access icon free Load-insensitive active quasi-circulator for continuous-wave Doppler ultrasound applications

Circulators are often used in RF systems; however, their size, cost, and weight increase greatly at lower frequencies (<300 MHz). The development of a load-insensitive active quasi-circulator is presented as an alternative for the traditional circulators to be used in low-frequency systems such as Doppler ultrasound. Major challenges to these active devices are limited power and low isolation between non-consecutive ports. The use of current-feedback operational amplifiers allowed higher-power delivery to the load. Simulations using Monte Carlo method showed an isolation >19 dB for 20% of variation of the load impedance. The circuit was implemented and tested with an ultrasound probe in a water tank. The results show that the circuit was able to send and receive signals simultaneously from a single ultrasound transducer element.

Inspec keywords: circulators; Monte Carlo methods; operational amplifiers; Doppler effect; feedback amplifiers; ultrasonic transducers

Other keywords: load-insensitive active quasicirculator; load impedance variation; circuit testing; Monte Carlo method; water tank; continuous-wave Doppler ultrasound applications; active devices; ultrasound probe; current-feedback operational amplifiers; circuit implementation; nonconsecutive ports; low-frequency systems; single ultrasound transducer element; RF systems

Subjects: Waveguide and microwave transmission line components; Amplifiers; Monte Carlo methods; Sonic and ultrasonic transducers and sensors

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http://iet.metastore.ingenta.com/content/journals/10.1049/el.2016.2574
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