Ultrasound transducer design procedure:
Center Frequency:
The center frequency of an ultrasound transducer is determined by the application. A higher frequency generates an ultrasound beam with energy that is more confined, and attenuates faster. For imaging, it means better resolution and reduced imaging depth.
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Bandwidth
The bandwidth of ultrasound transducer is an important factor for imaging. When imaging is based on the ultrasound pulse-echo method, the bandwidth of the ultrasound transducer determines the pulse length, and thus, the axial resolution. The best axial resolution can be achieved is half of the pulse length. Normally, a transducer with a 50% bandwidth is an acceptable lower limit for B-mode imaging. Higher bandwidths correspond to heavier damping, causing a lower sensitivity.
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Geometry Size
Geometry size is determined by the target lateral resolution. For a round or square transducer shape, the lateral resolution can be calculated using our "Ultrasound Calculator". For a given depth, a focused transducer will provide a narrower beam with an increase in aperture size. If the application requires steering the beam or dynamically changing the focal depth, an array type of ultrasound transducer is necessary. Our "Beam Profile Simulation" can accurately predict the ultrasound beam from common ultrasound transducer shapes.
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Active Material Selection
If the ultrasound transducer equivalent diameter is bigger than 3~5 times of the active material thickness, the material will work in thickness mode. In thickness mode, the primary parameter to consider is a high kt. Otherwise, the parameter of interest should be k33. The second parameter to consider is the dielectric constant. Since most electronic cables and pulsers have an impedance of 50?, it is important to design a transducer that can match that same impedance to prevent loss. For a small area transducer, an active material with a higher dielectric constant is preferred. Our "Ultrasound Calculator", can quickly calculate the impedance.
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Matching and Backing Most piezoelectric material has a high Q-factor, which is the inverse of percentage bandwidth. Backing materials can provide damping to achieve a desired bandwidth. Matching layers can also be added to improve the energy coupling between the impedance of PZT (33MRyl) and target impedance (1.5MRyl for soft tissue). Our "Transducer KLM Model Simulation" can predict the electrical impedance and transmitted or received pulse of the transducer.
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Tuning or Electrical Matching Network The ultrasound transducer structure has a capacitive component at the center frequency. Simple tuning is to remove this capacitive element using a series, or shunt inductor. Our "Ultrasound Calculator" provides a quick value if the impedance of the transducer at center frequency is known. To match the cable and achieve best pulse shape, our "Transducer KLM Model Simulation" is best.
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Our Ultrasound Transducer Simulation or Modeling includes four parts: KLM model based transducer simulation or modeling, wave propagation, beam profile, and imaging simulation. There are three types of popular ultrasound transducer electrical equivalent models: The Mason model, The Redwood model, and The KLM model. The KLM model based simulation simulates the mechanical-electrical resonance property of the ultrasound transducer. The wave propagation simulation is based on the solution to the wave equation, and boundary conditions that model how a wave propagates and reflects when it encounters an object. Beam profile simulations predict the resolution of a transducer given a certain excitation. Imaging simulation gives simulated images from a phantom for theoretical conditions.
