Thermal impedance

To obtain temperatures above 4.2K, one can use the main 4He bath and regulate the experiment temperature by means of a thermal impedance and a heater. The method is expensive, in terms of helium consumption, especially for T > > 4K. 

Fig. 10.16. Example of the realization of the thermal impedance for the cold stage of Fig. 10.15 with sink...

K same as previous run, with a greater thermal impedance to reduce helium... 

K heat sink and dewar shield at 77 K, with a greater heat sink platform (Pf) thermal impedance. 

A novel method for achieving low thermal impedance between the chip and substrate has been developed at Stanford University (163-165). Reentrant microcapillaries (3-5 (xm wide) are etched into the substrate (either a silicon wafer or a ceramic coated with a polyimide) and partially filled with a fluid such as silicone oil. This structure increases the heat-transfer area, reduces the interfacial thermal resistance, and provides a stress-free, re-... 

Overheating of devices resulting in electrical malfunctioning or reduction in the life expectancy of the device and circuit can be the direct result of poor conductivity and high thermal impedance of the adhesive. Thermal conductivity of adhesives becomes critical as devices are operated at higher speeds, consume more power, and dissipate more heat. Semiconductor junction temperatures must remain within normal limits. 

The selection of highly conductive adhesives is a necessary factor, but not the only one in minimizing thermal impedance. Applying as thin a bond line as possible and avoiding the introduction or creation of voids are also essential in reducing thermal impedance. 

Thermal characterization of Li-ion batteries Accelerating Thermal Impedance Spectroscopy... 

Keywords. Thermal Impedance Spectroscopy parameter identification Li-ion batteries ... 

To describe the heat transfer behavior of a battery for a certain excitation frequency /, a thermal impedance is used. This impedance, representing the temperature response T ax)... 

Thermal impedances for different frequencies result in a characteristic impedance spectrum as illustrated in Figure 1. 

In addition to the heating power curve, a surface temperature curve is required as the second input for thermal impedance calculation. To overcome drawbacks of contact-based temperature sensors, radiation-based temperature sensors are used for surface temperature measurement, as described in [5]. The PerkinElmer A2TMPI 334 sensor used in this study is shown in Figure 3. 

As formulated in Equation (1), thermal impedance has to be calculated from surface temperature and heat losses. Firstly, measurement data are subdivided into sections for each frequency. Then, surface temperature curve and heat losses are approximated by an analytical expression that has been presented in [5] ... 

The ratio of values and the difference of a values from heating and temperature curves represent amplitude and phase of the thermal impedance for each frequency /. 

The implemented battery model is the basis for the identification of thermal cell parameters. With the battery model, TIS measurements are simulated. The same sinusoidal heat excitation as in the experiment is apphed to the thermal battery model. Simulation results dehver thermal impedances for each frequency, which form an entire impedance spectrum. The ability to simulate TIS measurements allows rapid creation of impedance spectra for arbitrary thermal cell parameters. 

Figure 8. Comparison of thermal impedance spectra from measurement and simulation.

E. Barsoukov, J.H. Jang, and H. Lee, Thermal impedance spectroscopy for Li-ion batteries using heat-pulse response analysis, Journal of power sources, vol. 109, no. 2, pp. 313-320, 2002. 

M. Fleckenstdn, S. Fischer, O. Bohlen, et al, Thermal Impedance Spectroscopy—A method for the thermal characterization of high power battery cells, Journal of Power Sources, vol. 223, pp. 259-267, 2013. 

P. Kdl, K. Rumpf, and A. Jossen, Thermal Impedance Spectroscopy for Li-Ion Batteries with an IR Temperature Sensor System, in The 27th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium and Exhibition, 11/2013. 

The major failure modes of adhesives include loss of adhesion, high thermal impedance, loss of electrical contact, and corrosion. To a lesser extent, failures may occur because of metal migration causing high leakage currents and even electrical shorting. Sloughing of particles from the... 

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