Sensing moisture level of human skin
A human skin moisture measuring device having an interdigitated resistive sensor formed on a plate-like transparent support is described, with a face designed to be placed into contact with the skin to be subjected to the moisture degree measurement. The device further comprises image sensing means turned towards the opposite face of the support and a lighting device arranged sideways relative to the support to direct the light radiation in the support at a prefixed angle. Means for processing the signal coming from the interdigitated resistive sensor and from the image sensing means give as output a value of the measured moisture degree that is normalized with respect to the actual surface of contact between skin and sensor.
1. A human skin moisture measuring device comprising:
a transparent interdigitated resistive sensor configured to contact the skin;
a plate-like transparent support comprising a first face in contact with the transparent interdigitated resistive sensor;
image sensing means turned towards a second face that is opposite said first face of said support;
a lighting device configured to direct light radiation within said support at a prefixed angle; and
means for processing a first signal from said transparent interdigitated resistive sensor and a second signal from said image sensing means,
wherein said processing includes calculating a contact area between the skin and the sensor based on said second signal, normalizing said first signal based on said contact area, and outputting a value of moisture degree based on the normalized first signal.
2. The device according to claim 1 , wherein
said plate-like transparent support is a flat plate defined by a side flank or thickness and
said lighting device is arranged substantially coplanar relative to said flat plate, whereby the plate is irradiated through its thickness.
3. The device according to claim 2 , wherein an incidence angle (θ 1 ) of the light radiation emitted by said lighting device is comprised between 45° and 80°.
4. The device according to claim 1 , wherein said lighting device is formed by one or more lighting sources of LED type.
5. The device according to claim 1 , wherein said image sensing means comprise a video camera, a CCD device or a CMOS device.
6. A human skin moisture measurement method comprising:
measuring skin resistance by a transparent interdigitated resistive sensor;
acquiring an image of a skin portion contacting a sensor surface through said sensor;
calculating, using a processing unit, a contact area between the skin portion and the sensor based on said image;
normalizing, using the processing unit, said skin resistance based on said contact area; and
determining, using the processing unit, skin moisture as a function of said normalized resistance.
7. The method according to claim 6 , wherein said acquiring the image is obtained by lighting the skin surface contacting the surface of the sensor by a light beam directed against a side of said sensor and inclined of an angle of at least 45° with respect to a perpendicular line thereof.
8. The method according to claim 7 , wherein the incidence angle of the light beam is comprised between 45° and 80°.
9. The method according to claim 6 , further comprising performing thresholding of the luminosity levels of the image of the skin portion in contact with the sensor surface and segmentation of the highest luminosity area to determine the measure of the skin-sensor contact surface area.
10. The method according to claim 6 , wherein the skin moisture as a function of the normalized resistance measure is determined through calibration curves or tables.