least one suitable ferrimagnetic crystal, or suitable ferromagnetic crystal and/or a suitable ferro(ferri)magnetic-photostrictive material heterostructure with a light-emitting diode (LED).
In some embodiments, the LED emits ultraviolet, visible, or infrared light.
As will be appreciated by one of skill in the art, the combination of at least one suitable ferrimagnetic crystal, or suitable ferromagnetic crystal and/or a suitable ferro(ferri)magnetic-photostrictive material heterostructure with an LED provides a coupled resonator which can then be used in various microwave signal processing devices including, but not limited to, filters, phase shifters, and delay lines, as discussed herein.
As used herein, the expression “suitable ferrimagnetic crystal or suitable ferromagnetic crystal” refers to any ferri(ferro)magnetic crystals in which the photoinduced magnetoelectric effect can be observed. While not wishing to be bound or limited to a particular theory or hypothesis, the inventors believe that such a suitable ferri(ferro)magnetic crystal should possess at least one but preferably both of the following properties: (1) semiconductor behavior; and (2) while the crystal is absorbing electromagnetic radiation, the generated photocurrent should be distinguished from the dark current that naturally flows through the crystal. As will be appreciated by one of skill in the art, these two properties are necessary for the magnetic to demonstrate a photoinduced magnetoelectric effect.
In addition, as discussed above, the photoinduced magnetoelectric effect can be observed in ferro(ferri)magnetic-photostrictive material heterostructures. As will be understood by one of skill in the art, the photostrictive material will create mechanical stress due to irradiation that will be transmitted to the ferri(ferro)magnetic material in the heterostructure. This mechanical stress will alter the internal magnetic properties of the magnetic materials resulting in the resonance frequency shift, creating the photoinduced magnetoelectric effect in photostrictive-ferro(ferri)magnetic heterostructure.
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 the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned hereunder are incorporated herein by reference.
Described herein is the use of a biased hexaferrite ferrimagnetic semiconductive crystal for detection of the radiation on GHz frequencies. Recently, the presence of current induced magnetoelectric effect has been demonstrated in hexaferrites (5-7). It was shown that the frequency of either ferromagnetic or multidomain resonance of the hexaferrite semiconductor crystal can be changed due to electric current flow. Furthermore, the value of current can be calculated based on the frequency shift measurement.
This principle can be used for radiation detection. We have successfully detected the internal photoelectric effect in Zn2Y hexaferrite crystal (
As will be appreciated by one of skill in the art, while this has been demonstrated for Zn2Y, any hexaferrite can be used until the hexaferrite crystal begins to exhibit semi-conductor behavior, as discussed herein.
Accordingly, the hexaferrite may be an M-type ferrite, a Z-type ferrite, a Y-type ferrite, a X-type ferrite or a U-type ferrite.
In some embodiments, the hexaferrite is a Y-type ferrite, having the general structure of (Ba/Sr)2Me2Fe12O12 where Me is a small 2+ ion such as for example cobalt, nickel or zinc and where Ba can be substituted by Sr.
Furthermore, any suitable ferrimagnetic crystal or suitable ferromagnetic crystal, for example, any ferri(ferro)magnetic crystals in which the photoinduced magnetoelectric effect can be observed, may be used within the invention, as discussed herein.
In addition, as discussed above, the photoinduced magnetoelectric effect can be observed in ferro(ferri)magnetic-photostrictive material heterostructures. As will be understood by one of skill in the art, the photostrictive material will create mechanical stress due to irradiation that will be transmitted to the ferri(ferro)magnetic material in the heterostructure. This mechanical stress will alter the internal magnetic properties of the magnetic materials resulting in the resonance frequency shift, creating the photoinduced magnetoelectric effect in photostrictive-ferro(ferri)magnetic heterostructure.
As will be appreciated by one of skill in the art, in some embodiments, the heterostructure comprises photostrictive material placed in mechanical contact with ferri(ferro)magnetic materials. The type of photostrictive material will depend on the type of radiation desired to be detected. For example, lead lanthanum zirconate titanate (PLZT) materials with a general structure Pb(1-x)Lax(ZryTi1-y)1-x/4O3 can be used as photostrictive material for UV light detection.
Since the photostrictive material will interact with the radiation initially, there are no restrictions on the type or composition of the magnetic materials used.
Accordingly, any ferro(ferri)magnetic material can be used in conjunction with photostrictive material to create a heterostructure. For example, the yttrium iron garnet (Y3Fe5O12) can be used as a ferrimagnetic material. Alternatively, hexaferrites mentioned above can be also utilized for engineering of ferrimagnetic-photostrictive heterostructures.
In some embodiments, the ferrite garnets with a general formula of Me3Fe5O12 (where Me is a metal cations) can be used in the discussed heterostructures.
As can be appreciated by one of skill in the art, any substituted materials could also be possible to use for the ferri(ferro)magnetic-photostrictive heterostructure.
While not wishing to be bound or limited to a particular theory or hypothesis, the inventors believe that such a suitable ferri(ferro)magnetic crystal or photostrictive-ferro(ferri)magnetic heterostructure should possess at least one but preferably both of the following properties: (1) semiconductor behavior; and (2) while the crystal is absorbing electromagnetic radiation, the generated photocurrent should be distinguished from the dark current that naturally flows through the crystal. As will be appreciated by one of skill in the art, these two properties are necessary for the magnetic to demonstrate a photoinduced magnetoelectric effect.
According to a first aspect of the invention, there is provided a method for determining intensity of electromagnetic radiation at at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure comprising:
providing at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure having a control resonance frequency;
exposing the suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure to electromagnetic radiation of unknown intensity or variable intensity such that the at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure undergoes an internal photoelectric effect;
measuring an irradiated resonance frequency of the irradiated at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure; and
determining the intensity of the electromagnetic radiation irradiating the at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal, or suitable ferro(ferri)magnetic-photostrictive material heterostructure from the control resonance frequency and the irradiated resonance frequency.
In some embodiments of the invention, there is more than one ferrimagnetic crystal, ferromagnetic crystal, and/or ferro(ferri)magnetic-photostrictive material heterostructure.
In some embodiments of the invention, wherein there is more than one ferrimagnetic crystal, ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure, each respective ferrimagnetic crystal ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure has a different control resonance frequency.
In some embodiments of the invention, wherein there is more than one ferrimagnetic crystal, ferromagnetic crystal, or ferro(ferri)magnetic-photostrictive material heterostructure, the ferrimagnetic crystals, ferromagnetic crystals, and/or ferro(ferri)magnetic-photostrictive material heterostructures are arranged in an array, as discussed herein.
In some embodiments of the invention, the suitable crystal is a hexaferrite crystal, as discussed herein.
According to another aspect of the invention, there is provided a detector comprising:
a plurality of suitable ferrimagnetic crystals, suitable ferromagnetic crystals, and/or suitable ferro(ferri)magnetic-photostrictive material heterostructures arranged in an array,
said array within a magnetic field such that each respective one suitable ferrimagnetic crystal, suitable ferromagnetic crystal and/or suitable ferro(ferri)magnetic-photostrictive material heterostructure has a unique resonance frequency; and
a microwave spectrometer for measuring resonance frequencies.
In some embodiments, the magnetic field is a two dimensional magnetic field gradient.
In addition to radiation detection, the described photoinduced nonlinear magnetoelectric effect can be utilized to create optically coupled ferromagnetic resonators with radiation source such as, but not limited to, light-emitting diode (LED) that emits ultraviolet, visible, or infrared light. These coupled resonators can then be used in various microwave signal processing devices including, but not limited to, filters, phase shifters, and delay lines. For example, by alternating voltage applied to LED, the spectral characteristics and phase characteristics of the resonators can be tuned. As can be understood by one of skill in the art, this will increase the dynamic range of the described microwave devices and will increase the quality factor of the microwave devices. As will be understood by one skilled in the art, these LED-coupled ferromagnetic resonators could be used as adaptive microwave antennas as well.
Accordingly, in some embodiments of the invention, there is provided use of at least one suitable ferrimagnetic crystal, or suitable ferromagnetic crystal and/or a suitable ferro(ferri)magnetic-photostrictive material heterostructure with a light-emitting diode (LED).
In some embodiments, the LED emits ultraviolet, visible, or infrared light.
As will be appreciated by one of skill in the art, the combination of at least one suitable ferrimagnetic crystal, or suitable ferromagnetic crystal and/or a suitable ferro(ferri)magnetic-photostrictive material heterostructure with an LED provides a coupled resonator which can then be used in various microwave signal processing devices including, but not limited to, filters, phase shifters, and delay lines, as discussed herein.
Accordingly, in some embodiments of the invention, there is provided a coupled resonator comprising at least one suitable ferrimagnetic crystal, suitable ferromagnetic crystal and/or suitable ferro(ferri)magnetic-photostrictive material heterostructure and a light-emitting diode (LED).
In some embodiments, the LED emits ultraviolet, visible, or infrared light.
Following the detection of photoelectric effect in Zn2Y crystal, we have successfully detected a photoinduced nonlinear magnetoelectric effect in the monocrystal of Zn2Y (
These results demonstrate how radiation can be detected by exploiting this photoinduced nonlinear magnetoelectric effect. Specifically, once the crystal is irradiated, the photocurrent induces change in resonance frequency (
This phenomenon can be extended for the detection of any type of electromagnetic radiation. If hexaferrite crystal is biased and irradiated by any electromagnetic waves, and/or experiences an internal photoelectric effect, the frequency of ferromagnetic resonance will be changed proportionally to the intensity of absorbed radiation. Therefore, by conducting frequency measurement of the ferromagnetic resonance similar to the approach demonstrated above, it is possible to measure the intensity of the incoming radiation.
As will be appreciated by one of skill in the art, using a matrix of hexaferrite resonators placed for example on copper transmission lines produces a radiation detector capable of detecting radiation locally.
In some embodiments, to make the resonance frequency of every resonator unique, a matrix or array of crystals can be placed in a 2D magnetic field gradient. In these embodiments, the reference signal can be generated by, for example, a sweep generator with a spectrum broad enough to cover all resonance frequencies of the crystals in the hexaferrite matrix. In these embodiments, the resonance frequency measurements are made using for example a microwave spectrometer. Since the resonance frequency of each crystal is unique, it is easy to quantify the intensity of electromagnetic radiation which was absorbed by every pixel on the matrix. As will be apparent to one of skill in the art, detectors built using this approach can be used for detection of any radiation for example but by no means limited to visible light, ultraviolet light, X-rays and the like. Thus, these detectors can be implemented in a variety of spectrometers and medical imaging modalities.
For example, to perform X-ray imaging using photoinduced non-linear magnetoelectric effect as described herein, an array of M×N hexaferrite resonators as described herein is arranged. As will be apparent to one of skill in the art, the matrix size can vary depending on the end application. For, example, a CT detector matrix will be larger than a digital mammography detector or a fluoroscopy detector. The shape of the detector may also vary depending on the potential application—for example, CT detectors would likely be curved but in other applications, the detector may be flat or substantially flat. As discussed above, the M×N hexaferrite matrix is placed in a gradient magnetic field in order to magnetize ferrimagnetic resonators and to create a specific resonance frequency for each respective one resonator. The array size will also vary depending on the application. For instance, for digital mammography, the array might be on the order of 25×25 cm2 so as to be similar in size to previously developed direct digital detectors. An example of a suitable detector construction can be seen in
Specifically, as can be seen from
Unlike radiation detectors that rely on photocurrent measurement and quantification, an array of hexaferrite resonators does not require any additional electronic circuits designed for charge collection and/or current measurement. Therefore, manufacturing of the hexaferrite radiation detector described herein will avoid the difficulties associated with solid-state radiation detectors. In addition, unlike conventional radiation detectors that frequently utilize amorphus and polycristaline materials, the hexaferrite radiation detector utilizes hexaferrite monocrystals, which significanity improves the charge carrier mobilities. Finally, the hexaferrite radiation detector has a working frequency of 10-100 GHz which is up to 4 orders of magnitude higher than currently available radiation detectors. Utilization of such operating frequencies produces increases in signal detection speed and will result in significant reduction of radiation dose required for a single scan. In addition, faster performance of the hexaferrite radiation detector will allow for a substantial increase in the resulting image quality.
The primary advantage of this radiation detection device is the high operating frequencies, as discussed above, which result in a significantly shorter dead time for the detector. For example, the known hexaferrite crystal Zn2Y experiences ferromagnetic resonance around 12 GHz. Barium hexaferrite (BaFe12O19) has a resonance frequency ˜50 GHz. These operating frequencies are several orders of magnitude higher compared to the frequencies commonly used with for example x-ray detection. Therefore, hexaferrite detectors based on photoinduced magnetoelectric effect potentially will have significantly shorter dead-time which means that a lower radiation dose is needed to obtain the same signal-to-noise ratio of an x-ray image. This will also significantly improve safety of modern CT and fluoroscopy scans.
While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made therein, and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.
The instant application claims the benefit of U.S. Provisional Patent Application 63/225,102, filed Jul. 23, 2021 and entitled “X-ray and photodetection using photoinduced magnetoelectric effect”, the entire contents of which are hereby incorporated by reference for all purposes.
Number | Date | Country | |
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63225102 | Jul 2021 | US |