KR101581588B1 - Sensing System Using Positive Feedback - Google Patents

Abstract

A sensing system according to this embodiment includes an optical actuator for applying an optical stimulus to a detection material; A non-photo detector for outputting an electrical signal having a snapback shape corresponding to a non-optical response formed according to the nature of the medium to which the optical stimulus is applied; An amplifier for amplifying the electrical signal output from the non-optical detector and applying the amplified electrical signal to the optical actuator in a positive feedback manner; And an output unit receiving the electrical signal and detecting the property of the medium.

Description

[0001] Sensing System Using Positive Feedback [

The present invention relates to a sensing system using positive feedback.

Conventionally, a sensing system using an actuator and a sensor keeps the magnitude of an input signal generated by an actuator constant, and a sensor detects a change in a medium formed by an actuator. The sensing system according to the prior art forms an actuator, a medium and a sensor as a single end, or a sensing system in the form of a negative feedback for a more stable configuration.

For example, in the case of a turbidity sensor, when an actuator irradiates a certain amount of light to a medium containing a substance to be measured, the sensor senses the light transmitted through the medium, converts the light into an electrical signal, .

Conventional sensing systems have a limited detection limit (LOD). For example, when the sensor is used as a water quality sensor, the detection limit characteristic of the sensing system is high. Therefore, even if a substance to be detected in water contains a trace amount below the detection limit, it can not be determined that the substance is not included.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art sensing system, and it is an object of the present invention to provide a sensing system having a higher detection limit characteristic, It is one of the purposes.

A sensing system according to this embodiment includes an optical actuator for applying an optical stimulus to a detection material; A non-photo detector for outputting an electrical signal having a snapback shape corresponding to a non-optical response formed according to the nature of the medium to which the optical stimulus is applied; An amplifier for amplifying the electrical signal output from the non-optical detector and applying the amplified electrical signal to the optical actuator in a positive feedback manner; And an output unit receiving the electrical signal and detecting the property of the medium.

In addition, the sensing system according to the present embodiment includes an optical actuator for applying an optical stimulus to a medium; A non-optical detector to which a bias current is applied and to which the non-optical response of the medium is input; And a positive feedback unit for increasing the optical stimulus of the optical actuator as the bias current increases.

 According to the sensing system of the present embodiment, it is possible to detect a detection target substance of a low concentration that can not be detected by a conventional sensor.

1 is a block diagram showing an outline of a sensing system according to an embodiment of the present invention.
Fig. 2 is a circuit diagram showing an example in which an optical detector is used in the sensing system of Fig. 1; Fig.
Fig. 3 is a circuit diagram showing an example in which a non-optical detector is used in the sensing system of Fig. 1;
FIG. 4 is a current-voltage characteristic curve of an electrical signal output from an optical detector when detecting BSA (Bovine Serum Albumin), which is a substance included in a medium, according to an embodiment of the present invention.
FIG. 5 is a graph showing the measurement results of the current-voltage characteristics of the materials included in the medium in the snapback section according to the concentration. FIG.
FIG. 6A is a view showing a result of a BSA measurement measured by a sensor according to a related art, and FIG. 6B is a view showing a result of a BSA measurement measured by an embodiment. FIG. 6C is a diagram summarizing the BSA detection capability of the sensing system according to one embodiment.
FIGS. 7A to 7C are current-voltage characteristic curves obtained by measuring NADH using 270, 280, and 340 nm LEDs, and FIG. 7D is a diagram illustrating NADH measurement capability of a sensing system according to an exemplary embodiment.
8 is a current-voltage characteristic curve for a result of measuring the concentration of graphene oxide.
FIGS. 9A to 9C are current-voltage curves obtained by measuring turbidity using 880 nm, 405 nm and 280 nm infrared LEDs, respectively, and FIG. 9D is a view showing measurement limits using a sensing system according to an embodiment .

The description of the present invention is merely an example for structural or functional explanation, and the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, the embodiments are to be construed as being variously embodied and having various forms, so that the scope of the present invention should be understood to include equivalents capable of realizing technical ideas.

Meanwhile, the meaning of the terms described in the present application should be understood as follows.

It should be understood that the singular " include "or" have "are to be construed as including a stated feature, number, step, operation, component, It is to be understood that the combination is intended to specify that it is present and not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

The drawings referred to for explaining embodiments of the present disclosure are exaggerated in size, height, thickness, and the like intentionally for convenience of explanation and understanding, and are not enlarged or reduced in proportion. In addition, any of the components shown in the drawings may be intentionally reduced, and other components may be intentionally enlarged.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Terms such as those defined in commonly used dictionaries should be interpreted to be consistent with the meanings in the context of the relevant art and can not be construed as having ideal or overly formal meaning unless explicitly defined in the present application .

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 1 is a block diagram showing an outline of a sensing system according to an embodiment of the present invention. Fig. 2 is a circuit diagram showing an example in which an optical detector is used in the sensing system of Fig. 1; Fig. Fig. 3 is a circuit diagram showing an example in which a non-optical detector is used in the sensing system of Fig. 1;

Referring to Figures 1-3, the sensing system includes an optical actuator (100). The optical actuator 100 applies an optical stimulus to the medium 200. Hereinafter, an actuator that provides ultraviolet light, visible light, infrared light, and laser light is defined as an optical actuator. For example, the optical actuator 100 may be implemented as a light emitting diode (LED), a laser diode (LD), or the like. The light emitting diode may emit visible light, ultraviolet light, or infrared light in the wavelength band of infrared light, and the laser diode may emit laser light having a specific band in the range of 270 nm to 3330 nm. It is preferable to provide the optical actuator 100 to irradiate light having a suitable band according to the property of the medium 200 to be detected by the sensing system.

The sensing system includes a medium (200). For example, the medium 200A is subjected to an optical stimulus from the optical actuator 100 to form an optical reaction. For example, the degree of the optical response of the medium 200A may be changed according to the property of the medium. The properties of the medium include, for example, the concentration of a predetermined substance contained in the medium, the temperature of the medium, the refractive index of the medium, the turbidity of the medium, and the density of the medium. For example, the material contained in the medium 200A is subjected to an optical stimulus from the optical actuator 100 to form an optical reaction. For example, BSA (Bovine Serum Albumin) has a characteristic of absorbing light of 270 to 280 nm. Therefore, when a laser beam having a wavelength of 275 nm is irradiated to a medium containing BSA, the BSA performs an optical reaction to absorb the applied light to the applied optical stimulus.

In another example, the medium 200B is subjected to an optical stimulus from the optical actuator 100 to form a non-optical response. For example, the degree of non-optical response of the medium 200B may be changed depending on the property of the medium. The properties of the medium include, for example, the concentration of a predetermined substance contained in the medium, the temperature of the medium, the refractive index of the medium, the turbidity of the medium, and the density of the medium. For example, the medium 200B may be an inorganic material (e.g., polyethylene terephthalate), and is subjected to an optical stimulus from the optical actuator 100 to form an ultrasonic wave that is a non-optical reaction. In this case, the optical actuator 100, the medium 200B and the non-optical detector 300B operate in a manner similar to photoacoustic spectroscopy.

The sensing system includes a detector (300). For example, the detector 300 may be an optical detector 300A, and the optical detector 300A detects an optical response generated by applying an optical stimulus to the medium 200A and outputs the detected optical response as an electrical signal. The optical response may vary depending on the nature of the medium 200A, and thus the electrical signal provided by the optical detector 300A may also vary.

For example, an optical detector 300A may be implemented with a photodiode, which detects the change in light due to the optical response generated by medium 200A and provides a corresponding current. In one example, the optical detector 300A may be provided with a drive current (i _pd ) from a power supply (PD bias) that provides a bias current and the sensing system may sweep the drive current provided by the power (PD bias) And detects the optical response provided by the medium 200A. As will be described later, as the drive current changes, the optical detector 300A outputs an electrical signal having a snapback form.

As another example, the detector 300 may be a non-photo detector 300B, and the non-optical detector 300B may detect a non-optical response generated by applying an optical stimulus to the medium 200B, Output. The non-optical response may vary depending on the nature of the medium 200B, and thus the electrical signals provided by the non-optical detector 300B may also vary.

As an example, a non-optical detector 300B may be implemented with a piezo-electric converter 310B, first and second diodes 320B and 330B, and a low pass filter 340B. The piezoelectric-to-electric converter 310B provides an alternating current corresponding to the change of the ultrasonic wave due to the non-optical reaction that the medium 200B generates. The first diode 320B half-wave rectifies the alternating current generated by the piezo-electric converter 310B with a direct current. The driving current i _pd supplied from the power supply (PD bias) passes through the second diode 330B. When the piezoelectric-to-electric converter 310B generates a current, a current reduced by the current generated in the driving current i _pd passes to the second diode 330B. The low pass filter 340B removes high band components from the voltage between the ends N3 and N4 of the second diode 330B. Optical detector 300B may be provided with a drive current i _pd from a power supply (PD bias) that provides a bias current and the sensing system may sweep the drive current provided by the power supply (PD bias) ) To detect the non-optical response provided by the medium (200B). As will be described later, as the driving current changes, the non-optical detector 300B outputs an electrical signal having a snapback form.

The amplifier 400 amplifies and outputs the electrical signal provided by the detector 300, and the amplified electrical signal is fed back to the actuator 100. Thus, the actuator 100, the medium 200, the detector 300, and the amplifier 400 form a positive feedback path. For example, the amplifier 400 may provide positive feedback so that the intensity of the optical stimulus provided by the actuator 100 increases as the current provided by the detector 300 increases. As an example, the amplifier 400 increases the forward voltage of the LEDs included in the optical actuator 100 as the bias current (PD bias) provided by the power increases.

For example, the amplifier 400 may be implemented as a current-to-voltage converter (IV converter) that converts the current provided by the detector 300 into a voltage signal form, and the output voltage of the current-voltage converter circuit is positively fed back. The current i _pd provided by the detector 300 is converted to a voltage signal v _fb by the amplifier 400. Since the voltage signal v _fb has a negative potential, the potential at the other end connected to the amplifier 400 becomes lower than the potential at one end of the actuator 100 to which the reference potential is connected. Accordingly, as the voltage v _fb of the amplifier increases, the bias applied to the actuator 100 increases, so that a larger stimulus is applied, so that the medium 200 reacts optically or non-optically with respect to the applied stimulus , The detector 300 detecting the optical or non-optical response provides a larger current (i _pd ). That is, it can be seen that the sensing system according to the present embodiment is constituted by a positive feedback path.

The output unit 500 receives the electrical signal output from the detector 300 and analyzes the electrical signal to detect the property of the medium 200. In one embodiment, the output 500 includes a lead-out circuit to detect the nature of the medium 200 by analyzing the electrical signal OUTPUT provided by the detector 300.

4 is a current-voltage characteristic curve of an electrical signal output by the optical detector 300A when detecting BSA (Bovine Serum Albumin) which is a substance contained in the medium 200A by the sensing system according to the present embodiment. The vertical axis is the value of the bias current (PD bias, i _pd ) applied to the optical detector 300A of Figs. 1 and 2, and the horizontal axis is the voltage value (v _pd ) formed at both ends of the optical detector 300A.

With reference to Figs. 1, 2 and 4, let us describe the change in voltage across the optical detector 300A while increasing the bias current provided to the optical detector 300A from zero. Increasing the bias current i _pd provided to the optical detector 300A also increases the voltage v _pd across the optical detector 300A and the optical actuator 100 still turns on ).

As the current applied to the optical detector 300A increases, the amplifier 400 applies a voltage greater than the turn-on voltage to the optical actuator 100 to turn on the optical actuator 100. [ The turned on optical actuator 100 applies an optical stimulus to the medium 200A and when the medium 200A provides light in an optical response, the optical detector 300A detects this light and changes it to current, do. In order to allow the optical detector 300 to flow a constant current at the time when the optical actuator 100 is turned on, the voltage across the optical detector 300A is set to compensate for the current due to the light emitted from the medium 200A by the optical reaction. Should be reduced. Therefore, the voltage moves in the decreasing direction. That is, even if the current value applied to the optical detector by the power source is increased, the voltage applied across the optical detector 300A is characterized by a negative resistance which is rather reduced.

The phenomenon that the voltage across the optical detector 300A decreases as the current applied to the optical detector 300A increases is referred to as a snapback phenomenon. The starting point at which the snapback phenomenon occurs is called a snapback point (SB point) The section where the voltage decreases even if the current increases due to the phenomenon is called the snapback section.

Further increasing the bias current of the optical detector 300A reduces the voltage across the optical detector to near zero. This time is called a saturation point (SAT point), and after saturation point is called a saturation point.

Saturation provides the optical detector 300A with light resulting from the more optical response of the medium that has undergone a greater optical stimulation by the positive feedback as the bias current of the optical detector 300A increases, Is considered to occur because the voltage across the optical detector 300A must be decreased in order to compensate for the current formed by the increased light. As the bias current is continuously increased, the voltage across the optical detector 300A is maintained near this point , There is almost no change in voltage even when the current is increased. Referring to FIG. 5, which is an enlarged view of approximately 100 V, the voltage of the photodetector 300A may be increased to about several volts as shown in FIG. 4. However, in the saturation section, Is insignificant.

In addition, the curve shown by the dotted line in FIG. 4 is a current-voltage characteristic curve obtained in a state in which the signal path is performed in an open loop without a positive feedback path. The optical actuator 100, the medium 200A, the optical detector 300A, and the amplifier 400 are connected to each other so as to provide positive feedback, so that the snap-back characteristic can be confirmed.

FIG. 5 is a graph showing the results of measurement of the current-voltage characteristics of each substance contained in the medium 200A in the snapback section. FIG. , And 1 mg, respectively, in a sensing system according to the present embodiment. As shown, applying a current of approximately 2.1 μA to 2.15 μA to the optical detector 300 results in a snapback phenomenon, and can be confirmed to saturate to a voltage of approximately 0 V at a current of 2.17 μA to 2.21 μA.

It can be seen that the current-voltage characteristic in the snapback section changes depending on the concentration of the substance contained in the medium 200A. The output section 500 therefore outputs the value of the optical detector 300A bias current after fixing the bias current of the optical detector 300A and reading the voltage across the optical detector 300A or fixing the voltage across the optical detector 300A You can read the concentration of the substance by reading it. For example, the output unit 500 can determine the concentration of the substance to be 1 ng when the voltage across the optical detector 300A is read as 66V after fixing the bias current of the optical detector 300A to 2.15 μA. As another example, after the output 500 has fixed the voltage across the optical detector 300A at 40V, if the optical detector 300A bias current is read at 2.18A, the concentration of the material can be understood as 100 ng. Also, the concentration of the substance may be measured by measuring the current and voltage value at the saturation point after the snapback period.

Figures 4 and 5 and the detailed description of the invention describe the current-voltage characteristic of the sensing system shown in Figure 2 including the optical detector 300A. The sensing system shown in FIG. 2 detects the optical response, and the sensing system shown in FIG. 3 detects the non-optical response, so that the sensing system of FIGS. 2 and 3 sends the signal provided by the detector 300 to the actuator 100). The sensing system including the non-optical detector 300B also has a positive feedback structure and therefore has a current-voltage characteristic similar to that shown in Figs. 4 and 5, and also has a snapback characteristic. Therefore, the current-voltage characteristic of the sensing system including the non-optical detector 300B is omitted for convenience of explanation.

Implementation examples and experimental results

Hereinafter, detection results of materials included in a medium will be described using an embodiment and an embodiment of a sensing system according to an embodiment. FIG. 2 is a circuit diagram of an embodiment of the sensing system according to the present embodiment. The power source for applying a bias current to the optical detector is a model 4156 of Agilent. The optical detector includes an ultraviolet-enhanced photodiode of Advanced Photonix (UV Enhanced Silicon Photodiode) model 100-13-23-222 was used. The operational amplifier OPA544, a high voltage high current operational amplifier manufactured by Burr Brown, was used. The feedback resistor included in the amplifier is 6.1 Mohm. In the optical actuator, an LED that emits light of a different wavelength for each target substance to be measured was used.

BSA with different concentrations ranging from 10 pM to 100 uM was measured to test the probability of protein detection in water. The results of the measurement with the sensor according to the related art are shown in FIG. 6A, and the measured values according to the present embodiment are shown in FIG. 6B. As described above, it is confirmed that the snapback phenomenon occurs due to the positive feedback. The BSA detection ability based on the above measurement results is shown in FIG. 6C. As shown in FIG. 6C, the sensing system according to the present embodiment can measure BSA protein having a concentration of 10 to 10 ³ pM, which could not be measured by a conventional sensor.

The concentration of NADH was measured to detect the presence of microorganisms in water. Nicotinamide Adenine Dinucleotide (NAD) is an important coenzyme found in cells. NADH is a reduced form of NAD, and is a substance that occurs according to the following reaction formula during cell metabolism.

NAD + + reducing material (2e- + 2H +) ⇔ NADH + H + + oxidizing substance

Therefore, by measuring the presence of NADH, it is possible to confirm the presence of microorganisms in water. Since NADH is the basic skeleton of the nucleotide, the maximum absorption wavelength is 260 nm and the DNA is the same. Since the wavelength of 340 nm is absorbed well by NADH, the activity of dehydrated coenzyme can be measured using a 340 nm LED. In this experimental example, NADH was measured using 270, 280, and 340 nm LEDs, and the current-voltage characteristics with respect to wavelengths are shown in FIGS. 7A, 7B, and 7C, respectively. In addition, the ability to measure NADH based on the above measurement results is summarized in FIG. 7d. As shown in FIG. 7D, it was confirmed that NADH up to 10 nM can be measured using the sensing system according to the present embodiment.

The concentration of graphene oxide (Graphene Oxide), which is one of the toxic substances in water, was measured. The current-voltage characteristic curve for the measurement result is shown in FIG. As can be seen from FIG. 8, it can be seen that the concentration can be detected up to 4 ng / ml, and the concentration of several μg / ml can be measured by using a conventional spectrometer. It is confirmed that the performance of the sensing system is superior.

Turbidity was measured using 880nm, 405nm, and 280nm infrared LEDs, respectively, in order to determine whether the suspended matter in the water could be detected. 9A, 9B and 9C are enlarged snap-back sections for respective wavelengths, and FIG. 9D is a view showing measurement limits using a sensing system according to an embodiment. As shown in FIG. 9A, it can be confirmed that the measurement can be performed at the 880 nm wavelength range to the most accurate and low concentration. If the detection limit is examined based on the above measurement results, it can be confirmed that 0.01 NTU can be detected as shown in FIG. 9D.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of illustration, It will be appreciated that other embodiments are possible. Accordingly, the true scope of the present invention should be determined by the appended claims.

100: actuator 200: medium
300: detector 400: amplifier
500: Output section

Claims (20)

In a sensing system,
An optical actuator for applying an optical stimulus to the detection material;
A non-photo detector for outputting an electrical signal having a snapback shape corresponding to a non-optical response formed according to the nature of the medium to which the optical stimulus is applied;
An amplifier for amplifying the electrical signal output from the non-optical detector and applying the amplified electrical signal to the optical actuator in a positive feedback manner; And
And an output unit receiving the electrical signal and detecting the property of the medium. The method according to claim 1,
Wherein the sensing system further comprises a power source for applying a bias current to the non-optical detector. The method according to claim 1,
Wherein the optical actuator includes at least one of a light emitting diode (LED) and a laser diode (LD). The method according to claim 1,
The non-optical detector detects any one of a sound wave, an ultrasonic wave, an electric field, and a magnetic field. The method according to claim 1,
Wherein the non-optical detector detects the non-optical response formed by applying the stimulus applied by the optical actuator to the medium and outputs the corresponding electrical signal. The method according to claim 1,
Wherein the amplifier is a current-voltage conversion amplifier that receives a current signal, converts the current signal into a corresponding voltage signal, and outputs the converted voltage signal. The method according to claim 1,
The electrical signal having the snap-back form is,
A snapback section in which the electrical signal decreases as the voltage across the non-optical detector increases from a smapback point, and a saturation section in which the electrical signal increases as the voltage across the non- And the snapback section and the saturation section are connected via a saturation point. 8. The method of claim 7,
The output unit includes:
And detecting a voltage across the non-optical detector when the constant current is provided to the non-optical detector in the snapback period to detect the property of the medium. 8. The method of claim 7,
The output unit includes:
And detecting the current flowing to the non-optical detector when the constant voltage is provided to the non-optical detector in the snapback period to detect the property of the medium. 8. The method of claim 7,
The output unit includes:
And detecting the current, voltage value at the saturation point to detect the property of the medium. 8. The method of claim 7,
The output unit includes:
And detecting the nature of the medium by detecting a ratio of a current and a voltage of the saturation section. The method according to claim 1,
Wherein the property of the medium includes at least one of a concentration of a substance contained in the medium, a temperature of the medium, a refractive index of the medium, a turbidity of the medium, and a density of the medium. An optical actuator for applying an optical stimulus to the medium;
A non-optical detector to which a bias current is applied and to which the non-optical response of the medium is input; And
And a positive feedback unit that increases the optical stimulus of the optical actuator as the bias current increases. 14. The method of claim 13,
The optical actuator may include at least one of a light emitting diode (LED) and a laser diode (LD), and the non-optical detector may include at least one of a sensing device for detecting at least one of a sound wave, system. 14. The method of claim 13,
Wherein the positive feedback unit increases the intensity of the optical stimulus applied by the optical actuator as the bias current increases. 14. The method of claim 13,
Wherein the positive feedback unit comprises a differential amplifier,
Wherein a reference voltage is applied to a first input terminal of the differential amplifier, a bias current is input to a second input terminal of the differential amplifier, a resistor is connected between the second input terminal and the output terminal of the differential amplifier, A sensing system coupled to an optical actuator. 14. The method of claim 13,
And the non-optical detector outputs the bias current and a sensing voltage corresponding to the non-optical response. 18. The method of claim 17,
Wherein the non-optical detector has a snapback section in which the sensing voltage decreases as the bias current increases. 19. The method of claim 18,
And an output unit for measuring a property of the medium by measuring the sensing voltage while providing a predetermined bias current in the snapback period. 20. The method of claim 19,
Wherein the property of the medium includes at least one of a concentration of a substance contained in the medium, a temperature of the medium, a refractive index of the medium, a turbidity of the medium, and a density of the medium.

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