GB2534343A

GB2534343A - Ozone generator plate

Info

Publication number: GB2534343A
Application number: GB1420022.4A
Authority: GB
Inventors: Gerald Charles Bostock John
Original assignee: Ozone Industries Ltd
Current assignee: Ozone Industries Ltd
Priority date: 2014-11-11
Filing date: 2014-11-11
Publication date: 2016-07-27
Also published as: GB201420022D0

Abstract

EMI suppression in a plate-based ozone generator (23) is achieved by physically separating (d, 34) a contact pad (30, 32) and an electrode (24, 26) on both upper and lower surfaces of a ceramic or dielectric substrate (12) and then providing a bridging impedance (40) therebetween. Dimensioning of the separation gap (34) maintains a minimum creepage distance for the voltage appearing across the bridging impedance. The bridging impedance (40), as shown in FIG. 2, may contain discrete distributed components or printed tracks in the form of one or more, or a combination of, resistors,capacitors or inductors. Attachment of thick-film based resistors to stainless steel electrodes of the plate-based ozone generator (23) may, optionally, make use of anisotropic adhesives, rather than solders.

Description

OZONE GENERATOR PLATE

Field of the Invention

This invention relates, in general, to ozone generators and is particularly, but not exclusively, applicable to the suppression of electromagnetic interference ("EMI") in ozone generator cells making use of corona discharge techniques.

Summary of the Prior Art

Ozone is an allotrope of oxygen comprising a molecule of three oxygen atoms. It is a strong oxidant that is unstable. In the later respect, decay of an ozone molecule typically occurs within about 30 minutes.

Since ozone spontaneously oxidizes many compounds, it is particularly useful as a disinfectant or a deodorant. Small-scale ozone generators can therefore be selectively employed and discontinuously activated in clinical cleanrooms, food preparation areas, washrooms and even within a home environment to bring about sterilization on a timed or ad hoc basis. Ozone has, in these respects, been used for more than 20 years.

The reactivity of ozone does, however, mean that circuit components must be selected with care so as to retard or suppress rates of erosion. Circuit component and particularly electrical contacts in an ozone-rich environment are therefore often made from stainless steel or titanium (or other inert materials), with these components often also changed-out at regular service intervals.

US 6,284,204 describes an ozone generating cell that includes at least two substantially planar electrodes held at a high potential difference and separated by a dielectric sheet or ceramic substrate, each electrode producing a corona (or coronal) discharge to convert a proportion of oxygen present in the surrounding atmosphere to ozone. The electrodes, when considered in plan, are generally offset so as to maximize the so-called fringe field through the air and to limit direct capacitance arising from a direct overlap of the electrodes and a direct path through the dielectric sheet. Indeed, this design has been found to be extremely attractive from the perspective of unit size and, more especially, because active edges of adjacent but vertically displaced electrodes operate to increase the potential gradient of the electric field. The ozone generating efficiency of this form of fringe-field device is therefore a function of its ability to increase the potential gradient through the air in vicinity of the edge, such that increased levels of electrical stress are induced and partial electrical breakdown/ionization of air molecules occurs.

More particularly, tightly packed lines of electric force that are associated with the fringing field and which emanate from the edges of the electrodes induce "spot charges" on the surfaces of the substrate immediately adjacent each edge. At voltage polarity transition (occurring at the switching frequency of the high voltage power supply), these spot charges effectively double the applied voltage seen across the substrate with the net effect being that ozone is more efficiently created from the higher temperatures and more concentrated field lines that produce an improved coronal discharge. As will be appreciated, electrical stress in the coronal discharge requires an electric field strength of about 3x106 Vm-I. With such high electric fields, ceramic or dielectric substrates are also selected so as to avoid substrate breakdown at peak voltages applied between plate electrodes.

GB 2318490 shows a pair of electrodes either side of a dielectric, one electrode being in the form of a sheet, whilst the opposing electrode features one or more extending thin flat wires. Whilst effective in producing ozone, the thin flat wires are fragile and difficult to apply. They may be applied as a conductive ink, though this process is inconvenient, and the resulting arrangement is still delicate.

Other ways to produce ozone are also known. These include a generating cell having a glass tube provided with an inner coating of aluminum. Concentrically surrounding the glass tube, but separated somewhat by spacers, is a stainless steel tube. The aluminum coating is connected to a high voltage supply while the steel tube is earthed. Oxygen-containing gas is passed between the tubes, with some of the oxygen molecules converted to ozone by the high voltage discharge between the electrodes. However, the high quantities of heat generated by the discharge makes the glass prone to failure or the generator subject to overheating.

With respect to, especially, home environments that contain electronic components (such as computers, smartphones, TVs and the like), the Applicant has recognized that a significant source of EMI emissions arises from the corona discharge in a plate-based ozone generator. The corona discharge comprises a very large number of random micro-discharges that each constitutes a displacement current (i.e. moving charges/electrons). The micro discharge currents exhibit a very high rate of change of current and therefore occupy a very wide bandwidth, with the result that ozone plate generators can generate energy over a very wide band of frequencies. Indeed, such a wideband noise source can excite the conductors used to connect the high voltage causing EM radiation particularly at frequencies at which circuit board conductors constitute an effective antenna. EMI has the effect of interrupting, obstructing or otherwise degrading or limiting the effective performance of affected electronic circuits in, for example, consumer equipment. In this respect, EMI may adversely affect data transmission integrity that makes use of low-power RF resources. such as those based on BluetoothThl techniques.

It would therefore be desirable to mitigate the effects of EMI (also known as radio frequency interference or "RFI") from ozone generators, in general.

Summary of the Invention

According to a first aspect of the invention there is provided an ozone generator plate including: a ceramic or dielectric substrate having upper and lower surfaces; a first electrode positioned on the upper surface and separated from a first contact pad by a separation gap; a second electrode positioned on the lower surface and separated from a second contact pad by a separation gap; a first bridging impedance providing a conductive path between the first electrode and its contact pad; and a second bridging impedance providing a conductive path between the second electrode and its contact pad; wherein the first and second bridging impedances are arranged to suppress EMI on either a selective frequency or wideband basis.

In a preferred embodiment, the first and second electrodes are generally offset and not overlapping, the arrangement thereby promoting, under applied potential, corona discharge from fringe field effects from edges of the electrodes to the surfaces of the substrate.

In a preferred embodiment, the bridging impedances are realized by film resistors, the film resistor electrically coupled at its ends to both the contact pad and electrode by an anisotropic adhesive.

In a second aspect of the invention there is provided an ozone generator including a power supply coupled across electrodes arranged, in use and under applied voltage potential, to produce a partial breakdown of air, the ozone generator including: a contact pad spaced apart from each electrode; and an EMI suppressor containing at least one circuit element arranged to produce a bridging impedance between each contact pad and its respective electrode (24, 26), the bridging impedance configured to provide high impedance to frequencies generated by action of corona discharge and low impedance to driving voltages fed to the electrodes by the power supply.

Advantageously, the preferred embodiments permit EMI suppression components to be placed closer to the source of EMI, thereby significantly improving their effectiveness of operation through better suppression of interference.

The present invention therefore provides a compact solution in which the components can, in a preferred embodiment, be contemporaneously formed during production of electrodes, connection pads and circuit board traces. Alternatively, the impedance (or more particularly any suitable reactive component) can be realized by a discrete distributed component placed and affixed to the ceramic or dielectric substrate.

Brief Description of the Drawings

Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which: FIG. 1 is an exploded view of an ozone generator of the prior art.

FIG. 2 is an orthographic projection showing a modified ozone generator incorporating the concepts of the present invention.

Detailed Description of a Preferred Embodiment

Turning to FIG. 1, an exploded view of a prior art ozone generator 10 is shown. The ozone generator comprises an insulative dielectric substrate 12, such as a ceramic or other material, having upper and lower faces on which is formed (or mounted) opposing orientated u-shaped electrodes 14, 16. Fingers 18, 20 of the u-shaped electrodes 14, 16 substantially interlock so that, under applied potential, fringe field effects are maximized along respective edges of the electrodes. As will be understood, a high voltage, alternating power supply 22 is coupled to the electrodes 14, 16 to produce a suitable coronal discharge. The exact shape and positioning of the electrodes may change (e.g. to include multiple parallel spines), but generally the edges between the upper and lower electrodes substantially align to maximize the potential gradient arising in the coronal discharge from about these edges.

With respect to FIG. 2, a design of the plate-based ozone generator 23 is not dissimilar to the arrangement shown in FIG. 1, although both an upper electrode 24 and a lower electrode 26 take a different (but exemplary) rectangular shape having a central void 28. Again, the electrodes are coupled to a thin ceramic plate 12 (or the like). In contrast with FIG. 1, physically distinct electrical contact pads 30, 32 are associated with each of the upper and lower electrodes 24, 26. The shape of the contact pads 30, 32 is not critical, although these are dimensioned (in a purely exemplary instance) to have a width corresponding to the upper and lower electrodes. The contact pads 30, 32 are preferably located at opposing ends (and opposite surfaces) of the ceramic substrate 12. The contacts pads 30, 32 are separated from their respective adjacent electrodes by a gap 34, which gap has a separation distance, d, maintains an adequate creepage distance. More particularly, the separation distance d is sufficient to avoid direct shorting between the respective contact pad 30, 32 and its electrode.

The upper and lower electrodes 24, 26 are made from a conductive material that has at least some resilience to ozone's corrosive effects. The upper and lower electrodes 24, 26 are preferably stainless steel, although other materials, such as titanium, can also be used (as will be understood).

An electrical conduit is established between each contact pad and its respective (substantially planar) electrode, which electrical conduit contains one or more EMI suppressors in the form of a reactive component, such as a bridging impedance 40 or an impedance network. The impedance (e.g. in the form of a filter network) can be realized by a discrete distributed component or as a circuit printed element. As will be understood, the term "distributed component" means that, with respect to a wave function through the component, not all points along the component are instantaneously at the same potential. All electrical energy to the electrodes (from the power supply, not shown) is therefore channeled and bridged from the contact pad to the substantially planar electrode through the impedance 40.

The impedance 40 is preferably realized by a single component, such as: i) an inductor; ii) a resistor; or iii) a capacitor (in the event that an earth point exists). As previously indicated, the impedance may alternatively comprise one or more circuit components realized by series elements, shunt elements or a combination of series and shunt elements. However, in all cases, the suppressor(s) provide high impedance to relevant EMI frequencies and suitably low impedance to the fundamental frequency of the power supply output. More particularly, the suppression components provide high impedance at the frequencies generated by the action of the coronal discharge, but provide low impedance to the driving voltage fed to the plate for the purpose of generating the corona discharge.

In the exemplary context of a single resistive element which may be a discrete device or a resistive ink printed or formed on the substrate 12, neglecting any parasitic effects within the resistor (i.e. its inherent shunt capacitance and series inductance), the resistor exhibits significant impedance at all frequencies, thereby providing substantial suppression across a wideband frequency spectrum. However, in another embodiment, the impedance(s) is/are tailored to suppress specific frequencies or frequency bands.

In a preferred embodiment, the EMI suppressor may include one or more polymeric thick film (PTF) resistors.

In an alternative approach to using solder, an impedance device can bridge the separation gap 34 and be attached to the contact pad and electrode through the use of an anisotropic adhesive, such as that described in EP-A-0562569. The adhesive has electrically conductive particles distributed therethrough for effecting the connection. The particles comprise hard, non-oxidizing crystallites (8) consisting of an electrically-conductive crystalline compound of an element of sub-group IV of the Periodic Table, together with nitrogen or carbon. The crystallites are distributed within the adhesive such that there is little or no physical contact between them and therefore the adhesive is non-conductive in a direction along the layer plane. In other words, the anisotropic adhesive permits conduction in the z-plane, but restricts connection in the x and y planes.

More particularly, a PFT resistor is assembled from a patch of polyester film having a conductive ink (resistive) track printed thereon. After drying, the patch is coated with a layer of anisotropic transfer adhesive, with this anisotropic adhesive then set to attach the ends of the ink track lo the electrode and contact pad, thereby providing a bridging impedance across the separation gap 34.

It is noted that the dimensioning of a resistive track to produce a desired impedance path requires consideration of a number of known factors, including: 1) The volume resistivity of the ink used to form the track once it is fully dried/cured; 2) The film thickness of the resistive track; 3) The width of the resistive track; and 4) The separation gap 34 between the contact pads and the electrode, as shown in FIG. 2.

The volume resistivity and the film thickness can be combined into one factor known as the sheet resistivity. In the case of the resistive ink, a preferred sheet resistivity is about 2 kil/per square for a film thickness of 12.5 micrometres (gm). Also, the effective width and length of the track can be combined into one factor known as the aspect ratio. Thus, as an example, to achieve a 10 kO. resistance (i.e. 5 squares) with a track width of 0.6 millimetres (mm), the separation gap would be dimensioned to be in the region of about 3 mm.

With respect to the formation of the EMI suppressor of the present invention, other embodiments contemplate that the impedance can be formed using printed circuit elements that make use of the geometry and arrangement of the electrodes 24, 26. For example, an inductor may be formed by a section of the electrode deliberately arranged so as to exhibit a significant inductance, e.g. in the form of a flat spiral.

In a similar vein, one particular embodiment may make use of a capacitor formed by means of overlapping areas of the electrodes 24, 26. In this particular respect, an area of an upper electrode 24 on one side of the ceramic substrate 12 would overlap a similar area of the lower electrode 26. As a result, enhanced by appropriate selection of the dielectric constant of the substrate 12, a significant capacitance could be provided and used.

While not wishing to be bound by theory, the applicant understands and has recognized that the efficiency of ozone production in a plate-based design (such as shown in FIGs. 1 and 2) that optimizes fringe field effects (and correspondingly reduces direct capacitance between plates) gives rise to increased EMI. Particularly, it is understood that such plate-based designs which produce tightly packed lines of electric force from the edges of the electrodes can greatly benefit from localized EMI suppression through the provision of a bridging impedance as hereinbefore described. Indeed, by making use of bridging impedance techniques between each electrode and its corresponding contact pad, plate based ozone generators can be operated at even higher voltages to produce even greater ozone production rates without causing disruptive EMI.

Indeed, because EMI suppression is generally improved by the techniques described herein and electrodes in ozone generators are replaced on a regular basis, the benefits acquired by this new design can be retrofitted into existing ozone generator devices to further reduce EMI at existing sites.

It will, of course, be appreciated that the above description has been given by way of example only and that modifications in detail may he made within the scope of the present invention. For example, whilst the preferred embodiment refers to the coronal discharge method involving layered but offset electrodes separated by a ceramic plate, the introduction of EMI suppressors (in the form of an impedance network or individual components) can be applied to other forms of ozone generators, including phosphor tube-based techniques where the wavelength of ultra-violet (uv) light can produce ozone when the emitted photon strikes an oxygen molecule.

The use of anisotropie adhesive to attach circuit components in an ozone generator is not considered as limited to merely the impedance of the suppressor. Application of anisotropic adhesive in an ozone generator can therefore be implemented independently of the EMI suppression technique described herein.

Claims

Claims 1. An ozone generator plate including: a ceramic or dielectric substrate having upper and lower surfaces; a first electrode positioned on the upper surface and separated from a first contact pad by a separation gap; a second electrode positioned on the lower surface and separated from a second contact pad by a separation gap; a first bridging impedance providing a conductive path between the first electrode and its contact pad; and a second bridging impedance providing a conductive path between the second electrode and its contact pad; wherein the first and second bridging impedances are arranged to suppress EMI on either a selective frequency or wideband basis.
2. The ozone generator according to claim 1, wherein the first and second electrodes generally offset and not overlapping. the arrangement thereby promoting, under applied potential, corona discharge from fringe field effects from edges of the electrodes to the surfaces of the substrate.
3. The ozone generator according to claim 1 or 2, wherein the bridging impedances provide high impedance to frequencies generated by action of coronal discharge and low impedance to driving voltage fed to the plate for the purpose of generating the corona discharge.
4. The ozone generator according to claim 1, 2 or 3, wherein the bridging impedances contain one or more electrical components selected from: discrete distributed reactive devices; film resistors; track-based inductors; and capacitors.
5. The ozone generator according to claim 1, 2 or 3, wherein a film resistor is coupled between the electrode (24, 26) and its respective contact pad (30, 32), the film resistor electrically coupled at its ends by an anisotropic adhesive.
6. The ozone generator according to claim 4, wherein a capacitor is formed by overlapping areas of the first and second electrodes (24, 26) and/or by overlapping areas of the first and second contact pads.
7. The ozone generator according to any preceding claim, wherein the bridging impedances are matched to suppress pre-selected frequencies in the RF spectrum.
8. The ozone generator according to any preceding claim, wherein the separation gap is about 3 millimetres.
9. An ozone generator including a power supply coupled across electrodes arranged, in use and under applied voltage potential, to produce a partial breakdown of air, the ozone generator including: a contact pad spaced apart from each electrode; and an EMI suppressor containing at least one circuit element arranged to produce a bridging impedance between each contact pad and its respective electrode (24, 26), the bridging impedance configured to provide high impedance to frequencies generated by action of corona discharge and low impedance to driving voltages fed to the electrodes by the power supply.
10. An ozone generator containing a circuit board and at least one discrete electrical component electrically coupled to a circuit board trace or contact pad of the circuit board with an anisotropic adhesive.
11. The ozone generator according to claim 10, wherein the anisotropic adhesive couples the discrete electrical component to a stainless steel surface.
12. An ozone generator substantially as hereinbefore described with reference to FIG. 2 of the accompanying drawings.