Ferrite Yoke Research Articles

Investigation of dielectric and magnetic properties of AL-800 ferrite

Ferrites are usually used in accelerators for tuning radiofrequency (RF) cavities and in nonreciprocal devices controlling the power flow in RF accelerating systems. The conventional parallel‐biased Ni Zn ferrites employed for varying the frequency of accelerating cavities have the disadvantage of high saturation magnetization (4πMs). Application of the transversely biased yttrium iron garnet (YIG) material in RF tuners promises a significant reduction of power loss compared with systems that use the longitudinal bias. To inject the beam and extract the beam out of the CERN accelerator rings the fast kicker magnets made from ferrite materials must be used. Power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. Investigation of the ferrite electromagnetic properties of materials up to the GHz frequency range is essential for a correct impedance evaluation. This report summarizes an approach for deriving electromagnetic properties as a function of both frequency and temperature of the AL-800 garnet material. This information will be useful for simulating ferrite behaviour under realistic operating conditions.

A facility for the characterisation of planar multilayer structures with preliminary niobium results

The maximum accelerating gradient of superconducting radio frequency cavities are currently reaching their theoretical limits, due to the magnetic field entering the superconductor in the form of vortices. To overcome these limits, thin film coated superconducting materials are required, however these need to be tested to optimise their properties. A system has been designed, built, and commissioned at Daresbury Laboratory that applies a local DC magnetic field parallel to the surface, from one side of a sample, similar to that in cavity operation. A magnetic flux density (up to 600 mT) is generated parallel to the sample surface in the 2 mm gap of a C-shaped ferrite yoke. Two Hall probe sensors are used to measure both the applied and penetrated magnetic field. The system operates in a cryogen free environment, with a minimum temperature of approximately 2.6 K. A Pb foil has been used to characterise the system, and determine how the sample size affects the results. Nb thin film samples have been tested for varying thickness to determine how the depth effects the field of full flux penetration, . The design, operation, methods of analysis and first results of this facility will be reported in this paper.

Quantitative mapping of depth profile of fatigue cracks using eddy current pulsed thermography assisted by PCA and 2D wavelet transformation

Fatigue cracks are widely generated in numerous engineering components under alternating loads, whose sudden brittle fracture would seriously shorten the service life and cause significant hazards. A large number of nondestructive testing (NDT) techniques have been utilized to quantitatively evaluate the fatigue cracks, however, most of these methods are difficult to be used for a full characterization of the cracks’ depth profile. The eddy current pulsed thermography (ECPT) as a promising NDT technique shows great potential for fatigue crack evaluation due to its high detection efficiency, large inspection area, and high spatial resolution. In this article, a ferrite yoke was utilized to generate a homogeneous eddy current field, and as such to enhance the detection sensitivity and to provide a wide open-view area for the camera. The hybrid processing strategy combining principal component analysis (PCA) and 2D wavelet transformation was proposed to extract spatial features of the thermographic image sequences. Firstly, numerical results demonstrate that the profiles of slot cracks can be identified directly from the thermographic images in the early heating stage. Afterward, the ECPT experiments on slot cracks with different depth profiles demonstrate the feasibility of the hybrid processing strategy. Then, three fatigue cracks were manufactured through the three-point bending method and detected by ECPT. The results of the hybrid processing method indicate that these three fatigue cracks have elliptical profiles. Finally, the authentic depth profile of a fatigue crack with an elliptical shape is extracted through a destructive experiment. The comparison results between the real depth profile and the profile characterized through the proposed strategy show great consistency and validate the superiority of the proposed strategy.

Multiphysics Structured Eddy Current and Thermography Defects Diagnostics System in Moving Mode

Eddy current testing (ET) and eddy current thermography (ECT) are both important nondestructive testing methods that have been widely used in the field of conductive materials evaluation. Conventional ECT systems have often employed to test static specimens even though they are inefficient when the specimen is large. In addition, the requirement of high-power excitation sources tends to result in bulky detection systems. To mitigate these problems, in this article, a moving detection mode of multiphysics structured ET and ECT is proposed in which a novel L-shape ferrite magnetic yoke circumambulated with array coils is designed. The theoretical derivation model of the proposed method is developed which is shown to improve the detection efficiency without compromising the excitation current by ECT. The specimens can be speedily evaluated by scanning at a speed of 50–250 mm/s while reducing the power of the excitation current due to the supplement of ET. The unique design of the excitation-receiving structure has also enhanced the detectability of omnidirectional cracks. Moreover, it does not block the normal direction visual capture of the specimens. Both numerical simulations and experimental studies on different defects have been carried out and the obtained results have shown the reliability and detection efficiency of the proposed system.

New spiral beam screen design for the FCC-hh injection kicker magnet

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept - a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.

Measurements of electromagnetic properties of ferrites as a function of frequency and temperature

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

Measurements of Electromagnetic Properties of Ferrites as a Function of Frequency and Temperature

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

Virtual Prototyping and Development of Rotary Field Ferrite Phase Shifter

<p>Review of the virtual prototyping and physical development of the rotary field ferrite phase shifter is presented. A description of the basic principle of operation of the rotary field ferrite phase shifter has been given along with the key aspects about the design and virtual prototyping of various parts of the phase shifter viz ferrite rod, yoke, polarisers and matching section using HFSS and 3-D Maxwell softwares. Calibrated simulation performance of the phase shifters is presented and it shows good agreement with physical measurement results. Three prototypes and one hundred production capable phase shifter modules were fabricated, functionally tested and RF characterised. This is an indigenous development of the physical prototypes of rotary field class of ferrite phase shifters of C-band. This class of ferrite phase shifters finds application in phased array radars, such as battery level radar and weapon locating radar, because of its high phase accuracy and high power handling capability.</p><p> </p>

Detection and evaluation of damage in aircraft composites using electromagnetically coupled inductors

The paper presents a quantitative damage evaluation of carbon-fibre reinforced polymer (CFRP) plates using a non-contact electromagnetic (EM) sensor. The EM sensor with coupled spiral inductors (CSI) is employed here to detect both impact induced and simulated damage leading to an accurate evaluation of the location, depth and width of sub-surface defects. The effect of inspection frequency, standoff distance and signal power are also investigated leading to the development of an engineering circuit design tool that relates the set up and calibration of the sensor to its detection performance. It is found that the dynamic range of the transmission coefficient is the limiting factor in the original Salski CSI sensor and this problem is addressed by adding ferrite layers to reduce the reluctance of the magnetic circuit, improving damage sensing by 22%. The study leads to a further development of utilising an open ferrite yoke with a pair of encircling coils, which shows a 57% sensitivity improvement and clearer identification of air gaps (voids) and delamination in CFRP laminates. The proposed EM yoke design CSI sensor is low cost and could be assembled into an array for non-contact, in situ mechatronic scanning of aircraft composite wings.

Automatic Scanning System for Back-Side Defect of Steel Structure Using Magnetic Flux Leakage Method

An automatic nondestructive evaluation system using the magnetic-flux-leakage method was developed for detecting the back-side defects of large structures in order to realize fast detection in a wide measurement area. A magnetic field was applied to an object using a ferrite yoke with an induction coil, and the leaked magnetic flux from the object was detected by a magnetoresistive sensor. This measurement probe was fixed on an automatic scanning system. The developed automatic scanning system detected magnetic signal changes corresponding to the back-side defects of the steel plates. To demonstrate the effectiveness of the developed system, we measured the steel plate of a cargo crane, which was corroded on the back side. We found that the detected magnetic signal changed markedly in the area with corrosion, whereas only a slight magnetic signal change was detected in the area without corrosion. Therefore, the developed system is useful for detecting the back-side defects in a wide area, and can be used for screening tests.

규소강판을 이용한 실드케이스의 차폐효과

The shield effect of 4 layered shield case was investigated in this paper. The material of the case was non-oriented SiFe sheet with a thickness of 0.5mm. The size of the case was 100mm wide, 100mm high and 300mm long. Relative permeability of SiFe sheet was needed to calculate shield effect. It was obtained from the measurement by a ferrite yoke and from the calculation by eddy current FEM analysis. Three configurations were used to connect both ends of SiFe sheet. First one is a connection by double-welded butt. Second one is to put the sheet the same material above the confronted both ends of the sheet to avoid a leakage magnetic flux. The last one is ideally without any connection. The shield effect of the second one agreed well with the last one and showed the shield effect of -40dB.

Optimal Design and Test of Main Magnet in Superconducting MRI

The magnet system is an important part in magnetic resonance imaging (MRI) equipment, the performance of which directly affects the quality of the imaging. Improving the homogeneity of the magnetic field is an effective means to increase the signal-to-noise ratio (SNR). A high SNR ensures a good imaging. This paper mainly investigates the optimal design and homogenizing field analysis of main magnet for ferrite yoke flat-board type in superconducting MRI using the finite element method (FEM). In order to get a high homogeneous magnetic field, the pole piece is added on the magnetic pole. We use electric pure iron as the material of the pole piece which has low coercive force, high permeability, and high saturation flux density. In order to increase the calculation speed, three-dimensional analysis is replaced by two-dimensional analysis while keeping the precision adequate. Through the optimizing algorithm, we can obtain an ideal pole piece dimension of the magnet. The distribution of the magnetic field was simulated and tested experimentally. By comparing the numerical calculation results with the experimental results, we find that a superconducting magnet MRI having homogeneity in volume of interest less than 600 ppm can be designed by optimizing the dimension of the pole piece using the proposed method without shimming.

Highly sensitive single pole head with laminated thin film coils

A novel single pole head with laminated thin film coils is proposed in this paper. Laminated thin film coils, between which a main pole is laid, are put very close to the media to capture most of the reproduced flux. In addition, a ferrite return yoke is placed just under the lower conductor to shorten the head magnetic flux path. These approaches bring high read/write efficiency and small head noise owing to low head impedance. With only one or two-turn coils, Co-Cr/Fe-Ni-Nb double-layered media were saturated at magneto-motive force of 0.05 ampere-turn, and overwrite of the two-turn head reached 35 dB. High normalized output of 1000 nV/sub p-p///spl mu/m/spl middot/turn/spl middot/m/s was obtained. Much higher recording and reproducing sensitivity than ordinary inductive single pole heads was achieved.

Wireless multi-temperature measurement for rotating cryogenic machines

A method of wireless and multitemperature measurement is proposed, in which the resonant frequency shift of the sensors caused by temperature is the detectable signal. LC resonant circuit sensors consisting of a ferrite yoke coil and a mica-type capacitance were used in the demonstration experiment. The experimental data show that the temperature of several points is discriminatively detectable in the rotating machine. The response time of the method for every measurement is about one minute to attain 10 mK resolution. It is believed that a frequency tracer technique for each sensor may be a way to improve the response time. However, the proposed measurement system should be restricted to the observation of the stationary temperature profile in a rotating cryogenic machine. >

An Fast Extraction Instrument of Low Charging Voltage with Small Residual Field using Series Blumlein Line Modulators.

A kicker magnet and a pulse modulator with a low charging voltage and a short rise time are designed and fabricated for an extraction instrument of an 1GeV electron synchrotron of Mitsubishi Electric Corp. The kicker magnet is a lumped type one with a C type ferrite yoke. The gap height of the magnet is 15mm and the yoke width is 30mm. Total length of the magnet is 0.6m and the inductance is about 1.5μH.The effect of the residual magnetic field of the magnet on the low energy electron beam is studied by a beam tracking method. The results show the residual field must be lower than 1 G to obtain enough dynamic aperture of the low energy beam.The modulator consists of two Blumlein line modulators, whose inpedance are 75Ω, and is switched by a single thyratron. At the magnet, the lines are connected in series such that the inner conductor of one line is connected to the outer conductor of the other line. Then, the current in each line are added at the kicker magnet. In our system, the magnet is connected to the modulators with a mismatched resistor. Therefore the current has a damping oscillation waveform.The rise time of the current is about 40ns and the charging voltage of the modulator at the extraction from the synchrotron is no more than 40kV and which is a quarter of the voltage when a conventional P. F. N type modulator is used. The flatness of the waveform is less than ±1% and the stability is no more than 0.1%. The restriction of the residual field is satisfied by using the damping oscillation waveform of the current. The measured value of the residual field is reduced by factor 4 (0.5G) compared with the one by a rectangular waveform.At the extraction operation, successful extraction of eight bunches from fifteen bunches in the synchrotron are measured by a wall current monitor at the extraction transport line.

Fabrication of a Composite Inductance Using Co-Metal Amorphous Multilayer Films

Multilayer films consisting of Co 84 Zr 5.5 Nb 10.5 and Co 79 Zr 10 Mo 9 Ni 2 amorphous layers with SiO 2 intermediate layers were prepared. An inductor for use in high frequency applications was fabricated from the film samples and an Ni-Zn ferrite yoke. In order to improve the high frequency characteristics, films fabricated into stripes were studied. Films were annealed in a magnetic field and the frequency response of multilayer films was measured at frequencies from 0.01 MHz to 200 MHz. Films with stripes showed better frequency characteristics than did films without stripes. An inductor fabricated from films with stripes with a total thickness of 20 ?m and ferrite yokes exhibited an inductance of over 10 ?H at 1 MHz, with frequency characteristics improved over those of Ni-Zn alone.

Sputtered sandwich heads for high-density digital video recording

A sandwich type of head for application in high-frequency and high-density digital video systems is described. Amorphous CoNbZr films laminated with an Al/sub 2/O/sub 3/ insulator layer are used as core material. The influence of rotating and static field annealing on the domain structure and on the permeability is discussed. In order to achieve a sufficiently high efficiency, a polycrystalline ferrite back yoke is applied. Sandwich heads with several ceramic materials in the contact plane are evaluated. The performance of the heads is investigated on the basis of a signal-to-noise criterion, defined specially for the digital video application. A sandwich head made with 2 mu m*5 mu m amorphous CoNbZr, laminated with 0.1 mu m Al/sub 2/O/sub 3/, between glass-ceramic substrates fulfils the requirement on MP tape. >

Ｃｏ系非晶質積層膜を用いた複合インダクタンスの試作

Co84Zr5.5Nb10.5 and Co79Zr10Mo9Ni2 amorphous films were multilayered by sputtering with SiO2 as intermediate films. An inductor for high frequency application was fabricated with those films and Ni-Zn ferrite yoke. In order to improve the high frequency characteristics, stripe patterned films were studied. The films were annealed in a magnetic field and the frequency dependence of the multilayered films was measured in the frequency range 0.01∼200 MHz. The striped films showed better frequency characteristics than the unstriped films. An inductor made of striped films with a total thickness of 20μm and ferrite yokes exhibited an inductance of over 10μH at 1 MHz with frequency characteristics improved over those of Ni-Zn ferrite alone.

Fabrication of an inductor using amorphous films with a multilayered structure

By making use of the high permeability and the excellent high-frequency characteristics of Co-metal amorphous multilayered films, an inductor was fabricated. In order to improve the high-frequency characteristics, stripe patterned films were studied. The inductor consists of two of these films and a ferrite yoke. The value of inductance and quality factor were measured in the frequency range of 0.01–200 MHz. Although the value of the present inductance is small compared with other small size inductors developed so far, excellent high-frequency characteristics may be expected if an inductor is fabricated composed solely of these multilayered films.

Scanning and e.h.t. circuits for wide-angle picture tubes

One of the major factors which have contributed to the low cost of television receivers, despite the increased cost of production, is the introduction of a.c./d.c. technique. In this country this implies the rather low h.t. rail potential of about 190 V. The demand for bigger and brighter pictures, on the other hand, has led to an increase in the scanning angle of some c.r. tubes, and of the final anode potential. Both these factors imply greater scanning power. The paper is concerned with combined scanning and e.h.t. circuits developed to meet this situation.The operation of energy-recovery scanning circuits is explained, design procedures established and typical circuits are given in detail. Particular attention is paid to the problem of obtaining satisfactory linearity, and a method is described of correcting the horizontal nonlinearity by means of a saturated reactor. Details are also given of an efficient scanning coil wound on a slotted ferrite yoke.