The increased power consumption and power density demands of modern technologies have increased the technical requirements of DC/DC and AC/DC power supplies. In this regard, the primary objective of the power supply researcher/engineer is to build energy efficient, high power density converters by reducing the losses and increasing the switching frequency of converters respectively. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. Therefore, the thesis work is focussed on the design, analysis and evaluation of isolated converters operating in the 1 - 5MHz frequency region with the assistance of the latest semi conductor devices, both coreless and core based planar power transformers designed in Mid Sweden University and which are suitable for consumer applications of varying power levels ranging from 1 – 60W. In high frequency converter circuits, since the MOSFET gate driver plays a prominent role, different commercially available MOSFET gate drivers were evaluated in the frequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall times and electromagnetic interference (EMI) and a suitable driver was proposed. Initially, the research was focused on the design and evaluation of a quasi resonant flyback converter using a multilayered coreless PCB step down transformer in the frequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency of this converter is found to be 72 - 84% under zero voltage switching conditions (ZVS). In order to further improve the energy efficiency of the converter in the MHz frequency region, the new material device GaN HEMT was considered. The comparisons were made on a quasi resonant flyback DC-DC converter using both the Si and GaN technology and it was found that an energy efficiency improvement of 8 – 10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In order to minimize the gate drive power consumption, switching losses and to increase the frequency of the converter in some applications such as laptop adapters, set top box (STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a high voltage Si MOSFET was designed and evaluated using a multi-layered coreless PCB transformer in the MHz frequency region. Both the simulation and experimental results have shown that, with the assistance of the cascode flyback converter, the switching speeds of the converter can be increased with the benefit of obtaining a significant improvement in the energy efficiency as compared to that for the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the converter circuit, double ended topologies were considered. Due to the lack of high voltage high side gate drivers in the MHz frequency region, a gate drive circuitry utilizing the multi-layered coreless PCB signal transformer was designed and evaluated in both a half-bridge and series resonant converter (SRC). It was found that the gate drive power consumption using this transformer was around 0.66W for the frequency range of 1.5 - v 3.75 MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the SRC using multilayered coreless PCB power transformer was found to be 86.5% with an output power of 36.5W in the switching frequency range of 2 – 3MHz. In order to further enhance the energy efficiency of the converter to more than 90%, investigations were carried out by using the multiresonant converter topology (LCC and LLC), novel hybrid core high frequency planar power transformer and the GaN HEMTs. The simulated and experimental results of the designed LCC resonant converter show that it is feasible to obtain higher energy efficiency isolated DC/DC converters in the MHz frequency region. The peak energy efficiency of the LCC converter at 3.5MHz is reported to be 92% using synchronous rectification. Different modulation techniques were implemented to regulate the converter for both line and load variations using a digital controller. In order to realize an AC/DC converter suitable for a laptop adapter application, consideration was given to the low line of the universal input voltage range due to the GaN switch limitation. The energy efficiency of the regulated converter operating in the frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a load power of 45W and an output voltage of 22V dc. In order to determine an efficient power processing method on the secondary side of the converter, a comparison was made between diode rectification and synchronous rectification and optimal rectification was proposed for the converters operating in the MHz frequency range for a given power transfer application. In order to maintain high energy efficiency for a wide load range and to maintain the narrow switching frequency range for the given input voltage specifications, the LLC resonant converter has been designed and evaluated for the adapter application. From the observed results, the energy efficiency of the LLC resonant converter is maintained at a high level for a wide load range as compared to that for the LCC resonant converter. Investigations were also carried out on isolated class E resonant DC-DC converter with the assistance of GaN HEMT and a high performance planar power transformer at the switching frequency of 5MHz. The simulated energy efficiency of the converter for the output power level of 16W is obtained as 88.5% which makes it feasible to utilize the designed isolated converter for various applications that require light weight and low profile converters. In conclusion, the research in this dissertation has addressed various issues related to high frequency isolated converters and has proposed solution by designing highly energy efficient converters to meet the current industrial trends by using coreless and core based planar transformer technologies along with the assistance of GaN HEMTs. With the provided solution, in the near future, it is feasible to realize low profile, high power density DC/DC and AC/DC converters operating in MHz frequency region suitable for various applications. / High Frequency Switch Mode Power Supplies

Therapeutic ultrasound is a deep heating modality often used to produce vigorous heating (≥4°C Δ) in tissues. The vigorous heating effects of 3 MHz therapeutic ultrasound have only been tested to a 2.5 cm depth, but its maximal depth of producing vigorous heating has yet to be established. Objective: To investigate the tissue temperature change produced by a 3 MHz ultrasound treatment at depths of 3 and 3.5 cm in the human triceps surae muscle group. Design: Randomized control design. Setting: Therapeutic modalities research laboratory. Patients or Other Participants: Twenty healthy college-aged participants (male = 13, female = 7; age = 23.4 ± 1.31; calf subcutaneous fat thickness= 0.6 cm ± 0.2 cm). Participants were randomized into treatment (n = 15) and sham (n = 5) groups. Participants were blinded to their group assignment. Interventions: Two MT-26/6 needle thermocouples were inserted into the left posterior triceps surae at depths of 3.0 ± 0.1cm and 3.5 ± 0.1cm from the skin's surface. Participants in the treatment group received a continuous 3 MHz ultrasound treatment at 1.4 W/cm2 for 8 minutes with 10mL of 100% ultrasound gel as a coupling medium. Participants in the sham group received the same treatment parameters, but the ultrasound device was not turned on. The Omnisound 3000 ultrasound device (ERA = 4.2cm2, BNR = 3.0:1) was used for all treatments. A 15 cm2 template was used to ensure a constant and proper treatment size. Baseline temperature (TB) was established by taking a mean of intramuscular tissue temperature (TIM)for five minutes before the treatment and TIM were recorded every 10 seconds throughout the experiment session. Participants marked a visual analog scale (VAS) indicating heat sensation at pre-treatment and post-treatment. Main Outcome Measures: A 2 x 2 x 2 (probe depth x condition x time) ANCOVA with TB used as a covariate analyzed the difference in TIM. We only used the time points of baseline and final TIM for our analysis as we are only interested in the change in TIM from beginning to end of the ultrasound treatment. Descriptive statistics for TIM and VAS for heat sensation were computed as post-treatment minus pre-treatment for each condition and probe depth. Results: There was a significant difference in TIM between the conditions at the different probe depths from the beginning and end of the ultrasound treatment (F1,15 = 7.35, p = 0.016). The mean changes in TIM for each condition at each probe depth were: sham 3cm = -0.4 ± 0.3°C, sham, 3.5cm = -0.2 ± 0.3°C, treatment, 3cm = 4.4 ± 0.2°C, treatment, 3.5cm = 3.5 ± 0.2°C. Mean VAS scores for each group were: sham = 0 ± 0mm and treatment = 71.8 ± 11.8mm. Conclusions: At 3cm deep into the posterior calf, the Omnisound 3000 using a 3 MHz treatment produced vigorous heating (≥4°C Δ). Moderate heating (2-3°C Δ) occurred at 3.5cm deep into the calf. Three MHz ultrasound may be used to heat tissues deeper than previously theorized, but it does, however, create a moderately high level of heat sensation for the patient.

Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).