CN213337474U

CN213337474U - Ultrasonic sensor

Info

Publication number: CN213337474U
Application number: CN202022504079.5U
Authority: CN
Inventors: 王地宝; 范成至; 周正三
Original assignee: Egis Technology Inc
Current assignee: Egis Technology Inc
Priority date: 2020-03-24
Filing date: 2020-11-03
Publication date: 2021-06-01
Anticipated expiration: 2030-11-03
Also published as: TWM610272U; WO2021189861A1; CN112229916A; TWI758930B; TW202136984A

Abstract

The utility model provides an ultrasonic sensor. The ultrasonic sensor includes a sensing array. The sensing array comprises a plurality of sensing units arranged in an array. Each of the plurality of sensing units includes a first ultrasonic transducer and a second ultrasonic transducer. The first ultrasonic transducer is used for emitting sensing ultrasonic waves. The second ultrasonic transducer is used for receiving reflected ultrasonic waves corresponding to the ultrasonic waves. The first ultrasonic transducer and the second ultrasonic transducer are arranged on a plane in parallel. The first ultrasonic transducer and the second ultrasonic transducer have the same central axis perpendicular to the plane. Therefore, the utility model provides an ultrasonic sensor has good supersound fingerprint echo signal quality.

Description

Ultrasonic sensor

Technical Field

The utility model relates to a sensor especially relates to an ultrasonic sensor.

Background

In the currently known principles of Ultrasonic fingerprint scanning, a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) structure is mostly used alone to transmit and receive Ultrasonic waves. In contrast, the conventional ultrasonic sensing technology has a problem that it is difficult to penetrate a hard, thick or multi-layer solid structure due to insufficient ultrasonic Signal strength, or has a disadvantage that ultrasonic waves emitted by a plurality of PMUTs of the PMUT architecture are easy to diverge, resulting in a reflected sound wave having a low Signal Noise Ratio (SNR) and poor image contrast.

SUMMERY OF THE UTILITY MODEL

In view of this, the present invention provides an ultrasonic sensor with good quality of ultrasonic fingerprint echo signal.

According to the utility model discloses an embodiment, the utility model discloses an ultrasonic sensor includes the sensing array. The sensing array comprises a plurality of sensing units arranged in an array, wherein each of the sensing units comprises a first ultrasonic transducer and a second ultrasonic transducer. The first ultrasonic transducer is used for emitting sensing ultrasonic waves. The second ultrasonic transducer is used for receiving reflected ultrasonic waves corresponding to the ultrasonic waves. The first ultrasonic transducer and the second ultrasonic transducer are arranged on a plane in parallel. The first ultrasonic transducer and the second ultrasonic transducer have the same central axis perpendicular to the plane.

In an embodiment of the present invention, the first ultrasonic transducer is annular, and the first ultrasonic transducer is disposed around the second ultrasonic transducer on the plane.

In an embodiment of the present invention, the second ultrasonic transducer is annular, and the second ultrasonic transducer is disposed around the first ultrasonic transducer on the plane.

In the embodiment of the present invention, the method further comprises: the driving circuit is coupled to the first ultrasonic transducers of the sensing units and configured to output driving signals to the first ultrasonic transducers, wherein the first ultrasonic transducers emit sensing ultrasonic waves according to the driving signals, and the sensing ultrasonic waves are spherical waves.

In an embodiment of the present invention, the plurality of first ultrasonic transducers emit the plurality of sensing ultrasonic waves at the same time to form a surface of the plane wave transferred to the sensing target.

In the embodiment of the present invention, the method further comprises: a plurality of delay circuits respectively coupled between the first plurality of ultrasonic transducers and the driving circuit, wherein the first plurality of ultrasonic transducers emit the sensing ultrasonic waves in a phase-delayed manner to form a focused wave to be transmitted to the surface of the sensing target.

In the embodiment of the present invention, the method further comprises: a plurality of driving circuits respectively coupled to the plurality of first ultrasonic transducers of the plurality of sensing units and configured to output a plurality of driving signals to the plurality of first ultrasonic transducers, wherein at least a portion of the plurality of first ultrasonic transducers asynchronously emit the plurality of sensing ultrasonic waves according to the plurality of driving signals.

In the embodiment of the present invention, the method further comprises: a plurality of sensing circuits respectively coupled to the plurality of second ultrasonic transducers of the plurality of sensing units and configured to sense the plurality of second ultrasonic transducers to output a plurality of sensing signals; and an image synthesizing circuit coupled to the sensing circuits and configured to generate a sensing image according to the sensing signals.

In the embodiment of the present invention, the method further comprises: a plurality of band pass filters respectively coupled between the plurality of sensing circuits and the image synthesizing circuit and configured to provide the plurality of sensing signals to the image synthesizing circuit.

In an embodiment of the present invention, the image synthesizing circuit generates the sensing image according to a portion of the plurality of reflected ultrasonic waves corresponding to at least one of a frequency doubling and a frequency doubling among the plurality of sensing signals.

In an embodiment of the present invention, at least one of the first ultrasonic transducer and the second ultrasonic transducer is a capacitive ultrasonic micro-transducer and has a cavity made of a dielectric material.

In an embodiment of the present invention, the dielectric material is a soft material.

In an embodiment of the present invention, the dielectric material is a polymer material.

Based on the foregoing, the utility model discloses an ultrasonic sensor accessible array arrangement in the middle of the ultrasonic sensor and set up in a plurality of sensing units of coplanar transmit and receive the ultrasonic wave to but make ultrasonic sensor sensing have the reflection ultrasonic wave of good supersound fingerprint echo signal quality.

In order to make the aforementioned and other features and advantages of the disclosure more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1 is a schematic view of an ultrasonic sensor according to an embodiment of the present invention;

fig. 2 is a schematic top view of a sensing unit according to an embodiment of the present invention;

fig. 3 is a schematic side sectional view of a sensing unit according to an embodiment of the present invention;

fig. 4 is an operational schematic diagram of an ultrasonic sensor of a first embodiment of the present invention;

fig. 5A is a transmission circuit diagram of an ultrasonic sensor according to a first embodiment of the present invention;

fig. 5B is a receiving circuit diagram of the ultrasonic sensor according to the first embodiment of the present invention;

fig. 6 is an operational schematic diagram of an ultrasonic sensor according to a second embodiment of the present invention;

fig. 7A is a transmission circuit diagram of an ultrasonic sensor according to a second embodiment of the present invention;

fig. 7B is a receiving circuit diagram of an ultrasonic sensor according to a second embodiment of the present invention;

fig. 8 is an operational schematic diagram of an ultrasonic sensor according to a third embodiment of the present invention;

fig. 9A is a transmission circuit diagram of an ultrasonic sensor according to a third embodiment of the present invention;

fig. 9B is a receiving circuit diagram of an ultrasonic sensor according to a third embodiment of the present invention.

Description of the reference numerals

100. 400, 600, 800, ultrasonic sensor;

110, a sensing array;

120, an integrated circuit;

210. 431 to 437, 631 to 635, 831 to 837 sense units;

210C, a central shaft;

211. 212, 431T to 437T, 431R to 437R, 631T to 635T, 631R to 635R, 831T to 837T, 831R to 837R and an ultrasonic transducer;

2111. 2112, 2121, 2122 metal layer;

2113. 2123 dielectric layer;

2114. 2124, a cavity;

220. 420, 620, 820, a substrate;

230. 430, 630, 830 a support layer;

401. 601, 801 sensing a target;

440. 640, 840, an adhesive layer;

450. 650, 850: a panel;

460. 660, 861-867, a driving circuit;

470. 670, 870, an image synthesizing circuit;

481 to 487, 681 to 685, 881 to 887 sense circuits;

661-665 delay circuit;

891-897, band-pass filter;

d1, D2 and D3.

Detailed Description

Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings and the description to refer to the same or like parts.

Fig. 1 is a schematic view of an ultrasonic sensor according to an embodiment of the present invention. Referring to fig. 1, an ultrasonic sensor 100 includes a sensing array 110 and an integrated circuit 120. The sensing array 110 includes a plurality of sensing units arranged in an array, and the integrated circuit 120 is coupled to the plurality of sensing units of the sensing array 110. The integrated circuit 120 may be configured to drive the plurality of sensing units and receive sensing results of the plurality of sensing units. In this embodiment, the integrated circuit 120 may include at least one of the driving circuit, the sensing circuit, the delay circuit, and the image synthesizing circuit mentioned in the embodiments of the present invention, but the present invention is not limited thereto. In one embodiment, the integrated circuit 120 may include a programmable general-purpose or special-purpose microprocessor (microprocessor), a Digital Signal Processor (DSP), a programmable controller, an Application Specific Integrated Circuit (ASIC), a Graphics Processing Unit (GPU), or other similar components or combinations thereof, and may be used to implement the related functional circuits of the present invention.

Fig. 2 is a schematic top view of a sensing unit according to an embodiment of the present invention. Referring to fig. 2, a top view structure of each sensing unit in the sensing array 110 of fig. 1 may be the sensing unit 210 shown in fig. 2. In the present embodiment, the sensing unit 210 includes

ultrasonic transducers

211, 212. In the present embodiment, the

Ultrasonic transducers

211 and 212 may be Capacitive Ultrasonic micro transducers (CMUTs), but the present invention is not limited thereto. In the present embodiment, the

ultrasonic transducers

211, 212 are arranged in parallel to a plane as formed by extending along the directions D1, D2, wherein the directions D1, D2, D3 are perpendicular to each other. The

ultrasonic transducers

211, 212 have the same central axis 210C perpendicular to the plane. In the present embodiment, the ultrasonic transducer 211 has a ring shape, and the ultrasonic transducer 211 is disposed around the ultrasonic transducer 212 on the plane. It is noted that in the present embodiment, the ultrasonic transducer 211 may be configured to emit sensing ultrasonic waves, and the ultrasonic transducer 212 may be configured to receive reflected ultrasonic waves corresponding to the ultrasonic waves. However, in one embodiment, the ultrasonic transducer 212 may also be used to emit sensing ultrasonic waves, and the ultrasonic transducer 211 may also be used to receive reflected ultrasonic waves corresponding to the ultrasonic waves.

Fig. 3 is a schematic side sectional view of a sensing unit according to an embodiment of the present invention. Referring to fig. 2 and 3, fig. 3 is a side sectional view of the sensing unit 210 of fig. 2. In the present embodiment, the supporting layer 230 is formed on the substrate 220, and the sensing unit 210 is formed in the supporting layer 230. In the present embodiment, the ultrasonic transducer 211 includes

metal layers

2111 and 2112, and a dielectric layer 2113 and a cavity 2114 are included between the

metal layers

2111 and 2112, wherein the cavity 2114 may include a dielectric material, or a cavity structure with air or vacuum. The metal layers 2111, 2112 serve as electrodes and may be coupled to drive or sense circuitry. In the present embodiment, the ultrasonic transducer 212 includes

metal layers

2121 and 2122, and a dielectric layer 2123 and a cavity 2124 are included between the

metal layers

2121 and 2122, wherein the cavity 2124 may include a dielectric material or be a cavity. The metal layers 2121, 2122 serve as electrodes and may be coupled to a driving circuit or a sensing circuit. For example, in one embodiment, at least one of the

cavities

2114 and 2124 may be filled with the dielectric material, and the dielectric material may be a soft material. In another embodiment, the dielectric material may be a Polymer (Polymer) material.

In this embodiment, the

metal layers

2111, 2112, 2121, 2122 may be made of, for example, aluminum (Al), nickel (Ni), titanium (Ti), copper (Cu), silver (Ag), or the like. The

dielectric layers

2113 and 2123 may be made of a dielectric semiconductor material such as Silicon Dioxide (Silicon Dioxide), Aluminum Oxide (Aluminum Oxide), or Silicon Nitride (Silicon Nitride). The gap of the

cavities

2114, 2124 may be, for example, between 0.03 micrometers (um) to 1.5 micrometers.

Fig. 4 is an operation diagram of the ultrasonic sensor according to the first embodiment of the present invention. Fig. 5A is a transmission circuit diagram of an ultrasonic sensor according to a first embodiment of the present invention. Fig. 5B is a receiving circuit diagram of the ultrasonic sensor according to the first embodiment of the present invention. Referring to fig. 4, in the present embodiment, the ultrasonic sensor 400 includes a substrate 420, a support layer 430, an adhesive layer 440, and a panel 450, wherein the panel 450 may be a transparent panel or a non-transparent panel, such as glass, a display panel, or a general plate. In the present embodiment, the ultrasonic sensor 400 includes sensing units 431 to 437, wherein each of the sensing units 431 to 437 can be the sensing unit 210 shown in FIG. 2 and FIG. 3.

Referring to fig. 4 and 5A, the ultrasonic sensor 400 further includes a driving circuit 460, wherein the driving circuit 460 is disposed in the integrated circuit 120 in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the embodiment, the driving circuit 460 is coupled to the ultrasonic transducers 431T to 437T of the sensing units 431 to 437 in parallel to output driving signals to the ultrasonic transducers 431T to 437T. The ultrasonic transducers 431T to 437T of the sensing units 431 to 437 emit a plurality of sensing ultrasonic waves simultaneously according to the driving signal, wherein the plurality of sensing ultrasonic waves can be a plurality of spherical waves. The plurality of sensing ultrasonic waves form a plane wave. The plane wave is transmitted to the surface of the sensing target 401 through the supporting layer 430, the adhesive layer 440 and the panel 450, so that the surface of the sensing target 401 generates a reflected ultrasonic wave. The reflected ultrasonic waves are transmitted back to the sensing units 431 to 437 through the panel 450, the adhesive layer 440 and the supporting layer 430. The sensing target 401 may be a finger, and the surface of the sensing target 401 may have a fingerprint texture.

In the present embodiment, the ultrasonic transducers 431T to 437T may be, for example, one of the

ultrasonic transducers

211 and 212 shown in fig. 2. It should be noted that the ultrasonic transducers 431T to 437T of the sensing units 431 to 437 of the present embodiment can emit sensing ultrasonic waves (middle and low frequency mechanical elastic waves) with a first frequency, wherein the first frequency can be, for example, 5 to 50 megahertz (MHz).

Referring to fig. 4 and 5B, the ultrasonic sensor 400 further includes sensing circuits 481-487 and an image synthesis circuit 470, wherein the sensing circuits 481-487 and the image synthesis circuit 470 are disposed in the integrated circuit 120 described in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the present embodiment, the sensing circuits 481-487 are coupled to the ultrasonic transducers 431R-437R of the sensing units 431-437 in a one-to-one manner. The ultrasonic transducers 431R to 437R are used for receiving the reflected ultrasonic waves, and the sensing circuits 481 to 487 sense the ultrasonic transducers 431R to 437R and output a plurality of sensing signals to the image synthesizing circuit 470. The sensing circuits 481-487 are respectively coupled to the image synthesizing circuit 470. The image synthesis circuit 470 generates a sensing image (fingerprint image) from the plurality of sensing signals. In the present embodiment, the ultrasonic transducers 431R to 437R may be, for example, the other of the ultrasonic transducer 211 and the ultrasonic transducer 212 in fig. 2. It should be noted that the ultrasonic transducers 431R to 437 of the sensing units 431 to 437 of the present embodiment can receive a reflected ultrasonic wave with a frequency of one or two times of the first frequency, for example.

Fig. 6 is an operation diagram of an ultrasonic sensor according to a second embodiment of the present invention. Fig. 7A is a transmission circuit diagram of an ultrasonic sensor according to a second embodiment of the present invention. Fig. 7B is a receiving circuit diagram of an ultrasonic sensor according to a second embodiment of the present invention. Referring to fig. 6, in the present embodiment, the ultrasonic sensor 600 includes a substrate 620, a support layer 630, an adhesive layer 640, and a panel 650, wherein the panel 650 may be a transparent panel or a non-transparent panel, such as glass, a display panel, or a general plate. In the present embodiment, the ultrasonic sensor 600 includes, for example, sensing units 631 to 635, wherein each of the sensing units 631 to 635 can be the sensing unit 210 shown in fig. 2 and 3.

Referring to fig. 6 and 7A, the ultrasonic sensor 600 further includes delay circuits 661-665 and a driving circuit 660, wherein the delay circuits 661-665 and the driving circuit 660 are disposed in the integrated circuit 120 described in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the embodiment, the driving circuit 660 is coupled to the ultrasonic transducers 631T to 635T of the sensing units 631 to 635 in parallel, and the delay circuits 661 to 665 are coupled in series with the ultrasonic transducers 631T to 635T, respectively, one to one. Therefore, the driving circuit 660 outputs the driving signals to the delay circuits 661 to 665, so that the delay circuits 661 to 665 provide a plurality of driving signals with different phase delays to the ultrasonic transducers 631T to 635T. The ultrasonic transducers 631T-635T of the sensing units 631-635 emit a plurality of sensing ultrasonic waves having different phase delays according to the plurality of driving signals having different phase delays, wherein the plurality of sensing ultrasonic waves may be a plurality of spherical waves. The plurality of sensed ultrasonic waves having different phase delays may form a focused wave. The focused wave is transmitted to the surface of the sensing target 601 through the supporting layer 630, the adhesive layer 640, and the panel 650, so that the surface of the sensing target 601 generates a reflected ultrasonic wave. The reflected ultrasonic waves are transmitted back to the sensing units 631-635 via the panel 650, the adhesive layer 640 and the supporting layer 630. The sensing target 601 may be a finger, and the surface of the sensing target 601 may have a fingerprint texture.

In the present embodiment, the ultrasonic transducers 631T to 635T may be, for example, one of the

ultrasonic transducers

211 and 212 in fig. 2. It should be noted that the ultrasonic transducers 631T to 635T of the sensing units 631 to 635 of the present embodiment can emit sensing ultrasonic waves (middle and low frequency mechanical elastic waves) with a first frequency, for example, 5 to 50 mhz.

Referring to fig. 6 and 7B, the ultrasonic sensor 600 further includes sensing circuits 681-685 and an image synthesis circuit 670, wherein the sensing circuits 681-685 and the image synthesis circuit 670 are disposed in the integrated circuit 120 described in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the present embodiment, the sensing circuits 681 to 685 are coupled to the ultrasonic transducers 631R to 635R of the sensing units 631 to 635 one to one. The ultrasonic transducers 631R to 635R receive the reflected ultrasonic waves, and the sensing circuits 681 to 685 sense the ultrasonic transducers 631R to 635R and output a plurality of sensing signals to the image synthesizing circuit 670. The sensing circuits 681-685 are respectively coupled to the image synthesizing circuit 670. The image synthesis circuit 670 generates a sensed image (fingerprint image) from the plurality of sensing signals. In the present embodiment, the ultrasonic transducers 631R to 635R may be, for example, the other one of the ultrasonic transducer 211 and the ultrasonic transducer 212 in fig. 2. It should be noted that the ultrasonic transducers 631R 635R of the sensing units 631 to 635 of the present embodiment can receive the reflected ultrasonic waves with the first frequency being one or two times the frequency.

Fig. 8 is an operation diagram of an ultrasonic sensor according to a third embodiment of the present invention. Fig. 9A is a transmission circuit diagram of an ultrasonic sensor according to a third embodiment of the present invention. Fig. 9B is a receiving circuit diagram of an ultrasonic sensor according to a third embodiment of the present invention. Referring to fig. 8, in the present embodiment, the ultrasonic sensor 800 includes a substrate 820, a support layer 830, an adhesive layer 840, and a panel 850, wherein the panel 850 may be a transparent panel or a non-transparent panel, such as glass, a display panel, or a general plate. In the present embodiment, the ultrasonic sensor 800 includes sensing units 831 to 837, for example, wherein each of the sensing units 831 to 837 can be the sensing unit 210 as described above in fig. 2 and 3.

Referring to fig. 8 and 9A, the ultrasonic sensor 800 further includes driving circuits 861-867, wherein the driving circuits 861-867 are disposed in the integrated circuit 120 in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the embodiment, the driving circuits 861-867 are coupled to the ultrasonic transducers 831T-837T of the sensing units 831-837 one-to-one to output a plurality of driving signals to the ultrasonic transducers 831T-837T at different time points, respectively. At least a part of the ultrasonic transducers 831T to 837T of the sensing units 831 to 837 transmits a plurality of sensing ultrasonic waves in a time-sharing manner according to the plurality of driving signals received at different time points, wherein the plurality of sensing ultrasonic waves can be a plurality of spherical waves. For example, the

sensing units

833, 836 emit sensing ultrasonic waves first, then the

sensing units

832, 835 emit sensing ultrasonic waves, and then the

sensing units

831, 834, 837 emit sensing ultrasonic waves. Therefore, the plurality of sensing ultrasonic waves may form a plurality of highly directional ultrasonic waves. The plurality of high-directivity ultrasonic waves are transmitted to the surface of the sensing target 801 through the supporting layer 830, the adhesive layer 840 and the panel 850, so that the surface of the sensing target 801 generates reflected ultrasonic waves. The sensing target 801 may be a finger, and the surface of the sensing target 801 may have a fingerprint texture. The reflected ultrasonic waves are transmitted back to the sensing units 831 to 837 through the panel 850, the adhesive layer 840 and the supporting layer 830.

In the present embodiment, the ultrasonic transducers 831T to 837T may be, for example, one of the

ultrasonic transducers

211 and 212 shown in fig. 2. It should be noted that the ultrasonic transducers 831T to 837T of the sensing units 831 to 837 of the present embodiment can emit sensing ultrasonic waves (medium-high frequency mechanical elastic waves) with a second frequency, for example, wherein the second frequency can be greater than 50 megahertz (MHz).

Referring to fig. 8 and 9B, the ultrasonic sensor 800 further includes sensing circuits 881-887, band-pass filters (band-pass filters) 891-897, and an image synthesis circuit 870, wherein the sensing circuits 881-887, the band-pass filters 891-897, and the image synthesis circuit 870 are disposed in the integrated circuit 120 in the embodiment of fig. 1, for example, but the invention is not limited thereto. In the present embodiment, the sensing circuits 881-887 are coupled to the ultrasonic transducers 831R-837R of the sensing units 831-837 one-to-one, and the band-pass filters 891-897 are coupled to the sensing circuits 881-887 one-to-one. The ultrasonic transducers 831R to 837R are used for receiving the reflected ultrasonic waves, and the sensing circuits 881 to 887 sense the ultrasonic transducers 831R to 837R and output a plurality of sensing signals to the band pass filters 891 to 897. It should be noted that the ultrasonic transducers 831R to 837R of the sensing units 831 to 837 of the present embodiment can receive reflected ultrasonic waves with a frequency doubled or doubled by the second frequency, for example. In contrast, the band pass filters 891 to 897 can separate the sensing signal having the frequency of the second frequency multiplied by one or two and output the sensing signal having the frequency of the second frequency multiplied by one or two to the image synthesizing circuit 870. The band pass filters 891-897 are respectively coupled to the image synthesis circuit 870. The image synthesizing circuit 870 generates a sensed image (fingerprint image) from the plurality of sensed signals after filtering. In the present embodiment, the ultrasonic transducers 831R to 837R may be, for example, the other one of the ultrasonic transducer 211 and the ultrasonic transducer 212 shown in fig. 2.

To sum up, the utility model discloses an ultrasonic transducer of ultrasonic sensor accessible design special construction launches and receives the ultrasonic wave effectively. Furthermore, the utility model discloses an ultrasonic sensor accessible launches a plurality of sensing ultrasonic waves simultaneously and forms the mode of plane wave, or can have the mode of a plurality of sensing ultrasonic waves that different phase delay form the focus wave through the transmission, or can launch the mode of a plurality of high directive property ultrasonic waves through the timesharing, make ultrasonic sensor received reflection ultrasonic wave can have the advantage of high signal-to-noise ratio, and then can produce the sensing image that has good image quality.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention.

Claims

1. An ultrasonic sensor, comprising:

a sensing array comprising a plurality of sensing units arranged in an array, wherein each of the plurality of sensing units comprises:

a first ultrasonic transducer for emitting a sensing ultrasonic wave; and

a second ultrasonic transducer for receiving reflected ultrasonic waves corresponding to the ultrasonic waves,

wherein the first ultrasonic transducer and the second ultrasonic transducer are disposed parallel to a plane and have a same central axis perpendicular to the plane.

2. The ultrasonic sensor of claim 1, wherein the first ultrasonic transducer is annular and the first ultrasonic transducer is disposed around the second ultrasonic transducer on the plane.

3. The ultrasonic sensor of claim 1, wherein the second ultrasonic transducer is annular and is disposed around the first ultrasonic transducer on the plane.

4. The ultrasonic sensor of claim 1, further comprising:

the driving circuit is coupled to the first ultrasonic transducers of the sensing units and configured to output driving signals to the first ultrasonic transducers, wherein the first ultrasonic transducers emit sensing ultrasonic waves according to the driving signals, and the sensing ultrasonic waves are spherical waves.

5. The ultrasonic sensor of claim 4, wherein the plurality of first ultrasonic transducers emit the plurality of sensing ultrasonic waves simultaneously to form a plane wave for transmission to a surface of a sensing target.

6. The ultrasonic sensor of claim 4, further comprising:

a plurality of delay circuits respectively coupled between the first plurality of ultrasonic transducers and the driving circuit, wherein the first plurality of ultrasonic transducers emit the sensing ultrasonic waves in a phase-delayed manner to form a focused wave to be transmitted to the surface of the sensing target.

7. The ultrasonic sensor of claim 1, further comprising:

a plurality of driving circuits respectively coupled to the plurality of first ultrasonic transducers of the plurality of sensing units and configured to output a plurality of driving signals to the plurality of first ultrasonic transducers, wherein at least a portion of the plurality of first ultrasonic transducers asynchronously emit the plurality of sensing ultrasonic waves according to the plurality of driving signals.

8. The ultrasonic sensor of claim 1, further comprising:

a plurality of sensing circuits respectively coupled to the plurality of second ultrasonic transducers of the plurality of sensing units and configured to sense the plurality of second ultrasonic transducers to output a plurality of sensing signals; and

the image synthesis circuit is coupled to the sensing circuits and used for generating a sensing image according to the sensing signals.

9. The ultrasonic sensor of claim 8, further comprising:

a plurality of band pass filters respectively coupled between the plurality of sensing circuits and the image synthesizing circuit and configured to provide the plurality of sensing signals to the image synthesizing circuit.

10. The ultrasonic sensor of claim 8, wherein the image synthesis circuit generates the sensing image according to a portion of the plurality of reflected ultrasonic waves corresponding to at least one of a frequency doubling and a frequency doubling among the plurality of sensing signals.

11. The ultrasonic sensor of claim 1, wherein at least one of the first ultrasonic transducer and the second ultrasonic transducer is a capacitive ultrasonic micro-transducer and has a cavity of dielectric material.

12. The ultrasonic sensor of claim 11, wherein the dielectric material is a soft material.

13. The ultrasonic sensor of claim 11, wherein the dielectric material is a polymer material.