7.  Intangible Assets

Intangible assets consisted of the following (in thousands):

The Company recorded amortization expense of $0.1 million and $0.4 million for the three and nine months ended December 31, 2012, respectively. The Company recorded amortization expense of $0.2 million and $0.6 million for the three and nine months ended December 31, 2011, respectively. Intangible assets consisted of the following (in thousands):

Expected future amortization expense of intangible assets as of December 31, 2012 is as follows:

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 $19,500 and $16,900 were earned by Solar for the three months ended December 31, 2012 and 2011, respectively. Royalties of approximately $52,100 and $55,300 were earned by Solar for the nine months ended December 31, 2012 and 2011, respectively. Earned royalties of approximately $19,500 and $17,500 were unpaid as of December 31, 2012 and March 31, 2012, respectively, and are included in accounts payable and accrued expenses in the accompanying consolidated balance sheets.