BioSono provides a cyberspace (www.biosono.com) where researchers, engineers, and students can find useful reference and educational materials, conduct acoustic simulation, post questions on design and development, and get answers. The online KLM based transducer acoustic stack simulation, which is currently free, can help you choose piezoelectric, matching and backing material, and a tuning electrical network. The output from the model includes electrical transmit impedance, acoustic receive impedance, and the impulse or pulse-echo response. The ultrasound beam profile simulation provides the calculated transmitted ultrasound pressure field under certain excitation for a given transducer aperture in a number of different geometrical configurations, including circular elements (flat and concave piston), rectangular elements, linear arrays, convex arrays, and 2D arrays. The simulation is based on Field II, which is a free program that utilizes the spatial impulse response method, and has been validated by many researchers for accuracy. In addition to the web based acoustic simulation, we also provide pulse-echo system, transducers, and customized design and develop services.
Transducer KLM Model Simulation
Beam Profile Simulation
SonoLab Echo I
Time Gain Control
Ultrasound Unipolar Transmitter, Pulser
How it works:
This circuit transmits a short pulse at a low duty factor level, mainly for diagnostic applications. When there is no transmit signal, the MOSFET M1 is off and the capacitor C1 is charged through R1 by HV. When a transmit trigger signal arrives at the gate of M1, it will cause M1 to turn on and C1 will discharge to the load transducer (RL). A negative pulse will be applied on the transducer. The pulse width is determined by the time constant: Τ = RC.
If the trigger pulse width is narrower compared to 5RC, the transmitted pulse width will be determined by the trigger pulse as shown in the above right figure.
Guideline for the Component Value Selection:
R1: provides a charging current to C1 through HV. Its value is determined by the period of the pulse repetition. It has to be small enough to let C1 fully charged before the next transmit. If it is too small, big current will go through it when M1 is turned on, causing C1 not discharge properly to the load, or even the damage of M1.
M1: Three parameters for M1 are important.
Vds: how much voltage it can handle. This parameter has to be at least 1.2 times higher than your pulse amplitude. For example, if you want to transmit a 100v negative pulse on the transducer, the Vds for M1 should be 120 - 150 v.
Cgs, tr, tf: Switch speed. These parameters determine how fast M1 can turn on/off. Tr, tf, is determined by Cgs, and testing circuit. With a special designed driving circuit, a faster switch speed can be achieved. Normally, tr/tf should be less than a quarter of your center period. If you excite the circuit at 10MHz, the center period is 100ns, and tr+tf should be less than 50ns.
RDS(on): the on resistance. It should be less than five percent of the transducer impedance.
Voltage tolerance: should be at least 1.5 times higher than HV.
Capacitance: determined by the pulse width and transducer impedance. The time constant, RC, should be less than 20 percent of the pulse width.
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