Sensitive Skin

By | August 22, 2015

                  Sensitive skin is a large-area, flexible array of sensors with  data  processing  capabilities,  which  can  be  used  to  cover the  entire  surface of  a  machine  or  even  a  part  of  a human body.  Depending  on  the  skin electronics,  it  endows  its carrier with an ability to sense its surroundings via the skins proximity,  touch,  pressure, temperature,  chemical/biological, or  other  sensors.  Sensitive  skin  devices will  make  possible the use of unsupervised  machines  operating  in  unstructured, unpredictable  surroundings  among  people,  among many obstacles, outdoors on a crowded  street, undersea, or on far away planets. Sensitive skin will make machines cautious‚ and thus friendly to their environment. This will allow us to build  machine helpers  for the disabled  and elderly, bring sensing to human prosthetics, and widen the scale of machines use in service  industry. With  their ability  to produce  and process massive data flow, sensitive skin devices will make yet another  advance  in  the  information revolution. This paper surveys the state of the art and research issues that need to be resolved in order to make sensitive skin a reality.


Sensitive  skin  represents  a  new  paradigm  in sensing  and  control.  These devices  will open doors to  a whole class  of  novel  enabling  technologies,  with  a  potentially  very wide  impact.  Far-reaching  applications  not  feasible  today  will be realized, ranging from medicine and biology to the machine industry and defense. They will allow us to fulfill our dream for machines  sensitive  to  their  surroundings  and  operating  in unstructured environment.

Some  applications  that  sensitive  skin  devices  will  make possible  are  yet  hard  to  foresee.  Flexible  semiconductor  films and flexible  metal interconnects that will result from this work will allow us to develop new inexpensive consumer electronics products, new types of displays, printers, new ways to store and share  information  (like  electronic  paper  and  upgradeable‚ books  and  maps).  New  device  concepts  suitable  for  large  area flexible  semiconductor  films will  lead to  new  sensors that will find  applications  in  space  exploration  and  defense, specifically in mine detection and active camouflage.


Sketch of interconnects between sensors, intelligence, and actuators

The system consists of a number of distributed sensor, actuator, and intelligence units, which are connected by some network of interconnects.  The interconnects  are  necessary  for  providing power  to  the  system  as  well  as  for  communication.  The sensors/actuators  themselves  may  have  intelligence  associated with  them,  but  there  are  other  higher  levels  of  intelligence  to which they are connected. The  interconnects  shown  in  the  system  might  be  electrical (conventional wires) or optical (fibers). The communication via the  individual  units  might  in  some  cases  be  wireless (implying  also  fiber-less)  for  some  structures. For  delivering power,  it  was  thought  that the  system  probably  would require physical  interconnects  (i.e.  power  delivered  through  fibers  or wires),  and  that harnessing‚ energy  from  the  environment, such  as  via  solar  or  RF  pick-ups,  would  not  be  practical  for most  applications  (especially  for  wireless  systems).  Therefore in  all  cases  there  would  have  to  be  a  physical  interconnect between  the  individual  sensor  /  actuator  /  intelligence  blocks, and  so  a  major  part  of  this  report  addresses  issues  associated with this physical level of interconnection.

Potential applications of sensitive skin

Four  groups  of  research  issues  must  be  addressed  in  order  to develop sensitive skin: Skin Materials, Sensing Devices, Signal and  Data  Processing,  and Applications.


1. Human Skin or Wearable Skin

In the biomedical area, wearable sensitive skins can be used  to  restore  sensory  capability  to  people  who  have  lost  fine sensation  in  extremities  (such  as diabetics),  or  to  people  with spinal  cord  injuries.  A  relatively  simple  sensitive  skin  garment could  be  used  to  prevent  pressure  sores  in  bedridden  or wheel chair  bound  people.  A  wearable  sensitive  skin  would  also  be useful  for  overall  physiological  monitoring,  such  as  frostbite detection. If the wearable sensitive skin can also include even a simple  actuation  capability,  a  very  wide  range  of  further biomedical applications becomes promising. For example simple distributed  actuators  could  be  used  in  applications  such  as thermoregulation,  functional  neuromuscular  stimulation,  smart compression  for  lymphatic  system  drainage,  or  controllable damping/stiffness  for  tremor  reduction.  Of  course,  the  sensitive skin is not limited to the strain, vibration, and temperature senses of  human  skin.  Proximity  sensing  would  be  a  useful  capability for  the  visually  impaired.  For  military  applications,  sensors  for laser, radar, chemicals, or Puncture would be quite valuable.

2. Sensitive Skins for Machines

If  machines  are  to  work  nimbly  in  cluttered environments  or  with  humans,  they  need  sensitive  skins  with proximity  and  contact  sensors.  These sensors  would  provide information  so  the  machines could  protect  both themselves  and people  they  work  with.  For  human-computer  interaction,  robot companions  could  respond  appropriately  to  human  touch. Moving  vehicles  could  have  an  intelligent  skin,  which  allows easier  navigation  in  tight  spaces,  for  example  maneuvering automobiles on crowded streets.

3. Environmental Sensitive Skin

Even    fixed  structures  as  simple  as  floors  and  walls could  have  improved  functionality  using  a  low-cost  sensitive skin.  For  example,  a  floor  with distributed  pressure  sensors could  be  used  for  tracking,  or  a  safety  measure  to  warn  of slippery  spots  or  report  falls.  In  civil  engineering,  skins  for buildings and bridges  can warn  of fatigue or impending failure. For  human  computer  interaction,  surfaces  could  respond  to gestures and infer intent, such as changing a lighting level.

4. Actuated Sensitive Skin

There  is  overlap  between  applications  of  passive  sensitive skin and the whole area of active surfaces such as drag reduction in  aero-  and  hydrodynamics. For  example,  active  surface furniture such as chairs could increase comfort for people sitting for long periods of time. Active sensitive skin on walls could be used for sound and vibration canceling.


                 Sensitive  skin  is  a  large  array  of  sensors embedded  in  a  flexible,  stretchable,  and/or  fold-able substrate that might cover the surface of a moving machine. By  endowing  these  machines  with  ability  to  sense  their surroundings,  sensitive  skin  will  make  it  possible  to  have unsupervised  machinery  in unstructured,  unpredictable surroundings.  Sensitive  skin  will  make  the  machines cautious‚ and  thus  friendly  to  their  environment.  With these properties, sensitive  skin  will  revolutionize  important areas  of  service  industry,  make  crucial  contributions  to   human  prosthetics,  and  augment  human sensing  when fashioned into clothing. Being transducers that produce and process  information,  sensitive  skin  devices  will  be generating  and  processing  data  flows  in  real  time  on  a massive  scale,  which  will  lead  to  yet  another  leap  in  the information  revolution.

Sensitive  skin  presents  a  new paradigm  in sensing  and  control.  It  is  an  enabling technology  with  far  reaching  applications,  from  medicine and biology  to industry and defense. The  state of the art in the  areas  that  are  basic  to  development  of  the  skin technology  shows  that  highly  efficient  devices  should  be feasible,  meaning  by  this  high  density  of  sensors  on  the skin, and hierarchical and highly distributed real time sensor data  processing.  All  this  non  withstanding  the  fact  that  the existing  prototypes  are  clumsy,  have  low  resolution, accuracy  and  reliability,  and  are  not  yet  ready  for commercialization. Serious research issues elaborated in this paper have to be resolved before sensitive skins can become a  ubiquitous  presence  in  our  society.  We  hope  the  readers will  view  this  paper  as  our  first  effort  to  map  out  the  new territory, and as an invitation to join in the exploration.

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