The Company's intangible assets at September 30, 2017 include patents with estimated remaining economic useful lives ranging from 3.0 to 4.0 years.  For all periods presented, all of the Company's patents were subject to amortization.  The gross carrying amounts and accumulated amortization related to acquired intangible assets as of September 30, 2017 and December 31, 2016 were as follows:

Amortization expense for the three months ended September 30, 2017 and September 30, 2016 was $50,000 and $49,000, respectively.  Amortization expense for the nine months ended September 30, 2017 and September 30, 2016 was $150,000 and $760,000, respectively.  Future amortization of current intangible assets, net is as follows:

The Company's Remote Power Patent expires in March 2020. The expiration dates of the patents within the Company's Mirror Worlds Patent Portfolio range from April 2018 to February 2020 (six of the patents in the Mirror Worlds Patent Portfolio expired during the nine months ended September 30, 2016 and two of the patents in the Mirror Worlds Patent Portfolio expired during the nine months ended September 30, 2017).  The expiration dates of the patents within the Cox Patent Portfolio range from September 2021 to November 2023 and the expiration date of the QoS Patents is June 2019.