Loading...
 

Frequently used components

The following are frequently used commercial off-the-shelf (COTS) electronic components. These lists are not endorsements of the corresponding products and are provided exclusively for information purposes.

Semiconductor Components

Diodes

Fast Rectifier Diodes

These types of diodes are used in pairs ("crossed") to implement passive switch circuits such as detuning traps, T/R switches, etc. Some are already packaged in pairs to assist use in the crossed configuration. Schottky diodes consist of a junction between a semiconductor and metal and consequently have a lower turn-on voltage than standard PN diodes.

The main parameters to consider are

  • recovery time (ns): determines maximum frequency of operation of the switch of the switch
  • capacitance (pF): capacitance seen when the switch is OFF
  • forward current (A): maximum current handling of the switch
  • forward voltage (V): turn-on voltage of the switch
  • power dissipation (W)

Consult the corresponding data sheets for accurate information. The following are few examples (of likely hundreds of diodes available) that may be used in MRI applications.

Part Number Configuration Recovery Time (ns) Capacitance (pF) Forward Current (A) Forward Voltage (V) Power Dissipation (W)
BYW29 single with heatsink 25 10 (to heatsink) 8 0.9 ~10
BAW56 double 4 2 0.45 0.9 0.25
BAT54 Schottky 5 10 0.6 0.4 0.2
1N4148, 1N4448 single 4 4 0.2 0.9 0.5

PIN Diodes

PIN diodes use a junction with an undoped (intrinsic) region between the P and N regions. The intrinsic region stores charge and makes the PIN diode an excellent (low-resistance) switch at high frequencies. Carrier lifetime determines the ON resistance of the switch and influences the lowest frequency of operation.

PIN diodes are typically controlled with an external DC bias to act as switches or current-controlled resistors (e.g., in attenuators).

The diodes in the following table are commonly used in MRI applications. Consult the corresponding data sheets for accurate information.

Part Number Carrier Lifetime (µs) Resistance (ohm) Capacitance (pF) Power Dissipation (W) Reverse Voltage (V)
UM9401 2 0.75 1.1 5.5 50
MA4P4000 6 0.5 2.2 12 100

Transistor Cross Reference

Here are some popular transistors used in low-noise preamplifiers and their equivalents from alternate manufacturers.

Manufacturer Part Number Manufacturer Part Number
Broadcom/Avago/Agilent/HP ATF-33143*   Mini-Circuits SAV-331+
Broadcom/Avago/Agilent/HP ATF-54143*   Mini-Circuits SAV-541+
Broadcom/Avago/Agilent/HP ATF-55143*   Mini-Circuits SAV-551+
Broadcom/Avago/Agilent/HP ATF-58143*   Mini-Circuits SAV-581+

* now obsolete according to this notice

Passive Components

Nonmagnetic Inductors

These are some inductors known to have a non-ferromagnetic core and otherwise negligible ferromagnetic materials. Measured self-resonant frequency (SRF) is reported where available. The SRF is important when the inductor is used as an RF choke because at the SRF the series impedance of the inductor is maximal.

It is also common also to use self-wound inductors when the required inductance values are modest (e.g., below 100 nH).

Coilcraft

Supplier of numerous air-core and other nonmagnetic inductors. Tunable versions can be ordered with aluminum core instead of ferrite.

1008CS Series

Non-magnetic core.

1008HS Series

Non-magnetic core.

Part number Nominal Inductance (nH) Measured SRF (MHz)
1008HS-102T 1000 360

Delevan

2890 Series

Non-magnetic (phenolic) core up to 18µH and otherwise no measurable magnetism.

Panasonic

ELJ series

Non-magnetic core and otherwise no measurable magnetism.

Part number Nominal Inductance (nH) Measured SRF (MHz)
ELJNAR22 220 320
ELJNAR27 270 300
ELJNAR47 470 220

Vishay

IMC-1812 Series

Non-magnetic core up to 0.82µH.

IM-6-RFCS-40 Series

Non-magnetic core up to 2.2µH.

Nonmagnetic Capacitors

These are some capacitors known to contain negligible ferromagnetic materials. Important parameters to consider include

  • maximum voltage handling (V)
  • equivalent series resistance (ESR, ohm)
  • temperature coefficient of capacitance change (ppm/ºC)
  • capacitance tolerance (F)

Kemet

SMD Commercial High Voltage C0G

Surface mount, multilayer ceramic chip capacitors with low ESR and high voltage (kV range) rating. Confirmed very small magnetic attraction (C1812C151JHGACTU, 150pF).

Panasonic

ECC and ECK Series

Radial ceramic disk capacitors with leads, high voltage rating. Confirmed nonmagnetic (various part numbers beginning with ECCNVS).

TDK

CC45 Series

Radial ceramic disk capacitors with leads, high voltage (kV range) rating. Confirmed very small magnetic attraction (CC45SL3AD821JYNNA, 820pF).

CGA Series

Surface mount, multilayer ceramic chip capacitors with low ESR and high voltage (kV range) rating. Confirmed very small magnetic attraction (CGA8L1C0G3F151K160KA, 150pF).

Vishay

F Series

Radial ceramic disk capacitors with leads, high voltage (kV range) rating. Confirmed nonmagnetic (F102K43Y5RP6UK5R, 1000pF).