Agilent Measurement Journal - Issue 3 - 2007 - (Page 46)

Assessing spatial resolution The spatial resolution of the probe, relative to a typical loop probe, was determined by scanning the probe across a pair of differential traces. The reference probe, shown in Figure 6, has a loop area of approximately 1 mm2. Ideally, the measurement will show a strong, narrow peak in the magnetic ﬁeld over each trace that reduces quickly to zero between the traces. The width of the peak over the traces and the null between them is an indication of spatial resolution. The thin-ﬁlm probe and the conventional loop probe were scanned across the differential trace at a height of 250 µm. The measured signal power is shown in Figure 7. The thin-ﬁlm probe has a 3 dB decrease over 350 µm, which is 250 µm less than the conventional loop probe. The spatial resolution found in Figure 7 is a function of both the probe size as well as the height above the traces. Consider the differential traces shown in Figure 8. The position of the loop is indicated at coordinates (x, y). When the plane of the loop is perpendicular to the ground plane and parallel to the longitudinal axis of the trace (as indicated in Figure 9), only the x component of the magnetic ﬁeld contributes to the magnetic ﬂux through the loop. The magnetic ﬂux is given by: Bx = ⎞ m0I ⎛ yd yd ⎟ ⎜ − 2p d ⎜ ( ( x d − 1) 2 + ( y d ) 2 ) ( ( x d + 1) 2 + ( y d ) 2 ) ⎟ ⎝ ⎠ Figure 6. The thin-ﬁlm probe and a simple loop probe The magnitude of the ﬁeld is determined both by a ratio of the height of the probe to trace separation and the ratio of the horizontal position (x-direction) to trace separation. The effect is illustrated in Figure 10. Simple loop probe Thin-film probe -65 -70 Measured power (dBm) -75 -80 -85 -90 -95 350 µm -100 -105 -3000 x -2000 -1000 0 Distance (µm) 1000 2000 3000 600 µm y 90° Figure 7. Comparison of the spatial resolution of the thin-ﬁlm probe and of a simple loop probe 200 µm 118 µm (x, y) y 192 µm +I –I Figure 9. Measurement of differential traces x 2d Figure 8. Model for the magnetic ﬁeld produced by a differential pair 46 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 3 - 2007

Applying Ingenuity to the Measurement of Emerging Technologies Contents Emerging Innovations Department Delivering Bigger Benefits by Optimizing Customer Workflows Measuring Material Properties at the Nanoscale Utilizing In Situ Atomic Force Microscopy in Life Science, Pharmaceutical and other Bio-Related Applications WiMAX™: Plotting a New Path to Global Mobility Addressing the Triple Complexity of Triple-Play Networks What Next for Mobile Telephony? Exploring the Inner Workings of Tire-Pressure Monitoring Systems Developing, Assessing and Applying a High-Resolution Thin-Film Magnetic Probe Making Accurate Settling-Time Measurements Using a Vector Network Analyzer Applying Metabolomics Methods to the Study of Bacterial Leaf Blight in Rice Plants Measuring Stream Dynamics with Fiber Optics survey

Agilent Measurement Journal - Issue 3 - 2007

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