Patent Description:
Ultrasonic apparatuses are used in practice, in which an ultrasonic transducer transmits ultrasonic waves, receives reflected waves from an object to be detected, and thereby measures, for example, a distance to the object to be detected.

If a foreign substance, such as mud, adheres to the vibrating surface of the ultrasonic transducer, or if water droplets adhering to the vibrating surface freeze, an ultrasonic vibrator may be unable to properly perform transmission and reception. This may lead to failure in proper detection of an object to be detected existing in front of the ultrasonic vibrator.

<CIT> discloses an ultrasonic sensor that is capable of detecting adhesion of a foreign substance, such as mud. This ultrasonic sensor detects the resonant frequency of an ultrasonic vibrator, monitors and compares the resonant frequency with the natural frequency, and thereby detects an anomaly in the operation of the ultrasonic vibrator.

<CIT> discloses a configuration that measures the resonant frequency and the Q factor of an ultrasonic vibrator from reverberant vibration generated in the ultrasonic vibrator by transmitting an ultrasonic pulse, estimates an output amplitude using the measured resonant frequency and Q factor, and thus improves the performance of detecting an object located at a short distance.

The ultrasonic transducer (ultrasonic sensor) used in both <CIT> and <CIT> employs a so-called two-terminal ultrasonic vibrator in which a transmitting vibrator (transmitting electrode) for transmitting ultrasonic waves and a receiving vibrator (receiving electrode) for receiving reflected waves are combined. In the measurement of the resonant frequency and the Q factor in such a two-terminal ultrasonic transducer, the impedance of a transmitting circuit and a receiving circuit connected to a transmitting and receiving vibrator may interfere with accurate measurement of the resonant frequency and the Q factor.

Particularly in the configuration disclosed in <CIT>, where a transformer for boosting the voltage of a transmit signal is connected to the transmitting circuit (driving circuit), the inductance of the transformer affects the resonant frequency and the Q factor of the ultrasonic transducer.

<CIT> describes an ultrasonic piezoelectric transducer alternatingly operated in a transmitting mode and in a receiving mode. In the transmitting mode an electrical excitation signal is applied between one or more common electrodes and one or more transmission electrodes, and in the receiving mode an electrical reception signal is collected between the one or more common electrodes and one or more reception electrodes. Moreover, in the receiving mode one or more electrodes which are not used as reception electrodes are connected via a low impedance connection with the one or more common electrodes. This has the effect that in the receiving mode the resonance frequencies of the piezoelectric transducer are shifted to lower values so that with the same operating frequency the piezolectric transducer is in series resonance in the transmitting mode and in parallel resonance in the receiving mode. In this way, the piezoelectric transducer operates under better conditions with improved frequency matching for transmission and for reception.

<CIT> discloses an ultrasonic sensor device for which the performance of detecting an object at a short distance is improved, even when the vibration characteristic of an ultrasonic vibrator changes. The ultrasonic vibrator transmits an ultrasonic pulse and receives a reflection wave reflected at an object. The amplification unit amplifies an electric signal outputted from the ultrasonic vibrator. A first measurement unit measures, on the basis of the electric signal outputted from the ultrasonic vibrator, a Q value of reverberating vibration generated in the ultrasonic vibrator due to the ultrasonic pulse being transmitted. A second measurement unit measures the frequency of reverberating vibration on the basis of the electric signal outputted from the ultrasonic vibrator. A prediction unit predicts the output amplitude of the amplification unit on the basis of the Q value measured by the first measurement unit, the frequency measured by the second measurement unit, and the output amplitude in a non-saturated state outputted from the amplification unit. A comparison unit compares the output amplitude outputted from the amplification unit at a given point of time and the output amplitude predicted by the prediction unit at that point of time, and a determination unit determines, on the basis of the result of comparison, whether or not the object is present.

<CIT> discloses a device having at least one sensor and a controller, whereby the sensor is an acoustic sensor, especially an ultrasonic sensor, and the acoustic sensor values can be evaluated to detect objects. At least one acoustic sensor value can be evaluated by the controller for freedom from sensor faults, whereby the at least one measured sensor value can be compared with stored values of a normal sensor function.

<CIT> discusses an ultrasound sensor that can predict the reverberation time even in the presence of an obstacle. An ultrasound sensor comprises a piezoelectric vibrator, a drive unit that drives the piezoelectric vibrator, a variable capacity element connected in parallel to the piezoelectric vibrator, a signal processor that adjusts the capacity of the variable capacity element, and an attenuator that attenuates electric signals outputted from the piezoelectric vibrator and outputs the attenuated signals to the signal processor. The signal processor measures the peak voltage of reverberation signals that are generated when ultrasounds are transmitted from the piezoelectric vibrator, calculates the Q value of the piezoelectric vibrator on the basis of the measured peak voltage and adjusts the capacity of the variable capacity element on the basis of the calculated Q value of the piezoelectric vibrator.

<CIT> discusses an ultrasonic sensor that can suppress a reverberant vibration by using a simple circuit configuration. The ultrasonic sensor includes: a flat-plate-shaped piezoelectric body, which includes a transmission region for an ultrasonic wave and a reception region for a reflected wave of the ultrasonic wave; a common electrode that is provided in the transmission region and the reception region; a transmission electrode that is provided in the transmission region; a reception electrode that is provided in the reception region; a semiconductor element that is electrically connected to the transmission electrode and the reception electrode; and a semiconductor element that is electrically connected to the transmission electrode and the reception electrode and switches a path between a conductive state and a non-conductive state. The semiconductor element puts the path into the conductive state after application of the alternating-current voltage is stopped, and as a result, a reverberation signal, which is output from the reception region in accordance with a reverberant vibration of the ultrasonic wave, is fed back to the transmission electrode.

The present invention has been made in view of the problems described above. We have appreciated that it would be desirable to provide an ultrasonic apparatus that accurately measures the resonant frequency and the Q factor of an ultrasonic transducer, and thereby achieves improved accuracy in detecting anomalies of the ultrasonic transducer.

The invention is defined in the independent claim to which reference should now be made.

According to a first aspect of the invention, an ultrasonic apparatus comprises: a three-terminal ultrasonic transducer including a common electrode, a transmitting electrode, and a receiving electrode independent of the transmitting electrode; a piezoelectric body including a transmitting region for transmitting ultrasonic waves and a receiving region for receiving reflected ultrasonic waves, a transmitting circuit configured to output a driving signal to the transmitting electrode to cause the ultrasonic transducer to transmit ultrasonic waves; a receiving circuit configured to receive a receive signal from the receiving electrode; a frequency measuring circuit configured to measure a resonant frequency of the ultrasonic transducer from a reverberation signal in the receive signal; a Q-factor measuring circuit configured to measure a Q factor of the ultrasonic transducer from the reverberation signal, and an anomaly determining unit configured to determine an anomaly of the ultrasonic transducer on the basis of the Q factor measured by the Q-factor measuring circuit and the resonant frequency measured by the frequency measuring circuit, and determine an anomaly that results from a foreign substance adhering to the transducer based on changes in the Q factor or resonant frequency and by comparing the measured Q factor and the measured resonant frequency with known reference values for the Q factor and the resonant frequency measured when the ultrasonic transducer is clean.

Preferably, the anomaly determining circuit is configured to make an anomaly determination based on changes in the Q factor and resonant frequency due to the adhesion of mud or water droplets to the ultrasonic transducer.

Preferably, the transmitting electrode is disposed opposite the common electrode, with the transmitting region of the piezoelectric body interposed therebetween, and is electrically connected to the transmitting region, the receiving electrode is disposed opposite the common electrode with the receiving region of the piezoelectric body interposed therebetween, and is electrically connected to the receiving region, and the common electrode is electrically connected to both the transmitting region and the receiving region.

The ultrasonic apparatus preferably further includes a switching unit configured to ground the transmitting electrode when the Q-factor measuring circuit measures the Q factor and the frequency measuring circuit measures the resonant frequency.

The Q-factor measuring circuit preferably includes an envelope detecting circuit, a damping time measuring circuit, and a Q-factor calculating circuit. The envelope detecting circuit detects an envelope of an amplitude of the reverberation signal. The damping time measuring circuit measures a damping time taken by the amplitude to decay from a first amplitude to a second amplitude on the envelope. The Q-factor calculating circuit calculates the Q factor of the ultrasonic transducer on the basis of the first and second amplitudes, the damping time, and the resonant frequency of the ultrasonic transducer.

The ultrasonic apparatus preferably further includes a clock signal generating circuit configured to generate a clock signal used in common by the Q-factor measuring circuit and the frequency measuring circuit.

The present invention reduces the influence of the impedance of the transmitting circuit on the measurement of the resonant frequency and the Q factor of the ultrasonic transducer, and enables accurate measurement of the resonant frequency and the Q factor. This improves accuracy in detecting anomalies of the ultrasonic transducer.

Embodiments of the present invention will now be described in detail with reference to the drawings. The same or equivalent parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

<FIG> is a block diagram illustrating a general configuration of an ultrasonic apparatus <NUM> according to a first embodiment. Referring to <FIG>, the ultrasonic apparatus <NUM> includes a transmitting circuit <NUM>, an ultrasonic transducer <NUM>, an amplifier <NUM>, a receiving circuit <NUM>, an anomaly determining circuit <NUM>, and a detecting circuit <NUM>.

The transmitting circuit <NUM> is a circuit for transmitting ultrasonic waves from the ultrasonic transducer <NUM> by driving the ultrasonic transducer <NUM>. The transmitting circuit <NUM> includes a memory <NUM>, a control circuit <NUM>, and a signal generating circuit <NUM>. The control circuit <NUM> reads data stored in the memory <NUM> and outputs, to the signal generating circuit <NUM>, a control signal DRV suitable for driving the ultrasonic transducer <NUM>. On the basis of the control signal DRV output from the control circuit <NUM>, the signal generating circuit <NUM> generates an alternating-current voltage (ultrasonic pulse: transmit signal) from a direct-current voltage. The signal generating circuit <NUM> amplifies the generated alternating-current voltage as appropriate, and supplies the amplified alternating-current voltage to the ultrasonic transducer <NUM>. The configuration of the signal generating circuit <NUM> will be described in detail later on.

The ultrasonic transducer <NUM> is a so-called three-terminal ultrasonic transducer that includes a transmitting electrode <NUM> (terminal TX), a receiving electrode <NUM> (terminal RX), a common electrode <NUM> (terminal COM), and a piezoelectric body <NUM>. The transmitting electrode <NUM> and the common electrode <NUM> are connected to the signal generating circuit <NUM> of the transmitting circuit <NUM>. The receiving electrode <NUM> is connected to the receiving circuit <NUM> and the detecting circuit <NUM>, with the amplifier <NUM> interposed therebetween.

The piezoelectric body <NUM> includes a transmitting region 124A for transmitting ultrasonic waves, and a receiving region 124B for receiving reflected ultrasonic waves. The transmitting electrode <NUM> is disposed opposite the common electrode <NUM>, with the transmitting region 124A of the piezoelectric body <NUM> interposed therebetween, and is electrically connected to the transmitting region 124A. The receiving electrode <NUM> is disposed opposite the common electrode <NUM>, with the receiving region 124B of the piezoelectric body <NUM> interposed therebetween, and is electrically connected to the receiving region 124B. The common electrode <NUM> is electrically connected to both the transmitting region 124A and the receiving region 124B.

The transmitting electrode <NUM> receives a transmit signal from the signal generating circuit <NUM>. The transmitting region 124A of the piezoelectric body <NUM> vibrates the transmitting electrode <NUM> in accordance with the transmit signal, and thereby transmits ultrasonic waves from the transmitting electrode <NUM>, for example, into the air.

The ultrasonic waves transmitted from the transmitting electrode <NUM> are reflected by an object. The receiving electrode <NUM> receives the reflected waves from the object and vibrates. The receiving region 124B of the piezoelectric body <NUM> converts the vibration of the transmitting electrode <NUM> into an electric signal, and outputs the electric signal as a receive signal to the amplifier <NUM>.

The amplifier <NUM> is, for example, an inverting amplifier circuit that includes a resistor and an operational amplifier (neither of which is shown). The amplifier <NUM> amplifies the receive signal from the transmitting electrode <NUM> and outputs it to the receiving circuit <NUM> and the detecting circuit <NUM>.

The receiving circuit <NUM> receives the receive signal amplified by the amplifier <NUM>. The receiving circuit <NUM> detects the voltage value of the receive signal, and outputs a detected value RCV to the control circuit <NUM>.

On the basis of the receive signal amplified by the amplifier <NUM>, the detecting circuit <NUM> measures a resonant frequency (FRQ) and a Q factor (QV) of the ultrasonic transducer <NUM> as described below. The resonant frequency and the Q factor measured are output to the anomaly determining circuit <NUM>. In the present embodiment, the detecting circuit <NUM> is connected to the receiving electrode <NUM> of the three-terminal ultrasonic transducer <NUM>, in which the transmitting electrode <NUM> and the receiving electrode <NUM> are separated. This can reduce the influence of the impedance of the transmitting circuit <NUM> on the measurement of the resonant frequency and the Q factor.

Some recent systems that use an ultrasonic transducer originally have the function of detecting the envelope of a reverberation signal in a receive signal, such as that described above, and the function of measuring a resonant frequency. Therefore, when a Q-factor measuring circuit is connected to the receiving circuit, the envelope detecting function and the resonant frequency measuring function, which are originally included, can be combined for Q factor measurement. This makes it relatively easy to implement the Q-factor measuring circuit.

On the basis of the resonant frequency and the Q factor measured in the detecting circuit <NUM>, the anomaly determining circuit <NUM> makes an anomaly determination as to whether there is adhesion of, for example, water droplets or mud to the ultrasonic transducer <NUM>. The result of the determination made by the anomaly determining circuit <NUM> is output to the control circuit <NUM>. Although the anomaly determining circuit <NUM> in <FIG> is illustrated as a circuit independent of the control circuit <NUM>, the function of the anomaly determining circuit <NUM> may be included in the control circuit <NUM>.

On the basis of the detected value RCV from the receiving circuit <NUM>, the control circuit <NUM> identifies information about the presence and movement of an object and the distance to the object. If an anomaly is detected by the anomaly determining circuit <NUM>, the control circuit <NUM> notifies the user of the occurrence of the anomaly using a notification device (not shown). The ultrasonic apparatus <NUM> can be used, for example, as an ultrasonic sensor mounted on a vehicle.

<FIG> is a diagram for explaining details of the transmitting circuit <NUM> illustrated in <FIG>. Referring to <FIG>, the signal generating circuit <NUM> includes a positive power supply Vtx+, a negative power supply Vtx-, and switching elements (switching units) SW1 and SW2. The switching elements SW1 and SW2 are connected in series between the positive power supply Vtx+ and the negative power supply Vtx- to form a so-called half-bridge circuit. A connection node between the switching element SW1 and the switching element SW2 is connected to the transmitting electrode <NUM> (TX) of the ultrasonic transducer <NUM>. The switching elements SW1 and SW2 are controlled by the control signal DRV from the control circuit <NUM> and generate, from the direct-current positive power supply Vtx+ and negative power supply Vtx-, an alternating-current voltage (transmit signal) for driving the ultrasonic transducer <NUM>. Specifically, by bringing the switching element SW1 into conduction and bringing the switching element SW2 out of conduction, a positive pulse is output to the ultrasonic transducer <NUM>. Conversely, by bringing the switching element SW1 out of conduction and bringing the switching element SW2 into conduction, a negative pulse is output to the ultrasonic transducer <NUM>.

The common electrode <NUM> (COM) of the ultrasonic transducer <NUM> is connected to a ground potential GND in the transmitting circuit <NUM>.

<FIG> is a diagram illustrating another example of the transmitting circuit illustrated in <FIG>. A transmitting circuit 110A illustrated in <FIG> differs from the transmitting circuit in <FIG> in that a signal generating circuit 116A forms a full-bridge circuit.

Referring to <FIG>, the signal generating circuit 116A includes a direct-current power supply Vtx and switching elements (switching units) SW3 to SW6. The switching elements SW3 and SW4 are connected in series between the direct-current power supply Vtx and the ground potential GND. The switching elements SW5 and SW6 are also connected in series between the direct-current power supply Vtx and the ground potential GND. The switching elements SW3 to SW6 thus form a full-bridge circuit.

The transmitting electrode <NUM> (TX) of the ultrasonic transducer <NUM> is connected to a connection node between the switching element SW3 and the switching element SW4. The common electrode <NUM> (COM) of the ultrasonic transducer <NUM> is connected to a connection node between the switching element SW5 and the switching element SW6.

The switching elements SW3 to SW6 are controlled by the control signal DRV from the control circuit <NUM> and generate, from the direct-current power supply Vtx, an alternating-current voltage (transmit signal) for driving the ultrasonic transducer <NUM>. Specifically, by bringing the switching elements SW3 and SW6 into conduction and bringing the switching elements SW4 and SW5 out of conduction, a positive pulse is output to the ultrasonic transducer <NUM>. Conversely, by bringing the switching elements SW3 and SW6 out of conduction and bringing the switching elements SW4 and SW5 into conduction, a negative pulse is output to the ultrasonic transducer <NUM>.

With reference to <FIG> and <FIG>, a technique will be described which determines, from the resonant frequency and the Q factor of the ultrasonic transducer <NUM>, whether there is adhesion of water droplets and mud to the ultrasonic transducer <NUM>.

<FIG> is a graph showing how the resonant frequency and the Q factor change when water droplets adhere to the surface of the ultrasonic transducer <NUM>. <FIG> shows a relation between the amount of adhesion of water droplets (i.e., the number of water droplets) and the resonant frequency, and <FIG> shows a relation between the amount of adhesion of water droplets (i.e., the number of water droplets) and the Q factor. As can be seen from <FIG>, the resonant frequency decreases as the number of water droplets increases, whereas the Q factor stays substantially the same regardless of the number of water droplets.

<FIG> is a graph showing how the resonant frequency and the Q factor change when mud adheres to the surface of the ultrasonic transducer <NUM>. <FIG> shows a relation between the amount of adhesion of mud and the resonant frequency, and <FIG> shows a relation between the amount of adhesion of mud and the Q factor. As can be seen from <FIG>, when there is adhesion of mud, both the resonant frequency and the Q factor change depending on the degree of adhesion of mud (the amount of adhesion and the state of dryness).

Thus, measuring the changes in the resonant frequency and Q factor of the ultrasonic transducer <NUM> enables detection of an anomaly, that is, adhesion of water droplets or mud to the surface of the ultrasonic transducer <NUM>. To accurately detect an anomaly associated with adhesion of water droplets or mud to the ultrasonic transducer <NUM>, it is necessary to improve accuracy in measuring the resonant frequency and the Q factor.

<FIG> is a diagram illustrating details of the detecting circuit <NUM> illustrated in <FIG>. Referring to <FIG>, the detecting circuit <NUM> includes a Q-factor measuring circuit <NUM> and a resonant frequency measuring circuit <NUM>. The Q-factor measuring circuit <NUM> includes an envelope detector circuit <NUM>, a damping time measuring circuit <NUM>, and a Q-factor calculating circuit <NUM>.

The resonant frequency measuring circuit <NUM> receives a receive signal amplified by the amplifier <NUM>. From a reverberation signal in the receive signal, the resonant frequency measuring circuit <NUM> measures the resonant frequency of the ultrasonic transducer <NUM>. The measured resonant frequency is output to the Q-factor calculating circuit <NUM> and the anomaly determining circuit <NUM>.

The envelope detector circuit <NUM> calculates the envelope of the reverberation signal in the receive signal. The damping time measuring circuit <NUM> measures the damping time between amplitude voltages at any two points on the envelope obtained by the envelope detector circuit <NUM>. The Q-factor calculating circuit <NUM> calculates the Q factor using the amplitude voltages at two points on the envelope used in the damping time measuring circuit <NUM>, the damping time therebetween, and the resonant frequency measured by the resonant frequency measuring circuit <NUM>. The Q-factor calculating circuit <NUM> then outputs the calculated Q factor to the anomaly determining circuit <NUM>.

With reference to <FIG>, technical details of how the resonant frequency measuring circuit <NUM> and the Q-factor measuring circuit <NUM> measure the resonant frequency and the Q factor, respectively, will be further described.

Referring to <FIG>, when the transmitting electrode <NUM> transmits ultrasonic waves, the ultrasonic transducer <NUM> continues to vibrate at the natural frequency (resonant frequency) of the ultrasonic transducer <NUM> for a while even after the transmission ends. Generally, this vibration is referred to as "reverberant vibration", and the signal appearing in the receive signal at this point is referred to as "reverberation signal". As represented by a solid curve LN1 in <FIG>, the reverberation signal is a signal that vibrates while gradually decreasing in amplitude with time.

The period of time between adjacent peaks of the reverberation signal is a period TRES of reverberant vibration, and the reciprocal of the period TRES corresponds to the resonant frequency fRES (= <NUM>/TRES) of the ultrasonic transducer <NUM>. Therefore, the resonant frequency of the ultrasonic transducer <NUM> can be measured by measuring the time interval between adjacent peaks, or by measuring the time interval between zero-crossing points at which the amplitude is zero.

The Q factor can be typically expressed as Q = <NUM>/2ζ, where ζ is the damping ratio of a damping signal. When, as in <FIG>, the amplitude decays from an amplitude an to an amplitude an+m over m periods, the Q factor can be expressed by the following equation (<NUM>). [Equation <NUM>] <MAT>.

However, the calculation technique using the equation (<NUM>) requires an additional circuit that determines the amplitude of each peak of the reverberation signal. By using the envelope (indicated by a dot-and-dash curve LN2 in <FIG>) of the reverberation signal, the equation (<NUM>) can be rewritten as the following equation (<NUM>), where aHIGH and aLOW are amplitudes at any two points on the envelope, and tDMP is the damping time between the two points. [Equation <NUM>] <MAT>.

In <FIG>, for ease of understanding, the two amplitudes aHIGH and aLOW are expressed as peak amplitudes an and an+m, and the relation tDMP = m · TRES is satisfied. However, the two amplitudes do not necessarily need to be peak amplitudes, and may be any points on the envelope. That is, using the envelope makes it possible to measure the Q factor without detecting peak amplitudes.

<FIG> is a diagram illustrating details of the damping time measuring circuit <NUM> and the resonant frequency measuring circuit <NUM> in <FIG> that are configured to execute the computation illustrated in <FIG>.

Referring to <FIG>, the resonant frequency measuring circuit <NUM> includes a comparator <NUM>, a counter <NUM>, and a frequency calculating circuit <NUM>.

The comparator <NUM> compares an amplified receive signal to an alternating-current ground potential AC_GND, removes a direct-current bias in the receive signal, and converts the receive signal into an alternating-current signal. The counter <NUM> counts the time interval between zero-crossing points of the receive signal output from the comparator <NUM>. On the basis of the counter value from the counter <NUM>, the frequency calculating circuit <NUM> calculates the period TRES of the reverberation signal from the zero-crossing time points, and calculates the resonant frequency fRES (= FRQ) by taking the reciprocal of the period TRES.

The damping time measuring circuit <NUM> includes comparators <NUM> and <NUM>, an exclusive OR (XOR) circuit <NUM>, and a counter <NUM>.

The comparator <NUM> compares the envelope value to the threshold aHIGH on the high amplitude side, and the comparator <NUM> compares the envelope value to the threshold aLOW on the low amplitude side. From the outputs of the comparators <NUM> and <NUM>, the XOR circuit <NUM> continues to output a logical HIGH signal until the amplitude aHIGH on the envelope decays to aLOW. By counting the time during which the output from the XOR circuit <NUM> is logical HIGH, the counter <NUM> calculates the damping time tDMP taken by the amplitude on the envelope to decay from aHIGH to aLOW. Then, the Q-factor calculating circuit <NUM> calculates the Q factor from the equation (<NUM>) on the basis of the amplitudes aHIGH and aLOW, the damping time tDMP, and the period TRES.

A clock signal generating circuit <NUM> is further provided in <FIG>. The clock signal generating circuit <NUM> is configured to output a common clock signal fCLK to the counter <NUM> of the damping time measuring circuit <NUM> and the counter <NUM> of the resonant frequency measuring circuit <NUM>. When the common clock signal fCLK is used, the equations tDMP = NDMP/fCLK and TRES = NRES/fCLK hold, where NDMP is the count value of the counter <NUM> and NRES is the count value of the counter <NUM>. The equation (<NUM>) can thus be rewritten as the following equation (<NUM>). [Equation <NUM>] <MAT>.

That is, by using the common clock signal fCLK for the counters <NUM> and <NUM>, the Q factor can be measured using only the count values of the counters. This makes it possible to eliminate the influence of frequency accuracy of the clock signal, and thus to further improve accuracy in measuring the Q factor.

The Q factor and the resonant frequency measured as described above are input to the anomaly determining circuit <NUM>, which determines an anomaly associated with adhesion of water droplets and mud on the basis of such relations as those shown in <FIG> and <FIG>.

As described above, a three-terminal ultrasonic transducer is used, and a detecting circuit is connected to the receiving electrode of the ultrasonic transducer to measure the resonant frequency and the Q factor of the ultrasonic transducer. This reduces the influence of the impedance of the transmitting circuit, and improves accuracy in measuring the resonant frequency and the Q factor. It is thus possible to improve accuracy in detecting an anomaly associated with adhesion of water droplets and mud to the ultrasonic transducer.

<FIG> is a diagram illustrating a modification of the detecting circuit of the ultrasonic apparatus <NUM> according to the first embodiment. A detecting circuit 200A according to a first modification is obtained by adding a frequency divider circuit <NUM> to the resonant frequency measuring circuit <NUM> of the detecting circuit <NUM> illustrated in <FIG>. Referring to <FIG>, the resonant frequency measuring circuit 250A includes the comparator <NUM>, the frequency divider circuit <NUM>, the counter <NUM>, and the frequency calculating circuit <NUM>. Of the elements illustrated in <FIG>, the same ones as those illustrated in <FIG> will not be described again here.

Referring to <FIG>, the frequency divider circuit <NUM> divides the frequency of the receive signal output from the comparator <NUM>. On the basis of the signal frequency-divided by the frequency divider circuit <NUM>, the counter <NUM> calculates the period TRES of the reverberation signal. Since the frequency divider circuit <NUM> enables the period TRES (i.e., resonant frequency fRES) to be calculated on the basis of multiple periods of time, the resolution (precision) of the measured resonant frequency can be further improved.

<FIG> is a diagram illustrating a modification obtained by adding an A/D converter circuit <NUM> upstream of the detecting circuit <NUM> in the ultrasonic apparatus <NUM> of the first embodiment. In the modification illustrated in <FIG>, signal processing in the detecting circuit <NUM> is executed by a digital circuit.

The configuration of the second modification may be combined with the configuration of the first modification.

When a three-terminal ultrasonic transducer is used as in the first embodiment, the influence of the impedance of the transmitting circuit <NUM> can be reduced to a certain extent. When the impedance of the transmitting circuit <NUM> varies, however, the measured electrostatic capacitance value may also vary.

A second embodiment described herein provides a configuration in which, when the resonant frequency and the Q factor are measured in the detecting circuit <NUM> on the receiving side, the transmitting electrode <NUM> is grounded so as to fix the impedance of the transmitting circuit <NUM> and stabilize the measurement of electrostatic capacitance.

<FIG> is an overall block diagram of an ultrasonic apparatus <NUM># according to the second embodiment. In <FIG>, a transmitting circuit <NUM># replaces the transmitting circuit <NUM> of the first embodiment illustrated in <FIG>. The transmitting circuit <NUM># includes a switching unit (switching element) SW7, as well as the components of the transmitting circuit <NUM> illustrated in <FIG>. The switching element SW7 is capable of enabling and disabling conduction between the transmitting electrode <NUM> and the ground potential GND. When the detecting circuit <NUM> measures the resonant frequency and the Q factor, the switching element SW7 is brought into conduction to connect the transmitting electrode <NUM> to the ground potential GND.

<FIG> is a diagram corresponding to <FIG> of the first embodiment. <FIG> illustrates the transmitting circuit <NUM># in which the signal generating circuit <NUM> is formed as a half-bridge circuit. In the transmitting circuit <NUM>#, the switching element SW7 is electrically connected at one end thereof to a connection node between the switching element SW1 and the switching element SW2 (i.e., to the transmitting electrode <NUM>), and connected at the other end thereof to the ground potential GND. The switching element SW7 is driven by the control circuit <NUM> and brought into conduction when the resonant frequency and the Q factor are measured in the detecting circuit <NUM>.

The impedance between TX and COM is thus short-circuited and completely removed. This makes it possible to eliminate the influence of the impedance of the transmitting circuit.

While not shown, if the signal generating circuit <NUM> is formed as a full-bridge circuit, the influence of the impedance of the transmitting-side circuit can be eliminated in the same manner as in <FIG> without requiring the switching element SW7. More specifically, since TX and COM can be short-circuited by bringing the switching element SW4 into conduction in <FIG>, there is no need to add the switching element SW7.

<FIG> and <FIG> are graphs showing a result of simulation which simulated errors from the designed values of Q-factor and resonant frequency under conditions in which, during measurement of the Q factor and the resonant frequency, the transmitting electrode was grounded (second embodiment) and not grounded (first embodiment). For both the Q factor and the resonant frequency, the simulation was carried out at an element temperature of -<NUM>, +<NUM>, and +<NUM>.

<FIG> and <FIG> show that at any temperature, for both the Q factor and the resonant frequency, the measurement error that occurred when the transmitting electrode was grounded was smaller than the measurement error that occurred when the transmitting electrode was not grounded (i.e., the measurement error in the former case was closer to zero than that in the latter case was).

As described above, a three-terminal ultrasonic transducer is used, a detecting circuit is connected to the receiving electrode of the ultrasonic transducer to measure the resonant frequency and the Q factor of the ultrasonic transducer, and the transmitting electrode is grounded when the resonant frequency and the Q factor are measured. Thus, the influence of the impedance of the transmitting circuit on the resonant frequency and the Q factor can be eliminated. This further improves accuracy in measuring the resonant frequency and the Q factor, and improves accuracy in detecting an anomaly associated with adhesion of water droplets and mud to the ultrasonic transducer.

The second embodiment is also applicable to the modifications of the first embodiment.

Claim 1:
An ultrasonic apparatus (<NUM>) comprising:
a three-terminal ultrasonic transducer (<NUM>) including a common electrode (<NUM>), a transmitting electrode (<NUM>), a receiving electrode (<NUM>) independent of the transmitting electrode, and
a piezoelectric body (<NUM>) including a transmitting region (124A) for transmitting ultrasonic waves and a receiving region (124B) for receiving reflected ultrasonic waves;
a transmitting circuit (<NUM>) configured to output a driving signal to the transmitting electrode to cause the ultrasonic transducer to transmit ultrasonic waves;
a receiving circuit (<NUM>) configured to receive a receive signal from the receiving electrode;
a frequency measuring circuit (<NUM>, <NUM>) configured to measure a resonant frequency of the ultrasonic transducer from a reverberation signal in the receive signal;
a Q-factor measuring circuit (<NUM>, <NUM>) configured to measure a Q factor of the ultrasonic transducer from the reverberation signal, and
an anomaly determining unit (<NUM>) configured to determine an anomaly of the ultrasonic transducer on the basis of the Q factor measured by the Q-factor measuring circuit (<NUM>, <NUM>) and the resonant frequency measured by the frequency measuring circuit (<NUM>, <NUM>).