Abstract: A gas sensor and a method for detecting a small amount of a gas such as CO contained in air entering a space between electrodes ionized by a radiation source. At least one radiation source is provided for ionizing at least a part of the space between the electrodes disposed so as to oppose each other and a radio d/x of a distance d cm between the electrodes to a field strength x V/cm of the ionized space is set to be 0.4 or more so as to obtain a change in the ionic current sufficient to realize gas sensing based on the formation of cluster ions within the ionized space.

Abstract: A small volume electron capture detector has a cylindrical cell 120 inside which there is provided a generally funnel-shaped insert structure 130 having a cup-shaped section and a cylindrical section. The rims of the cup-shaped section nearly touch the inner walls of the cell 120 so as to separate the active volume from the areas at the top corners of the cell 120 which are not actively swept by the carrier gas, thus reducing the tailing of chromatographic peaks.

Abstract: In a method and apparatus for determining the fuel of a fire, an ionization detector is positioned to detect the ionization level in the fire gases. The natural logarithm of the ratio of the ambient ionization current when there is no fire to the change in ionization current from the ambient level is multiplied times a second characteristic, which may be the optical density, the change in carbon monoxide concentration from ambient, or the change in carbon dioxide concentration from ambient. The resulting product of this multiplication will be a value indicating the fuel being consumed in the fire. A chart recorder is connected to record the product of the multiplication.

Abstract: An electron capture detector for use with a capillary column is provided with a sample inlet comprising a tubular anode through which sample molecules and a make-up gas are introduced into the detector cell. The tubular anode has side ports for producing a plug-like flow inside the cell. The inner surface of the anode is protected by an insulating tube so that the capillary column can be extended to a point beyond the side ports without the fear of its electrical contact with the anode. This allows the sample molecules to flow nearly entirely in the center section of the cell. The peripheral regions of the cell where a radioactive foil is disposed is swept nearly entirely by the make-up gas entering the cell through the side ports. This has the effects of reducing sample dilution by the make-up gas and sample loss due to contact with the detector walls.

Abstract: In a smoke detector of the ionization type having inner, auxiliary and outer electrodes providing inner and outer ionization chambers disposed one within the other, the electrodes and the associated circuitry are mounted on one side of a printed circuit board, the outer electrode conforming to the configuration and dimensions of the circuit board so as to define a box-like enclosure.

Abstract: An outer electrode for a combustion products detector comprising a cylindrical body including a plurality of first slats alternating with a plurality of second slats, the first slats being segments of a first surface of revolution, the second slats being skewed from a second surface of revolution having a different diameter from the first surface of revolution.

Abstract: An ionization detector unit for use in a smoke detector includes a housing wall enclosing an ionization chamber, the wall having openings for passage of air through the chamber, the frontal surface of the wall that is exposed to an oncoming air flow from a given direction being inclined relative to an intersecting second surface exposed to the flow. The frontal surface is shaped and positioned to deflect the air flow generally toward the second surface, and the second surface is shaped and positioned to deflect the air flow generally toward the frontal surface, the shape and position of the surfaces cooperatively arranged to cause the deflected air flows to converge and form a region of air in the vicinity of the intersection of the surfaces that is at higher pressure and slower velocity than the oncoming air flow.

Abstract: A device employing ionization principles for fire detection disclosing a configuration which allows compensation for adverse effects due to the flow of the gas through the device or due to the accumulation of dust and dirt therein. The detecting device includes two ionization chambers, each having a first member, such as a cylindrically shaped cup, having first and second conductive surface portions. Each chamber also includes a second member, such as a circular, electrode disc having two conductive surface portions. There is disposed in each chamber a radioactive source for ionizing the gas in the volumes intervening between respective pairs of surfaces. The area dimensions of the respective pairs of surfaces, the intervening volumes and the distances there between, and the relative orientation of the respective pairs are calculated and placed such that the ionization currents flowing between pairs of conductive surfaces are substantially equal and orthogonal to each other.

Abstract: An ionization smoke detector is disclosed in which an electric field is established in an ionization chamber which includes an outer cup-shaped electrode defining the chamber and having side wall apertures for permitting airflow therethrough and a circular inner electrode within the chamber. A radiation source is arranged to produce bipolar and unipolar regions in the chamber. A cylindrical control screen coaxial with the outer electrode and spaced therefrom is electrically connected to and supported by the inner electrode in the chamber.

Abstract: A portable, battery powered smoke detector in which the operative components are compactly and efficiently arranged in such a manner that they may be housed in a pocket-sized casing approximating the shape and size of a cigarette package. A further embodiment shows an efficiently organized arrangement of the smoke detector components in a telephone set.

Abstract: An ionization detector of the type having a housing with electrodes and a radiation source for causing ion current flow between the electrodes, collector means for detecting, by a change in voltage, a drop in ion current flow, and means responsive to a predetermined change in collector voltage to provide an output signal, in which a test electrode is provided in the housing and means is provided for applying to the test electrode a predetermined voltage of a value that causes said predetermined change in voltage at the collector, whereby said output signal is provided when said predetermined voltage is applied to the test electrode if said detector is operating satisfactorily.

Abstract: An ionization type smoke detector (10) includes a chamber having a measuring electrode (12), the voltage on the measuring electrode being a function of the concentration of smoke in the chamber, and further includes a comparison device (A3) for comparing the voltage measured on electrode (12) at two different times, and an output device (K) for producing an output signal if the voltages differ by a predetermined value.

Abstract: An ion mobility detector has dual drift regions respectively on either side of a centrally located reaction region and respectively separated therefrom by dual shutter grids. Each drift region terminates in a Faraday cup. An ion accelerating electrical field gradient is provided between the Faraday cups so that negative ions are drawn into one drift region and positively charged ions are drawn into the other drift region.

Abstract: An ionization smoke detector having a sensing chamber and including: a screen or mesh electrode enclosing and forming the outer limits of said sensing chamber, while fully exposing said sensing chamber to the ambient atmosphere; a baffle means covering said electrode and in close proximity thereto, said baffle means having a plurality of slit-like openings spaced around the periphery thereof for permitting the transfer of ambient atmosphere to said sensing chamber; said openings of said baffle means constituting deflectors oriented to deflect any air currents directed normal to the surface of said baffle means so the air currents will enter said sensing chamber at an angle other than said normal angle.

Abstract: A single chamber ionization-type fire detector. The ionization current is directly amplified to provide a usable analogue signal by means of an operational amplifier which has a minimal effect in the ionization current. The operational amplifier is simultaneously employed to maintain a constant potential difference in the chamber so that the ionization current is not subjected to a fluctuating voltage. The amplified analogue signal drives a recorder and through analysis of the recorder output genuine fire alarm conditions can be distinguished from false alarm conditions.

Abstract: An ionization smoke detector device including means for insuring that adjustment can be made in the triggering potential for the alarm device so that should circumstances change, an operator can make a simple adjustment to take into account the changed circumstances. This means comprises a programmable Zener diode which is connected to a voltage dividing resistance network at the output of a field effect transistor, the other end of the Zener diode being connected to the input of a silicon controlled rectifier device which functions to trigger the alarm.Another primary feature of the present invention is the provision of a means for testing the operation of the system in such a way that all of the elements of the system will be tested rather than merely some of them.

Abstract: An ionization type smoke sensing device includes a printed board. An inner electrode made of heat-resistant metal is attached to the printed board and a radioactive source is fixed to the inner electrode. An outer electrode in the form of a bottomed cylinder made of heat-resistant metal and adapted to cover the inner electrode extends through the printed board and is integrally joined to a protective lid member made of heat-resistant metal at the back of the printed board. Therefore, the outer electrode and the lid member cooperate with each other to define an ionization chamber. The outer electrode is formed with smoke inlet ports for introducing smoke into the ionization chamber. The electric circuit serves to give pulse signals of a relatively high voltage to the outer electrode and to detect the presence of smoke on the basis of the amount of a current flowing through the inner electrode.

Abstract: The detector comprises a first electrode defined by a bolt mounted on an annular insulator which in turn is mounted on a printed circuit board and a second electrode defined by a cup shaped member which is aligned with the bolt and positioned with the interior thereof facing and being spaced from the bolt. A source of radiation is mounted on the head of the bolt and a third electrode is spaced outwardly from and laterally to one side of the head of the bolt. A box-shaped electrostatic shield is fixed to the printed circuit board and has an opening in which is positioned the cup shaped member. The shield serves to enclose the space between the rim of the cup shaped member and the printed circuit board. An annular insulator is mounted on and about the bolt.

Abstract: In an alarm installation containing a central evaluation unit and alarm devices arranged remotely therefrom, the transmission of energy from a radiation source and the reporting back of the signal occurs exclusively according to optical principles by means of radiation conducting elements, so-called light guides or conductors, by means of which the alarm devices are connected with the evaluation device. The alarm devices contain a preferably high-ohm sensor element, for instance a smoke-sensitive ionization chamber, whose operating voltage is infed by means of a solar cell which is irradiated by a light guide and whose output signal is fed back to the evaluation device by means of a high-ohm electrical transducer and a light guide. Such type alarm installation preferably is used for fire detection purposes, for gas, smoke temperature detection or intrusion protection, and is particularly suitable for use in an explosion-endangered environment or one subjected to electrical disturbances.

Abstract: An ionization smoke detector containing at least one ionization chamber operated at an extra low voltage or potential. The ionization chamber contains a sensor employing a measuring electrode and a counter electrode. Ambient air has practically free access to the ionization chamber and there are provided one or more radioactive sources for generating ions, a supply voltage source and an electrical circuit for triggering an alarm. The smoke detector possesses increased operational reliability since circuit elements are provided which enable signal reporting to a central station by means of a low-voltage of about 200 volts, however the sensor is operated at an extra low voltage.

Abstract: An improved drift tube wherein the high voltage electric field is generated as a function of atmospheric pressure. Such variation of the electric field provides good compensation for the effects produced by changes in atmospheric pressure. As a result, the identification of a particular compound at different altitudes is greatly simplified.

Abstract: A smoke sensing detector for use with an indicating device comprises a chamber adapted to allow smoke to pass therethrough, an inner electrode carrying a radioactive source, a collector electrode having one or more holes and mounted on the inner electrode by insulating pillars, and an outer electrode. The collector and outer electrodes define a first ionization region, and the collector and inner electrodes define a second or reference ionizaton region which is comparatively little affected by the passage of smoke. Mounting the collector electrode on the inner electrode reduces costs, is easy and ensures that, in the event of insulation failure, the device is fail safe.

Abstract: The invention relates to smoke detectors of the kind comprising first and second electrodes defining an ionization chamber permitting entry of smoke, said ionization chamber being optionally divided into two regions by a collector electrode, a radioactive source to ionize gas in the ionization chamber and a potential difference applied across the first and second electrodes to cause an ion current to flow, which current is affected by entry of smoke, and provides an auxiliary electrode positioned in the ionization chamber, and means to maintain or create a potential difference between the first electrode and the auxiliary electrode. The auxiliary electrode may be used for testing or for adjustment of sensitivity.

Abstract: A smoke sensing detector of the dual ionisation region type, including an inner electrode, an outer electrode, and a collector electrode mounted on the inner electrode by means of pillers of insulating material, a first ionisation region being formed by the outer electrode and the collector electrode, and a second or reference ionisation region being formed by the inner electrode and the collector electrode, wherein the collector electrode supports or incorporates a nickel-63 radioactive source emitting radiation into both ionisation regions.

Abstract: A combustion detection apparatus and method is provided for generating an alarm output when either a first alarm condition or a second alarm condition is present. A first alarm output is generated when a first predetermined concentration of combustion products is continuously present in a region being monitored for a preestablished period of time. A second alarm output is immediately generated when a second predetermined concentration of combustion products is present in the region being monitored. The second predetermined concentration of combustion products represents a relatively greater concentration of combustion products than the first predetermined concentration.

Abstract: A technique for calibrating an ionization detector by simulating the presence of particles of combustion. In one embodiment a test probe is employed extending into the chamber. The probe may be partially conductive and partially non-conductive and be either rotatable or able to be withdrawn or partially withdrawn to vary ionization current. In another embodiment the source may be moveable to alter the ionization current. In still another embodiment there is provided the temporary distortion of one electrode to change the geometry of the chamber to thereby effect ionization.

Abstract: Condensation of water vapor on a radiation source in a fire detector is prevented by heating the source using the Joule effect. The heat is provided by a resistor embedded in the ceramic support for the source.

Abstract: A fire alarm having in a single unit a battery and a fire detecting section energized by the battery to detect abnormal environmental conditions such as heat and smoke to provide an output signal. A voltage decrement detecting section detects a voltage decrement of the battery to provide an output signal. A warning unit such as a buzzer is coupled to a switching circuit for operating the warning unit upon reception of the output signal from either the fire detecting section or the voltage decrement detecting section through an input terminal thereof. To reduce power consumption, the system uses a multivibrator having C-MOS IC, inverters.

Abstract: A combustion products detection apparatus and method are provided. The apparatus is powered by an energy source which provides a relatively low DC output voltage. This DC voltage is multiplied by a voltage multiplier circuit in conjunction with a first oscillator having an output of a first predetermined frequency. The output voltage of the voltage multiplier circuit is applied to a combustion products sensor circuit. Upon detection of a predetermined concentration of combustion products in the region being monitored by the sensor circuit, a second oscillator is enabled. The second oscillator has an output of a second predetermined frequency which is a greater frequency than the first predetermined frequency. The second predetermined frequency output controls the voltage multiplier circuit when the predetermined concentration of combustion products is present.

Abstract: An ionization particle detector for indicating the presence of charged particles in a gas includes a single ionization chamber having two defined regions of electrical field intensity. The first region is of small geometric volume and high electric field intensity while the second region is of large geometric volume and low electric field intensity. The radioactive source for generating the ions is located near one electrode while the second electrode forming the walls of the chamber are located such that the walls are incident near the Bragg ionization peak of the detector. A probe is positioned between the two regions for detecting the maximum electric field change when particles enter the chamber.

Abstract: A fire detector comprising a socket and a detector head with an electric circuit therein. The socket is provided with couplings for voluntarily defining the structure of an engaging portion thereof to designate a detector head to be coupled and each engaging portion of the detector heads have a specific structure to engage with the engaging portion defined by the couplings. Hence, no detector head other than the designated detector head can be coupled to the socket plate.

Abstract: An ionization smoke detector having two ionization chambers, one completely open to the ambient atmosphere and the other, a reference chamber, in communication with the atmosphere only through a breather tube having a defined length to diameter ratio. The detector employs a piezoelectric horn mounted on a cylindrical tube-like structure and attached to a printed circuit board containing one or more holes opposite the horn element so as to form a resonant chamber. The invention further contemplates a test switch which can be used to determine whether the battery is charged and the circuits are functioning.

Abstract: The detector uses a single radioactive source, such as a beta ionization source, with a multiple chamber construction. The source is positionable relative to the center or node electrode to provide simple adjustment of ionization in each chamber of say a dual chamber detector. Adjustment may be achieved without altering the geometric volume of the chambers or electrode spacing, but instead by altering the ratio of the source area protruding into each chamber. In one embodiment the center or node electrode is fixed and the source is adjustable in a direction normal to the electrode or by tilting relative to the electrode. In another embodiment the source is fixed and the electrode is adjustable relative to the position of the source. The principles may also be embodied in a three-chamber detector.

Abstract: A circuit for reducing or eliminating the sensitivity of alarm circuitry to false alarms caused by noise occurring synchronously with a 60 Hz line voltage. The 60 Hz line signal is applied to a variable-threshold circuit which produces a 60 Hz clock signal. The clock signal produced by the variable-threshold circuit may be selected to occur at different points during a cycle of the 60 Hz line signal. In response to successive alarm signals, the clock signal produced by the variable-threshold circuit occurs with different phasing relationships to the 60 Hz line signal. Before an alarm indication is made, an alarm signal must be provided by the smoke sensor in response to a plurality of successive samples.

Abstract: A detecting circuit is responsive to the change in a physical parameter indicative of a fire such as smoke, heat, flame or the like, and a comparator circuit connected to the detecting circuit produces detection pulses in synchronism with an oscillator circuit when the change in the physical parameter exceeds a predetermined amount. A counter circuit counts the detection pulses and produces an output which triggers a switching circuit when a predetermined number of consecutive detection pulses are counted. When triggered, the switching circuit transmits an alarm signal to an alarm receiving panel. Connected between the counter circuit and the switching circuit is a monostable multivibrator having a time constant which is equal to or smaller than the supply voltage rise time constant of the counter circuit so as to prevent the trigger signal from being applied to the switching circuit during the transition period immediately following the connection of the power source.

Abstract: This electrode assembly includes two relatively large-diameter, parallel conductive discs spaced apart by an annular insulator which has peripheral flanges respectively encompassing the perimeters of the discs. The assembly is adapted to be disposed in an ionization chamber formed by a printed circuit board and a conductive cup mounted thereon. One of the discs has conductive mounting legs adapted to be snap-fitted into complementary openings in the circuit board for spacing the disc from the board a distance sufficient to permit the mounting of associated electronic components therebetween. Both discs have pronged attachment apertures adapted for one-way press-fitting engagement with corresponding attachment posts on the insulating body, one disc having a central aperture for mounting an associated radioactive source thereon. The other disc cooperates with the one disc to define a reference zone therebetween and cooperates with the metal cup to define a sampling zone of the ionization chamber.

Abstract: A smoke detector is battery operated and may employ an ionization chamber and/or an infrared detector. When the alarm circuit is actuated due to the presence of smoke levels above a predetermined value being sensed by the detector, the alarm is actuated and each of the built in lights is illuminated. An auxilliary light energizeable by said detector is adapted to disengage one of said lights electrically and to be energized at the same time the other of said lights is energized.

Abstract: In a smoke detector of the type wherein an alarm signal is generated to activate an audible indicator and an oscillator circuit drives a pulsating visual indication of standby readiness, the oscillation frequency increases between its standby and alarm modes. In addition, duty cycle means controls the operative period of the alarm indicator during each cycle of the increased frequency. The smoke detector includes a relaxation oscillator where the oscillation frequency is proportional to the charge rate of a capacitor. Independent current sources are connected through separate switches to change the charge rate of the capacitor and thus the oscillation frequency. Each switch is controlled by signals from a separate detector of a condition which requires that the oscillation frequency be changed, for example, the presence of smoke.

Abstract: A battery-powered fire alarm including a smoke detector circuit, a controllable horn circuit and a battery monitoring circuit. The smoke detector employs a pair of complementary field-effect transistor switches with gates respectively connected to an ionization chamber and a potentiometer of a Wheatstone bridge circuit connected across the battery. The field-effect transistors are biased off to minimize standby power consumption and are connected such that the threshold voltages thereof are offsetting to minimize supply voltage sensitivity of the detector. When the voltage from the ionization chamber assumes a value approximately equal to a preselected alarm voltage at the potentiometer, both field-effect transistors turn on to energize an alarm circuit to sound an alarm. Hysteresis circuitry is provided to ensure that the complementary switches, once turned on, will not turn off and thereby terminate the alarm until after the alarm condition has terminated.

Abstract: An ionization fire-signal device is provided which is compact in construction so that it has a small axial height. The housing for the device includes an axial extending outer wall and a transversely extending front wall to form a cup shaped housing. An insulator, including an axially extending circular wall which forms an enclosure, is positioned inside the housing and cooperates with the housing to form a measuring chamber. The axial dimension of the circular insulator wall and outer housing wall are approximately equal. In addition, a reference chamber is formed between the circular wall of the insulator and the outer wall of the housing such that the reference chamber is arranged transversely adjacent to the measuring chamber. A radiation source for ionizing the measuring chamber and reference chamber is also provided.

Abstract: Method and apparatus for detecting the presence of very small concentrations of certain vapors and gases in air or other gaseous backgrounds. A gas sample is ionized by a source of ionizing radiation. The ionized gas is then directed through a first drift region where the ions are subjected to a drift potential. Electrical biased grid means are provided to allow only heavier ions of lower mobility to pass through the first drift region into a second drift region, where electrical shutter means are provided to allow discrete packets of ions to pass and to drift at speeds depending upon their mobilities and be detected. In an alternate embodiment, the first draft region is positioned downstream from the second drift region.

Abstract: An ionization type smoke detector includes an element for giving a visible indication of operativeness of the system together with a component responsive thereto for representing impending failure of the power source. A housing for the system includes a battery-containing well that includes a channel permitting finger-access to the batteries. A pushbutton is located in a wall of the housing. An electrically-conductive probe is positioned within an ionization chamber and is associated with the pushbutton for addressing the probe in a manner that creates a simulation of the existence of combustion. In response to a signal from the ionization chamber, digital processing is employed in order to enable alarm indication as appropriate as well as to monitor continued capability of the battery power source. Special circuitry cooperates advantageously with those features as well as in interrelating the different features so as to minimize complexity.

Abstract: An alarm device for detecting smoke, fire or the like includes a reference and measurement chamber for comparing the character of the ambient atmosphere with a volume of reference gas, and a radioactive source for ionizing the contents of each of the chambers. Electrodes communicating with each of the chambers measures an electric field within each of the latter indicative of the degree of ionization of the contents thereof. An electronic circuit senses the relative difference of the signals produced by the electrodes associated with each of the chambers and activates an alarm when a signal of predetermined magnitude is sensed indicating the presence of smoke or the like in the area of the detector.

Abstract: In an ion type smoke sensor including a smoke sensor having an internal electrode, an intermediate electrode and an external electrode, and a field effect transistor having a control input terminal connected to the intermediate electrode, a first output terminal connected to the internal electrode and a second output terminal connected to the external electrode, an ion type smoke sensor of this invention comprises an oscillator circuit for generating an oscillating output having a predetermined oscillating frequency; a reference level source for intermittently producing an output signal with a predetermined reference level in response to the oscillating output from the oscillator circuit; and a comparing circuit for comparing a sensing output between the first and second output terminals of the field effect transistor with the reference level from the reference level source to produce a fire sensing signal in accordance with the result of the comparison.

Abstract: An improved fire detector has both ionization chamber and photoelectric type products of combustion sensing devices, both of which must detect combustion for an alarm to be generated. The sensing devices are each adjusted to a quiescent sensitivity, but upon combustion being detected by one of the devices the sensitivity of the other device is automatically increased. In this manner, the detector operates very reliably to generate an alarm in the very early stages of a fire irrespective of whether the combustion process generates primarily visible or generally invisible type products of combustion, yet spurious generation of false alarm is minimized.

Abstract: A fire alarm system comprises a central control station feeding through a plurality of parallel supply lines a direct current voltage to a corresponding plurality of remote alarm stations. Each station has a fire sensor including a reference ionization chamber and a measuring ionization chamber, both chambers being connected in series between the two supply lines and having a common intermediate electrode. A field effect transistor has a gate electrode connected to the intermediate electrode of the ionization chambers and a source drain conducting channel the conductivity of which is controlled by the gate electrode. The input resistance and the input capacitance of the field effect transistor is connected parallel to the reference ionization chamber and defines therewith a first relatively short time constant of about two seconds.

Abstract: An ionizing type smoke detector device has an output voltage which is compared with a reference voltage and upon the output dropping below the reference, a horn is energized. The reference voltage is normally quite low to reduce the number of false alarms and thus the smoke detector is relatively insensitive to smoldering fires which may require a high sensitivity of the smoke detector device. A timer means periodically modifies the reference voltage to a high value for a short period of time to make the smoke detector more responsive to smoldering fires and yet with the higher sensitivity for the short period of time the number of false alarms are kept at a minimum. Additionally a counter circuit is provided for counting the outputs of the smoke detector over three timing periods and if an output exists for three consecutive periods, an output to the horn is provided.

Abstract: An ionization fire-signal device with an ionized measuring chamber, a reference element connected in series with the reference chamber, an amplifier stage controlled by the electric potential of the connection point of the measuring chamber and the reference element and comprising a field effect transistor, and a signal circuit controlled by the amplifier stage and comprising another transistor. A bistable behavior of the ionization fire-signal device is achieved by a positive signal feedback from the signal circuit to the substrate of the field effect transistor.

Abstract: A high output smoke and heat detector alarm system comprises a high output audible alarm means which includes a piezoelectric transducer and a voltage doubling means in combination with an improved smoke and heat detector which includes a low voltage power supply source, an ambient temperature detecting means, at least one ionization sensing chamber, a voltage amplitude comparing means, and a low voltage sensing means.

Abstract: An ionization chamber for use in determining the spatial distribution of x-ray photons in tomography systems comprises a plurality of substantially parallel, planar anodes separated by parallel, planar cathodes and enclosed in a gas of high atomic weight at a pressure from approximately 10 atmospheres to approximately 50 atmospheres. The cathode and anode structures comprise metals which are substantially opaque to x-ray radiation and thereby tend to reduce the resolution limiting effects of x-ray fluoresence in the gas.In another embodiment of the invention the anodes comprise parallel conductive bars disposed between two planar cathodes.Guard rings eliminate surface leakage currents between adjacent electrodes.