WO1996013751A1

WO1996013751A1 - Regulating systems

Info

Publication number: WO1996013751A1
Application number: PCT/US1995/013971
Authority: WO
Inventors: Erez Yahalomi
Original assignee: Friedman, Mark, M.
Priority date: 1994-10-27
Filing date: 1995-10-26
Publication date: 1996-05-09
Also published as: AU4137396A

Abstract

A system for regulating the value of a radiation dependent parameter has an electrically controlled variably transmissive element (56), a sensor (52) and an adaptation unit (54) responsive to the signal from the sensor to provide a voltage to vary the transmissivity of the element over a substantially continuous range, so as to regulate the radiation dependent parameter. The element may be of liquid crystal type or electrochromic. The adaptation unit may correct for non-linear properties of the system or the system may function in a feedback mode. Additional sensors may be used to prompt switching of the adaptation unit between different modes. The system may regulate several parameters. A multiple layer element structure (171) is also disclosed.

Description

REGULAΉNG SYSTEMS FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to systems for regulating a radiation dependent parameter in general. In particular the systems use elements which have variable transmissivity to certain frequency ranges of electromagnetic radiation to regulate radiation transfer.

Various types of variably transmissive elements are known. The current invention in some of its embodiments uses existing variably transmissive elements which may be of many different types. Some of these existing elements will now be described with reference to Figures 1 and 2.

One type of electrically controlled variably transmissive elements contains molecules or particles which change their orientation in an electric field, thereby altering the optical properties of the element. The most common elements of this type use liquid crystal technology. The best known liquid crystal light valves are twisted nematic devices or similar devices using at least one fixed polarizer, but for many applications the light loss from polarizers is unacceptable. An alternative approach has been offered by me development of encapsulated liquid crystals (NCAP films), polymer dispersed liquid crystal (PDLC) films and Ferroelectric liquid crystal devices. Figure 1 shows a schematic representation of a PDLC film device generally designated 14. Device 14 has a functional layer 16 interposed between two transparent electrodes 18, 20. Each electrode 18, 20 has an electrical contact 22, 24 for connection to an electrical power source (not shown). Functional layer 16 contains liquid crystal droplets 26 dispersed in a polymer film 28. Polymer film 28 is chosen such that the refractive index closely matches that of the liquid crystal along a first of its axes and differs from that along a second of its axes.

In the absence of an electric field droplets 26 are randomly aligned in relation to functional layer 16 so that incoming light encounters a range of different refractive indices not matching that of polymer film 28. Droplets 26 will therefore act as scattering centers causing functional layer 16 to become opaque. When a voltage is applied across electrical contacts 22, 24, generating an electric field between transparent electrodes 18, 20, the first axis of the liquid crystal molecules in droplets 26 largely align with the field. In this configuration the effective refractive index both of the polymer and the liquid crystal droplets for normally incident light are substantially the same and functional layer 16 appears transparent. This technology is described in Electronics & Communication Engineering Journal, April 1992, pp. 91-100.

5 Certain liquid crystals also allow selection of specific frequency ranges, for example cholesteric/polymer dispersed materials (see Appl. Phys. Lett. 63 (11), 13 September 1993 pp. 1471-3). Alternatives to liquid crystal for devices of this type include suspended particle or electrophoretic devices in which the functional layer contains tiny needle-like particles of polyiodides or paraphathite suspended in a

10 substrate between electrodes.

Elements of this type have been used for shading exclusively in on-off switching applications. Although it is known that an intermediate degree of shading is produced when a weaker field is used, these properties have not been exploited. A problem for some applications of these materials is their temperature

15 dependence. The properties of most liquid crystal type devices are somewhat temperature dependent, increased temperature causing disalignment of the molecules and thereby decreasing transmissivity. This may hamper efforts for precise control of transmissivity.

Referring now to Figure 2, another type of electrically controlled variably

20 transmissive elements will be described. This is electrochromic elements, in which a current flows through the element thereby altering the chemical composition of some part thereof between a more transparent composition and a less transparent composition.

Figure 2 shows a schematic representation of a typical electrochromic element,

25 generally designated 30. Element 30 contains a functional layer 32 interposed between two transparent electrodes 34, 36. Each electrode 34, 36 has an electrical contact 38, 40 for connection to an electrical power source (not shown). Element 30 may be mounted on one, or between two passive transparent sheets 42, or they may be omitted. In this example, functional layer 32 has a substructure including a layer

30 44 of the electrochromic material itself, a layer 46 acting as an electrolyte and an ion storage layer 48. The number and arrangement of layers varies according to the materials being used. Materials suitable for electrochromic devices include tungsten(VI) oxide which is transparent and is converted in a cathodic reaction to tungsten bronze which is a dark blue color. Other possibilities include nickel oxides, nickel hydroxide and various organic compounds including viologens and polyaniline. 5 Choice of particular electrochromic materials enables control of radiation within a specific frequency range. Crystalline tungsten oxide film, for example, exhibits a reflectance modulation at infra-red frequencies while maintaining a relatively constant high transmissivity to visible light (see SPIE Vol. 1536 Optical Materials Tech. for Energy Efficiency and Solar Energy Conversion X(1991) pp. 16-

10 17 Fig. 8(b) ). Some Nickel/manganese oxide devices, on the other hand, exhibit switching primarily at visible frequencies with little change in infra-red transmission (ibid. pp. 98-99 Fig. 10).

Regarding the applications of electrochromic devices, U.S. Patent No. 5,105,303 to Bertil Ilhage describes a covering element including an electrochromic

15 layer to which power is supplied by a photoelectric layer. The transmission is therefore reduced depending on the intensity of light reaching the photoelectric layer. The power supplied to the electrochromic layer may be reduced when a temperature sensor or manual control indicates that the shading effect is not required. Electrochromic elements may also be incorporated into mirrors to control glare. A 0 variety of mirror constructions are possible, for example diffusion-controlled electrochromic mirrors in which coloring occurs by diffusion through an outwardly reflecting electrode.

Electrochromic elements generally have a limited lifetime, such that after some number of switching operations their switching is impaired. 5 It would be highly desirable to produce systems making best use of variably transmissive elements to regulate radiation dependent parameters, improving personal comfort and making optimal use of desired radiation while reducing undesired radiation transfer.

SUMMARY OF THE INVENTION The present invention relates to systems for regulating at least one radiation dependent parameter through use of electrically controlled variable transmissivity elements.

Hence, there is provided according to the teachings of the present invention, a system for regulating the value of a first radiation dependent parameter, the system comprising: (a) an electrically controlled first element having at least two electrical connections, the first element containing molecules which change their orientation when a voltage is applied between two of the electrical connections thereby varying the transmissivity of the first element to radiation of at least a first range of frequencies; (b) a first sensor providing a signal indicative of the value of the first radiation dependent parameter; and (c) a first adaptation unit responsive to the signal from the first sensor to provide a voltage to vary the transmissivity of the first element over a substantially continuous range, so as to regulate the first radiation dependent parameter. According to a further feature of the present invention the first adaptation unit produces substantially linear variation of the transmissivity of the first element with respect to the value of the first radiation dependent parameter.

According to a further feature of the present invention the first element is included in a reflector. According to a further feature of the present invention there is also provided a temperature sensor which provides data indicative of the temperature of the first element, the first adaptation unit responding to the data.

According to a further feature of the present invention the first adaptation unit compares the signal with a reference value. According to a further feature of the present invention the first adaptation unit additionally responds to the rate of change of the signal.

According to a further feature of the present invention there is also provided: (a) an electrically controlled second element having at least two electrical connections, the transmissivity of the second element to radiation of at least a second range of frequencies varying when a voltage is applied between two of the electrical connections; (b) a second sensor providing a signal indicative of the value of a second radiation dependent parameter; and (c) a second adaptation unit responsive to the signal from the second sensor to provide a voltage to vary the transmissivity of the second element, so as to regulate the second radiation dependent parameter.

According to a further feature of the present invention the first adaptation unit and the second adaptation unit are included within one adaptation system. According to a further feature of the present invention the first element and the second element are included within one element.

There is also provided according to the teachings of the present invention, a system for regulating the temperature in an enclosed space, the system comprising: (a) a primary element having at least two electrical contacts, the transmissivity of the primary element to at least some frequencies of infra-red radiation varying when a voltage is applied between two of the electrical contacts; (b) a temperature sensor providing a signal indicative of the temperature in the enclosed space; and (c) an adaptation unit responsive to the signal to apply a voltage between the electrical contacts to vary the transmissivity of the primary element as a function of the temperature in the enclosed space.

According to a further feature of the present invention the adaptation unit acts to vary the transmissivity of the primary element substantially continuously.

According to a further feature of the present invention there is also provided a device providing a reference signal indicative of a required temperature, the adaptation unit being responsive to the difference between the signal and the reference signal.

According to a further feature of the present invention the adaptation unit responds to the rate of change of the signal.

According to a further feature of the present invention in which the system has a plurality of the primary elements, there is also provided: (a) a first radiation sensor associated with a first of the primary elements; and (b) a second radiation sensor associated with a second of the primary elements, each of the radiation sensors providing data, the adaptation unit being responsive to the data to vary the transmissivity of the primary elements selectively. According to a further feature of the present invention the adaptation unit is switchable between a first mode and a second mode, the adaptation unit responding in a first manner to the signal when in the first mode, and the adaptation unit responding in a second manner to the signal when in the second mode.

According to a further feature of the present invention there is also provided a sensor providing data, the adaptation unit being responsive to the data to switch between the first mode and the second mode.

According to a further feature of the present invention there is also provided means for regulating the brightness of visible light in the enclosed space.

According to a further feature of the present invention the means includes a electrically controlled variably transmissive secondary element. According to a further feature of the present invention the primary element and the secondary element are included in a single window.

There is also provided according to the teachings of the present invention, a system for adjusting an electrically controlled variably transmissive element to achieve a required value of a radiation dependent parameter, the system comprising: (a) a sensor providing a signal indicative of the value of the radiation dependent parameter; (b) a device providing a reference signal indicative of a required value of the radiation dependent parameter; and (c) an adaptation unit providing a voltage to control the element, the adaptation unit iteratively responsive to the signal and the reference signal to vary the voltage so as to adjust the transmissivity of the element, thereby regulating the value of the radiation dependent parameter.

According to a further feature of the current invention the adjustment is interrupted when the radiation parameter is close to the required value.

There is also provided according to the teachings of the present invention, an electrically controlled variably transmissive element, the element comprising: (a) a plurality of substantially transparent sheet electrodes; and (b) a plurality of layers having a variable transmissivity to electromagnetic radiation, each of the layers being interposed between two of the electrodes, the transmissivity of each of the plurality of layers varying in relation to a voltage applied across the two of the plurality of electrodes. According to a further feature of the present invention a first of the layers has a variable transmissivity over a range of frequencies substantially outside the frequency range of visible light, and a second of the layers has a variable transmissivity to visible light.

According to a further feature of the present invention the variable transmissivity of a first of the plurality of layers and the variable transmissivity of a second of the plurality of layers occur at substantially the same range of frequencies.

According to a further feature of the present invention the first of the plurality of layers has a first minimum transmissivity and the second of the plurality of layers has a second minimum transmissivity.

According to a further feature of the present invention the plurality of layers includes an electrochromic material, and wherein the transmissivity of the plurality of layers is varied substantially simultaneously.

There is also provided according to the teachings of the present invention, a head protector comprising at least one section having a variable transmissivity to some frequencies of visible light. According to a further feature of the present invention the head protector is a hat.

According to a further feature of the present invention the head protector is an umbrella.

According to a further feature of the present invention the section is photochromic.

According to a further feature of the present invention the section is electrically controlled.

According to a further feature of the present invention there is also provided:

(a) a light sensor producing a signal corresponding to the intensity of at least one frequency of visible light; (b) an electrical power source; and (c) an adaptation unit responsive to the signal to supply electrical power to vary the transmissivity of the section.

According to a further feature of the present invention there is also provided at least one photoelectric cell mounted on the head protector. There is also provided according to the teachings of the present invention, a system for controlling the supply of power to a demisting device for demisting a window, the supply being switchable between a connected state and a disconnected state, the system comprising: (a) a first temperature sensor providing a first signal indicative of the air temperature on a first side of the window; (b) a second temperature sensor providing a second signal indicative of the air temperature on an opposing side of the window; and (c) a control unit responsive to said first signal and said second signal to switch between the connected state and the disconnected state.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic representation of a conventional polymer dispersed liquid crystal film element;

FIG. 2 is a schematic representation of a conventional electrochromic element;

FIG. 3 is a block diagram of a system for regulating a radiation dependent parameter, the system being constructed and operative according to the teachings of the present invention; FIG. 4 is a graph of transmittance against control voltage for a typical liquid crystal type element;

FIG. 5 is a block diagram of a temperature control system (T.C.S.) constructed and operative according to the teachings of the present invention;

FIG. 6 is a block diagram of a brightness control system (B.C.S) constructed and operative according to the teachings of the present invention;

FIG. 7 is a schematic diagram of the operation of one embodiment of the invention, the embodiment being constructed and operative according to the teachings of the present invention;

FIG. 8 is a block diagram of a system for regulating light intensity and temperature, the system being constructed and operative according to the teachings of the present invention;

FIG. 9 is a schematic representation of a first electrically controlled variably transmissive element constructed and operative according to the teachings of the present invention; FIG. 10 is a schematic representation of a second electrically controlled variably transmissive element constructed and operative according to the teachings of the present invention;

FIG. 11 is a simplified schematic representation of a multi-layer electrically controlled variably transmissive element constructed and operative according to the teachings of the present invention;

FIG. 12 is a perspective view of a first embodiment of a head protector, constructed and operative according to the teachings of the present invention;

FIG. 13 is a perspective view of a second embodiment of a head protector, constructed and operative according to the teachings of the present invention; and

FIG. 14 is a block diagram of a system for controlling a window demisting system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of systems for controlling radiation dependent parameters.

The principles of systems according to the present invention may be better understood with reference to the drawings and the accompanying description.

With reference now to Figure 3, there is shown a block diagram of a system generally designated 50 for controlling a radiation dependent parameter, system 50 being constructed and operative according to the teachings of the current invention. System 50 has a sensor 52, an adaptation unit 54 and an electrically controlled variably transmissive element 56. System 50 may also have a setting device 58 providing a reference signal indicative of the required value of the radiation dependent parameter. System 50 may be used to regulate any parameter which depends substantially on the transfer of electromagnetic radiation of some range of frequencies. Examples of such parameters include the brightness of visible light and temperature. Sensor 52 provides a signal indicative of the value of the parameter to be regulated. Adaptation unit 54 is responsive to this signal. Adaptation unit 54 provides a regulating voltage to vary the transmissivity of element 56, over a substantially continuous range, to radiation in the relevant frequency range, thereby regulating the radiation dependent parameter. In this way, adaptation unit 54 adapts element 56 to a state appropriate for the current conditions.

In a first set of embodiments, element 56 is of the liquid crystal type, herein taken to mean any electrically controlled variably transmissive element which contains molecules or particles whose orientation changes when they are exposed to an electric field, thereby changing the optical properties of the element. This includes liquid crystal devices, such as PDLC film and NCAP devices, Surface Stabilized Ferroelectric devices and also those which do not use liquid crystal materials such as electrophoretic devices. It is a particular feature of certain embodiments of the invention that adaptation unit 54 varies the transmissivity of element 56 substantially continuously to control radiation transfer precisely. The specific design and function of adaptation unit 54 to achieve this depends both on the properties of the particular type of element 56 used, and on the type of application. Details specific to each application will be described with reference to the embodiments below.

With reference now to Figure 4, there is shown a plot 62 of the relation between voltage and transmittance for a typical liquid crystal type element. It is seen that the transmittance varies continuously over a specific range of voltage, in this example 7 - 30 V. r.m.s., as the proportion of molecules aligned with the electric field varies. Elements of the liquid crystal type generally require a continuous voltage of the appropriate amplitude to maintain the desired transmissivity. In most cases, A.C. voltage is used to avoid causing breakdown of the liquid crystal. Adaptation unit 54 is therefore designed to produce an A.C. regulating voltage varying over the relevant range. In certain cases a voltage is required only to effect a change in transmissivity, for example with surface stabilized ferroelectric devices. For such devices, adaptation unit 54 is designed to produce an appropriate regulating voltage to change the transmissivity when required, and then to interrupt the supply until a further change is required. In certain embodiments, the operation of system 50 is improved by designing adaptation unit 54 to vary the transmissivity of element 56 linearly with respect to the signal from sensor 52. For a given element, this requires inverting the function represented by plot 62, by use of analogue circuitry, computerized control programmed with the appropriate characteristic, or any other known method.

Embodiments in which system 50 includes feedback, examples of which will be described below, have an advantage since corrections for non-linearity and temperature variation become less significant, and are generally omitted.

In some embodiments, the regulating voltage from adaptation unit 54 is scaled or otherwise modified in response to the signal provided by setting device 58. Variations of this and other features of system 50 will be described with reference to the specific examples below. With reference now to Figures 5 and 6, two specific embodiments of system

50 and variations thereof will be described. It should be noted that system 50 is a generalized system which may be used to regulate any radiation dependent parameter, and to which further features may be added. The following embodiments are intended only by way of example, to illustrate features which may be used in any other embodiment, as appropriate.

Figure 5 is a block diagram of an embodiment of the invention, generally designated 64, for regulating the temperature within an enclosed space, which may be, for example, a building or a single room, system 64 being constructed and operative according to the teachings of the current invention. In this embodiment, system 64 has a temperamre sensor 66, an adaptation unit 68 and an electrically controlled element 70 having a variable transmissivity to at least some frequencies of infra-red radiation. System 64 also has a setting device 72 providing a reference signal indicative of a desired temperamre, and a radiation sensor 74.

Temperature sensor 66 may be chosen from the wide range of commercially available temperature sensors suited to a range of temperamre which includes the desired temperature. Suitable sensors include those which themselves produce a signal voltage and those which modify a supplied voltage to provide a signal. Temperamre sensor 66 may also be an infra-red sensor. Temperamre sensor 66 is positioned within the enclosed space to sense me prevailing temperamre in the space. Alternatively, temperamre sensor 66 may be positioned close to a point at which temperamre regulation is particularly critical. Element 70 may be positioned in one of a wide range of positions in which variation of the transmissivity of element 70 alters the amount of heating or cooling of the enclosed space. In window-type applications, element 70 is used for glazing which variably restricts the amount of heat energy entering from incident sunlight, 5 or the amount of radiant heat loss from warm surfaces within the enclosed space. Alternatively, element 70 may be part of a variable reflector. This may be achieved by placing element 70 in front of a passive reflector, or the structure of element 70 may itself include a reflector as an electrode. In this form, element 70 may be used as external cladding for walls to variably reduce solar heating of the

10 walls and thereby of the enclosed space. Element 70 constructed as a variable reflector may also be used as a back reflector for a furnace or other heating system to vary the rate of heat-loss through adjacent walls.

In some embodiments of the invention, adaptation unit 68 is a combination of electronic components which produces a voltage to vary the transmissivity of element

15 70 linearly with respect to the parameter indicated by the signal from temperamre sensor 66 as mentioned above. Correction may also be made for any non-linearity of temperature sensor 66. However, in many embodiments, adaptation unit 68 has one or more additional features as will be described. In some embodiments, adaptation unit 68 is a computerized control system.

20 In one embodiment, adaptation unit 68 compares the signal provided by temperamre sensor 66 with the reference signal from setting device 72, indicative of the required temperature, to determine the direction and size of the required temperamre change. If the current temperamre is higher than the required temperature, adaptation unit 68 changes the regulating voltage to reduce the

25 transmissivity of element 70. If the current temperamre is too low, adaptation unit 68 changes the regulating voltage to increase the transmissivity of element 70. The change is added to the previous level of the regulating voltage. Adaptation unit 68 then pauses to allow the change to take effect before repeating the process. Thus the control voltage is modified iteratively, adjusting element 70 towards the optimal state

30 for current conditions.

A further preferred feature of certain embodiments of the current invention is that adaptation unit 68 also responds to the rate of change of the signal from temperature sensor 66 to alter, for example, the magnitude of change of transmissivity. The way in which the change in transmissivity depends on the rate of change of temperature and on its current deviation from the required value may take many forms. In one example, if the temperature is moving away from the 5 required temperature, adaptation unit 68 changes the transmissivity in proportion to the magnitude of the rate and with opposite sign. When the temperature is static or changing towards the required temperature, adaptation unit 68 changes the transmissivity in proportion to the deviation from the required temperature. An alternative example uses both measurements simultaneously, modifying the

10 dependence on temperature deviation according to the rate of change. Thus if a first change of transmissivity does not effect the temperature sufficiently, adaptation unit 68 will produce a larger change. If the temperature is rapidly approaching the required value, adaptation unit 68 reduces the size of the changes in transmissivity and then reverses the direction of the changes to prevent overshooting of the required

15 temperature.

A further preferred feature of certain embodiments of the current invention is that adaptation unit 68 is programmed to be self-adaptive to learn, for example, what size of changes in transmissivity are effective to alter the temperature.

In some embodiments, adaptation unit 68 alters the transmissivity of element

20 70 until it is optimally adjusted to maintain the required temperamre in the current conditions, and then maintains a constant state until those conditions change.

In many applications, system 64 needs to function in more than one mode, depending on environmental factors. For example in a window type application, during the day when sunlight is incident on element 70 high transmission causes

25 heating of the enclosed space and low transmission reduces heating. At night, if surfaces within the enclosed space are warmer than the surfaces viewed through element 70, high transmission allows radiant heat loss, and low transmission reduces cooling. Thus in this example system 64 is required to decrease the transmissivity of element 70 when the temperamre rises during daylight whereas at night the

30 transmissivity should be increased when the temperamre rises. Certain applications may also have a summer mode and a winter mode. In applications requiring more than one control mode, adaptation unit 68 is made to be switchable between the appropriate number of modes of operation. Switching between the modes may be done manually or automatically in response to the signal from radiation sensor 74 (day/night switching) or an additional outdoor temperature sensor (summer/winter switching). System 64 may control a plurality of elements similar to element 70. In window type applications each element 70 may be provided with a separate radiation sensor 74 appropriately positioned to identify which elements 70 are admitting most radiant heat during daytime functioning. In this case, adaptation unit 68 will control each element 70 independently. Referring now to Figure 6, mere is shown a block diagram of an embodiment of the invention, generally designated 76, for regulating the intensity of at least one range of frequencies of visible light, system 76 being constructed and operative according to the teachings of the current invention. System 76 has a light sensor 78, an adaptation unit 80 and an electrically controlled variably transmissive element 82. System 76 may also have a setting device 84 providing a reference signal indicative of the required light intensity, and a sensor 86 for measuring the temperamre of element 82.

Light sensor 78 can be any conventional type of sensor which provides data indicative of the intensity of at least one frequency of visible light falling on it. In one embodiment, light sensor 78 is located such that the incident radiation to the sensor in not effected by the transmissivity of element 82, for example outside a window containing element 82. This embodiment is particularly useful when system 76 is used to control glare from an area viewed through element 82. In such a case, the transmissivity of element 82 must be a function of the brightness of the light from the area viewed only, remaining constant when another light source illuminates the inside of element 82.

In a further embodiment, light sensor 78 is located so as to be directly or indirectly shaded by element 82. In this embodiment, system 76 provides feedback thereby precisely maintaining the required intensity. The response of a liquid crystal type element is typically sufficiently fast that substantially continuous adjustment may be made without causing oscillation. In certain embodiments, adaptation unit 80 additionally responds to the signal from sensor 86 indicative of the temperature of element 82. As the temperature rises, adaptation unit 80 increases the voltage supply to compensate for the tendency of the molecules to disalign. Returning now to the generalized system of Figure 3, it should be noted that there is a further set of embodiments in which element 56 is of the electrochromic type. Use of an electrochromic element requires a different design of adaptation unit 54, since when no voltage is applied element 56 remains in a constant state and a d.c. voltage is applied to reduce the transmissivity and reversed to increase the transmissivity. Adaptation unit 54 may produce a step type voltage in which a constant voltage is switched on for a specific duration to cause a certain change in transmissivity, the duration corresponding to the size of the change. A variable voltage may also be used. To reverse the direction of change, the polarity of the voltage is reversed. With this redesigned adaptation unit 54, an electrochromic element may be used for element 56 in the temperature regulation and feedback brightness regulation systems described above, in both transmissive and reflective applications. Electrochromic variable reflectors of designs other than those described above may also be used. Certain other features differ between applications using liquid crystal type elements and electrochromic elements. Electrochromic elements do not generally require the temperature compensation which was described above for liquid crystal elements. When an electrochromic element is used in a light control system with feedback, adaptation unit 54 must pause after each adjustments to allow the element to reach its new state before calculating the next adjustment. This pause is not required in the equivalent liquid crystal system since the response is very rapid.

As mentioned above, in some embodiments, adaptation unit 54 alters the transmissivity of element 56 until it is optimally adjusted to maintain the radiation dependent parameter at the required value in the current conditions, and then maintains a constant state until reactivated. This feature is of particular importance for electrochromic applications since it minimizes the number of adjustments made to element 56, thereby prolonging its lifetime. Reactivation may be in response to manual control, or automatically when the parameter varies unacceptably from the required value.

Figures 7A, 7B, 7C and 7D illustrate the operation of an embodiment of the invention for regulating temperature which utilizes absorptive and reflective low- transmissivity properties. In this embodiment, element 56 includes a first variably transmissive layer 88 having a predominantly absorptive low-transmissivity state and a second variably transmissive layer 90 having a predominantly reflective low- transmissivity state. Ray 92 represents a path of infra-red radiation from hot surfaces within a room, and ray 94 represents a path of incoming solar radiation. Figures 7A and 7B illustrate the function of this embodiment in a summer mode, and Figures 7C and 7D in a winter mode. Layers 88, 90 are controlled independently and continuously by adaptation unit 54 to achieve the optimal combination of reflection and absorption. The Figures represent only the extremes of these ranges. Figure 7A shows both layers 88, 90 in reduced transmissivity states, layer 88 being predominantly absorptive and layer 90 being predominantly reflective. This configuration is used when the temperature is above that required and intense sunshine is incident on element 56. In this case, ray 94 is reflected by layer 90 as ray 96, thereby excluding incident sunlight. At the same time, the internal reflection of radiant heat from appliances and other heat sources, represented by ray 92, is controlled by varying the absorbance of layer 88.

Figure 7B shows both layers 88, 90 in high transmissivity states. This configuration is used when the temperamre is below that required and intense sunshine is incident on element 56, thereby allowing radiant heating (ray 98). Figure 7C corresponds to a winter scenario in which the external level of thermal radiation is weak compared to that produced by an appliance inside the room. When the temperature is above that required, both layers 88, 90 change towards high transmissivity states, allowing radiant heat loss (ray 100) from the room.

Figure 7D corresponds to a similar winter scenario, when the temperature is below that required. In this case, layer 88 is maintained at high transmissivity while the transmissivity of layer 90 is reduced, thereby reflecting radiant energy (ray 102) back into the room. This embodiment may switch between the summer mode and the winter mode in response to an additional sensor, for example an outdoor temperature sensor, or a sensor measuring the intensity of sunlight incident on element 56.

This two layer element may be expanded by addition of a tiiird layer so that a variably reflective layer is interposed between two variably absorbent layers, or vice-versa. This enables independent selection of absorbent or reflective properties to radiation incident from each side, or high two-way transparency.

This element may also be used in other applications, including visible light regulation. In temperature regulation applications, a layer with variable transmissivity to visible light may be added to enable additional control of brightness.

In a further embodiment, element 90 may be replaced by a bi-directional reflector, or variable reflector which is not transparent. In this embodiment, element 56 has extreme states equivalent to Figures 7 A and 7D.

Other embodiments of the invention regulate more than one radiation dependent parameter. Figure 8 shows a block diagram of an system, generally designated 108, for regulating light intensity and temperature, system 108 being constructed and operative according to the teachings of the current invention. System 108 has a light sensor 110, a first adaptation unit 112, an electrically controlled element 114 with a variable transmissivity to light, and may also have a sensor 116 . measuring the temperature of element 114 for temperamre compensation. A setting device (not shown) may also be added, providing a signal indicative of the required brightness. System 108 also has a temperamre sensor 118, a second adaptation unit 120 and an electrically controlled element 122 with a variable transmissivity to infra¬ red. System 108 is further provided with a setting device 124 providing a reference signal indicative of a desired temperamre, and an additional sensor 126. Element 114 and element 122 may be included within a single window 128.

It may be seen that system 108 is a modular system made up of two sub¬ systems. The first sub-system 130 is similar in construction and operation to system 76 for control of light intensity, and may have any combination of the features described therein. The second sub-system 132 is similar in construction and operation to system 64 for control of temperamre, and may have any combination of the features described therein. Sub-systems 130, 132 may be operated together or independently, as desired.

Elements 114 and 122 may be separate window or reflector type elements. Alternatively, two electrochromic or liquid crystal type elements with frequency 5 selective low-transmissivity states as described previously can be used. In this case elements 114 and 122 may be placed one behind the other or be included within window 128. Window 128 may be a single multi-layered element, as described below.

System 108 may control independently a plurality of elements 114 and a 10 plurality of elements 122 to achieve the optimal state for each element separately.

Adaptation units 112, 120 may be two separate single parameter adaptation units or a single multi-parameter adaptation unit.

Additional sensor 126 is a radiation sensor to cause switching between day¬ time and night-time modes of temperamre control as described above. Alternatively, 15 additional sensor 126 is an outside temperamre sensor to cause switching between summer and winter modes. In the latter case, the signal from light sensor 110 may additionally be used to causing switching between a day-time and a night-time mode of adaptation unit 120.

With reference now to Figures 9, 10 and 11, a new electrically controlled 0 variably transmissive element will be described. Figure 9 shows a schematic representation of an electrically controlled variably transmissive element generally designated 140, constructed and operative according to the teachings of the current invention. Element 140 has a first functional layer 142 interposed between transparent electrodes 144, 146 and a second functional layer 148 interposed between

25 transparent electrodes 150, 152. Functional layers 142, 148 may be of electrochromic or liquid crystal type, and may have a substructure as known in the art. Each electrode 144, 146, 150, 152 has an electrical contact 154, 156, 158, 160 respectively. Electrodes 146 and 150 are separated by an insulating transparent sheet

162. Element 140 may be faced on one or both sides with passive transparent layers

30 164.

Figure 10 shows a schematic representation of an electrically controlled variably transmissive element generally designated 166, constructed and operative according to the teachings of the current invention. Element 166 is similar to element 140 and equivalent elements are labelled similarly. Element 166 has a common electrode 168 between functional layers 142 and 148. Common electrode 168 has an electrical contact 170. Although the illustrations are of two layer structures (meaning two functional layers with their respective electrodes), many layer structures are intended within the scope of the current invention. Figure 11 is a simplified schematic representation of a multi-layer electrically controlled variably transmissive element, generally designated 171, constructed and operative according to the teachings of the current invention. Element 171 is similar to element 140, with variable transmissivity layers 172, 174, 176 and 178 each including a functional layer and two electrodes (not shown). Layers 172, 174, 176 and 178 are separated by passive transparent sheets 180.

The choice of materials and structure of functional layers 142, 148 will depend on the intended application as will be explained.

In a first application, functional layer 142 is chosen to have variable transmissivity specifically in a first range of frequencies whilst maintaining a high transmissivity in a second range of frequencies, and functional layer 148 is chosen to have a variable transmissivity at least in the second range of frequencies, preferably mamtaining a high transmissivity in the first range of frequencies. Thus by applying a voltage across the appropriate electrodes it is possible to control the transmission of two different frequency ranges through element 140 or 166 substantially independently.

In a second application, particularly important for electrochromic elements, functional layers 142, 148 contain the same electrochromic material and are varied simultaneously to produce an effect equivalent to a single thicker layer of electrochromic material. Since the speed of response of an electrochromic element is limited by diffusion processes, a reduction in layer thickness significantly reduces response time. Furthermore, when several layers are controlled in parallel, a small change in the transmissivity of each layer produces the equivalent of a large change in a single layer, reducing the response time significantly. Excellent results are given by a multi-layer structure of five layers, in one example reducing the response time for a given change in transmissivity from five seconds for a single layer device to less than 0.4 seconds for a device containing five equivalent layers. When element 166 with common electrode 168 is used, simultaneous control of multiple layers may be simplified by constructing adjacent layers 142, 148 with opposite polarity, alternate electrical connections 154, 160 being at equal potential relative to electrical connection 170.

In a further application, relevant to both electrochromic and liquid crystal elements, functional layers 142, 148 are constructed to have different minimum transmissivities such that, at constant voltage, different transmissivities can be produced by selection of electrical connections 154 and 156, or 158 and 160. In electrochromic elements the switching is performed between constant voltage of one polarity and the reverse polarity. In liquid crystal type elements on-off switching is used. In one example, element 140 or 166 is expanded to have seven or eight layers having minimum transmissivities in binary ratio. In this case, a wide range of transmissivities can be produced by simple switching of selected layers at constant voltage.

In a further application, element 140 or 166 is used to extend the low end of the range of variable transmissivity. If, for example, functional layers 142, 148 provide variable transmission between 30% and 90%, element 140 or 166 provides control between 9% and 81 % transmission (neglecting reflective losses). This application is of particular importance in cases in which structural or production limitations preclude control at low transmissivities using a single layer.

In any of the above applications, undesired reflections from internal interfaces of element 140 or 166 may be minimized by choice of material for transparent layers 164 and for transparent sheet 162 to best match the refractive index of adjacent electrode 144, 146, 150, 152 or 168. A further method is the use of anti-reflective coatings to reduce undesired reflection at internal interfaces.

With reference now to Figures 12 and 13, various forms of head protector, constructed and operative according to the current invention, will be described. The term head protector as herein used includes hats, visors and other head coverings, as well as umbrellas, parasols and sunshades, both of hand-held and fixed varieties. Figure 12 shows an embodiment of the head protector, generally designated 182, in the form of a hat. Head protector 182 has a part 184 having a variable transmissivity to light. Head protector 182 may also have a light sensor 185, an adaptation unit 186 and a photoelectric cell 188. Part 184 may be the whole or a part of a visor, or any other portion of head protector 182. Head protector 182 itself may be in the form of a visor.

In a simplified embodiment of the invention, part 184 is made of at least partially transparent material with a photochromic layer, so that part 184 becomes less transmissive when exposed to bright light. In this case light sensor 185, adaptation unit 186 and photoelectric cell 186 are omitted.

In a second embodiment, part 184 contains an electrically controlled variably transmissive element of one of the aforementioned types. In this embodiment, adaptation unit 186 is responsive to the signal provided by light sensor 185 to control the transmissivity of part 184 as in the previously described control systems. The electrical power required may be provided by one or more photoelectric cell 188 as shown, or by a battery pack (not shown). Part 184 may additionally or alternatively be manually adjustable.

Figure 13 shows an embodiment of the head protector, generally designated

190, in the form of an umbrella, having a protective surface 192 and a support 194. Protective surface 192 has at least one part 196 having a variable transmissivity to light and is provided with a light sensor 198. There is also an adaptation unit 200 and a battery 202 built into support 194.

The function of head protector 190 is equivalent to that of head protector 182. Head protector 190, just like head protector 182, has a simplified photochromic embodiment in which light sensor 198, adaptation unit 200 and battery 202 are omitted, as well as a second embodiment using an electrical control system.

Battery 202 may be replaced by one or more photoelectric cell mounted on head protector 190.

It is an additional feature of head protector 190 that support 194 provides a convenient housing for adaptation unit 200 and battery 202. The positions mentioned here are by way of example and may be varied as required. Support 194 may be for hand-held use as shown, or attachable to a base for freestanding use. With reference now to Figure 14, a further regulating system will be described. Figure 14 shows a system, generally designated 210, for controlling the supply of power to a window demisting device. System 210 has a first temperature sensor 212, a second temperature sensor 214, a control unit 216 and a demisting device 218.

Control unit 216 is responsive to the signal from first temperamre sensor 212 indicative of the air temperature inside the window, for example inside a car or a room, and to the signal from second temperature sensor 214 indicative of the air temperature outside the window to connect or disconnect demisting device 218 from a power supply (not shown).

Demisting device 218 is a hot air fan. Alternatively it may be electrical heating elements within the window.

In one embodiment, condensation conditions are indicated when the signal from second sensor 214 is indicative of an outside temperamre below a certain value, and when the difference between the two signals is indicative of a temperature difference between inside and outside the window which is greater than some predetermined value. In this case, control unit 216 connects demisting device 218 to the power supply. The power may be disconnected, either after a fixed time period, or when the conditions change.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope and the spirit of the invention.

Claims

WHAT IS CLAIMED IS:

1. A system for regulating the value of a first radiation dependent parameter, the system comprising:

(a) an electrically controlled first element having at least two electrical connections, said first element containing molecules which change their orientation when a voltage is applied between two of said electrical connections thereby varying the transmissivity of said first element to radiation of at least a first range of frequencies;

(b) a first sensor providing a signal indicative of the value of the first radiation dependent parameter; and

(c) a first adaptation unit responsive to the signal from said first sensor to provide a voltage to vary the transmissivity of said first element over a substantially continuous range, so as to regulate said first radiation dependent parameter.

2. A regulating system as in claim 1, wherein said first adaptation unit produces substantially linear variation of the transmissivity of said first element with respect to the value of the first radiation dependent parameter.

3. A regulating system as in claim 1, wherein said first element is included in a reflector.

4. A regulating system as in claim 1, further comprising a temperamre sensor which provides data indicative of the temperature of said first element, said first adaptation unit responding to said data.

5. A regulating system as in claim 1, wherein said first adaptation unit compares said signal with a reference value.

6. A system for regulating the temperamre in an enclosed space, the system comprising: (a) a primary element having at least two electrical contacts, the transmissivity of said primary element to at least some frequencies of infra-red radiation varying when a voltage is applied between two of said electrical contacts;

(b) a temperature sensor providing a signal indicative of the temperature in the enclosed space; and

(c) an adaptation unit responsive to said signal to apply a voltage between said electrical contacts to vary the transmissivity of said primary element as a function of the temperature in the enclosed space.

7. A regulating system as in claim 6, wherein said adaptation unit acts to vary the transmissivity of said primary element substantially continuously.

8. A regulating system as in claim 6, further comprising a device providing a reference signal indicative of a required temperature, said adaptation unit being responsive to the difference between said signal and said reference signal.

9. A regulating system as in claim 6, wherein said adaptation unit responds to the rate of change of said signal.

10. A regulating system as in claim 6, having a plurality of said primary elements, further comprising:

(a) a first radiation sensor associated with a first of said primary elements; and

(b) a second radiation sensor associated with a second of said primary elements, each of said radiation sensors providing data, said adaptation unit being responsive to said data to vary the transmissivity of said primary elements selectively.

11. A regulating system as in claim 6, wherein said adaptation unit is switchable between a first mode and a second mode, said adaptation unit responding in a first manner to said signal when in said first mode, and said adaptation unit responding in a second manner to said signal when in said second mode.

12. A regulating system as in claim 11, further comprising a sensor providing data, said adaptation unit being responsive to said data to switch between said first mode and said second mode.

13. A regulating system as in claim 6, further comprising means for regulating the brightness of visible light in the enclosed space.

14. A regulating system as in claim 13, wherein said means includes a electrically controlled variably transmissive secondary element.

15. A system for adjusting an electrically controlled variably transmissive element to achieve a required value of a radiation dependent parameter, the system comprising:

(a) a sensor providing a signal indicative of the value of the radiation dependent parameter;

(b) a device providing a reference signal indicative of a required value of the radiation dependent parameter; and

(c) an adaptation unit providing a voltage to control the element, said adaptation unit iteratively responsive to said signal and said reference signal to vary said voltage so as to adjust the transmissivity of the element, until the value of the radiation dependent parameter is close to said required value.

16. An electrically controlled variably transmissive element, the element comprising: (a) a plurality of substantially transparent sheet electrodes; and (b) a plurality of layers having a variable transmissivity to electromagnetic radiation, each of said layers being interposed between two of said electrodes, the transmissivity of each of said plurality of layers varying in relation to a voltage applied across said two of said plurality of electrodes.

17. A variably transmissive element as in claim 16, wherein one of said layers has a predominantly reflective low-transmissivity state.

18. A variably transmissive element as in claim 16, wherein a first of said layers has a variable transmissivity over a range of frequencies substantially outside the frequency range of visible light, and a second of said layers has a variable transmissivity to visible light.

19. A variably transmissive element as in claim 16, wherein the variable transmissivity of a first of said plurality of layers and the variable transmissivity of a second of said plurality of layers occur at substantially the same range of frequencies.

20. A variably transmissive element as in claim 19, wherein said first of said plurality of layers has a first minimum transmissivity and said second of said plurality of layers has a second minimum transmissivity.

21. A variably transmissive element as in claim 19, wherein said plurality of layers includes an electrochromic material, and wherein the transmissivity of said plurality of layers is varied substantially simultaneously.

22. A head protector comprising at least one section having a variable transmissivity to some frequencies of visible light.

23. A head protector as in claim 22, wherein the head protector is a hat.

24. A head protector as in claim 22, wherein the head protector is an umbrella. 27

25. A head protector as in claim 22, wherein said section is photochromic.

26. A head protector as in claim 22, wherein said section is electrically controlled.

27. A head protector as in claim 26, further comprising:

(a) a light sensor producing a signal corresponding to the intensity of at least one frequency of visible light;

(b) an electrical power source; and

(c) an adaptation unit responsive to said signal to supply electrical power to vary the transmissivity of said section.

28. A head protector as in claim 26, further comprising at least one photoelectric cell mounted on the head protector.

29. A system for controlling the supply of power to a demisting device for demisting a window, the supply being switchable between a connected state and a disconnected state, the system comprising:

(a) a first temperature sensor providing a first signal indicative of the air temperamre near a first side of the window;

(b) a second temperamre sensor providing a second signal indicative of the air temperamre near an opposing side of the window; and

(c) a control unit responsive to said first signal and said second signal to switch between the connected state and the disconnected state.