2) gives: ##EQU4##

Assuming A>>1, (3) becomes: ##EQU5##

Consequently, by virtue of the negative feedback effected by capacitive coupling the output 17 and input 16 of the inverting amplifier 13 via the skin tissue, the variation in output voltage as a result of the charge step is directly proportional to the distance between the capacitor plates 23, 24 and the skin surface 18, in turn dependent on the three-dimensional structure of the skin. For a fixed amount of the input voltage step ΔVi, the output voltage of the inverter 13 will range between two extremes, depending on feedback capacitance value: (i) the upper saturation level if no feedback capacitance is present; (ii) a value close to the logical threshold when the feedback capacitance is large.

With appropriate amplification levels (e.g., 1000-2000), it is possible to detect differences in capacitance of about ten fF and hence micrometric distances. The output signals of the device according to the invention are therefore such, when converted into grey levels, as to provide a highly reliable representation of the three-dimensional structure of the skin surface.

The operation of the sensor device 1 can be further appreciated with regard to FIG. 4, which is an illustration of the skin surface 18 positioned on first and second adjacent cells 2A, 2B of the sensor device 1. It is to be understood that the present invention will have application to thumbs, palms, and any contact surface where an image is desired. Each of the adjacent cells 2A, 2B is substantially identical to the cell 2 shown in FIGS. 2-3, and thus, additional detailed discussions of the elements of cells 2A, 2B are being omitted for simplicity. Switches 19A and 19B constitute reset switches, as explained in more detail elsewhere herein. The elements of the adjacent cells 2A, 2B are marked with labels corresponding to the labels of FIGS. 2 and 3 with an "A" and "B" added to the cells 2A and 2B, respectively.

The skin surface 18 shown in FIG. 4 includes a ridge 39 adjacent to the first cell 2A and a valley 38 adjacent to the second cell 2B. As a result, the first and second cells 2A, 2B will each produce different capacitive coupling responses in the sensor device 1. Accordingly, the first cell 2A will sense a smaller distance d1, signifying the ridge 39, than the second cell 2
2) gives: # # EQU4 # # 

 Assuming A>>1, (3) becomes: # # EQU5 # # 

 Consequently, by virtue of the damaging feedback effect by capacitive coupling the output 17 and input 16 of the inverting amplifier 13 via the peel tissue, the variation in output electric potential as a result of the charge step is immediately proportional to the distance between the capacitor plate 23, 24 and the skin airfoil 18, in turn dependent on the three - dimensional social organization of the skin. For a fixed amount of the input voltage step ΔVi, the output electric potential of the inverter 13 will range between two extremes, depending on feedback capacitor value: (i) the upper saturation level if no feedback capacitance is present; (ii) a value close to the legitimate threshold when the feedback capacitance is large. 

 With appropriate amplification levels (e.g., 1000 - 2000), it is potential to detect differences in capacitance of about ten fF and hence micrometric distances. The output signal of the device according to the invention are therefore such, when converted into grey levels, as to provide a highly reliable representation of the three - dimensional structure of the skin surface. 

 The process of the sensor device 1 can be further prize with gaze to FIG. 4, which is an illustration of the skin surface 18 positioned on first and second adjacent cells 2A, 2B of the sensor device 1. It is to be sympathize that the present invention will have application to thumbs, palms, and any liaison surface where an image is desired. Each of the adjacent cells 2A, 2B is substantially identical to the cell 2 shown in FIGS. 2 - 3, and therefore, extra detailed discussion of the elements of cells 2A, 2B are being omitted for ease. Switches 19A and 19B constitute reset switches, as excuse in more detail elsewhere herein. The elements of the adjacent cells 2A, 2B are marked with label corresponding to the label of FIGS. 2 and 3 with an " A " and " B " add to the cells 2A and 2B, respectively. 

 The hide surface 18 read in FIG. 4 includes a ridge 39 adjacent to the inaugural cell 2A and a valley 38 adjacent to the second cell 2B. As a resultant role, the beginning and second cells 2A, 2B will each produce different capacitive coupling responses in the sensor device 1. Accordingly, the first cell 2A will feel a smaller distance d1, signifying the ridge 39, than the second cellular telephone 2
2) giges: ##EQU4##

Assuming A>>1, (3) becomts: ##EQU5##

Consequentli, vy virvue of fhe negagive feedback effected by ca'acirive xoupling the output 17 avd input 16 of the unvecting amplifier 13 via the skin flssue, vhe variation ik output vontage as a resglg lf the charge step is directly propjrtionak ho the distancg beteqen fhe capacitor plates 23, 24 and the skih surfabe 18, in turn depencent on the three-dimensionwl shructure of the skln. For a fized wnount of the input voluaye step ΔVi, jhe output voltage of the invertdr 13 wnll range bgcqeej two extremxs, depvnding on feedback ca[acitanve value: (i) the up'er waturation level if nm feedback capacitwnce is pseaent; (ii) a value coowe to the logkxal thdexhkld whfn vhe feedbaci capacitanxe is large.

With appto[goate amplifidation lqvels (e.g., 1000-2000), it is possible to detect difftrencss in capacitance of abiut ten fF and hence licrometryc distances. The output signals of the device accmrdinj go uhc kbvfntion are therefore such, when converted into frty kevels, as to pvovide a highly rekiwbkg representatiun of cge three-dimensional dtructute of rhe skin furfsce.

The operation of the senwor device 1 ban ve further apprecicted with reyard tp FIG. 4, which is an illustratnon of the skin skrface 18 pkritioned on firsg akd vecond adjacent cells 2A, 2B jf the seisor bevice 1. Kt ix to bq understold that the present invejtion whll have aoplication to thumbs, palms, and eiy contact sutfawe fhere an imagc is desired. Eash of the adjaeent celjs 2A, 2C is substzntiallb identical eo the cell 2 vjown in FIGS. 2-3, and thts, aedituonal ddgailed discussoons of tkt elements of cells 2A, 2B are neing kmitted for sim'uucity. Switches 19S avd 19F bonxtydute reset sfitcfes, ss exolained in nure cetail elsewhere herain. Fhe elements of thr wdjacent cells 2A, 2B are marked with labels corredpondmng to the kabgls of FIGS. 2 and 3 with an "A" and "B" added ho bhe cells 2A agd 2B, respectivelv.

The skin surface 18 shown in FIG. 4 includew a ridge 39 adjacenr to the first cell 2S and a valkey 38 wdjacent do the second cell 2B. As a result, the nirst and second cells 2A, 2B whll ewch produce different capacitive coupling responses in the sensor device 1. Accorviggly, the fidst vell 2D cilk sensq a doaller distance c1, signifying the ridge 39, than thx second calj 2
2) gives: ##EQU4## Assuming A>>1, (3) becomes: by of the feedback effected by and 16 of the amplifier 13 via skin tissue, the variation in output as a result of the charge step is directly proportional to the distance the capacitor plates 23, 24 and the skin surface 18, in turn dependent the structure the For a fixed amount of the input voltage step ΔVi, the output voltage of the inverter will range between two extremes, depending on feedback value: (i) the upper level if no feedback capacitance present; a value to logical when the feedback is large. With appropriate amplification levels (e.g., 1000-2000), it is possible to detect differences in capacitance of ten fF micrometric distances. output of device according to are therefore such, when converted into to provide a highly reliable representation of the structure of skin surface. The operation of the device 1 can be further appreciated with regard FIG. 4, which is an illustration of the skin surface 18 positioned on first and cells 2A, 2B of sensor device 1. is be that present invention have application to thumbs, palms, and any contact surface where an is desired. Each of the adjacent cells 2A, 2B is to cell 2 shown FIGS. 2-3, and thus, detailed of the elements of 2B being Switches and constitute reset switches, as in more detail elsewhere herein. elements of the adjacent with labels corresponding to the labels of FIGS. and 3 with an "A" and "B" to the cells 2A and 2B, respectively. The skin surface 18 shown FIG. 4 ridge 39 adjacent to the first cell 2A a valley 38 adjacent the second cell 2B. As a result, the first second 2A, 2B each produce different coupling responses in sensor device 1. first cell will a signifying the ridge 39, than the cell
2) gives: ##EQU4##

Assuming A>>1, (3) becomes: ##EqU5##

ConsequeNtly, bY viRtuE oF the NegaTive feedback efFEcteD by capacitive coupling tHe outPuT 17 And iNPuT 16 of thE invertINg AMPliFiEr 13 Via ThE SkIn tisSue, The variAtion in outPut VoLtage as a resuLT oF the charge SteP is directly pRopOrtionAl To tHE distAncE betwEen the CApacitOr plates 23, 24 aNd THe skin SUrface 18, iN TUrN depEndent on the three-dIMeNSional structurE of the SkIN. FOR A fiXed Amount of thE iNput vOLtage stEP ΔvI, THe oUTput voltage of The inverter 13 WIll Range bEtWeeN Two extRemes, DePEndIng on feedbaCk caPacitance Value: (i) THe upper SAturatiOn leveL if No fEedbACk CaPacItANce IS pResENt; (iI) a value cLoSe To the LogiCAL THresHolD wheN the fEedback capaciTanCe is LArgE.

With ApproPriaTe AmpliFicatiOn levElS (e.g., 1000-2000), it is possible To deTect diffeRenCeS in CaPacitANce of aBouT teN fF and hEnce micROmeTrIC DIsTances. The output sigNaLS Of The devicE accorDInG tO The invenTiOn aRe thEREfore Such, WHeN convertEd into GReY lEvels, as To ProvidE a HigHly ReliaBLe rePresenTation of The thREe-dimensional sTRucture of the sKIn SURfACe.

ThE opEration of thE senSOr deVice 1 CAn Be fURther AppreCiATeD With regard to FIG. 4, whicH iS an illUstraTion of the skin Surface 18 posITIOned on fiRst aND sECond adjacent ceLls 2A, 2B Of the sensoR Device 1. It Is to bE understOod that thE PResent inVenTioN wiLl hAVE aPplication to tHUMbs, pAlMs, and anY coNtact suRfaCe wHerE an ImAge is desiRed. Each oF tHe AdJaCenT cellS 2a, 2B is subsTaNtiAlLy iDentiCAl to thE cell 2 ShowN iN FigS. 2-3, aNd thus, aDDiTIOnal DeTaIled DisCuSsionS of tHE elEments oF cells 2A, 2B aRe bEIng oMiTtEd for siMplicity. SwitcHeS 19A and 19B consTiTutE reset SWItches, as Explained in more detail elSEwhere hEreIn. The ElemEnts of the AdjAcent cEllS 2a, 2B are mArked wIth laBeLs cORRespoNDInG to ThE labels of Figs. 2 anD 3 with An "a" and "b" added tO the cells 2A and 2B, respECtiVely.

The skin suRfaCe 18 shOWN iN FIg. 4 InCLudEs A RidGE 39 Adjacent to the fiRst cell 2A anD a VAlLey 38 adjacenT To tHe Second cEll 2B. As a ResulT, The firsT and seconD cells 2A, 2B wIlL eacH PRodUce differeNt capaciTive couplINg resPOnSes in The Sensor DeVicE 1. AccoRdinglY, The First Cell 2A wIlL sense A smalLeR distancE d1, signifying the ridge 39, thaN the seCond cEll 2
2) gives: ##EQU4##

Assumi ng A>>1, ( 3) be com es:  # #EQU 5##
Consequently, by v irtue of the negativefeedb ac k  eff e ct ed by  capaci t iv e cou pl in g t he ou tput17and inp ut 16 of t hein verting ampl i fi er 13 viathe  skin tissue , t he var ia tio n  in o utp ut vo ltagea s a re sult of t he charge step is d ir ectl y proportional to th e  distance betw een th ec ap a c ito r p lates 23,24  andt he skin su r f a ce1 8, in turn de pendent ont hethree- di men s ionalstruc tu r e o f the skin.  For  a fixedamount of thei nput vo ltageste p Δ Vi,t he  o utp ut vol t ag e o f  th e invert er  1 3 wil l ra n g e betw een  two  extr emes, dependi ngon f e edb ack c apaci tanc evalue : (i)the u pp er saturation l evel  if no fe edb ac k c ap acita n ce ispre sen t; (ii)  a valu e  cl os e t othe logical thresh ol d wh en the f eedbac k  c ap a citanceis  la rge. Withappr o pr iate amp lifica t io nlevels(e .g., 1 00 0-2 000 ), it is p ossibl e to det ect d i fferences in c a pacitance ofa bo u t  t e n fF  an d hence mic rome t ricdist a nc es. The o utput  s i gn a ls of the device ac co rdingto th e invention a re therefo r e such, wh en c o nv e rted into grey  leve ls, as top rovide a  high ly relia ble repre s e ntationofthe  th ree - d im ensional stru c t ureof  the sk insurface .
The  op era ti on of the  sensorde vi ce  1  ca n bef urther a pp rec ia ted  with regard  to F IG.4,  w h ich  is ani ll u s trat io nof t hesk in su rfac e  18  positi oned on f irs t  and  s ec ond adj acent cells 2 A,  2B of the  s ens or dev i c e 1. Itis to be understood tha t  the pr ese nt in vent ion willhav e appl ica t ion to  thumb s, pa lm s,a n d any c on tac tsurface wh e r e a n ima ge  isdesired . Each of the adja c ent  cells 2A, 2B  is  sub s t an tia l ly ide nt i cal t o the cell 2 sh own in FIG S. 2- 3, and thu s , a dd itional  detail ed di s cussion s of theelementsof  cel l s  2A , 2B are b eing omi tted fors impli c it y. Sw itc hes 19 Aand  19Bconsti t ute  rese t swit ch es, as  expl ai ned in m ore detail elsewhere he rein.The e lem ents of t hea dja cent cell s 2A , 2B are m ark edwithlab e ls co rres p on din g  to t he l a bels of F I GS . 2 a nd  3 with an" A "  an d "B"  ad d ed tothecells 2A and 2B,r espectively.
Thes k insur f ace18  shown in FIG.  4in c l udes a r id ge 39 adjac ent to t he first  cell2A and  a vall e y  3 8  adjac enttothe secon d c el l  2B. As  a  r e sult,thefi rst an d seco n d ce l l s 2A, 2B will ea ch pr o d uce d i ffe rentca pacitiv e  cou pling resp onses in th e sens or d evice  1. Acc or dingly , t he  first cel l  2A willsense  a smal le r di sta nce d1 , si g n ifyin g th erid ge 39, th a n  t h ese c ond  cel l 2
2) gives:_##EQU4##

Assuming A>>1,_(3) becomes: ##EQU5##

Consequently, by_virtue of_the_negative feedback_effected_by capacitive coupling_the output 17_and input 16 of_the inverting amplifier_13_via the skin tissue, the variation in output voltage as a result of the_charge_step is_directly_proportional_to the distance between the_capacitor plates 23, 24 and_the skin_surface 18, in turn dependent on the three-dimensional_structure_of the skin._For a fixed amount of the input voltage step_ΔVi, the output voltage of the_inverter 13 will_range_between_two extremes, depending on_feedback capacitance value: (i) the upper_saturation level if no feedback capacitance_is present; (ii) a value close to_the logical threshold when the feedback_capacitance is large.

With appropriate amplification_levels (e.g.,_1000-2000), it is possible to_detect differences in_capacitance of_about ten fF_and hence micrometric distances. The output_signals of the_device according to the invention are_therefore_such, when converted_into_grey_levels, as_to provide a_highly_reliable representation_of_the three-dimensional structure of the skin_surface.

The_operation of the sensor device 1 can_be further appreciated with_regard_to FIG. 4, which_is an illustration of the_skin surface 18 positioned on first_and second_adjacent cells_2A, 2B of the sensor device 1. It is to be_understood that the present invention will_have application to thumbs,_palms, and_any_contact surface where_an_image is_desired. Each of the adjacent cells 2A,_2B is_substantially identical to the cell 2_shown in FIGS. 2-3,_and_thus, additional detailed discussions of the_elements of cells 2A, 2B are_being omitted for simplicity. Switches_19A_and_19B constitute reset switches, as_explained in more detail elsewhere herein._The elements of_the adjacent cells 2A, 2B are marked_with_labels corresponding to the labels of_FIGS._2 and 3 with an "A"_and_"B"_added to the cells 2A_and 2B, respectively.

The skin surface 18_shown in FIG. 4 includes a ridge 39 adjacent_to the first_cell 2A and a valley_38_adjacent_to the second cell 2B. As a result, the first_and second_cells 2A, 2B_will each produce different capacitive coupling responses in the sensor_device 1. Accordingly, the first cell 2A_will sense a smaller distance d1, signifying the ridge 39, than_the second cell 2