Cross sections of coaxial line.

<p>(A) Outline of electric (E) and magnetic (H) field lines; note radial the decrease in H-density. The outer diameter of the innner conductor is 2a and the inner diameter of the outer conductor is 2b. (B) Definition of eccentricity of an off-axis inner conductor. (C) Illustration of a coaxial cell in which a paramagnetic sample (white area) is contained in a diamagnetic holder (grey area).</p

Frequency-dependent EPR signal assigned to S = 1 Ni(0) in male SMA connectors.

<p>The minimum of the broad signal (determined as the zero crossing of the derivative) was followed with frequency decreasing in 0.1 GHz steps until disappearance in zero field. Two points around 4 GHz were obtained with an S-band bridge as source and power-meter detection; two points at 9.1 and 10.0 GHz obtained with an X-band bridge (not shown) were also on the straight-line fit that extrapolates to a zero-field splitting of 1.37 GHz or 0.0457 cm⁻¹.</p

Signal intensity as afunction of TEM versus B orientation.

<p>Bar A is the Mn(II) reference signal from the 42 mm standard cell. Red bars are measured intensities and blue bars are theory-predicted. Bars E, F, and G are from 82 mm Al cells with inner diameter of the outer conductor 8, 6, and 4 mm, respectively. Bars G’ and G_⊥ are for the 4 mm i.d. cell with TEM axis at 45 and 90 degrees versus B. The lower panel shows a full 360 degree rotation experiment for the 4 mm i.d. cell with intensity data fitted to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059874#pone.0059874.e030" target="_blank">eqn (30</a>).</p

Transmission EPR of solid MnSO₄⋅H₂O in a 42 mm standard cell.

<p>Traces a and a’ are for TEM || B orientation, and traces b and b’ are for TEM ⊥ B. The primed traces a’ and b’ are baselines from short-circuited leads without transmission cell. Trace c is for the 82 mm aluminum cell in TEM || B orientation.</p

Estimation of tempo detection limit at 800 MHz.

<p>The 12 m cell was filled with 300 µM HO-tempo in 100 mM KC,l and increasing numbers of averages were collected of 10+10 s forward-return scans. From the differentiated spectrum of 10,000 averages (67 hours data colletion) a detection limit of circa 5 µM was determined.</p

Signal intensity as a function of sample-compartment geometry.

<p>The 42 mm standard cell is partially filled with teflon spacers to displace paramagnetic sample. Bar A is the Mn(II) signal amplitude for a fully sample-filled cell in TEM || B orientation. Red bars are measured intensities and blue bars are theory-predicted. Subscript ⊥ indicates TEM ⊥ B orientation. In B a teflon spacer occupies half of the cell; in C the spacer is a cylinder around the inner conductor over the full cell length; in D two sector spacers occupy opposite positions in ‘butterfly’ orientation along the full length of the cell. The lower panel shows a full 360 degree rotation experiment for the ‘butterfly’ setup with intensity data fitted to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0059874#pone.0059874.e030" target="_blank">eqn (30</a>).</p

High-resolution transmission EPR spectra of 0.2 mol% Mn(II) in ZnSO₄⋅H₂O.

<p>The 220 cm cell held circa 5 g of powder of which circa 10 mg originated from MnSO₄⋅H₂O. Each trace is the differentiated average of circa 2500 forward scans of 100 s. The main trace was taken at 2.7 GHz; the left insert is a blow-up of a small section to illustrate detection of fine spectral details. The right insert shows very strong frequency dependence of the low-field part of the spectrum. Notethat these spectra are sums of spectra for all possible orientations of B’ versus B.</p

Long helical cells with continuously varying B₁ versus B angle.

<p>The sample-compartment lengths are 75, 300, and 1215 cm, respectively. The coax is wound around a supporting piece of elastomer into a helix or a toroidal helix.</p

A coaxial structure with its TEM propagation axis perpendicular to the B-axis of an external magnetic field.

<p>The microwave magnetic-field component B₁ in the sample compartment runs through all possible angles with respect to the external field vector B.</p

Rapid-scan transmission EPR to improve signal-to-noise ratio.

<p>A thick outer wall 40 cm cell was filled with solid DPPH, and a 2.7 GHz single-scan spectrum was taken in 30 s over a 959±20 gauss field range using a low-intensity microwave of −60 dBm incident power from the VNA to the amplifier to produce a spectrum with visible noise (red trace). Then a second spectrum was taken with the field at 959±0 gauss but with the field modulation unit set to 35 Hz and with a nominal peak-to-peak modulation amplitude of 40 gauss. The resulting data were mapped with a dedicated LabVIEW program to a sinusoidallly varying field and then interpolated to a 1024 point spectrum (blue trace). The increased width of the blue trace shows that the actual modulation amplitude felt short of 40 gauss, which illustrated that this experiment can be used as a convenient way to calibrate modulation coils. The rapid-scan EPR blue trace has reduced signal-to-noise (see text for details).</p