Electronics enclosure and methods for controlling diffusion therefrom

Abstract

An electronics enclosure is described comprising: a closed housing formed from a plurality of walls and wherein the plurality of walls consists of a plurality of continuous walls and one discontinuous wall having an opening or a plurality of openings; and a single vent arrangement. The single vent arrangement comprises a protective membrane positioned over the opening or plurality of openings, wherein the protective membrane is air-permeable and liquid-impermeable; a cover positioned over the opening or plurality of openings, wherein the cover is movable relative to the opening or plurality of openings between a first diffusion position and a second diffusion position to allow for different rates of moisture diffusion between the inside of the closed housing and an external environment via the opening or plurality of openings in the first diffusion position and the second diffusion position, wherein the cover allows for diffusion in both the first diffusion position and the second diffusion position; and an actuator arrangement configured to move the cover between the first diffusion position and the second diffusion position in response to a threshold temperature or temperature difference being crossed.

Description

[0001] Electronics Enclosure and Methods for Controlling Diffusion therefrom

[0002] Field

[0003] The present disclosure relates to electronics enclosures, in particular electronics enclosures having a single vent arrangement which allows for variable diffusion between the inside of the enclosure and an external environment. Also disclosed are methods of controlling diffusion from an electronics enclosure.

[0004] Background

[0005] Electronics enclosures, for example housings for electrical components, have a risk of internal condensation which can potentially lead to damage and corrosion to any components inside the housing or to the housing itself. Condensation can also cause malfunction in enclosures with optical components or lights. The risk of condensation is higher when the electronics enclosure, or the components housed by the enclosure, comprise materials that are water absorbing, for example plastic materials. These materials tend to release moisture when their temperature increases, leading to an increased dew point in the internal air. This increases the likelihood of condensation inside the enclosure.

[0006] Active moisture removal devices use desiccant to adsorb the moisture inside the enclosure and transport it to the outside. These devices are typically large, heavy and expensive. These devices also consume electricity, add a significant temperature increase to the enclosure when operated, and it can take a significant amount of time (e.g., days) until the moisture is removed from the enclosure.

[0007] Passive desiccants are hygroscopic materials that are used to remove humidity from an environment. Desiccants can be placed inside an enclosure and are able to significantly reduce the moisture in the enclosure fora certain amount of time. However, once the desiccant is saturated it can even have a negative effect on the moisture content and condensation inside an enclosure. Therefore, the desiccant needs to be replaced occasionally. Accordingly, the enclosure and the desiccant needs to be accessible to allow for replacement. However, opening the enclosure creates the risk of contamination entering the enclosure and there is also a risk that the enclosure may not be properly closed again. This may lead to dust and water ingress into the enclosure.

[0008] There is therefore a need for electronics enclosures having improved moisture management systems, and methods. Summary

[0009] According to a first aspect of the present disclosure, there is provided an electronics enclosure comprising: a closed housing formed from a plurality of walls and wherein the plurality of walls consists of a plurality of continuous walls and one discontinuous wall having an opening or a plurality of openings; and a single vent arrangement comprising: a protective membrane positioned over the opening or plurality of openings, wherein the protective membrane is air- permeable and liquid-impermeable; a cover positioned over the opening or plurality of openings, wherein the cover is movable relative to the opening or plurality of openings between a first diffusion position and a second diffusion position to allow for different rates of moisture diffusion between the inside of the closed housing and an external environment via the opening or plurality of openings in the first diffusion position and the second diffusion position, wherein the cover allows for diffusion in both the first diffusion position and the second diffusion position; and an actuator arrangement configured to move the cover between the first diffusion position and the second diffusion position in response to a threshold temperature or temperature difference being crossed.

[0010] Electronics enclosures of the present disclosure are configured to allow for improved moisture management by reducing the likelihood of the formation of condensation. This is achieved by allowing for moisture diffusion from the inside of the housing to an external environment via the single vent when the cover is in the first diffusion position and second diffusion position. Furthermore, by allowing for moisture diffusion in both the first diffusion position and the second diffusion position, the single vent is also configured to allow for pressure equalization of the enclosure in both diffusion positions of the cover. In other words, the single vent is also a pressure equalization vent.

[0011] The first diffusion position may be a position having a reduced diffusion flow area compared to a diffusion flow area in the second diffusion position. The first diffusion position may be a position having an extended diffusion flow path compared to a diffusion flow path in the second diffusion position. In the first diffusion position, the cover may be arranged to cover the opening or plurality of openings in a non-sealing manner. The cover in the first position maintains a gap between the cover and the opening or plurality of openings. The diffusion flow area and diffusion flow path in the first diffusion position are defined by the gap between the cover and the opening or plurality of openings. In the second diffusion position, the cover is arranged to be distant from the opening or plurality of openings. The diffusion flow area and diffusion flow path in the second diffusion position is defined by the opening or the plurality of openings. The electronics enclosure comprising a closed housing formed from a plurality of walls and wherein the plurality of walls consists of a plurality of continuous walls and one discontinuous wall having an opening or a plurality of openings, and the single vent arrangement for variable diffusion is advantageous over known electronics enclosures which often rely on housings having openings in multiple walls of the housings. Such arrangements allow for convection airflow and also can be utilised to allow for renewal of desiccants placed inside the housing. In contrast, the electronics enclosure of the present disclosure relies on only one wall of the housing being discontinuous. As used herein, discontinuous is taken to mean that the wall of the housing has an opening or a plurality of openings, as opposed to a continuous wall which is taken to mean that the wall is sealed from the external environment such that there is no airflow path through the continuous wall. For examples, a continuous wall may encompass a wall that is uninterrupted across the surface area of the wall, i.e., comprises no openings or breaks. However, a continuous wall may also encompass an enclosure wall comprising sealed interruptions across the surface area of the wall, for example electrical connections and fluid connections which pass through the wall.

[0012] The electronics enclosure of the present disclosure allows for controlled diffusion from the enclosure. For example, the temperature or temperature difference threshold may be a temperature or temperature difference threshold that is indicative of high moisture inside the enclosure. Accordingly, when the temperature or temperature difference threshold is exceeded, the cover may be moved to the second diffusion position. This may allow for a higher rate of moisture diffusion from the enclosure compared to the rate of moisture diffusion should the cover remain in the first position. When the temperature or temperature difference falls below the temperature or temperature difference threshold, the cover may be moved to the first diffusion position. In the first diffusion position, the cover permits a relatively small rate of moisture diffusion from the enclosure compared to the rate of moisture diffusion should the cover remain in the second position. This also advantageously acts to mitigate against moisture from the outside environment from entering into the enclosure when the cover is in the first position. Accordingly, the single vent arrangement is configured such that the diffusion position of the cover is selected to allow for moisture inside of the enclosure to be minimised, depending on temperature. The single vent arrangement may be operable to reduce the dew point of a volume of air contained inside the closed housing.

[0013] The actuator arrangement may comprise a temperature-driven mechanical actuator. The temperature-driven mechanical actuator may be one of: a bi-metal switch, a temperature- driven spring, or a wax-based actuator. The temperature-driven mechanical actuator may have a threshold temperature at which the temperature-driven mechanical actuator is configured to move the cover from the first diffusion position to the second diffusion position, and vice versa.

[0014] The actuator arrangement may comprise a first temperature sensor positioned inside the closed housing, and an electrically-driven actuator that is configured to move the cover between the first diffusion position and the second diffusion position based on a measured temperature value from the first temperature sensor being above or below the threshold temperature. In some applications, the enclosure may further comprise a second temperature sensor positioned outside of the closed housing, and wherein the electrically-driven actuator is configured to move the cover between the first and second positions based on a calculated temperature difference being above or below the threshold temperature difference. The temperature difference may be the difference between a measured temperature value from the first temperature sensor and the second temperature sensor.

[0015] The actuator arrangement may comprise a first temperature sensor positioned outside the closed housing, and an electrically-driven actuator which is configured to move the cover between the first diffusion position and the second diffusion position based on a measured temperature value from the first temperature sensor being above or below the threshold temperature.

[0016] The electrically-driven actuator may be one of: an electric motor, a solenoid or a piezo-electric actuator.

[0017] The cover may be positioned inside of the closed housing. This may allow for the external profile of the enclosure to compact.

[0018] The cover may be positioned outside of the closed housing. This may allow for the space inside the enclosure to be utilised only for electronics component parts, thus maximising the available space for said electronics component parts.

[0019] The closed housing may be formed from a moisture absorbing material. The threshold temperature or temperature difference may be a temperature or temperature difference at which the moisture absorbing material can release moisture. The moisture absorbing material may be, for example, plastic. The moisture absorbing material may release moisture as temperature increases. Accordingly, when the temperature inside the electronics enclosure increases, the likelihood of condensation increases, for example, especially at colder surfaces of the housing. The closed housing may be formed from a non-moisture absorbing material.

[0020] The protective membrane may be impermeable to solid contaminants. Accordingly, the protective membrane may prevent ingress of dirt, dust and other solid contaminants into the enclosure. The protective membrane may be affixed to the housing. The protective membrane may be arranged to cover the opening or plurality of openings irrespective of whether the cover is in the first diffusion position or the second diffusion position. Accordingly, the protective membrane may be able to prevent at least ingress of liquid into the housing when the cover is in the first diffusion position and the second diffusion position. When the protective membrane is also impermeable to solid contaminants, the protective membrane may be able to prevent ingress of liquid and solid contaminants when the cover is in the first diffusion position and the second diffusion position.

[0021] The closed housing does not comprise a desiccant. As used herein, desiccant is intended to mean a hygroscopic substance or device provided for the primary purpose of moisture absorption. This term is not intended to encompass components or component parts which may absorb moisture as an auxiliary function.

[0022] The closed housing may be a sealed closed housing. The sealed closed housing may prevent ingress of contaminants. Furthermore, because the electronics enclosure of the present disclosure does not require the use of a desiccant, no access to the inside of the enclosure is routinely required.

[0023] The closed housing may be configured for use as a lamp. The closed housing may be configured for use as a head lamp. The closed housing may be configured for use as a solar panel. The closed housing may be configured for use as an electronic control unit. The closed housing may be configured for use as a motor control unit. The closed housing may be configured for use as an inverter. The closed housing may be configured for use as a visual sensor. The closed housing may be configured for use as a camera. The closed housing may be configured for use as housing for power electronics. The closed housing may be configured for use as housing for control electronics. The closed housing may be configured for use as housing for an electric motor. The closed housing may be configured for use as at least one of: a lamp, a head lamp, a solar panel, electronic control unit, motor control unit, inverter, visual sensor, camera, power electronics, control electronics, electric motor. The closed housing may be configured to house an electrical component. The closed housing may be configured to house a motor. The closed housing may be configured to house an optical component. The closed housing may be configured to house at least one of: an electrical component, a motor, an optical component.

[0024] According to a second aspect of the present disclosure, there is provided a method for controlling diffusion from an electronics enclosure according to the first aspect. The method comprises: reconfiguring the cover from the first diffusion position to the second diffusion position to increase diffusion from the inside of the closed housing to the external environment and reduce the humidity inside the closed housing.

[0025] The temperature threshold at which the cover is moved from the first position to the second position may be a temperature which is indicative of high humidity inside the closed housing. The method may further comprise reconfiguring the cover from the second position to the first position to reduce diffusion from the inside of the closed housing to the external environment.

[0026] Brief Description of the Figures

[0027] Embodiments of the present invention will now be described, by way of non-limiting example, with reference to the accompanying drawings.

[0028] Figure 1a: A schematic drawing of an electronics enclosure according to the present disclosure with a single vent in a closed position.

[0029] Figure 1 b: A close up view of the opening in Figure 1a, showing the diffusion flow path.

[0030] Figure 2a: A schematic drawing of an electronics enclosure according to the present disclosure with a single vent in an open position.

[0031] Figure 2b: A close up view of the opening in Figure 2a, showing the diffusion flow path.

[0032] Figure 3a: A schematic drawing of an electronics enclosure according to the present disclosure having a temperature sensor inside the enclosure.

[0033] Figure 3b: A schematic drawing of an electronics enclosure according to the present disclosure having a temperature sensor inside and outside the enclosure.

[0034] Figure 3c: A schematic drawing of an electronics enclosure according to the present disclosure having a temperature sensor outside the enclosure.

[0035] Figure 4: A photograph of a cross-section of an electronics enclosure according to the present disclosure.

[0036] Figure 5: A photograph of an electronics enclosure not forming part of the present disclosure. Detailed Description

[0037] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

[0038] Electronics enclosure 10 has a closed housing 11 formed from a plurality of continuous walls 15 and one discontinuous wall 13. The discontinuous wall 13 has an opening 17. In other examples, the opening 17 may consist of a plurality of openings. The opening 17 is covered by protective membrane 16. A temperature-driven mechanical actuator 12 is operable with a cover 14 to move between a first diffusion position (Figure 1a) and a second diffusion position (Figure 2a). Importantly, the electronics enclosure 10 can provide for improved moisture management inside of the enclosure 10 without the need for a desiccant to be placed inside the enclosure.

[0039] Figure 1 b shows a close up view of the cover 14 in the first position. In the first position, the cover 14 is positioned to cover the opening 17 but to maintain a moisture diffusion (and air) flow path 50. This moisture diffusion flow path 50 is defined by a gap 52 between the cover 14 and the discontinuous wall 13 of the housing 11.

[0040] Figure 2b is a close up view of the opening 17 when the cover 14 is in the second diffusion position. In the second diffusion position, the cover 14 is distant from the opening, and the moisture diffusion flow path 55 is unobstructed by the cover 14, such that the moisture diffusion flow path 55 is defined only by the opening 17.

[0041] Electronics enclosures 10 of the present disclosure can be exposed to pressure variations. The opening 17 allows for pressure equalization when the cover 14 is in both the first diffusion position and the second diffusion position. A protective membrane 16 is positioned over the opening 17 and is affixed to the housing 11. The protective membrane 16 is air-permeable and liquid-impermeable. The protective membrane 16 can also prevent ingress of solid contaminants such as dust and dirt particles.

[0042] The temperature-driven mechanical actuator 12 may be one of: a bi-metal switch, a temperature-driven spring, or a wax-based actuator. The temperature-driven mechanical actuator 12 has a threshold temperature at which the temperature-driven mechanical actuator 12 is configured to move the cover 14 from the first diffusion position to the second diffusion position, and vice versa. The temperature threshold is selected as a temperature that is indicative of high moisture inside the enclosure 10. This will be dependent upon the intended purpose of the electronics enclosure 10, the material of construction, and the components to be housed inside the electronics enclosure.

[0043] Electronics enclosure 100 has a closed housing 111 formed from a plurality of continuous walls 115 and one discontinuous wall 113. The discontinuous wall 113 has an opening 117. In other examples, the opening 117 may consist of a plurality of openings. The opening 117 is covered by protective membrane 116. An electrically-driven actuator 112 is arranged to move cover 114 between a first diffusion position (shown in Figure 3a) and a second diffusion position (similar to the position of cover in Figure 2a). The electrically-driven actuator 112 is operatively associated with a control system 120 and temperature sensor 122. The electrically- driven actuator is one of: an electric motor, a solenoid or a piezo-electric actuator. The temperature sensor 122 is positioned inside the enclosure 111 and is configured to measure the temperature of the air inside the enclosure 111. The control system 120 is configured such that the actuator 112 can move the cover 114 to the second diffusion position when the temperature measured by the temperature sensor 122 exceeds a threshold temperature. The temperature threshold is selected as a temperature that is indicative of high moisture inside the enclosure 100. When the temperature measured by the temperature sensor 122 falls below the threshold temperature, the control system 120 is configured such that the actuator can move the cover 114 to the first diffusion position.

[0044] Electronics enclosure 200 has a closed housing 211 formed from a plurality of continuous walls 215 and one discontinuous wall 213. The discontinuous wall 213 has an opening 217. In other examples, the opening 217 may consist of a plurality of openings. The opening 217 is covered by protective membrane 216. An electrically-driven actuator 212 is arranged to move cover 214 between a first diffusion position (shown in Figure 3b) and a second diffusion position (similar to the position of cover in Figure 2a). The electrically-driven actuator 212 is operatively associated with a control system 220 and a first temperature sensor 222 positioned inside the enclosure 211 , and a second temperature sensor 224 that is positioned outside of the enclosure 211. The electrically-driven actuator is one of: an electric motor, a solenoid or a piezo-electric actuator. The first temperature sensor 222 is positioned inside the enclosure 211 and is configured to measure the temperature of the air inside the enclosure 211. The second temperature sensor 224 is positioned outside of the enclosure 211 and is configured to measure the temperature of the air external to the enclosure 211 . The control system 220 is configured to calculate the difference in the temperatures measured by the first temperature sensor 222 and the second temperature sensor 224. The control system 220 is configured such that the actuator 212 can move the cover 214 to the second diffusion position when the temperature difference calculated by the control system 220 exceeds a threshold temperature difference. The temperature difference threshold is selected as a temperature difference that is indicative of high moisture inside the enclosure 200. When the temperature difference falls below the threshold temperature difference, the control system 220 is configured such that the actuator 212 can move the cover 224 to the first diffusion position.

[0045] Electronics enclosure 300 has a closed housing 311 formed from a plurality of continuous walls 315 and one discontinuous wall 313. The discontinuous wall 313 has an opening 317. In other examples, the opening 317 may consist of a plurality of openings. The opening 317 is covered by protective membrane 316. An electrically-driven actuator 312 is arranged to move cover 314 between a first diffusion position (shown in Figure 3c) and a second diffusion position (similar to the position of cover in Figure 2a). The electrically-driven actuator 312 is operatively associated with a control system 320 and temperature sensor 324. The temperature sensor 324 is positioned outside of the enclosure 311 and is configured to measure the temperature of the air external to the enclosure 311. The electrically-driven actuator is one of: an electric motor, a solenoid or a piezo-electric actuator. The control system 320 is configured such that the actuator 312 can move the cover 314 to the second diffusion position when the temperature measured by the temperature sensor 324 exceeds a threshold temperature. The temperature threshold is selected as a temperature that is indicative of high moisture inside the enclosure 300. When the temperature measured by the temperature sensor 324 falls below the threshold temperature, the control system 320 is configured such that the actuator can move the cover 314 to the first diffusion position.

[0046] Example 1 - Automotive Headlamp

[0047] Automotive headlamps contain a large amount of plastics that absorb moisture (e.g., up to 10g in total at 22°C, at 50% relative humidity). This moisture partly gets released when the temperatures increase and is resorbed when temperatures reduce again.

[0048] Figure 4 shows an example electronics enclosure 400 with a prototype setup for the single vent arrangement according to the present disclosure. The electronics enclosure 400 is plastic (polycarbonate (PC)) and houses a cover 414 for a single opening (not visible in Figure 4). The single opening has a diameter of about 10 mm and is formed in one wall of the enclosure 400. The cover 414 is movable by a temperature-driven mechanical actuator 412 having a temperature threshold of about 40 °C. The single opening is covered by a protective membrane (W. L. Gore & Associates GmbH, part number: VE70919, not visible in Figure 4). The cover 414 and actuator 412 can be used to reduce the total amount of moisture in the enclosure 400. The enclosure 400 permits a high diffusion rate from the inside of the enclosure 400 when the moisture is high inside the enclosure.

[0049] There is also a direct correlation between humidity inside the material of the enclosure 400 and the enclosure 400 internal temperature. The cover 414 needs to move to the second diffusion position, when a typical internal temperature is exceeded. The dew point of the enclosure 400 was compared to the dew point of similar electronics enclosure 90 that did not comprise the vent cover and actuator arrangement of the present disclosure. Enclosure 90 is also formed from polycarbonate and has a single pressure equalization opening 95 of 10 mm diameter. The opening is covered with a protective membrane (W.L. Gore & Associates GmbH, part number VE70919).

[0050] Both electronic enclosures 400 and 90 were mounted on a combustion car engine within a car. The car was driven at least once a day for at least 30 minutes each time, and this was repeated over seven days. The total number of times the car was driven over the seven-day period was at least ten. The dew point inside the enclosure 400 was shown to be reduced on average by 5 °C compared to the enclosure 90 during the seven-day period. Accordingly, the electronics enclosure 400 equipped with vent cover 414 and actuator arrangement 412 was shown to reduce the likelihood of condensation formation inside the enclosure.

[0051] While there has been hereinbefore described approved embodiments of the present invention, it will be readily apparent that many and various changes and modifications in form, design, structure and arrangement of parts may be made for other embodiments without departing from the invention and it will be understood that all such changes and modifications are contemplated as embodiments as a part of the present invention as defined in the appended claims.

Claims

Claims1 . An electronics enclosure comprising: a closed housing formed from a plurality of walls and wherein the plurality of walls consists of a plurality of continuous walls and one discontinuous wall having an opening or a plurality of openings; and a single vent arrangement comprising: a protective membrane positioned over the opening or plurality of openings, wherein the protective membrane is air-permeable and liquid-impermeable; a cover positioned over the opening or plurality of openings, wherein the cover is movable relative to the opening or plurality of openings between a first diffusion position and a second diffusion position to allow for different rates of moisture diffusion between the inside of the closed housing and an external environment via the opening or plurality of openings in the first diffusion position and the second diffusion position, wherein the cover allows for diffusion in both the first diffusion position and the second diffusion position; and an actuator arrangement configured to move the cover between the first diffusion position and the second diffusion position in response to a threshold temperature or temperature difference being crossed.

2. The electronics enclosure of claim 1 , wherein the actuator arrangement comprises a temperature-driven mechanical actuator.

3. The electronic enclosure of claim 2, wherein the temperature-driven mechanical actuator is one of: a bi-metal switch, a temperature-driven spring, or a wax-based actuator.

4. The electronics enclosure of claim 1 , wherein the actuator arrangement comprises a first temperature sensor positioned inside the closed housing, and an electrically-driven actuator which is configured to move the cover between the first diffusion position and the second diffusion position based on a measured temperature value from the first temperature sensor being above or below the threshold temperature.

5. The electronics enclosure of claim 4, further comprising a second temperature sensor positioned outside of the closed housing, and wherein the electrically-driven actuator is configured to move the cover between the first and second positions based on a calculated temperature difference being above or below the threshold temperature difference; and wherein the calculated temperature difference is the difference between a measured temperature value from the first temperature sensor and the second temperature sensor.

6. The electronics enclosure of claim 1 , wherein the actuator arrangement comprises a first temperature sensor positioned outside the closed housing, and an electrically-driven actuator which is configured to move the cover between the first diffusion position and the second diffusion position based on a measured temperature value from the first temperature sensor being above or below the threshold temperature.

7. The electronics enclosure of any one of claims 4 to 6, wherein the electrically-driven actuator is one of: an electric motor, a solenoid or a piezo-electric actuator.

8. The electronics enclosure of any one of the preceding claims, wherein the cover is positioned inside of the closed housing.

9. The electronics enclosure of any one of the preceding claims, wherein the cover is positioned outside of the closed housing.

10. The electronics enclosure of any one of the preceding claims, wherein the closed housing is formed from a moisture absorbing material.11 . The electronics enclosure of any of claims 1 to 9, wherein the closed housing is formed from a non-moisture absorbing material.

12. The electronics enclosure of claim 10, wherein the threshold temperature or temperature difference is a temperature or temperature difference at which the moisture absorbing material can release moisture.

13. The electronics enclosure of any one of the preceding claims, wherein the single vent arrangement is operable to reduce the dew point of a volume of air contained inside the closed housing.

14. The electronics enclosure of any one of the preceding claims, wherein the protective membrane is impermeable to solid contaminants.

15. The electronics enclosure of any one of the preceding claims, wherein the closed housing does not comprise a desiccant.

16. The electronics enclosure of any one of the preceding claims, wherein the closed housing is a sealed closed housing.

17. The electronics enclosure of any one of the preceding claims, wherein the closed housing is configured for use as at least one of: a lamp, a head lamp, a solar panel, electronic control unit, motor control unit, inverter, visual sensor, camera, power electronics, control electronics, electric motor.

18. The electronics enclosure of any one of claims 1 to 17, wherein the closed housing is configured to house at least one of: an electrical component, a motor, an optical component.

19. A method for controlling diffusion from an electronics enclosure according to any one of the preceding claims, wherein the method comprises: reconfiguring the cover from the first diffusion position to the second diffusion position to increase diffusion from the inside of the closed housing to the external environment and reduce the humidity inside the closed housing.

20. The method of claim 19, wherein the temperature threshold at which the cover is moved from the first position to the second position is a temperature which is indicative of high humidity inside the closed housing.21 . The method of claim 19 or 20, wherein the method further comprises reconfiguring the cover from the second position to the first position to reduce diffusion from the inside of the closed housing to the external environment.

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