Patent Publication Number: US-9889677-B2

Title: Ion writing unit with rate control

Description:
BACKGROUND 
     Electronic paper (“e-paper”) is a display technology designed to recreate the appearance of ink on ordinary paper. Some examples of e-paper reflect light like ordinary paper and may be capable of displaying text and images. Some e-paper is implemented as a flexible, thin sheet, like paper. One familiar e-paper implementation includes e-readers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is block diagram schematically illustrating an ion writing unit for imaging passive e-paper, according to one example of the present disclosure. 
         FIG. 2  is block diagram schematically illustrating an ion writing unit with air flow control, according to one example of the present disclosure. 
         FIG. 3  is block diagram schematically illustrating an ion writing unit with heat control, according to one example of the present disclosure. 
         FIG. 4  is block diagram schematically illustrating an ion writing unit with flux control, according to one example of the present disclosure. 
         FIG. 5  is block diagram schematically illustrating an ion writing unit with multiple corrosion-control modalities, according to one example of the present disclosure. 
         FIG. 6  is a block diagram schematically illustrating an ion generator, according to one example of the present disclosure. 
         FIG. 7  is a diagram including a side sectional view schematically illustrating an ion writing unit, according to one example of the present disclosure. 
         FIG. 8  is a diagram including a side sectional view illustrating an addressable ion writing unit for imaging e-paper, according to one example of the present disclosure. 
         FIG. 9A  is a diagram illustrating the operation of an ion writing unit in the “on” state, according to one example of the present disclosure. 
         FIG. 9B  is a diagram illustrating the operation of an ion writing unit in the “off” state, according to one example of the present disclosure. 
         FIG. 10A  is a diagram including a sectional view of an electrode array taken along the line  10 A- 10 A in  FIG. 10B , according to one example of the present disclosure. 
         FIG. 10B  is a diagram including a plan view schematically illustrating individual electrodes with nozzles as formed in a first layer on a dielectric material layer, according to one example of the present disclosure. 
         FIG. 11A  is a diagram including a sectional view as taken along lines  11 A- 11 A in  FIG. 11B  and schematically illustrating an ion writing unit, according to one example of the present disclosure. 
         FIG. 11B  is a diagram including a side view schematically illustrating an ion writing unit, according to one example of the present disclosure. 
         FIG. 110  is a diagram including an end view schematically illustrating an ion writing unit, according to one example of the present disclosure. 
         FIG. 12A  is a diagram including sectional views schematically illustrating an ion writing unit including air flow control, according to one example of the present disclosure. 
         FIG. 12B  is a diagram including a partial sectional view of an ion writing unit with air flow control, according to one example of the present disclosure. 
         FIG. 12C  is a flow diagram schematically illustrating a method of manufacturing an ion writing unit including air flow control, according to one example of the present disclosure. 
         FIG. 12D  is a diagram schematically illustrating an ion writing unit with air flow control, according to one example of the present disclosure. 
         FIG. 13A  is a block diagram schematically illustrating an ion writing unit including a heat control mechanism, according to one example of the present disclosure. 
         FIG. 13B  is a diagram including a side sectional view schematically illustrating an ion writing unit including a heating element on an exterior of a housing, according to one example of the present disclosure. 
         FIG. 13C  is a diagram including a side sectional view schematically illustrating an ion writing unit including a heating element within a housing, according to one example of the present disclosure. 
         FIG. 14A  is a diagram including a side sectional view schematically illustrating an ion writing unit including a heating element on an electrode array external to a housing, according to one example of the present disclosure. 
         FIG. 14B  is a diagram including a sectional view of an electrode array including a heating element, as taken along the line  14 A- 14 A in  FIG. 14C , according to one example of the present disclosure. 
         FIG. 14C  is a diagram including a plan view schematically illustrating individual electrodes with nozzles as formed in a first layer on a dielectric material layer with a heating element extending across a portion of the individual electrodes, according to one example of the present disclosure. 
         FIG. 15A  is a diagram including a side sectional view schematically illustrating an ion writing unit including a heating element incorporated within an electrode array, according to one example of the present disclosure. 
         FIG. 15B  is a diagram including an enlarged, partial sectional view of  FIG. 15A , according to one example of the present disclosure. 
         FIG. 15C  is a diagram including a sectional view of an electrode array including a heating element forming a portion of one electrode layer, according to one example of the present disclosure. 
         FIG. 16  is a flow diagram schematically illustrating a method of manufacturing an ion writing unit including heat control, according to one example of the present disclosure. 
         FIG. 17  is a block diagram schematically illustrating a control portion for an image writing unit, according to one example of the present disclosure. 
         FIG. 18A  is a block diagram schematically illustrating a flux control manager including an ion generation control module, according to one example of the present disclosure. 
         FIG. 18B  is a block diagram schematically illustrating a flux control manager including an electrode nozzle control module, according to one example of the present disclosure. 
         FIG. 18C  is a diagram schematically illustrating patterns of electrode nozzles of an ion writing unit being operated in a first state or second state, according to one example of the present disclosure. 
         FIG. 19  is a flow chart diagram schematically illustrating a method of manufacturing an ion writing unit including flux control, according to one example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
     At least some examples of the present disclosure are directed to providing corrosion-resistance to an ion writing unit used in non-contact application of charges (e.g. ions) onto a spaced apart, passive e-paper media. In some examples, the ion writing unit includes a charge generator and an electrode array, with some examples including a corona wire acting as the charge generator. The electrode array includes nozzles extending through a dielectric material, wherein the nozzles are individually addressable to separately control charges from the charge generator. In one aspect, by controlling an on/off state of nozzles of the electrode array, the nozzles act as gates to block or enable passage of charges through the nozzles. 
     In general terms, in some examples, corrosion protection for the electrode array is implemented via at least one modality aimed at reducing or eliminating moisture and/or aimed at preventing migration of ions that carry the moisture. In particular, when a passive e-paper is electrically biased during (or just before, or just after) a writing operation via the ion writing unit, secondary ions are produced that have a charge opposite the primary, generated ions from the corona wire. These secondary ions carry available moisture as they migrate toward the exposed electrode array of the ion writing unit. Accordingly, in some examples of the present disclosure, corrosion protection is achieved via eliminating the moisture and/or preventing the secondary ions from migrating to the electrode array of the ion writing unit. By doing so, longevity of the electrode array and/or the corona wire is significantly increased. 
     In some examples, corrosion protection for an ion writing unit is provided via an air flow control mechanism, which provides air flow on an electrode array and/or within a chamber in which a charge generator (i.e. ion generator) is housed. In some examples, the air flow also minimizes dendritic growth on the ion generator, thereby contributing to its longevity and performance. 
     In some examples, corrosion protection for an ion writing unit is provided via a heat control mechanism, which provides heat to an electrode array and/or within a chamber in which the charge generator is housed. 
     In some examples, corrosion protection is provided via a flux control mechanism, which controls a flow rate of ions from the ion writing unit to ensure that at least a low flow rate of ions is being emitted to prevent migration of secondary ions toward/onto the electrode array. 
     In some examples, corrosion protection is implemented via some combination of air flow, heat, and/or flux control. 
     These examples, and additional examples, are described throughout the present disclosure and in association with at least  FIGS. 1-19 . 
       FIG. 1  is a block diagram schematically illustrating an ion writing unit  12  for causing image formation on passive e-paper  14 , according to one example of the present disclosure. As shown in  FIG. 1 , the ion writing unit  12  and passive e-paper  14  are capable of movement relative to each other during such image formation, as represented via directional arrow Y. In one aspect, the ion writing unit directs air-borne charges (e.g. charged ions) in a directed pattern onto an imaging surface of the passive e-paper, which responds by switching colored particles based on the location of the received charges on the imaging surface. In one aspect, the e-paper media is passive in the sense that it is re-writable and holds an image without being connected to an active power source during the writing process and/or after the writing is completed. In another aspect, the e-paper media lacks internal circuitry and does not have an internal power supply. 
     In at least some examples, the e-paper media includes a charge-responsive layer that includes components that switch colors when a field or charges are applied to it. In some examples, the e-paper includes the charge-responsive layer and a conductive layer that serves as a counter-electrode on one side of the e-paper. In some examples, the color-switching components within the charge-responsive layer include pigment/dye elements, which are contained in microcapsules present in a resin/polymer material. In some examples, an additional functional coating is included on top of the charge-responsive layer. 
     In some examples, the electrode array comprises a two-dimensional array of individually addressable nozzles to provide high speed directing of charges while the various nozzles are strategically patterned (e.g. location and spacing) to prevent unwanted charge deposition patterns on the imaging substrate (e.g. e-paper media) that would otherwise hamper quality imaging. Further details regarding these structures are described later in association with at least  FIGS. 7-9B . 
     At least some examples of the present disclosure are directed to reducing or eliminating corrosion on nozzles of the ion writing unit  12 .  FIGS. 2-5  provide an introduction to several modalities to reduce or eliminate such corrosion while  FIGS. 11A-19  provide greater details regarding such modalities. 
       FIG. 2  is block diagram schematically illustrating an ion writing unit including an air flow control mechanism, according to one example of the present disclosure. As shown in  FIG. 2 , ion writing assembly  20  includes an ion writing unit  21  and an air flow control mechanism  40 . The ion writing unit  21  includes a housing  22  containing and at least partially enclosing an ion generator  24 . An electrode array  30  is located at one exterior portion  26  of the housing  22 . The electrode array  30  includes an array of ion passage nozzles  32 , which are selectively activatable to be open or closed with open nozzles allowing the passage of ions therethrough and closed nozzles blocking the passage of ions, as further described later in association with at least  FIGS. 7-9B . The ion generator  24  is positioned within housing  22  to be spaced apart from electrode array  30  and is spaced apart from a wall defining housing  22 . 
     As further shown in  FIG. 2 , air flow control mechanism  40  includes at least one of a first air flow path  42  and a second air flow path  43 . In some examples, the first air flow path  42  directs air flow into an interior of housing  22  for passage at least near or by ion generator  24 . In some examples, the second air flow path  43  directs air flow across the nozzles  32  on an outer surface of electrode array  30 . In some examples, the air flow control mechanism  40  includes a treatment element to dry and/or filter the air, as further described later in association with at least  FIGS. 12A-12E . 
     In one aspect, the air flow produced via the air flow mechanism  40  reduces moisture within housing  22 , thereby minimizing corrosion of at least conductive elements within housing  22  and/or adjacent conductive elements, such as any exposed portions of electrode array  30  that face inwardly into the interior of housing  22 . 
     By reducing such potential corrosion, the air flow control mechanism  40  increases the longevity of the electrode array  30  and any related conductive elements, thereby prolonging the useful life of the ion writing assembly  20 . In addition, in examples in which the ion generator  24  includes a corona wire, air flow within housing  22  inhibits dendritic growth on the corona wire, thereby increasing its longevity and performance. Further details regarding at least some examples of an air flow control mechanism are described later in association with at least  FIGS. 12A-12E . 
       FIG. 3  is block diagram schematically illustrating an ion writing assembly  50  including a heat control mechanism  60 , according to one example of the present disclosure. In some examples, the ion writing assembly  50  comprises substantially the same features and attributes as the ion writing assembly  20  ( FIG. 2 ), except for including the heat control mechanism  60  instead of the air flow control mechanism  40  of  FIG. 2 . 
     As shown in  FIG. 3 , heat control mechanism  60  includes at least one of a first heating location  62  and a second heating location  64 . In some examples, the first heating location  62  causes heating of housing  22  as a whole or portions of housing  22 . In some examples, the first heating location  62  causes heating of other components within an interior of the housing  22 . Meanwhile, in some examples, the second heating location  64  causes heating of at least some portions of electrode array  30 . 
     Via heat produced at the first and/or second heating locations  62 ,  64 , the heat control mechanism  60  reduces moisture within housing  22 , thereby minimizing corrosion of at least conductive elements within housing  22  and/or adjacent conductive elements, such as any exposed portions of electrode array  30 . 
     By reducing such potential corrosion, the heat control mechanism  60  increases the longevity of the electrode array  30  and any related conductive elements, thereby prolonging the useful life of the ion writing assembly  50 . Further details regarding some examples of a heat control mechanism are described later in association with at least  FIGS. 13A-15C . 
       FIG. 4  is block diagram schematically illustrating an ion writing assembly  70  including a flux control mechanism  80 , according to one example of the present disclosure. In some examples, the ion writing assembly  70  comprises substantially the same features and attributes as the ion writing assembly  20  ( FIG. 2 ), except for including the flux control mechanism  80  instead of the air flow control mechanism  40  of  FIG. 2 . 
     In general terms, flux control mechanism  80  ensures a regular flow of ions from the ion writing unit  101  whenever a passive e-paper is electrically biased for forming images upon receiving ions from the ion writing unit  101 . The ions neutralize secondary ions (produced during the passive imaging process and having a charge opposite to the primary generated ions) that would otherwise tend to carry moisture toward and onto the electrode array  30 , thereby reducing or eliminating corrosion of the electrode array  30 . In one aspect, a normal writing process, which directs ions toward the passive e-paper, provides this type of corrosion protection. However, when an active imaging operation is not taking place, but the passive e-paper is still electrically biased for imaging, such corrosion can take place. In this situation, the flux control mechanism  80  directs ion writing assembly  70  to emit ions toward the passive e-paper at a rate high enough to neutralize migration of the “moisture-carrying” secondary ions toward electrode array  30  but with the rate low enough to avoid causing imaging of the passive e-paper. 
     As shown in  FIG. 4 , flux control mechanism  80  includes at least one of a first flux control  82  and a second flux control  84 . The first flux control  82  generates the desired maintenance flow rate of ions via controlling operational aspects of ion generator  24 . Meanwhile, the second flux control  84  generates the desired maintenance flow rate of ions via controlling operational aspects of electrode array  30 . In some examples, both first and second flux controls  82 ,  84  are engaged to provide corrosion protection. 
     Via the first and/or second flux controls  82 ,  84 , the flux control mechanism  80  prevents moisture from being carried to electrode array  30 , thereby minimizing corrosion of electrode array  30 , as well as any exposed conductive elements within housing  22 . 
     By reducing such potential corrosion, the flux control mechanism  80  increases the longevity of the electrode array  30  and any related conductive elements, thereby prolonging the useful life of the ion writing assembly  70 . Further details regarding some examples of a flux control mechanism are described later in association with at least  FIGS. 18A-19 . 
       FIG. 5  is block diagram schematically illustrating an ion writing assembly  100  including a combination  110  of corrosion-protection modalities, according to one example of the present disclosure. In some examples, the ion writing assembly  100  comprises substantially the same features and attributes as the ion writing assembly  20  ( FIG. 2 ), except for including more than one corrosion-protection modality selected from the group of the air flow control mechanism  40 , the heat control mechanism  60 , and the flux control mechanism  80 . 
     In some examples, an air flow path  42  of air flow control mechanism  40  operates in combination with heat control  64  of heat mechanism. In some examples, flux control mechanism  80  operates in combination with air flow control mechanism  40  or heat control mechanism  60 . Of course, other combinations can be implemented. In some examples, aspects of all three corrosion-protection modalities (e.g. air flow, heat, and flux control) are implemented in one ion writing assembly. 
     By preventing or minimizing potential corrosion of an electrode array of an ion writing unit, a combination of the corrosion-protection modalities increases the longevity of the electrode array  30  and any related conductive elements, thereby prolonging the useful life of the ion writing assembly  100 . 
       FIG. 6  is a block diagram schematically illustrating an ion generator, according to one example of the present disclosure. As shown in  FIG. 6 , ion generator  112  comprises a corona wire  114 . In some examples, the ion generator  112  can serve as the ion generator  24  of any one of the examples previously described in association with  FIGS. 1-5 . Further details regarding at least one example of an ion generator comprising a corona wire are described in association with at least  FIGS. 7-9B . 
       FIG. 7  is a diagram schematically illustrating, in one example of the present disclosure, an ion writing unit  120  that can be used to write a marking material, such as e-paper. In one example, the ion writing unit  120  corresponds to the ion generator  112  described in association with at least  FIG. 6 . Ion writing unit  120  includes a device  122  that generates charges and an electrode grid array  124 . The term “charges” as used herein refers to ions (+/−) or free electrons and in  FIG. 7  device  122  generates positive charges  126 . Electrode array  124  is held in spaced apart relation to device  122  by a distance D1. In some examples, device  122  is a corona generating device, such as a thin wire that is less than 100 micrometers in diameter and operating above its corona generating potential. In some examples, while not shown in  FIG. 7 , device  122  generates negative charges that move under existing electrical fields. 
     In some examples, electrode array  124  includes a dielectric film  128 , a first electrode layer  132 , and a second electrode layer  130 . Dielectric film  128  has a first side  134  and a second side  136  that is opposite first side  134 . Dielectric film  128  has holes  138 A and  138 B that extend through dielectric film  128  from first side  134  to second side  136 , with the respective holes acting as nozzles. In some examples, each of the holes  138 A and  138 B is individually addressable to control the flow of electrons through each of the holes  138 A and  138 B separately. 
     First electrode layer  132  is on first side  136  of dielectric film  128  and second electrode layer  130  is on second side  134  of dielectric film  128  such that dielectric film  128  is sandwiched between the two respective layers  132 ,  134 . In some examples, second electrode layer  130  is a generally continuous electrode material and is formed around the circumferences of holes  138 A and  138 B to surround holes  138 A and  138 B on second side  134 . First electrode layer  132  is formed into separate electrodes  132 A and  132 B, where electrode  132 A is formed around the circumference of hole  138 A to surround hole  138 A on first side  136  and electrode  132 B is formed around the circumference of hole  138 B to surround hole  138 B on first side  136 . 
     In operation, an electrical potential between first electrode layer  132  and second electrode layer  130  controls the flow of charges  126  from device  122  through holes  138  in dielectric film  128 . In some examples, electrode  132 A is at a higher electrical potential than second electrode layer  130  and the positive charges  126  are prevented or blocked from flowing through hole  138 A. In some examples, electrode  132 B is at a lower electrical potential than second electrode layer  130  and the positive charges  126  flow through hole  138 B to a collector (not shown). 
       FIG. 8  is a diagram schematically illustrating, in one example of the present disclosure, an ion writing unit  151  including an addressable corona, ion writing unit  150  for imaging e-paper  152 . Ion writing unit  150  images digital media on e-paper  152  using positive or negative charges. E-paper  152  is bi-stable, such that a collection of light absorbing and light reflecting states across e-paper  152  remains until sufficient charges or electrical fields are applied to e-paper  152 . In some examples e-paper  152  is a passive e-paper that does not include electronics for changing the state of the e-paper. 
     In general terms, ion writing unit  150  is held in spaced apart relation to e-paper  152  by a distance D2. In particular, as further shown in  FIG. 8 , in some examples the ion writing unit  151  includes a support  190  to releasably support e-paper  152  (at least during relative motion between ion writing unit  150  and e-paper  152 ) to enable e-paper  152  to position e-paper  152  to receive charge directed through holes  180 A,  180 B of ion writing unit  150 . In one aspect, support  190  is arranged as part of a positioning mechanism that controls relative movement between ion writing unit  150  and support  190 , as represented via directional arrow Y. In another aspect, a top surface  191  of support  190  is spaced from bottom surface of the electrode array (i.e. the location of holes  180 A,  180 B) by a distance D2. 
     In some examples, e-paper  152  includes charge-responsive layer  154  and a counter electrode layer  156 . Charge-responsive layer  154  includes charged color components that switch colors when charges  158  are applied to the imaging surface  160  of e-paper  152 . Counter electrode layer  156  is a conductive layer secured to charge-responsive layer  154  and is the non-imaging surface  162  of e-paper  152 , which is opposite imaging surface  160  of e-paper  152 . In some examples, an additional coating is included on charge-responsive layer  154  and this additional coating comprises an imaging surface  160  of e-paper  152 . In some examples, the color-switchable components of charge-responsive layer  154  include pigment/dye elements with a resin or polymer encapsulating microcapsules containing the color-switchable components of charge-responsive layer  154 . With further reference to  FIG. 8 , in some examples, ion writing unit  150  includes a corona generating device  166  (such as a corona wire) that generates charges and a non-charge generating addressable electrode grid array  168 . In  FIG. 8 , corona generating device  166  generates positive charges  158 , however, in some examples corona generating device  166  can generate positive or negative charges. Non-charge generating addressable electrode array  168  is held in spaced apart relation to corona generating device  166  by a distance D1. In some examples, corona generating device  166  is a thin wire that is less than 100 micrometers in diameter and operating above its corona generating potential, such as above 3 kilovolts. In some examples, corona generating device  166  is a thin wire, such as a 70 micrometer diameter tungsten wire coated with gold. 
     Non-charge generating addressable electrode array  168  provides spatially varying electric potential along the length of corona generating device  166  to selectively block or allow charges  158  to pass through addressable electrode array  168 . The addressable electrode array  168  provides for temporal and spatial control of charges  158  onto e-paper  152 . 
     Electrode array  168  includes a dielectric film  170 , a first electrode layer  174 , and a second electrode layer  172 . Dielectric film  170  has a first side  178  and a second side  176  that is opposite first side  178 . Dielectric film  170  has holes  180 A and  180 B that extend through dielectric film  170  from first side  178  to second side  176 , with holes acting as nozzles. Each of the holes  180 A and  180 B is individually addressable to control the flow of electrons through each of the holes  180 A and  180 B separately. 
     First electrode layer  172  is on first side  178  of dielectric film  70  and second electrode layer  174  is on second side  176  of dielectric layer  70 . Second electrode layer  174  is formed around the circumferences of holes  180 A and  180 B to surround holes  180 A and  180 B on second side  176 . First electrode layer  172  is formed into separate electrodes  174 A and  174 B, where electrode  174 A is formed around the circumference of hole  180 A to surround hole  180 A on first side  178  and electrode  174 B is formed around the circumference of hole  180 B to surround hole  180 B on first side  178 . 
     In operation, addressable corona generator  166  of ion writing unit  150  generates charges  158  that drift toward and through nozzles of the addressable electrode array  168  and then travel through the air for deposit onto e-paper  152  to selectively switch the optical state of the pigment/dye in e-paper  152 . Imaging surface  160  of e-paper  152  is opposite conductive counter electrode  156  and a ground return path connected to counter electrode  156  provides a path for counter charges to flow to counter electrode  156 , which keeps e-paper  152  substantially charge neutral in spite of charges  158  on imaging surface  160 . In some examples, counter electrode  156  is at ground. In some examples, counter electrode  156  is at any suitable reference potential to provide the fields suitable to extract charges  158  from corona generating device  166 . 
     Electric potential between first electrode layer  172  and second electrode layer  174  controls the flow of charges  158  from corona generating device  166  through holes  180 A,  180 B in dielectric film  170 . In some examples, electrode  174 A is at a higher electrical potential than second electrode layer  174  and the positive charges  158  are prevented or blocked from flowing through hole  180 A. However, in some examples, electrode  174 B is at a lower electrical potential than second electrode layer  174  and the positive charges  158  flow through hole  180 B to e-paper  152 . 
       FIGS. 9A and 9B  are diagrams including a side sectional view schematically illustrating the operation of an ion writing unit  200 , according to one example of the present disclosure, which includes an addressable corona ion writing unit  202  and e-paper  204 . In one example, the ion writing unit  200  corresponds to the ion generator  112  described in association with at least  FIG. 6 . Ion writing unit  202  is held in spaced apart relation to e-paper  204  by a distance D2 with e-paper  204  and ion writing unit  202  arranged for relative movement with respect to each other such that ion writing unit  202  causes image formation on e-paper  104 . While not shown in  FIGS. 9A, 9B , it will be understood that in some examples, e-paper  204  is releasably supported by support  190 , as in  FIG. 2  with support  190  maintaining the spaced apart distance D2. In some examples distance D2 is 0.5 millimeters. 
     With this arrangement, ion writing unit  202  controls the temporal and spatial transference of positive charges onto e-paper  204  to provide digital media images on e-paper  204 . E-paper  204  is bi-stable, such that e-paper  204  retains the images until sufficient charges or electrical fields are applied to erase the images. In some examples e-paper  204  is passive e-paper that does not include electronics for changing the state of the e-paper. 
     It will be understood that while  FIGS. 9A, 9B  show just one hole  240  (i.e. nozzle), these Figures are representative of the operation of an electrode array having many such holes, with each hole being individually controllable in an “on” or “off” state. 
     In some examples, e-paper  204  includes a functional coating layer  206 , a charge-responsive layer  208 , and a counter electrode layer  210 . Functional coating layer  206  is situated on one side of charge-responsive layer  208  and includes imaging surface  212 . In some examples, charged components within charge-responsive layer  208  switch color when charges are applied to imaging surface  212 . Counter electrode layer  210  is a conductive layer on another side of charge-responsive layer  208 , opposite functional coating layer  206 . In one aspect, counter electrode layer  210  is the non-imaging surface of e-paper  204 , which is opposite imaging surface  212 . 
     In some examples, charge-responsive layer  208  includes capsules  214  containing a dispersion of charged color particles (e.g. pigment or dye) in dielectric oils. This dispersion of charged color particles includes black or dark, light absorbing, particles  216  and white, light reflecting, particles  218 . A resin or polymer binder  220  encapsulates pigment capsules  214  of charge-responsive layer  208 . In some examples, black particles  216  drift toward functional coating layer  206  and white particles  218  drift toward counter electrode layer  210  after positive charges are placed on imaging surface  212 . In some examples, white particles  218  drift toward functional coating layer  206  and black particles  216  drift toward counter electrode layer  210  after positive charges are placed on imaging surface  212 . It will be understood that an alternate paradigm is employable in which black particles  216  drift toward electrode layer  210  and white particles  218  drift toward functional coating layer  206  after positive charges are placed on imaging surface  212 . 
     In some examples, addressable ion writing unit  202  generates positive charges that are selectively applied to imaging surface  212  to image digital media images on e-paper  204 . A ground return path connected to counter electrode layer  210  provides a path for counter charges to flow to counter electrode layer  210 , which keeps e-paper  204  substantially charge neutral in spite of the positive charges placed on imaging surface  212 . Counter electrode layer  210  is at any suitable reference potential to provide the appropriate fields to extract positive charges from addressable corona ion writing unit  202 . 
     In some examples, ion writing unit  202  includes a corona wire  222 , an addressable electrode grid array  224 , and a housing  226 . Electrode array  224  is held in spaced apart relation to corona wire  222  by a distance D1 and corona wire  222  operates at 3000-5000 volts to generate positive charges  228 . In some examples, corona wire  222  is 70 micrometers in diameter. In some examples, corona wire  222  is a tungsten wire coated with gold. In some examples, distance D1 is 1.5 millimeters. 
     Electrode array  224  provides temporally and spatially varying electric potential along the length of corona wire  222  to selectively block or allow charges  228  to pass through electrode array  224  and onto e-paper  204 . 
     In some examples, addressable electrode array  224  includes dielectric material  230 , a first electrode layer  234 , and a second electrode layer  232 . Dielectric material  230  has a thickness T1 and a first side  238  and an opposite second side  236 . Dielectric material  230  has a hole or nozzle  240  that extends through dielectric material  230  from first side  238  to second side  236 . In some examples, thickness T1 is 50 micrometers. 
     First electrode layer  234  is on first side  238  and second electrode layer  232  is on second side  236 . First electrode layer  234  is formed around the circumferences of hole  240  to surround hole  240  on first side  238  and second electrode layer  232  is formed around the circumference of hole  240  on second side  236 . 
       FIG. 9A  is a diagram schematically illustrating, in one example of the present disclosure, the operation of ion writing unit  202  in the “on” state, where positive charges  228  are transferred from ion writing unit  202  to imaging surface  212 , which is sometimes referred to as the collector electrode. In some examples, corona wire  222  is held at 3000-8000 volts (as represented by V1) to generate positive charges  228  and housing  226  is held at 0 volts (ground). Second electrode layer  232  is held at an intermediate potential (represented by V3) in a range between V1 and V2. In some examples, V3 is computed as V3=V2+α(V2−V1), where is α a number between 0 and 1 representing a fraction of the overall ΔV between V1 and V2, with typical values for a ranging from 0.65 to 0.75 depending on the geometry and causing positive charges  228  drift from corona wire  222  to electrode array  224  and second electrode layer  232 . First electrode layer  234  is switched to and held at a negative potential (represented by V4) relative to the second electrode and positive charges  228  pass through hole  240  in dielectric material  230  biased by the electric field between second electrode layer  232  and first electrode layer  234 . 
     In one aspect, the e-paper  204  is electrically biased with the collector electrode of e-paper  204  being held at a negative potential in the range of 500-4000 volts (represented by V2), which pulls positive charges  228  that pass through hole  240  onto imaging surface  212 . The positive charges  228  on imaging surface  212  bias particles, such as black particles  216 , toward imaging surface  212  to provide digital media images on e-paper  204 . In some examples, negative charges are used to bias suitably colored particles. 
       FIG. 9B  is a diagram illustrating in some examples of the present disclosure the operation of ion writing unit  200  in the “off” state, where positive charges  228  from ion writing unit  202  are blocked by electrode array  224  from being transferred to imaging surface  212 . In some examples, corona wire  222  is held at a potential in the range of 3000-8000 volts (represented by V1) to generate positive charges  228  and housing  226  is held at an intermediate potential between corona wire  222  and e-paper electrode  204 . Second electrode layer  232  is held in the range between V1 and V2. In some example, V3 is computed as V3=V2+α(V2−V1), where is α a number between 0 and 1 representing a fraction of the overall ΔV between V1 and V2, with typical values for a range from 0.65 to 0.75 depending on the geometry and causing positive charges  228  drift from corona wire  222  to electrode array  224  and second electrode layer  232 . However, first electrode layer  234  is switched to and held a potential difference (ΔV) with respect to the second electrode layer  232  in the range of 50-300 volts depending on the geometry, such that positive charges  228  are blocked from passing through hole  240  in dielectric material  230  by the electric field between first electrode layer  234  and second electrode layer  232 . 
     In this situation, despite the e-paper  204  being electrically biased via the collector electrode of e-paper  204  being held at a large negative potential, the positive charges  228  do not pass through hole  240  and onto imaging surface  212 . Particles, such as white particles  218 , which may have been previously biased toward imaging surface  212  remain at that surface to provide digital media images on e-paper  204 . In some examples, negative charges are used to bias suitably colored particles. 
     In some examples of ion writing unit  200 , second electrode layer  232  is held at a positive potential difference with respect to the housing in both the on state and the off state, and first electrode layer  234  is switched between a negative potential and a positive potential relative to the second electrode layer  232  to switch between the on state and the off state, respectively. 
     While the ion writing unit of  FIGS. 9A-9B  has been described in one example according to a mode of generating positive ions, it will be understood that in some examples, the ion writing unit  202  of  FIGS. 9A-9B  is operated to generate negative ions. 
       FIGS. 10A-10B  are diagrams illustrating examples of non-charge generating addressable electrode grid arrays that can be used in ion writing units  120 ,  150 , and  202  of  FIGS. 7-9B , according to at least some examples of the present disclosure. The electrode grid arrays enable high resolution imaging of passive e-paper medias. 
     In general terms, at least some of the electrode arrays include a plurality of nozzles or holes extending through a dielectric material layer and through at least two layers of conductive material separated by the dielectric material layer, which has a thickness T. In some examples, the conductive layers are made of copper and include at least one additional plated layer, such as electroless nickel and gold or immersion Tin. In one aspect, this arrangement provides thin protective finishing layers on the copper and prevents corrosion of the copper in the charge plasma environment. 
     In one aspect, the size of the holes in the electrode array limits the minimum size of dots for imaging digital media images. Circular holes have a diameter Dm, but the holes can be other suitable shapes, such as rectangular. In some examples, each of the holes is circular and less than 150 micrometers in diameter. In some examples, each of the holes is circular and less than 100 micrometers in diameter to provide 300 dots per inch and higher resolution. 
     In each of the electrode arrays, there is a range of aspect ratios T/Dm for which conditions exist where charges can be blocked and passed through the electrode arrays. If the aspect ratio T/Dm is much greater than 1, it is difficult to pass charges through the holes in the electrode array, and if the aspect ratio T/Dm is much less than 1, it is difficult to prevent charges from passing through the electrode array. In some examples, the optimal aspect ratio T/Dm is about 1, such that the dielectric material layer is relatively thin and on the order of 25-100 micrometers in thickness T for high resolution imaging. In some examples, the dielectric material layer is a flexible circuit material. In some examples, the dielectric material layer is a polyimide that has a high dielectric strength and provides for chemical etching or laser ablation to open small accurate holes with non-conductive walls. 
       FIGS. 10A and 10B  are diagrams schematically illustrating a non-charge generating, addressable electrode grid array  300 , according to one example of the present disclosure. The array  300  includes multiple holes or nozzles  302  that extend through dielectric material layer  304 , first conductive electrode layer  306 , and second conductive electrode layer  308 . In some examples, dielectric material layer  304  is a dielectric film. In some examples, each of the first and second conductive electrode layers  306  and  308  includes copper. 
       FIG. 10A  is a cross-section diagram of electrode array  300  taken along the line  10 A- 10 A in  FIG. 10B . Dielectric material layer  304  has thickness T, a second side  310 , and a first side  312  that is opposite second side  310 . Second electrode layer  306  is on second side  310  of dielectric material layer  304  and first electrode layer  308  is on first side  312  of dielectric material layer  304 . Dielectric material layer  304  includes the holes  302  that extend through dielectric material layer  304  from second side  310  to first side  312  and that extend through second electrode layer  306  and first electrode layer  308 . Second electrode layer  306  is formed around the circumference of each of the holes  302  to surround the holes  302  on second side  310  and provide a common electrode for the holes  302 . Each of the holes  302  has a diameter Dm. 
       FIG. 10B  is a diagram illustrating, in one example of the present disclosure, finger electrodes  308 - 308 H formed in second electrode layer  308  on dielectric material layer  304 . Each of the finger electrodes  308 A- 308 H has a circular landing pad formed around the circumference of a corresponding one of the holes  302 A- 302 H on second side  312 , such that finger electrode  308 A is formed around the circumference of hole  302 A, finger electrode  308 B is formed around the circumference of hole  302 B, and so on. Each of the finger electrodes  308 A- 308 H surrounds the corresponding one of the holes  302 A- 302 H to provide a single finger electrode  308 A- 308 H for the corresponding one of the holes  302 A- 302 H. Also, each of the finger electrodes  308 A- 308 B is individually addressable, such that each of the holes  302 A- 302 H is individually addressable to control the flow of charges through each of the holes  302 A- 302 H separately. 
     In operation, temporal and spatial control of charges flowing through electrode array  300  is achieved by individually addressing finger electrodes  308 A- 308 H to apply on state or off state electrical potentials between finger electrodes  308 A- 308 H and the common electrode of second electrode layer  306 . 
     While  FIGS. 7-10B  provide at least some examples of the present disclosure regarding an ion generator including a corona wire which is at least partially contained within a housing, it will be understood that an ion generator in examples of the present disclosure can take many forms and that the forms of the housing shown in  FIGS. 7-10B  do not strictly limit the manner in which corrosion-control modalities (e.g.  FIGS. 2-6 ) in examples of the present disclosure are implemented relative to an electrode array and/or a corona wire. In particular, a housing need not take the form shown for housing  226  in  FIGS. 9A-9B . Rather, in some examples, such housings have a non-circular cross-sectional shapes, partially circular cross-sectional shapes, etc. 
     Once such example is shown in  FIG. 11A , which is a sectional view schematically illustrating an ion generator  350 , according to one example of the present disclosure. As shown in  FIG. 11A , ion generator  350  includes a first portion  352  including an array  354  of electrode nozzles  356  and a housing  362  formed by at least one wall  364 . A corona wire  360  is positioned adjacent the electrode array  354 . In some examples, housing  362  defines a chamber around corona wire  360 . 
     As shown in  FIG. 11A , in some examples, the at least one wall  364  defines a generally rectangular cross-sectional shape. However, in some examples, the at least one wall  364  defines other cross-sectional shapes, such as irregular shapes, triangular shapes, polygonal shapes, etc. Moreover, in some examples, the size and/or shape of the housing  362  varies along a length (L1 in  FIG. 11B ) of the housing  362 , such that the width (W1) and height (H1) of the housing  362  is not necessarily uniform along the length (L1) of the housing  362 . 
     In some examples, at least some of the walls  364  of housing  362  are electrically conductive and held a fixed potential. In some examples, at least some of the walls  364  of the housing  362  are electrically conductive, and exhibit a floating potential. In some examples, at least some of the walls  364  of the housing  362  are electrically insulating, such as a polymer material. 
     In some examples, the at least one wall  364  of housing  362  of ion generator  350  includes multiple apertures. In some examples, the at least one wall  364  forms a partial enclosure. 
     With this in mind, in some examples of the present disclosure, an ion generator  370  as shown in  FIG. 11C  has an open architecture in which the corona wire  360  is positioned adjacent the electrode array  354  but no formal structure encloses the corona wire  360  relative to the first portion  352  defining the electrode array  354 . 
     With this in mind, at least some of further examples of corrosion-control modalities as described in association with  FIGS. 12A-19  are not strictly limited to the particular structures of housings shown in those Figures but can take other forms consistent with the examples described in association with at least  FIGS. 11A-11C . 
       FIG. 12A  is a diagram including sectional views schematically illustrating an ion writing assembly  400  including an air flow control mechanism  440 , according to one example of the present disclosure. In some examples, ion writing assembly  400  comprises at least some of the substantially the same features and attributes as ion writing assembly  20 , as previously described in association with  FIG. 2  and the components of ion writing unit, as previously described in association with  FIGS. 7-9B . 
     As shown in  FIG. 12A , the ion writing assembly  400  includes an ion writing unit  401 , which comprises a housing  402  having a body  404  defining a chamber  407  and having a first exterior surface  408 . In some examples, the chamber  407  at least partially encloses an ion generator and includes an opening  409  at the first exterior surface  408  of the housing. In some examples, the ion generator includes a corona wire  424  and chamber  407  at least partially encloses the corona wire  424 . A flexible circuit  430  including an electrode array (having electrode nozzles) is mounted onto the first exterior surface  408  with the electrode nozzles aligned with the opening  409  to selectively permit passage of a flow of ions through selected electrode nozzles toward an imaging surface  410  of passive e-paper  410 . 
     In some examples, as shown in  FIG. 12A , the ion writing assembly  400  comprises an air flow control mechanism  440  including an air source  442 , such as an air pump, and a treatment element  444 . In some examples, the treatment element  444  includes a drying element, such as a desiccator, to remove moisture from the air provided via the air source  442 , thereby minimizing potential for corrosion. In some examples, the desiccator is formed with silica gel or a molecular sieve material. In some examples, the desiccator is split into two parts, such that at any given time, one part is actively employed to dry air while the other part is being regenerated via heating (e.g. 150 degrees C.). 
     In some examples, the treatment element  444  includes a filter to remove organic contaminants from the air provided via the air source  442 , thereby minimizing the potential for dendritic growth on a corona wire  424  of an ion generator. In some examples, the contaminant filter includes charcoal or activated carbon. In some examples, the treatment element  444  includes both a drying component and a filter component. 
     In some examples, as further shown in  FIG. 12A , the air flow control mechanism  440  includes a first air flow path  445  directed for passage, via director  446  with a port  448  (e.g. an air knife), across the electrode array  430  to remove moisture and/or prevent moisture from accumulating on the electrode array of the flex circuit  430 . In general terms, the air flow is directed to pass adjacent the electrode array. In some examples, the air flow is directed along a first orientation (as represented via directional arrow F) that is generally parallel to a plane P1 through which the electrode array (of the flex circuit  430 ) extends. In some examples, the air flow is directed along a first orientation (as represented via directional arrow F) that is generally perpendicular to a plane P2 through which an opening  409  (such as electrode nozzles) extends. In some examples, the air flow is directed at other orientations to move air across or onto the electrode array of the flexible circuit  430 . 
     In some examples, as further shown in  FIG. 12A , the air flow control mechanism  440  includes a second air flow path  450  directed for conveying air through conduit  452  extending within body  404  of housing  402  to exit into chamber  407 . This air helps to remove moisture or prevents its accumulation generally within chamber  407 , and near/on electrode array  430 . In addition, this air flow passes around and by corona wire  424 . By doing so, in some examples, the second air flow path  450  also limits undesired dendritic growth on the corona wire  424 , thereby contributing to long term stability in the corona discharge. 
     In general terms, air flows produced via the air flow control mechanism occur at a low flow rate. In some examples, the first and second air flow paths  445 ,  450  each produce an air flow rate on the order of 0.2 Liters/minute at electrode array  430  and/or near corona wire  424 , respectively. 
     In some examples, the air flow mechanism  440  protects the chamber  407  without a second air flow path  450 , such that no conduit  452  is provided through housing  402 ,  472 . In this instance, the first air flow path  445  provides a sufficient flow of air past opening  409  to effectively seal the chamber  407  from external moisture, thereby establishing a corrosion-protection barrier for corona wire  424  and/or exposed electrically conductive elements (e.g. interior electrode portions). 
     In some examples, by positioning the port  454  (of second air flow path  450 ) at a back of chamber  407 , the directed air flow moves toward a front of the chamber  407  adjacent opening  409  to effectively seal the opening  409  and prevent organic-laden moisture from entering the chamber  407 , and thereby inhibit dendritic growth on corona wire  424 . In some examples, the air introduced into the chamber  407  provides an internal air pressure that produces the effective seal and/or augments the seal produced by the air flowing through the opening  409 . Moreover, as previously described, the directed air flow around and on the corona wire  424  also inhibits such dendritic growth. By inhibiting this potential dendritic growth, the longevity and effectiveness of the corona wire  424  is enhanced. 
       FIG. 12B  is diagram including a partial side sectional view schematically illustrating an ion writing assembly  471 , according to one example of the present disclosure. In some examples, the ion writing unit  471  includes at least some of substantially the same features and attributes as the ion writing unit  401  in  FIG. 12A , except for having a housing  472  defining an at least partially hollow interior  477  defined by wall  475  with air conduit  452  passing through the interior  477 . In addition, chamber  407  is defined by a tube  476  extending through the interior  477  of the housing  472  with air conduit  473  coupled to tube  476  to permit air to enter tube  476  via exit port  478  of conduit  452 . In some examples, air enters tube  476  through multiple locations via multiple exit ports  478  associated with air conduit  473 . 
     In general terms, tube  476  is a thin-walled structure, which has at least one opening to enable ions (generated by corona wire  424 ) to exit. However, in some examples, tube  476  has additional openings. In some examples, tube  476  as a generally circular cross-sectional shape as shown in  FIG. 12B . However, in some examples, tube  476  has a different cross-sectional shape, such as a rectangular, a polygon, semicircular shape, etc. Moreover, in some examples, the cross-sectional shape and/or size of the tube  476  varies along a length of the tube (i.e. a direction generally parallel to a length of the corona wire  424 ). In some examples, tube  476  has a shape that is similar to a shape of the housing walls defining the chamber enclosing the tube  476  while in some examples, tube  476  has a shape different than a shape of the walls defining the chamber enclosing the tube  476 . 
     In some examples, the tube  476  is not enclosed by chamber walls, such as when an ion generator takes a form consistent with the example ion generator shown in  FIG. 110 . In such an example, tube  476  at least partially encloses a corona wire  424  but the ion generator otherwise omits a formal housing to enclose the tube  476  and corona wire  424 . 
     While this tube-chamber arrangement does not directly affect the transmission of air into chamber  407  (which at least partially encloses corona wire  424 ) via conduit  454 , this arrangement enables implementing additional modalities such as (but not limited to) those described later in more detail (e.g.  FIG. 13C ) in which heating elements are applied to an outer surface of tube  476  to apply heat to chamber  407  without heating an entire body of the housing. 
       FIG. 12C  is a flow chart diagram  480  illustrating in one example of the present disclosure a method  481  of manufacturing an ion writing unit. In some examples, method  491  is performed using at least some of the components, assemblies, arrays, systems as previously described in association with at least  FIGS. 1, 2, 7-9B, and 12A-12B . In some examples, method  481  is performed using at least some of the components, assemblies, arrays systems other than those previously described in association with at least  FIGS. 1-2, 7-9B, and 12A-12B . 
     As shown at  482  in  FIG. 12C , in some examples, method  481  includes providing a housing including a chamber to at least partially enclose a corona wire. An electrode array (including electrode nozzles) is secured onto an exterior surface of the housing while arranging the electrode nozzles to receive and guide ions (generated by the corona wire) to a target external to the housing, as shown at  484  in  FIG. 12C . At  486 , method  481  includes positioning a nozzle of an air flow mechanism to cause at least one of an air flow across the respective electrodes nozzles and an air flow within the chamber. However, it will be understood that in some examples, ion generation is provided via mechanisms other than a corona wire and may or may not include a housing enclosing the ion generator. In such examples, the air flow mechanism still causes air flow across the respective electrode nozzles. In some examples, air flow is directed through a chamber of the housing at least partially enclosing the non-corona ion generator. However, in some examples, air flow is not directed adjacent to the non-corona ion generator and is just directed across or adjacent the electrode nozzles. 
       FIG. 12D  is a diagram  490 A schematically illustrating an ion writing unit  491 A with a recirculating air flow mechanism  492 A, according to one example of the present disclosure. In some examples, the ion writing unit  491 A includes at least some of substantially the same features and attributes as the ion writing units (and their associated air flow mechanisms) described in association with at least  FIGS. 2, 7-10B, and 12A-12B . 
     As shown in  FIG. 12D , the ion writing unit  491 A includes a housing  493 A defining a chamber  493 B, which at least partially encloses an ion generator and through which the ion generator extends. In some examples, the ion generator comprises a corona wire. As further shown in  FIG. 12D , in some examples, the air flow recirculation mechanism  492 A includes an input conduit  492 B coupled to a first portion  496 A of the chamber (such as, but not limited to a first end portion) and an output conduit  492 C coupled to an opposite second portion  496 B of the chamber (such as, but not limited to a second end portion). The input conduit  492 B guides air into the chamber  493 B, as represented by directional arrow Qin, while the output conduit  492 C guides air out of the chamber  493 B, as represented by directional arrow Qout. An air mover  494 A and treatment element  444  are interposed between the output conduit  492 C and the input conduit  492 B such that air continuously recirculates along a recirculation path  495  including the chamber  493 B, the output conduit  492 C, the air mover  494 A, the treatment element  444 , and the input conduit  492 B. 
     In some examples, the air mover  494 A includes a pump or fan. In some examples, the treatment element  444  includes at least some of substantially the same features and attributes as the treatment element  444  previously described in association with  FIGS. 12A-12B , such as a dryer component and/or a contaminant filter. 
     In some examples, the air flow recirculation mechanism  492 A also includes an air intake  496 A positioned along the output conduit  492 C between the chamber  493 B and the air mover  494 A to introduce air at a first flow rate into the recirculation path  495 , as represented by Qinlet. In some examples, at least some of the electrode nozzles  493 C act as an air outlet to permit air to exit the recirculation path  495  at a second flow rate generally matching the first flow rate, as represented by Qnozzles. 
     With this arrangement, air flows from the chamber  493 B and out of the electrode nozzles  493 C to prevent corrosion and/or dendritic growth in substantially the same manner as described above in association with at least  FIGS. 12A-12C . However, by providing a recirculation path, the same volume air is effectively used over and over again, generally retaining its purity, instead of the system having to continually purify environmental air, which contains contaminants and/or moisture. In some examples, this effect, in turn, prolongs longevity of the treatment element. In some examples, this recirculation mechanism  492 A also provides for a generally larger flow of air within chamber  493 B to more easily carry away contaminants (e.g. organics, ions) from an ion generator in the chamber  493 B while still providing a sufficient flow of air through the electrode nozzles  493 C to inhibit corrosion on the electrodes. 
     In some examples, by providing a larger volume of air moving through the chamber  493 B, the recirculation mechanism  492 A helps to create an internal air pressure within chamber  493 B that effectively seals an opening (e.g. the electrode nozzles) of the chamber  493 B to prevent the entry of moisture and/or contaminants into the chamber  493 B. 
       FIGS. 13A-13C, 14A, and 15A  are diagrams including a sectional view schematically illustrating ion writing assemblies  500 ,  510 ,  550 ,  600 ,  650 , respectively, including a heat control mechanism, according to examples of the present disclosure. In some examples, ion writing assemblies  500 ,  510 ,  550 ,  600 ,  650  comprise at least some of the substantially the same features and attributes as ion writing assembly  50 , as previously described in association with  FIG. 3  and the components of ion writing assemblies described in association with  FIGS. 7-9B . 
       FIG. 13A  is a block diagram schematically illustrating an ion writing assembly  500  including a heat control mechanism for applying heat  504 , according to one example of the present disclosure. In some examples, the heat control mechanism for applying heat  504  corresponds to a heat control  62  of heat control mechanism  60  in  FIG. 3  and, as such, prevents moisture buildup on various components of the ion writing unit. In some examples, a heat control mechanism is configured and positioned relative to ion writing unit  502  to apply heat  504  to at least an electrode array of the ion writing unit  502  and/or to structures adjacent the electrode array, such as but not limited to, structures associated with a corona wire of the ion writing unit  502 . In some examples, heat  504  is applied via radiation  505 , such as but not limited to, an external lamp heating the targeted components. 
     In some examples, heat  504  is applied via conduction  506 , such as but not limited to at least some of the examples provided in association with  FIGS. 13B-15C  in which a heating element directly contacts at least some components associated with an ion writing unit. 
     In some examples, heat is applied via convection  507  in which heated air flow is circulated around/across the targeted components. Accordingly, in some examples, convection  507  is achieved via aspects of a heat control mechanism being combined in a complementary manner with an air flow mechanism (e.g.  FIGS. 12A-12C ) in examples of the present disclosure. In some examples, application of heat via convection  507  is achieved via structures and components independent of the example air flow mechanism described in association with  FIGS. 12A-12C . 
     In some examples, heat  504  is applied via various combinations of the heat modalities  505 - 507 . 
       FIG. 13B  is a diagram including a side sectional view of an ion writing assembly  510  including a heat control mechanism  528 , according to one example of the present disclosure, which applies heat via conduction  506 . As shown in  FIG. 13B , ion writing assembly  510  comprises a housing  522  including a solid body  525  defining at least a chamber  527  (having wall  526 ), a first exterior surface  521  and an opposite exterior surface  529 . A flex circuit  530  including an electrode array with addressable nozzles is mounted on exterior surface  521  of housing  522 . A corona wire  524  at least partially enclosed within chamber  527  acts as an ion generator, with ions emitted via gap  526  extending through exterior surface  521  of housing  522  and of the electrode array of flex circuit  530 . In some examples, the electrode array of flex circuit  530 , corona wire  524 , and chamber  527  comprises at least some of substantially the same features and attributes as the electrode array, corona wire, and chamber previously described in association with  FIGS. 7-9B . In some examples, chamber  527  has a diameter on the order of 4 to 8 millimeters. 
     As further shown in  FIG. 13B , the heating element  528  is mounted to exterior surface  529  of body  525  of housing  522 . In some examples, the heating element  528  is an electrically resistive-based heating element, which when activated, heats the entire body  525  of housing  522 . By doing so, the entire electrode array of flex circuit  530  is heated to a temperature sufficient to prevent and/or overcome moisture accumulation on conductive elements of the electrode array (and any related structures within or near chamber  527 ), which in turn prevents corrosion of electrode array of flex circuit  530 . 
     In some examples, a typical start-up time for heating the housing  522  (and therefore heating the electrode array) to a desired temperature is about 30 to 60 seconds, such as when the housing is made of aluminum and the imaging portion of the electrode array is about 20 millimeters wide. Accordingly, in one aspect, this example is well suited to higher volume production runs of imaging passive e-paper, such as but not limited to, high quantities of financial or information transaction media. 
     In some examples, the heat control mechanism  528  corresponds to a heat control  62  of heat control mechanism  60  in  FIG. 3 . 
       FIG. 13C  is diagram including a side sectional view of an ion writing assembly  550  including a heat control mechanism  590 , according to one example of the present disclosure. As shown in  FIG. 13C , ion writing assembly  550  includes at least some of substantially the same features and attributes as ion writing assembly  510  ( FIG. 13B ), except for including heat control mechanism  590  instead of heat control mechanism  528 , while including adaptations to an interior of housing  552 . 
     As shown in  FIG. 13C , housing  552  includes a first exterior surface  558  and a second exterior surface  559 , with a body  554  having a first interior surface  555 . A flex circuit  580  is mounted to two spaced apart supports  560  of the body  554  of the housing  552 , thereby defining a first chamber  562  in which a tube  556  is mounted. In one aspect, the housing  552  can be said to form a shell defining first chamber  562 , with examples of the present disclosure not being limited to the particular shape of the body  554  shown in  FIG. 13C . In one aspect, tube  556  is generally spaced apart from the first interior surface  555  of the body  554  of housing, and is generally spaced apart from inner surface  581  of flex circuit, except where upper portion  558  of tube  556  meets a central portion  585  of flex circuit  580 . 
     In general terms, the heat control mechanism  590  is located within the first chamber  562  of the housing  552  and at least partially surrounds the tube  556  to provide heat directly to the tube  556  instead of attempting to heat an entire body of a housing, as in the example of  FIG. 13B . In some examples, heat control mechanism  590  comprises several heating elements  591  located adjacent to each other and secured relative to an outer surface of tube  556 . In some examples, a single arcuate heating element is used to at least partially surround tube  556  instead of using separate elements  591 . 
     In some examples, the heat control mechanism  590  corresponds to a heat control  62  of heat control mechanism  60  in  FIG. 3 . 
     In one aspect, because tube  556  has a thermal mass that is orders of magnitude less than a thermal mass of a solid housing (such as body  525  in  FIG. 13B ), and because the heat control mechanism  590  directly heats tube  556 , typical start-up times to heat the electrode array  580  to a sufficient temperature (to prevent moisture accumulation) is on the order of 1 to 2 seconds. Accordingly, this example is well suited for short volume production runs, with the heat control mechanism  590  being suited for quickly starting up off and shutting down for each desired use. 
     In some examples, the heat control mechanism  590  is turned on a first time period prior to activation of the corona wire  574  to ensure adequate time for heating up the electrode array of the flex circuit  580  to protect against moisture accumulation and related corrosion. The heat control mechanism  590  is then turned off after a second time period after de-activation of the corona wire  574  with the second time period being sufficient for any potentially corrosive ionic species to have recombined or to have diffused out of the chamber  557  and/or away from the electrode array of flex circuit  580 . By limiting the heating of the flex circuit (and surrounding/exposed corrosion-susceptible elements) to relatively short periods of time, the temperature within chamber  557  is not elevated to high temperatures at all, and/or elevated to high temperatures for a sufficiently short period of time, such that dendritic growth on corona wire  574  is minimized. 
     In some examples, to address cases in which the heat control mechanism  590  is continuously active for longer periods of time, or under a high duty cycle, one implementation of the ion writing assembly  550  further incorporates an air flow mechanism, such as air flow mechanism  440  ( FIGS. 12A-12B ) to cause a small flow of air through chamber  557  to prevent significant thermal diffusion from tube  556  through the air to corona wire  574 , and thereby minimizing undesired dendritic growth on corona wire  574 . 
       FIG. 14A  is a diagram including a side sectional view of an ion writing assembly  600  including a heat control mechanism  640 , according to one example of the present disclosure. As shown in  FIG. 14A , ion writing assembly  600  includes at least some of substantially the same features and attributes as ion writing assembly  550  ( FIG. 13 ), except for including heat control mechanism  640  instead of heat control mechanism  590 . As shown in  FIG. 14A , heat control mechanism  640  comprises at least one heating element  641  secured onto an outer surface of electrode array of flex circuit  630 . In general terms, the heating element  641  comprises an electrically-resistive heating element that directly heats a portion of the electrode array of flex circuit  630 . 
     In one aspect, heat control mechanism  640  corresponds to heat control  64  in  FIG. 3 . 
     One example of a heat control mechanism  640  is described in association with  FIGS. 14B-14C , which depict an electrode assembly  635  having substantially the same features and attributes as the electrode array of  FIGS. 7-9B , except further including at least one heating element  641 .  FIG. 14B  is a diagram including a sectional view of an electrode array  635  taken along the line  14 B- 14 B in  FIG. 14C , according to one example of the present disclosure, while  FIG. 14C  is a diagram including a plan view schematically illustrating individual electrodes formed as a first layer on a dielectric material layer, according to one example of the present disclosure. 
     As shown in  FIGS. 14B-14C , heating element  641  is mounted onto first electrode layer  308 , such that heating element  641  is in contact with all of the individual finger electrodes  308 A,  308 B,  308 C,  308 D, etc. Accordingly, activation of heating element  641  simultaneously heats all of the finger electrodes of first electrode layer  308 . In some examples, heating element  641  also causes heating of additional electrode layers in physical continuity with layer  308 , such as layer  306 , to prevent moisture accumulation and associated corrosion on those additional layers as well. 
     By activating heating element  641 , moisture is not able to collect on the first electrode layer  308  and/or second electrode layer  306 , and therefore corrosion of individual electrodes  308 A,  308 B, etc. is prevented. In some examples, heating element  641  is always activated to ensure protection against corrosion. In some examples, activation of heating element  641  is limited to time periods when ion writing system acts to electrically bias a passive e-paper during imaging operations and related time periods. 
       FIG. 15A  is a diagram including a side sectional view of an ion writing assembly  650  including a heat control mechanism  690 , according to one example of the present disclosure. As shown in  FIG. 15A , ion writing assembly  650  includes at least some of substantially the same features and attributes as ion writing assembly  650  ( FIG. 14A ), except for including heat control mechanism  690  instead of heat control mechanism  640 . As shown in  FIG. 15A  and the enlarged partial sectional view of  FIG. 15B , heat control mechanism  690  is incorporated within a portion of the electrode array  683  of flex circuit  680  adjacent opening  692  and therefore is not exposed on exterior surface  681  of flex circuit  680 . In general terms, heat control mechanism  690  comprises an electrically-resistive heating structure that directly heats a portion of the electrode array  683 . It will be further understood that opening  692  provides a generalized representation of at least some electrode nozzles of the electrode array  683 , which is further illustrated in more detail in association with at least  FIG. 15C . 
     In one aspect, heat control mechanism  690  corresponds to heat control  64  in  FIG. 3 . 
     One example of a heat control mechanism  690  is described in association with  FIG. 15C , which depicts an electrode assembly  683  having substantially the same features and attributes as the electrode array of  FIGS. 7-9B , except with second electrode layer  306  incorporating or defining the heat control mechanism  690 . In some examples, heat control mechanism  690  is implemented via forming generally the entire second electrode layer  306  at least partially from a resistance heating element. In some examples, the material used to form second electrode layer  306  is a nichrome material (e.g. a non-magnetic alloy of at least nickel and chromium) material suitable for use as a heating element. In some examples, just a portion of the second electrode layer  306  is formed from a resistance heating element, such as but not limited to, nichrome. 
     Accordingly, activation of heat control mechanism  690  (embodied in second electrode layer  306 ) heats the entire second electrode layer  306 , and heats the electrode array  683  in general, including first electrode layer  308 . 
     By activating heat control mechanism  690 , moisture is not able to collect on the first electrode layer  308  and second electrode layer  306  (and any related conductive components), and therefore corrosion of the electrode array is prevented. In some examples, heat control mechanism  90  is always activated to ensure protection against corrosion. In some examples, activation of heat control mechanism  690  is limited to time periods when ion writing system acts to electrically bias a passive e-paper during imaging operations and related time periods, including the above-described first and second time periods before and after activation of the corona wire  674 . 
     Accordingly, examples associated with  FIGS. 12-15C  act to significantly increase longevity of the electrode array of an ion writing unit by eliminating moisture that could otherwise lead to corrosion. 
     As previously mentioned in association with at least  FIG. 5 , in some examples, various corrosion-control modalities are combined. In some examples, a heat control mechanism is combined in a complementary fashion with an air flow control mechanism. For example, heat is applied to the nozzles of the electrode array of an ion writing unit to avoid intentionally or unnecessarily heating a corona wire of the ion writing unit, which could otherwise potentially cause dendritic growth on the corona wire. At the same time, an air flow source is coupled to the ion writing unit to cause air flow at least adjacent the corona wire to inhibit such dendritic growth on the corona wire. Moreover, to the extent that any heat energy becomes unintentionally transferred to the corona wire (or its surrounding environment), the air flow around the corona wire will act to inhibit potential dendritic growth on the corona wire. Moreover, as previously mentioned in association with the air flow control examples associated with  FIGS. 12A-12C , the air flow control can be further implemented to prevent or inhibit entry of organic contaminants into the chamber, which at least partially encloses the corona wire. 
       FIG. 16  is a flow chart diagram  700  illustrating in one example of the present disclosure a method  701  of manufacturing an ion writing unit. In some examples, method  701  is performed using at least some of the components, assemblies, arrays, systems as previously described in association with at least  FIGS. 1, 3, 7-9B, and 13A-15C . In some examples, method  701  is performed using at least some components, assemblies, arrays systems other than those previously described in association with at least  FIGS. 1, 3, 7-9B, and 13A-15C . 
     As shown in  FIG. 16 , at  702  method  701  includes providing an ion generator including housing having a chamber that at least partially encloses a corona wire. An electrode array including electrode nozzles is arranged to be exposed on an exterior surface of the housing and aligned to receive and guide ions generated by the corona wire toward a passive e-paper external of the housing, as shown at  704 . 
     As shown at  705 , a heating mechanism is provided to heat at least one of the chamber and the electrode nozzles. In some examples, as previously noted in association with at least  FIG. 13A , the heating mechanism transfers energy to the target chamber or nozzle array via at least one of the three basic heat transfer modes: conduction, convection or radiation. A biasing mechanism is arranged to be releasably couplable to, and electrically bias, the passive e-paper, as shown at  706 . 
     As shown at  708 , a controller to the heating element to cause heating at least when the biasing mechanism is active. 
       FIG. 17  is a block diagram schematically illustrating a control portion  720 , according to one example of the present disclosure. In some examples, control portion  720  includes a controller  722 , a memory  724 , and a user interface  726 . 
     In general terms, controller  722  of control portion  720  comprises at least one processor  723  and associated memories that are in communication with memory  724  to generate control signals directing operation of at least some components of the systems and components described throughout the present disclosure. In some examples, these generated control signals include, but are not limited to, activating and controlling corrosion-protection modalities (e.g. air flow, heat, flux control) via a corrosion-control manager  725 . In some examples, a control portion  720  is present in the ion writing assemblies  20   50 ,  70 ,  100  of  FIGS. 2-5 , respectively, and in the ion writing assemblies in association with  FIGS. 7-16  for controlling ion generation, ion flow, and corrosion-protection modalities. 
     In particular, in response to or based upon commands received via a user interface  726  and/or machine readable instructions (including software), controller  722  generates control signals to perform imaging of passive e-paper (including but not limited to transaction media) in accordance with at least some of the previously described examples and/or later described examples of the present disclosure. In some examples, controller  722  is embodied in a general purpose computer while in other examples, controller  722  is embodied in the various ion writing assemblies described throughout the present disclosure. 
     For purposes of this application, in reference to the controller  722 , the term “processor” shall mean a presently developed or future developed processor (or processing resources) that executes sequences of machine readable instructions (such as but not limited to software) contained in a memory. In some examples, execution of the sequences of machine readable instructions, such as those provided via memory  724  of control portion  720  cause the processor to perform actions, such as operating controller  720  to perform imaging while preventing corrosion as generally described in (or consistent with) at least some examples of the present disclosure. The machine readable instructions may be loaded in a random access memory (RAM) for execution by the processor from their stored location in a read only memory (ROM), a mass storage device, or some other persistent storage (e.g., non-transitory tangible medium or non-volatile tangible medium, as represented by memory  724 . In some examples, memory  724  comprises a computer readable tangible medium providing non-volatile storage of the machine readable instructions executable by a process of controller  722 . In other examples, hard wired circuitry may be used in place of or in combination with machine readable instructions (including software) to implement the functions described. For example, controller  722  may be embodied as part of at least one application-specific integrated circuit (ASIC). In at least some examples, the controller  722  is not limited to any specific combination of hardware circuitry and machine readable instructions (including software), nor limited to any particular source for the machine readable instructions executed by the controller  722 . 
     In some examples, user interface  726  comprises a user interface or other display that provides for the simultaneous display, activation, and/or operation of at least some of the various components, functions, features, and of control portion  720  and/or ion writing assemblies, as described throughout the present disclosure. In some examples, at least some portions or aspects of the user interface  726  are provided via a graphical user interface (GUI). 
       FIG. 18  is a block diagram schematically illustrating a flux control manager  740 , according to one example of the present disclosure. In some examples, flux control manager  740  acts as the corrosion control manager  725  of  FIG. 17  for control portion  720 . 
     In general terms, the flux control manager  740  operates to control an ion writing assembly, such those previously described in association with at least  FIGS. 1, 4, and 7-9B  to prevent corrosion. 
     Accordingly, consistent with those prior examples, In some examples an ion writing assembly with a flux control manager  740  includes an ion writing unit including a housing at least partially containing an ion generator, as well as an electrode array (including electrode nozzles) on one exposed exterior surface of the housing and aligned to receive and guide generated ions. 
     In particular, flux control manager  740  ensures that, whenever a passive e-paper is electrically biased for image formation, at least some electrode nozzles of the electrode array emit an ion flow at a rate sufficient to prevent corrosion but low enough to avoid unwanted image formation on the passive e-paper. 
     In some examples, as shown in  FIG. 18A , flux control manager  740  comprises an ion generation control module  742 , which includes a first mode  744  and a second mode  746 , wherein the ion writing unit convertibly operates between the first mode  744  and the second mode  746 . 
     In the first mode  744 , ions flow from the ion generator (e.g. corona wire) through selected nozzles at a first flow rate to cause image formation on an electrically biased passive e-paper spaced apart from the electrode nozzles. In the second mode  746 , ions flow from the ion generator (e.g. corona wire) through at least some electrode nozzles at a second flow rate (less than the first flow rate) that does not cause image formation on the electrically biased passive e-paper. In some examples, the second mode is automatically engaged when the first mode is inactive. In some examples, the second flow rate is at least one order of magnitude less than the first flow rate. 
     Operation in the second mode  746  according to the second flow rate provides sufficient flow of ions to neutralize the secondary ions. In one aspect, the secondary ions have a charge opposite the generated, primary ions and are produced during image formation while the passive e-paper is electrically biased. Without such neutralization, the secondary ions would otherwise carry moisture to the electrode array. In this way, operation in the second mode  746  prevents or mitigates corrosion of the electrode array on the ion writing head by taking advantage of the natural action of the generated ions as they flow out of the electrode array. 
     In some examples, the second flow rate in second mode  746  is produced via operating ion generator (e.g. corona wire) at a lower voltage than the first mode  744  (i.e. the image-formation writing mode) so as to produce a smaller volume of ions, which in turn results in fewer ions being available to be directed through electrode nozzles of electrode array. For example, with further reference to  FIGS. 9A-9B , in the second mode  746  the corona wire is operated at a lower voltage, such as 3000 Volts instead of 5000 Volts to produce a lower flow rate of positive ions. 
     Accordingly, in this example, the feature of producing a non-writing, lower flow rate in a second mode  746  is accomplished via manipulating the volume or intensity of ion production by the ion generator (e.g. corona wire in housing). In one aspect, via the ion generation control module  742 , the second mode  746  does not operate at the same time as the first mode  744 . 
     In some examples, the ion writing head operates in a third mode in which the no ions flow and the e-paper is not electrically biased. In this instance, when the passive e-paper is not electrically biased, the corroding, secondary ions are not produced. Therefore, without a flow of the undesired secondary ions toward the electrode array, operation in the second mode  746  may be omitted. 
     In some examples, as shown in  FIG. 18B , a flux control manager  741  comprises an electrode nozzle control module  750 , which includes a first state  754  and a second state  756 . 
     In the first state  754 , an ion writing unit permits ion flow at a first flow rate through selectively activated electrode nozzles to cause image formation on an electrically biased passive e-paper spaced apart from the electrode nozzles. In the second state  756 , at any given point in time, the ion writing unit permits ion flow through at least some electrode nozzles that are not selected for writing. However, this ion flow occurs at a second flow rate (less than the first flow rate) that does not cause image formation on the passive e-paper. Accordingly, in order to provide corrosion protection, the ion writing unit automatically causes at least some non-activated electrode nozzles (those not selected for writing) to operate in the second state. Of course, the identity of the selected writing electrode nozzles and the non-writing electrode nozzles will change rapidly as the ion writing head and passive e-paper move relative to each other during a writing operation to form an image on the passive e-paper. 
     In some examples, the lower flow rate in the second state is achieved via manipulating the respective voltages of the first and second electrode layers of the electrode array. In particular, in some examples the voltage of the second electrode layer (e.g. layer  232  in  FIGS. 9A-9B ) generally remains at an intermediate potential between V1 and V2. In some examples, V3 could be computed as V3=V2+α(V2−V1), where is α a number between 0 and 1 representing a fraction of the overall ΔV between V1 and V2, with typical values for a range from 0.65 to 0.75 depending on the geometry. In one aspect, the voltage of the first electrode layer (e.g. layer  234  in  FIGS. 9A-9B ) is generally at potentials relative to the second electrode which are positive ( FIG. 9B ) to close a nozzle and negative ( FIG. 9A ) to open the nozzle at the first flow rate. Accordingly, in order to achieve a lower flow rate, such as the second flow rate, in some examples the first electrode layer is set to a Voltage between these two levels. In some examples, a second flow rate is achieved via setting the voltage of first electrode layer to be at the midpoint of the writing and blocking potentials. Other voltage levels (e.g. 15%, 30%, 50%, 70%, 85%, of the operating range between the writing and blocking potentials etc.) can be set depending on the desired flow rate. However, the voltage is to be selected to achieve an ion flow through at least some of the electrode nozzles but without causing image formation on the targeted passive e-paper. 
     In some examples, during preparation for a writing operation or after completion of a writing operation, the passive e-paper will be electrically biased but none of the electrode nozzles are emitting ions according to the first state for causing imaging on e-paper. In this situation, the ion writing unit causes at least some electrode nozzles to operate in the second state to emit a low flow rate of ions to provide corrosion protection for the electrode array, thereby increasing longevity of the electrode array and ion writing unit. 
     In some examples, the ion writing unit determines which nozzles of the electrode array will operate (at any given point in time) in the second state  756 . 
     In some examples, when the ion writing unit is not actively causing image formation on e-paper, but the e-paper is electrically biased, the ion writing unit determines a pattern of which nozzles will operate in the second state. In some examples, as shown in  FIG. 18C , one such pattern  770  involves every other column of electrode nozzles operating in the second state (as represented by black dots  771 A) while the electrode nozzles in the remaining columns are dormant, as represented by white dots  771 B. In this way, a sufficient volume of ion flow occurs to achieve a corrosion protective effect, but without involving all of the electrode nozzles. In some examples, the ion writing unit periodically switches which columns of electrode nozzles are active in the second state and which columns are dormant. 
     In some examples, as shown in  FIG. 18C , another such pattern  772  intersperses dormant nozzles among non-dormant nozzles in the second state. 
     In other instances, some electrode nozzles operate in the second state  756  at the same time that other electrode nozzles are operating in the first state to cause image formation on a passive e-paper. Accordingly, In some examples, as shown in  FIG. 18C , pattern  774  represents some electrode nozzles operating in the second state (represented by the identifier NW for Non-Writing), some electrode nozzles operating in the first state to cause image formation (represented by the identifier W for writing), and other electrode nozzles operating in neither the first state or second state (as represented by the identifier D for Dormant). As previously noted, these designations change rapidly over time as an ion writing unit and passive e-paper are in movement relative to each other during a writing operation. 
     In some examples, the features and components of the respective flux control managers  740  ( FIG. 18A ) and  741  ( FIG. 18B ) are both included in a single flux control manager such that an operator (or an automatic controller) can operate either an ion generation control module  742  ( FIG. 18A ) or an electrode nozzle control module  750  ( FIG. 18B ). In some examples, features of the ion generation control module  740  ( FIG. 18A ) and of the electrode nozzle control module  741  ( FIG. 18B ) are deployed together. For instance, in one arrangement, a non-writing, protective flow of ions is accomplished via operating in the second mode  746  and by operating at least some electrode nozzles in the second state  756 . 
       FIG. 19  is a flow chart diagram  800  illustrating a method  801  of manufacturing an ion writing unit, according to one example of the present disclosure. In some examples, method  801  is performed using at least some of the components, assemblies, arrays, systems as previously described in association with at least  FIGS. 1, 4, 7-9B, and 18A-18B . In some examples, method  801  is performed using at least some components, assemblies, arrays systems other than those previously described in association with at least  FIGS. 1, 4, 7-9B, and 18 . 
     At  802 , method  801  comprises providing an ion generator including housing having a chamber that at least partially encloses a corona wire. An electrode array including addressable electrode nozzles arranged to be exposed on an exterior surface of the housing and aligned to receive and guide ions (generated by the corona wire) toward a passive e-paper external of the housing, as shown at  804 . 
     At  806 , method  801  includes arranging a biasing mechanism to electrically bias the passive e-paper. A controller is coupled to the ion generator to cause, when the biasing mechanism is active, at least a first flow rate of ion flow, where the first flow rate is less than a second flow rate of ion flow used for image formation on the passive e-paper, as shown at  808 . In some examples, the first flow rate is one order of magnitude less than the second flow rate. 
     At  810 , method  801  includes arranging the controller to automatically cause operation according to the first flow rate when the second flow rate is not applied. 
     As previously mentioned in association with at least  FIG. 5 , a combination of corrosion-protection modalities can be implemented in a complementary manner on a single ion writing unit. In some examples, a heat control  62  of a heat control mechanism is implemented on the electrode array while an air flow path  42  of air flow control mechanism is implemented within a chamber, which at least partially encloses a corona wire. In particular, the air flow within the chamber acts to minimize dendritic growth on the corona wire. Meanwhile, heating of the electrode array minimizes or prevents corrosion on the individual components of the electrode array without heating the corona wire in the chamber of the housing, which might otherwise cause undesired dendritic growth on the corona wire. 
     At least some examples of the present disclosure are directed to increasing longevity of an ion writing unit by minimizing corrosion on an electrode array and/or minimizing dendritic growth on a corona wire. 
     Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein.