A non-invasive microwave method for assessing solid-state ammonia storage

Jon Hartley*, Adrian Porch, Martin Jones

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


A 2.45 GHz microwave cavity resonator is used to measure the change in dielectric properties of alkali halide salts (such as CaI2) when exposed to ammonia gas. This technique is based on the change in electric dipole moment of the material that occurs as a function of ammonia content, and so can be used to determine ammonia concentration in solids in a non-invasive way. When a powdered sample is placed in the electric field of the TM010 mode of a resonant cylindrical cavity, we find that ammonia absorption gives a first order change in material polarisation (i.e. real permittivity), related to the ammonia sequestered within the solid. The associated dielectric losses (i.e. imaginary permittivity) exhibit second order transitions, which we believe are due to order-disorder transitions between the different coordination complexes of the halide salt.

Original languageEnglish
Pages (from-to)726-730
Number of pages5
JournalSensors and Actuators B: Chemical
Publication statusPublished - 2015


  • Alkali halide materials
  • Ammonia storage
  • Microwave characterisation


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