Method for testing piezoelectric acoustic transducers

Abstract

Providing a test method for piezoelectric acoustic transducers. [Solution] A method for testing a drug delivery device comprises a piezoelectric transducer, a microcontroller, and a DC power supply, wherein the piezoelectric transducer has operating and non-operating states. The method includes the steps of providing a drive signal to the piezoelectric transducer of the drug delivery device, determining an operating voltage value or operating current value, and comparing the operating voltage value or operating current value to a baseline value to determine whether the piezoelectric transducer is in an operating or non-operating state.

Description

Technical Field

[0001] Cross-reference of related applications This application claims priority to U.S. Provisional Application No. 63 / 114,879, filed on November 17, 2020, entitled "Method for Testing a Piezoacoustic Transducer," which is hereby incorporated by reference in its entirety.

[0002] This disclosure relates to a method for testing a piezoacoustic transducer for a drug delivery device.

Background Art

[0003] Wearable medical devices, such as automatic injectors, have the advantage of providing treatment to patients while discretely worn away from clinical facilities and / or under the patient's clothing. A wearable medical device can be applied to a patient's skin and configured to automatically deliver a dose of a pharmaceutical composition within a predetermined time period, for example, after a 27-hour delay, after the wearable medical device has been applied to the patient's skin. After the device has delivered the pharmaceutical composition to the patient, the patient may then remove and discard the device.

[0004] A wearable medical device may have audible, tactile, or visual indicators for indicating the state of the device, such as when drug delivery has started or completed, or when a malfunction has been detected. Piezoelectric transducers are used to provide audible and / or tactile indicators for wearable medical devices. Since the indicators for wearable medical devices play an important role in the function of the medical device, the function of the indicators is tested during the manufacture of the medical device. One solution for testing an audible indicator is to use a microphone to test the function of the audible indicator, which has limitations depending on the external noise level in the manufacturing or test environment.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] U.S. Patent No. 10,449,292 [Overview of the project]

[0006] In one aspect or embodiment, a method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power source, wherein the piezoelectric transducer has an operative state and an inoperative state, includes the steps of: providing a drive signal to the piezoelectric transducer of the drug delivery device; determining an operating voltage value or an operating current value; and comparing the operating voltage value or operating current value to a baseline value to determine whether the piezoelectric transducer is in an operative state or an inoperative state.

[0007] The operating voltage or operating current may be determined from the average of several values ​​measured over a given period. Alternatively, the operating voltage or operating current may be determined from a subset of several values ​​measured over a given period. Curvefitting may be used to determine the operating voltage or operating current. At least one of the Fourier transform and the Fast Fourier transform may be used to determine the operating voltage or operating current. The signal used to determine the operating voltage or operating current may be calculated over a time period exceeding 10 ms. The signal used to determine the operating voltage or operating current may be calculated over a time period exceeding 1 ms.

[0008] The operating voltage value may be the voltage frequency of the DC power supply when the drive signal is provided to the piezoelectric transducer, and the baseline value may be the known voltage frequency of the DC power supply when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in operation. The operating voltage value may also be the frequency of the maximum voltage drop when the drive signal is provided to the piezoelectric transducer, and the baseline value may be the known frequency of the maximum voltage drop when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in operation.

[0009] The operating voltage values ​​may be the minimum and maximum voltages of the DC power supply when a drive signal is provided to the piezoelectric transducer, and the baseline values ​​may be the known minimum and maximum voltages when a drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in operation.

[0010] A piezoelectric transducer may be determined to be operating when its operating voltage is within a predetermined range of a baseline value. The piezoelectric transducer may be activated in the operating state and not activated in the non-operating state. Determining the operating voltage may involve measuring the voltage at the terminals of a DC power supply or the voltage at the terminals of the piezoelectric transducer. The DC power supply may be a battery.

[0011] In a further embodiment, a computer-implemented method for testing a drug delivery device having an operating and non-operating state for a piezoelectric transducer includes a piezoelectric transducer, a microcontroller, and a DC power supply, the method comprising the steps of: providing a drive signal to the piezoelectric transducer of the drug delivery device; determining an operating voltage value or an operating current value; and determining whether the piezoelectric transducer is in an operating or non-operating state by comparing the operating voltage value with a baseline voltage value using at least one processor.

[0012] In further embodiments or designs, the drug delivery device includes a DC power supply, a cannula, a reservoir configured to receive fluid, a pump configured to deliver fluid from the reservoir to the cannula, a piezoelectric transducer having an operating state in which the piezoelectric transducer produces an audible sound and a non-operating state in which the piezoelectric transducer does not produce an audible sound, and a microcontroller including at least one processor programmed or configured to provide a drive signal to the piezoelectric transducer, determine an operating voltage value, and determine whether the piezoelectric transducer is in an operating or non-operating state by comparing the operating voltage value or operating current value with a baseline value using at least one processor.

[0013] In a further embodiment or part of the set, a computer program product for testing a drug delivery device includes a piezoelectric transducer, a microcontroller, and a DC power supply, wherein the piezoelectric transducer has operating and non-operating states, and the computer program product includes at least one non-transitory computer-readable medium containing program instructions that, when executed by the microcontroller, cause the microcontroller to provide a drive signal to the piezoelectric transducer, determine an operating voltage or operating current value, and determine whether the piezoelectric transducer is in an operating or non-operating state by comparing the operating voltage or operating current value with a baseline value. [Brief explanation of the drawing]

[0014] The above and other features and advantages of this disclosure, as well as the methods for achieving them, will become more apparent and the disclosure itself will be better understood by referring to the following description of embodiments of this disclosure in conjunction with the accompanying drawings. [Figure 1] This is a perspective view of a drug delivery device according to one aspect or embodiment of the present application. [Figure 2]Figure 1 is a perspective view of the drug delivery device with the top cover removed. [Figure 3] Figure 1 is a partial perspective view of a drug delivery device. [Figure 4] Figure 1 is a schematic diagram of a drug delivery device. [Figure 5] This is a schematic diagram of a piezoelectric transducer circuit of the drug delivery device shown in Figure 1, according to one aspect or embodiment of the present application. [Figure 6A] Figure 1 shows a voltage-to-time graph of the power supply and piezoelectric transducer of the drug delivery device when the drug delivery device is activated and the piezoelectric transducer circuit is inactive. [Figure 6B] This is a histogram of the graph in Figure 6A. [Figure 7A] Figure 1 shows power supply and piezoelectric transducer voltage versus time graphs for the drug delivery device and piezoelectric transducer when the drug delivery device is activated, the piezoelectric transducer circuit is activated, and the piezoelectric transducer is disconnected. [Figure 7B] This is a histogram of the graph in Figure 7A. [Figure 8A] Figure 1 shows a voltage-versus-time graph of the power supply for the drug delivery device and the piezoelectric transducer when the drug delivery device is activated, the piezoelectric transducer circuit is activated, and the piezoelectric transducer is connected. [Figure 8B] This is a histogram of the graph in Figure 8A. [Figure 9] Figure 1 is a voltage-to-time graph of the power supply for the drug delivery device, showing the voltage with the piezoelectric transducer connected and the voltage without the piezoelectric transducer connected. [Figure 10] Figure 1 is a voltage-to-time graph of the power supply for the drug delivery device, showing the frequency of the maximum voltage drop. [Figure 11] Figure 1 is a voltage-to-time graph of the power supply for the drug delivery device, showing a comparison between the voltage with the piezoelectric transducer connected and the voltage without the piezoelectric transducer connected. [Figure 12] A graph of the voltage of the power supply over time of the drug delivery device of FIG. 1 showing a comparison between the voltage frequency of the power supply with the piezoelectric transducer connected and the 250 Hz frequency of the piezoelectric transducer. [Figure 13] A graph of the voltage of the power supply over time of the drug delivery device of FIG. 1 showing a comparison between the voltage frequency of the power supply with the piezoelectric transducer connected and the 500 Hz frequency of the piezoelectric transducer. [Figure 14] A graph of the voltage of the power supply over time of the drug delivery device of FIG. 1 showing a comparison between the voltage frequency of the power supply with the piezoelectric transducer connected and the 750 Hz frequency of the piezoelectric transducer. [Figure 15] A schematic diagram of a method for testing a drug delivery device according to one aspect or embodiment of the present application. [Figure 16] A graph of the voltage of the power supply of the drug delivery device of FIG. 1 against the sample number showing the voltage with the piezoelectric transducer connected. [Figure 17] A graph of the voltage of the power supply of the drug delivery device of FIG. 1 against the sample number showing the voltage with the piezoelectric transducer not connected.

[0015] Corresponding reference numerals indicate corresponding parts throughout several views. The examples presented in this specification illustrate exemplary embodiments of the present disclosure, and such examples should not be construed as limiting the scope of the present disclosure in any way.

Mode for Carrying Out the Invention

[0016] Spatial or directional terms such as "left", "right", "inner", "outer", "above", "below", etc. should not be considered limiting since the present invention can assume various alternative orientations.

[0017] All figures used herein and in the claims should be understood to be modified in all examples by the term “about,” which means a range of plus or minus 10 percent of the stated value. Where used herein and in the claims, the singular forms “a,” “an,” and “the” refer to multiple subjects unless the context clearly indicates otherwise. The terms “first,” “second,” etc., are not intended to refer to any particular order or chronology, but rather to different conditions, characteristics, or elements. “At least” means “greater than or equal to.”

[0018] As used herein, “at least one” is synonymous with “one or more.” For example, the phrase “at least one of A, B, and C” means any one of A, B, or C, or any combination of two or more of A, B, or C. For example, “at least one of A, B, and C” includes one or more A alone, or one or more B alone, or one or more C alone, or one or more A and one or more B, or one or more A and one or more C, or one or more B and one or more C, or one or more A, B, and C.

[0019] As used herein, the term “processor” may refer to one or more electronic devices configured to process data. In some examples, a processor may include components necessary for receiving, processing, and outputting data, such as a processor, display, memory, input devices, network interfaces, and / or similar. A processor may be a mobile device. A processor may also be a desktop computer or other form of non-mobile computer.

[0020] Referring to Figures 1 to 4, the drug delivery device 10 includes a reservoir 12, a power supply 14, an insertion mechanism 16, control electronics 18, a cover 20, and a base 22. In one aspect or embodiment, the drug delivery device 10 is a wearable automated injector, such as an insulin or bone marrow stimulant delivery device. The drug delivery device 10 may be fitted onto the patient's skin and triggered to inject a pharmaceutical composition into the patient from the reservoir 12. The drug delivery device 10 may be pre-filled with the pharmaceutical composition or filled with the pharmaceutical composition by the patient or healthcare professional before use.

[0021] The drug delivery device 10 is configured to deliver a pharmaceutical composition, such as any desired drug, in a dose into the patient's body by subcutaneous injection at a slow, controlled infusion rate. The exemplary duration of delivery achieved by the drug delivery device 10 may range from about 5 minutes to about 60 minutes, but is not limited to this exemplary range. The exemplary volume of the pharmaceutical composition delivered by the drug delivery device 10 may range from about 0.1 milliliters to about 10 milliliters, but is not limited to this exemplary range. The volume of the pharmaceutical composition delivered to the patient may be adjusted.

[0022] Referring again to Figures 1 to 4, in one aspect or embodiment, the power supply 14 is a DC power supply including one or more batteries. The control electronics 18 includes a microcontroller 24, sensing electronics 26, a pump and valve controller 28, sensing electronics 30, and deployment electronics 32, which control the operation of the drug delivery device 10. The drug delivery device 10 includes a reservoir 12, a volume sensor 34 for the reservoir 12, a reservoir fill port 36, and a fluidics subsystem including a metering subsystem 38 which includes a pump and valve actuator 40 and a pump and valve mechanism 42. The fluidics subsystem may further include an occlusion sensor 44, a deployment actuator 46, and a cannula 48 for insertion into the patient's skin. In one aspect or embodiment, the insertion mechanism 16 is configured to move the cannula 48 from a retracted position, where it is fully positioned within the drug delivery device 10, to an extended position, where it extends outside the drug delivery device 10. The drug delivery device 10 may operate in a manner similar to that discussed in Patent Document 1 to Pizzochero et al.

[0023] Referring to Figures 3 and 5, the drug delivery device 10 also includes a piezoelectric transducer 50 configured to provide the user with an audible and / or tactile indication of the state of the drug delivery device 10. In one aspect or embodiment, the piezoelectric transducer 50 is connected to a control electronic device 18 via one or more spring contacts 60. The piezoelectric transducer 50 has an operating state in which the piezoelectric transducer 50 is activated and produces an audible sound, motion, and / or vibration when a signal from a signal generation system, such as a microcontroller 24, is supplied, and a non-operating state in which the piezoelectric transducer 50 is not activated and does not produce an audible sound, motion, and / or vibration.

[0024] Referring to Figures 6A to 15, according to one aspect or embodiment of the present application, a method for testing a drug delivery device 10 includes the steps of: providing a drive signal to the piezoelectric transducer 50 of the drug delivery device 10; measuring an operating voltage value; and comparing the operating voltage value to a baseline voltage value to determine whether the piezoelectric transducer 50 is operating or not. If the operating voltage value is within a predetermined range of the baseline value, such as within 5% of the baseline value, the piezoelectric transducer 50 is determined to be operating and has a passed test state 78. If the operating voltage value is not within a predetermined range of the baseline value, such as within 5% of the baseline value, the piezoelectric transducer 50 is determined to be not operating and has a failed test state 80. One possible cause of a failed test is insufficient contact between the spring contact 60 of the piezoelectric transducer 50 and the control electronic equipment 18. The present method enables self-testing of the drug delivery device 10 to determine whether the piezoelectric transducer 50 is properly connected and operating without requiring dedicated circuitry or hardware, and without requiring separate data handling, data processing, and traceability. The present method 70 requires no additional equipment and is not sensitive to ambient noise. Furthermore, the present method 70 utilizes voltage readings from a power supply 14, as detailed below, which is typically already monitored by a microcontroller 24 to detect the level of the power supply 14. Thus, the present method 70 does not require any further connections between electronic components.

[0025] Referring to Figures 6A to 14, in one aspect or embodiment, the operating voltage value is the voltage frequency of the DC power supply 14 when a voltage drive signal is provided to the piezoelectric transducer 50, and the baseline value is the known voltage frequency of the DC power supply 14 when the drive signal is provided to the piezoelectric transducer 50 and the piezoelectric transducer 50 is in operation. More specifically, the operating voltage value is the frequency of the maximum voltage drop when the drive signal is provided to the piezoelectric transducer 50, and the baseline value is the known frequency of the maximum voltage drop when the drive signal is provided to the piezoelectric transducer 50 and the piezoelectric transducer 50 is in operation. In one aspect or embodiment, the drive signal is a square wave of a predetermined frequency. In a further aspect or embodiment, the operating voltage value is the minimum and maximum voltage of the DC power supply 14 when the drive signal is provided to the piezoelectric transducer 50, and the baseline value is the known minimum and maximum voltage when the drive signal is provided to the piezoelectric transducer 50 and the piezoelectric transducer 50 is in operation. In further embodiments or designs, the operating frequency may be modulated over a second lower frequency, essentially turning the transducer operating circuit on and off as part of a test procedure. The voltage value may be calculated from the difference between the operating voltage and the non-operating voltage measured at a selected location directly or indirectly connected to the piezoelectric transducer 50. The reference and measured values ​​may be voltage or current.

[0026] As shown in Figures 6A and 6B, when the drug delivery device 10 is activated or awake and no drive signal is provided, the voltage of the power supply 14 measured at the power terminals oscillates between 1.505V and 1.525V, while the drive signal remains constant at 1.5V. As shown in Figures 7A and 7B, when the drug delivery device 10 is activated or awake, a drive signal is provided, and the piezoelectric transducer 50 is disconnected, the voltage of the power supply 14 measured at the power terminals oscillates between 1.425V and 1.455V, a shift of approximately 0.12V from Figures 6A and 6B, while the drive signal oscillates between 1.358V and 1.61V. As will be described in more detail below, the high-frequency spike in the maximum voltage drop occurs when the drive signal voltage and the power supply voltage are equal. As shown in Figures 8A and 8B, when the drug delivery device 10 is activated or started, a drive signal is provided, and the piezoelectric transducer 50 is connected, the voltage of the power supply 14 measured at the power terminals oscillates between 1.41V and 1.455V, and the drive signal oscillates between 1.358V and 1.61V. Compared to the states in Figures 7A and 7B, the voltage distribution in Figures 8A and 8B is shifted by approximately 5mV. Therefore, the operating state of the piezoelectric transducer 50 can be determined by comparing the minimum and maximum voltages of the power supply with the known minimum and maximum voltages when the piezoelectric transducer 50 is correctly connected and operating. Also, as shown in Figure 8A, the pattern of high-frequency spikes or harmonics of the maximum voltage drop value differs from the pattern in Figure 7A, which will be discussed in more detail below. The pattern can be observed by analyzing the signal in either the time domain or the frequency domain using the Fast Fourier Transform (FFT).

[0027] Referring to Figure 9, a voltage drop of approximately 0.15V occurs at the start of the drive signal operation, which occurs when the piezoelectric transducer 50 is connected and when the piezoelectric transducer 50 is disconnected. The 0.15V voltage drop occurs over 0.005 seconds. However, as shown in Figure 9, when the piezoelectric transducer 50 is connected, the voltage of the power supply 14 recovers to a slightly lower level, with a difference of approximately 0.02V. In a further aspect or embodiment, a method 70 for testing the drug delivery device 10 to determine the operating state of the piezoelectric transducer 50 includes the step of comparing the voltage recovery values ​​after the drive signal is first provided.

[0028] Referring to Figure 10, the inverted power supply 14 is shown while the piezoelectric transducer 50 is connected and operating at 2.9 kHz. The frequency of the maximum voltage drop or spike of the power supply 14 corresponds to the frequency of the drive signal, which occurs only when the piezoelectric transducer 50 is properly connected. Therefore, the operating state of the piezoelectric transducer 50 can be determined by comparing the frequency of the maximum voltage drop of the power supply 14 with the known frequency of the maximum voltage drop of the drive signal at a given frequency. In other words, if the frequency of the maximum voltage drop of the power supply 14 matches the known frequency of the maximum voltage drop when the piezoelectric transducer 50 is properly connected, the piezoelectric transducer 50 can be determined to be in an operating state. If the frequency of the maximum voltage drop of the power supply 14 does not match the known frequency of the maximum voltage drop when the piezoelectric transducer 50 is properly connected, the piezoelectric transducer 50 can be determined to be in a non-operating state. If a spike or frequency of the maximum voltage drop is present but does not match the known value for a properly connected piezoelectric transducer 50, it can also be determined that the drive signal is functioning.

[0029] Referring to Figure 11, a comparison of the voltages of the power supply 14 is shown with the drive signal provided and the piezoelectric transducer 50 disconnected, and with the piezoelectric transducer 50 connected. As discussed above, the frequency of the maximum voltage drop occurs only at the frequency of the drive signal when the piezoelectric transducer 50 is properly connected.

[0030] As shown in Figures 12 to 14, the maximum voltage drop values ​​at drive signal frequencies of 250 Hz (Figure 12), 500 Hz (Figure 13), and 750 Hz (Figure 14) are shown. The frequency of the maximum voltage drop value occurs at the drive signal frequency when the piezoelectric transducer 50 is properly connected across various drive signal frequencies.

[0031] In one aspect or embodiment, the voltage is measured further away from the power supply 14 and closer to where the power is supplied to the piezoelectric transducer 50. In another aspect or embodiment, instead of measuring an operating voltage value, an operating current value is measured and used to determine whether the piezoelectric transducer 50 is operating or non-operating. The operating current value is used in the same manner as the operating voltage value, as described above, to determine whether the piezoelectric transducer 50 is operating or non-operating. The operating current value may be calculated by measuring the voltage drop across a resistor, but other suitable configurations for measuring the operating current value may be used.

[0032] Referring to Figures 16 and 17, in a further aspect or embodiment, a method 70 for testing the drug delivery device 10 includes the steps of: activating the piezoelectric transducer 50 in an on / off pattern at a rate of 5 Hz per second; recording the battery voltage at the start of a second on / off sequence; recording 12 voltage value samples at a sampling frequency of 120 Hz during seven on / off periods; calculating and storing the average of the on / off voltage values; using the least squares method to fit a line to all data points during the seven recorded on / off periods; calculating the vertical distance from the seven average point to the fitted line; returning the minimum value of the distance; and determining whether the minimum value of the distance is less than 1.5. In one aspect or embodiment, if the minimum value of the distance is less than 1.5, the piezoelectric transducer 50 is determined to be unconnected. In one aspect or embodiment, if the final recorded voltage value is less than 2V, the drug delivery device 10 is determined to fail. In one aspect or embodiment, instead of 12 voltage value samples being recorded, two or more voltage value samples are recorded. In one aspect or embodiment, instead of recording voltage values ​​during seven on / off periods, voltage values ​​are recorded over two or more on / off periods. Furthermore, while a sampling frequency of 120 Hz is discussed, other suitable sampling frequencies may be utilized.

[0033] The present invention has been described in detail for illustrative purposes based on what is currently considered to be the most practical and preferred embodiment; however, such details are for that purpose only, and it should be understood that the present invention is not limited to the disclosed embodiments, but rather intended to encompass modifications and equivalent arrangements that fall within the spirit and scope of the appended claims. For example, it should be understood that, wherever possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

Claims

1. A method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, wherein the method is A step of operating the piezoelectric transducer by an on / off pattern at a predetermined modulation rate, A process of recording multiple voltage value samples via a detection circuit during multiple on / off periods, The steps include: calculating an average voltage value for at least a portion of the recorded samples using the microcontroller; The process involves performing least-squares linear approximation on the recorded voltage value samples using the microcontroller, The steps include determining a distance metric, which includes the vertical distance from the average voltage value to the approximate straight line, using the microcontroller, A step of determining whether the piezoelectric transducer is in an operating state or a non-operating state based on whether the distance metric satisfies a predetermined threshold, A method that includes this.

2. The method according to claim 1, wherein the predetermined modulation rate is 5 Hz.

3. The method according to claim 1, wherein the plurality of voltage value samples include at least 12 samples collected at a sampling frequency of 120 Hz.

4. The method according to claim 1, further comprising the step of recording the battery voltage at the start of the on / off pattern.

5. The method according to claim 1, wherein the distance metric includes the minimum vertical distance between the mean sample value and the least-squares approximation line.

6. The method according to claim 1, wherein the predetermined threshold includes a value of 1.

5.

7. The method according to claim 1, further comprising the step of determining that the piezoelectric transducer is disconnected when the minimum distance value is less than the predetermined threshold.

8. The method according to claim 1, wherein the microcontroller determines that the drug delivery device has failed if the final recorded voltage value is less than 2V.

9. The method according to claim 1, wherein the plurality of voltage value samples are recorded over two or more on / off periods.

10. The method according to claim 1, wherein the plurality of voltage value samples are recorded over seven on / off periods.

11. The method according to claim 1, wherein the least squares calculation is performed using a linear regression technique stored in memory.

12. The method according to claim 1, wherein the average voltage is calculated separately using the average of the values ​​during the on period and the average of the values ​​during the off period.

13. DC power supply and Piezoelectric transducer and A microcontroller programmed to perform the following, Equipped with, The aforementioned microcontroller is The piezoelectric transducer is activated by an on / off pattern at a predetermined modulation rate. Record multiple voltage value samples during multiple on / off periods. Least-squares linear approximation is performed on the voltage value samples, A distance metric including the vertical distance from the average voltage value to the aforementioned approximation line is calculated. A drug delivery device that determines whether the piezoelectric transducer is operating or not based on whether the distance metric satisfies a predetermined threshold.

14. The apparatus according to claim 13, wherein the microcontroller is further configured to record 12 voltage value samples at 120 Hz.

15. The apparatus according to claim 13, wherein the predetermined modulation rate is 5 Hz.

16. The apparatus according to claim 13, wherein the microcontroller determines that the drug delivery device has failed if the final recorded voltage value is less than 2V.

17. The apparatus according to claim 13, wherein the microcontroller calculates the least squares approximation using coefficients stored in a non-volatile memory.

18. When executed by the microcontroller of the drug delivery device, the microcontroller: The piezoelectric transducer is operated in an on / off pattern. Record multiple voltage value samples during the on / off period. Perform least-squares linear approximation on the voltage sample, The distance metric from the average voltage value to the approximate straight line is calculated, and A non-temporary computer-readable medium including an instruction that causes the piezoelectric transducer to determine whether it is operating or not based on the distance metric.

19. The computer-readable medium according to claim 18, wherein the instruction further causes the microcontroller to record an initial battery voltage at the start of the on / off pattern.

20. The computer-readable medium according to claim 18, wherein the instruction further causes the microcontroller to calculate the distance metric using seven on / off periods and twelve voltage samples collected at 120 Hz.

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