Actual vs textbook transformers

The current in the secondary coil of a transformer acts to oppose the flux generated by current in the primary coil, by Lenz’s law. According to most physics textbooks, the total flux is then zero, so transformers should stop working. Something is missing in the textbook accounts.

Abstract 1122‐000164: Peri‐embolization Use of Stent Retrievers as a Rescue Tool in Patients with Subarachnoid Hemorrhage

Introduction : Coil migration after endovascular embolization of intracranial aneurysms is one of the periprocedural complications in 2–6% of patients. Stent retriever use is well‐established in treatment of ischemic stroke but has not been well established to address coil retrieval as rescue therapy. We describe three cases with successful removal of migrated coils using stent retrievers. Methods : A retrospective review at a single center university hospital was performed for all Neuro‐endovascular case log from December 2018 to November 2020. Cases of coil migration were reviewed and coil retraction with Stent Retriever with successful coil mass extraction was considered an endpoint. Number of attempts, types of stent retrievers used and time taken for extraction were noted. Results : Case 1: 56‐year‐old female presented with ruptured tri‐lobed 4 × 3 mm Anterior communicating artery aneurysm. Hunt and Hess (H&H) Grade 2. Modified Fisher scale (MFS) 4. Underwent primary coil embolization. Two 2mmx2cm Galaxy Orbit coils were deployed within aneurysm. During deployment of third coil the first two coils displaced out of the aneurysm migrating into left A2 segment. Stryker’s Trevo 3 × 20 mm stent retriever was used for retrieval of coils however they dislodged at the left internal carotid artery (ICA) terminus and migrated distally into the left middle cerebral artery (MCA) M2 superior division. Subsequently, Medtronic’s Solitaire 4 × 40 mm stent retriever was successfully deployed retrieving the migrated coils with full recanalization. Case 2: 64‐year‐old female presented with ruptured 3 × 5.3 mm right posterior communicating artery (Pcom) aneurysm. H&H 5 and MFS 4. Underwent primary coil embolization with placement of Galaxy Orbit 2.5mmx3.5cm coil. On follow up run, coil mass had migrated into the origin of right fetal Pcom. Migrated coil was successfully retrieved using Stryker’s 4 × 40 mm stent retriever with complete recanalization. Case 3: 65‐year‐old female with presented ruptured 8.5 × 6.8 mm right supraclinoid ICA irregular aneurysm. H&H Grade 1. MFS 3. Underwent primary coil embolization with one Galaxy coil (5mm x 10cm) with plan for future flow diversion. Two weeks later, patient experienced acute neurological worsening with new left sided hemiparesis and right gaze deviation. Imaging revealed acute occlusion of right middle cerebral artery M1 segment occlusion with thrombosed migrated coil. Patient underwent retrieval of the coil and superimposed thrombus utilizing Stryker’s Trevo (4*30 mm) stent retriever with resultant full recanalization. Conclusions : These cases demonstrate successful endovascular mechanical removal of migrated coils using stent retrievers. They add to the limited experience of stent retrievers utilization as effective tools for dealing with such complications.

Compensation for Lateral Misalignment in Litz Wire Based on Multilayer Coil Technology

This study applies a multilayer coil technology that can compensate for a decrease in transfer efficiency due to a lateral misalignment in a practical 100 kHz-band wireless power transfer system and validates its effect on the efficiency of compensation. The effectiveness is investigated using coils fabricated with Litz wires. Three-turn rectangular assistant coils 22.4 × 45.3 mm2 in size were stacked on a five-turn circular primary coil with a diameter of 45.3 mm in a 2 × 1 array. Transfer efficiency between two such coils was measured by producing lateral misalignment, while maintaining the vertical distance between the Tx and Rx coils at 7 mm. The experimental results showed that the transfer efficiency was compensated by approximately 46.1%P maximum in a misalignment state of 30 mm, which corresponded to 67% of the maximum size of the coil, compared to the transfer efficiency of the structure, in which the multilayer coil was not applied. Furthermore, transfer efficiency was compensated by 37.6%P, even in an asymmetric system in which the multilayer structure was applied only to the Tx coil, thereby confirming an excellent multilayer coil technology effect on compensation for lateral misalignment in practical cases.

Research on Characteristics of Wireless Power Transfer System Based on U-Type Coupling Mechanism

Aiming at the power supply problem of high-speed rotating equipment, a wireless power transfer system based on U-shaped core coupling mechanism with a primary coil is proposed. Firstly, the transfer model of the U-type coupling mechanism wireless power transfer system is established. The expressions of transfer power and transfer efficiency are obtained by theoretical calculation, and the factors affecting the transfer characteristics of the system are analyzed. At the same time, the magnetic field distribution of the system and the coupling parameters change when the relative position of the primary and secondary coils changes through simulation analysis. Finally, an experimental platform is established for experimental verification. The results show that the system can obtain 1.72 w output power with 51.19% transfer efficiency when the distance between the secondary coil and U-core is 15 mm and 30 mm, respectively. The transmission efficiency and power of the primary coil and secondary coil under different misalignments are tested and compared. It is proved that the wireless power transfer system based on U-type coupling mechanism can effectively realize the stable power supply of the rotating equipment monitoring system.

Perancangan Sensor LVDT dan Potensiometer Geser Sederhana Sebagai Alat Potensial Pendeteksi Pergeseran Tanah

A preliminary study on the design of a Linear Variable Differential Transformer (LVDT) sensor and a sliding potentiometer has been carried out. It is a distance measuring sensor that can be used as a ground shift sensor. This study aims to develop a new type of low cost mechanical sensor which has a high enough accuracy. The LVDT sensor is built using affordable materials such as PVC pipes, winding wires and iron cores, which is varied based on the number of primary coil and its diameter. While the potentiometer sensor is prepared by using linear bearing using electrode sheets of nickel and copper which is arranged by implemented the concept of the Newton-Wheatstone Bridge. The measurement value shows that the LVDT sensor with the number of primary coil of 110 and a diameter of 4 mm can measure with an accuracy of 0.5 mm and a range of more than 4 cm. While the sliding potentiometer using a sheet of copper electrodes can measure 0.5 mm with a range of more than 4 cm. The average error shown by the LVDT sensor and the sliding potentiometer is 5.2% and 6.4%, respectively.

Non-Destructive Evaluation for Sectional Loss of External Tendon of Prestressed Concrete Structures Using Total Flux Leakage

A non-destructive evaluation method is proposed to identify the sectional loss of the external tendon of prestressed concrete structures by detecting the change of the magnetic flux in the external tendon exposed to a magnetic field. The method uses a solenoid-shaped device with two coils: a primary coil for producing magnetic field and secondary coil for damage detection, wrapping the external tendon. A current applied to the primary coil in the device causes the magnetic field. Then, the change in the magnetic flux by the damage in the external tendon is detected by the variation of the voltage in the secondary coil in the device as the device moves along the tendon. An alternating current is applied to the primary coil to minimize the effect of the moving speed of the device. As a result, the damaged area can be detected with a low-level energy current. In addition, a wrapping solenoid-shaped device that is easy to disassemble and assemble was developed for in situ inspection. The measured signal from the secondary coil has a sinusoidal form with the same frequency as the applied current to the primary coil, and the peak curve of the measured signal provides enough information to detect the damage. It is shown that the proposed method can quantitatively identify one or multiple damaged-tendon locations as well as damages of at least 2 cm.

An Inductive Sensor for Two-Dimensional Displacement Measurement

The simultaneous and independent measurements of two-dimensional (2D) displacements are significant for 2D positioning. Here a planar inductive sensor which is based on the principle of electromagnetic induction is proposed. The sensor is composed of a primary coil and a secondary coil. The primary coil consists of an array of planar spiral coils which are arranged as an m × n matrix. The primary coil is supplied with 4 kHz alternating current to generate an array of pulsating magnetic field. The secondary coil contains four spiral coils which are arranged as a 2 × 2 matrix. Thereby, four roads of modulated signals whose amplitudes vary with displacements of the secondary coil along x- and y-axis are induced. An algorithm based on the Coordinate Rotation Digital Computer algorithm is introduced to resolve the planar displacements. The structure and working principle of the sensor are proposed firstly. Then, the finite element analysis of the electromagnetic model and the numerical simulation of the algorithm are given. An experiment has been performed on a sensor prototype and the results show that the proposed scheme is feasible. Measurement error analysis of the sensor has been pursued at the end of the paper.

Analysis of the Influence and Number of Turns on the Smartphone Wireless Charger on the Output Power of the Wireless Charger

Charging the smartphone battery can be done via powerbank or default charger from the smartphone still using the cable for charging the electricity. Charging using a cable certainly limits the use of the smartphone when it is charging. Smartphone users can not be far from the electric socket which of course is troublesome if this happens in the middle of a room that has a few electrical sockets. To solve this problem, now many wireless charging smartphones or smartphones have been developed wireless charger. Behind the benefits obtained from a wireless charger, it also has disadvantages, namely the transmission distance is short, even there is no distance and the transmitted power is unstable. Wireless chargers are based on the principle of magnetic induction in which electricity is transferred between two objects through a coil. Wireless charger consists of the primary coil as a charger (usually in the form of a thin board or cylinder), and the secondary coil is located on the back of the cellphone. Based on the results, the output power is obtained. The largest wireless charger is 0.027W with a coil diameter of 8cm in all the number of primary coils, namely 40 turns, 50 turns, and 60 turns at a primary and secondary coil distance of 0cm to 1cm. The farthest distance from the wireless charger output power test is 6cm as well as the 8cm coil diameter for all the number of primary coil turns, namely 40 turns, 50 turns, and 60 turns.