US3668417A - Touch-sensitive switch employing electret foil - Google Patents

Touch-sensitive switch employing electret foil Download PDF

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Publication number
US3668417A
US3668417A US101536A US3668417DA US3668417A US 3668417 A US3668417 A US 3668417A US 101536 A US101536 A US 101536A US 3668417D A US3668417D A US 3668417DA US 3668417 A US3668417 A US 3668417A
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United States
Prior art keywords
electret
conductive
touch
foil
displacement
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Expired - Lifetime
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US101536A
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English (en)
Inventor
Gerhard Martin Sessler
Robert Lee Wallace Jr
James Edward West
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AT&T Corp
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Bell Telephone Laboratories Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/02—Constructional features of telephone sets
    • H04M1/23—Construction or mounting of dials or of equivalent devices; Means for facilitating the use thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
    • H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
    • H01G7/021—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric
    • H01G7/023—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric of macromolecular compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
    • H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
    • H01G7/025—Electrets, i.e. having a permanently-polarised dielectric having an inorganic dielectric
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/965—Switches controlled by moving an element forming part of the switch
    • H03K17/975—Switches controlled by moving an element forming part of the switch using a capacitive movable element
    • H03K17/98—Switches controlled by moving an element forming part of the switch using a capacitive movable element having a plurality of control members, e.g. keyboard

Definitions

  • a keyboard switching arrangement that is mechanically simple, reliable, and which can be fabricated with an overall thickness of less than /4 inch, includes a plurality of independent conductive elements aligned with holes in a protective front cover.
  • a single sheet of a metallized foil electret is interposed between the cover and the conductive members.
  • the metal layer of the foil forms a capacitive transducer with each backplate section.
  • Each switch is operated by touching the foil electret through one of the cover holes. The resulting displacement generates an electric output signal which is utilized for actuating an associated switching element or the like.
  • This invention relates to a signalling apparatus and more particularly to key selector apparatus that is sensitive to the touch. It has for its principal object the improvement of touch selectors through a simplification of their mechanical construction, the elimination of metallic contacts, and an increase in reliability. Other objects are a reduction of size, an improvement in sensitivity, the reduction of cost, and the generation of an output signal that may be used without additional detection or processing.
  • electrostatic and film membrane units are compact, they nevertheless require auxiliary energizing power and detector and signal generating equipment to prepare suitable switching signals.
  • a charged thin film membrane Such a charged film is known as an "electret and, when the film is provided with a thin conductive coating on one of its surfaces, it is generally known as a metallized foil electret or simply as a metallized electret.”
  • Electrets exhibit a permanent charge and, when employed in a transducer-like configuration, develop sizable output signals when displaced.
  • a plurality of separated conductive elements are supported in any desired pattern in an insulating member. All of the elements are covered by a thin metallized electret sheet, or a plurality of such sheets, held a slight distance away from the elements and from each other.
  • a front cover equipped, for example, with apertures of finger size, is supported in alignment with the metallic conductive elements. As the foil is mechanically displaced in relation to one of the conductive elements, a signal pulse is produced in a connecting output circuit. No auxiliary detector is required.
  • the signal is sufficient for actuating auxiliary oscillators, switching elements, amplifiers, or the like.
  • the touch selector in accordance with the invention, may be modified in a number of ways to adapt it to a particular application.
  • an auxiliary, uncharged, film may be placed between the metallized foil electret and the aperture cover to protect the electret against environmental, manual, or other hazards.
  • pushbuttons may be employed as an interface between the user and the electret foil.
  • several metallized electret sheets may be sandwiched between the aperture plate or protective membrane and the array of conductive backplate elements to provide trains of pulses of positive and negative polarity. Such pulse trains may be used to address the logic circuits of connecting devices.
  • the electret touch selector in accordance with the invention, is extremely compact, simple to implement, and reliable.
  • an output signal of more than 8 volts into a load 10'' ohms was produced by a unit having an overall thickness of less than It inch in response to an applied force in the neighborhood of 5 X 10 dynes.
  • FIG. 1 is an exploded view of the basic elements of a touchsensitive selector in accordance with the invention
  • FIG. 2 illustrates, in cross section, the basic arrangement of a call selector in accordance with the invention, which employs an auxiliary protective film and pushbutton guide members;
  • FIG. 3 illustrates an arrangement in accordance with the invention in which a multiplicity of individual metallized foil electrets are employed to produce coded pulse trains of two polarities;
  • FIG. 4 illustrates a trapezoidal displacement of the foil of an electret selector in accordance with the invention and the voltage response of the unit for two different time constants
  • FIG. 5 illustrates the voltage of one unit of an electret touch-sensitive selector in accordance with the invention as a function of the applied force for various terminating resistances.
  • FIG. 1 illustrates, by means of an illustrative exploded view, the major elements of a touch-sensitive selector switch in accordance with the invention.
  • the selector employs a plurality of conductive backplates 11,, 11,, embedded in an insulating support member 12.
  • backplates l 1 are recessed a slight distance beneath the front surface of support member 12.
  • each of the backplate members 11 is approximately 1.6 cm. in diameter and the support 12 is composed of a plastic insulating material.
  • the backplates in this embodiment are recessed by approximately 50 am. into the insulator.
  • the individual backplate members may be conductive areas printed on a circuit board. If the conductive portions are on the surface of the board, an apertured insulating layer is used to establish the required recess. Otherwise, the conductive elements may be deposited in recesses in the board.
  • a sheet of a metallized electret material 13 is positioned over the backplates and rests generally on the surface of support 12.
  • an electret foil was prepared from a single 2 mil (51 pm.) thin film of polyfluoroethylenepropylene plastic material, marketed commercially as Teflon FEP, with a 1,000 A. metallic layer on mm ul its surfaces.
  • Teflon FEP polyfluoroethylenepropylene plastic material
  • Metallized electret 13 is held in place by a thin cover 14 having a plurality of holes 15 1 m aligned with the conductive backplates ll,,, 11,,, in support 12.
  • the metallic layer on film 13 faces aperture plate 14.
  • plate 14 may be formed of conductive material to provide additional electrical shielding for the unit.
  • the coverplate is secured for example to a conductive case 16 which encloses insulating member 12.
  • Each of conductive plates 11 is connected to one of terminals 17 17 which extend through the unit and are exposed for external connections.
  • the other electrical connection (not shown) is made to metallized coating 13c on foil 13. If coverplate 14 is conductive, and if no auxiliary layers are used, connection may be made to plate 14. Obviously, other mounting techniques may be employed.
  • the selector mechanism is operated by touching one of the exposed foil sections briefly through one of apertures 15 in coverplate 14. As the foil is touched, it is displaced nonuniformly over the area of the aligned backplate 11. After the foil is released it returns to its quiescent position due to its tension and stiffness. As a result of these operations, the foil electret 13 and the juxtaposed backplate act as an electromechanical transducer, as opposed to an electroacoustic transducer, and generate a voltage pulse v(t) across an impedance connecting the metallic surface 130 of electret 13 to backplate terminal 17.
  • the generated voltage pulse may be described by either of the convolutions (2) where s(t) is the (spatial) average displacement of the foil electret, .i-(t) is the time derivative of s(t), and h(t) and a(t) are the unit-impulse and unit-step responses to displacement, respectively.
  • the selector can thus be visualized as a circuit which includes a series connection of the capacitance Got one of the electret transducers (foil 13 and conductive element 11), a terminating resistor R (not shown), and a voltage source responsible for the voltage generated by the electret transducer.
  • This circuit is characterized by a(t) Ae' for re where 8(1) is the Dirac delta function and A is the ratio of voltage generated by the voltage source to average displacement of the foil electret.
  • A is given by A a'D/(D+ed),,. s
  • Equation o is the effective surface charge density of the electret on its nonmetallized surface
  • D and d are the thicknesses of electret and air layer between electret 13 and backplate 11, respectively
  • 6 is the dielectric constant of the electret material and s the permittivity of free space. Equation (5) holds if the displacement s(!) is much smaller than the spacing d.
  • the voltage v(t) for the trapezoidal displacement function shown in FIG. 4a is given by where At t t, is the risetime of the displacement function, and s the maximum (spatially averaged) displacement.
  • the electrical output signal across a terminating resistor consists of a pair of oppositely poled spikes with durations comparable to the time constant of the system if the time constant is smaller than the duration of the displacement. For time constants greater than this, the electrical output approximates the displacement. Since the output voltage of the unit is dependent upon the product of the field in the air gap between the foil and the backplate and the displacement of the foil into the gap, the extent of the air gap, as determined for example by the depth of the recess in support member 12, should be selected in accordance with foil parameters and expected displacement. If the recess is too large, the field is small; if the recess is too small, displacement is restricted. It has been found that a recess depth on the order of the foil thickness is satisfactory.
  • Signal voltages of this sort can be used directly without further detection and often without additional processing.
  • the produced signal may be coupled directly into an amplifier circuit having a reasonably high input impedance.
  • a single-stage, field-effect transistor amplifier has been found to be a suitable input circuit element.
  • output signals may be amplified in any bi-polar transistor amplifier, for example, one using multiple stages and negative feedback to achieve the required input impedance.
  • FIG. 2 An alternative configuration which may be used in the fabrication of a selector switch in accordance with the invention, is illustrated schematically in FIG. 2.
  • the construction shown in cross section is much the same as that of the apparatus in FIG. 1 except that an auxiliary, uncharged, thin pliable film 18 is interposed between foil electret 13 and apertured coverplate 14. It is often desirable to use such an auxiliary layer to protect the foil electret from environmental or other damage, and to assure maintenance-free operation.
  • Film 18 preferably is bonded to case 16 (FIG. 1) to provide maximum protection for the selector unit.
  • buttons 19 are formed with a concave surface configuration and are held captive in the apertures of plate 14.
  • the button shape and size is a mere matter of design choice. When depressed, they cause the necessary displacements of electret 13 with respect to backplate member 11 to generate an output signal.
  • a stop-action is assured to prevent possible physical damage to the foils.
  • the pliable films are generally resilient enough to return the buttons to their withdrawn position, it may be desirable to employ auxiliary spring elements.
  • auxiliary means may be employed to 1 provide an indication that contact has been achieved.
  • the finger aperture or button element may be illuminated as contact is made, or an audible or other visual indication may be provided to notify the user of a completed contact.
  • Such indicating elements are well known to those skilled in the art and include such things as buzzers, cricket devices, and analog or digital display-windows.
  • electrical contact between a portion of a pushbutton, e.g., 19, and printed circuit connectors on auxiliary layer 18 or in insulated channels associated with cover 14 may be used.
  • suitable identification marks may be used in association with each of the touch selector positions.
  • suitable position indications may be printed or individually attached to the outward surface of the foil in each aperture position. If auxiliary protective film is employed, such indications preferably are placed beneath the protective layer. If button elements are used, the position designation preferably is placed in the button housing in the usual fashion.
  • multiple foils of electret material are employed to generate a train of either positive or negative polarity pulses for each displacement.
  • Such pulse trains are generated by employing a plurality of metallized foil electrets.
  • two foils 13 and 20 are placed across a single backplate member 11, with both metallic layers 13c and 20c facing away from the electrode.
  • a slight air gap 21 is maintained between the foil layers, for example, by insulating spacers 22.
  • Spacers 22 may be in the form of discrete insulators, a grid configuration, or an insulating aperture plate aligned with backplate members 11. Electrical connections are made between the conductive surfaces 13c and 20c of foils l3 and 20 and terminal 17.
  • the conductive layer of the outer foil e.g., 200 is maintained at ground potential to provide electrostatic shielding for the unit.
  • the several signals from the foils are delivered directly to adder 23 and the signal from electrode 11 developed on terminal 17 is passed through delay element 24 and thence to adder 23.
  • the interval of delay of unit 24, d is selected to provide the desired spacing between the pulses of the resulting train.
  • electret foil 20 acts together with the conductive layer 130 of foil 13 as one switching element and electret 13 in cooperation with backplate 11 constitutes the other.
  • an initial signal output is developed between electret foil 20 and conductive layer 13c which acts as its associative backplate.
  • This signal delivered by way of adder 23, constitutes the first pulse in the train.
  • a second signal is generated as foil 13 is moved in relation to backplate 11. This signal is delayed in unit 24 so that it occurs at a time d following the generation of the first pulse.
  • both foils are of like polarity to give rise to two positive pulses. If the foils are both negatively or both positive- 1y polarized, spaced apart pulses of like polarity are produced. If one foil is positive and the other negative, pulses of opposite polarity are produced.
  • delay unit 24 may be placed, for example, in the conductor interconnecting foil 20 with adder 23. By this expedient, the signal developed between foil 13 and backplate 11 can be made to appear in advance of the pulse produced between foil 20 and the conductive layer of foil 13 in the pulse train. Obviously, by selecting the polarities of the foil electret layers and the position and number of delay units employed, any desired pulse train configuration may be produced.
  • the output signal developed between one foil electret and the conductive element of another electret may be delivered to an output circuit independent of the output circuit which receives the signal derived at the same touch location between a foil electret and the corresponding conductive backplate element.
  • an electret foil may be polarized with opposite polarities at discrete lateral locations
  • the portion of the electret foil aligned with each touch location may be either positively or negatively polarized. Accordingly, the signal developed at each touch location is coded according to polarity.
  • similar polarity coding may be used at each touch location.
  • signals derived from different electret layers at a single touch location, being of different polarity may be delivered to separate utilization circuits, independent of the circuits used to accept delayed signals from that touch location.
  • Additional flexibility is obtained by restricting the metallized layer on selected electret foils to discrete areas in the vicinity of each touch location, and by independently connecting the metallized areas of those foils to external circuits. Known techniques may be used to establish such areas. Regardless of the way in which the signals are derived or combined as a composite signal, they are typically delivered to a utilization device such as amplifier 25, or the like.
  • the aperture arrangement of FIG. 1 may be implemented with a plurality of electret films, as shown in FIG. 3, and may additionally employ a protective film of the sort shown in FIG. 2.
  • a single electret foil may be used as opposed to the foil and protective film arrangement illustrated.
  • a single electret foil may be used as opposed to the foil and protective film arrangement illustrated.
  • a multiple electrets may be used in this configuration. Suffice it to say, the arrangements illustrated are merely representative of numerous alternatives.
  • touch points may be arrayed in any desired configuration, e.g., circular, in-line, or the like.
  • the touch sensitive selector described herein has not exhibited any adverse effect as a result of frequenttouching.
  • the output voltage of a unit similar to that shown in FIG. 1 did not change measurably after more than 400,000 automatic touch operations performed with a motor-driven plunger directly contacting the metallized layer of the electret foil. Even so, it is desirable, as illustrated in FIG. 2, to use an additional plastic film for protection against hazards of manual use.
  • sensitivity of the selector elements to airborne sound is comparatively small. It was found that a pistol shot fired at a distance of 3 feet generated a signal more than 70 db. less than that resulting from a touch operation.
  • a touch-sensitive signalling device which comprises,
  • a conductive member and spaced apart metallized electret means supported together in spaced juxtaposition in a transducer-like configuration for generating a voltage pulse in response to a tactile displacement of said electret means with relation to said conductive member, the thickness of said electret means and the spacing between said conductive member and said electret means being respectively proportioned to render said configuration insensitive to nontactile displacement forces,
  • said metallized electret means comprises a plurality of thin film electrets, each with a conductive coating on one surface.
  • said metallized electret means comprises at least one thin film electret with a conductive coating on one surface thereof, and
  • a touch-sensitive signalling device which comprises, an array of independent conductive members, metallized electret means supported in spaced juxtaposition to said conductive members,
  • said metallized electret means comprises a thin film electret with a conductive coating on one surface thereof.
  • said metallized electret means comprises a plurality of thin film electrets, each with a conductive coating on one surface, and
  • said metallized electret means comprises at least one foil electret and an overlaying uncharged pliable protective layer.
  • said means for restricting the application of an externally applied displacement force to said electret means comprises, an apertured cover member overlaying said electret means 10 with said apertures in substantial alignment, respectively, with said conductive members.
  • said means for restricting the application of an externally applied displacement force to said electret means comprises, a plurality of individual pushbuttons in substantial alignment, respectively, with said conductive members. 2o 10.
  • a touch-sensitive selector which comprises, in combination,
  • a single sheet foil electret comprising a thin film electret metallized with a conductive coating on one surface thereof, supported in spaced juxtaposition to said members with said conductive coating away from said members, an insulating apertured cover member overlaying said foil electret with said apertures in substantial alignment with said conductive members, and
  • a touch-sensitive selector as defined in claim 10 is responsive to the voltage developed between a conductive member and said conductive coating on said electret occasioned by the displacement of that foil electret portion in juxtaposition to said member.
  • said array of conductive members comprises, an insulating support with recesses at selected locations therein, a plane conductive element embedded in each of said recesses at a slight distance beneath the front surface of said support, and means for connecting said conductive elements indepen-. dently to said voltage responsive means.
  • said foil electret is polarized with different polarities at discrete areas substantially aligned with said conductive elements.
  • An electro-mechanical transducer which comprises,
  • At least two of said thin pliable films are foil electrets held slightly apart from one another, each with their conductive elements facing away from the conductive elements of said array, and
  • said means responsive to a voltage change includes means for delivering voltage changes occasioned by the individual displacement of each of said foil electrets to an external circuit.
  • said means responsive to a voltage change includes means for altering the time of delivery of said individual voltage changes to said external circuit.
  • each of said foil electrets is polarized with selectively different polarities at discrete areas substantially in the vicinity of said conductive elements.
  • At least two of said thin pliable films are foil electrets held slightly apart from one another, each with their conductive coating facing away from the conductive elements of said array, and
  • said voltage responsive means associated with each of said independent conductive elements includes,
  • said conductive element on said surface of said foil electret is restricted to areas substantially aligned with said independent conductive elements.
  • a touch-sensitive signalling device which comprises,
  • selected ones of said electret films are of one polarity and the remaining ones are of the opposite polarity.
  • said electret films are polarized with selected polarities at different lateral locations therein.
  • said means for delivering said developed voltage changes to an external circuit includes, means for altering the time of delivery of said individually developed voltagechanges.
  • said conductive diaphragm comprises at least one metallized electret film
  • a multiple element electrostatic transducer which comprises, in combination,
  • said means for directing an externally applied tactile force to said configuration comprises mechanical actuator means as an interface between an applied tactile force and said electret means.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Signal Processing (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Push-Button Switches (AREA)
  • Electronic Switches (AREA)
US101536A 1970-12-28 1970-12-28 Touch-sensitive switch employing electret foil Expired - Lifetime US3668417A (en)

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US10153670A 1970-12-28 1970-12-28

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US3668417A true US3668417A (en) 1972-06-06

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US (1) US3668417A (xx)
JP (1) JPS5436311B1 (xx)
BE (1) BE777202A (xx)
CA (1) CA1009764A (xx)
DE (1) DE2164202C3 (xx)
ES (1) ES398773A1 (xx)
FR (1) FR2120902A5 (xx)
GB (1) GB1380709A (xx)
IT (1) IT943354B (xx)
NL (1) NL159837B (xx)
SE (1) SE377974B (xx)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3751612A (en) * 1971-08-30 1973-08-07 Colorado Instr Inc Snap action capacitive type switch
US3786495A (en) * 1972-05-17 1974-01-15 Ncr Stored charge transducer
US4336529A (en) * 1980-02-19 1982-06-22 Pitney Bowes Inc. Postage meter having shielded keyboard to protect against electromagnetic radiation
US4456800A (en) * 1983-05-25 1984-06-26 Allen-Bradley Company Planar contact array switch having improved ground path for dissipating electrostatic discharges
US4561002A (en) * 1982-08-30 1985-12-24 General Electric Company Capacitive touch switch arrangement
US5034740A (en) * 1988-09-30 1991-07-23 Siemens Aktiengesellschaft Capacitive card module
US5835027A (en) * 1996-11-07 1998-11-10 Tyburski; Robert M. Residual charge effect traffic sensor
WO2006003249A2 (en) * 2004-07-07 2006-01-12 Emfit Oy Electrical coupling of an electromechanical control unit
US20060267962A1 (en) * 2004-02-02 2006-11-30 E.G.O. Elektro-Geraetebau Gmbh Operating device with an operating field and a sensor element for an electrical appliance and method for operating the operating device
WO2015007948A1 (en) * 2013-07-18 2015-01-22 Nokia Corporation Apparatuses, methods and computer programs for expanding the use of touch-sensitive input apparatus
EP1444861A4 (en) * 2001-10-09 2018-02-28 Frank Joseph Pompei Ultrasonic transducer for parametric array

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4593191A (en) * 1982-12-29 1986-06-03 At&T Bell Laboratories Pressure and optical sensitive device with deformable protrusions

Citations (6)

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Publication number Priority date Publication date Assignee Title
US2610245A (en) * 1946-02-18 1952-09-09 Robert H Rines Electret array sensitive to radio waves
US3118022A (en) * 1961-08-07 1964-01-14 Bell Telephone Labor Inc Electroacoustic transducer
US3290439A (en) * 1963-04-29 1966-12-06 Willcox Data encoding keyboard
US3308253A (en) * 1965-03-25 1967-03-07 Ibm Diaphragm switch having a diaphragm supported on an incompressible layer and an elastomer overlaying the diaphragm
CA822821A (en) * 1969-09-09 W. Reedyk Cornelis Directional electret transducer
US3503031A (en) * 1969-02-11 1970-03-24 Control Data Corp Printed circuit keyboard

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA822821A (en) * 1969-09-09 W. Reedyk Cornelis Directional electret transducer
US2610245A (en) * 1946-02-18 1952-09-09 Robert H Rines Electret array sensitive to radio waves
US3118022A (en) * 1961-08-07 1964-01-14 Bell Telephone Labor Inc Electroacoustic transducer
US3290439A (en) * 1963-04-29 1966-12-06 Willcox Data encoding keyboard
US3308253A (en) * 1965-03-25 1967-03-07 Ibm Diaphragm switch having a diaphragm supported on an incompressible layer and an elastomer overlaying the diaphragm
US3503031A (en) * 1969-02-11 1970-03-24 Control Data Corp Printed circuit keyboard

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3751612A (en) * 1971-08-30 1973-08-07 Colorado Instr Inc Snap action capacitive type switch
US3786495A (en) * 1972-05-17 1974-01-15 Ncr Stored charge transducer
US4336529A (en) * 1980-02-19 1982-06-22 Pitney Bowes Inc. Postage meter having shielded keyboard to protect against electromagnetic radiation
US4561002A (en) * 1982-08-30 1985-12-24 General Electric Company Capacitive touch switch arrangement
US4456800A (en) * 1983-05-25 1984-06-26 Allen-Bradley Company Planar contact array switch having improved ground path for dissipating electrostatic discharges
US5034740A (en) * 1988-09-30 1991-07-23 Siemens Aktiengesellschaft Capacitive card module
US5835027A (en) * 1996-11-07 1998-11-10 Tyburski; Robert M. Residual charge effect traffic sensor
US6130627A (en) * 1996-11-07 2000-10-10 Tyburski; Robert M. Residual charge effect sensor
EP1444861A4 (en) * 2001-10-09 2018-02-28 Frank Joseph Pompei Ultrasonic transducer for parametric array
US20060267962A1 (en) * 2004-02-02 2006-11-30 E.G.O. Elektro-Geraetebau Gmbh Operating device with an operating field and a sensor element for an electrical appliance and method for operating the operating device
US7786400B2 (en) * 2004-02-02 2010-08-31 E.G.O. Elektro-Geraetebau Gmbh Operating device with an operating field and a sensor element for an electrical appliance and method for operating the operating device
WO2006003249A2 (en) * 2004-07-07 2006-01-12 Emfit Oy Electrical coupling of an electromechanical control unit
WO2006003249A3 (en) * 2004-07-07 2006-04-13 Emfit Oy Electrical coupling of an electromechanical control unit
WO2015007948A1 (en) * 2013-07-18 2015-01-22 Nokia Corporation Apparatuses, methods and computer programs for expanding the use of touch-sensitive input apparatus

Also Published As

Publication number Publication date
CA1009764A (en) 1977-05-03
DE2164202C3 (de) 1974-05-09
DE2164202B2 (de) 1973-10-18
DE2164202A1 (de) 1972-07-13
NL7117891A (xx) 1972-06-30
ES398773A1 (es) 1974-08-16
SE377974B (xx) 1975-08-04
NL159837B (nl) 1979-03-15
FR2120902A5 (xx) 1972-08-18
JPS5436311B1 (xx) 1979-11-08
GB1380709A (en) 1975-01-15
JPS4713585A (xx) 1972-07-13
IT943354B (it) 1973-04-02
BE777202A (fr) 1972-04-17

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