The devices made by Gary Bolton, 47, were simply boxes with handles and antennae, the Old Bailey heard.
The prosecution said he sold them for up to £10,000 each, claiming they could detect explosives. The trial heard the firm had a £3m annual turnover selling the homemade devices.
Bolton, of Redshank Road, Chatham, Kent, had denied two charges of fraud.
As he passed sentence, Judge Richard Hone QC described the equipment as "useless" and "dross" and said Bolton had damaged the reputation of British trade abroad.