Dual Radio Frequency Research Articles

Digitally generated high-resolution mid-infrared dual-comb spectroscopy system based on electro-optic modulation.

In this Letter, we propose a high-resolution dual-comb spectroscopy (DCS) in the mid-infrared (MIR) region. A broadband electro-optic frequency comb (EOFC) with a line spacing of 13 GHz is generated in the near-infrared region. The injection locking technique is employed to lock the distributed feedback (DFB) laser to each comb line of the 34 comb lines as the seed laser for the subsequent electro-optic modulation. A dual radio frequency (RF) comb source with a 50 MHz line spacing and a 13 GHz bandwidth drives a single IQ Mach-Zehnder modulator (IQ-MZM), functioning as a single-sideband (SSB) generator and producing a DCS with high spectrum flatness and resolution flexibility. The generated DCS is converted to the MIR region via a nonlinear difference frequency generation (DFG) system. A DCS with a bandwidth of 442 GHz and a resolution of 50 MHz is achieved in the 3.3 µm region, and the figure of merit reaches 2.94×106 H z 12 in a 183.6 ms measurement time.

Incremental high power radiofrequency ablation with multi-electrodes for small hepatocellular carcinoma: a prospective study

Radiofrequency ablation (RFA) offers a minimally invasive treatment for small hepatocellular carcinoma (HCC), but it faces challenges such as high local recurrence rates. This prospective study, conducted from January 2020 to July 2022, evaluated a novel approach using a three-channel, dual radiofrequency (RF) generator with separable clustered electrodes to improve RFA’s efficacy and safety. The study employed a high-power, gradual, stepwise RFA method on HCCs (≤ 4 cm), utilizing real-time ultrasound-computed tomography (CT)/magnetic resonance imaging (MRI) fusion imaging. Involving 110 participants with 116 HCCs, the study reported no major complications. Local tumor progression (LTP) and intrahepatic remote recurrence (IRR) rates were low, with promising cumulative incidences at 1, 2, and 3 years for LTP (0.9%, 3.6%, 7.0%) and IRR (13.9%, 20.5%, 31.4%). Recurrence-free survival (RFS) rates were similarly encouraging: LTP (99.1%, 96.4%, 93.0%) and IRR (86.1%, 79.5%, 68.6%). This innovative gradual, incremental high-power RFA technique, featuring a dual switching monopolar mode and three electrodes, represents an effective and safer management option for small HCCs.Trial registrationclinicaltrial.gov identifier: NCT05397860, first registered on 26/05/2022.

Dual-energy lattice-tip ablation system for persistent atrial fibrillation: a randomized trial

Clinical outcomes of catheter ablation for atrial fibrillation (AF) are suboptimal due, in part, to challenges in achieving durable lesions. Although focal point-by-point ablation allows for the creation of any required lesion set, this strategy necessitates the generation of contiguous lesions without gaps. A large-tip catheter, capable of creating wide-footprint ablation lesions, may increase ablation effectiveness and efficiency. In a randomized, single-blind, non-inferiority trial, 420 patients with persistent AF underwent ablation using a large-tip catheter with dual pulsed field and radiofrequency energies versus ablation using a conventional radiofrequency ablation system. The primary composite effectiveness endpoint was evaluated through 1 year and included freedom from acute procedural failure and repeat ablation at any time, plus arrhythmia recurrence, drug initiation or escalation or cardioversion after a 3-month blanking period. The primary safety endpoint was freedom from a composite of serious procedure-related or device-related adverse events. The primary effectiveness endpoint was observed for 73.8% and 65.8% of patients in the investigational and control arms, respectively (P < 0.0001 for non-inferiority). Major procedural or device-related complications occurred in three patients in the investigational arm and in two patients in the control arm (P < 0.0001 for non-inferiority). In a secondary analysis, procedural times were shorter in the investigational arm as compared to the control arm (P < 0.0001). These results demonstrate non-inferior safety and effectiveness of the dual-energy catheter for the treatment of persistent AF. Future large-scale studies are needed to gather real-world evidence on the impact of the focal dual-energy lattice catheter on the broader population of patients with AF. ClinicalTrials.gov identifier: NCT05120193.

Linear Ion Trap Mass Spectrometer (LITMS) Instrument Field and Laboratory Tests as Part of the ARADS Field Campaigns.

The highly compact Linear Ion Trap Mass Spectrometer (LITMS), developed at NASA Goddard Space Flight Center, combines Mars-ambient laser desorption-mass spectrometry (LD-MS) and pyrolysis-gas chromatography-mass spectrometry (GC-MS) through a single, miniaturized linear ion trap mass analyzer. The LITMS instrument is based on the Mars Organic Molecule Analyser (MOMA) investigation developed for the European Space Agency's ExoMars Rover Mission with further enhanced analytical features such as dual polarity ion detection and a dual frequency RF (radio frequency) power supply allowing for an increased mass range. The LITMS brassboard prototype underwent an extensive repackaging effort to produce a highly compact system for terrestrial field testing, allowing for molecular sample analysis in rugged planetary analog environments outside the laboratory. The LITMS instrument was successfully field tested in the Mars analog environment of the Atacama Desert in 2019 as part of the Atacama Rover Astrobiology Drilling Studies (ARADS) project, providing the first in situ planetary analog analysis for a high-fidelity, flight-like ion trap mass spectrometer. LITMS continued to serve as a laboratory tool for continued analysis of natural Atacama samples provided by the subsequent 2019 ARADS final field campaign.

Dual low pressure plasma process for SiCN:H thin films deposition: A comparative study

SiCN:H thin films have large possibilities of applications due to their versatile chemical and physical properties. Plasma Assisted Chemical Vapor Deposition (PACVD) process is widely used for SiCN:H deposition. Here we discuss on the potentialities of dual Electron Cyclotron Resonance (ECR) and Radio Frequency Magnetron Sputtering (rf MS) plasmas coupling for SiCN:H deposition in Ar/N2/Si(CH3)4 gas mixture. The study is carried out by varying the autopolarisation voltage Vbias of the silicon target. ECR plasma gives low deposition growth rate about 50 nm/h. The films are transparent. SiCN nanopillars with high aspect ratio are obtained. Rf MS plasma gives high deposition growth rate up to 2200 nm/h. The films are opaque in the near UV and transparent in the visible depending on their thickness. The optical index at 630 nm is 1.95, the Tauc's band gap is 3.0 eV and do not change with Vbias. Dual ECR/rf MS plasma gives high deposition growth rate up to 2300 nm/h. The films are transparent. The optical index varies between 1.7 and 2.05 at 630 nm and the Tauc's band gap decreases linearly between 4.75 and 3.4 eV with Vbias. Dual ECR/rf MS plasma coupling is a very promising PACVD process for thin films deposition.

Numerical characterization of dual radio frequency micro-discharges

Micro-discharges have many excellent characteristics, such as generation of high-density and non-equilibrium plasmas at atmospheric pressure. In this paper, we used an implicit particle-in-cell/Monte Carlo collision method for three-dimensional velocities in a one-dimensional space combined with the secondary electron emission model to study the characteristics of micro-discharges driven by dual radio frequency (RF) power. The effect on plasma parameters was observed by varying the voltage of the RF power, the frequency, and the gas pressure of the discharge. Since the electrode spacing is very small in micro-discharges, the voltage change will affect the characteristics of micro-discharges. In addition, the plasma density increases with the frequency and the discharge mode changes at different frequencies. Finally, the influence of gas pressure on the characteristics of micro-discharges cannot be ignored. When the air pressure decreases, the ion flux reaching the electrodes is significantly increased, and the energy distribution of ions increases in the high-energy portion.

Measurement of Dielectric Properties in Soil Contaminated by Biodiesel-Diesel Blends Based on Radio Frequency Heating

Several recent studies have found that measuring the dielectric permittivity of soil can be used to determine the level of environmental pollution. However, there is limited research on the measurement of dielectric properties in soil contaminated with biodiesel-diesel blends from Thailand. This paper presents to monitor the dielectric properties of soil contaminated with biodiesel-diesel blends. Specifically, we use the commercial grade diesel B7 to contaminate a sample of sand soil. We also study the measurement of dielectric properties in contaminated soil with the diesel B7 using a dual electrode plate-based radio frequency (RF) heating system. This allows us to observe the behavior of the contaminated soil before and after RF heating treatment. The experimental result showed that the dielectric properties of uncontaminated and contaminated soil were different. In addition, the RF heating system utilizing the electric field intensities of 450 kV/m resulted in the dielectric properties of the contaminated soil becoming similar to those of uncontaminated soil. These findings suggest that using RF heating on contaminated soil samples improve the air in the pore space compared to unheated contaminated soil. This approach may be effective for the treatment of soil in Thailand using an RF heating system with dual electrode plates.

A Motion Compensation Method for Shipborne HFSWR by Using Dual Reference RF Signals Generated Onshore

The echo of shipborne high-frequency surface wave radar (HFSWR) is modulated by six-degrees-of-freedom (6-DOF) motion, affecting the detection of the target and the remote sensing of ocean surface dynamics parameters. Commonly, motion compensation methods of shipborne HFSWR describe each aspect of the 6-DOF motion as the superposition of sinusoidal motion, which results in the effect of motion compensation affected by the precision of 6-DOF motion parameters. A motion compensation method based on dual reference radio frequency (RF) signals is proposed in this paper, without depending on a sinusoidal motion model to describe the 6-DOF motion. By using the motion compensation parameters, which are relevant to the motion attitude and calculated from the information of dual reference RF signals located onshore, the method realizes the compensation of shipborne HFSWR echo modulated by platform 6-DOF motion. This paper proposes the extraction of reference RF signals from radar echo and analyzes the influence of the location of the reference RF signals’ emission source on the motion compensation method. The result shows that a good motion compensation effect is achieved in eliminating the influence of 6-DOF motion modulation. In addition, a traversal of different reference RF signals’ emission source locations is conducted, and the simulation results show that the method proposed in this paper has universality.

Comb-based photonic neural population for parallel and nonlinear processing

It is believed that neural information representation and processing relies on the neural population instead of a single neuron. In neuromorphic photonics, photonic neurons in the form of nonlinear responses have been extensively studied in single devices and temporal nodes. However, to construct a photonic neural population (PNP), the process of scaling up and massive interconnections remain challenging considering the physical complexity and response latency. Here, we propose a comb-based PNP interconnected by carrier coupling with superior scalability. Two unique properties of neural population are theoretically and experimentally demonstrated in the comb-based PNP, including nonlinear response curves and population activities coding. A classification task of three input patterns with dual radio-frequency (RF) tones is successfully implemented in a time-efficient manner, which allows the comb-based PNP to make effective use of the ultra-broad bandwidth of photonics for parallel and nonlinear processing.

Plasma Polymerized SiCOH Films from Octamethylcyclotetrasiloxane by Dual Radio Frequency Inductively Coupled Plasma Chemical Vapor Deposition System.

We have fabricated porous plasma polymerized SiCOH (ppSiCOH) films with low-dielectric constants (low-k, less than 2.9), by applying dual radio frequency plasma in inductively coupled plasma chemical vapor deposition (ICP-CVD) system. We varied the power of the low radio frequency (LF) of 370 kHz from 0 to 65 W, while fixing the power of the radio frequency (RF) of 13.56 MHz. Although the ppSiCOH thin film without LF had the lowest k value, its mechanical strength is not high to stand the subsequent semiconductor processing. As the power of the LF was increased, the densities of ppSiCOH films became high, accordingly high in the hardness and elastic modulus, with quite satisfactory low-k value of 2.87. Especially, the ppSiCOH film, deposited at 35 W, exhibited the highest mechanical strength (hardness: 1.7 GPa, and elastic modulus: 9.7 GPa), which was explained by Fourier transform infrared spectroscopy. Since the low-k material is widely used as an inter-layer dielectric insulator, good mechanical properties are required to withstand chemical mechanical polishing damage. Therefore, we suggest that plasma polymerized process based on the dual frequency can be a good candidate for the deposition of low-k ppSiCOH films with enhanced mechanical strength.

Tuning of relative spatial distributions of a two-component ion system to improve sympathetic cooling efficiency

Herein, a fine-tuning method is proposed for the spatial distributions of a mixed three-dimensional (3D) ion system in dual radio frequency (RF) linear Paul traps to achieve efficient sympathetic cooling. The dual RF field matching, efficient capture method and transient process of the intrinsic micromotion of the mixed ion system are analyzed quantitatively by numerical simulations. The 3D correlation coupling characteristics between intrinsic micromotion and secular motion of ion system are obtained. It is found that reasonable low-frequency trapping potential can produce ultra-low-frequency pulling effect on ions with low mass-to-charge ratio (M/Q), which is beneficial to the dynamic coupling between ions with large M/Q differences. The effects of equivalent stiffness coefficients [Formula: see text] on the relative spatial configuration and dynamic coupling process of mixed 3D ion crystals with large M/Q differences are discussed. By tuning [Formula: see text], radial distributions of laser-cooled ions (LCIs) and sympathetically cooled ions (SCIs) that do not conform to the rules based on M/Q are realized. The optimum sympathetic-cooling efficiency occurs, where [Formula: see text] is approximately equivalent to [Formula: see text]. These results are applicable to studies such as cold ion clocks, quantum logic manipulation, antimatter synthesis, regulation of cold chemical reaction, and precise spectral measurements based on sympathetic cooling.

Comparative study on the dynamics and the composition between a pulsed laser deposition (PLD) and a plasma enhanced PLD (PE-PLD)

We report the effect of single and dual radio frequency (RF) plasma discharge on the composition and dynamics of a titanium plasma plume produced in a plasma-enhanced pulsed laser deposition (PE-PLD) system. The study was carried out in a nitrogen environment at different pressures. Time-resolved images, optical emission spectroscopy, and interferometry were employed to analyze the plasma. We were able to fit time-resolved images using different expansion models, obtained an expansion velocity between 6 and 30 × 103 m/s. Emission lines from N II, Ti II, were observed by changing the pressure and RF conditions. An increase in emission line intensity from N II was observed by increasing the pressure and RF power. We used Ti II lines to estimate the plasma temperature by using the Boltzmann equation, and we obtained the density from the Ti II line (454.9 nm) through Stark broadening. In addition, a Mach-Zehnder interferometer was employed to make a two-dimensional map of the electron density at early times. The estimated temperatures and densities are between 0.8 and 2.0 eV and 1017 – 1018 cm−3, respectively. The results suggest that increasing RF power enhanced the Ti-N atoms interaction, which is crucial in titanium nitride film applications.

Study on the high-efficiency sympathetic cooling of mixed ion system with a large mass-to-charge ratio difference in a dual radio-frequency field by numerical simulations

This study proposes a method to achieve stable confinement and efficient sympathetic cooling of a mixed ion system in dual radiofrequency (RF) traps by numerical simulations. The dynamic coupling behavior, sympathetic cooling mechanism, and efficiency-affecting factors of the dual RF ion trap system were quantitatively analyzed by molecular dynamics simulations, yielding the stable confinement conditions of three-dimensional (3D) cold ion system in dual RF confinement fields and the characteristics of 3D correlation coupling between intrinsic micromotion and secular motion. The transient processes of ion intrinsic micromotion were also investigated. Herein, a reasonable second trapping potential contributed to the efficient cooling of the ion system and suppression of its micromotion. The effects of the dual RF trapping field strength on the spatial configuration and the dynamic coupling process of sympathetic cooling were investigated in mixed 3D ion crystals with a large mass-to-charge ratio (M/Q) difference, which reveals that simultaneous stable trapping and matching dynamic modes are the key to achieving efficient sympathetic cooling in the two-component ion system. These results are applicable to studies such as quantum logic manipulation, antimatter synthesis, dark ion detection, regulation of ultracold chemical reaction processes, and precision spectral measurements based on sympathetic cooling.

Noise and distortion analysis of dual frequency comb photonic RF channelizers.

Dual frequency combs are emerging as highly effective channelizers for radio frequency (RF) signal processing, showing versatile capabilities in various applications including Fourier signal mapping, analog-to-digital conversion and sub-sampling of sparse wideband signals. Although previous research has considered the impact of comb power and harmonic distortions in individual systems, a rigorous and comprehensive performance analysis is lacking, particularly regarding the impact of phase noise. This is especially important considering that phase noise power increases quadratically with comb line number. In this paper, we develop a theoretical model of a dual frequency comb channelizer and evaluate the signal to noise ratio limits and design challenges when deploying such systems in a high bandwidth signal processing context. We show that the performance of these dual comb based signal processors is limited by the relative phase noise between the two optical frequency combs, which to our knowledge has not been considered in previous literature. Our simulations verify the theoretical model and examine the stochastic noise contributions and harmonic distortion, followed by a broader discussion of the performance limits of dual frequency comb channelizers, which demonstrate the importance of minimizing the relative phase noise between the two frequency combs to achieve high signal-to-noise ratio signal processing.

Combination of cryothermy with radiofrequency energy sources during hybrid atrial fibrillation ablation- impact on lesion quality and outcomes

Abstract Background Whereas pulmonary vein isolation lays the groundwork of endocardial atrial fibrillation (AF) ablation, it leaves patients undertreated. Additional substrate modification of the left atrium is often required, but lesion gaps and non-transmurality limit restoration of sinus rhythm. Moreover, some low voltage areas and conduction abnormalities are located exclusively on the epicardial aspect, and endocardial ablation alone does not address these issues. Our hybrid endo-/epicardial ablation strategy overcomes all these shortcomings. Purpose To test if the combination of epicardial cryo and radiofrequency (RF) ablation (dual) further improves the quality of ablation lines, and if the combined endo-/epicardial ablation can treat intractable cases of AF. Methods Twenty-six patients (13 paroxysmal, 13 long-persistent; 20 patients with 1–5 prior endocardial AF ablations) first underwent epicardial, total thoracoscopic beating heart ablation (TTA). Lesion sets included bilateral PVI, left atrial appendage closure, as well as superior (roof) and inferior (floor) interpulmonary vein lines. Roof and floor lines were alternatingly ablated by dual energy or RF only. Three months post TTA, endocardial mapping with optional gap closure completed this two-stage hybrid concept. Results Intraoperatively, 24 of 40 (60%) previous left or right endocardial PVIs were found incomplete. Apart from two post-TTA pacemaker insertions and one mini-thoracotomy for bleeding, respectively, no major morbidity was observed during follow up. The full protocol of the hybrid concept was applied in 24 patients. Forty-five of 47 (96%) epicardial PVIs were found gap-less during endocardial mapping, and the remaining 2 PVIs were readily re-ablated. In contrast, only 32 of 46 (70%) roof and floor lines were complete, and endocardial touch up was required in one of three patients. Of note, dual energy lines were more likely to be complete than RF only lines (17 of 22, 77%, vs. 15 of 24, 62%; p NS). Among 19 patients with continuous monitoring, only 4 (21%) had any AF burden including two patients within blanking period and before endocardial gap closure. The remaining 7 patients without continuous monitoring never experienced any symptoms related to recurrent AF, and serial Holter EKG were without pathology. Conclusions Hybrid ablation and dual energy provides a strong armamentarium for extra-pulmonary venous triggers of AF. Linear ablation lines were more likely to be gap-less and transmural, if dual energy sources were used. Dual energy TTA is highly efficient to restore sinus rhythm in patients with prior failed endocardial AF ablation. However, one of three patients will require endocardial gap closure to realize the full benefit of our two-stage hybrid concept. Further study will evaluate if dual energy lines outside the box can improve outcome in these challenging cases of intractable AF. Funding Acknowledgement Type of funding source: None

Study of titanium nitride film growth by plasma enhanced pulsed laser deposition at different experimental conditions

In this work, we have combined a conventional pulsed laser deposition (PLD) system with a dual radio frequency (RF) discharge to create a plasma-enhanced PLD system, known as (PE-PLD). This system was used to grow titanium nitride (TiN) thin films in order to study the feasibility of obtaining control over the nitrogen concentration and the deposition rate. The characterization of the RF plasma was performed using an RF compensated Langmuir probe, while atomic force microscopy (AFM), optical profilometry, Raman spectroscopy, and x-ray diffraction (XRD) were used to analyze the deposited thin films. We observed a significantly enhanced nitrogen concentration and deposition rate as a function of the RF plasma parameters, substrate temperature, and deposition time. Furthermore, we have observed that, using a dual RF configuration, it becomes possible to modify independently the flow and the bombardment energy of the nitrogen ions that impact the substrate. These means allow the control of the nitrogen concentration and deposition rate.

Dual frequency DBD: influence of the amplitude and the frequency of applied voltages on glow, Townsend and radiofrequency DBDs

To study dual frequency Townsend glow and radio frequency DBDs in an Ar/NH3 Penning mixture, different voltages are applied on each electrode of a plane/plane DBD. The one which has the higher amplitude and frequency, V H, determines the discharge regime. The other one, which has a lower amplitude and frequency, V L, is more similar to a bias voltage. V H frequency ranges from 50 kHz to 13.56 MHz and V L frequency from 1 kHz to 2 MHz. The amplitude of V L is always kept lower than the breakdown voltage. The discharge behavior is characterized by space and phase resolved optical emission spectroscopy and Fourier transform of the plasma induced light intensity. When the frequencies of two voltages are close to each other, V L higher than 150 V increases the discharge light intensity. In glow and Townsend discharges, this increase is attributed to the enhancement of the plasma density, due to the ions drift from the plasma bulk to the cathode, which produces a higher secondary electron emission. For the radiofrequency discharge, the enhancement of the light intensity is attributed to an enhancement of the positive space charge due to the higher voltage amplitude.When the frequencies of two voltages are very different, e.g. for V L between 1 and 100 kHz and a 5.5 MHz α-RF discharge, the behavior largely depends on V L amplitude. Above some low frequency (LF), the discharge tends to extinguish when V L amplitude is at its maximum. This is explained by a diminution of the plasma density resulting from the ion drift to the cathode due to V L. When V L is very high, it enhances the discharge intensity. This discharge amplification is associated with a transition from α to γ RF mode, which only occurs when the two voltages have the same polarity. Whatever the RF discharge mode, γ or α, the discharge is diffuse. To determine the interest of LF-RF dual frequency DBD for the PECVD, SiOx coatings, made with a single and a dual LF-RF frequency DBDs, are compared. It is concluded that the ɣ dual frequency removes OH functions from the material lattice and densifies the layer.

On the physical layer security of hybrid RF-FSO system in presence of multiple eavesdroppers and receiver diversity

This paper investigates the physical layer security (PLS) performance analysis for dual hop mixed radio frequency (RF)-hybrid RF/free space optics (FSO), the first hop is considered as RF and second hop consists of two independent RF and FSO links and hybrid RF-RF/RF-FSO with two separate dual hop paths including RF-RF and RF-FSO links. The communication takes place in the presence of RF as well as optical based eavesdroppers which are trying to intercept the signal from legitimate links. Moreover, considering an urban environment the RF links are modelled by Rayleigh distribution and the FSO links are characterized by Málaga (M) distribution. To investigate the system, secrecy performance metrics such as secrecy outage probability (SOP) and effective secrecy throughput (EST) are derived in its closed form. The effect of selection combining (SC) and maximal ratio combining (MRC) diversity techniques on the system performance is also depicted. In addition, some practical issues of FSO links such as the effect of atmospheric turbulence, optical signal detection techniques and pointing error effects on the system performance are discussed. To get more insight, the asymptotic expressions are obtained for each scenario. Then the results are compared with results obtained for mixed FSO/RF system and also discussed in brief. Finally, the results are verified through Monte-Carlo simulation.

Construction of Hybrid Dual Radio Frequency RSSI (HDRF-RSSI) Fingerprint Database and Indoor Location Method.

Radio frequency communication technology has not only greatly improved public network service, but also developed a new technological route for indoor navigation service. However, there is a gap between the precision and accuracy of indoor navigation services provided by indoor navigation service and the expectation of the public. This study proposed a method for constructing a hybrid dual frequency received signal strength indicator (HDRF-RSSI) fingerprint library, which is different from the traditional RSSI fingerprint library constructing method in indoor space using 2.4G radio frequency (RF) under the same Wi-Fi infrastructure condition. The proposed method combined 2.4G RF and 5G RF on the same access point (AP) device to construct a HDRF-RSSI fingerprint library, thereby doubling the fingerprint dimension of each reference point (RP). Experimental results show that the feature discriminability of HDRF-RSSI fingerprinting is 18.1% higher than 2.4G RF RSSI fingerprinting. Moreover, the hybrid radio frequency fingerprinting model, training loss function, and location evaluation algorithm based on the machine learning method were designed, so as to avoid limitation that transmission point (TP) and AP must be visible in the positioning method. In order to verify the effect of the proposed HDRF-RSSI fingerprint library construction method and the location evaluation algorithm, dual RF RSSI fingerprint data was collected to construct a fingerprint library in the experimental scene, which was trained using the proposed method. Several comparative experiments were designed to compare the positioning performance indicators such as precision and accuracy. Experimental results demonstrate that compared with the existing machine learning method based on Wi-Fi 2.4G RF RSSI fingerprint, the machine learning method combining Wi-Fi 5G RF RSSI vector and the original 2.4G RF RSSI vector can effectively improve the precision and accuracy of indoor positioning of the smart phone.

Sub-Sm–1 electromagnetic induction imaging with an unshielded atomic magnetometer

Progress in electromagnetic induction imaging with atomic magnetometers has brought its domain to the edge of the regime useful for biomedical imaging. However, a demonstration of imaging below the required 1 Sm−1 level is still missing. In this Letter, we use an 87Rb radio frequency atomic magnetometer operating near room temperature in an unshielded environment to image calibrated solutions mimicking the electric conductivity of live tissues. By combining the recently introduced near-resonant imaging technique with a dual radio frequency coil excitation scheme, we image 5 ml of solutions down to 0.9 Sm−1. We measure a signal-to-noise ratio of 2.7 at 2 MHz for 0.9 Sm−1, increased up to 7.2 with offline averaging. Our work is an improvement of 50 times on previous imaging results and demonstrates the sensitivity and stability in unshielded environments required for imaging biological tissues, in particular for the human heart.