Ultra low power solid state spectral radiometer

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.

FIELD OF THE INVENTION

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

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' needs. There are no alternative devices having comparably small dimensions.

SUMMARY OF THE INVENTION

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

The subject invention is a spectral radiometer100with sensitivity in several, adjustable wavelength-bands having adjustable detector sensitivity. Novel aspects of the exemplary embodiments of the spectral radiometer100include 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).

Description: The device is shown in a three-diode sensor section201configuration inFIG. 1; however, the configurations of exemplary embodiments of the spectral radiometer100can include four or more diodes102, where the number of diodes102incorporated 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 radiometer100design can incorporate less than three diodes. A diode102is 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 diode102, a second diode102and a third diode102is formed from a semiconductor material of different effective bandgap energy. The bandgap energy, the reflection and absorption properties of each diode102define the wavelength range within which the first, second and third diodes102can absorb light. As shown inFIG. 2B, several diodes102can be encapsulated in a single, small housing forming the encapsulated three diode sensor section201, where the housing of the encapsulated three diode sensor section201can 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 anode104of each diode102is connected to ground (110). The cathode105of each diode102is connected to a first port109, a second port109and a third port109of a central processing unit101, (herein referred to as CPU101), where CPU101can have a plurality of input-output ports. In addition CPU101includes a computer processor and computer program code stored in memory of the CPU101, 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 device119, 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 diode102generally 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 capacitors107connected in parallel and/or in series with the diodes102. In addition by implementing an electrical switch108, which can operate either mechanically or electronically, additional capacitance, such as one or more of a capacitor107in parallel and/or in series with the diode102can be added which allows the modification of the overall capacitance across the diode102before or during measurements. A high precision clock or oscillator117is connected via a first data wire116from a port on the CPU101. An integrated data storage unit119is connected via a second data wire116from a second port109of the CPU101.

FIG. 4illustrates an ultra low power (where an average power consumption is 100 microwatts (μW)) solid state spectral radiometer100, 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 toFIG. 4, the solid state spectral radiometer100as used in a military maneuver includes a housing or container, such as case406covered by a top covering assembly, such as lid404, where the case406and lid404can be molded, with the lid404secured with fasteners, such as screws, clips or clamps or any other suitable fasteners. Furthermore, the case406contains connecting wire402, where connecting wire402connects various components of the solid state spectral radiometer100, including CPU101, coin cell battery408and several encapsulated three diode sensor sections201, where a typical coin cell battery408operates 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 battery408is implemented into the solid state spectral radiometer100. The several diodes102encapsulated as the three-diode sensor section201components are situated in openings at different sides of the case406and are used to detect and measure the light intensity from different directions. The case406, including the lid404, encasing the solid state spectral radiometer100of 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 case406can be even smaller or larger depending on the number of diode102and capacitor107components added to or subtracted from the solid state spectral radiometer100system configurations. In exemplary embodiments, there can be as few as one diode102(a one channel device), or two diodes102(a two channel device), or three diodes102(a three channel device) or four diodes102(a four channel device) or five diodes102(a five channel device) or more diodes102/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.

Operation: In the first exemplary embodiment the operation of the spectral radiometer100is illustrated inFIG. 3AandFIG. 3B, shown for one diode102. Controlled by program code executing on CPU101, at the beginning of the measurement cycle, in coordination with clock117, at time t0, the state of a port109of the CPU101is set to high and low-ohmic status, so that it provides an output signal with positive voltage. During this process the diode102and the connected capacitor(s)107are electrically charged. The charge depends on the overall capacitance across the diode102and the applied positive voltage. After a settling time, at time t1, the port109of the CPU101is set to high-ohmic status. Depending on the bandgap energy and the optical reflection and absorption properties of the diode102, 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 diode102and the connected capacitors107leading to a decrease of the voltage across the diode102. The higher the light intensity, the faster the discharge process happens and the faster the voltage decreases. In a second exemplary embodiment, if the CPU101offers 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 CPU101offers 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 port109changes from high to low.

Referring again toFIGS. 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:
decay time˜1/(light intensity).

Again referring toFIG. 1,FIG. 3AandFIG. 3B, before the start of the next measurement cycle, at time t4, the diode102and its attached capacitor(s)107are charged again, from time t3 to t4, as described above.

Referring again toFIG. 1,FIG. 3AandFIG. 3B, with the diodes102being sensitive in different spectral bands, and by measuring the time of the voltage decay of the respective diodes102, the light intensity in different spectral bands can be measured. This can be done simultaneously for all diodes102.

Referring toFIG. 1,FIG. 3AandFIG. 3B, by changing the value of the external capacitor(s)107, the decay time (i.e., the time until the voltage across the diode102decreases below a threshold voltage) can be adjusted. This allows the adaption of the system to expected levels of incoming light intensity.

Again referring toFIG. 1,FIG. 3AandFIG. 3B, the amount of electrical energy needed to charge the diode102and the connected capacitor107is relatively small thereby significantly boosting the lifetime of the sensor system.

Thus, the spectral radiometer100can achieve sensitivity in several, adjustable wavelength-bands having adjustable detector sensitivity. Further, novel aspects of the exemplary embodiments of the spectral radiometer100include 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).

Other exemplary embodiments include: ultra low power consumption; easy adaptability to wavelength regions of interest by choosing diodes102with corresponding bandgap(s) to the adjustable wavelength-bands and/or modification of the reflection and/or transmission properties of the respective diodes102; 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 CPU101without 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.

Additional exemplary embodiments include: the usage of different bandgap energies for spectral sensing, by selecting different diodes; ease of encapsulation of diodes102integrated in one small housing, such as the 3 diode sensor section201; individual addressability of all diodes102, where diodes102with different sensitivity (i.e. different capacitance) can be used at the same time leading to a simultaneously multi-light-level sensitive sensor section201, and where the sensitivity of each diode102can be changed before and/or after and/or during each measurement cycle (such as optionally actuating switch108for adding or removing capacitors107in the diode102circuits).

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 section201system. Optimization of the interplay between the microcontroller (i.e., CPU101, the clock117, the data storage119unit and other electrical components provides tuning for ultra-low power consumption.

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: