Radio Frequency Processing Research Articles

Hot air-assisted radio frequency drying of apricots: Mathematical modeling study for process design.

Conventional hot air and solar energy processes have been used for apricot. These processes had adverse effects on the quality due to the longer process times, and this indicates the need for an innovative approach. Radio frequency (RF) processing has innovation potential for drying with its volumetric heating feature, but an optimal process should be designed for process efficiency in industrial-scale applications. Therefore, the objective of this study was to confirm the RF process for industrial-scale apricot drying. For this purpose, a mathematical model was developed to predict temperature and moisture content change of apricots during drying, and experimental validation study was carried out. For the RF drying process, pre-dried apricots (0.58-0.75kg water/kg dry matter, db) by solar energy were used. The purpose was to start the RF process at a suitable moisture content level as this process was not feasible to apply directly due to the high initial moisture content of apricots (up to 4kg water/kg dry matter, db). RF drying experiments were carried out in a 10kW hot air-assisted (50-60°C) staggered through electrode system. Optimum electrode gap was 81mm with 2500V potential of the charged electrode. Final moisture content of the dried apricots was 0.25-0.33kg water/kg dry matter (db). Following the model validation for temperature and moisture content change, industrial-scale apricot drying scenarios were demonstrated to confirm the RF process for feasibility and process design. PRACTICAL APPLICATION: A comprehensive mathematical model was developed for radio frequency (RF) drying of apricots. This model was experimentally validated with respect to the temperature and moisture content change. Various process design studies were carried out for an industrial-scale apricot drying process to confirm the process feasibility. With this background, the results of this study can be directly used in an industrial drying for an optimal process design and energy efficiency.

Computational study for natural convection effects on temperature during batch and continuous industrial scale radio frequency tempering/thawing processes

Radio frequency (RF) processing have been used for tempering and thawing. There have been significant experimental and mathematical model based studies for this process especially in the last two decades. The modeling studies applied the convective boundary condition with effective heat transfer coefficient and constant medium temperature in through field flat plate RF systems. The objective of this study was first to develop a mathematical model for conjugate heat transfer (natural convection) in a staggered through field electrode RF system and to use this model for natural convection effects in industrial scale processes. For this purpose, the developed comprehensive mathematical model was experimentally validated using the data from frozen tuna samples. The air temperature variation was also used for validation. Then, the developed model was used in industrial scale process simulations with the presence of natural convection. The industrially preferred flat plate systems were used in this part to determine the temperature and electric field evolutions. The results demonstrated the significant effect of the natural convection on sample surface temperature distribution and temperature change of air within the cavity. The evolved natural convection resulted in the variation of the heat transfer coefficient along the sample surfaces with significant changes in temperature. Based on these results, it might be concluded that the effect of air temperature change within the cavity during an RF processes should also be controlled and considered for industrial system design and process optimization.

Hybrid Precoding and Combining Strategy for MMSE-Based Rate Balancing in mmWave Multiuser MIMO Systems

In this paper, a new hybrid precoding and combining method is proposed for the downlink of multiuser multiple-input multiple-output (MU-MIMO) millimeter wave (mmWave) channels. The proposed method designs the precoders and combiners for radio frequency (RF) and baseband processing, respectively, based on the minimum mean square error (MMSE) criterion and the rate fairness among users. To design the RF precoder and combiners implemented by phase shifters, a new matrix factorization algorithm is devised by combining the gradient method with the projection to the nearest unitary matrix. Under the total transmit power constraint, the proposed factorization method increases the achievable rate by making the columns of the RF precoder near-orthogonal and growing the Frobenius norm of the baseband precoder. In addition, a new MMSE-based rate balancing algorithm is proposed to design the baseband precoder and combiners in terms of maximizing the minimum user rate. The proposed rate balancing scheme iteratively updates the baseband precoder, the transmit power constraint for the baseband precoder, the baseband combiners, and the weighting vector for rate balancing. Through theoretical analysis, it is shown that the proposed design method has a polynomial complexity order. Numerical simulations present that the proposed matrix factorization method outperforms existing schemes requiring low computational complexity and the proposed rate balancing scheme converges to a stationary point satisfying the total transmit power constraint. Moreover, simulation results in MU-MIMO channels are provided to show that the proposed design scheme performs better than existing hybrid processing schemes while achieving the minimum user rate close to the upper bound of MMSE processing.

Radio-frequency (RF) room temperature plasma treatment of sweet basil seeds (Ocimum basilicum L.) for germination potential enhancement by immaculation

Ocimum basilicum L. is an antiviral and immunity boosting medicinal plant and culinary herb. Potential use of sweet basils in COVID 19 prevention and management is making its demand rise. This study is aimed at germination potential enhancement of sweet basil seeds. Reported study is evidenced with scientific data of radio-frequency cold plasma treatment using Ar + O2 feed gas. O. basilicum seeds, placed inside the rotating glass bottle, were directly exposed to RF (13.56 MHz) plasma produced in Ar + O2 feed gas. Seed treatment was done using RF source power (60 W, 150 W, 240 W), process pressure (0.2 mbar, 0.4 mbar, 0.6 mbar), and treatment time (5 min, 10 min, 15 min) at different combinations. Results show that, the most efficient treatment provide up to ∼89 % of the germination percentage which is an enhancement by 32.3 % from the control. SEM images revealed slight shrinkage in the seed size with eroded appearance over the seed. Enhancement of lipid peroxidation, show that oxidation of seed coat may propagate internally. Water imbibition analysis, of the treated seeds, was carried out for 2−12 hours. Further analysis of seed weight, on every one hour, after soaking shows enhanced water absorption capability except the treatment at 240 W, 0.6 mbar and 15 min. Plasma treatment enhanced carbohydrate content and protein content which is reported to be due to increased primary metabolism. Whereas, increased activity of secondary metabolism results in the enhancement of enzymatic (catalase) and non-enzymatic antioxidants (proline). Vital growth parameters, such as SVI I and SVI II, got amplified by 37 % and 133 % respectively after treatment. Ameliorative effects of plasma treatment are found highly significant with a positive and significant correlation value (p < 0.01) between germination percentages, SVI I, SVI II, carbohydrate, protein and proline show their interrelationship. Ar + O2 plasma treatment is found to bring forth significant changes in the O. basilicum seeds which eventually enhanced the germination potential and it could be a very promising technology for the medicinal crop.

Intelligent reflected surfaces assisted code domain non-orthogonal multiple access scheme

Abstract The propagation medium plays a crucial role in any wireless communication networks, the channel between the transmitter and the receiver, deteriorate the quality of the received signal due to the uncontrollable interactions such as scattering, reflection, and refraction in the channel with the surrounding objects. To overcome this challenge, the recent advent of recongurable intelligent surfaces can be helpful, in which the network operators can control the radio waves, eg, the phase, amplitude, frequency, and even polarization, of the impinging signals without the need of complex decoding, encoding, and radio frequency processing operations. On the other hand, few research papers reported an efficient code domain non orthogonal multiple access (NOMA) such as Interleave division multiple access (IDMA) system for wireless information transfer. Persuaded by the capability of this arising RIS technology, the present article is aimed to provide the modified framework of IDMA (code-domain NOMA) communication system based on RIS technology. Simulation results demonstrate that the proposed system achieves better SNR performance than the conventional IDMA framework.

Effects of various directional movements of milled rice on radio frequency heating uniformity

Mixing and moving of samples during radio frequency (RF) processing have been demonstrated to be efficient ways for improving the heating uniformity. However, the current single or limited moving direction of samples requires a comprehensive and systematic investigation of combined movements in multi-directions. The purpose of this research was to compare the RF heating uniformity of milled rice with movement and layer/part rearrangement in three directions, as well as mixing. The results showed that the RF heating uniformity was not significantly (P > 0.05) improved when the rice samples were moved horizontally and only under the top electrode, while slightly improved for moving the rice samples gradually in and out of the two sides below the top electrode. Moving samples in vertical direction, rearranging sample parts horizontally and layers vertically all clearly improved the RF heating uniformity. Mixing with two times was the most effective method to improve the RF heating uniformity. These results may provide the useful methods to ensure the RF heating uniformity in industrial applications and help to develop effective RF treatment protocols in low-moisture granular agricultural products.

Heating of milk powders at low water activity to 95°C for 15 minutes using hot air-assisted radio frequency processing achieved pasteurization

Salmonella persistence in milk powders has caused several multistate foodborne disease outbreaks. Therefore, ways to deliver effective thermal treatment need to be identified and validated to ensure the microbial safety of milk powders. In this study, a process of hot air-assisted radio frequency (HARF) followed by holding at high temperatures in a convective oven was developed for pasteurization of milk powders. Heating times were compared between HARF and a convection oven for heating milk powders to a pasteurization temperature, and HARF has been shown to considerably reduce the come-up time. Whole milk powder (WMP) and nonfat dry milk (NFDM) were inoculated with a 5-serotype Salmonella cocktail and equilibrated to a water activity of 0.10 to simulate the worst case for the microbial challenge study. After heating the sample to 95°C using HARF, followed by 10 and 15 min of holding in the oven, more than 5 log reduction of Salmonella was achieved in WMP and NFDM. This study validated a HARF-assisted thermal process for pasteurization of milk powder based on previously collected microbial inactivation kinetics data and provides valuable insights to process developers to ensure microbial safety of milk powder. This HARF process may be implemented in the dairy industry to enhance the microbial safety of milk powders.

Numerical Investigation of the Deformable Porous Media Treated by the Intermittent Microwave

A 2D axi-symmetric theoretical model of dielectric porous media in intermittent microwave (IMW) thermal process was developed, and the electromagnetic energy, multiphase transport, phase change, large deformation, and glass transition were taken into consideration. From the simulation results, the mass was mainly carried by the liquid water, and the heat was mainly carried by liquid water and solid. The diffusion was the dominant mechanism of the mass transport during the whole process, whereas for the heat transport, the convection dominated the heat transport near the surface areas during the heating stage. The von Mises stress reached local maxima at different locations at different stages, and all were lower than the fracture stress. A material treated by a longer intermittent cycle length with the same pulse ratio (PR) tended to trigger the phenomena of overheat and fracture due to the more intense fluctuation of moisture content, temperature, deformation, and von Mises stress. The model can be extended to simulate the intermittent radio frequency (IRF) process on the basis of which one can select a suitable energy source for a specific process.

Effect of radio frequency processing on physical, chemical, rheological and bread-baking properties of white and whole wheat flour

Low moisture foods with their low water activity do not favor microbial growth, but they are liable to contamination. Hence, decontamination process is required. Radio frequency (RF) processing is possible approach for this purpose with its heating efficiency. Considering the wheat flour in food processing and RF as a promising thermal approach, the objectives of this study were to process white and whole wheat flours with RF heating and determine the physicochemical changes (sedimentation value, falling number, phenolic content, antioxidant activity and farinograph and extensograph properties). In addition, bread loaves produced from the RF processed flours were also analyzed for loaf weight, volume, textural properties and color changes.The results indicated that the RF process did not cause a significant change in the physicochemical and rheological properties of the flours while the RF process to temperature range of 75–85 °C resulted in certain changes in the bread loaves. In overall, RF process was verified for thermal processing of flours, and it was concluded that a process design and optimization study should be considered for quality changes of the original and final products.

Radiofrequency pasteurization against Salmonella and Listeria monocytogenes in cocoa powder

In this study, thermal processes were developed for cocoa powder against Salmonella and Listeria monocytogenes in a pilot Radiofrequency (RF) unit and validated using their respective surrogates Enterococcus faecium NRRL B-2354 and Listeria innocua. For 1.0 kg cocoa powder samples, RF heating to 90 °C provided 1.74–1.84 log reduction of E. faecium. A 48 min holding post-RF heating provided an additional 3.65 and 2.24 log10 CFU/g reduction of E. faecium for insulated and non-insulated samples, respectively. Compared to E. faecium, L. innocua was less resistant to RF heating in aw 0.45 cocoa powder; RF heating to 75 °C coupled with 24 min insulated holding resulted in an additional 5.64 log10 CFU/g reduction. These data suggested that E. faecium was a conservative surrogate strain for controlling Salmonella and L. monocytogenes during RF processing of cocoa powder. To achieve maximal microbial reduction and improve energy efficiency, an insulated holding following RF heating is highly recommended. According to the predictive line obtained from the Bigelow model, a 7.6 min RF heating plus 48 min insulated holding attained a 5-log reduction of E. faecium without a negative impact on the color of cocoa powder.

Implantable wirelessly powered optoelectronic device for optogenetics

In vivo optogenetics provide special and powerful capabilities in regulation of neurons, research of neural circuits and even in treatment of brain diseases. However, conventional hardware for such studies tethers the experimental animals to remote light sources, power sources, or other functional modules, which imposes considerable physical constrains on natural behaviors and limits the range of the experiment. To enable flexible and convenient optogenetic manipulation of neural circuit with finite disruption of animal behavior, a wirelessly powered optoelectronic device, composing mainly of a radio frequency (RF) energy harvester and a high-performance GaN-based light-emitting diode (LED), is demonstrated and can be used to construct an implantable optrode for optogenetics. The wireless RF power signal is collected through an antenna and a two-stage voltage doubling rectifier circuit, and finally converted into high-amplitude DC voltage. Provided with 25-dBm RF power with a distance of 0.2 m, the RF energy harvesting and processing circuit can output a stable 2.81 V DC voltage and drive the designed GaN-based LED to work normally. After being successfully lit, the emission peak wavelength of the LED locates 455 nm and the output optical power density reaches 214.9 mW / mm2, which is fully capable of activating light-sensitive ion channel channelrhodopsin-2. The total area of the device is 3 mm × 3.2 mm, which is suitable for subdermal implantation.

Pasteurization of dried basil leaves using radio frequency heating: A microbial challenge study and quality analysis

The current microbial reduction techniques have low consumer acceptance or may have an adverse effect on the quality of spices and herbs. This requires a need for an alternative decontamination method that can effectively reduce the microbial load and minimize the food quality losses. Radio frequency (RF) heating is a dielectric heating method that has been proven effective to pasteurize various low-moisture foods. The present research was designed to evaluate the efficacy of RF heating for the reduction of Salmonella in dried basil leaves, evaluate the suitability of Enterococcus faecium NRRL B-2354 as a surrogate for Salmonella, and assess the quality of dried basil leaves post RF treatment. Dried basil leaves inoculated with a Salmonella cocktail or E. faecium were conditioned to a higher moisture content such that the moisture content of the treated sample post RF treatment fall within the typical range. The inoculated samples were packaged in the teabag and placed in the identified cold spot (top center) of a laminated paper tray filled with uninoculated sample. Samples were subjected to RF heating for 45, 55, and 65 s during which the cold-spot temperature reached 65, 80, and 100 °C, respectively. The results showed that at 55 s, Salmonella and E. faecium population decreased by 4.8 and 2.7 log CFU/g, respectively. Both microorganisms reached below the detection limit (>6.5 log CFU/g reduction) at 65 s of RF heating. Therefore, the quality analysis of the dried basil leaves was performed with the samples treated with RF for 65 s. The results showed that the RF heating had no significant effect on the quality parameters (color, total volatiles, total phenolics, and antioxidant activity) of the dried basil leaves. Therefore, RF processing results in rapid heating of the dried basil leaves enhancing food safety with insignificant impact on quality. Furthermore, the food processing facility may use E. faecium as an appropriate surrogate for Salmonella when conducting an in-plant validation study.

Effect of radio frequency tempering on the color of frozen tilapia fillets

Radio frequency (RF) processing has been widely used for thawing and tempering of frozen products for further processing and consumption. RF tempering could improve the color and other qualities compared with traditional methods, but the specific mechanism to ensure the color is not clear. Effect of different RF treatments on the color of frozen tilapia fillet was to investigate in this study. The color of tempered tilapia fillets under different RF conditions (based on power (300, 600, 900 W) and electrode gap (10, 12, 14 cm)) and the myoglobin oxidation, lipid oxidation, and moisture migration and other influencing factors on color were determined. Relationships between relative impact indicators and color attributes were investigated by multivariate analysis (visual network analysis). The results showed that hue angle and whiteness between 600 W and other power had significant differences under the electrode gap of 10 cm and 14 cm. The difference in color attributes under different RF tempering conditions had a relatively strong correlation with pH, migration of bound water to immobilized water, content of immobilized water, and drip loss during RF tempering. Besides, the difference of color attributes weakly correlated with myoglobin oxidation and lipid oxidation during RF tempering.

Photonic RF and Microwave Fractional Differentiation, Integration, and Hilbert Transforms With Kerr Optical Micro-Combs

Integrated Kerr micro-combs are a powerful source of multiple wavelength channels for photonic radio frequency (RF) and microwave signal processing, particularly for transversal filter systems. They offer significant advantages featuring a compact device footprint, high versatility, large numbers of wavelengths, and wide Nyquist bands. We present our recent progress on photonic RF and microwave high bandwidth temporal signal processing based on Kerr micro-combs with comb spacings from 49GHz to 200GHz. We focus on integral and fractional Hilbert transforms, differentiators as well as integrators. The future potential of optical micro-combs for RF photonic applications in terms of functionality and ability to realize integrated solutions is also discussed.

A novel method for utilizing RF information from IEEE 802.11 frames in Software Defined Networks

Wireless security research using Radio Frequency (RF) data is complex and costly, often requiring expensive equipment and extensive offline processing. To make wireless research more accessible, we have integrated RF signal features with the existing IEEE 802.11 frame layer 2/3 data using the Software Defined Networking (SDN) paradigm. Combining low-cost RF hardware, a novel SDN processing method, and unique RF processing architecture has resulted in a framework that enables advanced wireless security and control research at a significantly lower cost. The method for enabling such functionality consist of the following stages:•During the demodulation process, extract Carrier Frequency Offset (CFO) and Pilot Sub-Carrier Offset from the Frequency Offset Correction section, in addition to the Vector Magnitude from the equalization section.•Append the new RF information to the wireless frame buffer and pass it to the SDR kernel driver module to further process before transferring them to a P4 application via a single API instantiation.•Compile a custom P4 application that combines the new RF features alongside higher OSI layer features to perform advanced networking, security, or control plane operations.

On Efficient DCT Type-I Based Low Complexity Channel Estimation for Uplink NB-IoT Systems

Channel estimation is a challenging and timely issue for the 3rd Generation Partnership Project (3GPP) standardized low power wide-area network technology named narrowband Internet of Things (NB-IoT). Channel estimation is crucial to achieve extended radio coverage, energy efficiency, coherent detection, and channel equalization for signal repetition dominated NB-IoT uplink transmission. The NB-IoT inherits simplified baseband radio frequency processing, physical channels, reference signal structure, and numerology from existing Long Term Evolution (LTE) systems to save power and costs. Thus, channel estimation methods extensively employed in LTE systems may not be applied to the NB-IoT uplink systems. In this paper, efficient discrete cosine transform type-I (DCT-I)-based transform-domain channel estimation approaches are proposed by modifying the original definition of DCT-I. The proposed methods can mitigate the problems experienced in the discrete Fourier transform (DFT)-based channel estimation, such as signal aliasing error, and border effect. The proposed approaches improve channel estimation precision by reducing signal distortion from the high-frequency region in the time-domain when non-sample-spaced path delays exist in multipath fading channels. Signal aliasing error experienced from the virtual subcarriers is also minimized with the anticipated schemes. The proposed methods are applied on simple least squares (LS) estimates in time-domain to eliminate estimation noise. The viability of the proposed estimators is verified as compared to the conventional LS, DFT-based de-noising LS, and standard DCT-I based methods through extensive numerical simulations. Based on the numerical simulations, the proposed estimators show better mean square error and bit error rate performances than their competitors in extremely low coverage conditions.

Hybrid Beamforming for Sum Rate Maximization in Wideband Multi-User MIMO Relay Systems

Hybrid precoding has a great potential to achieve near-optimal performance with few radio-frequency (RF) chains in comparison to the number of antennas. This paper proposes a novel hybrid beamforming solution for sum rate maximization in a wideband multi-user multi-input multi-output (MU-MIMO) relay system. The problem at hand is non-convex and hence mathematically intractable due to the constant modulus constraints associated with the analog beamforming design at communicating nodes shared by all sub-carriers. Furthermore, relaying in MU-MIMO systems under frequency-selective channels is also a challenging task as it requires complicated signal processing. To address this problem, source analog beamformer, relay RF combiner and phase-only processing component at each destination are obtained by deriving the common RF processing matrix which enables beamforming gain over all sub-carriers. This process involves reconstruction loss minimization for designing the required analog beamforming vectors having ability to maximize end-to-end signal-to-interference plus noise ratio (SINR). The relay analog precoder is designed by maximizing the received power at each destination through gain maximization of the equivalent baseband channel over the allocated frequency spectrum. To reduce the computational complexity of the iterative approach used to find the relay RF precoding matrix, the closed form expression is derived for achieving the desired objective. Finally, digital baseband processing components are obtained from the equivalent baseband channels by suppressing the interference among transmitted signals indirectly. Simulation results for different system configurations reveal that the proposed algorithm can achieve near-optimal performance.

Blanching effects of radio frequency heating on enzyme inactivation, physiochemical properties of green peas (Pisum sativum L.) and the underlying mechanism in relation to cellular microstructure

Fresh green peas require blanching to terminate enzymatic reaction induced quality deterioration before frozen storage. Radio frequency (RF) heating is a novel way of dry blanching for fruits and vegetables with high processing efficiency. In this study, blanching effects of RF heating on relative activities of lipoxygenase (LOX) and peroxidase (POD), physiochemical properties as well as cellular morphology changes of green peas were investigated. Results showed relative activities of pea LOX and POD reduced to 0.90 ± 0.78% and 1.10 ± 0.71%, respectively at 85 °C by RF heating with an electrode gap 105 mm. Weight loss, color, texture and electrolyte leakage of peas changed significantly with increasing temperature (60–85 °C). Ascorbic acid, chlorophyll and mineral contents had different loss after RF processing and long term heating at 115 mm exacerbated the loss of nutrients. Microstructure features showed the deconstruction of pea cell well and starch granule gelatinization.

Computational modelling of survival of Aspergillus flavus in peanut kernels during hot air-assisted radio frequency pasteurization

In recent years, radio frequency (RF) heating is getting popular as an alternative pasteurization method for agricultural commodities and low moisture foods. Computer simulation is an effective way to help understand RF interactions with food components and predict temperature distributions among food samples after RF treatments. In this study, a computer model based on Joule heating and thermal inactivation kinetic of A. flavus was established to predict both temperature distribution and microbial reduction among peanut kernels after RF processing. For the process validation, three 2-g peanut samples inoculated with 40 μL A. flavus were placed at three representative locations among 2.17 kg peanut kernels and subjected to various processing conditions in a 27.12 MHz, 6 kW RF heating unit together with hot air system. Results showed that the average difference of the sample temperature and microbial reduction between simulation and experiment was small with RMSE values of 0.009 °C and 0.012 °C, and 0.31 log CFU/g and 0.42 log CFU/g for peanut moisture contents of 7.56% and 12.02% w. b., respectively. Nonuniform RF heating resulted in the least lethality of A. flavus at the cold spot. The validated computer model was further used to estimate microbial reduction distributions at other target temperatures based on predicted temperature profiles. This computer model may help design the RF pasteurization protocols for peanut kernels without extensive experiments in food industry.

Development of effective drying strategy with a combination of radio frequency (RF) and convective hot-air drying for inshell hazelnuts and enhancement of nut quality

Drying characteristics of combined radio frequency (RF) and hot-air (HA) were investigated for inshell hazelnuts (Corylus avellana L.), which have air-gap between kernel and shell (shell, kernel, and air-gap between them). Inshell hazelnuts were subjected to HA, HA followed by RF (HAFRF), RF followed by HA (RFHA), and HA assisted RF (HARF) drying (simultaneous process). Fiber optic sensors were used to monitor temperature profiles for both hazelnut kernels and shells at three representative locations (center, edge, and corner) in a tray in 6-kW 27.12-MHz RF system with or without HA (~75 °C). RF heating resulted in higher kernel temperature than shell and was effective to remove kernel moisture. When RF heating was applied during or before HA drying, energy efficiency, drying efficacy, and nut quality were enhanced. This study provided a better understanding of drying characteristics of combined RF and HA process and suggested efficient RF-implemented drying strategies for inshell hazelnuts.