CN114465521A

CN114465521A - Method of operating an electroacoustic transducer, and corresponding circuit and device

Info

Publication number: CN114465521A
Application number: CN202111312717.6A
Authority: CN
Inventors: M·帕索尼
Original assignee: STMicroelectronics SRL
Current assignee: STMicroelectronics SRL
Priority date: 2020-11-09
Filing date: 2021-11-08
Publication date: 2022-05-10

Abstract

Embodiments of the present disclosure relate to methods of operating electroacoustic transducers, and corresponding circuits and devices. An electro-acoustic transducer, such as a piezoelectric micromachined ultrasonic transducer, is coupled with an adjustable load circuit having an adjustable load parameter set including a resistance parameter and an inductance parameter. Starting from at least one resonance frequency or at least one ring down parameter of the electroacoustic transducer, a set of model parameters is calculated for a Butterworth-Vandyk (BVD) model of the electroacoustic transducer. The BVD model comprises an equivalent circuit network having a constant capacitance coupled to the RLC branch, and the adjustable load circuit is coupled with the electroacoustic transducer at an input port of the equivalent circuit network of the model of the electroacoustic transducer. The adjustable load parameters are adjusted according to a set of model parameters calculated for the BVD model of the electro-acoustic transducer to increase the bandwidth or sensitivity of the electro-acoustic transducer.

Description

Method of operating an electroacoustic transducer, and corresponding circuit and device

Technical Field

The present description relates to electroacoustic transducers, i.e. components capable of converting electrical signals into acoustic signals and/or components capable of converting acoustic signals into electrical signals.

An ultrasonic transducer is an example of such a transducer.

Background

Ultrasonic transducers are contemplated for use in a variety of applications.

For example, they may be used in acoustic localization methods in vehicles, where (ultra) sound waves may be used to determine the distance and/or direction of a source or reflector.

Such transducers may be used in Doppler effect (Doppler effect) based and/or time of flight (TOF) acoustic wave based techniques. Obstacle detection (one-dimensional, two-dimensional, three-dimensional), volume measurement, gesture recognition and (doppler-based) flow metering are examples of possible application areas.

Ultrasonic transducers currently known as PMUT (piezoelectric micromachined ultrasonic transducer) are MEMS-based piezoelectric transducers (where MEMS is an acronym for microelectromechanical systems) that utilize the bending motion of a membrane coupled to a piezoelectric membrane, unlike bulk piezoelectric transducers that rely on thickness mode motion.

Compared to body transducers, PMUTs may exhibit an underdamped mechanical response, thus involving many oscillation cycles once the membrane moves from a steady-state position back to a stationary state; this may be due to reduced internal energy losses of the transducer (due to the micro silicon membrane) and reduced damping applied by the medium (air). In other words, they may exhibit a narrow bandwidth, since the excitation and damping membranes may include several oscillation cycles, resulting in possible differences in the resonant frequency of each individual membrane due to manufacturing tolerances, which may affect the duration, accuracy and resolution of measurements in applications (e.g., distance measurements) utilizing PMUTs.

Thus, certain advantages associated with the use of PMUTs (such as small size and low drive voltage) may be adversely offset by narrow available bandwidth, dependence on manufacturing tolerances, and differences in resonant frequency.

In applications where multiple PMUTs are used (such as, for example, echo location), mechanical crosstalk in combination with a narrow bandwidth may limit the ability to measure objects in close proximity, as the receiver membrane(s) may be "blocked" for an undesirable amount of time.

Other problems may be related to the undesired extension of certain (mechanical) parameter values of different PMUTs (in particular, the resonance frequency), where low damping may further hinder communication between different PMUT devices (e.g., where the transmitter and receiver cannot communicate with each other).

Italian patent application No. 102019000003613 addresses the problem of resonant frequency spread by exploiting the dependence of the resonant frequency on voltage bias.

Various files are examples of activities directed to bandwidth manipulation methods in transducers as contemplated herein.

For example, "Frequency Tuning Technique of Piezoelectric Ultrasonic Transducers for Ranging Applications", Journal of Microelectromechanical Systems27(2018):570-579, doi: 10.1109/mems.2018.2831638, of robichoud, a., p.cic, d.deslandes, and f.nabki, discusses a low cost Technique for Frequency Tuning of Piezoelectric Micromachined Ultrasonic Transducers (PMUT), where the resonant frequencies of the first and second modes are 1.4MHz and 5MHz, respectively. This technique is based on a single post-treatment deposition of parylene-C on all elements of the chip, thereby providing uniform frequency tuning of all exposed elements.

De Marneffe and a. premium in 2008 "Vibration damping with reactive damping mounts: the organic and experimental", doi:10.1088/0964-1726/17/3/035015 in Smart Materials and Structures (Smart Materials and Structures) discusses enhancing piezoelectric stack transducers by means of the well-known 'negative' capacitive shunt, where two different implementations (series and parallel) were studied and the parallel application to truss Structures.

Ramos A, San Emeterio JL, Sanz PT., "Improvement in transformed pixel electric responses of NDE transformed using selective damping and tuning networks", IEEE Trans Ultrason ferroelctr Freq Control, 2000; 826-35, doi:10.1109/58.852064 discusses non-destructive inspection ultrasound applications for quality control purposes based on piezoelectric devices operating as pulsed ultrasound probes, which typically include some tuned circuitry across the pulser output connector or near the piezoelectric probe electrodes, with the positive effects of certain selective damping and tuning networks on the time and frequency behavior of the NDE piezoelectric transceiver being analyzed in detail.

"electric impedance matching network structures for high frequency uplink transceivers" in sens.actuators a, by j.y.moon, j.lee, j.h.chang, 2016, doi: 10.1016/j.sna.2016.10.025 discusses proposing an Electrical Impedance Matching (EIM) network to achieve a wide bandwidth of a high-frequency ultrasound transducer and to improve a signal-to-noise ratio (SNR) of an ultrasound image, wherein the EIM network is based on a general filter structure, i.e., a Low Pass Filter (LPF) structure or a High Pass Filter (HPF) structure composed of a capacitor and an inductor.

Existing solutions have drawbacks such as:

adding complexity and cost, for example due to the introduction of additional manufacturing steps;

increased bandwidth involves reduced sensitivity; and

compared with limited improvement, the transceiver is not suitable for operation and tedious arrangement.

Disclosure of Invention

Despite the activities in this area, there is still an interest in providing further improved solutions that can overcome the drawbacks of the existing solutions.

Embodiments of the present disclosure help to provide such an improved solution.

In accordance with one or more embodiments, there is provided a method comprising: obtaining at least one of a resonant frequency and at least one ring down parameter of an electro-acoustic transducer having a sensitivity and a frequency bandwidth; calculating a set of model parameters of a Butterworth-Van Dyke (BVD) model of the electroacoustic transducer based on at least one of the resonance frequency and the at least one ring down parameter, the BVD model comprising an equivalent circuit network having a constant capacitance coupled to the RLC branches; coupling an adjustable load circuit with the electroacoustic transducer, the adjustable load circuit having an adjustable load parameter set comprising at least one resistance parameter and one inductance parameter, wherein the adjustable load circuit is coupled with the electroacoustic transducer at an input port of the equivalent circuit network of the BVD model; and adjusting the set of adjustable load parameters to increase at least one of the bandwidth and the sensitivity of the electro-acoustic transducer as a result of the adjusting according to the calculated set of model parameters of the BVD model of the electro-acoustic transducer.

One or more embodiments may relate to a corresponding circuit.

One or more embodiments may relate to a corresponding device (an acoustic position sensor module is an example of such a device).

Obstacle detection systems (e.g. for the automotive field), volume measurement systems, gesture recognition systems or flow metering systems are examples of such systems.

The claims are an integral part of the technical teaching provided herein with reference to the examples.

One or more embodiments may facilitate broadening the bandwidth while achieving or maintaining a sufficient level of sensitivity for the ultrasound transducer.

Drawings

One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 is a diagram of the operating principle of a PMUT transducer device;

FIGS. 2, 3A, 3B, 4 and 5 illustrate models that may be applicable to an embodiment;

FIGS. 6, 7A and 7B illustrate possible utilizations of models in embodiments;

FIG. 8 is an example of a flow chart of possible actions in an embodiment;

FIG. 9 is an example of a possible hardware architecture for an embodiment;

10A and 10B are examples of criteria that may be employed in embodiments to identify certain parameters of an electroacoustic transducer;

11, 12 and 13 illustrate a possible alternative utilization of the model of FIG. 6 in an embodiment; and

fig. 14 is an example of a system operable according to an embodiment.

Detailed Description

In the following description, one or more specific details are set forth in order to provide a thorough understanding of the examples of embodiments described herein. The embodiments may be practiced without one or more of the specific details or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to not obscure certain aspects of the embodiments.

Reference to "one embodiment" or "an embodiment" within the framework of the specification is intended to indicate that a particular configuration, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, phrases such as "in an embodiment" or "in one embodiment" that may be present at one or more points in the specification do not necessarily refer to the same embodiment. Furthermore, in one or more embodiments, particular conformations, structures or features may be combined in any suitable manner.

References used herein are for convenience only and do not limit the scope or the breadth of the embodiments.

It should be appreciated that one or more embodiments apply to electro-acoustic transducers, i.e., components capable of acting as a transducer between the electrical domain and the acoustic domain by converting electrical signals to acoustic signals and/or acoustic signals to electrical signals; that is, the term "electro-acoustic" must not be interpreted, even indirectly, as being limited to merely converting an electrical signal into an acoustic signal.

Furthermore, for simplicity and ease of understanding, the exemplary description provided below refers to an arrangement that includes at least one of a "transmitter" section configured to convert electrical signals to transmitted acoustic signals (e.g., toward an obstacle) and a "receiver" section configured to convert received acoustic signals (e.g., reflected from an obstacle) to electrical signals.

However, embodiments are not limited to such possible arrangements and may be advantageously applied to arrangements comprising both a "transmitter" section and a "receiver" section, which for the sake of brevity are referred to as "transceivers".

Also, while the exemplary description provided below refers to an ultrasonic transducer for simplicity and ease of understanding, in general, one or more embodiments may be applied to an electro-acoustic transducer capable of acting as a transducer between the electrical and acoustic domains. In this regard, while reference is made throughout to PMUTs for simplicity and ease of understanding, embodiments may be advantageously applied to electroacoustic transducers other than PMUTs where problems such as those discussed above may arise.

Finally, while one or more embodiments may consider using different transducers for transmission and reception, certain embodiments may consider a single transducer configured to function as both a transmitter and a receiver.

As illustrated in fig. 1, the PMUT transducer device 10 includes a MEMS-based piezoelectric layer 12 sandwiched between electrodes or

terminals

14a and 14b and suspended from a (silicon) substrate 16, thereby forming a

membrane stack

14a, 12, 14b, 16.

The device 10 as exemplified herein may function as both a transmitter and a receiver.

When operating as a transmitter, a voltage generator configured to generate an alternating voltage is connected to the

contacts

14a, 14b so as to generate a corresponding electric field in the piezoelectric layer 12, causing a deformation thereof (due to the inverse piezoelectric effect), and so that the deformation caused also causes a deflection of the membrane, also due to the geometry of the device 10, in which a corresponding pressure wave emission is generated in the surrounding medium.

When operating as a receiver, the incoming pressure wave causes deflection of the piezoelectric layer 12, causing charge polarization at the transducer contacts 12a, 12b due to the (direct) piezoelectric effect; the polarization may be detected by an amplifier (e.g., a transimpedance amplifier) connected to the

transducer terminals

14a, 14 b.

Fig. 1 illustrates a possible opposite deflection or deformation of the layer 12 as a result of the application of a suitable alternating voltage at its

contacts

14a, 14 b.

As discussed, the number of membranes used may be from one (membrane stack for transmission then switched to receiver) to more than one at transmission and from one to more than one at reception.

For example, when performing 2D or 3D echo localization, it may be advantageous to use multiple membranes, as this may increase the sensitivity when transmitting or receiving. Sensitivity may be defined as the maximum (amplitude) value of the relevant frequency response or transfer function.

The arrangement as illustrated in fig. 1 is otherwise conventional in the art, which makes it unnecessary to provide a more detailed description herein.

As discussed in the foregoing, the obstacle detection/ranging transducer arrangement as considered herein is an example of a number of possible applications (volume measurement, gesture recognition, flow metering, to name a few), including applications that consider only the "transmitter" segment or only the "receiver" segment.

As discussed, when an ultrasound transducer such as PMUT 10 is used for such applications, the bandwidths of the transmitter and/or receiver segments do not overlap, or only partially overlap, so that there may be little or even no information about the reflected sound in the acquired signal.

As illustrated in fig. 2, the piezoelectric ultrasonic transducer device 10 illustrated in fig. 1 may be modeled using a butterworth-vandyke model (BVD). As known to those skilled in the art, the BVD model is an electrical equivalent network of lumped elements that models the behavior of device 10 in at least one of the mechanical, acoustic, and electrical domains.

By way of background only, the butterworth-vandyke model (also referred to as the "Mason" model or "KLM" model) is an electrical equivalent circuit of an electroacoustic transducer that includes an electrical domain coupled to a mechanical domain (theoretically having multiple normal modes) via an electromechanical coupling. The mechanical domain is in turn coupled to the acoustic domain via a mechanical acoustic coupling. Butterworth-Vandyk/Mason/KLM is known to those skilled in the art and therefore a more detailed description is not necessary here.

As an electrical equivalent circuit, the electrical domain may be represented using an equivalent network as seen at the electrical contacts or

terminals

14a, 14b, as shown in fig. 2, e.g. comprising a value C in parallel with the RLC branches when performing impedance measurements₀The RLC branch comprises a series connection of a resistor of value R, an inductor of value L and a capacitor of value C.

Fig. 3A and 3B are example graphs of the amplitude (dBOhm-ordinate in fig. 3A) and phase (deg. -ordinate in fig. 3B) versus frequency (kHz-abscissa in fig. 3A and 3B) of the impedance Z as seen at the input port of the equivalent circuit discussed with reference to fig. 2.

The following relationship may apply to the equivalent circuit illustrated in fig. 2:

f₀＝(1/2π)(L/[C₀C/(C₀+C)])^1/2

τ＝2(L/R)

wherein f is₀And τ indicate the resonance frequency and the decay time, respectively. These may be obtained from the measurement/detection of ring down signals, as discussed below.

There are two equations and four unknowns (i.e., BVD model parameters L, R, C, C)₀) Such a system does not allow a univocal solution. However, in the current context (e.g., PMUT), a (sensible) assumption may be made, i.e., C₀Much larger than C (so that a constant value can be used for C₀). The value of the resistor R may be determined from the amplitude of the ring down signal discussed below so that the system may be solved.

In view of the impedance Z at the input port of the equivalent circuit, a simplified BVD model may be provided for the transmitter transducer (electrical to acoustic) and the receiver transducer (acoustic to electrical) as represented in fig. 4 and 5, respectively, wherein components or elements already discussed in connection with previous figures are indicated by the same reference numerals.

In the transmitter model of fig. 4, ES represents an (electrical) excitation signal that is applied to the transmitter transducer device via a (voltage) generator 50 coupled at its nodes (e.g. at

electrodes

14a and 14b of device 10 in fig. 1), which generator 50 produces a current a in the RLC branch of the circuit that is indicative of (proportional to) the (ultra) sound pressure level transmitted by transducer 10.

The circuit as illustrated in fig. 4 has a response or transfer function H_T(s) the response or transfer function H_T(s) can be expressed as:

in the receiver model of fig. 5, PV represents a voltage (proportional) indicative of the incident (and (ultrasonic) sound pressure level (e.g., sensed at the membrane layer 12 in fig. 1), and SM represents a measured (current) signal that may be sensed via a transimpedance amplifier 60 coupled at a node of the device 10 (e.g., at the

electrodes

14a and 14b of the device 10 in fig. 1).

Due to reciprocity, the response or transfer function H of the circuit as illustrated in FIG. 5_R(s) is equal to the response or transfer function H of the transmitter mode_R(s), it can therefore be expressed as:

for simplicity, since the response/transfer functions of the receiver/transmitter arrangements are equal, in the following discussion a single common transfer function g(s) is mentioned.

It should be noted that broadening the bandwidth BW of the transfer function g(s) of the device 10 without desensitizing it may improve the performance of the latter.

As illustrated in fig. 6, the widening approach to the bandwidth of the device 10 may include coupling a (passive) load circuit block 70 interposed between the generator 50 (or amplifier 60) and the input port (as modeled by the equivalent network) to the device 10.

For example, load circuit block 70 may include a load resistor R arranged in series between a node of generator 50 (or amplifier 60) and node 14a of the BVD model equivalent circuit_LAnd a load inductor L_L。

The common transfer function g(s) of the arrangement as illustrated in fig. 6 may be expressed as:

wherein

Is a capacitor C₀The impedance of (a) of (b) is,

Z_RLC(s) is the impedance of the RLC leg, an

Z_TOT(s) is the impedance seen from the input port at ES.

Fig. 7A and 7B show the absolute value | g(s) and phase < g(s) of the transfer function g(s) of the arrangement of fig. 4, 5 (solid line, labeled RLC) and the arrangement of fig. 6 including a load (dash-dotted line, labeled RLC + RL) compared to frequency, respectively.

In the exemplary case of fig. 7A, 7B, a resonance frequency of 100kHz and a fractional bandwidth of 1% may be considered for deriving parameters of the equivalent circuit based on the BVD model.

As illustrated herein, parameter R, L, C, C₀And resonant frequency f of the BVD model circuit₀And the decay time tau may be measured and calibrated using the method as discussed in US 2020/0292684 a 1.

Fig. 7A and 7B illustrate an example in which the load block 70 includes a resistor having a (first) resistance value R_LAnd a resistor having an inductance value L_LIn the case of an inductor L (e.g., about millihenry), the transfer function of the circuit as illustrated in fig. 6 and the transfer function of the circuit as illustrated in fig. 4 (or fig. 5).

As illustrated in fig. 7A and 7B:

the ring shaped symbols in fig. 7A and 7B are at a first peak frequency f of the device 10₀At least one of (1) and (b);

the dot-shaped symbols in fig. 7A and 7B are at a second peak frequency f of the device 10 coupled to the load 70₀' at;

the diamond-shaped mark pair indicates the first (-3dB) cut-off frequency pair f₁、f₂(ii) a And

the square mark pair indicates the second (-3dB) cut-off frequency pair f₁’、f₂’。

Fig. 7A and 7B are examples of possibilities to widen the-3 dB bandwidth (referring to the maximum value of the absolute value of the transfer function) from a first value BW ═ 1% (RLC) to a second value BW' ═ 6.3% (RLC + RL) as a result of coupling the load block 70 to the device 10.

This result can also be understood via a simple visual comparison between the amplitude values of the transfer functions g(s) of the equivalent circuits of RLC and RLC + RL.

Although there are examples of advantageous choices, the numerical values mentioned above should not be construed as even indirectly limiting the embodiments.

Fig. 7A also demonstrates the possible improvement in sensitivity, e.g., +10dB, as the peak (absolute value) of the transfer function g(s) increases due to the load 70 coupled to the device 10.

In one or more embodiments, the load block 70 may be configured to (ideally) maximize the bandwidth of the transfer function g(s), while facilitating compliance of the sensitivity with certain specifications.

This may involve a parameter (e.g., R) of load block 70 determined as a function of the value of parameter R, L, C, C0 of the equivalent network circuit based on the BVD model of FIG. 2_L、L_L) Selection of the value of (c).

As illustrated in fig. 6, the external load 70 may include a circuit configured (for the resistance RL and/or for the inductor L)_L) An adjustable (e.g., programmable) load whose value is adjusted in time.

This may facilitate maintaining a wide bandwidth BW for extended periods of time, compensating for possible changes in PMUT parameters over time (e.g., due to aging, drift, hysteresis in voltage bias changes, etc.).

Advantageously, the load inductor L_LThere may be a "synthetic" Inductor, e.g. a circuit configured to mimic the behavior of an inductance, as exemplified by "Analytical Study of Inductor Simulation Circuits" in Active and Passive elec.comp.1999 to u.kumar et al. The use of such a composite inductor may facilitate achieving inductance values in the millihenry range as well as facilitate circuit integration.

In one or more embodiments, is the load parameter R_L、L_LSelecting a theoretical "optimal" value can be burdensome. The external load 70 adds two new poles to the transfer function g(s); ideally, these poles are complex with each otherConjugate and is located at a frequency close to the frequency of the RLC leg of device 10.

In one or more embodiments, the following scenarios may exist:

a) the capacitance values of BVD model circuits C0 and C satisfy the following expression:

b) the transducer may have a very narrow bandwidth (e.g., Q factor ≈ 100).

In this exemplary scenario, an approximation of a load 70 may be calculated, the load 70 including a resistance R_L0And an inductance L_L0The resistor R of_L0And an inductance L_L0Matches the RLC resonant circuit of the BVD model, which can be expressed as:

where k may be in the range of 5 to 10 in order to further increase the bandwidth of the transducer.

In one or more embodiments, to account for situations in which the Q factor may have a lower value, e.g., Q factor ≈ 10, the calculation of the value of the parameter of external load 70 may be performed iteratively.

For example, due to an approximate optimum value of R_L0、L_L0Is based on the BVD model parameters, the load parameter R can be further adjusted starting from the calculated value_L、L_LTo compensate for other elements of a particular implementation, such as the non-zero output impedance of the voltage generator modeled as block 50 in fig. 4.

For example, to adapt the model to include any Q factor value, the parameter R of the load block 70 may be iteratively determined_L、L_LThe value of (c).

As illustrated in fig. 8, to illustrate an exemplary manner of iterative determination of values, since these parameters may be determined independently of each other, a different index, denoted N, M, P, and combinations thereof are used below to represent a certain number of sample values of a certain parameter.

For example, a possible process for determining these values may include the following, as illustrated in fig. 8:

determining (block 100) the equivalent network circuit of the BVD model of the device 10 and determining (in a manner known per se to the person skilled in the art) its circuit parameters R, L, C, C₀And resonant frequency f₀A starting value of;

generating (block 102) a first external load parameter L by sampling (block 102) values within a respective (e.g., different) range using a certain (e.g., different) sampling step size_L1、……、L_LNAnd/or a second external load parameter R_L1、……、R_LMWherein the range center value is equal to the calculated approximate "best" value R of the respective first parameter and/or second parameter_L0、L_L0At least one value of;

by using a certain sampling step pair at the resonance frequency f₀Sampling values within a central frequency range to generate (block 104) a set of frequency values f₁、……、f_P；

By using a parameter L for the first external load_LAnd a second external load parameter R_LWhile the obtained first and second sets of values are computed (block 106) each at a set f of frequency values₁、……、f_PSet of transfer functions (power spectrum) G₁(s)、……、G_NM(s)；

Computing (block 108) the set of computed (squared) transfer functions G₁(s)、……、G_NMBandwidth set BW of the respective (squared) transfer function in(s)₁、……、BW_NMAnd sensitivity set S₁、……、S_NM；

A comparison is made between the calculated bandwidth and the sensitivity (block 110),at squared transfer function G₁(s)、……、G_NM(s) selecting the "best" squared transfer function G from the set_i(s) the "best" squared transfer function has a relative maximum bandwidth and sensitivity above or below a certain threshold; and

applying an external load parameter R_L、L_LIs set (block 112) equal to the value used to calculate the set of squared transfer functions G₁(s)、……、G_NM(s) the external load parameter L of the selected "best" squared transfer function_L1、……、L_LNAnd R_L1、……、R_LMOf the set of values of the external load parameter.

In one or more embodiments, the threshold value of the sensitivity value may be customized according to the application for the PMUT device 10.

This approach may ignore some non-idealities or other effects related to the physical PMUT arrangement, and may further adjust for external loads R_L、L_LThe values found to compensate for other elements of the particular implementation, such as, for example, a non-zero output impedance of the voltage generator modeled as block 50 in fig. 4.

Alternatively, the load parameter R of the external load 70_L、L_LCan be determined using experimental methods, as discussed below.

To do so, as illustrated in fig. 9:

the PMUT 10 may be coupled to a measurement unit MU configured to measure its actual resonance frequency f₆And damping parameter τ_i(ii) a For example, the measurement may be performed in real time;

load 70 may include components that are adjustable in real time; as discussed, for example, inductor L_LAnd a resistor R_LBoth may be programmable in real time; and

the control unit CU coupled to the voltage generator 50, the load 70 and the measurement unit MU may be configured (in a manner known per se to the person skilled in the art) to receive the measured resonance frequency f from the measurement unit MU₆Controls the voltage generator 50, andmaking the load parameter R as required_L、L_LA change occurs.

Load parameter R for determining an external load 70 in an arrangement as illustrated in fig. 9_L、L_LThe experimental method of (3) may comprise:

the resonant frequency f of the PMUT device 10 is measured (again in a manner known per se to the person skilled in the art)₆；

By using a certain (e.g. different) sampling step size pair with the calculated near-optimal value R_L0、L_L0Are sampled to provide a first external load parameter L, a value within a respective (e.g., different) range centered at the respective value of_L1、……、L_LNAnd a second external load parameter R_L1、……、R_LMA set of values of (a);

for example, the resistance R of the load 70 is coupled via the control unit CU_LAnd an inductance L_LIteratively adjusted to be equal to for the external load parameter L_L1Iterative adjustment of L_LNAnd R_L1Iterative adjustment of R_LMWhile the first parameter L in the provided set of values_LAnd a second parameter R_LThe ith value of (d);

applying an excitation signal ES to the device 10, e.g. controlling its frequency to be equal to the measured resonance frequency f₆The generator 50 of (a);

for example, an ith ring-down signal RDi is acquired via the measurement unit MU, which indicates the ring-down behavior of the transducer 10 after the end of the excitation signal ES;

the acquired ring-down signal RDi is processed, and the following are obtained as a result of such processing:

a) i-th decay time constant tau of the bandwidth of the pointing device 10_i(ii) a And

b) the (initial, maximum peak-to-peak) amplitude RDA of the ring-down signal indicating the sensitivity of the transfer function g(s) of the device 10, as illustrated in fig. 10A and 10B;

collecting each ith decay time constant τ_iAnd the amplitude of the ith ring down signal RDi;

for example, via the control unit 10, in indicating the sum of the bandwidthsPerforming a comparison between the collected signals of the sensitivities, according to which a comparison is made of the provided external load parameter L_L1、……、L_LNAnd R_L1、……、R_LMSelects a load parameter L indicating a relative maximum bandwidth and a sensitivity above or below a certain threshold value from the set of values of_L*、R_LThe "best" value of; and

for example, via the control unit 10, a load block 70 (e.g., a load resistance and an inductance R)_L、L_L) Set or arranged to be equal to at a load parameter L_L1、……、L_LNAnd R_L1、……、R_LMTo select an external load parameter R from a set of values of_L*、L_LThe "best" value of.

Fig. 10A and 10B are examples of sensed ring down signals RDi, RD, where

FIG. 10A is a detected ring down signal RDi, e.g., ring down signal RDi without any external load block coupled to device 10; and

FIG. 10B is the (ith) ring down signal detected by load block 70 coupled to device 10, as illustrated in FIG. 6, for example, by using the "best" load parameter R selected in accordance with the preceding discussion_L*、L_LRing down signal RD detected by configured load block 70.

Fig. 11, 12 and 13 are examples of possible alternative architectures for load block 70.

Fig. 11-13 are examples of possible alternative implementations of load 70 to which the previously discussed standards may be applied mutatis mutandis:

as illustrated in fig. 11, the load 70 includes a first input node and a second input node configured to receive an input signal ES therebetween; and a first output node and a second output node, wherein the inductor L_LArranged between the first input node and the first output node, and a resistor R_PArranged between two output nodes, i.e. with the capacitance C₀In parallel, the capacitor C₀Can be regarded as L in nature_L(upper arm) and R_P(lower branch) voltage dividerAn arrangement wherein the first output node is coupled to a division point of the voltage divider; and

as illustrated in fig. 12 and 13, another resistor R_SAnd an inductor L_LIn series arrangement (as illustrated in fig. 12) or in which the inductor L is located_LIs coupled to a resistor R_PAnd a first output node (as illustrated in fig. 13).

If it is approximate to C₀> C applies and satisfies the following equation, then an arrangement as illustrated in FIG. 11 may be suitable for use and may correspond to the arrangement of FIG. 7:

an arrangement as illustrated in fig. 12 and 13 may be suitable for use when the following conditions are true, and may correspond to the arrangement of fig. 7:

a)C₀an approximation applicable to > C;

b) resistor R_SAnd R_PThe following conditions are satisfied:

c) resistor R as illustrated in FIGS. 12 and 13_S、R_PIs configured such that the resistor R_SCan be expressed as a total load resistance R_LThe function of (a), for example,

and is

d) Resistor R_PMay be expressed as a function of the total load resistance and BVD model parameters, e.g.,

it should be noted that, in addition, in the arrangements as illustrated in fig. 11 to 13, the load parameter R may be determined in accordance with the foregoing discussion with respect to fig. 7_L、L_LFrom which the values of the respective placement parameters (e.g., Rs, Rp) can be calculated. For the sake of brevity, the corresponding description of the method operations will not be repeated, as the foregoing (and in particular, with respect to fig. 8 and 9) discussion applies mutatis mutandis.

The arrangements as illustrated in fig. 7, 11-13 may be suitable for use, for example, with an acoustic position sensor module 1000, which acoustic position sensor module 1000 may be configured to be mounted on a motor vehicle, such as a motor vehicle. As illustrated in fig. 14, this may include an analog front end 1002, the analog front end 1002 being coupled to one or more transducers 10(PMUT is an example of such a transducer); and software components 1004 running on processing circuitry such as a microcontroller unit (MCU) such as a peripheral device with a processing unit, possibly at least partially comprised in a hardware architecture at 1002.

It should be otherwise understood that a microcontroller is just one example of one of a plurality of processing units that may be used with an embodiment.

In one or more embodiments, the analog front end 1002 and the processing unit 1004 may be powered as needed via the power management circuitry 1006.

As previously discussed, fig. 14 is an example of a circuit/system architecture configured to host (e.g., at 1004) a software program capable of performing adjustments (online, real-time) such as R of a load block 70 coupled to the appliance 10_LAnd L_LLike to increase its bandwidth BW and may increase its sensitivity in view of possible drawbacks related to the narrow available bandwidth available and/or transducer parameters that may be subject to manufacturing spread/time variations.

As exemplified herein, a method comprises:

obtaining (e.g., 100) a resonant frequency (e.g., f) of an electroacoustic transducer (e.g., 10) having a sensitivity and a frequency bandwidth₀) And at least one ring down parameter (e.g., τ)_iRDA);

according to the resonant frequency and at least oneA function of the at least one of the ring-down parameters, calculating a set of model parameters (e.g., R, L, C, C) of a Butterworth-Vandyk (BVD) model of the electro-acoustic transducer₀) The BVD model includes an equivalent circuit network having a constant capacitance (e.g., C) coupled to an RLC branch (e.g., R, L, C)₀)；

An adjustable load circuit (e.g., 70) is coupled with the electroacoustic transducer, the adjustable load circuit having an adjustable load parameter set (e.g., L)_L、R_L) The set of adjustable load parameters comprising at least one resistance parameter (R)_L) And an inductance parameter (e.g., L)_L) Wherein an adjustable load circuit is coupled with an electroacoustic transducer at an input port of the equivalent circuit network of the BVD model of the electroacoustic transducer; and

adjusting the set of adjustable load parameters according to the calculated set of model parameters of the BVD model of the electro-acoustic transducer to increase at least one of the bandwidth and the sensitivity of the electro-acoustic transducer as a result of the adjusting.

As exemplified herein, the method (further) comprises:

generating (e.g., 102) a set of load candidate values (e.g., L) for a set of adjustable load parameters_L1、……、L_LN；R_L1、……、R_LM) The set of load candidate values includes at least one set of initial configuration values (e.g., R)_L0、L_L0)；

Generating (e.g., 104) a set of frequency values (e.g., f) distributed across a frequency range₁、……、f_P) The set of frequency values comprising frequency values equal to said resonance frequency;

obtaining (e.g., 106) at least one set of signals indicative of a bandwidth and a sensitivity of an electroacoustic transducer from the set of frequency values and the set of load candidate values;

performing a comparison (e.g., 110) between a sensitivity threshold and signals in the obtained at least one set of signals, and selecting a subset of signals in the at least one set of signals as a result of the comparison;

selecting (e.g., 112) a set of bandwidth maximizing load candidate values (e.g., L) among a set of load candidate values_L*、R_L-wherein the bandwidth maximizing load candidate value is a set of load candidate values in the set of load candidate values corresponding to a bandwidth maximizing signal (e.g., G (s)) having a relatively maximum bandwidth in the selected subset of signals indicative of the bandwidth and sensitivity of the electro-acoustic transducer; and

adjusting the set of adjustable load parameters of the adjustable load circuit network to be equal to the set of bandwidth maximizing load candidate values.

As illustrated herein, obtaining (e.g., 106) at least one set of signals indicative of a bandwidth and a sensitivity of an electroacoustic transducer comprises: a set of frequency responses of the electro-acoustic transducer is calculated from the set of frequency values and the set of load candidate values.

As exemplified herein, the method comprises:

generating (e.g., 102) a set of adjustable load parameters (e.g., L)_L、R_L) The load candidate value set comprises at least one initial configuration value set;

performing an iterative acquisition of a ring down signal sequence indicative of a bandwidth and sensitivity of an electroacoustic transducer coupled to a load circuit network;

performing (e.g., 110) a comparison of a sensitivity threshold with initial amplitude values of the acquired ring down signal sequence, and selecting a subset of ring down signals (e.g., RD ″) in the ring down signal sequence as a result of the comparison;

selecting a bandwidth maximized set of load candidate values among a set of load candidate values, wherein a bandwidth maximized load candidate value is a set of load candidate values among the set of load candidate values corresponding to a bandwidth maximized ring down signal having a relatively maximum bandwidth (e.g., at least one damping parameter τ) in the sequence of ring down signals indicative of the bandwidth and sensitivity of the electro-acoustic transducer; and

adjusting the set of adjustable load parameters to be equal to the set of bandwidth maximizing load candidate values.

As exemplified herein, for each candidate value in the sequence of load candidate values, the iterative obtaining comprises a sequence of operations comprising:

i) adjusting an adjustable load parameter set of the adjustable load circuit network to be equal to an ith load candidate value in a load candidate value set;

ii) applying an excitation signal (e.g., 50, ES) to the transducer for an excitation interval; and

iii) acquiring (e.g., 60, PV) a ring down signal at the transducer indicative of ring down behavior of the transducer after the end of the excitation interval.

As exemplified herein, the initial set of configuration values for the load circuitry comprises at least one of:

i) initial configuration value L of inductor₀Expressed as:

ii) initial resistance configuration value R_L0Expressed as:

wherein

C. C0, R, L, f0 are parameters of the calculated BVD model, an

k is a number, preferably in the range of 5 to 10.

As exemplified herein, a circuit comprising:

at least one electroacoustic transducer (e.g., 10) having a sensitivity and a frequency bandwidth;

an adjustable load circuit (e.g., 70) having an adjustable load parameter set (e.g., L)_L、R_L) The set of adjustable load parameters includes a resistance parameter (e.g., R)_L) And an inductorParameter (e.g., L)_L) At least one of; and

processing circuitry (e.g., 50, 60, MU, CU) coupled to the at least one electroacoustic transducer and the adjustable load circuitry, the processing circuitry configured to perform the acts of:

obtaining (e.g., 100) a resonant frequency (e.g., f) of an electroacoustic transducer₀) And at least one ring down parameter (e.g., τ)_iRDA);

computing the set of model parameters (e.g., R, L, C, C0) for a Butterworth-Vandyk (BVD) model of an electro-acoustic transducer; and

adjusting the set of adjustable load parameters according to the calculated set of model parameters of the BVD model in the method as exemplified herein.

As exemplified herein, the electro-acoustic transducer is an ultrasonic electro-acoustic transducer, preferably a piezoelectric micromachined ultrasonic transducer PMUT.

As exemplified herein, the adjustable load circuit comprises one of:

resistors (e.g. R)_L) And an inductor (e.g., L)_L) Are connected in series; and

voltage divider including an inductor (e.g., L)_L) And at least one resistor (e.g., R)_P、R_S)。

As exemplified herein, a device comprising circuitry as exemplified herein is selected from the following:

an obstacle detection device, preferably an in-vehicle (e.g., V) device;

an echo location device; and

an acoustic time-of-flight measurement device.

Without prejudice to the underlying principles, the details and the embodiments may vary, even significantly, with respect to what has been described by way of example only, without departing from the scope of protection.

The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments and equivalents of the full scope of such claims. Accordingly, the claims are not limited by the disclosure.

Claims

1. A method, comprising:

obtaining at least one of a resonant frequency and at least one ring down parameter of an electro-acoustic transducer having a sensitivity and a frequency bandwidth;

calculating a set of model parameters for a Butterworth-VandyK BVD model of the electroacoustic transducer from the at least one of the resonant frequency and the at least one ring down parameter, the BVD model comprising an equivalent circuit network having a constant capacitance coupled to an RLC branch;

coupling an adjustable load circuit with the electroacoustic transducer, the adjustable load circuit having an adjustable set of load parameters, the adjustable set of load parameters including at least one resistive parameter and one inductive parameter, wherein the adjustable load circuit is coupled with the electroacoustic transducer at an input port of the equivalent circuit network of the BVD model of the electroacoustic transducer; and

adjusting the set of adjustable load parameters in accordance with the calculated set of model parameters of the BVD model of the electro-acoustic transducer to increase at least one of the bandwidth and the sensitivity of the electro-acoustic transducer as a result of the adjustment.

2. The method of claim 1, comprising:

generating a set of load candidate values for the set of adjustable load parameters, the set of load candidate values comprising at least one set of initial configuration values;

generating a set of frequency values distributed across a frequency range, the set of frequency values comprising frequency values equal to the resonant frequency;

obtaining at least one set of signals indicative of a bandwidth and a sensitivity of the electro-acoustic transducer from the set of frequency values and the set of load candidate values;

performing a comparison between a sensitivity threshold and the obtained signals in the at least one signal set, and selecting a subset of the signals in the at least one signal set as a result of the comparison;

selecting a bandwidth maximizing set of load candidate values among the set of load candidate values, wherein the bandwidth maximizing load candidate value is the set of load candidate values in the set of load candidate values corresponding to a bandwidth maximizing signal having a relatively maximum bandwidth among the selected subset of signals indicative of bandwidth and sensitivity of the electro-acoustic transducer; and

3. The method of claim 2, wherein obtaining at least one set of signals indicative of a bandwidth and a sensitivity of the electro-acoustic transducer comprises: a set of frequency responses of the electro-acoustic transducer is calculated from the set of frequency values and the set of load candidate values.

4. The method of claim 2, comprising:

generating a sequence of load candidate values for the set of adjustable load parameters, the set of load candidate values comprising at least one set of initial configuration values;

performing an iterative acquisition of a ring down signal sequence indicative of a bandwidth and sensitivity of the electroacoustic transducer coupled to the load circuit network;

performing a comparison between a sensitivity threshold and the acquired initial amplitude value of the ring-down signal sequence, and selecting a subset of ring-down signals in the ring-down signal sequence as a result of the comparison;

selecting a bandwidth-maximized set of load candidate values in the set of load candidate values, wherein the bandwidth-maximized set of load candidate values is the set of load candidate values in the set of load candidate values corresponding to a bandwidth-maximized ring-down signal having a relatively maximum bandwidth among the sequence of ring-down signals indicative of the bandwidth and sensitivity of the electro-acoustic transducer; and

5. The method of claim 1, comprising:

selecting a bandwidth-maximized set of load candidate values in the set of load candidate values, wherein the bandwidth-maximized set of load candidate values is the set of load candidate values in the set of load candidate values corresponding to a bandwidth-maximized ring-down signal having a relatively maximum bandwidth in the sequence of ring-down signals indicative of the bandwidth and sensitivity of the electro-acoustic transducer; and

6. The method of claim 5, wherein the iterative obtaining comprises, for each candidate value in the sequence of load candidate values, a sequence of operations comprising:

adjusting the set of adjustable load parameters of the network of adjustable load circuits to be equal to a load candidate value of the set of load candidate values;

applying an excitation signal to the transducer for an excitation interval; and

acquiring a ring down signal at the transducer indicative of ring down behavior of the transducer after the end of the excitation interval.

7. The method of claim 1, wherein the initial set of configuration values for the load circuitry comprises at least one of:

initial configuration value L of inductor₀Expressed as:

or initial resistance configuration value R_L0Expressed as:

wherein

C. C0, R, L, f0 are the calculated parameters of the BVD model, an

k is a number.

8. The method of claim 7, wherein k is a number in the range from 5 to 10.

9. A circuit, comprising:

at least one electroacoustic transducer having a sensitivity and a frequency bandwidth;

an adjustable load circuit having an adjustable load parameter set comprising at least one resistance parameter and one inductance parameter; and

processing circuitry coupled to the at least one electroacoustic transducer and the adjustable load circuitry, the adjustable load circuitry having an adjustable set of load parameters including at least one resistive parameter and one inductive parameter, the processing circuitry configured to:

obtaining at least one of a resonant frequency and at least one ring down parameter of the electro-acoustic transducer;

calculating a set of model parameters for a Butterworth-VandyK BVD model of the electroacoustic transducer in accordance with the at least one of the resonant frequency and the at least one ring down parameter, the BVD model comprising an equivalent circuit network having a constant capacitance coupled to an RLC branch, wherein the adjustable load circuit is coupled with the electroacoustic transducer at an input port of the equivalent circuit network of the BVD model of the electroacoustic transducer; and

adjusting the set of adjustable loading parameters to increase at least one of the bandwidth and the sensitivity of the electro-acoustic transducer according to the calculated set of model parameters of the BVD model of the electro-acoustic transducer.

10. The circuit of claim 9, wherein the processing circuitry is configured to:

11. The circuit of claim 10, wherein the processing circuitry is configured to obtain at least one set of signals indicative of a bandwidth and a sensitivity of the electroacoustic transducer by calculating a set of frequency responses of the electroacoustic transducer from the set of frequency values and the set of load candidate values.

12. The circuit of claim 10, wherein the processing circuitry is configured to:

selecting a bandwidth maximized set of load candidate values in the set of load candidate values, wherein the bandwidth maximized set of load candidate values is the set of load candidate values in the set of load candidate values corresponding to a bandwidth maximized ring down signal having a relatively maximum bandwidth in the sequence of ring down signals indicative of the bandwidth and sensitivity of the electro-acoustic transducer; and

13. The circuit of claim 9, wherein the processing circuitry is configured to:

14. The circuit of claim 13, wherein the iterative obtaining comprises, for each candidate value in the sequence of load candidate values, a sequence of operations comprising:

applying an excitation signal to the transducer for an excitation interval; and

acquiring a ring down signal at the transducer indicative of the ring down behavior of the transducer after the end of the excitation interval.

15. The circuit of claim 9, wherein the electro-acoustic transducer comprises an ultrasonic electro-acoustic transducer.

16. The circuit of claim 15, wherein the electro-acoustic transducer comprises a piezoelectric micromachined ultrasonic transducer.

17. The circuit of claim 9, wherein the adjustable load circuit comprises one of:

a series connection of a resistor and an inductor; or

A voltage divider comprising an inductor and at least one resistor.

18. An apparatus, comprising:

a circuit, the circuit comprising:

adjusting the set of adjustable loading parameters to increase at least one of the bandwidth and the sensitivity of the electro-acoustic transducer in accordance with the calculated set of model parameters of the BVD model of the electro-acoustic transducer,

wherein the device is at least one of: an obstacle detection device (preferably, a vehicle-mounted device), an echo location device, or a sonic time-of-flight measurement device.

19. The device of claim 18, wherein the processing circuitry is configured to:

20. The apparatus of claim 19, wherein the processing circuitry is configured to obtain at least one set of signals indicative of a bandwidth and a sensitivity of the electroacoustic transducer by calculating a set of frequency responses of the electroacoustic transducer from the set of frequency values and the set of load candidate values.