5. Intangible Assets

Intangible assets consisted of the following (in thousands):

 

 

 

Amortization expense for the intangible assets was $0.3 million for each of the fiscal years ended March 31, 2018 and 2017.

Expected future amortization expense of intangible assets as of March 31, 2018 is as follows (in thousands):

 

The manufacturing license provides the Company with the ability to manufacture recuperator cores previously purchased from Solar Turbines Incorporated (“Solar”). The Company is required to pay a per‑unit royalty fee over a seventeen-year period for cores manufactured and sold by the Company using the technology. Royalties of approximately $30,900 and $32,100 were earned by Solar for the fiscal years ended March 31, 2018 and 2017, respectively. Earned royalties of approximately $8,000 and $10,000 were unpaid as of March 31, 2018 and 2017, respectively, and are included in accrued expenses in the accompanying balance sheets.