Determination of efficiencies, loss mechanisms, and performance degradation factors in chopper controlled dc vehical motors. Section 2: The time dependent finite element modeling of the electromagnetic field in electrical machines: Methods and applications

The time dependent solution of the magnetic field is introduced as a method for accounting for the variation, in time, of the machine parameters in predicting and analyzing the performance of the electrical machines. The method of time dependent finite element was used in combination with an also time dependent construction of a grid for the air gap region. The Maxwell stress tensor was used to calculate the airgap torque from the magnetic vector potential distribution. Incremental inductances were defined and calculated as functions of time, depending on eddy currents and saturation. The currents in all the machine circuits were calculated in the time domain based on these inductances, which were continuously updated. The method was applied to a chopper controlled DC series motor used for electric vehicle drive, and to a salient pole sychronous motor with damper bars. Simulation results were compared to experimentally obtained ones

Microfabricated Implantable Parylene-Based Wireless Passive Intraocular Pressure Sensors

This paper presents an implantable parylene-based wireless pressure sensor for biomedical pressure sensing applications specifically designed for continuous intraocular pressure (IOP) monitoring in glaucoma patients. It has an electrical LC tank resonant circuit formed by an integrated capacitor and an inductor coil to facilitate passive wireless sensing using an external interrogating coil connected to a readout unit. Two surface-micromachined sensor designs incorporating variable capacitor and variable capacitor/inductor resonant circuits have been implemented to realize the pressure-sensitive components. The sensor is monolithically microfabricated by exploiting parylene as a biocompatible structural material in a suitable form factor for minimally invasive intraocular implantation. Pressure responses of the microsensor have been characterized to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) in both sensor designs, which confirms the feasibility of pressure sensing with smaller than 1 mmHg of resolution for practical biomedical applications. A six-month animal study verifies the in vivo bioefficacy and biostability of the implant in the intraocular environment with no surgical or postoperative complications. Preliminary ex vivo experimental results verify the IOP sensing feasibility of such device. This sensor will ultimately be implanted at the pars plana or on the iris of the eye to fulfill continuous, convenient, direct, and faithful IOP monitoring

Design criteria of a transcutaneous power delivery system for implantable devices.

Implantable cardiac assist devices such as artificial hearts and blood pumps are a rapidly growing therapy used for treating moderate to severe congestive heart failure. While current treatments offer improved heart failure survival and increased patient functionality with enhanced quality of life, powering these devices are still constraining. In practice, percutaneous cables passing through skin are used for power and control data transmission requiring patients to maintain a sterile dressing on the skin cable-exit site. This contact site limits patient movement as it is vulnerable to wound infection due to trauma and poor healing. As a result, a sterile dressing has to be maintained and nursed regularly for treating the wound. Complications from the exit site infections are a leading cause of death in long-term support with these devices. Wireless power and control transmission systems have been studied and developed over years in order to avoid percutaneous cables while supplying power efficiently to the implanted device. These power systems, commonly named Transcutaneous Energy Transfer (TET) systems, enable power transmission across the skin without direct electrical connectivity to the power source. TET systems use time-varying electromagnetic induction produced by a primary coil that is usually placed near skin outside the body. The induced voltage in an implanted secondary coil is then rectified and regulated to transfer energy to an implanted rechargeable battery in order to power the biomedical load device. Efficient and optimum energy transfer using such transcutaneous methods is more complex for mobile patients due to coupling discrepancies caused by variations in the alignment of the coil. The research studies equivalent maximum power transfer topologies for evaluating voltage gain and coupling link efficiency of TET system. Also, this research adds to previous efforts by generalizing different scenarios of misalignments of different coil size that affects the coupling link. As a whole, this study of geometric coil misalignments reconsiders potential anatomic location for coil placement to optimize TET systems performance in anticipated environment for efficient and safe operation.--Abstract

Detection of NMR signals with a radio-frequency atomic magnetometer

We demonstrate detection of proton NMR signals with a radio frequency atomic magnetometer tuned to the NMR frequency of 62 kHz. High-frequency operation of the atomic magnetometer makes it relatively insensitive to ambient magnetic field noise. We obtain magnetic field sensitivity of 7 fT/Hz$^{1/2}$ using only a thin aluminum shield. We also derive an expression for the fundamental sensitivity limit of a surface inductive pick-up coil as a function of frequency and find that an atomic rf magnetometer is intrinsically more sensitive than a coil of comparable size for frequencies below about 50 MHz.Comment: 7 page

Alternating current potential drop and eddy current methods for nondestructive evaluation of case depth

Case hardening treatments offer a means of enhancing the strength and wear properties of parts made from steels. Generally applied to near-finished components, the processes impart a high-hardness wear-resistant surface which, with sufficient depth, can also improve fatigue strength. Applications range from simple mild steel pressings to heavy-duty alloy-steel transmission components. The characteristics of case hardening are the surface hardness, effective case depth, and depth profile of the residual stress. The specified case depth varies for different applications. It is useful to be able to measure the case depth nondestructively to ensure the specification is met.;In the work outlined in this dissertation, the aim is to evaluate the properties of case hardened parts nondestructively. The case hardening process produces a change in the electromagnetic properties of the steel components in the near surface region. Consequently, the electrical conductivity and magnetic permeability have different values near the surface compared with those of the substrate. It is assumed that the conductivity and permeability variation with depth is indicative of the hardness profile allowing the case depth to be estimated from electromagnetic measurements. A two-layer model is adopted to approximate the case hardened steel parts as a homogeneous substrate layer surrounded by a homogeneous surface layer with uniform thickness. Alternating current potential drop (ACPD) theoretical calculations have been performed and compared with experimental measurements for both case hardened cylindrical rods and homogeneous metal plates. Driver and pick-up coils have been used for eddy current induction measurements on the cylindrical rod specimens. The multi-frequency measurement data are used to estimate the case depth by model-based inversion. The measured case depth is in reasonable agreement with the effective case depth from the measured hardness profile. Excellent agreement is observed between the measurement data and the theoretical calculation on homogeneous metal plates

Metamaterial MRI-based sensor for the post-operative monitoring of colorectal anastomosis

Anastomotic leakage (AL) is the leading cause of morbidity and mortality after bowel anastomosis, a surgical procedure used to restore luminal continuity after bowel tumour resection. Even after years of research, its occurrence has not decreased, and new methods of monitoring the wound and predicting anastomotic failure are therefore urgently required. Here we propose the use of an internal coil to increase the signal-to-noise ratio (SNR) during Magnetic Resonance Imaging (MRI ) and/or Spectroscopy (MRS). Both methods may be used to identify ischemia and oedema, considered to be clinical indications of AL. The annular nature of the anastomotic surgical wound suggests the use of a coil with an annular field-of view, mounted on a Biodegradable Anastomosis Ring (BAR), a surgical device commonly used as a temporary mechanical support that is fragmented and excreted from the body after wound healing. The proposed solution is a Magneto-Inductive (MI) ring resonator, based on a set of magnetically coupled L-C resonators. Its advantages are that its separate elements fit comfortably inside the BAR, are not mechanically connected, and consequently may be fragmented and excreted with the BAR itself. A coupled pair of 8-element MI ring resonators is proposed, operating on an anti-symmetric spatial mode to avoid coupling to the B1 field during the excitation phase of MRI. However, the electrical response of an early prototype shows that insufficient rejection of uniform fields is achieved using the most obvious arrangement. Therefore, a search of the effect of design parameters on the spectra of resonant modes supported by the electrical system is carried out to identify an arrangement offering improved decoupling. A suitable design is developed, based on physical overlap between adjacent elements in the same ring, which alters the sign and magnitude of a key magnetic coupling coefficient. MRI fields-of-view are theoretically estimated for several different arrangements for signal extraction, including devices that are mutually coupled to an external read coil and directly coupled devices. Difficulties with combining mutual coupling and B1 field rejection are identified, and wired connections are proposed as a solution. It is found that a device with a single such connection gives a sensitivity pattern with partial symmetry, whereas a quadrature tap restores full symmetry. In vitro 1H MRI is then carried out at 1.5 T and 3.0 T using agar gel immersion phantoms, both for mutually coupled systems and for directly coupled systems. As expected, mutual coupling is found to be an unsuitable readout method for a device operating on its anti-symmetric mode, but does allow analysis of the effectiveness of B1 field decoupling. Directly coupled devices operate essentially as expected, providing up to 15-fold local enhancement in SNR, compared to the system body coil.Open Acces

Printed Spiral Coil Design, Implementation, And Optimization For 13.56 MHz Near-Field Wireless Resistive Analog Passive (WRAP) Sensors

Noroozi, Babak. Ph.D. The University of Memphis. June 2020. Printed Spiral Coil Design, Implementation, and Optimization for 13.56 MHz Near-Field Wireless Resistive Analog Passive (WRAP) Sensors. Major Professor: Dr. Bashir I. Morshed.Monitoring the bio-signals in the regular daily activities for a long time can embrace many benefits for the patients, caregivers, and healthcare system. Early diagnosis of diseases prior to the onset of serious symptoms gives more time to take some preventive action and to begin effective treatment with lower cost. These health and economy benefits are achievable with a user-friendly, low-cost, and unobtrusive wearable sensor that can easily be carried by a patient with no interference with the normal life. The easy application of such sensor brings the smart and connected community (SCC) idea to existence. The spread of a designated disease, like COVID-19, can be studied by collecting the physiological signals transmitted from the wearable sensors in conjunction with a mobile app interface. Moreover, such a comfortable wearable sensor can help to monitor the vital signals during fitness activities for workout concerns. The desire of such wearable sensor has been responded in many researches and commercial products such as smart watch and Fitbit. Wireless connection between the sensor on the body and the scanner is the key and common factor of all convenient wearables. This essential feature has been currently addressed by the costly techniques which is the main impediment to be widely applicable. The existing wireless methods including WiFi, Bluetooth, RFID, and NFC impose cost, complexity, weight, and extra maintenance including battery replacement or recharging, which drove us to propose a low-cost, convenient, and simple technique for wireless connection suitable for battery-less fully-passive sensors. Using a pair of coils connected by the near-field magnetic induction has been copiously used in wireless power transfer (WPT) for medical and industrial applications. However, near field RFID and NFC rely on this technique with active circuits. In contrast, we have proposed a wireless resistive analog passive (WRAP) sensor in which a resistive transducer at the secondary side, affects the primary quality factor (Q) through the inductive connection between a pair of square-shaped Printed Spiral Coils (PSC). The primary 13.56 MHz (ISM band) signal is modulated in response to the continuous change of bio-signal and the amount of response to the unit change in transducer resistance is defined as sensitivity. A higher sensitivity enables the system to respond to the smaller bio-signals and increases the coils maximum relative mobilities. The PSCs specifications and circuit components determine the sensitivity and its tolerance to the coils displacements. We first define and formulize the objective function for coil and components optimization to achieve the maximum sensitivity. Although the optimization methods do not show much different results, due to the speed and simplicity, the Genetic Algorithm (GA) technique is chosen as an advanced method. Then in second optimization stage, the axial and lateral distances that affect the mutual inductance are introduced to the optimization process. The results as a pair of PSCs profiles and the associated circuit components are obtained and fabricated that produced the maximum sensitivity and misalignment tolerance. For the sake of patient comfort, the secondary coil size is fixed at 20 mm and the primary coil is optimized at 60 mm with the maximum (normalized) sensitivity 1.3 m for 16 mm axial distance. If the Read-Zone is defined as the space in which the center of secondary coil can move and the sensitivity keeps at least half of its maximum value, the best Read-Zone has a conical shape with the base radius 22.5 mm and height 14 mm. The analytical results are verified by the measurement results on the fabricated coils and circuits