共查询到20条相似文献,搜索用时 15 毫秒
1.
This paper presents a study of the thermal spreading resistance Rth of a small heat source on a conductive substrate subject to bottom-side convective cooling. This problem has been investigated for a very long time and is well covered in the literature. However, instead of using the design curves found in many papers, the results are presented as function of the heat transfer coefficient h. Doing so, a remarkable property is revealed. The thermal resistance is proportional to the logarithm of the reciprocal heat transfer coefficient, for a broad range of at least three decades . This behaviour can be reasonably explained using an approximate one-dimensional heat spreading model. Being dictated by a logarithmic law, the dependency of Rth on h is rather weak. This is made clearer by the temperature profiles at the substrate bottom. Decreasing h leads to a wider spreading and hence a larger surface with the coolant is utilised, which partly compensates the poorer cooling. 相似文献
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Heat exchanges occurring between the electronic assemblies and their environment are an essential data in order to control their temperature, enhance their performance and improve their reliability. In this survey, the average natural convective heat transfer coefficient is determined for an assembly constituted by a Quad Flat Non-lead QFN64 generating a high power ranging from 0.1 to 1.0 W during operation. It is welded on a PCB which may be inclined with respect to the horizontal plane by an angle varying between 0° and 90°. The calculations done by means of the finite volume method show how the free convective heat transfer on every part of this electronic assembly is influenced by these physical parameters. The correlations proposed in this work allow calculating the convective heat transfer coefficient in any area of the considered assembly according to the generated power and the tilt inclination. These original and unpublished tools allow increasing reliability and better thermal control of this conventional device widely used in electronics for many engineering applications. 相似文献
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In vivo measurement of surgical gestures 总被引:3,自引:0,他引:3
Virtual reality techniques are now more and more widely used in the field of surgical training. However, the realism of the simulation devices requires a good knowledge of the mechanical behavior of the living organs. To provide perioperative measurement of laparoscopic surgical operations, we equipped a conventional operating grasper with a force sensor and a position sensor. The entire apparatus was connected to a PC that controlled the real-time data acquisition. After calibrating the sensors, we conducted three series of in vivo measurements on animals under video control. A standardized protocol was set up to perform various surgical gestures in a reproducible manner. Under these conditions, we can assess an original tool for a quantitative approach of surgical gestures' mechanics. The preliminary results will be extended by measurements during other operations and with other surgical instruments. The in vivo quantification of the mechanical interactions between operating instruments and anatomical structures is of great interest for the introduction of the force feedback in virtual surgery, for the modeling of the mechanical behavior of living organs, and for the design of new surgical instruments. This quantification of manipulations opens new prospects in the evaluation of surgical practices. 相似文献
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In vivo measurement of fundus pulsations by laser interferometry 总被引:1,自引:0,他引:1
A new noninvasive interferometric technique is described that yields information about the hemodynamic conditions at the fundus. Typical results as obtained from normal subjects are presented and briefly discussed. There is a typical position-dependent time course of the blood pulse induced dilatation of the fundus tissue. 相似文献
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Tomasz Zawada 《Microelectronics Journal》2006,37(4):340-352
An estimation of unknown properties of materials arises naturally when one considers some aspects of thermal modeling, especially carried out by widely used numerical methods, e.g. Finite Element Method (FEM).We propose a new approach of simultaneous thermal conductivity and heat transfer coefficient estimation based on thermographic measurements. A linear, steady-state distributed parameter model is used in order to describe the test sample. Thermal properties measurement is equivalent to the unknown parameter estimation of this system. The proposed method is practically applied for estimation of thermal conductivity and heat transfer coefficient of thick-film modules made on alumina (96% Al2O3) and DP951 ceramic substrates. In these experiments a high-resolution thermographic scanner is used.The obtained results for thermal conductivity and heat transfer factor are fully comparable with previously published ones. 相似文献
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Smith DG Potter SR Lee BR Ko HW Drummond WR Telford JK Partin AW 《IEEE transactions on bio-medical engineering》2000,47(10):1403-1405
A noninvasive electromagnetic method has been developed that can effectively measure the in-vivo conductivity difference between rat tumor lines having a low and high metastatic potential. These tumor lines are used in the study of human prostate tumor. 相似文献
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Tsai JZ Will JA Hubbard-Van Stelle S Cao H Tungjitkusolmun S Choy YB Haemmerich D Vorperian VR Webster JG 《IEEE transactions on bio-medical engineering》2002,49(5):472-483
We used a four-terminal plunge probe to measure myocardial resistivity in two directions at three sites from the epicardial surface of eight open-chest pigs in-vivo at eight frequencies ranging from 1 Hz to 1 MHz. We calibrated the plunge probe to minimize the error due to stray capacitance between the measured subject and ground. We calibrated the probe in saline solutions contained in a metal cup situated near the heart that had an electrical connection to the pig's heart. The mean of the measured myocardial resistivity was 319 ohm x cm at 1 Hz down to 166 ohm x cm at 1 MHz. Statistical analysis showed the measured myocardial resistivity of two out of eight pigs was significantly different from that of other pigs. The myocardial resistivity measured with the resistivity probe oriented along and across the epicardial fiber direction was significantly different at only one out of the eight frequencies. There was no significant difference in the myocardial resistivity measured at different sites. 相似文献
8.
In vivo measurement of the oxygen saturation of retinal vessels in healthy volunteers 总被引:1,自引:0,他引:1
Schweitzer D Hammer M Kraft J Thamm E Königsdörffer E Strobel J 《IEEE transactions on bio-medical engineering》1999,46(12):1454-1465
A new method for the spatially resolved measurement of the oxygen saturation of retinal vessels is described. Imaging spectrometry was used for both measurements of transmission and reflectance spectra of whole blood in cuvettes as well as for fundus reflectance spectra. A model was developed for the calculation of the oxygen saturation, valid in the wavelength range between 510 nm and 586 nm, in that the internal reflectance is constant and only the transmitted light depends on layer thickness and hematocrit. Altogether 265 measurements were performed in different number at 30 eyes. In each measurement, the oxygen saturation was simultaneously determined for 193 locations along a line of 1.5 mm at the fundus. The mean oxygen saturation in retinal arteries was (92.2 +/- 4.1)% and (57.9 +/- 9.9)% in retinal veins. The mean retinal arterio-venous difference of the oxygen saturation was (35.1 +/- 9.5)%. The venous oxygen saturation depended on distance from the optic disc. The measured mean of the arterio-venous difference of the oxygen saturation corresponded well to the value of the brain (34%). The utilization of oxygen in the temporal quadrants (inferior: 39.4 +/- 10.4%) is significantly (p = 0.05) higher than in the nasal quadrants (inferior: 31.3 +/- 6.7%). 相似文献
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In vitro and in vivo measurement for biological applications using micromachined probe 总被引:1,自引:0,他引:1
Jung-Mu Kim Donghoon Oh Jeonghoon Yoon Sungjoon Cho Namgon Kim Jeiwon Cho Youngwoo Kwon Changyul Cheon Yong-Kweon Kim 《Microwave Theory and Techniques》2005,53(11):3415-3421
We developed a small-sized micromachined probe for the measurement of biological properties using microelectromechanical systems (MEMS) technology. We also experimentally showed the suitability of the micromachined probe for biological applications through in vivo, as well as in vitro measurements of various types of tissue. We measured the permittivities of 0.9% saline and the muscle and fat of pork using the micromachined probe after liquid calibration. The measured permittivities of 0.9% saline and pork agreed well with both the expected values of the Cole-Cole equation along with the measured values obtained through the use of a 1-mm-diameter open-ended coaxial probe. We also performed in vivo measurements of breast cancer tissue implanted in an athymic nude mouse to show the suitability of the small-sized micromachined probe for practical biological applications. Through the obtained data, the capability of the micromachined probe of distinguishing different tissue types from one another was shown. The actual aperture size of the micromachined probe is only 240 /spl mu/m /spl times/ 70 /spl mu/m and, therefore, we can extract the biological information from very small biological tissues and drastically decrease the invasiveness of this method through the implementation of the small probe created through the use of MEMS technology. 相似文献
10.
The authors propose a new method of measuring the frequency characteristics of phase velocity along a bone for bending vibration modes to diagnose its mechanical characteristics. By introducing a simple model of a distributed-constant network, the phase velocity is determined for each frequency from the spatial distribution of velocity along a radius bone surface which is measured by the ultrasonic Doppler method 相似文献
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对流热损失对双曲两步热传导的影响 总被引:1,自引:1,他引:0
在激光热源加热时间远小于达到热平衡所需时间的条件下,研究了对流热损失对金属薄膜热行为的影响。指出当热源强度非常高且薄膜厚度满足L<20hc,e/G时,电子气的对流热损失对薄膜热行为的影响是不能忽略的;当L<20hc,l(θl-1)/Gθe时,固体晶格的对流热损失对薄膜行为有显著的影响。从双曲两步热传导模型出发,运用Laplace变换给出在考虑对流热损失的情况下,金属薄膜的电子气和固体晶格温度在Laplace变换域内的解析表达式,同时给出各种工作条件和材料参数对薄膜热损失的影响。 相似文献
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In vivo measurement of 3-D skeletal kinematics from sequences ofbiplane radiographs: Application to knee kinematics 总被引:1,自引:0,他引:1
Current noninvasive or minimally invasive methods for evaluating in vivo knee kinematics are inadequate for accurate determination of dynamic joint function due to limited accuracy and/or insufficient sampling rates. A three-dimensional (3-D) model-based method is presented to estimate skeletal motion of the knee from high-speed sequences of biplane radiographs. The method implicitly assumes that geometrical features cannot be detected reliably and an exact segmentation of bone edges is not always feasible. An existing biplane radiograph system was simulated as two separate single-plane radiograph systems. Position and orientation of the underlying bone was determined for each single-plane view by generating projections through a 3-D volumetric model (from computed tomography), and producing an image (digitally reconstructed radiograph) similar (based on texture information and rough edges of bone) to the two-dimensional radiographs. The absolute 3-D pose was determined using known imaging geometry of the biplane radiograph system and a 3-D line intersection method. Results were compared to data of known accuracy, obtained from a previously established bone-implanted marker method. Difference of controlled in vitro tests was on the order of 0.5 mm for translation and 1.4 degrees for rotation. A biplane radiograph sequence of a canine hindlimb during treadmill walking was used for in vivo testing, with differences on the order of 0.8 mm for translation and 2.5 degrees for rotation. 相似文献
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有源器件的端口反射系数是器件的主要参数,端口反射系数的大小直接影响信号的输出功率。为实现有源器件在“射频开”状态下端口反射系数的测量,开展了阻抗调谐器法和网络分析仪频率偏移法的源端口反射系数测量方法研究,并针对信号源和放大器开展了相应的实验。测量结果表明,10 dBm输出时2种方法测得反射系数模值的差别小于0.06,相位变化差别优于10°,为有源器件端口反射系数的测量提供了可行的方法。 相似文献
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屏蔽电缆转移阻抗和转移导纳的宽频测量 总被引:2,自引:0,他引:2
转移阻抗和转移导纳是表征外界电磁场对屏蔽电缆耦合机理的两个重要参量.基于传输线理论,提出了一种新的测量屏蔽电缆转移阻抗和转移导纳的简便方法.该方法既可以得到转移阻抗和转移导纳的幅频特性,又可以得到其相频特性,且测试系统比较简单.测试频率范围满足电力系统电磁兼容所关心的频段(0.1MHz~10MHz),对于更高频率屏蔽电缆转移阻抗和转移导纳的测量,可以通过选择更短的电缆样品来实现.为了验证测量方法的正确性,与现有方法的测量结果进行了对比.该测量方法可推广用于多芯屏蔽电缆的转移阻抗和转移导纳测量. 相似文献
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Chieh JJ Tseng WK Horng HE Hong CY Yang HC Wu CC 《IEEE transactions on bio-medical engineering》2011,58(10):2719-2724
Magnetic nanoparticles have been widely applied to biomagnetism, such as drug deliver, magnetic labeling, and contrast agent for in vivo image, etc. To localize the distribution of these magnetic particles in living organism is the first important issue to confirm the effects of magnetic nanoparticles and also evaluate the possible untoward effects. In this study, a scanning high T(c) rf-SQUID superconducting quantum interference devices (SQUIDs) biosusceptometry, composed of static SQUID unit and scanning coil sets, is developed for biomedicine study with the advantages of easy operation and unshielded environment. The characteristics tests showed that the system had the low noise of 8 pT/Hz at 400 Hz and the high sensitivity with the minimum detectable magnetization around 4.5 × 10(-3) EMU at distance of 13 mm. A magnetic nanoparticle detection test, performed by ex vivo scanning of the magnetic fluids filled capillary under swine skin for simulation of blood vessels in living bodies, confirmed that the system is feasible for dynamic tracking of magnetic nanoparticles. Based on this result, we performed further studies in rats to clarify the dynamic distribution of magnetic nanoparticle in living organism for the pharmacokinetics analysis like drug delivers, and propose the possible physiological metabolism of intravenous magnetic nanoparticles. 相似文献
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《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1983,71(9):1113-1115
The voltage transfer function of a network may be determined by measuring its reflection properties. Unless the network meets certain conditions, the difference between the actual and measured functions can be significant. The relation between these two quantities is investigated. Its application is illustrated by measurements made on a bandpass network. 相似文献