Description

RESONANCE CHARACTERISTIC MEASUREMENT

APPARATUS OF CANTILEVER STRUCTURE AND

MEASUREMENT METHOD THEREOF

Technical Field

[1] The present invention relates to an apparatus and method for measuring resonance characteristics of a cantilever structure.

[2] More specifically, the present invention relates to an apparatus and method for measuring resonance characteristics of a cantilever structure, which include outputting each different actuating signal corresponding to each single-frequency component in the frequency range of analysis, or outputting a spectrum actuating signal containing all the frequencies of the frequency range of analysis, or dividing the frequency range of analysis into a plurality of regions, selecting a frequency from the frequencies contained in the divided regions and outputting an actuating signal corresponding to the selected frequency, inducing oscillation of the cantilever structure in response to the actuating signal, and converting the cantilever oscillation into an excitation signal to detect amplitude and phase of the excitation signal such that resonance characteristics of the cantilever structure related to the frequency range of analysis can be assayed.

[3]

Background Art

[4] In general, a biosensor is a sensor that performs quantitative analysis of a target substrate in the sample of interest, through application of a biological entity as a molecular recognition device, based on a molecular recognition ability of biological entities such as microorganisms, enzymes, antibodies, DNA, RNA, and the like. That is, the biosensor is a device that performs quantitative analysis of the substrate contained in the suspect sample, taking advantage of the reaction which takes place when the biological entity recognizes the target substrate, such as consumption of oxygen by microbial respiration, enzymatic reaction, luminescence, or the like. Particularly among a variety of biosensors, a great deal of attention has been focused on practical application of an enzyme sensor. For instance, an enzyme sensor, which is a biosensor for assay of glucose, lactic acid, cholesterol, amino acid, or the like, is employed in medical measurement or the food industry. This enzyme sensor is configured to carry out quantitative analysis of a sample of interest in a manner that electron carriers are reduced by electrons produced from reaction of a substrate in the sample with an enzyme or the like, and a reduction level of the electron carriers is elec-

trochemically measured by a measurement device.

[5] A gas sensor is a device that detects a variety of air-polluting toxic gases, exhaust gases, explosive gases and the like, produced by rapid industrial development, urbanization, increased consumption of materials and resources or the like, and provides the detected information to users.

[6] An explosive sensor is a sensor which is intended to detect landmines hidden or buried on or under the ground in an unexploded state. The detection of explosive munitions is largely carried out by surface acoustic wave devices, gas chromatography apparatus, mass spectrometers, neutron activation analyzers, electron capture devices, etc. These detection apparatus usually require a large-scale operation power source, necessarily need filtration processes for accurate detection of analytes, under the specific surrounding conditions (for instance, when a variety of organic solvents are present), and are expensive equipment that cannot be handled by an ordinary person without professional skill. To this end, there is a need for development of a sensor which has an excellent explosive detection function in conjunction with easy personal portability.

[7] The above-illustrated sensors may be embodied by application of an optical mechanism, but suffer from difficulties in miniaturization of a sensor size due to the minimum specification of the optical mechanism.

[8] Alternatively, these sensors may also be embodied by application of a piezoelectric mechanism. The piezoelectric principle will be briefly described as follows. When pressure is applied to a crystal plate made of a metal material from a given direction, positive/negative charges proportional to the external force are developed on both sides of the plate. Piezoelectricity is weak with one crystal plate, but significantly increases by stacking of plural plates with insertion of metal foils therebetween. The crystal plate exhibits its own characteristic oscillation. Synchronization between the elastic oscillation and the electrical oscillation in combination with piezoelectricity produces stronger oscillation of the plate.

[9] Through application of such a piezoelectric mechanism, a desired type of biosensor, gas sensor or explosive sensor can be fabricated which measures an oscillation- generated resonance frequency to examine the current status of a target subject.

[10] Hereinafter, a conventional piezoelectric device to which the above-described principle is applied will be illustrated. As shown in FIG. 1, the piezoelectric device includes a piezoelectric material 10 and electrodes 20a,20b formed on both sides thereof. When a force is externally applied to the piezoelectric material 10, charges are developed on the electrodes 20a,20b. Lm, Cm and Rm values of the piezoelectric material 10 vary with the magnitude of force exerted on the piezoelectric material 10. The symbol Cshunt represents parasitic capacitance which mechanically occurs

between the upstream node and the downstream node. Among the output signals, the signal generated by parasitic capacitance is larger than the signal generated by Cm, so this may be an obstacle to reading of changes in the Cm value.

[11] Further, fabrication of the device encounters difficulties associated with complexity of design and processes resulting from various factors such as minimization of parasitic capacitance upon processing of two electrodes, setting of an oscillation frequency, mechanical design of an oscillator, etc.

[12] Unfortunately, close relationship between the individual design factors requires great efforts for improvements of device performance in design of the device, in conjunction with essential demonstration of such improvements through processes and experiments.

[13] Further, a sophisticated circuit is necessary to separate signals generated by a force of the device from signals generated by the parasitic capacitance among the output signals. Further, higher complexity of the circuit leads to an increase of noise occurring in the circuit, which may be dis advantageously a great obstacle to reading of signals.

[14]

Disclosure of Invention Technical Problem

[15] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus and method for measuring resonance characteristics of a cantilever structure, which include outputting each different actuating signal corresponding to each single-frequency component in the frequency range of analysis, or outputting a spectrum actuating signal containing all the frequencies of the frequency range of analysis, or dividing the frequency range of analysis into a plurality of regions, selecting a frequency from the frequencies contained in the divided regions and outputting an actuating signal corresponding to the selected frequency, inducing oscillation of the cantilever structure in response to the actuating signal, and converting the cantilever oscillation into an excitation signal to detect amplitude and phase of the excitation signal such that resonance characteristics of the cantilever structure related to the frequency range of analysis can be assayed.

[16] It is another object of the present invention to fabricate a biosensor using an apparatus for measuring resonance characteristics of a cantilever structure. For this purpose, an apparatus and method for measuring resonance characteristics of a cantilever structure are configured to sequentially perform the following operations. When a surface of the device is processed to have a certain pattern (conformational form of microscopic materials such as proteins, enzymes, etc.) and blood is flowed

thereinto, the corresponding enzyme in the blood sample is positioned on the pattern. Such an event leads to an increase in weight of the device or changes in an elastic coefficient of the cantilever, consequently resulting in changes in an oscillation frequency of the cantilever. Then, the thus-changed frequency is measured to quantitatively assay an amount of the enzyme in the blood.

[17] It is a further object of the present invention to provide an apparatus and method for measuring resonance characteristics of a cantilever structure which are capable of significantly reducing structural complexity of a piezoelectric device upon use of a single line and are capable of improving the precision and productivity of a device.

[18] It is another object of the present invention to provide an apparatus and method for measuring resonance characteristics of a cantilever structure which are capable of improving accuracy of the measurement due to exclusion of electrical interference between input signals and oscillation signals by receiving electrical oscillation of the oscillating device through the same line immediately after application of electrical signals to the device.

[19] It is yet another object of the present invention to provide an apparatus and method for measuring resonance characteristics of a cantilever structure which are capable of overcoming weakness of signals encountered in the excitation signal measurement, through application of a digital signal processing mode.

[20] It is yet another object of the present invention to provide an apparatus and method for measuring resonance characteristics of a cantilever structure which are capable of reducing testing times by splitting the frequency range of analysis into sub-band regions through application of single frequency spectroscopy, instead of a test for the entire frequency range of analysis, and which are capable of realizing lower power consumption of a sensor by terminating a test process when a result value is deduced during the test, thereby resulting in reduced power consumption of the device.

[21] A structure such as cantilever usually has a natural frequency and is always in motion with a natural frequency, i.e. resonance frequency, irrespective of electrical signals applied from an external source. Further, such a structure oscillates with maximum amplitude of oscillation when an electrical signal such as resonance frequency is applied.

[22] Therefore, the apparatus and method for measuring resonance characteristics of a cantilever structure in accordance with the present invention comprise applying an electrical signal from an external source, analyzing a frequency of the resulting excitation signal to predict a resonance frequency of a cantilever structure, applying an electrical signal containing the predicted frequency to the cantilever, and measuring a resonance frequency of the cantilever when it has a maximum amplitude.

[23] It is to be understood that the resonance frequency corresponding to the electrical

signal is offered as a result value, when a frequency difference between the externally applied electrical signal and the resonance signal falls within a given reference range, depending upon characteristics of the structure. [24]

Technical Solution [25] In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of an apparatus for measuring resonance characteristics of a cantilever structure comprising, [26] a cantilever structure;

[27] an analysis device for predetermining the frequency range of analysis, outputting actuating signals corresponding to the frequencies contained in the frequency range, analyzing excitation signals being input from the outside and providing the measured value; [28] an excitation signal-generating section for allowing the cantilever structure to oscillate by the actuating signals and generating and outputting excitation signals in response to the cantilever oscillation;

[29] a signal processing section for amplifying and filtering the excitation signals; and

[30] a signal conversion section for converting the amplified and filtered excitation signals into digital signals and outputting the digital signals to the analysis device. [31] In accordance with another aspect of the present invention, there is provided a method for measuring resonance characteristics of a cantilever structure comprising, [32] (1) checking through an analysis device whether the set command is input for a frequency range by a manager and predetermining the frequency range as the frequency range of analysis if the set command is input; [33] (2) generating and outputting actuating signals corresponding to frequencies contained in the frequency range of analysis by the analysis device; [34] (3) generating and transmitting excitation signals by an excitation signal-generating means in response to oscillation of a cantilever when the cantilever structure oscillates in response to the actuating signals; and [35] (4) receiving the excitation signals, and detecting and outputting amplitudes and phases thereof on a display screen by the analysis device. [36]

Advantageous Effects

[37] As illustrated hereinbefore, the present invention provides an apparatus and method for measuring resonance characteristics of a cantilever structure, which include outputting each different actuating signal corresponding to each single-frequency component in the frequency range of analysis, or outputting a spectrum actuating

signal containing all the frequencies of the frequency range of analysis, or dividing the frequency range of analysis into a plurality of regions, selecting a frequency from the frequencies contained in the divided regions and outputting an actuating signal corresponding to the selected frequency, inducing oscillation of the cantilever structure in response to the actuating signal, and converting the cantilever oscillation into an excitation signal to detect amplitude and phase of the excitation signal such that resonance characteristics of the cantilever structure related to the frequency range of analysis can be assayed.

[38] The present invention can avoid electrical interference between input/output signals due to input/output of electrical signals through a single electric wire connected to the cantilever structure, and can improve convenience, reliability and productivity of a device manufacturing process.

[39] Further, the present invention is intended to fabricate a biosensor using an apparatus for measuring resonance characteristics of a cantilever structure. For this purpose, an apparatus and method for measuring resonance characteristics of a cantilever structure are configured to sequentially perform the following operations. When a surface of the device is processed to have a certain pattern (conformational form of microscopic materials such as proteins, enzymes, etc.) and blood is flowed thereinto, the corresponding enzyme in the blood sample is positioned on the pattern. Such an event leads to changes in a weight or elastic coefficient of the device, consequently resulting in changes in an oscillation frequency of the device. Then, the thus-changed frequency is measured to quantitatively assay an amount of the enzyme in the blood. Therefore, it is possible to readily assay an amount of the target enzyme using a trace amount of blood.

[40] Further, the present invention is capable of significantly reducing structural complexity of a piezoelectric device upon use of a single line and is also capable of improving the precision and productivity of a device.

[41] Further, the present invention is capable of improving the accuracy of the measurement due to exclusion of electrical interference between input signals and oscillation signals by receiving electrical oscillation of the oscillating device through the same line immediately after application of electrical signals to the device.

[42] Further, the present invention is capable of overcoming weakness of signals encountered in the excitation signal measurement, through application of a digital signal processing mode.

[43] Further, the present invention is capable of rapidly measuring resonance characteristics of the cantilever structure by application of single frequency spectroscopy in measurement of resonance characteristics of the cantilever structure.

[44] Further, the present invention is capable of reducing testing times by splitting the

frequency range of analysis into sub-band regions through application of single frequency spectroscopy, instead of a test for the entire frequency range of analysis, and is capable of realizing lower power consumption of a sensor by terminating a test process when a result value is deduced during the test, thereby resulting in reduced power consumption of the device. [45]

Brief Description of the Drawings

[46] FIG. 1 is a schematic cross-sectional view of a conventional piezoelectric device;

[47] FIG. 2 is an equivalent circuit diagram of FIG. 1;

[48] FIG. 3 is a block diagram illustrating Embodiment 1 of an apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention; [49] FIG. 4 is a block diagram illustrating Embodiment 2 of an apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention; [50] FIG. 5 is a block diagram illustrating Embodiment 3 of an apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention;

[51] FIGS. 6 through 8 are circuit diagrams showing embodiments of excitation signal- generating section which are applied to FIGS. 3 and 4;

[52] FIG. 9 is a circuit diagram showing an embodiment of an excitation signal- generating section which is applied to FIG. 5; [53] FIG. 10 is an operation flow chart illustrating Embodiment 1 of a method for measuring resonance characteristics of a cantilever structure in accordance with the present invention; [54] FIG. 11 is an operation flow chart illustrating Embodiment 2 of a method for measuring resonance characteristics of a cantilever structure in accordance with the present invention; [55] FIG. 12 is an operation flow chart illustrating Embodiment 3 of a method for measuring resonance characteristics of a cantilever structure in accordance with the present invention; and [56] FIGS. 13 and 14 are graphs illustrating a natural frequency of a cantilever structure in accordance with the present invention. [57]

Best Mode for Carrying Out the Invention [58] Now, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings, such that those skilled in the art

can easily practice the present invention.

[59] Hereinafter, configuration of an apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention will be given with reference to the accompanying drawings.

[60] The apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention is based on the principle that a certain object exhibits an oscillatory motion with a natural frequency regardless of actuating signals applied from an external source, when it is allowed to oscillate.

[61]

[62] Embodiment 1

[63] As shown in FIG. 3, an apparatus for measuring resonance characteristics of a cantilever structure includes an input section 10 connected to an analysis device 30 which will be illustrated hereinafter and outputting a key signal according to the manipulation of an operator; a cantilever structure 20; the analysis device 30 for defining the frequency range of analysis, outputting an actuating signal corresponding to the frequency contained in the frequency range of analysis, analyzing an excitation signal being input from a signal conversion section 60 which will be illustrated hereinafter and providing the measured value; an excitation signal-generating section 40 for allowing the cantilever structure 20 to oscillate by the actuating signal and generating and outputting an excitation signal in response to the cantilever oscillation; a signal processing section 50 consisting of an amplification device and a filter, and for amplifying and filtering the excitation signal; a signal conversion section 60 as an A/D converter and for converting the amplified and filtered excitation signal into a digital signal and outputting the digital signal to the analysis device 30; and an output section 70 connected to the analysis device 30, and outputting the oscillation amplitude and phase signal detected by the analysis device 30 on a display screen.

[64] The analysis device 30 generates and outputs actuating signals of single frequency components contained in the frequency range of analysis when the frequency range of analysis and resolution thereof are determined. Further, the device 30 detects the amplitudes and phases of the excitation signals and provides the results as measured values.

[65] That is, the analysis device 30, as shown in FIG. 4, includes an actuating signal- generating module 31 for dividing a frequency range of interest into sub-band regions to be searched and generating and sequentially transmitting actuating signals corresponding to each divided region, and a result value-output module 35 for analyzing excitation signals being input from the signal conversion section 60, detecting the amplitude and phase of the excitation signals, and outputting the thus-detected amplitude and phase as the result values.

[66] As shown in FIG. 6, the excitation signal-generating section 40 may include an amplification device (OPl) having an inverting terminal (-) connected to the cantilever structure 20 and a non-inverting terminal (+) for receiving a supply of the actuating signal, and a negative feedback device (Cf) for subjecting the inverting terminal (-) to negative feedback from the output thereof.

[67] As shown in FIG. 7a, the excitation signal-generating section 40 may include an amplification device (OP2) having an inverting terminal (-) connected to the cantilever structure 20 and a non-inverting terminal (+) that is grounded, a switch (SWl) connected to one end of the inverting terminal (-) and switching on/off a supply of an actuating signal to the inverting terminal (-), and a negative feedback device (Rf) for subjecting the inverting terminal (-) to negative feedback from the output thereof. Herein, the switch (SWl) is switched on/off under control of the analysis device 30 or according to the manipulation of a manager.

[68] Alternatively, the negative feedback device (Rf) may be replaced with a capacitor device (Cf), as shown in FIG. 7b.

[69] As shown in FIG. 8, the excitation signal-generating section 40 may include an amplification device (OP3) having an inverting terminal (-) feedback-connected to an output terminal and a non-inverting terminal (+) connected to the cantilever structure 20, and a switch (SW2) connected to one end of the non-inverting terminal (+) and switching on/off a supply of an actuating signal to the non-inverting terminal (+). Herein, the switch (SW2) is switched on/off under control of the analysis device 30 or according to the manipulation of a manager.

[70] Preferably, the negative feedback device may be a resistor or capacitor.

[71] A measuring method using the apparatus for measuring resonance characteristics of the cantilever structure constructed as above will be described as follows.

[72] As shown in FIG. 10, when a manager predetermines the frequency range of analysis while setting test environment conditions through an input section 10 (S200), an actuating signal-generating module 31 sequentially generates electrical signals, i.e. actuating signals, corresponding to each single-frequency component contained in the frequency range set by an operator, and then outputs the thus -generated actuating signals to an excitation signal-generating section 40 (S210). Thereafter, when outputting of the actuating signals to the excitation signal-generating section 40 is blocked by control of the analysis device 30 or the manipulation of the switches SWl, SW2 (as shown in FIG. 7a, FIG. 7b and FIG. 8) by the manager, the cantilever structure 20 is oscillated by the actuating signals. The excitation signal- generating section 40 generates excitation signals being excited in response to the oscillation of the cantilever structure 20 and outputs the excitation signals to a signal processing section 50 (S220). That is, a natural frequency (resonance frequency) of the cantilever

structure 20 is variable depending on the magnitude of force applied to the cantilever structure 20, so it is possible to calculate the magnitude of applied force if the natural frequency is known.

[73] The signal processing section 50, consisting of an amplification device and a filter, amplifies the input excitation signals, filters them to remove noise, and then outputs the signals to a signal conversion section 60 which is an A/D converter (S230).

[74] When the signal conversion section 60 converts the input excitation signals into digital signals and outputs the digital signals to the analysis device 30 (S240), the result value-output module 35 of the analysis device 30 detects amplitudes and phases of the excitation signals converted into the digital signals, and outputs the thus- detected amplitudes and phases on a display screen through an output section 70 such that the manager can confirm the results (S250).

[75] The above procedure is repeated for single frequency components contained in the frequency range as specified above. That is, if 10 single frequencies (fl~flθ) are contained in the specified frequency range, the above procedure is repeated 10 times. The amplitude and phase data detected during 10 times repetition of the procedure are matched with the corresponding single frequencies and are all output on a display screen.

[76]

[77] Embodiment 2

[78] As shown in FIG. 4, an apparatus for measuring resonance characteristics of a cantilever structure includes an input section 10 connected to an analysis device 30 which will be illustrated hereinafter and outputting a key signal according to the manipulation of an operator; a cantilever structure 20; the analysis device 30 for defining the frequency range of analysis, outputting an actuating signal corresponding to the frequency contained in the frequency range of analysis, analyzing an excitation signal being input from a signal conversion section 60 which will be illustrated hereinafter and providing the measured value; an excitation signal-generating section 40 for allowing the cantilever structure 20 to oscillate by the actuating signal and generating and outputting an excitation signal in response to the cantilever oscillation; a signal processing section 50 consisting of an amplification device and a filter, and for amplifying and filtering the excitation signal; a signal conversion section 60 as an A/D converter and for converting the amplified and filtered excitation signal into a digital signal and outputting the digital signal to the analysis device 30; and an output section 70 connected to the analysis device 30, and outputting the amplitude and phase signal detected by the analysis device 30 on a display screen.

[79] The analysis device 30 generates and outputs a spectrum actuating signal containing all the frequencies of the frequency range of analysis when the frequency range of

analysis and resolution thereof are determined.

[80] The analysis device 30 detects the amplitudes and phases of the excitation signals and provides the results as measured values.

[81] The analysis device 30 performs Fourier transformation or discrete cosine transform

(DCT) of excitation signals being input correspondingly to the spectrum actuating signal, and detects the amplitudes and phases of the individual frequencies and provides the results as measured values.

[82] The analysis device 30 includes an actuating signal-generating module 31 for defining the frequency range of analysis and generating and transmitting a spectrum actuating signal containing all the frequencies of the frequency range; a signal conversion module 37 for receiving input of excitation signals from the signal conversion section 60, performing Fourier transformation or discrete cosine transform (DCT) of the excitation signals to detect the amplitude and phase of each frequency of the excitation signals; and a result value-output module 35 for outputting the result values of the signal conversion module 37 on a user interface display screen.

[83] Construction of the excitation signal-generating section 40 is identical with that of

Embodiment 1, so details thereof will be omitted herein.

[84] A measuring method using the apparatus for measuring resonance characteristics of the cantilever structure constructed as above will be described as follows.

[85] As shown in FIG. 11, when a manager predetermines the frequency range of analysis while setting the test environment conditions through an input section 10 (S300), an actuating signal-generating module 31 generates electrical signals, i.e. actuating signals, corresponding to all the frequency components contained in the frequency range set by an operator and then outputs the thus-generated actuating signals to an excitation signal-generating section 40 (S310). Thereafter, when outputting of the actuating signals to the excitation signal-generating section 40 is blocked by control of the analysis device 30 or the manipulation of the switches SW1,SW2 (as shown in FIG. 7a, FIG. 7b and FIG. 8) by the manager, the cantilever structure 20 is oscillated by the actuating signals. The excitation signal-generating section 40 generates excitation signals being excited in response to the oscillation of the cantilever structure 20 and outputs the excitation signals to a signal processing section 50 (S320).

[86] The signal processing section 50, consisting of an amplification device and a filter, amplifies the input excitation signals, filters them to remove noise, and then outputs the signals to a signal conversion section 60 which is an A/D converter (S330).

[87] When the signal conversion section 60 converts the input excitation signals into digital signals and outputs the digital signals to the analysis device 30 (S340), the analysis device 30 applies the thus -converted excitation signals to a fast Fourier transformation or discrete Fourier cosine transform or discrete cosine transform (DCT)

algorithm to thereby detect the amplitudes and phases of the excitation signals corresponding to each frequency, and outputs the thus-detected amplitudes and phases on a display screen through an output section 70 such that the manager can confirm the results (S350).

[88] The fast Fourier transformation or discrete Fourier cosine transform or discrete cosine transform (DCT) algorithm is a program plot of Fourier transformation or discrete cosine transform (DCT) equation. Specifically, when excitation signals, generated by actuating signals which are electrical signals containing all the frequency components for the predetermined frequency range of analysis, are converted into digital signals and are then applied to the above-mentioned program, the amplitude and phase data are yielded corresponding to each frequency component.

[89]

[90] Embodiment 3

[91] As shown in FIG. 5, the apparatus for measuring resonance characteristics of a cantilever structure in accordance with the present invention includes a cantilever structure 20; an analysis device 30 which divides a frequency range into multiple regions of analysis, outputs an actuating signal corresponding to a first region out of the divided regions, analyzes the converted excitation signal being input from an A/D signal converter section 60 and outputs the measured result value or re-selects any region out of the remaining regions except for the above- selected region and re-outputs a corresponding actuating signal; an excitation signal-generating section 40 which has one end connected to the cantilever structure 20 and the other end connected to the analysis device 30, thereby receiving an input of an actuating signal, produces oscillation in response to the actuating signal, and generates and outputs an excitation signal corresponding the oscillation; a signal processing section 50 which consists of an amplification device and filter, and amplifies and filters the excitation signal; and an A/D signal converter section 60 which converts the amplified and filtered excitation signal into a digital signal and outputs the thus -converted excitation signal as a feedback signal to the analysis device 30.

[92] The analysis device 30 includes an actuating signal-generating module 31 which divides a frequency range into plural regions of analysis, and generates and transmits actuating signals corresponding the divided regions; a frequency check module 33 which analyzes an excitation signal being input from the A/D signal converter section 60 to calculate a frequency difference between the excitation signal and the actuating signal, and outputs the input excitation signal as a result value when the frequency difference falls within the stored reference range; and a result value-output module 35 which outputs the result value of the frequency check module 33 on a user interface display screen.

[93] When the frequency difference is outside the above- specified reference range, the frequency check module 33 predetermines a frequency skip region according to a degree of deviation from the reference range, and outputs information of the predetermined frequency skip region to the actuating signal-generating module 31 to thereby output an actuating signal contained in a frequency range of the corresponding region.

[94] The frequency check module 33 produces the entire range reconfiguration information such that an entire range of the frequency range can be reset according to the frequency difference and then outputs the reconfiguration information to the actuating signal-generating module 31.

[95] As shown in FIG. 9, the excitation signal-generating section 40 includes an amplification device (OP) having an inverting terminal (-) connected to the cantilever structure 20 and a non-inverting terminal (+) for receiving a supply of the actuating signal, a charge device (Cf) connected between the inverting terminal (-) and an output of the amplification device (OP), a phase delay-preventing device (R) connected in parallel to the charge device (Cf), and a switch (SW) for connecting the charge device (Cf) or phase delay-preventing device (R) to the inverting terminal (-) according to the manipulation of a manager.

[96] The phase delay-preventing device (R) is a resistive element, and the charge device

(Cf) is a capacitor element. Therefore, when the test environment is susceptible to high probability of phase delay, switching is driven toward the resistive element by provision of the resistive element (R) between the input and output of the amplification device (OP). On the other hand, when the test environment is highly susceptible to the occurrence of noise, switching is induced toward the capacitor element by provision of the capacitor element (Cf) between the input and output of the amplification device (OP). The switch is provided in a state where switching is previously set according to the measurement environment upon shipping of the sensor.

[97] A measuring method using the apparatus for measuring resonance characteristics of the cantilever structure constructed as above will be described as follows.

[98] As shown in FIG. 12, when a manager predetermines the frequency range of analysis while setting the test environment conditions through an input section 10, an actuating signal-generating section 31 divides the frequency range set by the operator into plural regions to be searched (SlOO).

[99] Then, the actuating signal-generating section 31 selects a frequency range of the first region out of the divided frequency regions (Sl 10), and outputs an actuating signal corresponding to the selected frequency range, such that the cantilever structure 20 oscillates.

[100] The excitation signal-generating section 40 generates an excitation signal in response

to oscillation of the cantilever structure 20, and transmits the excitation signal to the signal processing section 50 (S 130).

[101] When the signal processing section 50 amplifies and filters the excitation signal (S 140) and then outputs the signal to the A/D signal converter section 60, the A/D signal converter section 60 converts the amplified and filtered excitation signal into a digital signal.

[102] The frequency check module 33 analyzes the converted excitation signal to calculate a frequency difference between the excitation signal and the actuating signal, checks whether the frequency difference falls within the specified reference range (S 160), and then finally determines whether the frequency difference is in the given range, based on the check results (S 170).

[103] When the frequency difference falls within the reference range according to the determination of Step S 170, the input excitation signal is output as a result value on a user interface display screen (S 180). When the frequency difference is outside the above-specified reference range, a frequency skip region is set according to a degree of deviation from the reference range. Then, information of the predetermined frequency skip region is output to the actuating signal-generating module 31 to thereby output an actuating signal contained in a frequency range of the corresponding region (S 190). Then, the cantilever structure 20 oscillates again in response to the re-input actuating signal, followed by repetition of the above procedure.

[104] In a further embodiment of the present invention, the frequency check module 33 produces the entire range reconfiguration information such that an entire range of the frequency range can be reset according to the frequency difference and then outputs the reconfiguration information to the actuating signal-generating module. For example, if the frequency range is set in a range of 1 to 100, this range may be changed in a range of 1 to 50, if necessary.

[105] FIGS. 13 and 14 are graphs illustrating a natural frequency of the cantilever structure, as measured by a piezoelectric measuring device in accordance with the present invention. The measurement involves environment setting (such as amplitude, offset, frequency, etc.), application of an actuating signal to the cantilever, and use of an excitation signal being output from the cantilever. The value of amplitude or the like may vary depending on a length of the cantilever. When a signal with large amplitude is input, the received signal, i.e. excitation signal (exc_s), also has large amplitude.

[106] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.