another MRI system (9.4-T Bruker Biospec MRI system, Bruker BioSpin Corporation) and an ECG EES placed over cadaveric rat tissue (Fig. 4A) shows no observable magnetically induced displacement forces or torques and no measurable changes in temperature. The results meet FDA requirements for an “MRI-safe” label for medical devices (25). Imaging results indicate that the ECG EES causes less shadowing and image distortion compared to a conventional NICU ECG electrode (Fig. 4B). The EES eliminates radio-opaque wires, thereby improving evaluation by x-ray imaging, a modality required for 90% of low–birth weight neonates (26). Experimental results show that an ECG EES placed over the same tissue in a rodent Chung et al., Science 363, eaau0780 (2019) 1 March 2019 7 of 12 Fig. 6. Operational characteristics of the PPG EES. (A) Block diagram of in-sensor analytics for detection of peaks and valleys from PPG waveforms and for dynamic baseline control. (B) A circuit diagram with GPIO-enabled baseline control scheme. (C) Demonstration of dynamic baseline level control with a sinusoidal input (blue) and corresponding output changes (red). (D) Demonstration of operation of a PPG EES with (blue and red) and without (black dashed line) dynamic baseline control. Analytics on baseline level serves as an input to a control system that combines a GPIO port on the NFC SoC with an offset to ensure that the signal input to the ADC lies within its dynamic range (orange dashed lines). (E) Convention for calculating direct and alternating components of PPG waveforms collected in the red and IR, for purposes of calculating SpO2. (F) Empirical formula for SpO2 calculation using Roa based on comparison to a commercial pulse oximeter. (G) SpO2 determined using in-sensor analytics during a period of rest followed by a breath hold and then another period of rest. (H) Convention for measuring pulse arrival time (PAT) from R-peaks in the ECG waveforms and valleys in the PPG waveforms. (I) Values of 1/PAT acquired using an ECG EES and a PPG EES versus systolic BP data acquired using a cuff monitor. (J) Correlation curve between PAT and systolic BP with linear fit. (K) Bland-Altman plot for SpO2 collected from three adults using a PPG EES and a clinicalstandard system. (L) Temperature plot showing the capability for measuring differential skin temperatures between the torso and the foot using an ECG EES and a PPG EES. RESEARCH | RESEARCH ARTICLE Downloaded from https://www.science.org on July 15, 2022 model imaged using a computed tomography/ x-ray system (nanoScan PET/CT, Mediso) exhibits improved radiolucency in comparison to standard ECG electrodes and wires (Fig. 4, C and D). The optical transparency of the silicone and the open mesh designs of the electronics and antenna structures also provide direct visual access to the skin and tissue beneath the sensor (fig. S35), thereby obviating the need to remove the sensor tomonitor the underlying skin for signs of infection or irritation. Real-time measurements, in-sensor analytics, and data transmission Exploiting this collection of attractive electronic, mechanical, and radiolucent properties for practical use in a NICU environment requires insensor processing and data analytics to reduce bandwidth requirements on wireless transmission and to ensure operational robustness. For example, computational facilities on the NFC SoC of the ECG EES can support a streamlined version of the Pan-Tompkins algorithm (27) for accurate, on-board analysis of the QRS complex of ECG signals in real-time to yield HR and HRV on a beat-to-beat basis. Figure 5A summarizes an approach that starts with digital bandpass filtering (fc1 = 5 Hz, fc2 = 15 Hz) to attenuate the noise. Differentiating and squaring the resulting data yields the slope of QRS peaks and prevents false peak detection associated with the T wave. Applying a moving average and a dynamic threshold identifies a running estimate of the R peak and the magnitude of the noise. Automatic adjustments of the threshold rely on these estimates for the preceding beat cycle (fig. S36). The R-to-R intervals determined in this way yield the instantaneous HR. Simultaneous recordings obtained using a clinical-standard system, henceforth referred to as “gold standard” data, validate the ECG EES module hardware and in-sensor analytics via measurements on a healthy adult volunteer (Fig. 5, B and C). The ECG signals and computed HR values from these two platforms show no measurable differences. Periodic modulations of the amplitude of the R peak define the RR (Fig. 5D), which also agrees with the gold standard (visual counting by a physician in this case; Fig. 5E). Measurements of skin temperature rely on sensors internal to the NFC SoC in each EES, where transmission at a sampling frequency of 1 Hz is sufficient for monitoring purposes. The low thermal mass of the EES and the small thickness of the substrate layer (PDMS; 50 mm in thickness) that separates the SoC from the skin ensure fast thermal response times and excellent thermal coupling, respectively. Comparisons against readings from a thermometer (Fisherbrand 13202376, Fisher Scientific) serve as means to calibrate the sensor (Fig. 5F) via testing in a water bath (fig. S37). Thermal images captured with an IR camera (FLIR A325SC, FLIR Systems) during operation indicate negligible heating associated with the electronics or the antenna structures (Fig. 5G). Figure 5H shows temperature readings from the ECG EES for 60 s. Comparison tests of this system against FDAcleared monitoring equipment (Dash 3000, GE Chung et al., Science 363, eaau0780 (2019) 1 March 2019 8 of 12 Fig. 7. Data collection from neonates in clinical and home settings. (A) A healthy term neonate with an ECG EES and a PPG EES on the chest and the bottom of the foot, respectively. (B and C) A mother holding a healthy term neonate showing skin-to-skin interaction with an ECG EES mounted on the chest (B) and an ECG EES mounted on the back (C). (D) A mother holding her neonate in the NICU; the inset is a magnified view of the ECG EES. (E) A neonate in the NICU with a PPG EES mounted on an