Theoretical and Experimental Studies of Epidermal Heat Flux Sensors for Measurements of Core Body Temperature

Abstract

Long-term, continuous measurement of core body temperature is of high interest, due to the widespread use of this parameter as a key biomedical signal for clinical judgment and patient management. Traditional approaches rely on devices or instruments in rigid and planar forms, not readily amenable to intimate or conformable integration with soft, curvilinear, time-dynamic, surfaces of the skin. Here, materials and mechanics designs for differential temperature sensors are presented which can attach softly and reversibly onto the skin surface, and also sustain high levels of deformation (e.g., bending, twisting, and stretching). A theoretical approach, together with a modeling algorithm, yields core body temperature from multiple differential measurements from temperature sensors separated by different effective distances from the skin. The sensitivity, accuracy, and response time are analyzed by finite element analyses (FEA) to provide guidelines for relationships between sensor design and performance. Four sets of experiments on multiple devices with different dimensions and under different convection conditions illustrate the key features of the technology and the analysis approach. Finally, results indicate that thermally insulating materials with cellular structures offer advantages in reducing the response time and increasing the accuracy, while improving the mechanics and breathability.

Battery-free, wireless sensors for full-body pressure and temperature mapping

“…The total thermal mass per unit area of the device is, therefore, 48.1 µJ·mm −2 ·K −1 . Although this number is considerably higher than that associated with the most advanced, wired epidermal temperature sensors (1.5 to 30 µJ·mm −2 ·K −1 ) (31–34), it is lower than that of the skin itself ( C = 3391 J·kg −1 ·K −1 , ρ = 1109 kg·m −3 , and thickness = 1 mm yield a thermal mass of ~380 µJ·mm −2 ·K −1 ). Thermal imaging (Fig.…”

Multimodal epidermal devices for hydration monitoring

“…Here we describe recent advances in multimodal sensors of skin hydration, via measurements of intrinsic thermal and electrical properties, in which advanced materials, mechanics and concepts render devices that have soft, 'skin-like', or 'epidermal', formats [11][12][13][14][15][16][17][18][19][20] . The thin geometries and compliant mechanics lead to a mode of integration with the skin that does not require application of pressure, and instead relies on van der Waals adhesion forces alone.…”

Designing Thin, Ultrastretchable Electronics with Stacked Circuits and Elastomeric Encapsulation Materials

“…The resulting overall thickness of the device is only ≈370 μm, almost one-fourth of previously reported devices. [39,42] In each circuit layer, 36 square electronic “islands” with side length L island = 5 mm are densely distributed in a 4 × 9 matrix, with the spacing among islands set as L spacing = 1.25 mm. The areal coverage η 0 of a single circuit layer is 64%.…”

“…For instance, Zhang et al measured core-body temperature using two sets of heat flux sensors vertically separated by a silicone matrix. [42] Here, the two overlapping sensors provide a differential temperature reading necessary for thermal characterization. Recently, Lee et al proposed a skin-mountable power management device with high functional density and reduced planar dimensions (Figure 1).…”