1. Field of the Invention
The present invention relates to MUTs and, more particularly, to a MUT circuit with an electrically controllable membrane.
2. Description of the Related Art
A transducer is a device that converts an electrical signal into a type of energy, such as acoustic energy, and converts the type of energy, such as the acoustic energy, into an electrical signal. A micromachined ultrasonic transducer (MUT) is a micromachined transducer that converts an electrical signal into a transmitted ultrasonic wave, and converts a received ultrasonic wave into an electrical signal.
The basic component of a MUT is a suspended membrane or diaphragm which is capable of vibrating. When the membrane vibrates due to electrical stimulation, the membrane outputs ultrasonic waves. On the other hand, when the membrane vibrates due to an incoming ultrasonic wave, the movement of the membrane generates an electrical signal or a change in a measurable electrical property of the device. Two common types of MUTs are a capacitive MUT (CMUT), and a piezoelectric MUT (PMUT).
As further shown in
For example, transmit circuit 114 can be implemented with a pulse generator 120 that is electrically connected to MUT membrane 112, and a controller 122 that is electrically connected to pulse generator 120. Receive circuit 116, in turn, can be implemented with an amplifier/filter circuit 124, and an analog-to-digital (A/D) converter 126 that is electrically connected to amplifier/filter circuit 124 and digital signal processing circuit 118.
In operation, when MUT circuit 100 transmits, controller 122 commands pulse generator 120 to output a voltage pulse VP to MUT membrane 112. The voltage pulse VP, in turn, causes MUT membrane 112 to vibrate at the natural mechanical resonant frequency of MUT 110, and thereby generate an ultrasonic wave UW at that frequency.
As shown in
When MUT circuit 100 receives, an incoming ultrasonic wave causes MUT membrane 112 to vibrate. The vibration of MUT membrane 112 generates an electrical signal or a change in a measurable electrical property of the device that causes an output voltage to vary. Amplifier/filter circuit 124 amplifies and filters the varying output voltage, while A/D converter 126 generates a digitized signal that represents the varying output voltage. The digitized signal is then processed by digital signal processing circuit 118 as required by the application to generate, for example, an ultrasonic image or a simple distance measurement.
Although MUT circuit 100 works well for numerous applications, such as contact or near contact body imaging applications like echo cardiograms, MUT circuit 100 lacks sufficient bandwidth for some airborne applications. Thus, there is a need for a MUT circuit which can operate in those airborne applications that require a larger bandwidth.
As shown in
As further shown in
In the present example, transmit circuit 314 includes a controller 330, a memory 332 that is electrically connected to controller 330, and a driver circuit 334 that is electrically connected to MUT membrane 312 and memory 332. Driver circuit 334, in turn, is implemented with a digital-to-analog (D/A) converter 336 that is electrically connected to the output of memory 332, and a driver 338 that is electrically connected to MUT membrane 312 and the output of D/A converter 336. In addition, receive circuit 316 includes an amplifier/filter circuit 340, and an analog-to-digital (A/D) converter 342 that is electrically connected to processing circuit 318 and amplifier/filter circuit 340.
In operation, when MUT circuit 300 transmits, a transmit signal is stored as a series of digital values in a series of memory locations in memory 332. Controller 330 commands memory 332 to sequentially output the series of digital values that are stored in the series of memory locations to D/A converter 336, which converts the stored digital values into an analog signal.
The analog signal is then amplified and driven by driver 338 onto or across MUT membrane 312 as the transmit signal. The transmit signal transfers energy to MUT membrane 312, which causes MUT membrane 312 to vibrate due to the high quality factor (Q) of the mechanical system around its resonant frequency.
As shown in
The initial voltage waveform 410 can have any shape and duration required to transfer the required energy. In the present example, the initial voltage waveform 410 transfers energy that is equal to or less than the maximum energy that is required to move MUT membrane 312 to its maximum point of deflection. In the present example, the initial voltage waveform 410 is illustrated in
The initial amount of energy transmitted to MUT membrane 312 causes MUT membrane 312 to first move in one direction from the at-rest position to an initial position (e.g., position P1 or P2), and then move in the opposite direction from the initial position to a next position (e.g., position P1 or P2). As shown in
In the present example, in addition to the initial voltage waveform 410, the transmit signal TS also has one or more additional voltage waveforms 412 that each transmits and transfers an additional amount of energy to MUT membrane 312 after MUT membrane 312 has moved to the initial position. The additional voltage waveforms 412 can be the same or different to transfer the same or differing amounts of energy to MUT membrane 312.
As further shown in
Further, each additional voltage waveform 412 can have any shape and duration required to transfer the necessary energy to MUT membrane 312. In the present example, the additional voltage waveforms 412 are illustrated in
Thus, the initial voltage waveform 410 and a number of additional voltage waveforms 412 can be used to form a multi-cycle ultrasonic wave where each ultrasonic cycle has substantially the same amplitude (and MUT membrane 312 moves substantially the same distance away from the at-rest position, measured orthogonally from the at-rest position). Multiple equal-amplitude ultrasonic cycles transmit the maximum amount of ultrasonic energy in the shortest period of time.
In addition, after the initial voltage waveform 410 and any additional voltage waveforms 412, the transmit signal TS output by driver 338 has a cancellation waveform 414 that transmits and transfers a cancellation amount of energy to MUT membrane 312 which is sufficient to substantially stop MUT membrane 312 at the at-rest position. As shown in
As shown in
Thus, one advantage of MUT circuit 300 is that MUT circuit 300 allows an ultrasonic wave to be transmitted that has a number of cycles which have substantially the same amplitude, thereby transmitting the maximum amount of acoustic energy in the shortest period of time. In addition, another advantage of MUT circuit 300 is that MUT circuit 300 can substantially stop the ultrasonic wave after the number of cycles have been transmitted.
MUTs which are used in medical imaging applications utilize relatively high frequencies, and have wider fractional bandwidths which are often as high as 100%. At a result, the time required for a pulsed membrane to stop vibrating due to the inherent dampening (as illustrated in
Thus, the advantage of substantially stopping the ultrasonic wave is that substantially stopping MUT membrane 312 eliminates the long period of mechanical oscillation caused by the higher mechanical Q factor of MUT 310, increases the effective system bandwidth of MUT 310, and allows MUT 310 to generate shorter transmit pulses.
The series of digital values stored in the series of memory locations in memory 332, which represent the transmit signal TS, including the initial voltage waveform 410, any additional voltage waveforms 412, and the cancellation voltage waveform 414, can be determined by an external tester.
For example, controller 330 can load a test signal into memory 332 as a series of digital values, and then command memory 332 to output the series of digital values. D/A converter 336 converts the series of digital values into an analog signal, which is then amplified and driven by driver 338 onto or across MUT membrane 312 as the test signal.
The test signal causes MUT membrane 312 to vibrate, which generates a test ultrasonic wave. The external tester receives the test ultrasonic wave, and transduces the test ultrasonic wave to form a membrane electrical signal. The external tester also amplifies, filters, and digitizes the membrane electrical signal to form a digitized test signal. In addition, the external tester also compares the digitized test signal to a digitized golden signal.
The series of digital values can then be changed as needed and the process repeated until a good test signal is identified that generates a good test ultrasonic wave, which is received, transduced, amplified, filtered, and digitized by the external tester to form a digitized test signal that matches the digitized golden signal (within an error tolerance).
After a good digitized test signal has been identified, the series of digital values that represent the corresponding good test signal are written into memory 332 by controller 330 as the transmit signal. Computer modeling and simulation as well as prior test results can limit the number of test signals which must be generated for testing.
The ultrasonic wave UW illustrated in
When MUT circuit 300 receives, an incoming ultrasonic wave causes MUT membrane 312 to vibrate. The vibration of MUT membrane 312 generates an electrical signal or a change in a measurable electrical property of the device that causes an output voltage to vary. Amplifier/filter circuit 340 amplifies and filters the varying output voltage, while A/D converter 342 generates a digitized signal that represents the varying output voltage. The digitized signal is then processed by digital signal processing circuit 318 as required by the application to generate, for example, an ultrasonic image or a simple distance measurement.
As shown in
Once control has been received, digital signal processing circuit 512 sequentially outputs a series of digital values to D/A converter 336, which then converts the series of digital values into an analog signal. The analog signal is then amplified and driven by driver 338 onto or across MUT membrane 312 as a test signal.
The test signal causes MUT membrane 312 to vibrate, which generates a test ultrasonic wave, a portion of which is reflected back from a test structure. After MUT membrane 312 has stopped in the at-rest position, the reflected ultrasonic wave from the test structure causes MUT membrane 312 to again vibrate. The vibration of MUT membrane 312 generates an electrical signal or a change in a measurable electrical property of the device that causes the output voltage to vary.
Receive circuit 316 detects the varying output voltage, and generates a digitized signal that represents the varying output voltage. In the present example, the varying output voltage is amplified and filtered by amplifier/filter 340, and digitized by A/D converter 342 to form a digitized signal. Digital signal processing circuit 512 then compares the digitized signal to the digitized golden signal.
When the digitized signal matches the digitized golden signal within an error tolerance, the series of digital values that represent the test signal are written into memory 332 by digital signal processing circuit 512 as the transmit signal. Digital signal processing circuit 512 then passes control back to controller 330.
When the digitized signal fails to match the digitized golden signal within the error tolerance, digital signal processing circuit 512 changes the series of digital values output by digital signal processing circuit 512 to generate a different test signal, and continues generating different test signals until a digitized signal matches the digitized golden signal within the error tolerance.
When the digitized signal matches the digitized golden signal within the error tolerance, the series of digital values that represent the test signal are written into memory 332 by digital signal processing circuit 512 as the transmit signal. Digital signal processing circuit 512 then passes control back to controller 330. Computer modeling and simulation as well as prior test results can limit the number of different test signals that must be generated for testing. Alternately, optimization algorithms, such as a Least Mean Square (LMS) optimization, can be used to determine the test signal that must be generated for testing.
One of the advantages of MUT circuit 500 is that digital signal processing circuit 512 of MUT circuit 500 performs a calibration procedure that allows the series of digital values that are stored in memory 332, which represent the transmit signal, to be determined at predetermined times or upon command. As a result, MUT circuit 500 can compensate for changes, such as temperature and pressure, which can affect the accuracy of MUT 310.
Alternately, rather than utilizing a reflected ultrasonic wave, the output voltage from MUT membrane 312, which results from the movement of MUT membrane 312, can be used by receive circuit 316 to generate a digitized signal. For example, the output voltage can be amplified and filtered by amplifier/filter 340, digitized by A/D converter 342, and then compared to the digitized golden signal by digital signal processing circuit 512 during the intervals between the initial voltage waveform 410, the additional voltage waveforms 412, and the cancellation voltage waveform 414.
As shown in
In operation, digital signal processing circuit 612 of MUT circuit 600 performs a calibration procedure to identify the transmit signal that produces a digitized signal that matches the digitized golden signal (within an error tolerance) in the same manner that digital signal processing circuit 512 identifies the transmit signal to be stored in memory 332.
However, unlike MUT circuit 500, digital signal processing circuit 612 of MUT circuit 600 continues to compare every digitized signal to the digitized golden signal, and can adjust the digital values that are output by digital signal processing circuit 612 as needed each time a transmit signal is to be output.
Thus, in addition to performing a start-up or commanded calibration to determine the transmit signal that will move MUT membrane 312 in the desired manner, MUT circuit 600 continuously monitors the movement of MUT membrane 312 and compares that movement to digital values that represent the desired movement of MUT membrane 312.
It should be understood that the above descriptions are examples of the present invention, and that various alternatives of the invention described herein may be employed in practicing the invention. Thus, it is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
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Number | Date | Country | |
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20130188458 A1 | Jul 2013 | US |