Mett Richard R, Sidabras Jason W, Golovina Iryna S, Hyde James S
Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226-0509, USA.
Rev Sci Instrum. 2008 Sep;79(9):094702. doi: 10.1063/1.2976033.
The coupled system of the microwave cylindrical TE(011) cavity and the TE(01delta) dielectric modes has been analyzed in order to determine the maximum achievable resonator efficiency parameter of a dielectric inserted into a cavity, and whether this value can exceed that of a dedicated TE(01delta) mode dielectric resonator. The frequency, Q value, and resonator efficiency parameter Lambda for each mode of the coupled system were calculated as the size of the dielectric was varied. Other output parameters include the relative field magnitudes and phases. Two modes are found: one with fields in the dielectric parallel to the fields in the cavity center and the other with antiparallel fields. Results closely match those from a computer program that solves Maxwell's equations by finite element methods. Depending on the relative natural resonance frequencies of the cavity and dielectric, one mode has a higher Q value and correspondingly lower Lambda than the other. The mode with the higher Q value is preferentially excited by a coupling iris or loop in or near the cavity wall. However, depending on the frequency separation between modes, either can be excited in this way. A relatively narrow optimum is found for the size of the insert that produces maximum signal for both modes simultaneously. It occurs when the self-resonance frequencies of the two resonators are nearly equal. The maximum signal is almost the same as that of the dedicated TE(01delta) mode dielectric resonator alone, Lambda congruent with40 G/W(1/2) at X-band for a KTaO(3) crystal. The cavity is analogous to the second stage of a two-stage coupler. In general, there is no electron paramagnetic resonance (EPR) signal benefit by use of a second stage. However, there is a benefit of convenience. A properly designed sample-mounted resonator inserted into a cavity can give EPR signals as large as what one would expect from the dielectric resonator alone.
为了确定插入腔体内的电介质可实现的最大谐振器效率参数，以及该值是否能超过专用的TE(01δ)模式介质谐振器的效率参数，对微波圆柱TE(011)腔与TE(01δ)电介质模式的耦合系统进行了分析。随着电介质尺寸的变化，计算了耦合系统各模式的频率、品质因数Q和谐振器效率参数Λ。其他输出参数包括相对场强和相位。发现了两种模式：一种模式下电介质中的场与腔中心的场平行，另一种模式下电介质中的场与腔中心的场反平行。结果与通过有限元方法求解麦克斯韦方程组的计算机程序的结果非常吻合。根据腔体和电介质的相对固有谐振频率，一种模式的Q值较高，相应地Λ值较低。具有较高Q值的模式优先被腔壁内或附近的耦合膜片或环激发。然而，根据模式之间的频率间隔，两种模式都可以通过这种方式被激发。对于同时为两种模式产生最大信号的插入物尺寸，发现了一个相对较窄的最佳值。当两个谐振器的自谐振频率几乎相等时出现该最佳值。最大信号几乎与单独的专用TE(01δ)模式介质谐振器的信号相同，对于钽酸锂（KTaO₃）晶体，在X波段Λ约为40 G/W(¹/₂)。该腔体类似于两级耦合器的第二级。一般来说，使用第二级不会带来电子顺磁共振（EPR）信号增强的好处。然而，在便利性方面有好处。插入腔体内的经过适当设计的样品安装谐振器可以产生与单独的介质谐振器预期的信号一样大的EPR信号。
