Abstract:
A spectral radiometer system, measures incoming light intensity and spectral distribution in different wavelength-bands. An additional data storage device allows recording of the measured data. The inclusive sensor system yields very high sensitivity to incoming light. Furthermore, outstanding linearity of the detector response over several orders of magnitude of incoming light is achieved. Additional benefits are ultra low power consumption and minimum size. The sensor system can be used in remote solar radiation monitoring applications like mobile solar power units as well as in long-term environmental monitoring systems where high precision and low power consumption is a necessity.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is generally related to measuring incoming light, data acquisition and power control. In particular the present invention includes a data storage device for recording measured data, and a sensor system yielding very high sensitivity to incoming light, where an increase of linearity of detector response to incoming light is achieved by several orders of magnitude over conventional sensor systems. The present invention provides ultra low power consumption and minimum size. The sensor system can be used in remote solar radiation monitoring applications like mobile solar power units as well as in long-term environmental monitoring systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Mobile solar power units are recognized as promising means of decreasing the dependence of the military on fossil fuel generated power. To date, a multitude of mobile solar powered systems are under development that range from human portable, highly flexible, photovoltaic blankets, solar powered aircraft, trailer based hybrid power units, and underwater sensor applications. Spectral radiometers are widely used to measure the spectrum of emitted, transmitted or reflected light of a given material in numerous fields of the modern economy. Applications of spectral radiometers include environmental monitoring (Sun, water, soil, flora, etc), production control (liquids, solids, solutions, etc), medicine (tissue, blood, drugs, solutions, etc), opto-electronics (light emitters), trade (food, and other perishable goods) as well as monitoring in the fields of military and security operations (such as, object identification and sensing). Current spectral radiometers generally require either sophisticated optical components for beam forming and diffraction, refined electronic components for the signal readout or moving parts which often lead to high production costs. Furthermore, conventional spectral radiometry systems are shock-sensitive; they require long measurement times, and they consume considerable amounts of electrical power, making their use in remote environments disadvantageous. In contrast, the instant invention discloses a spectral radiometer having a novel minimum size, having ultra-low power, having integrated data storage functionality and a battery lifetime of up to several years, including a range of from less than about 2 years or less up to at least about 5 years or more, such that 10 or 15 years or more can be achieved. In addition, the system can be produced at the expense of less than twenty dollars ($20) and features very high sensitivity and linearity. Because of the modularity of the system, adjustment to different wavelength-bands, as well as operational capabilities involving different light intensities are easily possible, providing a tailored solution to the customers&#39; needs. There are no alternative devices having comparably small dimensions. 
       SUMMARY OF THE INVENTION 
       [0003]    Exemplary embodiments describe a novel spectral radiometer system, which measures incoming light intensity and spectral distribution in different wavelength-bands. An additional data storage device allows recording of the measured data. The inclusive sensor section yields very high sensitivity to incoming light. Furthermore, outstanding linearity of the detector response over several orders of magnitude of incoming light is achieved. Additional benefits are ultra low power consumption and minimal size. The sensor system can be used in remote solar radiation monitoring applications, such as mobile solar power units, as well as in long-term environmental monitoring systems, where high precision and ultra low power consumption are required. 
         [0004]    Exemplary embodiments have wide applications in military and civilian tactical solar power radiation assessments, such as with solar power plant planning, and solar radiation monitoring. In addition, exemplary embodiments have wide application in radiation assessments related to agriculture, architecture, construction, power plant operations, environmental protection, ergonomics and the practice of medicine. Also, the measurement of the energy in different wavelength-bands of short-duration light pulses (burst measurements) can be carried out. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  illustrates a schematic diagram of a diode  102  based spectral radiometer  100 , having three diodes  102 . 
           [0006]      FIG. 2A  illustrates a schematic of the three-diode sensor section  201 , the diode  102  based spectral radiometer  100 , where three diodes  102  have a common anode ( 104  connectors). The cathode  105  of each of the three diodes  102  has its own connector pin. The three diodes  102  are encapsulated in a small transparent housing (i.e., 3 diode sensor section  201 ), with dimensions including a diameter of roughly 5 mm. Such a package is commercially available and used for LEDs. 
           [0007]      FIG. 2B  illustrates the encapsulated three-diode sensor section  201  component of the spectral radiometer  100 . 
           [0008]      FIGS. 3A and 3B  illustrate graphs of the electrical operation cycles of the diode  102  based spectral radiometer  100 . 
           [0009]      FIG. 4  illustrates an ultra low power solid state spectral radiometer  100  used in a military maneuver. Encapsulated three-diode sensor section  201  components are used to detect and measure the light intensity from different directions. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]    The subject invention is a spectral radiometer  100  with sensitivity in several, adjustable wavelength-bands having adjustable detector sensitivity. Novel aspects of the exemplary embodiments of the spectral radiometer  100  include the ability to achieve fast, precise, multi-wavelength-band sensitive measurements with extraordinary linearity and the ability to operate over several orders of magnitude of incoming light intensity at low cost, (where an order of magnitude ratio scaled to 10, yields linear operability approaching at least over three orders of magnitude of incoming light intensity). 
         [0011]    Description: The device is shown in a three-diode sensor section  201  configuration in  FIG. 1 ; however, the configurations of exemplary embodiments of the spectral radiometer  100  can include four or more diodes  102 , where the number of diodes  102  incorporated is limited only by cost and space (i.e., design choice of the size requirement) of the desired physical configuration of the device. In addition, exemplary embodiments of the spectral radiometer  100  design can incorporate less than three diodes. A diode  102  is referred to in this context as an element with spectrally dependent charge generation or recombination properties and/or spectrally dependent electrical resistance properties. In a configuration of the exemplary embodiment, each junction of a first diode  102 , a second diode  102  and a third diode  102  is formed from a semiconductor material of different effective bandgap energy. The bandgap energy, the reflection and absorption properties of each diode  102  define the wavelength range within which the first, second and third diodes  102  can absorb light. As shown in  FIG. 2B , several diodes  102  can be encapsulated in a single, small housing forming the encapsulated three diode sensor section  201 , where the housing of the encapsulated three diode sensor section  201  can be a molded housing having dimensions of only a few millimeters (i.e., 1 or 2 mm) up to about 5 mm or more diameter and/or length or height. The anode  104  of each diode  102  is connected to ground ( 110 ). The cathode  105  of each diode  102  is connected to a first port  109 , a second port  109  and a third port  109  of a central processing unit  101 , (herein referred to as CPU  101 ), where CPU  101  can have a plurality of input-output ports. In addition CPU  101  includes a computer processor and computer program code stored in memory of the CPU  101 , and when executed by the computer processor, the program code causes the computer processor to measure data, calculate light intensity and other values, and record data in data storage device  119 , which can have a capacity of at least up to about 128 megabytes (MB) or more; the storage capacity can be increased or reduced and is unlimited other than by size and space of existing storage technology available either as virtual storage capacity or physical memory. Each semiconductor diode  102  generally has a small inherent capacitance, where this inherent capacitance of the diode integrates the total energy of a light pulse (decoded as a voltage decrease), which can be easily read out later with slow standard electronics. The capacitance across the diode can be modified by first, second and third external capacitors  107  connected in parallel and/or in series with the diodes  102 . In addition by implementing an electrical switch  108 , which can operate either mechanically or electronically, additional capacitance, such as one or more of a capacitor  107  in parallel and/or in series with the diode  102  can be added which allows the modification of the overall capacitance across the diode  102  before or during measurements. A high precision clock or oscillator  117  is connected via a first data wire  116  from a port on the CPU  101 . An integrated data storage unit  119  is connected via a second data wire  116  from a second port  109  of the CPU  101 . 
         [0012]      FIG. 4  illustrates an ultra low power (where an average power consumption is 100 microwatts (μW)) solid state spectral radiometer  100 , where power consumption can vary from about 25 microwatts or less (approaching zero watts) up to about 125 microwatts or more, i.e., up to a few milliwatts (i.e., one or two milliwatts). Again referring to  FIG. 4 , the solid state spectral radiometer  100  as used in a military maneuver includes a housing or container, such as case  406  covered by a top covering assembly, such as lid  404 , where the case  406  and lid  404  can be molded, with the lid  404  secured with fasteners, such as screws, clips or clamps or any other suitable fasteners. Furthermore, the case  406  contains connecting wire  402 , where connecting wire  402  connects various components of the solid state spectral radiometer  100 , including CPU  101 , coin cell battery  408  and several encapsulated three diode sensor sections  201 , where a typical coin cell battery  408  operates between about one half volts (½ v) up to about 2 to 6 volts or more (in exemplary embodiments, lithium-ion batteries exhibited about 3.7 v). Furthermore, in exemplary embodiments, more than one coin cell battery  408  is implemented into the solid state spectral radiometer  100 . The several diodes  102  encapsulated as the three-diode sensor section  201  components are situated in openings at different sides of the case  406  and are used to detect and measure the light intensity from different directions. The case  406 , including the lid  404 , encasing the solid state spectral radiometer  100  of the instant invention, has a minimal size and weight of approximately 6 cm×4 cm×2.5 cm, weighing about 45 grams (approximately corresponding to English units of measure in size and weight of: a width ranging from about 2 inches up to about 3 inches; a depth ranging from about 1½ inches up to about 2 inches; and a height ranging from about 3 inches up to about 5 inches, and weighing about one tenth of a pound). In additional exemplary embodiments, the size of the case  406  can be even smaller or larger depending on the number of diode  102  and capacitor  107  components added to or subtracted from the solid state spectral radiometer  100  system configurations. In exemplary embodiments, there can be as few as one diode  102  (a one channel device), or two diodes  102  (a two channel device), or three diodes  102  (a three channel device) or four diodes  102  (a four channel device) or five diodes  102  (a five channel device) or more diodes  102 /channels. The units have a dynamic range of at least 0.01-2 suns measured in 30 second intervals (where different time intervals are possible, either longer or shorter intervals), which is an important measure regarding when and how long (in long term expeditionary environments) mobile solar power units can be in the Sun. Thus, exemplary embodiments exhibit long-term monitoring operational capability in remote locations. 
         [0013]    Operation: In the first exemplary embodiment the operation of the spectral radiometer  100  is illustrated in  FIG. 3A  and  FIG. 3B , shown for one diode  102 . Controlled by program code executing on CPU  101 , at the beginning of the measurement cycle, in coordination with clock  117 , at time t0, the state of a port  109  of the CPU  101  is set to high and low-ohmic status, so that it provides an output signal with positive voltage. During this process the diode  102  and the connected capacitor(s)  107  are electrically charged. The charge depends on the overall capacitance across the diode  102  and the applied positive voltage. After a settling time, at time t1, the port  109  of the CPU  101  is set to high-ohmic status. Depending on the bandgap energy and the optical reflection and absorption properties of the diode  102 , incoming light of a specific wavelength range can be absorbed that can then lead to the generation or recombination of carriers. These photo-induced carriers discharge the diode  102  and the connected capacitors  107  leading to a decrease of the voltage across the diode  102 . The higher the light intensity, the faster the discharge process happens and the faster the voltage decreases. In a second exemplary embodiment, if the CPU  101  offers analog sensing, also known as analog to digital conversion, the change in voltage with time is recorded which allows the determination of the light intensity. In instances where the CPU  101  offers only digital sensing, the time is measured until the voltage drops below a threshold voltage, at which time the binary reading of the voltage of the port  109  changes from high to low. 
         [0014]    Referring again to  FIGS. 3A and 3B , the time span it takes until the voltage drops below a certain voltage level is generally reciprocal to the incoming light intensity: 
         [0000]      decay time˜1/(light intensity).
 
         [0015]    Again referring to  FIG. 1 ,  FIG. 3A  and  FIG. 3B , before the start of the next measurement cycle, at time t4, the diode  102  and its attached capacitor(s)  107  are charged again, from time t3 to t4, as described above. 
         [0016]    Referring again to  FIG. 1 ,  FIG. 3A  and  FIG. 3B , with the diodes  102  being sensitive in different spectral bands, and by measuring the time of the voltage decay of the respective diodes  102 , the light intensity in different spectral bands can be measured. This can be done simultaneously for all diodes  102 . 
         [0017]    Referring to  FIG. 1 ,  FIG. 3A  and  FIG. 3B , by changing the value of the external capacitor(s)  107 , the decay time (i.e., the time until the voltage across the diode  102  decreases below a threshold voltage) can be adjusted. This allows the adaption of the system to expected levels of incoming light intensity. 
         [0018]    Again referring to  FIG. 1 ,  FIG. 3A  and  FIG. 3B , the amount of electrical energy needed to charge the diode  102  and the connected capacitor  107  is relatively small thereby significantly boosting the lifetime of the sensor system. 
         [0019]    Thus, the spectral radiometer  100  can achieve sensitivity in several, adjustable wavelength-bands having adjustable detector sensitivity. Further, novel aspects of the exemplary embodiments of the spectral radiometer  100  include the ability to achieve fast, precise, multi-wavelength-band or adjustable wavelength-band adjustable detector sensitive measurements with extraordinary linearity and the ability to operate over several orders of magnitude of incoming light at low cost, (when an order of magnitude ratio is scaled to 10, the linearity and ability to operate, at least, approaches over three orders of magnitude of incoming light). 
         [0020]    Other exemplary embodiments include: ultra low power consumption; easy adaptability to wavelength regions of interest by choosing diodes  102  with corresponding bandgap(s) to the adjustable wavelength-bands and/or modification of the reflection and/or transmission properties of the respective diodes  102 ; fast measurement; shock resistant properties; no degradation or wear off; no moving parts; low cost; different optical acceptance angles realized by modification of the optics of the encapsulation; very small dimensions; no sophisticated electronics or optics; direct readout from CPU  101  without external circuitry; very good linearity; operational over several orders of magnitude of incoming light intensity; can be used in harsh environments; and easy encapsulation of different diodes in very small housings. 
         [0021]    Additional exemplary embodiments include: the usage of different bandgap energies for spectral sensing, by selecting different diodes; ease of encapsulation of diodes  102  integrated in one small housing, such as the 3 diode sensor section  201 ; individual addressability of all diodes  102 , where diodes  102  with different sensitivity (i.e. different capacitance) can be used at the same time leading to a simultaneously multi-light-level sensitive sensor section  201 , and where the sensitivity of each diode  102  can be changed before and/or after and/or during each measurement cycle (such as optionally actuating switch  108  for adding or removing capacitors  107  in the diode  102  circuits). 
         [0022]    In additional exemplary embodiments, apart from pn-diodes, such as diode(s)  102 , also spectrally sensitive resistors, Schottky diodes or any other spectrally sensitive element with photon-dependent charge generation/recombination or resistance properties can be used. Different elements can be used together and/or used at the same time to further increase the versatility of the sensor section  201  system. Optimization of the interplay between the microcontroller (i.e., CPU  101 , the clock  117 , the data storage  119  unit and other electrical components provides tuning for ultra-low power consumption. 
         [0023]    The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments claimed herein and below, based on the teaching and guidance presented herein and the claims which follow: