text: fig1 ( a ) shows a side view of retractable snap dome 100 , according one embodiment of the present invention . fig1 ( b ) shows a first perspective view of retractable snap dome 100 , from a first direction that is roughly 45 degrees out of the page from the side view of fig1 ( a ) . fig1 ( c ) shows a second perspective view of retractable snap dome 100 , from a second direction that is roughly 45 degrees into the page from the side view of fig1 ( a ) . as shown in each of fig1 ( a ), 1 ( b ) and 1 ( c ) , retractable snap dome 100 include sections 101 - 1 , 101 - 2 , 101 - 3 , 101 - 4 and 101 - 5 , which are joined by folding ridges 102 - 1 , 102 - 2 , 102 - 3 , and 102 - 4 . these folding ridges are hinge points that facilitate and define the upright and collapsed positions of retractable snap dome 100 . the upright position of retractable snap dome 100 is maintained by both the elasticity of segments 101 - 1 to 101 - 5 and shape - retention characteristics of folding ridges 102 - 1 to 102 - 4 . sections 101 - 1 and 101 - 5 are also joined by hinge bars 103 - 1 , 103 - 2 and 103 - 3 which form a bi - stable hinge between sections 101 - 1 and 101 - 5 of retractable snap dome 100 . the bi - stable hinge has a first bi - stable state and a second bi - stable state , as described in further details below . as shown in fig1 ( b ) , the bi - stable hinge connects between sections 101 - 1 and 101 - 5 at curved boundaries 104 - 1 and 104 - 2 . alternatively , section 101 - 1 and 101 - 5 may also be joined by an elastic ribbon to provide the same bi - stable states , as described in further details below . embedded in section 101 - 5 is emp actuator 105 adjacent to curve boundary 104 - 2 of section 101 - 4 . in one embodiment , emp actuator 105 may be provided by a bimorph emp actuator which can be selectively actuated to provide a mechanical response ( e . g ., bending ) in either one of two directions . a bimorph emp actuator has two active regions , such that electrical stimulation in the first active region provides bending in one direction , and electrical stimulation in the second region provides bending in a second or opposite direction . an electromechanical polymer ( emp ) actuator typically includes one or more emp layers formed out of a relaxor ferroelectric fluoropolymer and electrodes bonded thereto . when an external electric field is imposed across an emp layer , the emp layer becomes charged . the emp layer thus behaves electrically as a capacitor . the electric field also provides an electromechanical response in the form of elongation in the transverse directions relative to the imposed electric field . the electromechanical property of the emp layer is used to create the emp actuator . emp actuators are described , for example , in copending u . s . patent application (“ copending application ”), ser . no . 13 / 683 , 963 , entitled “ localized multimodal electromechanical polymer tranducers ,” filed on nov . 21 , 2012 , naming b . zellers et al . as inventors . the copending application is hereby incorporated by reference herein . fig2 ( a ), 2 ( b ) and 2 ( c ) each illustrate three stages of retractable snap dome 100 in a conventional ( i . e ., key depression ) operation . fig3 shows a force profile of retractable snap dome 100 during the conventional operation . fig2 ( a ) shows , in the left portion , a first stage in which retractable snap dome 100 is in its up position supporting a key ( not shown ) ready to receive the downward force of a key depression . retractable snap dome 100 is designed to collapse and rise with little force . a downward force on segments 101 - 3 and 101 - 4 pushes segments 101 - 2 and 101 - 5 in opposite outward directions . the downward force is represented in fig3 by curve segment 301 . in the middle portion , fig2 ( a ) shows a second stage in which sections 101 - 3 and 101 - 4 of retractable dome 100 are depressed to horizontal positions . in this stage , sections 101 - 2 and 101 - 3 are designed to be angled to the left of vertical and to be substantially vertical , respectively , so as to predispose retractable dome 100 to collapse to the left . initially , the depression increases the load on section 101 - 2 , with corresponding increased resistance , as represented by curve segment 302 of fig3 . upon further depression , retractable snap dome 100 buckles to the left . the buckling action is represented by curve segment 303 of fig3 . the buckling brings retractable snap dome 100 to its collapsed position . the force profile in this configuration is represented by curve segment 304 in fig3 . in the right portion , fig2 ( a ) shows a collapsed position of retractable snap dome 100 upon further depression . fig2 ( b ) illustrates the same three stages of retractable snap dome 100 of fig2 ( a ) in the conventional operation , as seen from the first direction . fig2 ( c ) illustrates the same three stages of retractable snap dome 100 of fig2 ( a ) in the conventional operation , as seen from the second direction . according to one embodiment of the present invention , emp actuator 105 may be actuated to bring retractable snap dome 100 to a collapsed position that may persist indefinitely , even after electrical stimulation is withdrawn . fig4 ( a ) illustrates three stages of retractable snap dome 100 — from upright to collapsed — under powered , activated and powered and activated and unpowered states of emp actuator 105 , in accordance with one embodiment of the present invention . in the left portion , fig4 ( a ) shows retractable snap dome 100 when activation of emp actuator 105 is initiated by application of a voltage across one or more emp layers in emp actuator 105 . initially , retractable snap dome 100 is in its upright position , bi - stable hinge is in a first bi - stable state , and emp actuator 105 is unpowered . as shown in the left portion of fig4 ( a ) , activation causes emp actuator 105 to provide an electromechanical response ( e . g ., bending ) that acts on curved boundary 104 - 1 and pushes section 101 - 5 towards the right , and eventually causes the bi - stable hinge to the second bi - stable state . as mentioned above , hinge bars 103 - 1 , 103 - 2 and 103 - 3 form the bi - stable hinge . ( the bi - stable hinge can also be formed by an elastic ribbon , as also mentioned above ). the two bi - stable states are lower energy configurations than the unstable intermediate state in which curved boundaries 104 - 1 and 104 - 2 have the greatest distance from each other at hinge bars 103 - 1 and 103 - 3 . this configuration compresses hinge bar 103 - 2 and puts hinge bars 101 - 1 and 101 - 3 in greatest tension . the unstable state may resolve into either one of the bi - stable states , in which hinge bars 103 - 1 and 103 - 3 are relatively unstrained . as further electrical stimulation is applied to emp actuator 105 , retractable snap dome 100 flattens to the right , the tension in each of hinge bars 101 - 1 and 101 - 3 increases towards the unstable state . when the bi - stable hinge reaches the unstable state , further bending of emp actuator 105 pushes the bi - stable hinge to rapidly snap into the second bi - stable state . at this point , retractable snap dome 100 has buckled and collapsed to the right , as shown in the middle portion of fig4 ( a ) . as mentioned above , emp actuator 105 remains charged even when power is withdrawn . even when disconnected from power , emp actuator 105 maintains its mechanical state at the time of power disconnection . therefore , if power is disconnected after the bi - stable hinge settles in the second bi - stable state , emp actuator 105 locks retractable snap dome 100 in the collapsed state , as shown in the right portion of fig4 ( a ) . fig4 ( b ) illustrates the same three stages of retractable snap dome 100 of fig4 ( a ) under the powered , the activated and powered and the activated and unpowered states of emp actuator 105 , as seen from the first direction . fig4 ( b ) illustrates the same three stages of retractable snap dome 100 of fig4 ( a ) under the powered , the activated and powered and the activated and unpowered states of emp actuator 105 , as seen from the second direction . to return retractable snap dome 100 to the upright position , emp actuator 105 may be provided the electrical stimulation in reverse from that illustrated by fig4 ( a ), 4 ( b ) and 4 ( c ) . fig5 ( a ) illustrates three stages of retractable snap dome 100 — from collapsed to upright — under powered , activated and powered and activated and unpowered states of emp actuator 105 , in accordance with one embodiment of the present invention . in the left portion of fig5 ( a ) , retractable snap dome 100 is shown initially in the locked - down collapsed state shown in the right portion of fig4 ( a ) . in the embodiment in which emp actuator 105 is implemented by a bimorph emp actuator , emp actuator 105 is activated to bend in the opposite direction to drive the bi - stable hinge from the second bi - stable state to the first bi - stable state , which is shown in the middle portion of fig5 ( a ) . after retractable snap dome 100 is returned to the upright position , as shown in the right portion of fig5 ( a ) , electrical stimulation of emp actuator 105 may be withdrawn . retractable snap dome 100 is thus locked - down to the upright position to be ready to perform conventional operation . fig5 ( b ) illustrates the same three stages of retractable snap dome 100 of fig5 ( a ) under the powered , the activated and powered and the activated and unpowered states , as seen from the first direction . fig5 ( b ) illustrates the same three stages of retractable snap dome 100 of fig5 ( a ) under the powered , the activated and powered and the activated and unpowered states , as seen from the second direction . in one embodiment , emp actuator 105 produces a force in the ˜ 10 g range to facilitate retractable snap dome 100 to rise to the upright state or to fall to the collapsed state through the action of the bi - stable hinge . ( movement in the bi - stable hinge is realized by a weak pull / push horizontal force ). in comparison , from the locked - down upright position of retractable snap dome 100 , a downward force in the range of ˜ 50 - 200 g is required to collapse retractable snap dome 100 in conventional operation . a retractable snap dome of the present invention consumes power only for collapsing the structure for storage or returning the structure back to its upright position . in a keyboard application , for example , the emp actuator is not involved in the conventional typing operation , and thus the advantages are achieved with little power consumption . the above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting . numerous variations and variations within the scope of the present invention is possible . the present invention is set forth in the accompanying claims .