Ultrasound Electronics

High Intensity Focus Ultrasound,HFU, multi-channel transmitter, freqeuncy tracking

Pulse width modulated (PWM) wave is commonly used to drive HIFU transducer element through a class-E amplifier. For a fixed transmit voltage, the power applied on the transducer element is controlled by the duty factor of the PWM. When duty factor is 100 percent, the element gets its maximal power, which is inverse proportional to its absolute impedance value.

Voltage and current of the channel need to be monitored in case of a short in the load and also for the frequency tracking purpose. The center frequency of the piezoelectric element may drift when temperature is increased.

The following is a description of a typical multi-channel HIFU system. It consists of a control unit and several RF modules.

As shown in the above figure, the control unit includes user interface and control logic. The user interface takes parameter inputs such as transmit voltage, center frequency, duty factor, delays for each element. It passes the parameters to RF modules via RS-232 ports. It also sends out a master synchronization clock and a master trigger to each RF module using a digital edge signal.

A RF module includes several channels upon user needs, normally up to 8. A channel will be shut down automatically by hardware if the output current exceeds the limit. An A/D is included to digitize the sensed voltage and current of the selected channel via a multiplexer.

Rs-232 port will talks to a control unit or a PC to receive transmit voltage, center frequency, and delay profile. All the channels share the same one HV source within one RF module and it is programmable through D/A control. Different RF modules will be synchronized by trigger and master clock signals.

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