Supporting Information. Self-Powered Analogue Smart Skin

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1 Supporting Information Self-Powered Analogue Smart Skin Mayue Shi,, Jinxin Zhang, Haotian Chen, Mengdi Han, Smitha A. Shankaregowda, Zongming Su, Bo Meng, Xiaoliang Cheng, and Haixia Zhang *, National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Peking University, Beijing, , China. School of Electronic and Computer Engineering, Peking University, Shenzhen, Guangdong, , China. * zhang-alice@pku.edu.cn

2 1. Supplementary Notes 1.1 Resolution of anologue smart skin The resolution of anologue smart skin is defined based on the statistical results of repeated experimental tests at each point to ensure reliability and validity. For example, at point (1,2), 160 repeated experimental tests are applied (Figure 3b). For each test, R ac and R bd can be determined from four electrode peak voltages. Therefore, there will be 160 pairs of R ac and R bd as is shown in Figure 3c, which are two dimensional samples for further statistical analysis. To obtain average and dispersion of 160 samples obeying two dimensional normal distribution, we confirm the statistical distribution characteristic (expectation, variance and correlation coefficient) of this samples from repeated experimental tests. More specifically, the point estimation is used in this process. Point estimation method is a kind of parameter estimation method. In statistics, point estimation involves the use of sample data coming from repeated experiments to calculate a single value of an unknown (fixed or random) population parameter. After confirming the statistical distribution characteristic, the half width at half maximum (HWHM) is determined at each direction. At point (1,3), the same statistical process is applied and the expectation and HWHM can be determined as well. Then the solution at the direction from electrode a to lectrode c can be defined as HWHM HWHM ac,12 ac,13 ac,12 ac,13 HWHM HWHM ac,12 ac,13 Here, maeans the resolution of voltage ratio (or resolution in the ac,12 ac,13 ratio-space), means the voltage ratio difference between (1,2) and (1,3) which are 1 cm apart along the direction from electrode a to lectrode c. Therefore, the whole function defines the spatial resolution in this derection.

3 2. Supplementary Figures Fig. S1. Transmittance of Ag NW electrode and microstructured PDMS film. PET film is placed as the substrate. The blue line represents the PET film covered with microstructured PDMS film, the orange line represents the PET film with Ag NW electrode, the black line represents the PET film with Ag NW electrode and microstructured PDMS film.

4 Fig. S2. Conductivity of Ag NW electrode on PET substrade with a) plain form and b) bend form. The gap between two point is 2 cm.

5 Fig. S3. Fourier analysis of typical signals. a), Typical time-domain voltage output of electrode b in Figure 3b. The vibration frequency is 8 Hz and the amplitude is kept at 11 mm with a vibration generator system. The inset shows one cycle. b), Signals in Figure S1a was transformed to frequency domain through fast fourier transform (FFT) algorithm.

6 Fig. S4. Voltage distribution with finite element analysis in three-dimensional space. The upper frictional surface (finger) is set to 5 cm away from the smart skin. The unit of voltage is volt.

7 Fig. S5. Voltage of the electrode-a with finite element analysis when the location of contact point changes. With the increasing distance between electrode-a and contact piont, the absolute value of the voltage decreases.

8 Fig. S6. Voltage ratio distribution of every testing point (25 in total). All of distribution figures use double logarithmic coordinates, the same with Figure 3d.

9 Fig. S7. Experimental verification of millimeter resolution. a) Point 1 (2.00,3.50) and Point 2 (2.00,3.30) are pressed successively. b) The location result proved these two pionts are distinguishable with analogue smart skin.

10 Fig. S8. With the increasing of vibration frequency (higher frequency means higher contact velocity when the gap between two friction surfaces is a constant) from 2 Hz to 5 Hz, the electrode voltage rises.

11 Fig. S9. The smart skin shows good stability which keep the similar output after cycles.

12 Fig. S10. Structure of one-dimensional analogue smart skin. Only two Ag NW electrodes are necesarry for one-dimensional location.

13 Fig. S11. Measurment of one-dimensional analogue smart skin. a) Photograph showing the testing environment of the smart skin which is fixed on the glass plate. b) Voltage output and c) voltage ratio of opposite electrodes when pressures are applied at 5 point from left to right. With the movement of testing point, the ratio monotonically decreases. The location of testing point can be uniquely determined by the voltage ratio of opposite electrodes.

14 Fig. S12. Measurment of a gryllus on the smart skin. a) Photograph showing the gryllus on the smart skin. b) The output voltages of four electrodes when the gryluss which is 1.49 g landing on the samr skin. The location result of this gryllus is (1.46,3.73) which matches the video.

15 3. Supplementary Tables Table S1. Resolution of all regions in x direction. Tests are performed on a plain surface. y[cm] x[cm] to 2 a) to to to a) 1 to 2 means the region from y=1 cm to y=2 cm Table S2. Resolution of all regions in y direction. Tests are performed on a plain surface. x[cm] y[cm] to to to to Table S3. Resolution of all regions in x direction. Tests are performed on artificial hand. y[cm] x[cm] to to to to

16 Table S4. Resolution of all regions in y direction. Tests are performed on artificial hand. x[cm] y[cm] to to to to