A pressure-neutral acoustic transmit receive module (PR-TRM) with integrated data processing for deep sea applications

Hardware, i.e. electronics and sensors, have to be packaged in a special way to bear the heavy mechanical loads, which are encountered in deep sea applications. Expensive materials and pressure resistant housings are often used. Another way to fulfill the requirements is to use a pressure neutral (pressure tolerant) approach by casting the components into an appropriate material. This might be a hard elastomer to protect components like quartz oscillators which have gas filled voids against being crushed or a synthetic rubber that is used to enclose electronic boards to disperse the pressure over the complete surface (components and circuit board). A pressure-tolerant system has been developed that can be used to perform different ultrasonic measurements under deep sea conditions like the detection of obstacles, distance or flow metering, concentration & compressibility measurements, Doppler logging, side scanning or acoustic communication. Depending on these different applications high sampling rates and fast detection times as well as a real-time signal processing are required. PN-TRM is a pressure neutral single channel transmit-receive-module that can be used to a depth of 6000 m. 8 ultrasound transducers with frequencies up to 25 MHz can be connected by a multiplexer. The system is equipped with a DSP and can operate as a stand-alone system. The communication with an external PC can be done via different interfaces (CAN, ISA, etc.). To ensure the operation under high pressure conditions, different parts of the circuit as well as the complete system were tested in a chamber that supports pressures up to 600 bar. Among pure mechanical pressure tests, quantitative functional tests (distance metering) were performed.