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Research Papers

Use of a Gel Finger to Feel the Skin Temperatures of a Smartphone

[+] Author and Article Information
Akshay Sripada

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: akshay.sripada@colorado.edu

Morgan Rohlfing

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: morgan.rohlfing@gmail.com

Raymond Vijaendreh

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: vijaendrehraymond@gmail.com

Brenden Spetzler

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: spetzleb@colorado.edu

Ramsey Abdulhamid

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: ramsey.abdulhamid@gmail.com

Aaron Porras

Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: j.aaron.porras@gmail.com

Y. C. Lee

Professor
Department of Mechanical Engineering,
University of Colorado at Boulder,
Boulder, CO 80309
e-mail: leeyc@colorado.edu

Ashish Gupta

Intel Co.,
Chandler, AZ 85226
e-mail: ashish.x.gupta@intel.com

Enisa Harris

Intel Co.,
Chandler, AZ 85226
e-mail: enisa.harris@intel.com

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 16, 2015; final manuscript received April 6, 2016; published online May 16, 2016. Assoc. Editor: Yi-Shao Lai.

J. Electron. Packag 138(3), 031001 (May 16, 2016) (8 pages) Paper No: EP-15-1085; doi: 10.1115/1.4033376 History: Received September 16, 2015; Revised April 06, 2016

It is important to control the skin temperatures of smartphones, tablets, and wearable electronics. The comfort levels of the skin temperatures are determined by surveys with subjective evaluations on a limited number of configurations and/or materials. This study is the first attempt to develop a characterization tool that is objective, repeatable, and predictable. The first step is to apply a gel finger that replaces the human finger to measure temperatures after gel finger's contact with the skin, i.e., the case of a mobile system. The second step is to establish a model calibrated by the experimental results. The calibrated model can be used to simulate different effects on the temperatures at the interface between the gel finger and the skin. The temperatures of the polycarbonate skin “felt” by the gel finger are always lower than those of the aluminum skin. The difference could reach 2–6 °C depending on heat spreading inside the system and heat sources in the finger. The difference can be reduced from 6 to 3 °C by using a novel casing with thin film metal on polymer. The transient periods are approximately 100–200 s with shorter transient periods for the aluminum skin.

Copyright © 2016 by ASME
Topics: Temperature , Aluminum , Skin
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References

Moritz, A. R. , and Henriques, F. C., Jr. , 1947, “ Studies of Thermal Injury—II: The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns,” Am. J. Pathol., 23(5), pp. 695–720. [PubMed]
Lawrence, J. C. , and Bull, J. P. , 1976, “ Thermal Conditions Which Cause Skin Burns,” Eng. Med., 5(3), pp. 61–63. [CrossRef]
Subramanian, B. , and Chato, J. C. , 1998, “ Safe Touch Temperatures for Hot Plates,” ASME J. Biomech. Eng., 120(6), pp. 727–736. [CrossRef]
Roy, S. K. , 2011, “ An Equation for Estimating the Maximum Allowable Surface Temperatures of Electronic Equipment,” 27th Annual IEEE Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM), San Jose, CA, Mar. 20–24, pp. 54–62.
Berhe, M. E. , 2007, “ Ergonomic Temperature Limits for Handheld Electronic Devices,” ASME Paper No. IPACK2007-33873.
Lefevre, J. , 1901, “ Studies of the Thermal Conductivity of Skin In-Vivo and the Variations Induced by Changes in the Surrounding Temperature,” J. Phys. Théor. Appl., 10(1), pp. 380–388. [CrossRef]
Zhang, H. , Hedge, A. , and Guo, B. , 2015, “ User's Thermal Response to a Simulated Tablet Computer Surface,” ASME Paper No. IPACK2015-48787.
Wasner, G. L. , and Brock, J. A. , 2008, “ Determinants of Thermal Pain Thresholds in Normal Subjects,” Clin. Neurophysiol., 119(10), pp. 2389–2395. [CrossRef] [PubMed]
Egilmez, B. , Memik, G. , Ogrenci-Memik, S. , and Ergin, O. , 2015, “ User-Specific Skin Temperature-Aware DVFS for Smartphones,” Design, Automation & Test in Europe Conference & Exhibition (DATE), Grenoble, France, Mar. 9–13, pp. 1217–1220.

Figures

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Fig. 1

A smartphone's skin temperatures defined as the temperature of the case's exterior surface touched by fingers, ears, or other part of a human body

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Fig. 2

Maximum allowable temperatures with respect to different materials and contact times (calculated using Eq. (14) from Ref. [4])

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Fig. 3

Experimental setup with the use of a gel finger to characterize materials and other effects on the skin temperatures of a smartphone

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Fig. 4

Basic layers and gel holder setup: (a) basic layers of the test vehicle representing smartphone and (b) a gel finger with three holes to be placed with thermocouples for temperature measurements

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Fig. 5

Middle layer consisting of a heater and a heat spreader

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Fig. 6

Top layer of the aluminum or polycarbonate skin with thermocouples to be glued for skin temperature measurements

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Fig. 7

Temperatures at TC1, TC2, TC3, and TC4 measured as a function of time for the setup with the aluminum skin

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Fig. 8

Temperatures at TC1, TC2, TC3, and TC4 measured as a function of time for the setup with the polycarbonate skin

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Fig. 9

Measured and simulated temperatures (TC5, TC6, and TC7) in the gel finger after the contact with touching the aluminum skin

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Fig. 10

Measured and simulated temperatures at TC5, TC6, and TC7 in the gel after the contact with finger after it touches the polycarbonate skin

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Fig. 11

Top view of the CAD model showing the convection coefficients and the meshes

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Fig. 12

Bottom view of the CAD model showing the convection coefficients and the meshes

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Fig. 13

CAD model with the boundary condition for the gel holder with h = 10 W/m2 K and ambient temp = 23.5 °C

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Fig. 14

Temperature distributions of the aluminum skin (a) at steady-state and (b) 10 mins after gel touching the skin

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Fig. 15

Temperature distributions of the polycarbonate skin (a) at steady-state and (b) 10 mins after gel touching the skin

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Fig. 16

Simulated and measured temperatures at TC2 on the aluminum skin

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Fig. 17

Simulated and measured temperatures at TC2 on the polycarbonate skin

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Fig. 18

Comparison between the interface temperatures simulated and curve-fitted

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Fig. 19

Using the curve-fitting model to find interface temperature with experimental data

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Fig. 20

Skin temperatures felt by the gel finger with respect to three different cases

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Fig. 21

Skin temperatures felt by a heated gel finger with respect to three different cases

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Fig. 22

Skin temperatures felt by the gel finger in a new case with polycarbonate skin having the same power level as that with the aluminum skin

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