Biometric-Tuned E-Skin Sensor with Real Fingerprints Provides Insights on Tactile Perception: Rosa Parks Had Better Surface Vibrational Sensation than Richard Nixon

Abstract

The dense mechanoreceptors in human fingertips enable texture discrimination. Recent advances in flexible electronics have created tactile sensors that effectively replicate slowly adapting (SA) and rapidly adapting (RA) mechanoreceptors. However, the influence of dermatoglyphic structures on tactile signal transmission, such as the effect of fingerprint ridge filtering on friction-induced vibration frequencies, remains unexplored. A novel multi-layer flexible sensor with an artificially synthesized skin surface capable of replicating arbitrary fingerprints is developed. This sensor simultaneously detects pressure (SA response) and vibration (RA response), enabling texture recognition. Fingerprint ridge patterns from notable historical figures - Rosa Parks, Richard Nixon, Martin Luther King Jr., and Ronald Reagan - are fabricated on the sensor surface. Vibration frequency responses to assorted fabric textures are measured and compared between fingerprint replicas. Results demonstrate that fingerprint topography substantially impacts skin-surface vibrational transmission. Specifically, Parks' fingerprint structure conveyed higher frequencies more clearly than those of Nixon, King, or Reagan. This work suggests individual fingerprint ridge morphological variation influences tactile perception and can confer adaptive advantages for fine texture discrimination. The flexible bioinspired sensor provides new insights into human vibrotactile processing by modeling fingerprint-filtered mechanical signals at the finger-object interface.

Keywords: fingerprint pattern types; graphene oxide; manual fabric texture recognition; mechanoreceptors; tactile sensors.

Figure 1

Design, construction, and fabrication of electronic skin inspired by fingertip. A) Perceptual mechanisms of the human haptic system. B) Schematic diagram of the layout of the WFES sensor and the study on the vibrational signal of different sensor structures using the WFES sensor, including i) The effect of the spacing of the stripe sensor structure on the tactile vibrational signal. ii) The effect of different fingerprint structures on the tactile vibrational signal. C–F) The optical image of the main components of the WFES sensor, from left to right are the fingerprint film electrode, P‐GO/PDMS dielectric layer, parylene electrode, and the assembled sensor. G) Illustration of the manufacturing process of the main components of the WFES sensor. I) Modeling of the fingerprint structure of the sensor. II) Fabrication of fingerprint film electrode. III) Fabrication of dielectric layer with arc‐top cylindrical structure. IV) Fabrication of parylene electrode film. V)Assembled WFES sensor.

Figure 2

Characterization of the sensor performance including sensitivity, repeatability, resolution, and vibration response. A) Optical image of the WFES sensor attached to the fingertips and an optical 3D profile image of the fingerprint structure. B) Change in the sensor's capacitance over a pressure range of up to 250 kPa. C) Variation in capacitance over a pressure range of up to 5 kPa. D) The sensor's working stability was determined after 26 000 cycles from 0.5 to 3 kPa, inlets show the close‐up views at the beginning and end of the test. E) Response to the placement and removal of a petal on top of the sensor. F) Vibrational spectra of a smartphone and an electric toothbrush; insets show the time‐domain signal of the test.

Figure 3

The effect of scanning speed and sample surface roughness on vibrational signals. A) Schematic diagrams of the experimental setup and WFES sensor deformation during scanning. B) The vibrational spectrum generated by the WFES sensor upon scanning Si microstrip (λ_s30, λ_s50, λ_s100, and a smooth Si surface) with the fingerprint structure of Subject 1 at 1 mm s⁻¹; insets show images of microstrip samples. C) Vibrational spectra at different scanning speeds. D) Relationship between the characteristic peaks in the vibrational spectrum, the interridge distance of the test sample, and the scanning speed with fingerprint patterns of a male subject (Subject 1) and a female subject (Subject 2) as the outer structure of the sensor, respectively.

Figure 4

The effects of different sensor structures on captured vibrational signals. A) Vibrational spectra were acquired by the sensor with a striped structure (λ_f220) by manually scanning various printed microstrips at an average speed of 15 mm s⁻¹. B) The vibrational spectra were obtained by scanning the microstrip (λ_s900) with WFES sensors having different interridge distances. C) The vibrational spectra were obtained by scanning the microstrip (λ_s900) with WFES sensors having different ridge depths. D) The vibrational spectra were obtained by scanning the microstrip (λ_s900) with WFES sensors having different ridge widths. E) Relationship between the interridge distance of the sensor structure, the interridge distance of the scanned sample, and the characteristic frequencies. F) Comparison of the effects of sensor structures with different ridge depths and ridge widths on vibrational signal amplitude.

Figure 5

Fabric texture recognition test. A) Schematic diagram of the interaction between the WFES sensor and fabric. B) 3D fabric surface profile images of four fabrics (twill cotton, corduroy, 70% cotton + 30% polyester, and polyamide) were measured by the optical profilometer. C) Vibrational spectra were obtained by scanning four fabrics (twill cotton, corduroy, 70% cotton + 30% polyester, and polyamide) using a linear actuator (WFES sensor) I), PGI profilometer II), and manually scanning (WFES sensor) III). D) Comparison of fabric interridge distance measurement under four experimental conditions.

Figure 6

Testing the effect of fingerprint pattern type on fabric texture recognition signals. A) Fingerprints of four influential figures from the realms of politics and civil rights were chosen as samples for the research (Rosa Parks, Getty Images; Richard Nixon, Bachrach/Getty Images; Martin Luther King, Jr., Getty Images; Ronald Reagan, Universal History Archive/Getty Images).^{[ 68} , ⁶⁹ , ⁷⁰ , ^{71 ]} B) Comparison of vibrational spectra obtained from WFES sensors of the famous political and civil rights leaders.