Particle detection techniques

Abstract

Certain aspects are directed towards a particle detection device. The particle detection device generally includes: an oscillator including a coil, wherein the coil is configured to generate a magnetic field; and a frequency detector coupled to an output of the oscillator and configured to detect a frequency of an output signal of the oscillator, wherein the detected frequency of the output signal indicates a particle concentration associated with a sample within the magnetic field.

Description

PARTICLE DETECTION TECHNIQUESTECHNICAL FIELD

[0001] Certain aspects of the present disclosure generally relate to particle detection techniques, and more particularly, techniques for detecting particle concentration using induction heating and oscillator frequency detection.BACKGROUND

[0002] Subsurface storage of gases is becoming increasingly important for mitigating carbon dioxide (CO2) emissions and storing dense energy carriers such as hydrogen as part of an ongoing energy transition. Providing for the security of subsurface CO2 storage, especially at early stages, is a technically challenging task due to the risk associated with the high mobility of CO2, which may lead to leakage. In general, the storage security depends on a combination of evolving physical and geochemical trapping mechanisms. It has been shown that the use of CO2 foams improves mobility control in injection operations and leads to increased storage capacity within geological settings. The primary advantage of foams, compared to CO2, is their significantly higher apparent viscosity. However, foams are often thermodynamically unstable. One approach to increasing their stability is to use nanoparticles along with surfactants. Nanoparticles (NPs) such as iron oxide have been shown to enhance the stability of foams when combined with surfactants. Due to their paramagnetic properties, these magnetic nanoparticles can be detected in in-situ fluid samples and, thus, serve as tracers that enable monitor the geographic extent of the injected fluids and the CO2 plume in the subsurface.SUMMARY

[0003] The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims that follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description,” one will understand how the features of this disclosure provide the advantages described herein.

[0004] Certain aspects are directed towards a particle detection device. The particle detection device generally includes: an oscillator including a coil, wherein the coil is configured to generate a magnetic field; and a frequency detector coupled to an output of the oscillator and configured to detect a frequency of an output signal of the oscillator, wherein the detected frequency of the output signal indicates a particle concentration associated with a sample within the magnetic field.

[0005] Certain aspects are directed towards a particle detection device. The particle detection device generally includes: a coil configured to generate a magnetic field; a power supply configured to provide a drive signal to the coil; and a temperature sensor configured to sense a temperature of a sample in the magnetic field, wherein the sensed temperature indicates a particle concentration associated with the sample.

[0006] Certain aspects are directed towards a method for particle detection. The method generally includes: generating an oscillating signal via an oscillator including a coil, wherein generating the oscillating signal includes generating a magnetic field via a coil of the oscillator; detecting, via a frequency counter, a frequency shift of the oscillating signal; and identifying a particle concentration associated with a sample within the magnetic field based on the frequency of the oscillating signal.

[0007] Certain aspects are directed towards a method for particle detection. The method generally includes: providing, via a power supply, a drive signal to a coil to generate a alternating magnetic field; sensing, via a temperature sensor, a temperature of a sample in the magnetic field; and identifying a particle concentration associated with the sample within the magnetic field based on the sensed temperature.

[0008] To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the appended drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

[0010] Figure 1 is a diagram illustrating changes in trapping mechanisms and geologic storage security over time, in accordance with certain aspects of the present disclosure.

[0011] Figure 2 illustrates graphs showing intensity versus particle size distribution, mean hydrodynamic diameter, polydispersity index, and zeta potentials, in accordance with certain aspects of the present disclosure.

[0012] Figure 3 is a table showing details of salts and surfactants, in accordance with certain aspects of the present disclosure.

[0013] Figure 4 illustrates graphs showing magnetization curves for nanoparticles, in accordance with certain aspects of the present disclosure.

[0014] Figure 5 illustrates a detection device with induction heating of magnetic nanoparticles, in accordance with certain aspects of the present disclosure.

[0015] Figure 6 illustrates a graph showing temperature change (AT) versus time for different nanoparticle solutions, in accordance with certain aspects of the present disclosure.

[0016] Figure 7 is a table illustrating maximum AT associated with each of multiple concentrations at the end of a heating period, in accordance with certain aspects of the present disclosure.

[0017] Figure 8A illustrates the relationship between AT and concentrations of nanoparticles, in accordance with certain aspects of the present disclosure.

[0018] Figure 8B illustrates a graph showing AT and ionic strength of a solution generated by adding various salts to DI water, in accordance with certain aspects of the present disclosure.

[0019] Figure 9 illustrates a table presenting factors, associated nomenclature, and levels used in factorial design used to detect the individual and combined effects of the different salts, a mixture of surfactants, and nanoparticle, in accordance with certain aspects of the present disclosure.

[0020] Figure 10 is a Pareto chart generated for an experimental design, in accordance with certain aspects of the present disclosure, in accordance with certain aspects of the present disclosure.

[0021] Figure 11 is a flow diagram illustrating example operations for particle detection, in accordance with certain aspects of the present disclosure.

[0022] Figure 12 illustrates a detection device including an oscillator for nanoparticle detection, in accordance with certain aspects of the present disclosure.

[0023] Figure 13 is a frequency versus time graph 1300 generated for 1,000 ppm NP#1 solution (e.g., FerOt) in DI water, in accordance with certain aspects of the present disclosure.

[0024] Figure 14 illustrates a graph showing frequency drop versus nanoparticle concentrations, in accordance with certain aspects of the present disclosure.

[0025] Figure 15 is a flow diagram illustrating example operations for particle detection, in accordance with certain aspects of the present disclosure.

[0026] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.DETAILED DESCRIPTION

[0027] Certain aspects of the present disclosure are directed towards techniques for particle detection. The particle detection may be performed by heating a sample (e.g., using induction heating). A particle concentration of the sample may be identified based on a temperature characteristic (e.g., temperature as a function of time) of the sample as compared to predetermined temperature characteristics associated with different concentrations. In some aspects, a sample may be placed within a magnetic field of a coil of an oscillator. Depending on the concentration of the sample, the inductance of the coil may vary, resulting in a change in the oscillator’s frequency. The oscillator’s frequency may be detected to identify the particle concentration of the sample.

[0028] Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein, one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.

[0029] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary'” is not necessarily to be construed as preferred or advantageous over other aspects.

[0030] As used herein, the term “connected with” in the various tenses of the verb “connect” may mean that element A is directly connected to element B or that other elements may be connected between elements A and / / (i.c., that element A is indirectly connected with element B). In the case of electrical components, the term “connected with” may also be used herein to mean that a wire, trace, or other electrically conductive material is used to electrically connect elements A and B (and any components electrically connected therebetween).

[0031] It should be understood that aspects of the present disclosure may be used in a variety of applications. Although the present disclosure is not limited in this respect, the circuits disclosed herein may be used in any of various suitable apparatuses, such as in the power supply, battery charging circuit, or power management circuit of a communication system, a video codec, audio equipment such as music players and microphones, a television, camera equipment, and test equipment such as an oscilloscope.Example Techniques for Particle Detection

[0032] Foams improve mobility control in injection operations within geological settings. Nanoparticles (NPs) such as iron oxide have been shown to enhance the stability of foams when combined with surfactants. Certain aspects leverage the magnetic properties of nanoparticles to detect their presence as a surrogate for monitoring the geologic extent of injected fluids in the subsurface. The feasibility of using these nanoparticles for monitoring purposes stems from their detectability at low concentrations in subsurface environments. Certain aspects provide techniques to detect the presence of magnetite nanoparticles in complex fluids. To simulate complex subsurface fluids in a laboratory setting, the effects of ions and surfactants on the detection of nanoparticles are investigated. Some aspects provide an induction heating (IH) technique and an oscillator frequency shift (OFS) technique. The IH technique may involve applying a high-frequency alternating magnetic field to a solution containing small amounts of magnetic nanoparticles and measuring the temperature response. The magnetic field may be generated for different samples, with temperature changes recorded by an infrared camera. The results indicate that nanoparticle concentrations linearly affect the rise in the temperature of the solution. However, thepresence of ions and surfactants also influences the temperature response. The OFS technique measures shifts in the resonance frequency of a circuit caused by changes in magnetic permeability inside a coil. This coil is part of a transistor oscillator circuit that produces a sinusoidal voltage waveform, with the oscillation frequency depending on the coil’s inductance. The presence of nanoparticles causes a shift in resonance frequency, which may be measured for various samples. The drop in resonance frequency may be a linear function of nanoparticle concentration, and the technique described herein may be used to detect concentrations as low as 150 ppm of magnetite (Fe.iOr) nanoparticles.

[0033] Figure 1 is a diagram 100 illustrating changes in trapping mechanisms and geologic storage security over time. Since physical trapping mechanisms dominate at the early stages of storage, achieving a high displacement efficiency is important for efficient storage. Due to the low density and viscosity of gases, CO2 exhibits high mobility within porous media, and continuous injection of CO2 into the subsurface can result in poor sweep efficiency. Injection methods, such as water-alternating gas (WAG) and C Ch-foam, help control gas mobility and improve displacement efficiency for CCh-enhanced oil recovery (CO2-EOR) and geologic carbon sequestration. It has been shown that the use of CO2 foams leads to increased storage capacity. Foams may include a discontinuous gas phase separated by a continuous liquid film known as lamellae. The use of foaming agents, such as surfactants, in conjunction with CO2 may increase the apparent viscosity of foams by one or two orders of magnitude. However, foams are often thermodynamically unstable.

[0034] One approach to increasing their stability is to use nanoparticles along with surfactants. Silica, fly ash, and iron-oxide (IO) nanoparticles have been shown to improve volumetric sweep efficiency when injected together with surfactants and CO2. Nanoparticle-stabilized CO2 foams may be more stable than conventional or surfactant- stabilized foams, especially under high salinity, high-temperature subsurface conditions. Therefore, applying nanoparticles for foam stabilization not only enhances the thermodynamic stability of foams, but also helps to control gas mobility, improve sweep efficiency, and enhance gas storage capacity. Some nanoparticles, such as IO, possess magnetic properties due to the atomic structure of iron. These properties makeIO nanoparticles useful in various fields, including medicine for cancer therapy, drug delivery, and obtaining high-contrast tomographic images of the human body. Recognizing these distinct properties, the potential use of paramagnetic IO nanoparticles as nano-sensors and for acoustic imaging of the subsurface has been investigated, particularly during EOR applications. For instance, it has been shown that paramagnetic nanoparticles used for formation evaluation can also be used for reservoir monitoring due to their unique magnetic properties. Reservoir monitoring is an important yet underdeveloped aspect of geological CO2 storage that is important for providing safety and security. Additionally, in the U.S., testing and monitoring the CO2 plume through direct and indirect methods is a federal condition for class VI wells, which are designated for geological CO2 storage. Currently, an effective method for subsurface monitoring is time-lapse seismic imaging, which is costly and has limited applicability for monitoring gases. Therefore, new monitoring technologies for subsurface gas storage are important.

[0035] Certain aspects provide techniques for detecting the presence of IO nanoparticles in subsurface fluid chemistry. The presence of these nanoparticles, particularly in the context of nanoparticle-stabilized CO2-foam injection, serves as an indicator for the extent of the CO2 plume in the subsurface. Consequently, these methods hold the potential to aid in monitoring CO2 plumes within the subsurface.

[0036] Two different nanoparticles, referred to herein as NP#1 and NP#2, were used during the experiments employing the two approaches. Transmission Electron Microscopy (TEM) results indicate that NP# l consists of FeaCU nanoparticles with an average size of 15 ± 5 nm, which is shown to enhance COr-foam stability and displacement efficiency. NP#2 comprised commercially available nanoparticles with an average particle size of 100 nm per transmission electron microscopy (TEM) results. Aqueous nanoparticle solutions were prepared under constant ultrasonication using a probe sonicator to prevent agglomeration prior to experiments. A Brookhaven Zeta PALS instrument was used to obtain the average hydrodynamic diameter, zeta potential, and particle size distribution data to determine the aqueous stability of the nanoparticles. Zeta potential measurements were performed using 0.01 M KC1nanoparticle solutions in deionized (DI) water to prevent polarization and maintain a constant ionic strength.

[0037] Figure 2 illustrates graphs 200, 250 showing the intensity (%) versus particle size distribution of the particles, and the mean hydrodynamic diameter, polydispersity index, and zeta potentials for NP#1 and NP#2, respectively, as tabulated in Table 260. DI water was used as the solvent during the experiments unless specified. Additionally, lab-grade salts - NaCl, KC1, CaC12-2H2O and MgCh'6H2O - and surfactants Alphaolefin sulfonate (AOS) and 35% active Lauramidopropyl betaine (LAPB) were used to replicate foams in subsurface settings.

[0038] Figure 3 is a table 300 showing details of salts and surfactants used for the inductive heating experiments. The magnetic properties of the nanoparticles were measured using vibrating-sample magnetometry (VSM) in a Physical Property Measurement System (PPMS).

[0039] Figure 4 illustrates graphs 400, 450 showing the magnetization curves for NP#1 and NP#2, respectively. The reported saturation magnetization values may be obtained using the asymptotes of the magnetization curves in Figure 4. The magnetometry results indicate that NP#1 has a saturation magnetization of 70.1 emu / g, whereas NP#2 has a saturation magnetization of 65.7 emu / g, with coercivities (He) of approximately I mT (107.5 forNP#l and 104.34 Oe for NP#2). These findings suggest that both nanoparticles are ferromagnetic.

[0040] Figure 5 illustrates a detection device 500 with induction heating of magnetic nanoparticles, in accordance with certain aspects of the present disclosure. The induction heating technique described herein may be used to detect the presence of nanoparticles in complex fluids. This technique involves recording the temperature rise of nanoparticle carrier fluid when exposed to a magnetic field. This rise in temperature is attributed to the losses incurred during the magnetization reversal process of magnetic nanoparticles exposed to an alternating magnetic field. Magnetic nanoparticles, including IO, may be used for similar approaches in various medical applications, such as intercellular hyperthermia. The colloidal suspension of nanoparticles in a carrier fluid, known as nanofluids, generates heat. This heat in magnetic nanofluids may be the sum of the relative contributions of hysteresis loss,Neel, and Brownian relaxations, which may depend on multiple factors, including particle size and composition. The following Rosensweig equation is an analytical formula that demonstrates the relationship between the dissipated power, P, the magnetic field, and the fluid’s magnetic properties:where / z0is the permeability of free space, Xo is the equilibrium magnetic susceptibility of the particles, H denotes the magnetic field intensity, f is the frequency of the magnetic field, and T is the effective relaxation time, a combination of Neel and Brownian relaxation times. The heating power loss may increase as a function of both the frequency (f) and the field intensity (H). Therefore, selecting a source with maximum field amplitude and frequency is important to achieve high heating power. However, obtaining a large field amplitude at high frequency presents a technical challenge and increases the power supply’s cost.

[0041] The detection device 500 may include an induction heater 504. The heater 504 may include a power supply unit. In some cases, the power supply unit may generate a signal within a 100-500 kHz frequency range with a maximum input power of 10 kW. The power supply unit may be coupled to a coil 512. In some aspects, the coil may be a custom C-shaped coil, although any suitable coil shape may be used. The C-shaped coil may produce a larger temperature change (AT) and offer a larger inner space for a sample holder compared to a cylindrical coil of similar overall dimensions. The heater 504 may be coupled with a water chiller 502 to prevent overheating the heater’s electronics and the induction coil.

[0042] As shown, a solution 516 (e.g., a nanofluid sample) may be placed in a holder within the magnetic field of the coil 512. A thermal measurement device 510 (e.g., pyrometer) may be used to measure the temperature of the sample while a drive signal is provided to the coil 512 by the power supply unit. Thermal measurements in an induced high-frequency magnetic field are challenging. In some cases, an infrared (IR) pyrometer with an 8-14 urn spectral range and adjustable emissivity and transmissivity functions may be used to measure and record the temperature changes of the sample from a distance on the surface of the solution. In some cases, multiple samples may be placed in the magnetic field of the coil for testing Sample holdersmay be used to insulate the samples as much as possible to prevent heat exchange between the samples and their surroundings. For example, the insulation may be implemented via glass wool insulation 508 and form insulation 514. The dimensions of the sample holder may be determined based on the distance-to-spot (D:S) ratio of the pyrometer, the distance from the induction coil, and the inner diameter of the coil. As will be described in more detail herein, the heating characteristics of the sample as a function of time may be compared with characterized temperature characteristics associated with different concentrations, allowing the concentration of the sample to be identified.

[0043] Solutions of NP#2 were exposed to an alternating magnetic field generated by the induction heater. Three identical samples of 60, 120, 250, 500, 1000 ppm concentrated FesOr were prepared using 10 ml DI water as the solvent. All samples were sonicated before being placed in the sample holder and exposed to the magnetic field for a period of 320 seconds at near room temperature. AT values across a wide range of NP concentrations were obtained. For comparison, initial temperature values were extracted from all curves, and the resulting data is plotted in Figure 6.

[0044] Figure 6 illustrates a graph 600 showing AT versus time for different nanoparticle solutions and DI water, in accordance with certain aspects of the present disclosure. The error bars are shown for every third data point to help with readability. Although an overall increasing trend is shown for all samples, those with higher magnetic particle concentrations generate more heat. The AT associated with DI water may be due to unwanted heat transfer from the induction coil. Water circulates inside the coil, which is cooled down by the chiller and operates in cycles. The cooling cycle rapidly cools the water for a few minutes, and the pump continuously circulates the water through the coil. Therefore, this is observed as temperature fluctuations (e.g., drops and rises) for DI water and samples with lower particle concentrations in graph 600. This heat may be accounted for in each sample’s analysis. The data shown in Figure 6 may be corrected by subtracting initial temperatures and adjusting for temperature fluctuations due to the cycles of the chiller. Notably, the lower error bar associated with the 60 ppm concentration overlaps with the positive error bar of DI water. Thus, the sensitivity of this approach may be between 60-120 ppm.

[0045] Figure 7 is a table 700 illustrating the maximum AT associated with each of multiple concentrations at the end of a 320 second heating period, in accordance with certain aspects of the present disclosure. Analyzing AT versus different concentrations of nanoparticles aids in understanding the relationship between the two parameters. Temperature is a directly measurable parameter that can be correlated to the concentration of nanoparticles in the solution. Although specific loss power and specific absorption rate are often calculated in magnetic hyperthermia applications due to regulatory' specifications associated with electromagnetic radiation and human health, temperature change (AT) can be measured to detect nanoparticles in solutions. A linear fit derived from 13 data points yields an R2value of approximately 0.98.

[0046] Figure 8A illustrates a graph 800 showing the relationship between AT and the concentrations of Fc.^CU nanoparticles. The data from 0 to 200 ppm in Figure 8 may have a different linear trend than the overall linear fit. This may be due to the contribution of measurement errors associated with preparing the nanoparticle in water and discrepancies resulting from the water chiller's circulation cycles.

[0047] Physiological components, such as ions and proteins, may impact the heat dissipation of magnetic IO nanoparticles in suspension. To test the effect of major ions commonly found in subsurface water chemistry' on AT, 15,000 ppm of four different chloride salts were added to 1000 ppm of NP#2 separately.

[0048] Figure 8B illustrates a chart 850 showing the AT and ionic strength of a solution, generated by adding various salts (15,000 ppm) to DI water along with 1,000 ppm of NP#2, in accordance with certain aspects of the present disclosure. The presence of ions and proteins may affect the heating efficiency of a solution under an applied magnetic field. Ions may contribute positively to heating efficiency due to mobility and diffusivity. In contrast, the presence of proteins may impede the overall rise in temperature. The same concentration of different salts may contribute differently to the temperature increase.

[0049] A two-level, 26-factorial design may be employed to detect the individual and combined effects of the different salts, as well as a mixture of surfactants (AOS and LAPB) and NP#1. The factorial designs may allow for the measurement of theeffect of each factor (independent variable) and the interactions of their impact on a single dependent variable (response variable). These independent variables can have different levels, but two-level factorial designs may be the most common. The high levels of these factors may be chosen based on the average concentrations of those ions in saline water and concentrations of surfactants and nanoparticles for foam stabilization.

[0050] Figure 9 illustrates a table 900 presenting the factors, associated nomenclature, and levels used in the factorial design. The effects of these factors were investigated based on the results from 128 experiments.

[0051] Figure 10 is a Pareto chart 1000 from the experimental design, where the response is AT and a is set at 0.005. Only 30 of the most significant effects are shown. The reference line 1002 indicates which effects are statistically important. The chart 1000 summarizes the magnitude and relative importance of factors and their combinations. As can be observed, the importance of Factor A, representing the presence of nanoparticles, is several times higher than that of other individual factors or their combinations.

[0052] Figure 11 is a flow diagram illustrating example operations 1100 for particle detection, in accordance with certain aspects of the present disclosure. The operations 1100 may be performed by a detection device, such as the detection device 500 of Figure 5.

[0053] At block 1102, the detection device provides, via a power supply (e.g., a power supply unit of heater 504), a drive signal to a coil (e.g., coil 512) to generate a magnetic field. At block 1104, the detection device may sense, via a temperature sensor (e.g., thermal measurement device 510), a temperature of a sample in the magnetic field. At block 1106, the detection device may identify a particle concentration associated with the sample within the magnetic field based on the sensed temperature.

[0054] In some aspects, the detection device may record the sensed temperature via a data recorder (e.g., via the data recorder 518). The particle concentration may be identified using the recorded sensed temperature.

[0055] In some aspects, the temperature may be sensed for a sampling period. Changes in the temperature as a function of time during the sampling period may indicate the particle concentration. In some aspects, the detection device may cool the coil via a chiller while providing the driving signal. For example, the chiller may be a water chiller. The detection device may provide water flow adjacent to the coil via one or more water pipes.

[0056] Certain aspects are directed towards an oscillator frequency shift technique for nanoparticle detection. The detection of magnetic nanoparticles may involve monitoring a frequency shift of a transistor oscillator circuit. This type of electronic oscillator generates a sinusoidal voltage waveform at an output, where the oscillation frequency depends on the inductance and capacitance in the feedback loop of the oscillator. The presence of magnetic nanoparticles creates a slight change in the magnetic permeability inside a coil used to implement the inductance, thereby altering the coil’s inductance and resulting in a shift in the oscillator’s frequency. In some cases, to increase the frequency shift, a Colpitts oscillator configuration may be used, which may use a single inductor and two capacitors.

[0057] Figure 12 illustrates a detection device 1200 including an oscillator 1201 for nanoparticle detection, in accordance with certain aspects of the present disclosure. The oscillator 1201 may include an inductor-capacitor (EC) circuit (e.g., a tank circuit) including capacitors Cl, C2 and inductor 1202 (e.g., coil). The oscillator 1201 may include a gain device, which may be implemented using a junction field-effect transistor (JFET) 1214, although any suitable type of transistor may be used. A feedback path 1216 may be coupled between the JFET 1214 and a node between capacitors Cl, C2. The capacitors C 1 , C2 provide voltage division to couple energy in and out of the tank circuit.

[0058] The inductor 1202 and capacitors Cl, C2 form a resonant tank circuit that sets the frequency of the oscillator 1201. The voltage across Cl is applied to the gatesourcejunction of the JFET 1214, providing feedback to create oscillations. As shown, the drain of the JFET 1214 may be coupled to a voltage source 1204. In some cases, the voltage source may provide a 6.0V output voltage, although any suitable voltage may be used. A resistor R1 may be coupled between the source of the JFET 1214 anda reference potential node (e.g., electric ground) for biasing. An alternating current (AC)-coupling capacitor C8 may be coupled between the source of the JFET 1214 and an input of an amplifier 1210. The negative input of the amplifier 1210 may be coupled to an output of the amplifier 1210, forming a buffer. In some aspects, a frequency detector 1218 may be coupled to the output of the amplifier 1210. The frequency detector 1218 may detect the frequency of an output signal of the amplifier 1210 for nanoparticle detection. In some cases, a resistor R2 may be coupled between the positive input of the amplifier 1210 and the reference potential node (e.g., electric ground).

[0059] For the detection scheme, the frequency stability of the oscillator is important, as the anticipated shift in frequency due to the magnetic nanoparticles may be small. There may be an inherent limit to the frequency stability related to the load / losses in the oscillator. Consequently, a JFET common drain (CD) amplifier configuration may be used as the gain device. The high input impedance of the JFET CD amplifier configuration results in reduced oscillator loading. While capacitors typically exhibit low loss, inductors may be quite lossy due to their construction (e.g., essentially a wire wrapped in a cylindrical fashion), which may reduce the frequency stability of the oscillator by lowering the quality factor (Q) of the resonant EC circuit. To reduce the inductor losses, the coil (e.g., inductor 1202) may use Litz wire with 175 strands of 46 AWG wire around a plastic tube with an outside diameter of just under 16mm. The 50 turns may result in a coil length of approximately 37.5mm and a free- air inductance of approximately 14.5 pH. However, any suitable inductance for the coil can be implemented, such as inductance between 1 pH and 20 pH.

[0060] The amplifier 1210 may serve as a buffer to prevent (or at least reduce) the loading of the oscillator by any connected devices. Resistor RI sets the bias of the CD amplifier stage to just under 3mA (although any suitable bias current may be used) and provides bias stability. The voltage source 1204 may be implemented via two Li batteries in series, providing low noise and drift, which are important to the frequency stability of the oscillator 1201. The capacitances of the feedback capacitor divider (e.g., capacitors Cl, C2) may be set to produce an oscillation frequency of around 500KHz per the equation:C1 / C2 ratio of around 0.25 may be selected to increase frequency stability. In some aspects, temperature-stable ceramic capacitors may be used. Although 500KHz is provided as an example oscillation frequency, any suitable frequency may be used.

[0061] Some aspects are directed towards reducing external influences on the oscillator frequency stability. For example, the oscillator 1201 may be housed in a metal box to shield the oscillator from surrounding electromagnetic fields and environmental temperature fluctuations. A hole may be drilled in the top of the box, directly above the coil, to allow for the placement of a sample inside the coil. For example, the coil may be implemented with a w’ire wound around a region where the sample may be placed. The sample may be placed within a magnetic field generated by the coil. The oscillator’s output may be connected to a frequency counter (e.g., frequency detector 1218), which may accurately measure the oscillation frequency with sample times of up to 10 seconds. The longer the sample time, the greater the precision that can be achieved in the frequency measurement. In some aspects, a 1 -second sample time may provide a reasonable compromise between displayed precision and thermal drift. As described, the frequency detector 1218 may detect the frequency of the output signal of the amplifier 1210 for nanoparticle detection. For example, as described in more detail herein, the detected frequency may be compared to predetermined frequency characteristics associated with different concentrations, allowing for the detection of the concentration in a sample.

[0062] In some aspects, frequency versus time data may be obtained by inserting samples with different nanoparticle concentrations inside the oscillator’s coil (e.g., within a magnetic field generated by the inductor 1202). This process may be repeated multiple times (e.g., at least three times) and the average frequency change (Af) (Hz) may be calculated for each sample. The frequency drop associated with the change in magnetic permeability inside the coil may be observed by plotting the frequency values against time for each concentration.

[0063] Figure 13 is a frequency versus time graph 1300 generated for 1,000 ppm NP#1 solution (e.g., FesCh) in DI water, in accordance with certain aspects of the present disclosure. As shown, each time a sample is inserted in the coil, the frequency of the oscillator drops by Afi, Af2, Af;. Experiments conducted with various concentrations show an overall increasing trend in Af corresponding to the increasing nanoparticle concentration as shown in Figure 14.

[0064] Figure 14 illustrates a graph 1400 showing corrected values of frequency drop versus nanoparticle (NP#1) concentrations, in accordance with certain aspects of the present disclosure. A good linear fit with an R2value of 0.93 indicates that the relationship between Af and nanoparticle concentration is linear. An average frequency shift of 17.6 Hz may be observed for the control sample (e.g., deionized water), which may be due to multiple effects, including the high dielectric constant of deionized water influencing parasitic capacitance, thermal instability of circuit elements (e.g., capacitors), and disruption of magnetization flux. Therefore, the sensitivity of this method may be estimated at approximately 150 ppm NP#1 concentration.

[0065] Figure 15 is a flow diagram illustrating example operations 1500 for particle detection, in accordance with certain aspects of the present disclosure. The operations 1500 may be performed by a detection device, such as the detection device 1200 of Figure 12.

[0066] At block 1502, the detection device may generate an oscillating signal via an oscillator (e.g., oscillator 1201) including a coil (e.g., inductor 1202). Generating the oscillating signal may include generating a magnetic field via a coil of the oscillator.

[0067] At block 1504, the detection device may detect, via a frequency detector (e.g., detector 1218), a frequency of the oscillating signal. At block 1506, the detection device may identify a particle concentration associated with a sample within the magnetic field based on the frequency of the oscillating signal. In some aspects, a change in the frequency of the oscillating signal in response to insertion of the sample in the magnetic field may indicate the particle concentration. In some aspects, the change in the frequency includes a reduction in the frequency. The change in the frequency may increase relative to increasing particle concentration. The oscillator may include a tank circuit the coil being part of the tank circuit

[0068] In some aspects, the oscillator may include a first capacitor (e.g., Cl of Figure 12) and a second capacitor (e.g., C2 of Figure 12). The oscillator may also include a gain device (e.g., JFET 1214) having an input (e.g., gate of JFET 1214) coupled to a node between the coil and the first capacitor and a feedback path (e.g., feedback path 1216) coupled between an output of the gain device (e.g., source of JFET 1214) and a node between the first capacitor and the second capacitor. A ratio between the capacitances of the first capacitor and the second capacitor may be between 0.2 and 0.3, although a ratio of 0.25 may provide reduce noise. In some aspects, the gain device includes a JFET (e.g., JFET 1214) having a source coupled to the output of the gain device and a gate coupled to the input of the gain device. The gain device may also include a resistor (e.g., resistor Rl) coupled between the source of the JFET and a reference potential node. The resistor may be configured to set a bias current for the gain device to be between 2mA and 4mA, although any suitable bias current may be used depending on circuit components used. The gain device may be configured as a common drain amplifier with the JFET.

[0069] In some aspects, the detection device may include a buffer (e.g., amplifier 1210) coupled between the output of the gain device and the frequency detector. In some aspects, an alternating-current (AC) coupling capacitor (e.g., C8 of Figure 12) may be coupled between the output of the gain device and an input of the buffer. In some aspects, the oscillator also include a voltage source (e.g., voltage source 1204) coupled to the gain device. The voltage source may include one or more lithium-ion batteries. The oscillator is configured to operate a frequency between 450 KHz and 550 KHz, although any suitable operating frequency may be used from 100s of hertz to gigahertz.

[0070] Certain aspects have described induction heating (IH) and oscillator frequency shift (OFS) nanoparticle detection techniques. Each approach aims to detect small amounts of magnetic IO nanoparticles in different solutions and to establish the relationships between response and nanoparticle concentration. The IH approach applies a high-frequency AC magnetic field around a nanoparticle solution, generating heat primarily based on the amount of nanoparticles present. This heat generation results from a combination of multiple relaxation mechanisms (e.g., Neel andBrownian) and hysteresis losses. Additionally, the presence of some ions and surfactants, which are present in subsurface fluid chemistry, may influence the generated heat. A linear relationship between the concentration of magnetic nanoparticles and the temperature response is established and used for particle detection. The IH approach may be used to detect, for example, 60-120 ppm of FcTTi nanoparticles in DI water. The OFS approach may be used to detect the presence of magnetic nanoparticles based on their relative magnetic permeability. A transistor oscillator circuit is provided herein with a stable resonance frequency. A shift in the resonance frequency was observed when changing the medium (e.g., sample) inside the coil of the circuit due to a change in inductance. This shift may be measured with different nanoparticle solutions, where a linear relationship exists between the concentration of magnetic nanoparticles and the frequency shift. The OFS method may be used to detect concentrations as low as, for example, 150 ppm of FcsCfi in DI water.Additional Considerations

[0071] The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and / or software components ) and / or module(s), including, but not limited to a circuit, an application-specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.

[0072] As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, “determining” may include resolving, selecting, choosing, establishing, and the like.

[0073] As used herein, a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a b or c” is intended to cover: a b c a b a c b c and a b c as well as anycombination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a- c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

[0074] The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and / or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and''or actions may be modified without departing from the scope of the claims.

[0075] It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

CLAIMSWhat is claimed is:1 . A particle detection device, comprising: an oscillator including a coil, wherein the coil is configured to generate a magnetic field; and a frequency detector coupled to an output of the oscillator and configured to detect a frequency of an output signal of the oscillator, wherein the detected frequency of the output signal indicates a particle concentration associated with a sample within the magnetic field.

2. The particle detection device of claim 1 , wherein the oscillator comprises a tank circuit, the coil being part of the tank circuit.

3. The particle detection device of claim 1 , wherein the oscillator further includes: a first capacitor; a second capacitor; a gain device having an input coupled to a node between the coil and the first capacitor; and a feedback path coupled between an output of the gain device and a node between the first capacitor and the second capacitor.

4. The particle detection device of claim 3, wherein a ratio between capacitances of the first capacitor and the second capacitor is between 0.2 and 0.3.

5. The particle detection device of claim 3, wherein the gain device includes a junction field effect transistor (JFET) having a source coupled to the output of the gain device and a gate coupled to the input of the gain device.

6. The particle detection device of claim 5, wherein the gain device further comprises a resistor coupled between the source of the JFET and a reference potential node.

7. The particle detection device of claim 6, wherein the resistor is configured to set a bias current for the gain device to be between 2mA and 4mA.

8. The particle detection device of claim 5, wherein the gain device is configured as a common drain amplifier with the JFET.

9. The particle detection device of claim 3, further comprising a buffer coupled between the output of the gain device and the frequency detector.

10. The particle detection device of claim 9, wherein an alternating-current (AC) coupling capacitor is coupled between the output of the gain device and an input of the buffer.

11. The particle detection device of claim 5, wherein the oscillator further comprises a voltage source coupled to the gain device.

12. The particle detection device of claim 11, wherein the voltage source comprises one or more lithium-ion batteries.

13. The particle detection device of claim 1, wherein a change in the frequency of the output signal in response to insertion of the sample in the magnetic field indicates the particle concentration.

14. The particle detection device of claim 13, wherein the change in the frequency comprises a reduction in the frequency, and wherein the change in the frequency increases relative to increasing particle concentration.

15. The particle detection device of claim 1, wherein the oscillator is configured to operate a frequency between 450 Khz and 550 KHz.

16. A particle detection device, comprising: a coil configured to generate a magnetic field; a power supply configured to provide a drive signal to the coil; anda temperature sensor configured to sense a temperature of a sample in the magnetic field, wherein the sensed temperature indicates a particle concentration associated with the sample.

17. The particle detection device of claim 16, wherein the temperature sensor comprises pyrometer.

18. The particle detection device of claim 16, further comprising a chiller configured to cool the coil.

19. The particle detection device of claim 18, wherein the chiller comprises a water chiller, the particle detection device further comprising one or more water pipes configured to provide water flow adjacent to the coil.

20. The particle detection device of claim 16, further comprising a data recorder configured to record the sensed temperature.

21. The particle detection device of claim 16, wherein the temperature sensor is configured to sense the temperature for a sampling period, wherein changes in the temperature as a function of time during the sampling period indicate the particle concentration.

22. A method for particle detection, comprising: generating an oscillating signal via an oscillator including a coil, wherein generating the oscillating signal includes generating a magnetic field via the coil of the oscillator; detecting, via a frequency detector, a frequency of the oscillating signal; and identifying a particle concentration associated with a sample within the magnetic field based on the frequency of the oscillating signal.

23. The method of claim 22, wherein a change in the frequency of the oscillating signal in response to insertion of the sample in the magnetic field indicates the particle concentration24. The method of claim 23, wherein the change in frequency comprises a reduction in frequency, and wherein the reduction in frequency increases relative to increasing particle concentration.

25. A method for particle detection, comprising: providing, via a power supply, a drive signal to a coil to generate a magnetic field; sensing, via a temperature sensor, a temperature of a sample in the magnetic field; and identifying a particle concentration associated with the sample within the magnetic field based on the sensed temperature.

26. The method of claim 25, further comprising recording the sensed temperature via a data recorder, wherein the particle concentration is identified using the recorded sensed temperature.

27. The method of claim 25, wherein the temperature is sensed for a sampling period, wherein changes in the temperature as a function of time during the sampling period indicate the particle concentration.

28. The method of claim 25, further comprising cooling the coil via a chiller while providing the driving signal.

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