Absorption Efficiency and Physical Bounds on
Antennas

<table>Geometry of the two arm spherical helix with circumscribing sphere radius <svg height="7.9499998" id="M168" style="vertical-align:-0.1638pt" version="1.1" viewbox="0 0 23.424999 7.9499998" width="23.424999" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,7.675)"><path d="M483 97q-42 -50 -88.5 -79.5t-68.5 -29.5q-37 0 -17 93l22 102h-2q-54 -79 -144 -149q-59 -46 -100 -46q-24 0 -43 29t-19 86q0 78 34.5 153t94.5 120q41 31 94 51.5t98 20.5q29 0 72 -9q26 -6 39 -6l2 -4q-30 -117 -67 -323q-8 -41 2 -41q16 0 79 58zM374 387
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</svg>62 mm and wire radius <svg height="15.3875" id="M169" style="vertical-align:-3.38113pt" version="1.1" viewbox="0 0 34.549999 15.3875" width="34.549999" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,11.112)"><path d="M627 18l-10 -26q-79 6 -116 27t-69 76q-41 71 -71 138q-13 29 -27.5 39t-42.5 10h-46l-27 -145q-13 -74 -2.5 -88.5t78.5 -20.5l-6 -28h-271l5 28q66 6 82.5 21.5t30.5 87.5l71 387q12 66 2 78.5t-77 19.5l8 28h233q102 0 147 -29q65 -43 65 -129q0 -69 -45.5 -117
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<g transform="matrix(.012,-0,0,-.012,11.013,15.187)"><path d="M696 437v-26q-37 -5 -50.5 -18.5t-28.5 -55.5q-36 -96 -120 -348h-29l-69.5 178.5l-52.5 132.5l-54.5 -141l-64.5 -170h-28q-71 229 -116 357q-13 39 -25.5 49.5t-48.5 15.5v26h207v-26q-45 -7 -53.5 -17t2.5 -44l74 -232h2l116 314h26q39 -111 120 -318h2q50 156 69 231
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<g transform="matrix(.017,-0,0,-.017,24.5,11.112)"><path d="M535 323h-483v50h483v-50zM535 138h-483v50h483v-50z" id="x3D"></path></g>
</svg>2 mm.</table>

International Journal of Antennas and Propagation

Absorption Efficiency and Physical Bounds on Antennas

Figure 4