Spiral Coil Research Articles

PCB Planar and Filamentary Planar Spiral Coils based Underground Magnetic Induction Communication with Enhanced Channel Model

A novel idea of using compact filamentary and printed circuit board (PCB) planar spiral coils for the magnetic induction (MI) based underground (UG) communication to achieve high received power and enhanced transmission distance is proposed. In the existing system, non-planar coils were employed as transceivers which lost their function due to their huge size and deployment difficulty. An enhanced MI UG channel model is proposed to accurately investigate the UG medium’s influence on the MI system performance by considering various soil properties that were considered negligible in the earlier models. An analytical approach to calculate self-inductance and mutual inductance of circular and square coils of filamentary planar and PCB planar spiral coils are described from which the communication parameters such as received power, path-loss, and signal-to-ratio are derived. The simulation results reveal that in both filamentary and PCB planar spiral coil, the square shape coil performs better than the circular coil. The filamentary planar spiral square coil (FPSSC) achieves 26.15% higher received power than the PCB planar spiral square coil (PPSSC) due to the former coil’s low resistance and strong mutual coupling. Further, the influence of coil parameters, coil misalignment, and soil properties on the received power is studied for both FPSSC and PPSSC systems, and their major performance influencing parameters are identified. The received power of the proposed FPSSC system exhibits a significant improvement of 31.24% as compared to the traditional non-planar MI coil system.

Development of an innovative rotating spiral heat exchanger with integrated microwave module for the olive oil industry

A new prototype of an integrated tube-in-tube heat exchanger with rotating spiral coil and microwave module is proposed. The prototype was installed in an industrial olive oil extraction plant and tested to determine how much it improved overall extraction performance of the plant and olive oil quality.Nominal mass flow rate showed that the prototype was perfectly integrated in the plant. Thanks to the transport action of the rotating spiral coil, the prototype did not affect the feed pressure of the olive paste from the crusher to the malaxer. Using the heat exchanger, malaxing time was reduced by 50% without decreasing oil extraction. The microwave module increased oil extractability.The new prototype applied to mechanical extraction of virgin olive oil enhanced the quantitative and qualitative composition of hydrophilic phenols without altering legal quality parameters or significantly modifying the volatile fraction.

Optimal Design of Spiral Coil EMATs for Improving Their Pulse Compression Effect

When chirp pulse compression technology (PCT) is applied in Electromagnetic Acoustic Transducers (EMATs), the frequency response characteristic of the EMAT testing system may be inconsistent with the chirp signal bandwidth. Furthermore, it causes a loss in the frequency spectrum and distortion of the ultrasonic echo waveform, leading to a decrease in the signal-to-noise ratio (SNR) and range resolution of the pulse compressed signal. To solve this problem which has not been further researched in the previous publications, we proposed a new circuit-field coupling finite element model for ultrasonic wave generation of the spiral coil EMAT for enhancing the pulse compression effect, and the excitation circuit for the EMAT is also considered in this model. Furthermore, the effects of the diameter of the spiral coil wire, matching method of the impedance matching network, and parameter of the matching components on the peak and width of the main lobe after pulse compression were analysed through simulations and experiments. Subsequently, the optimal combination of the EMAT coil conductor diameter, impedance matching method, and matching component parameters were determined and verified by experiments. The results show that the SNR and range resolution of the pulse compressed ultrasonic signal can be largely enhanced when the diameter of the spiral coil wire, impedance matching method, and the parameter of the matching components are chosen carefully. When the aforementioned parameters are appropriately selected, the amplitude of the main lobe can be increased 3.16 times, and the width of the main lobe is reduced by 31.7%.

Design of double-layer parallel printed spiral coil for wireless power transfer applied to rotating equipment

Wireless power transfer (WPT) is a promising technology for remotely powering a wide variety of applications in rotating electronic devices. Although this method was introduced a long time ago, it still faces several challenges. The main challenge is that the traditional Litz coil cannot be fixed in high-speed rotating equipment, and the existing single-layer printed spiral coil has low quality factor. Therefore, to increase the coils’ quality factor and improve the transmission efficiency and output power of the system, a novel double-layer parallel coil model is proposed and compared with a conventional single-layer coil. Through experimental validations and simulation analysis, this study shows that, when the system frequency is 100 kHz and a double-layer parallel coil is employed, the quality factor of the coil is enhanced by 57.4 % compared to a single-layer coil. In the case of an input voltage of 8 V and a transmission distance of 10 mm, the output power of the double-double coil is increased by 1.65 W compared with the single-single coil, and the transmission efficiency is increased by 22.5 %, thereby realizing efficient WPT and providing reliable power transmission for sensors on rotating machinery such as helicopters and aero engines.

A wireless passive pressure sensor using microstructured ferromagnetic films with tunable effective permeability

This paper presents a novel LC-based passive wireless flexible pressure sensor that employs microstructured ferromagnetic films with tunable effective permeability. The proposed device consists of a micromachined planar spiral coil and a polymer film with cilia arrays (CAs) realized by the ferrofluidic instability principle. The effective permeability of the polymer film can be tuned by deforming the CAs with externally applied pressure, which can be estimated in turn by detecting the resonant frequency of the device using the phase-dip technique. The fabrication parameters for synthesizing different dimensions and densities of CAs were investigated as well. Devices of different CA densities were measured and discussed. The measured results showed that the device quality factor and phase change both increased with applied pressure. Due to this characteristic, the proposed device is advantageous over typical capacitive LC-based devices and performs better in wireless interrogation while maintaining the sensitivity of pressure sensing.

Enhancement of Wireless Power Transmission Efficiency and Flexibility via an Optimized Three-Dimensional Coupled Magnetic Resonance System with Double Transmitter Coil

Wireless power transmission (WPT) has gained considerable attention in recent years due to its convenience. Moreover, various research especially 3D coil structure studies in WPT are emerging through continuous research. However, most of these power sources are too volumetric to charge mobile devices, and the recently proposed 3D couple magnetic resonance system (CMRS) represents not only a lower power transmission efficiency (PTE) than the 2D system, but the PTE decreases sharply as the distance between the coils increases. To improve these drawbacks, this study proposes a novel approach to power mobile devices using a 3D spiral coil structure and a double transmitter coil system simultaneously. The mathematical model is presented, and three different coil structures are designed to evaluate the most power-efficient 3D coil structure. The proposed model is obtained and verified based on the simulation and experiment results. The result showed that when the distance between coils is the closest (8 mm), the PTE was 55.77%, which is improvement compared to that of the pervious 3D CMRS studies. Moreover, the PTE did not decrease sharply since our proposed system has the double resonance frequencies. Mathematical model, simulation, and experiment are provided to verify the feasibility of the proposed model.

Development of an Omnidirectional SH0 Mode Electromagnetic Acoustic Transducer Employing a Circumferential Periodic Permanent Magnet Array

This work presents a new omnidirectional electromagnetic acoustic transducer (EMAT) employing a circumferential periodic permanent magnet array, which was proposed for generating and receiving shear-horizontal (SH) guided waves in an aluminum plate. The novel transducer consisted of 12 axially polarized sector magnets arranged in a circle, and the magnetic field directions of adjacent magnets were opposite. A spiral coil was arranged under the magnet array. A vertical magnetic field generated by the magnets and the circumferential eddy current generated by the spiral coil formed a Lorentz force in a plate acting in the radial direction of this new omnidirectional EMAT. By controlling the sizes of the sector magnets, the omnidirectional SH0 mode (fundamental SH guided wave mode) was generated. To maximize the output of the EMAT at the given excitation frequency, it was proposed to add acrylic spacers between the sector magnets and determine the size of the magnet based on the frequency bandwidth of the excitation signal while also optimizing the omnidirectional sound field. A three-dimensional (3D) finite element model of the EMAT was established using COMSOL Multiphysics to perform numerical simulations, and the effectiveness of the optimization method was verified. The effectiveness was verified by experiments. The simulations and experiments showed that the proposed EMAT could generate omnidirectional SH0 mode guided waves in an aluminum plate.

A low-power portable scanner for body-worn Wireless Resistive Analog Passive (WRAP) sensors for mHealth applications

Collecting multiple physiological signals with an embedded computing device can be more effective with battery-less zero-power sensors. We have previously reported our battery less, body-worn sensors named “Wireless Resistive Analog Passive (WRAP) sensors”. Here, we report design, prototyping and functional validation of a low-power, small and portable signal acquisition (scanner, revision 4) device for these sensors. The scanner couples with these sensors inductively by on-board printed spiral coils (PSC) that rely on impedance mismatch technique for physiological signal collection. The scanner was fully tested, characterized, and validated in lab, as well as through deployment to users’ home. As a test case, we show results of the scanner measuring temperature from WRAP temperature sensors with relative error within 0.01% range. The scanner measurement can distinguish between temperature of 1 °F difference and it shows excellent linear dependence between actual and measured resistance (R2=0.998). The scanner consumes 45.54 mJ of energy per scanning burst, it weighs 110 grams and measures 5.9”X 2.9”X 0.25”. This device has demonstrated the possibility of small, low-power portable scanner for zero-power WRAP sensors that shows promise for real-life data collection from our study participants in Memphis Smart and Connected Community (S&CC).

Investigating the effect of inserting longitudinal fins on the overall thermal performance of spirally coiled tubes

Flow in curved pipes have been considered as a well-known technique of passive enhancement of heat transfer rate. However, there exists a lack of research considering the impact of geometrical modifications on heat transfer properties of spiral coils. In the present study, thermal and hydrodynamic behavior of the flow in spirally coiled tubes equipped with longitudinal internal fins are numerically studied. Steady three dimensional flow of water is simulated. The geometrical parameters in the present study include fin number, fin height, and fin width. Results reveal that for the spirals with a pair of horizontal fins, the increase in fin protrusion leads to PEC as high as 2.99. However, inappropriate orientation of longitudinal fins severely deteriorates the heat absorption capability of the spiral while imposing excessive pressure drop. This inefficiency is attributed to the disruption in formation of Dean vortices due to the presence of radial bumps. Thus, four-fin and three-fin configurations are generally inefficient. Changing the fin orientation in the two-fin geometries from horizontal to vertical lead to a similar inefficiency with the PEC falling as low as 0.24. Finally, the effect of local curvature on the thermal behavior of the spiral tube is investigated.

Design and optimization of printed spiral coils for wireless passive sensors

Monitoring physiological signals during regular life might provide many benefits including early detection of abnormalities and tracking the severities of diseases. A wireless connection between the passive sensor and the scanner eliminates the obtrusive wires, resolves battery-related issues, and makes it easy-to-use. We have previously proposed a wireless resistive analogue passive sensor technique that operates with the help of inductive coupling. The variation of resistive physiological transducer (secondary side) leads to amplitude modulation on the scanner coil (primary side). The design of printed spiral coil (PSC) on printed circuit board, significantly affects the performance of the overall system in terms of sensitivity, the output voltage change as a reflection of the transducer change. To optimize the PSC's profile and maximize the sensitivity, we employ three methods: iterative, analytical, and genetic algorithm (GA). The GA optimized PSCs, as the best result, have been fabricated and the measurement showed a sensitivity of 0.72 mƱ which has 5% (8.8%) deviation from the simulation (theoretical) results. This method can be utilized to design a PSC pair in near-field applications to transfer amplitude modulation with various sizes and fabrication constraints.

Analysis of inductive characteristics for various helical and spiral coil configurations supported by COMSOL Multiphysics. (Dept. E)

Wireless power transfer system has a major concern for several decades since various benefits have been included against wired counterpart. In this context, coupling structure has been investigated for various coils having different shapes of both magnetic cores and windings. This investigation is implemented based on a mathematical and modeling analysis to calculate inductive values of charging setups. This paper provides an accurate evaluation of inductive characteristics for the proposed coreless helical and spiral coils. The evaluation considers the dependence of inductive parameters on distance, geometry, and misalignment of coupling coils. In addition, the evaluation method is verified by the COMSOL software. Moreover, an accurate approximation of required inductive parameters is provided for the design of wireless charging system. Furthermore, four ferrite cores are provided for both winding types; and their coupling coefficients are examined to show the best configuration. Results show the validity of both theoretical and simulated analysis.

Precise Modeling of Mutual Inductance for Planar Spiral Coils in Wireless Power Transfer and Its Application

In magnetic coupling resonant wireless power transfer devices, planar spiral coils are often used as the coupling mechanism. In such application area, the coils are often wound sparsely with wide screw pitches and often under complex relative position. An accurate model of mutual inductance for planar spiral coils wound either densely or sparsely is established in this article. Utilizing Euler Angles, an exact expression of mutual inductance for a couple of planar spiral coils under arbitrary relative position is proposed. Based on this expression and geometric mean distance principle, a self-inductance expression for planar spiral coils is derived. Based on numerical calculation of the expressions proposed in this article, the influence of precession and spin angle on mutual inductance is studied; the method of determining radius of each turn when using traditional concentric circular filaments cluster approximation model for self- and mutual inductance calculation is studied; the difference of calculation results between the accurate model and the traditional approximation model is compared. Finite element simulation and experimental results verify the correctness of the proposed models.

Estimation of the Maximum Efficiency and the Load Power in the Periodic WPT Systems Using Numerical and Circuit Models

The article presents an analysis of the maximum efficiency and maximum load power, which are available to obtain in periodic wireless power transfer (WPT) systems. The numerical computations of the proposed WPT structures are performed using the finite element method and branch current method. Two theoretical models are discussed, i.e., a numerical model with simplified structure and boundary conditions as well as an equivalent circuit model is proposed to solve WPT systems with many magnetically coupled planar coils. A multivariate analysis is performed, which takes into account the variability of the number of turns, distance between a transmitting and receiving coil, and the frequency of an energy source. The outputs, such as overall efficiency, power of the source and power transferred to a load are discussed. The formulas for the load impedance required to maximize the efficiency or load power, which are taking into account the electrical parameters of the system resulting from its geometry, are presented. The results obtained from proposed models are consistent, which confirm the correctness of the adopted circuit model, which is less complex and faster to compute than numerical one. It is also possible to perform a quick assessment of electrical parameters of the analyzed WPT structure, using presented analytical formulas and numerical model or experimental data. The results allow for a detailed discussion of the dependence of the efficiency and power of the WPT system with respect to geometry of spiral coils.

Adjustable current waveform via altering the damping coefficient: A new way to reduce Joule heating in electromagnetic forming coils

The temperature rise of the working coil due to Joule heating is a very important issue in electromagnetic forming processes. A technically simple and cost-effective method was proposed to address this problem, which only needs to introduce an additional resistor in the discharge circuit. The core of this method is to alter the current waveform during the forming process by adjusting the damping coefficient of the discharge circuit. The effectiveness of the method was numerically analyzed in detail and verified by the experimental investigations. It has been demonstrated that the Joule heating in the coil can be significantly reduced when a resistor was applied, while ensuring the forming depth of workpiece unchanged. As an example, more than 50 % of the Joule heating in a bobbin coil can be decreased when a resistor of 400 mΩ is applied. Meanwhile, the versatility of the developed method was further verified through the analysis of an electromagnetic forming system with a spiral coil and a high-frequency discharge. Furthermore, this work found that the line resistance of discharge circuit should not be as small as possible. It has been proved that when the line resistance is already small, further reducing it has little effect on the improvement of forming efficiency, but it will greatly increase the Joule heating in the coil. The developed method of achieving adjustable current waveform and its application in reducing the Joule heating of coil could be of great significance to the development of electromagnetic forming.

Strip Size Optimization for Spiral Type Actuator Coil Used in Electromagnetic Flat Sheet Forming Experiment

Flat spiral coil for electromagnetic forming system has been modelled in FEMM 4.2 software. Copper strip was chosen as material for designing the actuator coil. Relationship between height to width ratio (S-factor) of the copper strip and coil’s performance has been studied. Magnetic field intensities, eddy currents and Lorentz force were calculated for the coils that were designed using six different 'S-factor' values (0.65, 0.75, 1.05, 1.25, 1.54 and 1.75), keeping the cross-sectional area of strip same. Results obtained through simulation suggest that actuator coil with S-factor ~ 1 shows optimum forming performance as it exerts maximum Lorentz force (84 kN) on work piece. The same coils was fabricated and used for electromagnetic sheet forming experiments. Aluminum 6061 sheets of thickness 1.5 mm have been formed using different voltage levels of capacitor bank. Smooth forming profiles were obtained with dome heights 28, 35 and 40 mm in work piece at 800, 1150 and 1250 V respectively.

Design of novel coil structure for wireless power transfer system supporting multi-load and 2-D free-positioning

In the classical WPT technology, when the load coil and the receiving coil are not aligned, the receiving power will be significantly reduced. In this paper, a new type of receiving coil named spiral add planar (SAP) coil is proposed, which can make the receiving power of the load coil almost independent of its position. The T-type equivalent circuit analysis method is used to analyze the transmission performance of the WPT system. By calculating the mutual inductance between non-coaxial coils, it can be proved theoretically that when the load coils are located at different positions, the mutual inductance between the SAP coil and the load coil is more stable comparing to the spiral coil or the planar coil. In addition, this SAP coil can support multiple loads and arbitrary movement of the load within the area of the SAP coil. This paper also proposed the concept of radius ratio (that is, the ratio of the radius of the load coil to the radius of the RX coil), and found that when the radius ratio is less than 1/2, the free-positioning characteristic is good. The simulation and experimental results show that when the load coil moves within the range of the SAP coil, the volatility of its S21 value is less than ± 1 dB.

Array Integration and Far-Field Detection of Biocompatible Wireless LC Pressure Sensors.

In this paper, three configurations of LC (inductor-capacitor) pressure sensors are developed, namely series LC pressure sensors, compact LC pressure sensors, and far-field LC pressure sensor tags. The modified silk protein films have been chosen as substrates due to their good biocompatibility and air/water permeability, which is suitable for continuously pasting such substrates on skin. For series LC pressure sensors, conducting wire is used to connect the flexible capacitor and spiral inductor. It exhibits good cycling stability and high sensitivities, suitable for electronic skin. For compact LC pressure sensors, the spiral coil functions as inductor, antenna, and capacitor electrode simultaneously, minimizing the space cost and is suitable for array integration, while the sensitivities remain the same. By tailoring the turn of the spiral coil, the resonate frequency can be regulated continuously. An annular array of compact LC sensors with ten distinct resonate frequencies ranged from 400 to 1000MHz is developed to remotely monitor the press of number 0-9. Finally, far-field LC pressure sensor tags with elongated detection distances are developed in which each compact LC sensor acts as a filter. A wireless in-shoe plantar to detect the sole pressure distribution using the far-field LC sensor configuration is developed.

Experimental Investigation of the Nanofluid Heat Transfer in a Helical Coil

Today, many attempts have been made to introduce small particles with high thermal conductivity to the heat transfer fluids to improve the thermal properties of conventional fluids used in heat transfer. Therefore, in this paper nanoparticles are used as fluid additives to study properties of the laminar flow regime. So, the laboratory setup was designed to experimentally investigate the forced heat transfer in a copper spiral coil under constant heat flux. Furthermore, the effect of the alternating magnetic field on the improvement of the heat transfer rate of forced convection heat transfer has been studied in different Reynolds numbers. Ferrofluid additives caused a tremendous improvement in the heat transfer of the fluid. The use of the alternating magnetic field also led to an increase in the heat transfer rate along with the spiral coil. Based on the results obtained in the constant volume fraction, if pure water is considered as the base fluid, then the ferrofluid with a constant magnetic field, the ferrofluid without a magnetic field, the ferrofluid with an alternating magnetic field of 5 Hz, and the ferrofluid with an alternating magnetic field of 50 Hz increased the heat transfer by 19%, 26%, 33%, and 43%, respectively.

A new semi-analytical approach for self and mutual inductance calculation of hexagonal spiral coil used in wireless power transfer systems

Several methods have been proposed in the literature for the calculation of self and mutual inductance. These methods include the use of complex integral analysis, the necessity of having primary and secondary coils with the same dimensions and the limitations of the ratio of the coil dimension to the distance between the coils. To overcome these restrictions, a new semi-analytical estimation method has been proposed in this paper. Calculation the self and mutual inductance by using the same basic formula which is based on Biot Savart Law prevents the formation of complex integrals and helps create a simple solution method. In order to verify the results obtained with the analytical approach, two hexagonal coils with 10 and 20 cm outer side lengths were produced by using litz wire with a conductive cross section of 1.78 mm2. The results obtained with the new approach are compared with the finite element analysis, other work presented in the literature and experimental results in order to prove the accuracy of the proposed method.

Orthogonal Optimal Design Method for Spiral Coil EMAT Considering Lift-off Effect: A Case Study

This paper provided a method to improve the conversion efficiency and lessen the lift-off effect of spiral coil electromagnetic acoustic transducer (EMAT) for some specific situations, for example, irregular sample surface, online inspection and varying coating. Moreover, a new evaluation method for the performance of EMAT is proposed. To study the effect of the structural parameters on the performance of EMAT, the orthogonal test method with five factors and four levels is employed. Consequently, the degree of five factors on the lift-off performance and the theoretical maximum value of amplitude are obtained. The results show almost all factors have an obvious impact on the theoretical maximum value of amplitude, while only the magnet-to-coil distance can affect the lift-off performance effectively. The experiment results well agree with the numerical results, in which the improvement of the lift-off performance and the theoretical maximum value of amplitude is 31.94% and 78.79% respectively. In addition, the conversion efficiency of EMAT is increased by 125% when the lift-off is 1 mm. These imply the performance of spiral coil electromagnetic acoustic transducer is improved dramatically and the detectable lift-off is increased as well.