Electronic component promises savings for makers of MR scanners

November 7, 2005

Microsemi of Irvine, CA, a producer of semiconductors for MR manufacturers, has developed an electronic component that could save time and money in the assembly of MR coils.

Microsemi of Irvine, CA, a producer of semiconductors for MR manufacturers, has developed an electronic component that could save time and money in the assembly of MR coils.

The dual-diode module serves two purposes specific to MR systems. It protects MR receiver coils from high-radiofrequency energy fields, including long RF pulses and RF spike pulses, and it provides passive or semi-active switching of surface coil detuning and blocking circuits.

The module, called the UMX9989AP, solves a problem commonly encountered during the assembly of MR coils: diode polarity mistakes. These mistakes occur during switch assembly about 30% of the time, according to Microsemi. When this happens, one of the diodes must be removed and reattached with the correct polarity, a labor-intensive fix. The dual-diode module is designed as an alternative to save switch assembly costs.

UMX9989AP saves assembly labor by eliminating the potential for polarity error during assembly of a coil switch and by providing both diodes in one assembly for circuit attachment.

UMX9989AP features an antiparallel pair of rectifier diodes as a single assembly for insertion into the coil. This diode pair is connected so one diode is conducting while the other is off during the RF cycle. The new module optimizes performance by eliminating possible polarity mounting errors. Proper mounting ensures minimum parasitic inductance, capacitance, and thermal impedance, according to the company.

The market for the new module includes both the major coil manufacturers, which subcontract to OEMs, and the major vendors themselves. Small quantities of the new modules are already being shipped.

Effectiveness of the UMX9989AP results from a combination of thermally matched packaging, low-inductance Microsemi PIN diode silicon chips, and a proprietary construction process that uses full-faced metallurgical bonds to both surfaces of the chip. The device provides high-power handling capability with a lower bias current requirement. The product's proprietary dual surface mount module measures only 0.195 inches high x 0.175 inches wide x 0.09 inches deep.

Microsemi contends that the innovation represents a new standard for high-performance MR surface coil design. Already, the module has received high marks from leading manufacturers of high magnetic field MRI systems (with magnets of 1.5 T strength or greater), according to the company.