The Company’s intangible assets at March 31, 2020 include patents with estimated remaining economic useful lives ranging from 1.50 to 13.5 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 March 31, 2020 and December 31, 2019 were as follows:

 

		March 31, 2020				December 31, 2019
Gross carrying amount – patents		$	7,805,000			$	7,797,000
Accumulated amortization – patents			(6,050,000	)			(5,978,000	)
Patents, net		$	1,755,000			$	1,819,000

Amortization expense for the three months ended March 31, 2020 and March 31, 2019 was $72,000 and $54,000, respectively. Future amortization of intangible assets, net is as follows:

Twelve Months Ended March 31,
	2021			$	290,000
	2022				290,000
	2023				290,000
	2024				150,000
	2025 and thereafter				735,000
	Total			$	1,755,000

The Company’s Remote Power Patent expired on March 7, 2020. All of the patents within the Company’s Mirror Worlds Patent Portfolio have expired. The expiration dates of the patents within the Cox Patent Portfolio range from September 2021 to November 2023. The expiration dates of patents within the Company’s M2M/IoT Patent Portfolio range from September 2033 to May 2034.