Impact Of Air Gap Research Articles

Innovative Design and Optimization of Adjustable Capacitors for RadioFrequency new MRI Systems

This review delineates significant strides in the evolution of adjustable capacitors tailored specifically for highfrequency Magnetic Resonance Imaging (MRI) applications. The research spans critical phases, meticulously detailing the adaptation of electrode shapes to attain versatile capacitance within a high-frequency spectrum. The prototype, a key focal point, showcases distinctive attributes, featuring silver-fixed and CuNiZn half-disc mobile plates mounted on a MgTiCa ceramic pellet. Comprehensive evaluation, incorporating simulation and measurement at 10MHz, illuminates the prototype's capacitance dynamics. The optimization model scrutinizes pivotal parameters governing capacitor assembly, placing a specific emphasis on the profound influence of air gap thickness on rotor equilibrium. A granular analysis of the air gap's impact on capacitance and self-resonance frequency enriches the study, offering valuable insights into configurations optimized for highfrequency MRI applications. Validation of the prototype's electrical properties through the HP Agilent 4192A LF Impedance Analyzer establishes a robust correlation with simulation results, effectively aligning with stringent MRI system specifications. The intricate assembly process, inclusive of electrode optimization considering frequency nuances and the innovative use of silver glue, is meticulously expounded upon. In-depth discussion encapsulates the rigorous validation of the development process, the stability exhibited by chosen materials across varying frequencies, and the nuanced influence of the air gap on capacitance. After concluding that the prototype meets specifications, the study charts a course for future research toward competitive trimmers for highfrequency MRIs. What distinguishes this research is its meticulous exploration of electrode shapes, the unique composition of the prototype, and a comprehensive analysis of the intricate interplay between air gap variations and capacitor performance. This work is distinguished further by the inclusion of silver glue that enhances practical implementation.

Comparison of conventional versus customised Eurosil-4 Pink bolus for radiotherapy of the chest wall.

In radiotherapy, the presence of air gaps near a tumour can lead to underdose to the tumour. In this study, the impact of air gaps on dose to the surface was evaluated. 3D-printing was used to construct a Eurosil-4 Pink bolus customised to the patient and its dosimetric properties were compared with that of Paraffin wax bolus. Surface dose was measured for flat sheets of Eurosil-4 Pink bolus with different thicknesses. Different air gap thicknesses were inserted between the bolus and the surface, and dose was measured for each air gap using 10 cm × 10 cm fields. This was repeated with the effective field size calculated from the patient plan. Surface dose was measured for varying angles of incidence. A customised chest phantom was used to compare dose for two customised Eurosil-4 Pink boluses, and commonly used Paraffin wax bolus. The surface dose was found to be highest for 1.1 cm thick bolus. The decrease in surface dose for the Eurosil-4 Pink bolus was minimal for the 10 cm × 10 cm field, but higher for the effective field size and larger angles of incidence. For instance, the dose was reduced by 6.2% as a result of 1 cm air gap for the effective field size and 60 degree angle of incidence. The doses measured using Gafchromic film under the customised Eurosil-4 Pink boluses were similar to that of the Paraffin wax bolus, and higher than prescribed dose. The impact of air gaps can be significant for small field sizes and oblique beams. A customised Eurosil-4 Pink bolus has promising physical and dosimetric properties to ensure sufficient dose to the tumour, even for treatments where larger impact of air gaps is suspected.

Impact of air gap, range shifter, and delivery technique on skin dose in proton therapy.

Side effects of radiation therapy may include skin damage. The surface dose is of great interest and contains the buildup effect. In particular, the proton therapy community requires further experimental data to quantify doses in the surface region. This specification includes the skin dose, which is defined according to ICRU Report No. 39 at 70μm water equivalent depth. The aim of this study is to gather more knowledge of the skin dose by varying key parameters defined by the patient treatment plan. This consists of clinical aspects such as the influence of the air gap, the application of a range shifter (RS), or the proton delivery technique. Skin doses were determined with a PTW 23391 extrapolation chamber with three thin Kapton® entrance windows operated as a conventional ionization chamber. The impact on the skin dose for quasi-monoenergetic pencil beam scanning (PBS) proton beams was evaluated for clinical air gaps between 3.5 and 51.1cm. The differences in skin dose were assessed by irradiating equivalent fields with an RS of 51mm water equivalent thickness (RS51) and without. Furthermore, the delivery techniques PBS, uniform scanning (US), and double scattering (DS) were compared by defining a spread-out Bragg peak (SOBP). TOPAS (V.3.1.2) was used to model an IBA nozzle with PBS and to score dose to water at the surface of a water phantom. For the monoenergetic fields without the application of the RS the skin dose was constant down to an air gap of 6.2cm. A lower air gap of 3.5cm showed a variation in skin dose by up to 2.4% compared to the results obtained with larger air gaps. With the inserted RS51 an increase in the skin dose was found for air gaps smaller than 11.3cm. Experimentally, a dose difference of 1.4% was recorded for an air gap of 6.2cm by inserting an RS and none. With the Monte Carlo calculations the largest dose increase was observed at the air gap of 3.5cm with 1.7% and 4.0% relative to the skin dose results without the RS and to the largest evaluated air gap of 51.1cm, respectively. The SOBP comparison of the beam modalities at the measuring plane at the isocenter revealed higher skin doses without RS (including RS) by up to +1.9% (+1.5%) for DS and +1.3% (+1.1%) for US compared to PBS. For all three techniques an approx. 2% rise in skin dose was observed for the largest evaluated air gap of 37.7cm to an air gap of 6.2cm when using an RS51. The study investigated aspects of skin dose of a water equivalent phantom by varying key parameters of a proton treatment plan. Parameters like the RS, the air gap, and the delivery modality have an impact on the order of 4.0% for the skin dose at the depth of 70μm. The increases in skin dose are the effects of the contribution of the increased electron fluence at small air gaps and the emitted hadronic particles produced by the RS.

The impact of air gaps between needle and polymer on electrical treeing in needle-plane samples

Electrical trees are widely grown in laboratories from metallic needle electrodes to enable the degradation process to proceed rapidly at voltages of ∼10 kV AC. Here it is shown that cone-shaped air gaps may form at a needle tip, even when they are not visible optically. Using X-ray imaging techniques, samples with and without air gaps up to 55 μm long have been characterized. The presence of air gaps led to partial discharge (PD) patterns resembling void-discharges. Prior to tree initiation, discharge characteristics evolved with increased voltage increments and increased phase lag behind the applied voltage. These changes to PD characteristics reflect a change in the physical state of the air gap. Although samples with air gaps generally initiated trees quicker than those with no gap, PD activities did not appear to play a decisive role in tree initiation times. However, initial voids were found to have major impact on the subsequent tree growth. In samples with persistent pre-tree air-gap PDs, trees grew larger branchy structures with higher PD magnitudes. In addition, the PDs became more asymmetric between positive and negative half-cycles than occurred in samples with no air gaps. It is shown that understanding the interface between the needle and polymer at a micron scale is critical to interpretation of laboratory tree growth experiments.

SU‐E‐T‐454: Impact of Air Gap On PDDs of 6 MV Photon Beam for Various Field Sizes in Inhomogeneous Phantoms

Purpose:To investigate how the shape of air gap and its size will impact the percent depth doses (PDDs) of a 6MV photon beam for various field sizes.Methods:Two in‐house phantoms were manufactured containing rectangular (phantom A) and circular (phantom B) air gaps. Both phantoms A and B were composed of same top layer (solid‐water; 30×30cm2,5cm thickness) and bottom layer (solid‐water; 30×30cm 2,8cm thickness), but middle layer was varied to observe air gap effects and scatter contribution to the measurement point. In phantom A, a rectangular shaped air gap (30×30cm2,7cm thickness) was created by placing Styrofoam blocks between top and bottom layers of the phantom. In phantom B, middle layer was replaced by “inhomogenous block”, composed of acrylic plate (30×30cm2, 4cm thickness) followed by PVC(30×30cm2,3cm thickness). Additionally, circular air gap was created by drilling a hole (diameter=2.8cm, length=7cm) at the center of “inhomogenous block”. In both phantoms, measurement readings were obtained at 13cm depth (i.e., 1cm after air gap) and depth of maximum dose(6MV energy; 100 MUs; field sizes ranged from 3×3cm2 to 10×10cm2). The PDDs at 13cm depth were compared in both phantoms.Results:The measurements in both phantoms A and B showed an almost linear increase in PDDs with increasing field size, especially for smaller field sizes (from 3×3 to 7×7cm2). For each field size, the PDD in phantom A was smaller compared to the one in phantom B. The difference in PDDs between two phantoms decreased with an increase in field size as the PDD difference decreased from 9.0% to 6.4%.Conclusion:The shape and size of air gap affect the PDD measurements in secondary build‐up region as 6 MV primary beam traverses through the center of air gap. The scatter contribution due to increase in field size was more noticeable for field sizes ≤7×7cm2.

The impact of air gap on thermal performance of protective clothing against hot water spray

The air gap size and distribution developed between clothing and a human body play a critical role in clothing performance, specifically for thermal protective clothing. Hot liquid is considered as one of the common hazards in industrial working environments. In this study, the clothing air layer entrapped between protective clothing and a manikin body was determined using three-dimensional body scanning, and the protective performance provide by the clothing was predicted using an instrumented hot water spray manikin evaluation system. The relationship between the average air gap size and overall protective performance was analyzed. The impact of clothing air gap developed along the human body on predicted burn injury was considered. In addition, the air gap distribution and its relation to skin burn injury were compared for the selected garments. In general, the results indicated that the average air gap size showed positive effects on the overall protective performance. For all body parts except the pelvis, the air gap size presented a significant relationship with the percentage of burn injury. For an individual garment, there was no significant correlation found between the air gap distribution and skin burn injury. The garment with a larger air gap size and minimal air gap changes during hot water spray provided better protective performance. The research findings could provide the technical basis for further development of high performance protective clothing.

Dosimetric Comparison of Heterogeniety Versus Nonheterogeneity Corrected Dose Calculations in Vaginal Brachytherapy: The Impact of Air Gaps

The presence of air gaps between an HDR vaginal cylinder and the vaginal wall is potentially problematic as it may push the vaginal lymphatics outside the prescribed isodose line. This prospective study compares the volume of air gaps observed for two different diameter cylinders (2 cm and optimal) inserted in the same patient and evaluates the dosimetric impact on the target volume (vaginal lymphatics) and the surrounding normal tissues using both heterogeneity and non-heterogeneity corrected calculation algorithms.

An investigation of central axis depth dose distribution perturbation due to an air gap between patient and bolus for electron beams

Electron beams can be used for the radiotherapy treatment of superficial cancers. In many cases of electron beam radiotherapy, tissue equivalent bolus material placed on the skin is to be used to enhance skin dose. An air gap might be present between the bolus and the skin due to variation in the patient contour. The impact of semi-infinite air gaps under bolus material on central axis depth dose distributions for electron beams was investigated in this study. Semi-infinite air gaps were introduced between bolus and the surface of a water phantom for air gap sizes up to 20.0 mm and for bolus thicknesses of 5, 10 and 15 mm. The electron beams studied had nominal energies of 6, 10 and 14 MeV and circular fields of 3, 5, 7 and 9 cm diameter. Depth dose measurements were carried out in the water phantom with a Scanditronix p-Si electron diode. It was found that the impact of an air gap is dependent on beam energy, field size, air gap size and bolus thickness used. The impact of the air gap on central axis depth dose distribution increased with decreasing field size, increasing air gap size, decreasing electron beam energy and increasing bolus thickness. For 15 mm bolus, 3 cm diameter circular field, 6 MeV beam and the 20 mm air gap, the maximum dose and the surface dose was reduced by approximately 60% and the depth of dose maximum shifted 3.5 mm. An air gap between bolus and a patient should be avoided to ensure that there is no impact on the treatment. The measured data in this study can be used to determine the likely degree of impact on the treatment, of unavoidable air gaps between bolus and the patient.

Frequency selective surfaces on building materials – air gap impact

It is demonstrated how frequency selective surfaces (FSSs) can be deployed on conventional building materials, so as the FSS frequency response is not affected by the building material. This effectively means that the two surfaces, the FSS and the building wall surface, will affect radio propagation independently based on their own characteristics. When FSSs are attached to building walls, they can suffer significant detuning, compared to free-standing frequency response, which appears to fade away as the air gap between the two surfaces increases. Simulations and anechoic chamber measurements demonstrate that a 'break-point' air gap exists, beyond which the FSS response is not affected by the presence of the building wall.