Zhen Yao

Bio: Zhen Yao is an academic researcher from Intel. The author has contributed to research in topics: Electromagnetic coil & Electromagnetic shielding. The author has an hindex of 8, co-authored 31 publications receiving 255 citations. Previous affiliations of Zhen Yao include Case Western Reserve University.

Conduction cooled magnet design for 1.5 T, 3.0 T and 7.0 T MRI systems

Abstract: Main magnets for magnetic resonance imaging (MRI) are largely constructed with low temperature superconducting material. Most commonly used superconductors for these magnets are niobium-titanium (NbTi). Such magnets are operated at 4.2 K by being immersed in a liquid helium bath for long time operation. As the cost of liquid helium has increased threefold in the last decade and the market for MRI systems is on average increasing by more than 7% every year, there is a growing demand for an alternative to liquid helium. Superconductors such as magnesium-diboride (MgB2) and niobium-tin (Nb3Sn) demonstrate superior current carrying quality at higher critical temperatures than 4.2 K. In this article, electromagnetic designs for conduction cooled main magnets over the range of medium field strengths (1.5 T) to ultrahigh field strengths (7.0 T) are presented. These designs are achieved by an improved functional approach coming from a series of developments by the present research group and using properties of the state-of-the-art second generation MgB2 wires and Nb3Sn wires developed by Hyper Tech Research Inc. The MgB2 magnet designs operated at different field strengths demonstrate excellent homogeneity and shielding properties at an operating temperature of 10 K. At ultrahigh field, the high current density on Nb3Sn allowed by the larger magnetic field on wire helps to reduce the superconductor volume in comparison with high field NbTi magnet designs. This allows for a compact magnet design that can operate at a temperature of 8 K. Overall, the designs created show promise in the development of conduction cooled dry magnets that would reduce dependence on helium.

Modeling the Brownian relaxation of nanoparticle ferrofluids: Comparison with experiment

Abstract: Purpose: The authors investigate the ability of current models for magnetic nanoparticles immersed in dilute ferrofluids and external sinusoidal magnetic fields to explain recent experiments in which the relaxation effects are dominated by viscous damping. Methods: The Fokker–Planck (FP) equation appropriate for the nanoparticle magnetic moment distribution corresponding to the underlying stochastic Langevin model is numerically studied and solutions compared to experimental results. The FP equation is solved using an expansion in Legendre polynomials. The polydisperse properties of the ferrofluids are incorporated into the analysis. Results: By using a FP approach that includes polydispersion, the authors obtain good agreement with recent experimental results using ferrofluids containing nanoparticles with average hydrodynamic diameters in the 40–120 nm range. Conclusions: For nanoparticles used in recent magnetic spectroscopy experiments, the FP approach can be used to accurately model experimental data in the situation where Brownian relaxation effects are dominant and the ferrofluids are dilute.

Device dependent maximum coil current

Abstract: This disclosure describes methods, apparatus, and systems related to a maximum coil current system. A device may determine a presence of a first device placed on a charging area of the device, the charging area including a power transmitting surface. The device may establish a connection with the first device using one or more communication protocol. The device may identify device information associated with the first device using the established connection. The device may determine a maximum charging current for the first device based at least in part on the device information.

Parallel transmit excitation at 1.5 T based on the minimization of a driving function for device heating

Abstract: Purpose: To provide a rapid method to reduce the radiofrequency (RF) E-field coupling and consequent heating in long conductors in an interventional MRI (iMRI) setup. Methods: A driving function for device heating (W) was defined as the integration of the E-field along the direction of the wire and calculated through a quasistatic approximation. Based on this function, the phases of four independently controlled transmit channels were dynamically changed in a 1.5 T MRI scanner. During the different excitation configurations, the RF induced heating in a nitinol wire immersed in a saline phantom was measured by fiber-optic temperature sensing. Additionally, a minimization of W as a function of phase and amplitude values of the different channels and constrained by the homogeneity of the RF excitation field (B{sub 1}) over a region of interest was proposed and its results tested on the benchtop. To analyze the validity of the proposed method, using a model of the array and phantom setup tested in the scanner, RF fields and SAR maps were calculated through finite-difference time-domain (FDTD) simulations. In addition to phantom experiments, RF induced heating of an active guidewire inserted in a swine was also evaluated. Results: In the phantom experiment, heating atmore » the tip of the device was reduced by 92% when replacing the body coil by an optimized parallel transmit excitation with same nominal flip angle. In the benchtop, up to 90% heating reduction was measured when implementing the constrained minimization algorithm with the additional degree of freedom given by independent amplitude control. The computation of the optimum phase and amplitude values was executed in just 12 s using a standard CPU. The results of the FDTD simulations showed similar trend of the local SAR at the tip of the wire and measured temperature as well as to a quadratic function of W, confirming the validity of the quasistatic approach for the presented problem at 64 MHz. Imaging and heating reduction of the guidewire were successfully performed in vivo with the proposed hardware and phase control. Conclusions: Phantom and in vivo data demonstrated that additional degrees of freedom in a parallel transmission system can be used to control RF induced heating in long conductors. A novel constrained optimization approach to reduce device heating was also presented that can be run in just few seconds and therefore could be added to an iMRI protocol to improve RF safety.« less

Methods and apparatus to wirelessly power an unmanned aerial vehicle

Abstract: Methods, apparatus, systems and articles of manufacture to wirelessly power an unmanned aerial vehicle are disclosed. An example unmanned aerial vehicle (UAV) includes a first electrode assembly to capacitively couple to a first power cable. The example UAV includes a second electrode assembly to capacitively couple to a second power cable. The first and second electrode assemblies, when capacitively coupled to the respective first and second power cables, are to receive power from at least one of the first and second power cables. The example UAV includes a power storage circuit to store the received power.

Magnetic resonance imaging device

Abstract: By using a multiple receiving coil composed of receiving coils, an imaging portion of a subject is subjected to a first pulse sequence to create n sensitivity images (701 to 703) fewer than the examination images. When these sensitivity images are created, an NMR signal is measured for only the low-frequency region of the k space. A second pulse sequence from which a phase encode step is removed is conducted to create m (m>n) examination images (704, 705) of the subject by using the receiving coils. When sensitivity distributions (707, 708) of the receiving coils are determined for the sensitivity images (701 to 703), and if there are no sensitivity distributions corresponding to the slice positions of the examination images (704, 705), they are determined by slice interpolation using the sensitivity distributions (701 to 703), and the aliasing artifacts of the examination images (704, 705) are removed by matrix operation by using the sensitivity distributions (707, 708).

Fundamentals and advances in magnetic hyperthermia

Abstract: Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient's quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.

The Langevin Equation

Abstract: The generalized Langevin equation describes processes in a mechanical system with both deterministic and random forces which have comparable magnitudes (i.e., neither the deterministic nor random part can be neglected) and the random force is a transformed white noise. Examples of such processes are well known in physics. In this chapter, we use integral operators with Riemannian parallel translation in order to study the Langevin equations arising in geometric mechanics. Note that in the case under consideration the trajectories of the process are a.s. smooth. This makes the analysis of such systems technically much simpler than that of the general ones studied in Chap. 4.

Fundamentals and advances in magnetic hyperthermia

Abstract: Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.

Systems and Methods for Automatically Testing the Communication Between Wireless Power Transmitter and Wireless Power Receiver

Abstract: Systems and methods to use software to automatically test the communication between wireless power transmitter and wireless power receiver are described. The described systems include one or more wireless power transmitters, one or more wireless power receivers and one or more electronic devices. Electronic devices may be able to communicate with wireless power transmitters and wireless power receivers using suitable communications channels. The disclosed methods may be employed for antenna direction management and for transmission of power from transmitter to receiver in a wireless power transmission system.