TY - JOUR
AU1 - Follett, D H
AB - Small ultrasound catheter transducers such as intravenous Doppler probes present constructional problems regarding insulation integrity for patient safety and shielding to reduce electromagnetic interference. Electrical isolating transformers can solve both problems but the common mode rejection must be greater than 70 dB for effective interference reduction. A common solution is to cascade two transformers with the intermediate coupling circuit balanced to earth in the form of a bridge. This requires critical adjustment and works only over a narrow frequency band. The alternative adopted here uses a single-turn coupling loop through a toroidal core, which reduces stray capacitance sufficiently to need no adjustable balancing components. Patient safety requirements are also easily met. The penalty is poor magnetic coupling, but with optimum choice of core material a single design will cover 2-10 MHz with no more than 3-6 dB go and return loss and a common mode isolation over 80 dB. Surprisingly, the best core materials are found to be working well above their recommended frequency range such that the loss angle reaches 45 degrees near the lower frequency limit of the isolator.
TI - Transducer electrical isolators without critical adjustments
JF - Physics in Medicine and Biology
DO - 10.1088/0031-9155/38/11/012
DA - 1993-11-01
UR - https://www.deepdyve.com/lp/iop-publishing/transducer-electrical-isolators-without-critical-adjustments-v0k1Mi0Xdb
SP - 1675
VL - 38
IS - 11
DP - DeepDyve
ER -