Basic Discussion on Low Temperature Power Electronics

Introduction: Atrial fibrillation is a major cause of stroke, heart failure, and sudden death and is often associated with valve disease. The Maze procedure using the unipolar and bipolar radiofrequency devices is often combined with valvular surgery, especially mitral valve, to treat atrial fibrillation.
 Method: Cross-sectional descriptive study; 40 patientsss were treated for atrial fibrillation by COX-MAZE procedure combined with heart valve surgery in 2020-2021 at Cardiovascular Center- E Hospital.
 Result: In 40 patients, 23 males (57.5%), 17 females (42.5%), mean age 53.6 ± 8.3 (36-68) years. Mean time to dêtct atrial fibrillation 3.27 (1-9) years. 05 cases (12.5%) were preopration stroke history. Mean left atrial diameter before surgery 49.2 ± 10.1 (21-70) mm, thrombus in left atrial appendage was 8 cases (20%). All patients had mitral valve disease, accompanied by aortic valve disease 4 cases (10%) and tricuspid valve regurgitation 13 cases (32.5%). 100% of patients underwent COX-MAZE procedure. The rates of free from AF and sinus recovery after surgery 31 cases (77.5%). 02 patients (5%) sinus node dysfunction and 04 patients (10%) atrioventricular block I-II degree but they did not require temporary pacemaker placement, and recovered in 1-3 weeks.
 Conclusion: The Maze procedure by unipolar devices alone and combination with bipolar devices are effective and safe in patient atrial fibrillation combined with valvular surgery, especially mitral valve surgery.

Linear atrial radiofrequency lesions have been used effectively for the treatment of atrial fibrillation. In most cases an endocardial approach has been suggested. A method for epicardial placement of lesions would reduce the complexity of these procedures. We compared lesions created in ovine hearts in vivo using irrigated bipolar or unipolar handheld radiofrequency ablation devices. Radiofrequency lesions were produced around a left pulmonary vein, around the left atrial appendage and in the free wall of the right ventricle in ovine hearts. All lesions were created in the beating heart. A bipolar clamping device (n = 7) or a handheld unipolar device (n = 6) was used. Measurements of local electrograms and pacing thresholds were performed before and after ablation at each site to assess the electrical integrity of lesions. Tetrazolium and digital image analysis were used to assess lesion geometry. In atrial tissue continuous transmural lesions were achieved more often with the bipolar than with the unipolar device (92.3 vs. 33.3%, P < 0.02). In atrial tissue the reduction in signal amplitude caused by the lesions was significantly larger with the bipolar than the unipolar device (87.6+/-9.4% vs. 60.6+/-23.7% reduction, P < 0.01). There was a significant relationship between loss of pacing capture and lesion transmurality (P < 0.05). The bipolar device created narrower lesions than the unipolar device (4.1+/-0.9 mm vs. 5.9+/-2.1 mm, P < 0.001). The bipolar clamping device produces narrower lesions which are more likely to be transmural and lead to electrical isolation of ablated tissue than those produced by the unipolar device. However, both devices failed to consistently produce transmural lesions using the epicardial beating heart technique studied, particularly in thicker tissues. High output pacing within the ablated tissue partially predicts lesion transmurality and be a guide to the need for further ablation. However, endocardial ablation or transmural bipolar ablation are likely to remain the techniques of choice for linear radiofrequency ablation in the atria until improved techniques are developed.

Background:Hemiarthroplasty is currently the most common treatment for displaced femoral neck fractures in the elderly. While bipolar hemiarthroplasty was developed to reduce the risk of acetabular erosion that is associated with traditional unipolar hemiarthroplasty, meta-analyses have reported similar outcomes for bipolar and unipolar hemiarthroplasty devices. The primary objective of this study was to evaluate the risks of aseptic revision and periprosthetic fracture following bipolar versus unipolar hemiarthroplasty in a large integrated health-care system in the United States.Methods:We conducted a retrospective cohort study using data from the hip fracture registry of an integrated health-care system. Patients aged ≥60 years who underwent hemiarthroplasty for hip fracture between 2009 and 2019 were included. The primary outcome measure was aseptic revision, and the secondary outcome measure was revision for periprosthetic fracture. Cause-specific Cox proportional hazards regression was performed, with mortality considered as a competing event. In the multivariable analysis, estimates were adjusted for potential confounders such as age, sex, race/ethnicity, body mass index, American Society of Anesthesiologists classification, femoral fixation, surgeon volume, type of anesthesia, and discharge disposition.Results:The study sample included 13,939 patients who had been treated with hemiarthroplasty by 498 surgeons at 35 hospitals. The mean follow-up time was 3.7 ± 2.9 years. The overall incidence of aseptic revision at 5 years following hemiarthroplasty was 2.8% (386). In the multivariable analysis controlling for potential confounders, bipolar hemiarthroplasty was associated with a lower risk of aseptic revision than unipolar hemiarthroplasty (hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.59 to 0.94; p = 0.012). Rates of revision for periprosthetic fracture were similar between the bipolar and unipolar devices (HR, 0.79; 95% CI, 0.58 to 1.10; p = 0.16).Conclusions:In this study of hemiarthroplasty for hip fracture in elderly patients, bipolar designs were associated with a lower risk of aseptic revision than unipolar designs. In contrast to prior research, we did not find any difference in the risk of periprosthetic fracture between the 2 designs.Level of Evidence:Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Background:The bipolar hip prostheses after some time functions as a unipolar device. There is a need to change the design of bipolar hip prostheses to make it function as a bipolar device over a prolonged period of time. A bicentric bipolar hip prosthesis was used as an implant for various conditions of the hip. We evaluated the movement of this newly developed prosthesis at the interprosthetic joint radiologically at periodic intervals.Materials and Methods:Fifty two cases were operarted with the Bicentric bipolar prosthesis for indications like fracture neck of femur and various other diseases of the hip and were followed up with serial radiographs at periodic intervals to evaluate, what fraction of the total abduction at the hip was occurring at the interprosthetic joint.Results:In cases of intracapsular fracture neck of femur, the percentage of total abduction occurring at the interprosthetic joint at 3 months follow-up was 33.74% (mean value of all the patients), which fell to 25.66% at 1.5 years. In indications for bipolar hemireplacement other than fracture neck of femur, the percentage of total abduction occurring at the interprosthetic joint at 3 months follow-up was 71.71% (mean value) and at 1.5 years it was 67.52%.Conclusion:This study shows the relative preservation of inner bearing movement in the bipolar hip prosthesis with time probably due its refined design. Further refinements are needed to make the prosthesis work better in patients of intracapsular fracture neck femur.

Body: Newly emerged wide bandgap semiconductor (WBG) β-Ga2O3 has been extensively researched for power electronics, RF electronics and optoelectronics due to its large bandgap of 4.7- 4.9 eV and high breakdown field of ~ 8 MV/cm. Due to the absence of p-type Ga2O3, most of demonstrated β-Ga2O3 devices are unipolar devices such as high electron mobility transistors (HEMTs) and Schottky barrier diodes. To overcome this limitation, other p-type materials, such as GaN and NiO, have been investigated to produce Ga2O3 based p-n heterojunctions. Among these p-type materials, p-GaN has attracted especial interests since GaN is also a WBG semiconductor and has a clear crystallographic relationship to β-Ga2O3 for epitaxial growth. In addition, both β-Ga2O3 and GaN can be produced in the industrial standard tools, i.e., the metalorganic chemical vapor deposition (MOCVD). The growth of high-quality GaN on Ga2O3 by MOCVD has been recently reported. β-Ga2O3/GaN p-n heterojunction via mechanically exfoliation also showed decent rectifying behaviors. However, the breakdown capability of the β-Ga2O3 based p-n heterojunctions is still far from expectations due to the lack of effective edge terminations. Here we design and simulate mesa based edge terminations for the vertical β-Ga2O3/GaN p-n heterojunctions using SILVACO TCAD simulator. The model was first calibrated by the experimental results, including the conduction and valance band offsets of the heterojunction and electrical properties. The device structure consisted of n+-Ga2O3 n-contact layer, 5 µm unintentionally doped (UID) β-Ga2O3 drift layer and 500 nm p-GaN layer. The ideal breakdown voltage (BV) of the heterojunction was 1.37 kV, while the BV of the reference device without effect mesa edge termination dropped dramatically to 300 V due to the electric field crowding at the device edge. Therefore, it is critical to design and optimize the mesa edge termination to improve the BV of the β-Ga2O3/GaN p-n heterojunctions. Three mesa edge termination structures were investigated in this work: beveled mesa, step mesa, and deeply-etched mesa. The beveled mesa angle θ is the key parameter in determining the device BV. When θ was varied from 15° to 90°, the highest BV of 1224 V was obtained for θ =15°. For the step mesa edge termination, the width (W), depth (D), and the number of steps define the mesa structure. It was found that the BV of the devices increased with increasing number of steps. The combination of (W, D) values of (0.5,0.5) and (0.5,1.0) and (1.0,1,0) was investigated, where all the values are in µm. The highest value was obtained for W = 0.5µm, D = 1.0µm and the number of steps = 5. Smaller W and larger D led to better BV. The electric field distributions of devices with different mesa edge terminations were compared at –300V. Without effect mesa edge termination, the peak electric field at the junction edge was ~ 4.2 MV/cm. By incorporating the mesa edge termination techniques, the electric field crowding at the device edge was mitigated, and the peak electric fields were reduced to 1.8 MV/cm and 2.4 MV/cm for the beveled and step mesa edge terminations, respectively. For the deeply-etched mesa structure, it was found that a more uniform electric field distribution was observed when the mesa depth was increased from 0.5,1.0, 2.0, to 3.0 µm, where the peak electric fields were decreased from 2.1, 1.8 ,1.5 to 1.2 MV/cm, respectively. In summary, this work presents a comprehensive design and optimization of mesa edge terminations for the wide bandgap vertical β-Ga2O3/GaN p-n heterojunctions, which is first of its kind. Three mesa structures were explored, including beveled mesa, step mesa and deeply-etched mesa. It was found that these mesa edge terminations can alleviate the electric field crowding at the junction edge and increase the device BV. This work can provide critical guidance for the development of high-performance β-Ga2O3 based bipolar high voltage and high power devices.

Surgical ablation of atrial fibrillation with a novel bipolar radiofrequency device

We discuss the main characteristics of the intersubband transitions in III-V semiconductor heterostructures and in particular in nitride materials and describe the operation principles of the most important unipolar optoelectronic devices. An example of experimental and theoretical study of the intersubband transitions in GaN/AIN heterostrucure is given. The advantages of unipolar optoelectronic devices with respect to bipolar devices are explained. The high potential of nitride semiconductors as an emerging technology to develop ultra-fast unipolar optoelectronic devices operating at fibre-optics telecommunications wavelengths is demonstrated.

The aim of this paper is to evaluate experimentally the switching characteristics of discrete high voltage Super-Junction (SJ) MOSFET in the 650VDSS voltage class with respect to device package. The switching performance of the SJ MOSFET is evaluated in four different SMD packages, of which two with Kelvin source, each with respect to a soft recovery freewheeling diode, its own intrinsic body diode as freewheeling diode in half bridge configuration and with the latest generation Silicon Carbide (SiC) Schottky diode. The need for overall low inductance hardware design to attain better switching performance of the device is discussed. The influence of parasitic inductance, impacts of reverse recovery behavior of Si and SiC diodes on switching power device's turn-on, di/dt and dV/dt effects are also addressed. The merits of SiC diode, leadless package and Kelvin source on switching performance are demonstrated. Finally, suitable packages and freewheeling diode combination are identified for automotive applications like DC-DC converters and Power Factor Correction (PFC).

This paper reports a pioneering demonstration platform of a cryogenic propulsion unit at liquid nitrogen temperature. A high temperature superconducting (HTS) machine is connected with a cryogenic power rectifier in a generator mode to prove the feasibility of a cryogenic propulsion unit for electric aircraft propulsion applications. Machine operation was carried out with a special focus on the total heat dissipation inside the HTS AC windings. Different types of 2G HTS tapes were tested to provided data for stator coils’ design. The transient operation was carried out to represent a short-circuit failure in one of the power electronic devices. The test shows AC loss performance of the HTS windings using calorimetric method during the short circuit event, indicating the importance of developing protection schemes for the cryogenic propulsion units to prevent damage to the HTS components. The paper provides initial insights into the interaction between superconducting machines and cryogenic power electronics within a cryogenic propulsion unit. It is an important first step to understand and further develop cryogenic propulsion technology for future electric aircraft.

Trapped field recovery of bulk superconductor magnets by static field magnetization

An important characteristic of second breakdown in p-n junctions is the current constriction to a small region. This may be caused by a thermal feedback mechanism, as discussed by Scarlett and Shockley, and by Bergmann and Gerstner. A brief review of this theory is given, illustrated by experimental results of a simple model arrangement consisting of three thermally coupled transistors. The essential parameters influencing the thermal stability of the current distribution are device geometry, power density, and temperature dependence of current. It is widely known that second breakdown occurs at high voltages at a much lower power level than at low voltages. To allow a more detailed discussion of this effect in view of thermal stability, we determined experimentally the temperature coefficient of transistor current for various Si planar transistors as a function of current, voltage, and junction temperature. The experimental procedure is described and the results are discussed. The experimental values of the temperature coefficient range from 0.08 to 0.01 1/°C. The values for high currents are much lower than predicted by the theory of Ebers and Moll. It thus can easily be understood why, in the case of high current, and low voltage, the thermal stability of the current distribution is much better than in the case of low current and high voltage.

For circular ultra-high voltage (UHV) 300-V power nLDMOS devices, a novel device architecture of high voltage p-well (HVPW) zones is embedded into a high voltage n-well (HVNW) drift region to form superjunction (SJ) structures (radial-type). And, by the HVPW/HVNW SJ of the radial-type, eight types of area ratios are fabricated. However, the human-body model (HBM) capacity of this UHV nLDMOS reference group is only 2500 V. For equal partition radial-type SJ, due to more even HVPW distribution in the equal 32-partitions, the HBM level (6750 V) was the highest. Meanwhile, it can maintain a fairly high breakdown voltage as with the reference sample. Finally, for the radial-type 30 equal partitions with different HVPW/HVNW area ratios, because the HVPW area was large in the HVPW/HVNW ratio(≈2:1), more conduction current flowed into the BNW layer under these new inserted HVPWs and dispersed the conduction current; thus, the HBM (7000 V) was the best. Thus, the more even partition and higher proportion of HVPW/HVNW area ratio in drain-side SJ architecture, the stronger its electrostatic discharge reliability performance.

Electrosurgery is a commonly used technology in laparoscopy. Electrosurgical devices are being used in many medical subdisciplines in order to coagulate, cut, and ablate tissue and to produce hemostasis. The latest advance in electrosurgery is the introduction of novel simultaneous hemostatic sealing and cutting bipolar devices that minimize force by delivering energy as high current and low voltage output. One of these systems is the Gyrus Plasma Trissector (GPT), (Gyrus Group PLC, Gyrus International, Ltd.UK), a novel radiofrequency (RF) system based on bipolar technology, which consists of a proprietary PlasmaKinetic (PK) generator and specific instruments, designed as a system. The instrument consists of a 17 mm long gold‐coated curved jaw with a ceramic insulated cutting element. The PK system uses high‐powered pulsed bipolar energy to produce a plasmakinetic field around the working elements and is designed to operate at temperatures that allow effective tissue dissection but result in minimal collateral damage and adherence to tissue. The GPT was used with the Gyrus G400 WorkStation generator in laparoscopic radical prostatectomies (LRP). Our initial experience with this novel bipolar device demonstrates it to be safe and effective in dissection and hemostasis. The GPT permits us to act quickly when bloody fields are present, improves coagulation, reduces or eliminates sticking, seals large vessels such as dorsal vein complex (DVC) and allows secure grasping and dissecting of tissue.The urologist is familiar with electrosurgery, as we have become comfortable using GPT to dissect, cut, and coagulate tissue. We feel that the GPT can be used in a variety of laparoscopic procedures in urology.

AC HTS Transmission Cable for Integration into the Future EHV Grid of the Netherlands

Several new unipolar switching power device figures of merit are proposed based on proper consideration of power device conduction and switching losses. These figures of merit can be used for device and material comparison. The relative advantages of different semiconductor materials are then compared. Using the new figures of merit, the predicted advantages of power devices based on wide-bandgap materials are less than those predicted by other published figures of merits.